Retina Regeneration Targeting Muller Cells with Natural Products

Endogenous Retinal Progenitor Cell Regeneration and Reported Retinitis Pigmentosa Therapeutics Promoting Stem Cell Neurogenesis, or Photoreceptor Differentiation

Introduction

Retina Progenitor Cell Populations -- A population of very small embryonic-like stem cells (0.06% @ postnatal day 28) is in the ganglion cell layer of adult mice that is quiescent, but can differentiate into ectodermal retinal cells (including photoreceptors), and mesoderm, or endoderm under stimulation by appropriate cell culture protocols. 1

Another reported adult mouse stem cell population consists of relatively rare pigmented cells in the cilliary margin that have a multipotent ability to become photoreceptors, bipolar neurons, and Muller glia cells under appropriate in vitro conditions. 2 Muller cells can have self renewal, and multipotent development along basic retinal cell lines characteristic of stem cells. 3 Muller glia have an ability to regenerate retina in teleost fish that is remarkable, while a lesser degree of retinal repair occurs chicks, but there is limited Muller cell proliferation in response to injury for mammals, 4 and any regeneration is ordinarily meager. 5 However, reports of conditions under which retinal regenerative processes can be promoted are numerous.

Injury by explant culture induces dedifferentiated Muller cells that exhibit some proliferation, which can be increased by >20 fold with the addition of 100 ng/ml Wnt3a. 6

Photoreceptor differentiation can then be induced by subsequent application of retinoic

(0.3 μM), or valproic (1mM) acids. Error: Reference source not found 2

Retinitis Pigmentosa Progenitor Capacity -- Visual field enlargement was reported for 3

(37.5%) of 8 Retinitis Pigmentosa (RP) patients administered Nerve Growth Factor

(NGF) eye drops over 10 days. 7 Nerve growth factor signaling with Muller cell trans differentiation has been reported for the transient neurogenesis following sodium iodate injury to the retina that included some photoreceptor regeneration, 8 and for retinas having transplanted rat bone marrow stem cells. 9

Injury can produce dedifferentiation of Muller cells towards progenitor cells, and

Muller stem cell qualities are regulated by Wnt, and Notch signaling that governs the dominant pathway network of the developing retina. Error: Reference source not found

Retinal explants from 12 postnatal day rd-1Pde RP model mice treated with 100 ng/ml

Wnt3a increase cellular proliferation (indicated by BrdU labeling) that on Wnt3a withdrawal, and application of either retinoic, or valproic acids each increased the number of rhodopsin labeled cells (Valproic acid induces the NeuroD transcription factor that participates in photoreceptor differentiation by inhibiting histone deacetylases).

Error: Reference source not found Muller cell dedifferentiation gene expression study in

RP rd10Pde model mice included Notch signaling along with neurotrophic factors. 10 The faster degenerating RP model of the same gene but different amino acid mutation (also engineered with a reporter transgene) is the rd-1Pde Tcf-LacZ mouse, which exhibited increased Wnt signaling mainly localized to retinal Muller cells (glycogen synthetase+) of the retinal inner nuclear layer (though a few microglia cells in the outer nuclear layer had

Wnt signaling) [Differential Wnt ligand activity implicated in degeneration are Wnt5a & b, Wnt10a, and Wnt13]. 11 3

Though Muller cells in 12 day old rd-1Pde RP model mouse retinal explants can proliferate, these explants from 21 day old rd-1Pde mice are reported to lack proliferating cells (by BrdU labelling), Error: Reference source not found even though rd-1Pde Muller cells in vivo are reported to express the nestin neural stem cell antigen, and the rhodopsin rod phototransduction protein for up to 6 months of age. 12 This is long after complete photoreceptor degeneration at two months after birth). Error: Reference source not found

The transcription factor cyclic AMP Response Element Binnding protein 1 (CREB-1) is associated with nestin expression, neural progenitor cell proliferation, and relevant differentiation antigens in hippocampal neurogenesis. 13 However, active phosphorylated

CREB-1 transcription factor in the rd-1Pde RP model mouse is 30% of levels in the wild type mouse, 14 while the rd10Pde mouse (another mutation of the same gene yet having slower degeneration) had decreased phosphorylated CREB that was identified to be in

Muller cells, which had increased toward wild type by postnatal day 34 (when degeneration was nearly complete). 15 Adult mouse Muller cells without the degenerative mutation do not proliferate, or express either progenitor, or differentiation proteins.

Error: Reference source not found Intact retinal tissue may be required for stem cell proliferation, as in the Retinal Pigment Epithelium (RPE) regenerative proliferation was only observed on undamaged epithelium. Error: Reference source not found

Intravitreal injection of RHOS334ter RP model rats with Notch and Wnt stimulators

(Jag1 and Wnt3a, respectively) produced a significantly better optokinetic (visual head- neck) response that correlated to a 7.3 fold increase in dividing Muller cells identified by being glutamate synthetase+, but were presumptive photoreceptors with demonstrable opsin by immune histochemistry versus RHOS334ter controls. 16 4

Sonic hedgehog is a stem cell signalling pathway that promotes proliferation by relieving cell cycling inhibition on binding the membrane receptor called patched, but mutational inactivation of patched also increases cell division such that mice heterozygous for patched (ptc +/-) have a population of dividing progenitor cells

(Chx10+, nestin+) at the retinal margin that is reminiscent of the ciliary margin zone of lower vertebrates 17 capable of retinal regeneration. RHOP23H RP model mice with patched (ptc +/-) heterozygosis even had a 50% greater cell division at the retinal margin than ptc +/- heterozygotes without retinal degeneration, and produced progenitor cells evidencing the photoreceptor differentiation marker recoverin. a Error: Reference source not found

Mammalian Retinal Regeneration Inhibition Factors -- Transforming Growth Factor β

(TGFβ) maintains quiescence of rat progenitor and Muller cell mitosis, while TGFβ inhibitors restore cell proliferation in vitro, and in vivo. 18 TGFβ inhibits Muller cell proliferation by activation of Protein kinase C, Error: Reference source not found and by expression of P27Kip, a cyclin dependent kinase inhibitor. Error: Reference source not found ZacI is a zinc finger transcription factor that controls ectopic rod photoreceptor, and amacrine cell proliferation by causing cell cycle exit, and TGFβ2 regulated apoptosis involving activated Smad 2/3 signaling (report quantitates mainly amacrine cells). 19

TGF-α, and epidermal growth factor also inhibit rod photoreceptor differentiation, but

20 TGFβ3 does not inhibit rods. TGFβ1, TGFβ2, and TGFβ3 expression are all reported increased in the rd10Pde RP model mouse. Error: Reference source not found

a Recoverin is an antigen positive for rod and cone photoreceptors, as well as cone bipolar cells (Moshiri et al., 2004). 5

RCSMerTK rat retina with transplanted human Muller stem cells had Muller cell migration inhibited by chondroitin sulfate proteoglycans secreted in part by CD68 activated microglia, but Muller stem cell migration, and integration could be increased by transplantation with chondroitinase ABC, and maximized to almost 80% migration by adding 4 immunosuppressants. 21

Circulating Mesenchymal Stem Cells Contribute to Repair/Regeneration -- Peripheral injection of 106 culture expanded bone marrow-derived mesenchymal stem cells into

RCSMerTK RP model rats preserved photoreceptors, and increased optokinetic visual function with evident stem cell migration into the retina versus control rats. 22 Similar stem cell injections benefit other neurological deficit experimental models. Intravenous 3

X 106 bone marrow stromal/mesenchymal cells administered to rats one day after middle cerebral artery occlusion improved neurological recovery with the stem cells having the greatest accumulation in the brain damaged area. 23

Stromal cell-Derived Factor 1 (SDF-1/CXCL12) had observation in the rd10Pde mouse RP model, 24 and is a cytokine of the CXC chemokine family that attracts stem, as well as several types of immune cells. On massive sodium iodate retinal pigment epithelial injury in mice, bone marrow derived Green Fluorescent Protein labeled lin‒ stem/progenitor cells began to appear in the retina when histological damage was evident and retinal SDF-1/CXCL12 chemokine was expressed, but was not detectable in the blood. 25 Cell migration towards SDF-1/CXCL12 is indicated (in mouse embryonic fibroblasts & macrophage studies) to require activation of NF-κB isoforms simultaneously by both the canonical Inhibitor of κB Kinase (IKK) β pathway (which 6 maintains CXCR4 receptor expression), and the more inflammation resolving non- canonical IKKα pathway that is required to maintain polarity, and velocity of migration) towards a SDF-1 gradient. 26 SDF-1/CXCL12 activates IKKα, but the only other known activators of IKKα are CD40L, lymphotoxin β, and B cell activating factor (BAFF).

Error: Reference source not found

Intravenous infusion of mesenchymal stem cells distributes the cells all over the body with a low rate of engraftment, so in humans at least 1 to 2 X 106 MSCs per kilogram patient body weight, or 150 to 300 million cells administered twice per week over two weeks have been used, though optimum dosage is unclear. 27 Such numbers of

MSCs require in vitro culture expansion, but culture conditions alter MSC phenotype, and migratory pattern, which can degrade regenerative capacity. Error: Reference source not found Two natural products that increase CXCR4 are tanshinone IIA, and astragaloside IV, while transient hypoxia preconditioning increases CXCR4, and migratory ability through induction of hypoxia inducible factor 1α. Error: Reference source not found

rBMSC cultures produced NGF, BDNF, GDNF, CTNF, and bFGF. Error:

Reference source not found

Wnt activators protect dissociated primary retinal cultures from H2O2 induced oxidative stress. Error: Reference source not found

Regeneration of the Retinal Pigment Epithelium, and Other Ocular Tissues

[The RPE participates in some lower vertebrate retinal regeneration, and provides essential functions as well as factors for photoreceptors.] Mouse ocular organ culture 7 ablation by the diptheria toxin transgene produced by the promoter for a unique, essential

Retinal Pigment Epitherium (RPE) protein (tyrosinase related protein 1) indicates that the

RPE is required for neural retina development, and maintenance. 28 In culture, a population of human RPE cells can be induced to form self renewing multipotent stem cells that can differentiate along mesenchymal, osteogenic, adipogenic, chrondrogenic, and neurogenic lines. 29 Regeneration in low dose sodium iodate (15 mg/kg) mouse

Retinal Pigment Epithelium (RPE) injury had report of scotopic ERG b-wave improvement at 3 months post-injury with demonstration of pigment epithelia proliferation (double staining of proliferating cell nuclear antigen with RPE65), and observation of cell proliferation only on uninjured RPE tissue. 30 Although no RPE neurotrophin expression was observed, the RPE can express all the receptors for response

(TrkA, TrkB, TrkC, and p75). Error: Reference source not found

Several; three-dimensional (suspension) culture studies report the generation of optic cup-like structures reminiscent of embryology having multiple retinal tissue layers, of which the fastest most enhancing of eye cup-like structures from human ES included 5 or, 10 ng/ml of Insulin-like Growth Factor-1, and there was expression of proteins for accessory tissues such as lens, and cornea as well. 31

Progenitor Cell Signaling Pathways in Retinitis Pigmentosa Animal Models

IL-6 Family Cytokines -- Leukemia Inhibitory Factor (LIF) delays RHOVPP RP model mouse photoreceptor degeneration by upregulation of Endothelin 2 (Edn2), STAT3,

FGF2, and GFAP, whereof LIF is implicated to induce Edn2 from damaged photoreceptors, which stimulates a subset of Muller cells that have low glutamine synthetase activity. 32 LIF endothelin-2 (Edn-2), and Fibroblast Growth Factor-2 (FGF2) 8 are an upregulated pathway in the rd10Pde RP model that also had activation of Glial

Fibrilliary Acidic Protein (GFAP), and JAK-STAT3 signaling with increased p-JAK2, and p-STAT3 (and elevated CCAAT/enhancer binding protein). 33 Oncostatin M protects rods and promotes the regeneration of cone outer segments with phosphorylation of

STAT3 in Muller cells (but not photoreceptors), which indicates Muller cells mediate oncostatin M effects. 34 CNTF, LIF, and oncostatin M are of the IL-6 family of cytokines. Error: Reference source not found

Wnt Signaling -- Postnatal day 35 rd-1Pde retina expressed 3 fold more Dickkopf-3, 35 which is produced by Muller glia.

Dickkopf-3 potentiates Wnt 3a signaling under conditions of staurosporine promoted apoptosis through antagonizing Dickkopf-1-Kremen dependent inhibition of Wnt signalling, where Dickkopf 3 can bind both Kremen 1, or 2 in membrane vesicles that apparently eventually become peri-nuclear. 36 The Wnt signaling antagonists, Secreted

Frizzled-Related Proteins (SFRP) of SFRP1 and SFRP5 are restricted to surviving photoreceptors in human RP, while SFRP1, SFRP2, SFRP3, and SFRP5 are localized to the inner limiting membrane. 37

Intercellular/Paracrine Mechanisms -- Mammalian rod photoreceptors require a critical density of other cells for differentiation. Error: Reference source not found [ . . . ]

[Besides the importance of developmental signaliung pathways, and other critical influence of the extracellular matrix] Culturing retinal progenitor cells on lamin β2/S- laminin increases the number differentiating as rod photoreceptors, but soluble factors have a considerable role in photoreceptor development. Error: Reference source not found 9

Inflammation and Regeneration

Inflammation increases CXCR7, which influences SDF-1/CXCL12 induced chemotaxis because CXCR7 has a 10-fold greater affinity for SDF-1/CXCL12 than

CXCR4, and CXCR7 has anti-apoptotosis effects without being linked to the usual chemokine G-protein mechanism of CXCR4. 38

Reported Retinitis Pigmentosa Therapeutic Agents Affecting Regeneration

Vitamin A/Retinol -- A RCT found that 15,000 IU vitamin A daily for RP patients with preserved electroretinograms (ERG) retained ERG amplitudes more than patients on placebo. 39

Retinol is the alcohol form of vitamin A 40 that is systemically transported from hydrolysis of liver retinyl ester stores. 41 Cultures with 0.5 μM retinol are reported to maintain a proliferative pluripotent state in both mouse embryonic (from blastocyst inner cell mass), or induced Pluripotent Stem (iPS) cells (from fibrobroblasts} with the latter repotyed passaged in culture for over 100 days. 42 Retinol can sustain embryonic stem and iPS cell proliferation, and pluripotency without methods such as maintenance on a feeder cell culture, Error: Reference source not found or additional growth factors, and is compatible with suspension cultures. Error: Reference source not found Retinol promotes self renewal of embryonic stem cells that is independent of mouse strain origin, and that has pluripotency for all embryonic differentiation lineages, with germ cell development, as well as chimera integration. Error: Reference source not found 10

Retinol regulates the self renewal of stem cells by over expression of insulin-like growth factor II that activates the insulin-like growth factor 1 receptor tyrosine kinase, Error:

Reference source not found and the associated insulin receptor substrate-1 axis via the phosphoinositol three (PI3) kinase cascade resulting in the phpsphorylation of Akt/PKB on T308 and S473 with downstream involvement of mammalian Target of Rampamycin

Complexes (TORC) 1 and 2 having a resultant activation of p70S6 kinase, which is a key component of the cell protein synthetic machinery. 43 This pathway is part of the retinol

(vitamin A) ability to suppress differentiation, and maintains stem cell renewal that occurs by increased expression of the nuclear factors Nanog, and Oct4 Error: Reference source not found which is independent from other known pathways such as LIF/STAT3, bone morphogenic proteins, or Wnt/β-catenin. 44 Embryonic stem cells do not express the genes for retinol conversion toretinoic acid, or transport of retinoic acid to the nucleus, which causes differentiation of cells (as below). Error: Reference source not found

Vitamin A/Retinol effects on stem cells has detailed review. Error: Reference source not found

Retinoic Acid -- Human embryonic, or postnatal retina cell proliferation in vitro is reported for retinoic acid whereby a percentage of cells differentiates as photoreceptors indicated by recoverin+. 45 Injection of 30 mg/kg all-trans-retinoic acid into pregnant rats during embryonic photoreceptor generation increased the density of rat pup rod photoreceptors. 46 Ocular retinoic acid is synthesized primarily by the retinal pigment epithelium, although other cell lines produce this compound during earlier stages of development. Error: Reference source not found Retinoic acid is essential for neural tissue development in effecting the switch from progenitor cell proliferation to neuronal 11 cell differentiation by causing cell cycling exit along with gene expression controlled by both Retinoic Acid Receptor (RAR) α, and RARγ. 47 Retinoic acid induces neuron commitment in CGR8, or DBA-252 embryonic stem cells through inhibition of p38

Mitogen-Activated Protein Kinase (p38 MAPK), which when active in embryonic stem cells would produce cardiomyocytes. 48 However, in later neuron development, p38

MAPK is required for neurite formation, and neuron survival. Error: Reference source not found

9-cis-retinoic Acid -- A cross-over RCT of 300 mg/day 9-cis-β-carotene for 90 days in

29 RP patients increased dark adapted ERG by 8.4 μV versus ERG decline while on plcebo. 49 9-cis-β-carotene is metabolized by intestine mucosa to 9-cis-retinoic acid, 50 which is the vitamin A metabolite able to activate both the Retinoic Acid Receptor, and the Retinoic X Receptor (RXR) required for vitamin A gene transcription on heterodimerization of these receptors. 51 Dissociated high density 6-8 day retinal cultures exposed to all-trans-retinoic acid greatly increased rod photoreceptor differentiation, but

9-cis-retinoic acid increased by about ten times rod differentiation, yet after birth all- trans-retinoic acid had much less effect on rod differentiation in low density 6-8 day cultures (10 nM all-trans-retinoate = 14% rods recoverin+). 52

Taurine -- Taurine stimulated rod photoreceptor development of rat neonatal (<24 hr old) retinal gel cultures with a half maximal stimulation concentration of 2 μM, and is a component of the rod promoting activity of retinal cell conditioned media, but apparently does not require uptake into cells for this activity. 53 12

Ascorbic Acid (Vitamen C) -- Some of the aqueous humor enhancement of rat retinal precursor cell proliferation is due to ascorbic acid, which was maximal at 0.025 mg/ml of ascorbate. 54 In vitro ascorbate at 10 μg/ml alleviated the senescence roadblock for pluripotent reprogramming, and accelerated gene expression changes for induction of mouse or human pluripotent stem cells from somatic cells. 55 Vitamin C enhances the in vitro generation of induced Pluripotent Stem Cells (iPS) by regulating jhdm1a and -b histone demethylase expression that are involved in producing the master stem cell transcription factor Nanog. 56 Vitamin C also encourages iPS maintance in vitro partly by reduction of the p53 tumor suppressor protein. Error: Reference source not found

Numerous embryonic stem cell genes for neurogenesis are responsive to ascorbic acid that particularly include differentiation, and adhesion genes such as BDNF, and cadherin.

Nerve Growth Factor -- Visual field enlargement was reported for 3 (37.5%) of 8 RP patients administered murine NGF eye drops over 10 days. Error: Reference source not found NGF promotes the proliferation of human Muller glia with a half maximal concentration at 0.04 ng/ml (1.5 pM) in vitro. 58 NGF and NGF receptor immunoreactivity are reported from and on rat retinal Muller glia, as well as retinal pigment epithelium. 59 A transient neurogenesis first resulted after rat retina sodium iodate injury by dedifferentiated Muller cells that had cell proliferation from decrease of the p27kip1 inhibitor of cell cycling, and decrease of the Notch1-Hes1 pathway that allowed differentiation of photoreceptor markers each of which was associated with elevated Nerve Growth Factor (NGF) signaling, however the eventual predominant result was scar forming gliosis. Error: Reference source not found Muller cell dedifferentiation 13 and proliferation is induced by rat Bone Marrow Stem Cells (rBMSC) in vitro, and when rBMSC are subretinally transplanted into RCSMerTK RP model rats, endogenous Muller cells transdifferentiated with opsin (glutamate synthetase+, crx+) expression via Nerve

Growth Factor (NGF) activation of Tyrosine Kinase Receptor type 1 (TrkA) involving the pPI3K, pAkt, and pCREB pathway (along with more retention of the outer nuclear layer of photoreceptors versus control RCSMerTK rats). Error: Reference source not found

The aqueous extract of Ganoderma lucidum b (Reishi mushrooms) had no cytotoxicity, and was neuritogenic (at 75 μg/ml) in rat pheochromocytoma (PC-12) cultures with activation of NGF signaling such as the MEK/ERK1/2, and PI3K/Akt pathways. 60 PC-12 cultures were established from a rat adrenal medullary tumor, and has been extensively utilized as a model for neuronal proliferation, and differentiation investigations. Error: Reference source not found The alcohol extract of G. lucidum is reported to also have NGF-like promotion of non-amyloidogenic secretion in SH-SY5Y neuroblastoma cultures that is an essential pathway for transdifferentiating bone marrow progenitor cells to neurons. 61 The NGF signaling cascade reported activated by G. lucidum extract included Phosphatidylinositol 3 Kinase (PI3K), Phospholipase Cγ1

(PLCγ1), Protein Kinase C (PKC), and ERK1/2. Error: Reference source not found

Curcumin - Oral curcumin at 100 mg/kg dissolved in a powdered milk preparation is reported to improve transgenic RHOP23H rat RP model retina morphology and physiology.

Oral Curcuma longa extract at 300 mg/kg increased cell proliferation, and differentiation in the hippocampus dentate gyrus subgranular zone of normal, or galactose b Grifola frondosa, and G. neo-japonicum aqueous extracts mushrooms were also studied with similar results, but G. neo-japonicum was neuritogenic at 50 μg/ml. c Curcuminoids have very poor intestinal absorption. 14 aged mice that was attended by increased BDNF, and cAMP Response Element Binding protein (CREB) signaling. 63 CREB is heavily implicated in neurogenesis, as well as neuron development. 64 The extract improved learning, and spatial memory in normal, as well as mice aged by galactose treatment. Error: Reference source not found

Curcuminoid extracts consist of 75-80% curcumin, 15-20% Demethoxycurcumin

(DMC), and 3-5% Bisdemethoxycurcumin (BDMC). 65 Two months of oral Curcuma longa extract (95.9% curcuminoids) pretreatment at 10 mg/kg of aged (24 month) rats improved learning and spatial memory, which was correlated with serotonin levels in prefrontal cortex, and hippocampus. 66 Two year old rats dosed with curcuminoids also had decreased glutamate excitotoxicity, and plasma corticosterone levels. Error:

Reference source not found PC12 cell culture neurite outgrowth is promoted by 20 μM of individual curcuminoids to similar (16-22%) amounts through ERK1/2- and PKC- dependent pathways, but only curcumin and DMC induced phosphylorated CREB. Error:

Adult mice treated with intraperitoneal 500 nM/kg (184 mg/kg) d curcumin daily for 4 days had increased hippocampus dentate gyrus subgranular zone cell proliferation after day 1 (BrdU+) that by 4 weeks were distributed throughout the dentate gyrus with maturity of morphology, and neuron specific protein (BrdU+, NeuN+) labeling, but no double labeling occurred with BrdU for glial fibrillary acid protein. 67 Curcumin increased proliferation with an optimal concentration of 500 nM e by stimulating basal

ERK1/2, and p38 MAP Kinases in cultures of mouse C17.2 neural progenitor cells, and d 1 mole curcumin = 368.38 g/mole (Google value) x 0.0005 M (500 nM) = 0.18419 g = 184 mg. e Cell cultures exhibited curcumin cytotoxicity at > 10 μM, however Kim et al. 2008 state that there is no evidence that high doses of curcumin produced hippopampal toxcitity in vivo (intestinal absorption is very low). The authors estimate that 500 nM/kg i.p. would result in a 5-6 μM blood curcumin concentration, and that blood-brain barrier restriction would result in 1-2 μM brain curcumin concentration. 15 embryonic neural stem cells as determined by specific inhibitor studies. Error: Reference source not found Oral 12 mg/kg curcumin treatment for 3 months (but not 1.5 months) enhanced hippocampal dentate gyrus neurogenesis particularly in the hilus, but also in the subgranular zone of 1 1/2 year aged rats attended by improvements in both spatial, and non-spatial memory. 68 Gene expression in these 1 1/2 year old rats was related to neural plasticity, and growth, some of which involved Wnt signaling. Error: Reference source not found Oral 10 or 20 mg/kg curcumin in peanut oil for 21 days administered to rats under chronic unpredictable stress increased hippocampal hilar, and subgranular zone proliferation (BrdU+) by 20 - 28% (of which at 20 mg/kg 59% expressed the mature neuron marker NSE) versus vehicle treated stressed controls. 69 Oral 10 or 20 mg/kg curcumin in peanut oil treatment during 20 days of 6 hours/daily restraint stressed rats reversed the impeded learning, and dose dependently improved impaired memory versus vehicle treated restraint stressed rats, or unstressed rats. 70 The peanut oil dissolved curcumin doses reversed increases of corticosterone, and increased dendritic branching.

Error: Reference source not found In vitro curcumin prevents toxicity from corticosterone activation of the glucocorticoid receptor in primary fetal hippocampal cultures with down regulation of CaMKII, and NMDA receptor 2B mRNA. Error:

Reference source not found Oral 75 mg/kg f curcumin administered to adult, or aged g rats for 8 days h enhanced spatial learning, and dentate gyrus neuron arborization with a 2 fold increase in neurons having polysialylated neuron cellular adhesion molecule. 71

Curcumin binding to PKCδ caused phosphorylation of a tyrosine residue that promoted

PKCδ degradation, which allows polysialylated neuron adhesion molecule expression. f But not 37.5 mg/kg curcumin over 8 days. g About 1 1/2 year old. h 40 days of the curcumin dose produced no better learning. 16

Error: Reference source not found Elderly asians who regularly consumed curry had better cognitive function than rare, or non-consumers of curry. 72 Curry contains the dried rhizome of Curcuma longa known as the spice, tumeric, Error: Reference source not found from which curcuminoids, and pure curcumin is extracted.

Cannabinoids -- Intraperitoneal (i.p.) 100 μg/kg injection of the cannabinoid agonist

HU210 three times weekly in transgenic RHOP23H rats produced more retained ERG amplitude as well as less latency of a- and b-waves with preserved neuroretinal connectivity versus sham injected RHOP23H rats. 73 Vervet monkey Muller cells are reported to express Cannabinoid Receptor 2 (CB2R), which does not produce psychoactive effects. 74

Twice daily 100 mg/kg of the HU210 cannabinoid i.p. over 10 daye in chronically injected rats had increased BrdU determined neurogenesis in the hippocampal dentate gyrus that had fully differentiated granule neurons at one month after the final injection. 75 The HU210 induced neurogenesis had anxiolytic and antidepressant-like effects. Error: Reference source not found In vitro studies reported Hu210 promoted proliferation, but not differentiation of neural progenitor cells with indicated activation of the CB1 receptor having associated G i/o proteins, and ERK signaling. Error: Reference source not found

Cannabinoids modulate neural progenitor cells by direct cannabinoid receptor signaling, and interaction with pathways for differentiation. 76 Cannabinoid neurogenic roles include neuron specification, axon navigation, and morphogenesis. 77 Specific agonist, and CB1 receptor null mouse studies indicate that the endocannabinoid system promotes neural progenitor cell proliferation in vitro. 78 17

Non-psychoactive Cannabinoid receptor 2 (CB2) agonists stimulate neural progenitor cell

79 proliferation in vitro and in vivo. A diacylglycerol lipase-CB2 pathway regulates adult subventricular zone neurogenesis in an age-dependent manner. 80

Melatonin -- Daily intraperitoneal 10 mg/kg melatonin injection of rdsPeriph RP model mice slowed photoreceptor degeneration, but displayed no scotopic or photopic ERG changes (reference indicates melatonin antioxidant, Bcl2, & NF-κB influence, but also a promotion of light induced degeneration), 81 yet 2 mg/kg melatonin in drinking water for transgenic RHOP23H rats increased scotopic ERG b-wave with more retinal structural integrity versus the respective control RP model rodents (reference has melatonin for RP circadian disruption citations). 82

Melatonin release at night regulates circadian rhythm, and neurogenic mitosis in the subventricular zone occurs at night. 83 Neurogenic stem cells express the Metalonin receptor MT1, and MT2 with melatonin agonists increasing brain-derived neurotrophic factor expression in the hippocampus dentate gyrus. Error: Reference source not found

Wenyang Yiqi Huoxue Recipe -- Wenyang yiqi huoxue recipe treated rdsPeriph RP model mice had increased ERG a-, and b-wave amplitude with decreased latency, as well as increased basic fibroblast growth factor, and preserved photoreceptors compared to untreated rdsPeriph mice. 84 Wenyang huoxue recipe consists of Panax ginseng, Radix aconiti lateralis preparata, Radix Ilex pubesceus, and Herbal Leonuri. 85 CD34+ hematopoietic stem cell mobilization to peripheral blood occurred as early as 10 days of wenyang huoxue recipe treatment with eventual stem cell migration to stenosed areas of myocardial infarction patients Error: Reference source not found who had improved heart function. 86 18

Ginseng -- Red (steam treated) ginseng extract increased bullfrog visual sensitivity by

1.4 log units of light, and ERG dark adapted b-wave amplitude, apparently with chronically administered ginseng. 87

After traumatic brain injury of rats, the injection of 5-80 mg/kg extracted saponins from Panax ginseng improved memory and learning that was accompanied by BrdU+

(bromodeoxyuridine), and nestin+ cells in the hippocampus along with increased NGF,

GDNF, and NCAM, but with decreased neurogenesis suppressors, yet dose response dependence occurred up to 20 mg/kg with equivalent benefit thereafter. 88

Ginsengoside Rg1 increases proliferation of murine neural progenitor cells in vitro, and at 5 or 10 mg/kg in vivo of hippocampal dentate gyrus stem cells. 89 Gerbil ischemia-induced dentate gyrus cell proliferation and survival is reported increased by 5

90 or 10 mg/kg Rg1, and this Rg1 effect did not depend on BDNF. Rg1 promotes bone marrow stromal/mesenchymal cell proliferation by estrogen receptor mediated signaling, but does not displace estradiol from the estrogen receptor (with genes for MKP-1, and

91 SGK also responsive). Rg1 protects against β-amyloid-induced rat cortical neuron death by activating downstream events dependent on both the estrogen receptor α and glucocorticoid receptors that results in two pathways: (1) ERK1/2 phosphorylation, which inhibits iNOS generation of NO that nitrates protein tyrosine residues, and (2) NF-

92 κB activation. Mouse embryonic stem cell neuronal differentiation facilitated by Rg1 is reported dependent on the Glucocorticoid Receptor (GR) via the GR-MEK-ERK1/2-

PI3K-Akt signaling pathway as determined by inhibitor studies. 93 19

Rg1 increases Vascular Endothelial Growth Factor (VEGF) synthesis, and lengthens the cell cycle proliferative (S) phase with shortening of the resting (G0/G1) phase. Error: Reference source not found

Ginsenoside Rb1 treatment of neurosphere cultures from 14.5 day embryonic rat cortex progenitor cells protected against tert-butylhydroperoxide oxidative stress by Nrf induction of HO-1, but had no effect on proliferation, or differentiation of neural progenitor cells. 94

Ginsenoside Rg1 promotes the proliferation, migration, adhesion, and vasculogenesis of endothelial (hematopoietic) progenitor cells in vitro. 95

Panax notoginseng saponins up-regulated phosphorylation of MEK1/2, ERK1/2,

Akt1/2, and PI-3K protein kinases, as well as GATA1/2 transcription factors along with

GATA1/2 DNA binding in hemopoietic cell cultures. 96

Radix Aconiti lateralis preparata - Radix Aconiti lateralis preparata activates proliferation of mouse bone marrow mesenchymal stem cells, and induces osteogenic differentiation through the bone morphpogenic protein-2/Smad dependent Runx2 pathway (beginning with ERK-1/2) within 2 weeks, whereas osteogenesis by a usual protocol takes 3 weeks. 97

Herbal Leonuri - A plant of wide distribution, herbal leonuri contains alkaloids

(leonurine, stachydrine), and flavinoids (quercetin, kaempferol, rutin) that are beneficial under tissue damage conditions through anti-apoptotic, antioxidant, and anti- inflammatory effects in various animal model reports. 98 A flavonol (4.8% quercetin,

3.9% kaempferol, 0.7% isorhaminetin) extract at 50 mg/kg for 4 months increased the 20 hippocampal Brain-Derived Neurotrophic Factor levels in a transgenic Alzheimer's disease mouse model where treatment also improved spatial memory. 99 Kaempferol, and quercetin strongly induce neurofilament expression for neurite outgrowth. Error:

The citrus flavonoid glycoside rutin at 1 μg/ml pretreatment of HT22 hippocampal neuron cultures ameliorated the ethanol-induced decrease in NGF, GDNF, and BDNF. 100 Rutin also counteracted the ethanol-induced malonyldialdehyde increase with the accompanying decrease in reduced glutathione, SOD1, and catalase as well as elevated inflammatory indicators of IL-1β, COX-2, and iNOS with decreased viability indicated by LDH release. Error: Reference source not found Rutin increases the survival of neural crest cells, and quercetin reduces the H2O2 toxicity for neural progenitor cells. 101

Flavonoids -- Of 33 flavonoids tested in rat astrocyte cultures; calycosin, isorhamnetin, luteolin, and genistein produced NGF, GDNF, and BDNF, whereas other flavonoids yielded either NGF, or GDNF, but not BDNF. 102 Flavonoids induced phosphorylation of the estrogen receptor, and inhibition of this process reduced neurotrophin production.

Error: Reference source not found

Electrical Stimulation -- A randomized, sham-controlled, partly blinded 24 patient study of transcorneal electrical stimulation at 150% of phosphene threshold with 20 Hz, 5-ms biphasic pulses for 30 minutes per week over 6 months reported increased scotopic ERG b-wave amplitude, and kinetic visual field enlargment by 17%, but there was a decrease 21 in desaturated color discrimination. 103 Electrical stimulation features in an artificial silicon retina microchip implants for 6 RP patients had improved vision in areas too distant from the implant to be due to direct electrical stimulation, yet was attributed to neurotrophic factor stimulation of photoreceptor rescue, 104 [or neurogenesis].

Transcorneal 700 μAmpere electrical 10 ms biphasic rectangular pulse stimulation of transgenic RHOP34L rabbit left eyes increased rhodopsin, and photopic ERG waves along with the scotopic b-wave compared to sham treated right eyes. 105 Transcorneal

100 μAmpere electrical 1 hour stimulation weekly of RCSMerTK rat left eyes has report of preserving the photoreceptor (ONL) layer, and ERG up to 7 weeks of age compared to sham stimulated right eyes. 106 Transcorneal application of rectangular 1 ms biphasic 200

μAmpere electrical pulses at 20 Hz for 1 hour to the right eye of rats that had this stimulation 2 hours before 16,000 lux light exposure had report that the stimulated eye had a higher ERG saturation amplitude, and a lower rod response b-wave implicit time, while there was preservation of the outer nuclear layer, and outer segment length with less photoreceptor death compared to sham exposure. 107

Rescue of retinal ganglion cells from apoptosis induced by optic nerve transection is reported for transcorneal electrical stimulation, which increases IGF-1 secretion from Muller cells. 108

In vitro electrical stimulation (1 ms, 20 Hz pulses at 10 mA) of Muller cells had upregulated BDNF production that was not detected extracellularly at 6 hour, that may indicate autocrine stimulation (or a single determination artifact with subsequent secretion), which was fully suppressed by the voltage dependent calcium channel blocker nifedipine. 109 Magnetic fields also have similar calcium channel effects. Numerous 22 studies have reported that 50 Hz of 1 milliTesla magnetic flux applied to mesenchymal, or brain-derived stem cells report increased proliferation, and neural differentiation. 110

Cellular pathways indicated in these studies include increase of voltage-gated L-type

CaV1 calcium channels leading to an elevated CREB phosphorylation, while other transcription factors include Hes1, Ascl, Neurogenic Differentiation Factor 1 (NeuroD1),

NeuroD2, Neurogenin1, and HDAC. Error: Reference source not found Human mesenchymal stem cell neurogenesis occurred from 1000 seconds of pulsed or constant current 250 mV stimulation by gold coated culture surfaces every three days as indicated by numerous neuronal markers, and neurite outgrowth, but the greatest neurite outgrowth

(>150 mm) occurred on stimulation in culture with mature neurons. 111 Even two direct current exposures at 0.53 or 1.83 V/m (which are within physiological levels) for 10 minutes per day to brain derived neural stem/progenitor cells along with EGF/FGF, or the neural differentiation factor INFγ promoted neuron maturation, and neurite outgrowth that reached 600 μm (with INFγ_. 112

References 1 Liu Y, Gao L, Zuba-Suma EK, Peng X, Kucia M, Ratajczak MZ, Wang W, Enzman V, Kaplan HJ, Dean DC. Identification of small Sca-1+ , Lin-, CD45-, multipotential cells in the neonatal murine retina. Exp Hematol 2009;37:1096-1107 2 Tropepe V, Coles BLK, Chiasson BJ, Horsford DJ, Elia AJ, McInnes RR, van der Kooy D. Retinal stem cells in the adult mammalian eye. Science 2000;287:2032-6 3 Das AV, Mallya KB, Zhao X, Ahmad F, Bhattacharya S, Thoreson WB, Hegde GV, Ahmad I. Neural stem cell properties of Muler glia in the mammalian retina: Regulation by Notch and Wnt. Dev Biol 2006;299:283-302 4 Karl MO, Reh TA. Regenerative medicine for retinal diseases: activating the endogenous repair mechanisms. Trends in Mol Med 2010;16(4):193-202 5 Goldman D. Muller cell reprogramming and retina regeneration. Nat Rev Neurosci 2014;15(7):431-42 6 Osakada F, Ooto S, Akagi T, Mandai M, Akaike A, Takahashi M. Wnt signaling promotes regeneration in the retina of adult mammals. J Neurosci 2007;27(15):4210-19 7 Falsini B, Iarossi G, Chiaretti A, Ruggiero A, Luigi M, Galli-Resta L, Corbo G, Abed E. NGF eye-drop topical administration in patients with retinitis pigmentosa. J Transl Med 2016;14(1):8 doi: 10.1186/s12967-015-0750-3. 8 Jian Q, Tao Z, Li Y, Yin ZQ. Acute retinal injury and the relationship between nerve growth factor, notch1 transcription and short-lived dedifferentiation transient changes of mammalian Muller cells. Vision Res 2015;110(Pt A):107-17 9 Jian Q, Li Y, Yin ZQ. Rat BMSCs initiate retinal endogenous repair through NGF/TrkA signaling. Exp Eye Res 2015;132:34-47 10 Uren PJ, Lee JT, Doroudchi MM, Smith AD, Horsanger A. A profile of transcriptomic changes in the rd10 mouse model of retinitis pigmentosa. Mol Vis 2014;20:1612-28 11 Yi H, Nakamura REI, Mohamed O, Dufort D, Hackam AS. Characterization of Wnt signaling during photoreceptor degeneration. Invest Ophthalmol Vis Sci 2007;48(12):5733-41 12 Goel M, Dhingra NK. Muller glia express rhodopsin in a mouse model of inherited retinal degeneration. Neurosci 2012;225:152 13 Ortega-Martinez S. A new perspective on the role of the CREB family of transcription factors in memory consolidation via adult hippocampal neurogenesis. Front Mol Neurosci 2015;8:46 doi: 10.3389/fnmol.2015.00046. eCollection 2015 14 Paquet-Durand F, Azadi S, Hauck SM, Ueffing M, Van Veen T, Ekstrom P. Calpain is activated in degenerating photoreceptors of the rd1 mouse. J Neurochem 2006;96:802-14 15 Dong E, Bachleda A, Xiong Y, Osawa S, Weiss ER. Reduced phosphoCREB in Muller glia during retinal degeneration. Mol Vis 2017;23:90-102 16 Del Debbio CB, Balasubramanian S, Parameswaran S, Chaudhuri A, Qiu F, Ahmad I. Notch and Wnt signaling mediated rod photoreceptor regeneration by Muller cells in adult mammalian retina. PLoS One 2010;5(8):e12425 17 Moshiri A, Reh TA. Persistent proigenitors at the retinal margin of ptc +/- mice. J Neurosci 2004;24(1):229-37. 18 Close JL, Gumuscu B, Reh TA. Retinal neurons regulate proliferation of postnatal progenitors and Muller glia in the rat retina via TGFβ signaling. Development 2005;132(13):3015-26 19 Ma L, Cantrup R, Varrault A, Colak D, Klenin N, Gotz M, McFarlane S, Journot L, Schuurmans C. ZacI functions through TGFβII to negatively regulate cell number in developing retina. Neurol Dev 2007;2:11 20 Levine EM, Fuhrmann S, Reh TA. Soluble factors and the development of rod photoreceptors. Cell Mol Life Sci 2000;57:224-34 21 Singhal S, Lawrence JM, Bhatia B, Ellis JS, Kwan AS, MacNeil A, Luthert PJ, Fawcett JW, Perez MT , Khaw PT, Limb GA. Chondroitin sulfat proteoglycans and microglia prevent migration and integration of grafted Muller stem cells into degenerating retina. Stem Cells 2008;26:1074-82 22 Wang S, Lu B, Girman S, Duan J, McFarland T, Zhang Q, Grompe M, Adamus G, Appukuttan B, Lund R. Non- invasive stem cell therapy in a rat model of retinal degeneration and vascular pathology. PloS One 2010;5(2):e9200 23 Chen J, Li Y, Wang L, Zhang Z, Lu D, Lu M, Chopp M. Therapeutic benefit of intravenous administration of bone marrow stromal cells after cerebral ischemia in rats. Stroke 2001;32:1005-11 24 Guo C, Otani A, Oishi A, et al. Knockout of CCR2 alleviates photoreceptor cell death in a model of retinitis pigmentosa. Exp Eye Res 2012;104:39-47 25 Machalinska A, Klos P, Baumert B, Baskiewicz M, Kawa M, Rudnicki M, Lubinski W, Wiszniewska B, Karczewicz D, Machalinski B. Stem cells are mobilized from the bone marroiw into the peripheral circulation in response to retinal epithelium damage--A pathophysiological attempt to produce endogenous regeneration. Curr Eye Res 2011;36(7):663- 72 26 Penzo M, Habiel D, Ramadass M, Kew RR, Marcu KB. Cell migration to CXCL12 requires simultaneous IKKα and IKKβ-dependent NF-κB signaling. Biochim Biophys Acta 2014;1843(9);1796-1804 27 Marquez-Curtis L, Janowska--Wieczorek A. Enhancing the migrating ability of mesenchymal stromal cells by targeting the SDF-1/CXCR4 axis. Biomed Res Int 2013;2013:561098 28 Raymond SM, Jackson I. The retinal pigment epithelium is required for development and maintenance of the mouse neural retina. Curr Biol 1995;5(11):1286-95 29 Saini JS, Temple S, Stern JH. Human retinal pigment epithelium stem cells (RPESC). Adv Exp Med Biol 2016;854:557-62 30 Machalinska A, Kawa MP, Pius-Sadowska E, Roginska D, Klos P, Baumert B, Wiszniewska B, Machalinska B. Enogenous regeneration of damaged retinal pigment epithelium following low dose sodium iodate administration: An insight into the role of glial cells in retinal repair. Exp Eye Res 2013;112:68-78 31 Mellough CB, Collin J, Khazim M, White K, Sernagon E, Steel DHW, Lako M. IGF-1 signaling plays an important role in the formation of three-dimensional laminated neural retina and other ocular structures from human embryonic stem cells. Stem Cells 2015;33:2416-30 32 Joly S, Lange C, Thiersch M, Smardzija M, Grimm C. Leukemia inhibitory factor extends the lifespan of injured photoreceptors in vivo. J Neurosci 2008;28(51):13765-74 33 Samardzija M,.Wariwoda U, Imsand C, Huber P Heynen SR, Gubler A, Grimm C. Activation of survival pathways in the degenerationg retina of rd10 mice. Exp Eye Res 2012;99:17-26 34 Xia X, Li Y, Huang D, Wang Z, Luo L, Song Y, Zhao L, Wen R. Oncostatin M protects rod and cone photoreceptors and promotes regeneration of cone outer segments in a rat model of retinal degeneration. PLoS One 2011;6(3):e18282 35 Hackam AS, Strom R, Liu D, Qian J, Wang C, Otteson D, Gunatilaka T, Farkas RH, Chowers I, Kageyama M, Leveillard T, Sahel JA, Campophairo PA, Parmigiani G, Zack DJ. Identification of gene expression changes associated with the progression of retinal degeneration in the rd1mouse. Invest Ophthalmol Vis Sci 2004;45:2929-42 36 Nakamura REI, Hackam AS. Analysis of Dickkopf3 interactions with Wnt signaling. Growth Factors 2010;28(4):232-42 37 Jones SE, Jomary C, Grist J, Stewart HJ, Neal NJ. Modulated expression of secreted frizziled-related protein in in human retinal degeneration. Neuroreport 2000;11:3963-7 38 Merino JJ, Bellver-Landete V, Oset-Gasque MJ, Cubelos B. CXCR4/CXCR7 molecular involvement in neuronal and neural progenitor migration: Focus on CNS repair. J Cell Physiol 2015;230:27-42 39 Berson EL, Rosner B, Sandberg MA, Hayes KC, Nicholson BW, Weigel-DiFranco C, Willett W. A randomized trial of vitamin A and vitamin E supplementation for retinitis pigmentosa. Arch Ophthalmol 1993;111:761-72 40 Chen L, Khillan JS,. Promotion of feeder-independent self-renewal of embryonic stem cells by retinol (vitamin A). Stem Cells 2008;26:1858-64 41 Khillan JS. Vitamin A/retinol and maintenance of pluripotency of stem cells. Nutrients 2014;6:1209-22 42 Bhatia H, Sharma R, Dawes J, Khillan J. Maintenance of feeder free anchorage independent cultures of ES and iPS cells by retinol/vitamin A. J Cell Biochem 2012;113:3002-10 43 Chen L, Khillan JS. A novel signaling by vitamin A/retinol promotes self renewal of mouse embryonic stem cells by activating PI3K/Akt signaling pathway via insulin-like growth factor-1 receptor signaling. Stem Cells 2010;28:57-63 44 Chen L, Yang M, Dawes J, Khillan JS. Suppression of ES cell differentiation by retinol (vitamin A) via the overexpression oif Nanog. Differentiation 2007;75:682-93 45 Kelley MW, Turner JK, Reh TA. Regulation of proliferation and photoreceptor differentiation in fetal human retinal cell cultures. Invest Ophthalmol Vis Sci 1995;36(7):1280-9 46 Kelley MW, Williams WC, Turner JK, Creech-Kraft JM, Reh TA. Retinoic acid promotes rod photoreceptor differentiation in vivo. Neuroreport 1999;10(11):2389-94 47 Janesick A, Wu SC, Blumberg B. Retinoic acid signalling and neuronal differentiation. Cell Mol Life Sci 2015;72:1559-76 48 Aouadi M, Bost F, Caron L, Laurent K, Le Marchand Bruatel Y, Binetruy B. p38 mitogen-activated protein kinase activity commits embryonic stem cells to either neurogenesis or cardiomyogenesis. Stem Cells 2006;24(5):399-406 49 Rotenstreich Y, Belkin M, Sadetzki S, Chetrit A, Ferman- Attar G, Sher I, Haran A, Shaish A, Harats D. Treatment with 9-cis β-carotene-rich powder in patients with retinitis pigmentosa: a randomized crossover trial . JAMA Ophthalmol 2013;131(8):985-92 50 Wang XD, Krinsky NI, Benotti PN, Russell RM. Biosynthesis of 9-cis-retinoic acid from 9-cis-β-carotene in human intestinal mucosa in vitro. Arch Biochem Biophys 1994;313(1):150-5 51 Nagy L, Szanto A, Szatmari I, Szeles L. Nuclear hormone receptors enable macrophages and dendritic cells to sense their lipid environment and shape their immune response. Physiol Rev 2012;92:739-89 52 Kelley MW, Turner JK, Reh TA. Retinoic acid promotes differentiation of photoreceptors in vitro. Development 1994;120:2091-2102 53 Altshuler D, Lo Turco JJ, Rush J, Cepko C. Taurine promotes the differentiation of a vertebrate retinal cell type in vitro. Development 1993;119:1319-28 54 Yang J, Klassen H, Pries M, Wang W, Nissen MH. Aqueous humor enhances the proliferation of rat retinal precursor cells in culture, and this effect is partially reproduced by ascorbic acid. Stem Cells 2006;24:2766-75 55 Esteban MA, Wang T, Qin B, Yang J, Qin D, Cai J, Li W, Weng Z, Chen J, Ni S, Chen K, Li Y, Liu X, Xu J, Zhang S, Li F, He W, Labuda K, Song Y, Peterbauer A, Wolbank S, Redl H, Zhong M, Cai D, Zeng L, Pei D. Vitamin C enhances the generation of mouse and human induced pluripotent stem cells. Cell Stem Cell 2010;6:71-9 56 Nualart F, Salazar K, Oyarce K, Cisternas P, Jara N, Silva-Alvarez C, Pastor P, Martinez F, Garcia A, Garcia-Robles Mde LA, Carlos J. Typical and atypical stem cells in the brain, vitamin C effect and neuropathology. Biol Res 2012;45:245-56 57 Shin DM, Ahn JI, Lee KH, Lee YS. Ascorbic acid responsive genes during neuronal differentiation of embryonic stem cells. NeuroReport 2004;15:1959-63 58 Ikeda T, PuroDG. Nerve growth factor: a mitogenic signal for retinal Muller glial cells. Brain Res 1994;649:260-4 59 Chakrabarti S. Sima AAF, Lee J, Brachet P, Dicou E. Nerve growth factor (NGF), proNGF and NGF receptor-like immunoreactivity in BB rat retina. Brain Res 1990;523:11-15 60 Ling-Sing Seow S, Naidu M, David P, Wong KH, Sabaratnam V. Potentiation of neuritogenic activity of medicinal mushrooms in rat pheochromocytoma cells. BMC Complement Altern Med 2013;13:157 61 Pinweha S, Wanikiat P, Sanvarinda Y, Supavilai P. The signaling cascades of Ganoderma lucidum extracts in stimulating non-amyloidogenic protein secretion in human neuroblastoma SH-SY5Y cell lines. Neurosci Lett 2008;448:62-6 62 Vasireddy V, Chavali VRM, Joseph VT, Kadam R, Lin JH, Jamison JA, Kompella UB, Reddy GB, Ayyagari R. Rescue of photoreceptor degeneration by curcumin in transgenic rats with P23H rhodopsin mutation. PLoS One 2011;6(6):e21193 63 Nam SM, Choi JH, Yoo DY, Kim W, Jung HY, Kim JW, Yoo M, Lee S, Kim CJ, Yoon YS, Hwang IA. Effects of curcumin (Curcuma longa) on learning and spatial memory as well as cell proliferation and neuroblast differentiation in adult aged mice by upregulating brain-derived neurotrophic factor and CREB. J Med Food 2014;17(6):641-9 64 Merz K, Herold S. CREB in adult neurogenesis -- master and partner in the development of adult-born neurons? Eur J Neurosci 2011;33:1078-86 65 Liao KK, Wu MJ, Chen PY, Huang SW, Chiu SJ, Ho CT, Yen JH. Curcuminoids promote neurite outgrowth in PC12 cells through MAPK/ERK- and PKC-dependent pathways. J Agric Food Chem 2012;60(1):433-43 66 Pyrzanowska J, Piechal A, Blecharz-Klin K, Lehner M, Skorzewska A, Turzynska D, Sobolewska A, Plaznik A, Widy-Tyszkiewicz E. The influence of the long-term administration of Curcuma longa extract on learning and spatial memory as well as the concentration of brain neurotransmitters and level of plasma corticosterone in aged rats. Pharmacol Biochem Behav 2010;95:351-8 67 Kim SJ, Son TG, Park HR, Park M, Kim MS, Kim HS, Chung HY, Mattson MP, Lee J. Curcumin stimulated proliferation of embryonic neural progenitor cells and neurogenesis in the adult hippocampus. J Biol Chem 2008;283(21):14497-14505 68 Dong S, Zeng Q, Mitchell S, Xiu J, Duan Y, Li C, Tiwari JK, Hu Y, Cao X, Zhao Z. Curcumin enhances neurogenesis and cognoition in aged rats: Implications for transcriptional interactions related to growth and synaptic plasticity. PLoS One 2012;7(2):e31211 69 Xu Y, Ku B, Cui L, Li X, Barish PA, Foster TC, Ogle WO. Curcumin reverses impaired hippocampal neurogenesis and increases serotonin receptor 1A mRNA and brain-derived neurotrophic factor expression in chronically stressed rats. Brain Res 2007;1162:9-18 70 Xu Y, Lin D, Li S, Li G, Shyamala S, Barish PA, Vernon MM, Pan J, Ogle WO. Curcumin reverses impaired cognition and neuronal plasticity induced by chronic stress. Neuropharmacol 2009;57:463-71 71 Conboy L, Foley AG, O'Boyle NM, Lawlor M, Gallagher HC, Murphy KJ, Regan CM. Curcumin-induced degradation of PKCδ is associated with enhanced dentate NCAM PSA expression and spatial learning in adult and aged Wistar rats. Biochem Pharmacol 2009;77:1254-65 72 Ng TP, Chiam PC, Lee T, Chua HC, Lim L, Kua EH. Curry consumption and cognitive function in the elderly. Am J Epidemiol 2006;164(9):898-906 73 Lax P, Esquiva G, Altavilla C, Cuenca N. Neuroprotective effects of the cannabinoid agonist HU210 on retinal degeneration. Exp Eye Res 2014;120C:175-85 74 Bouskila J, Javadi P, Casanova C, Ptito M, Bouchard JF. Muller cells express the cannabinoid CB2 receptor in the vervet monkey retina. J Comp Neurol 2013;521:2399-2415 75 Jiang W, Zhang Y, Xiao L, Van Cleemput J, Ji SP, Bai G. Zhang X. Cannabinoids promote embryonic and adult hippocampus neurogenesis and produce anxiolytic- and antidepressant-like effects. J Clin Invest 2005;115(11):3104-16 76 Galve-Roperh I, Aguado T, Palazuelos J, Guzman M. The endocannabinoid system and neurogenesis in health and disease. Neuroscientist 2007;13(2):109-14 77 Diaz-Alonso J, Guzman M, Galve-Roperh. Endocannabinoids via CB1 receptors act as neurogenic niche cues during cortical development. Phil Trans R Soc Lond B Biol Sci 2012;367(1607):3229-41 78 Aguado T, Monory K, Palazuelos J, Stella N, Cravatt B, Lutz B, Marsicano G, Kokaia Z, Guzman M, Galve-Roperh I. The endocannabinoid system drives neural progenitor proliferation. FASEB J 2005;19(12):1704-6 79 Palazuelos J, Aguado T, Egia A, Mechoulam R, Guzman M, Galve-Roperh I. Non-psychoactive CB2 cannabinoid agonists stimulate neural progenitor proliferation. FASEB J 2006;20(13):2405-7 80 Goncalves MB, Suetterlin P, Yip P, Molina-Holgado F, Walker DJ, Oudin MJ, Zentar MP, Pollard S, Yanez-Munoz RJ, Williams G, Walsh FS, Pangalos MN, Doherty P. A diacylglycerol lipase-CB2 pathway regulates adult subventricular zone neurogenesis in an age-dependent manner. Mol Cell Neurosci 2008;38:526-36 81 Liang FQ, Aleman TS, Yang Z, Cideciyan AV, Jacobson SG, Bennett J. Melatonin delays photoreceptor degeneration in the rds/rds mouse. NeuroReport 2001;12(5):1011-14 82 Lax P, Otalora BB, Esquiva G, Roi MA, Madrid JA, Cuenca N. Circadian dysfunction in P23H rhodopsin transgenic rats: effects of exogenous melatonin. J Pineal Res 2911;50:183-91 83 Sarlak G, Jenwitheesuk A, Chetsawang B, Govitrapong P. Effects of melatonin on nervous system aging: Neurogenesis and degeneration. J Pharmacol Sci 2013;123:9-24 84 Deng TT, Dou RH, Pan L, Zhang YH, Yuan W, Deng H, Jin M. [Effect and mechanisms of wenyang yiqi huoxue recipe on the apoptosis of photoreceptor cells in retinal degeneration slow mice]. Zhongguo Zhong Xi Yi Jie He Za Zhi 2013;33(8):1122-8 85 Lin PC, Chang LF, Liu PY, Lin SZ, Wu WC, Chen WS, Tsai CH, Chiou TW, Harn HJ. Botanical drugs and stem cells. Cell Transplant 2011;20:71-83 86 Yang QY, Zhao LC. [Effect of yiqi wenyang huoxue recipe on bone marrow stem cells' mobilization and its influence on heart function in patients with myocardial infarction]. Zhongguo Zhong Xi Yi Jie He Za Zhi 2008;28(12):1078-81 87 Wahid F, Jung H, Khan T, Hwang KH, Kim YY. Effects of red ginseng extract on visual sensitivity and ERG b-wave of bullfrog's eye. Planta Med 2010;76:426-32 88 Hu BY, Liu XJ, Qiang R, Jiang ZL, Xu LH, Wang GH, Li X, Peng B. Treatment with ginseng total saponins improves the neurorestoration of rat after traumatic brain injury. J Ethnopharmacol 2014;155:1243-55 89 Shen L, Zhang J, Ginsenoside Rg1 promotes proliferation of hippocampal progenitor cells. Neurol Res 2004;26:422-8 90 Shen L, Zhang J. Ginsenoside Rg1 increases ischemia-induced cell proliferation and survival in the dentate gyrus of adult gerbils. Neurosci Lett 2003;344:1-4 91 Lu X, Wang H, Wu X, Zhou L, Wang L, Zhang X, Cao K, Huang J. Ginsenoside Rg1 promotes bone marrow stromal cells proliferation via activation of the estrogen receptor-mediated signaling pathway.. Acta Pharmacol Sin 2008;29(10):1209-14 92 Wu J, Pan Z, Wang Z, Zhu W, Shen Y, Cui R, Lin J, Yu H, Wang Q, Qian J, Yu Y, Zhu D. Ginsenoside Rg1 protection against β-amyloid peptide-induced neuronal apoptosis via estrogen receptor α and glucoortioid receptor- dependent anti-protein nitration pathway. Neuropharmaol 2012;63:349-61 93 Wu J, Pan Z, Cheng M, Shen Y, Yu H, Wang Q, Lou Y. Ginsengoside Rg1 facilitates differentiation of mouse embryonic stem cells via GR-dependent signaling pathway. Neurochem Int 2013;62:92-102 94 Ni N, Liu Q, Ren H, Wu D, Luo C, Li P, Wan JB, Su H. Ginsenoside Rb1 protects rat neural progenitor cells against oxidative injury. Molecules 2014;19:3012-24 95 Shi A, Wang X, Lu F, Zhu M, Kong X, Cao K,. Ginsenoside Rg1 promotes endothelial progenitor cell migration and proliferation. Acta Pharmacol Sin 2009;30(3):299-306 96 Sun X, Gao RI, Lin X, Xu W, Chen X. Panax notoginseng saponins induced up-regulation, phosphorylation, and binding activity of MEK, ERK, AKT, PI-3K protein kinases and GATA transcription factors in hematopoietic cells. Chin J Intgr Med 2013;19(2):112-8 97 Kim DR, Kim HY, Park JK, Park SK, Chang MS. Aconiti lateralis preparata radix activates the proliferation of mouse bone marrow mesenchymal stem cells and induces osteogenic lineage differentiation through the bone morphogenetic protein-2/Smad-dependent Runx2 pathway. Evid Based Complement Alternat Med 2013;e586741 10 p 98 Liu XH, Pan LL, Zhu YZ. Active chemical compounds of traditional Chinese medicine Herba Leonuri: implications for cardiovascular diseases. Clin Exp Pharmacol Physiol 2011;39(3):274-82 Ginsengoside RG1 99 Hou Y, Aboukhatwa MA, Lei DL, Maanaye K, Khan I, Luo Y. Anti-depressant natural flavonols modulate BDNF and beta amyloid in neurons and hippocampus of double TgAD mice. Neuropharmacol 2010;58:911-20 100 Song K, Na JY, Kim S, Kwon J. Rutin upregulates neurotrophic factors resulting in attenuation of ethanol-induced oxidative stress in HT22 hippocampal neuronal cells. J Sci Food Agric 2014; epub 101 Xu SL, Zhu KY, Bi CWC, Yan L, Men SWX, Dong TTX, Tsim KWK. Flavinoids, derived from traditional Chinese medicines, show roles in the differentiation of neurons: Possible targets in developing health food products. Birth Defects Res (Part C) 2013;99:292-99 102 Xu SL, Bi CWC, Choiu RCY, Zhu Ky, Miernisha A, Dong TTX, Tsim KWK. Flavoniods induce the synthesis and secretion of neurotrophic factors in cultured rat astrocytes: A signaling response mediated by estrogen receptor. Evid Based Complement Alternat Med 2013;epub 103 Schatz A, Rock T, Naycheva L, Willmann G, Wilhelm B, Peters T, Bartz--Schmidt KU, Zrenner E, Medssias A, Gekeler F. Transcorneal electrical stimulation for patients with retinitis pigmentosa: A prospective, randomized, Sham- controlled exploratory study. Invest Ophthalmol Vis Sci 2011;52(7):4485-96 104 Chow AY, Chow VY, Packo KH, Pollack JS, Peyman GA, Schuchard R. The artificial silicon retina microchip for the treatment of vision loss from retinitis pigmentosa. Arch Ophthalmol 2004;122:460-9 105 Morimoto T, Kanda H, Kondo M, Terasaki H, Nishida K, Fujikado T. Transcorneal electric stimulation promotes survival of pphotoreceptors and improves retinal function in rhodopin P347L transgenic rabbits. Invest Ophthalmol Vis Sci 2012;53:4254-61 106 Morimoto T, Fujikado T, Choi JS, Kanda H, Miyoshi T, Fukuda Y, Tano Y. Transcorneal electrical stimulation promotes the survival of photoreceptors and preserves retinal function in Royal college of surgeons rats. Invest Opthalmol Vis Sci 2007;48:4725-32 107 Schatz A, Arango-Gonzales B, Fischer D, Enderle H, Bolz S, Rock T, Naycheva L, Grimm C, Messias A, Zrenner E, Bartz-Schmidt KU, Willmann G. Transcorneal electrical stimulation shows neuroprotective effects in retinas of light- exposed rats. Invest Ophthalmol Vis Sci 2012;53(9):5552-61 108 Morimoto T, Miyoshi T, Matsuda S, Tano Y, Fujikado T, Fukuda Y. Transcorneal electrical stimulation rescues axotomised retinal ganglion cells by activating endogenous retinal IGF-1. Invest Ophthalmol Vis Sci 2005;46:2147-55 109 Sato T, Fujikado T, Lee TS, Tano Y. Direct effect of electrical stimulation on induction of brain-derived neurtrophic factor from cultured Muller cells. Invest POphthalmol Vis Sci 2008;49:4641-6 110 Leone L, Podda MV, Grassi C. Impact of electromagnetic fields on stem cells: common mechanisms at the crossroads between adult neurogenesis and osteogenesis. Front Cell Neurosci 2015;9:228 111 Park SJ, Park JS, Yang HN, Yi SW, Kim CH, Park KH. Neurogenesis is induced by electrical stimulation of human mesenchymal stem cells co-cultured with mature neuronal cells. Macromol Biosci 2015;15:1586-94 112 Korbelt LJ, Wilkinson AE, McCormick AM, Willits RK, Leipzig ND. Short duration electrical stimulation to enhance neurite outgrowth and maturation of adult neural stem progenitor cells. Ann Biomed Eng 2014;46(10):2164-76