Mitochondrial Peptides—Appropriate Options for Therapeutic Exploitation

Cell and Tissue Research (2019) 377:161–165 https://doi.org/10.1007/s00441-019-03049-z

MINI REVIEW

Mitochondrial peptides—appropriate options for therapeutic exploitation

Lucia-Doina Popov1

Received: 12 April 2019 /Accepted: 10 May 2019 /Published online: 27 May 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract Besides their well-known function in cellular bioenergetics, the role of mitochondria in signaling regulation of cells homeostasis and survival has been uncovered during the past few decades. Possessing an independent genome and a unique genetic code, mitochondria biosynthesize protective stress response factors, the Bmitochondrial-derived peptides,^ import and deposit peptides within their matrix and are the target of peptides bound to bioactive agents, aiming at alleviation of pathology-related malfunction of the electron transport chain. As the rapidly evolving field of mitochondrial peptides is appropriate for therapeutic exploitation, a brief overview of the major recent findings is timely needed. Here, the focus is on the following issues: (i) the biological effects of mitochondrial-derived peptides (humanin, humanin-like peptides and MOTS-c) and their use in therapy, (ii) the abnormal accumulation of β-amyloid peptide within the mitochondrial matrix and (iii) the effectiveness of Bmitochondrial cell-penetrating/ targeting peptides^ as vehicles for delivery of bioactive agents into dysfunctional mitochondria.

Keywords mtDNA . β-Amyloid . Humanin . Cell-penetrating peptides . Mitochondrial targeted peptides

Introduction functional Bmitochondrial-derived peptides^ (MDPs). This class of peptides comprises humanin, humanin-like peptides Mitochondria are well-known intracellular organelles with a and MOTS-c and expands the expression of mitochondrial vital role in ATP biosynthesis and thus, in cellular bioenerget- proteome (Kim et al. 2018). ics. Owing to their prokaryotic origin, mitochondria execute the Bquorum sensing^ coordination of intracellular processes by sending Bretrograde^ signals such as Ca2+, ROS and cyto- Naturally occurring mitochondrial-derived chrome C. to the other intracellular organelles and to the cy- peptides tosol (Lee et al. 2013, 2015; Popov 2017). The mitochondrial genome inherits bacterial-like traits: the The first MDP discovered back in 2001 was Humanin (HN); DNA molecules (mtDNA) are circular, double stranded, small the term originates from Nishimoto’s group based on the po- (16,569 nucleotides in humans) and compact. mtDNA con- tential of this peptide for restoring the Bhumanity^ of tains 37 genes, including 22 tRNAs, 2 rRNAs (12S and 16S Alzheimer’s disease (AD) patients (Hashimoto et al. 2001). rRNA) and 13 mRNAs encoding the proteins of the electron HN is encoded by the 75 bp ORF sequence within the 16S transport chain (Cobb et al. 2016; Lee et al. 2013, 2016). The rRNA gene of mtDNA. In response to cellular stress, HN is mtDNA has no introns but a few non-coding nucleotides be- secreted as a peptide made of 24 or 21 amino acids, depending tween adjacent genes and Bsmall open reading frames^ on the cytoplasmic or mitochondrial translation site, respec- (sORF, smaller than or equal to 300 nucleotides) that encode tively. At the neuronal cell surface, HN binds to a receptor composed of ciliary neurotrophic factor receptor α, the cyto- kine receptor WSX-1 and the transmembrane gp130 * Lucia-Doina Popov (heterotrimeric HN receptor); moreover, HN proved to be an [email protected]; [email protected] endogenous agonist peptide of the formyl peptide receptor 2 1 Institute of Cellular Biology and Pathology BNicolae Simionescu^ of (Hashimoto et al. 2013). the Romanian Academy, 8, B.P. Hasdeu Street, The intracellular roles of HN are as follows: (i) involve- 050568 Bucharest, Romania ment in the retrograde signaling pathway from the 162 Cell Tissue Res (2019) 377:161–165 mitochondria to the nucleus (Cobb et al. 2016); (ii) participa- misfolding, a key step in type 2 diabetes mellitus (Okada tion as a stress-responsive, cell survival factor (Nashine et al. et al. 2017). Specifically, SHLP2 has the following biological 2017); HN is cytoprotective against oxidative stressors, by effects: (i) acts as an insulin sensitizer, which operates both activation of the chaperone-mediated autophagy pathway peripherally and centrally (Cobb et al. 2016), (ii) restores the (Gong et al. 2018), (iii) protection from cells death by inhibi- normal levels of oxidative phosphorylation chain protein sub- tion of ROS generation, upregulation of mitochondrial GSH units, (iii) increases the number of mtDNA copies, (iv) re- and activation of caspase 3 and 4 (Minasyan et al. 2017), (iv) duces amyloid-β-induced cellular and mitochondrial toxicity defense against endoplasmic reticulum (ER) stress, by resto- and (v) has anti-apoptotic outcomes (Nashine et al. 2018). ration of the depleted mitochondrial glutathione (GSH) level Moreover, in AMD cells, in vitro, SHLP2 exerts protective (Sreekumar et al. 2017). effects (Nashine et al. 2018). HN has beneficial effects in pathologies that involve both The mitochondrial open-reading-frame of the 12S rRNA-c oxidative and ER stress, such as stroke, myocardial infarction, (MOTS-c, mitochondrial ORF of the twelve S c) (Lee et al. diabetes, cancer (Gong et al. 2018) and atherosclerosis (Lee 2015) is a recently identified MDP composed of 16 amino et al. 2013). HN treatment is neuroprotective in AD, by acids. Following stress induction, MOTS-c translocates into defending cells from β-amyloid (Aβ) toxicity (Cobb et al. the nucleus, binds to DNA and regulates transcription of stress 2016) and in age-related macular degeneration (AMD), a lead- response genes in the mitochondrial - nucleus crosstalk (Kim ing cause of blindness among the elderly population et al. 2018). Although MOTS-c signaling is only partially (Sreekumar et al. 2017). uncovered at present, the current data support numerous im- The analog of HN, humanin G (HNG) (in which the serine plications of this peptide in mediation of metabolic homeosta- 14 was replaced by glycine), has cardioprotective effects in sis, mitohormesis, cell survival, stimulation of glucose metab- myocardial ischemia reperfusion injury in vivo, by attenuation olism and insulin sensitivity (especially in the skeletal mus- of oxidative stress and activation of antioxidant defense mech- cle), as well as in the regulation of diet-induced obesity, dia- anisms (Klein et al. 2013). betes and longevity (Lee et al. 2015, 2016). HNG may be a potential therapeutic solution in dry AMD, an eye disease with no available treatment at present (Klein et al. 2013; Nashine et al. 2017). Mitochondrial matrix, a site for Aβ-peptides Recently, six additional peptides encoded within the mito- accumulation chondrial 16S rRNA region of mtDNA have been discovered and designed as Small HN-like peptides (SHLP1-6) (Fig. 1) It has been established that mitochondria can import cytosolic (Cobb et al. 2016; Nashine et al. 2018). SHLP2 and SHLP3 peptides. For Aβ-peptides present in the brain of AD patients, share similar biological effects with HN: are cytoprotective the issue starts with the γ-secretase complex located at and enhance mitochondrial metabolism (Cobb et al. 2016). mitochondria-associated endoplasmic reticulum membranes, Both HNG and SHLP2 inhibit islet amyloid polypeptide the intracellular site of Aβ production (Pinho et al. 2014).

Fig. 1 The mitochondrion- peptides relationship: the mitochondrial ribosomal RNAs biosynthesis of Bmitochondria- derived peptides^ (MDPs) and the mitochondrial matrix dual function: a deposit for β-Amyloid and a target for the bioactive cargoes transported by the chemical synthesized vectors such as the Bcell-penetrating peptides^ (CPPs), Bmitochondrial-penetrating peptides^ (mtCPPs) and Bmitochondria-targeted peptides^ (MTPs). HN, humanin; HNG, humanin G; humanin-like peptides (SHLP1-6) and MOTS-c Cell Tissue Res (2019) 377:161–165 163

Next, the mitochondrial translocase TOMM22 (in humans) penetrating peptides^ (mtCPPs). Recently, dual constructs recognizes the cytosolic Aβ and transfers it to TOMM40, with augmented scavenging ability have been launched: (i) another translocase subunit. Then, the peptide chain is direct- the mtCPP1-UPF25 (where mtCPP1 targets mitochondria, ed to the TOMM channel and enters mitochondria via the N- whereas UPF25—an antioxidative GSH analog—is active terminal Bpre^sequence, a structural prerequisite for import within the cytosol (Cerrato and Langel 2017) and (ii) the li- (Hu et al. 2018). Another key reaction takes place within the posomal system made of a CPP and a mitochondrial RNA mitochondrial matrix, where the Bpre^sequence (the aptamer; it has a higher mitochondrial targeting activity via hydrophobic fragment Aβ35-40) is cleaved by the an ATP-dependent pathway (Yamada et al. 2016). Bpre^sequence protease (PreP) in cooperation with neurolysin The Bcell-penetrating mitochondrial transit peptides^ peptidase (Taskin et al. 2017; Teixeira et al. 2018). This is a (CpMTP) is another term found in the literature for the turning point, as impairment or reduced efficiency of the mitochondrial-targeted CPPs (Jain and Chugh 2016). This cleaving reaction, causes PreP inhibition followed by abnor- term may be confusing due to the existence of a distinct class mal accumulation of toxic, immature Aβ within the matrix of Bmitochondria-targeted peptides^ (MTPs) that penetrate all and by mitochondrial dysfunction (respiratory chain malfunc- cells (even the blood-brain barrier) and transport and deliver tion, ROS generation, mitochondrial permeability transition bioactive cargoes (small molecules, peptides, liposomes and pore induction, calcium homeostasis imbalance, mitochondri- nanoparticles) into the mitochondrial matrix (Szeto 2018). al dynamics disturbance and mitochondrial DNA/RNA muta- Similar to CPPs, most MTPs are lipophilic (to cross the or- tions), all associated with AD (Pinho et al. 2014; Taskin et al. ganelle’s hydrophobic double membrane systems) and cat- 2017). These complex interactions anticipate mitochondria as ionic (to manage the negative membrane potential of mito- a potential therapeutic target for AD in the future (Han et al. chondria) (Jean et al. 2016). In particular, the MTP tetra- 2017). peptides (Szeto-Schiller peptides, SS) possess an aromatic- cationic motif with 3+ net charge, cross the outer mitochondrial membrane (OMM), localize to the inner membrane Mitochondria—a target for therapeutic (IMM) where they associate with cardiolipin (important for delivery of bioactive agents cristae curvatures), modify the spatial organization of electron transport proteins and improve electron transfer and ATP pro- Basic research is currently focused on the development of duction (Sabbah et al. 2016;Szeto2018; Szeto and Liu various peptide-based delivery scaffolds projected to be used 2018). The cell permeable, tetra-peptide Szeto-Schiller (SS)- as therapeutic agents. The class of Bcell-penetrating peptides^ 31 (D-Arg-dimethylTyr-Lys-Phe-NH2) deserves special at- (CPPs) covalently tethered to various cargoes (such as mac- tention based on biological effects and therapeutic potential. romolecules, genes, therapeutic agents) interact with the cell It prevents mitochondrial-dependent ROS generation and en- surface and cross the plasma membrane, or are taken up inside hances ATP synthesis in neurons, heart and kidney and in the cell by endocytosis (Jean et al. 2016). Once in the cytosol, several pathologies, atherosclerosis included. The peptide CPPs are directed to the mitochondrial compartment, where SS-31 is neuroprotective, safeguarding AD neurons from they deliver appropriate bioactive cargoes aimed to correct Ca2+-induced mitochondrial depolarization, swelling and cy- mitochondrial dysfunction. There are several structural and tochrome c release, is protective against Aβ-induced synaptic functional requirements for the CPPs: they must expose cat- and mitochondrial toxicity, reduces excessive mitochondrial ionic and/or amphipathic residues (to facilitate the pass fission and increases mitochondrial fusion (Reddy et al. through the plasma membrane), their size should be short, 2018). Known also under the name elamipretide, the chemical composition should mimic the mitochondrial (Bendavia™, MTP-131) it improves left ventricular systolic import sequence (to facilitate mitochondrial delivery) and they function, normalizes plasma biomarkers and reverses mito- should be lipophylic (to not disrupt the mitochondrial mem- chondrial abnormalities (Sabbah et al. 2016). Moreover, a branes); finally, the mitocondrial processing proteinase will single infusion of elamipretide proved to be safe and well release the delivered cargoes into the mitochondrial matrix tolerated in heart failure with reduced ejection fraction (Cerrato et al. 2015; Jain and Chugh 2016; Lin et al. 2015). (Daubert et al. 2017). In experimental models of Within the matrix, the covalent linker of the cargoes may glomerulosclerosis and senescence, the systemic administra- negatively influence its biological activity and therefore, the tion of SS-31 reduced collagen IV, pERK1/2 and α-smooth use of cleavable linkers is recommended (Lei and Kelley muscle actin (markers of parietal epithelial cell activation) 2017). Moreover, matrix accumulation of CPPs may have and improved desmin and synaptopodin (markers of cytotoxic effects; this is a key issue to be considered at the podocyte injury and cytoskeletal integrity, respectively) evaluation of novel designed constructs. (Sweetwyne et al. 2017). Other reports show that SS-31 pep- Based on the fact that the final target is mitochondrion, the tide suppresses the foam cell formation and atherosclerotic CPPs vehicles were designed also as Bmitochondrial cell- progression (Zhang et al. 2017). Based on the efficacy and 164 Cell Tissue Res (2019) 377:161–165 lack of toxicity in animal models, the clinical trials using SS- References 31 peptides are ongoing (Szeto 2018). Besides the SS-31 peptides, the class of cell-permeable tetra-peptides also in- Alta RY,Vitorino HA, Goswami D, Liria CW, Wisnovsky SP, Kelley SO, cludes SS-02, SS-19 and SS-20 peptides (Reddy et al. 2018). Machini MT, Espósito BP (2017) Mitochondria-penetrating peptides conjugated to desferrioxamine as chelators for mitochondrial To obtain a higher therapeutic efficacy, the SS peptides are labile iron. PLoS One 12:e0171729. https://doi.org/10.1371/journal. conjugated with bioactive molecules targeting mitochondria. pone.0171729 eCollection 2017 Examples are as follows: (i) the SS-31 peptide-conjugated Cerrato CP, Langel Ü (2017) Effect of a fusion peptide by covalent con- with geranylgeranylacetone-loaded poly(lactic-co-glycolic jugation of a mitochondrial cell-penetrating peptide and a glutathione analog peptide molecular therapy. Methods Clin Dev 5:221–231 acid) nanoparticles, to protect the inner ear hair cells from Cerrato CP, Pirisinu M, Vlachos EN, Langel Ü (2015) Novel cell- gentamicin, a well-known ototoxic agent (Kuang et al. 2017; penetrating peptide targeting mitochondria. FASEB J 29:4589– Zhou et al. 2018), (ii) the tagging of the SS peptides with GSH 4599. https://doi.org/10.1096/fj.14-269225 (MitoGSH), to restore mitochondrial GSH levels in heart dis- Cobb LJ, Lee C, Xiao J, Yen K, Wong RG, Nakamura HK, Mehta HH, ease and to preserve its redox buffering and signaling capacity Gao Q, Ashur C, Huffman DM, Wan J, Muzumdar R, Barzilai N, Cohen P (2016) Naturally occurring mitochondrial-derived peptides (Mailloux 2016), (iii) the tagging of dual function constructs, are age-dependent regulators of apoptosis, insulin sensitivity, and such as those containing SS02 peptide and an octaarginine inflammatory markers. Aging (Albany NY) 8:796–809. https://doi. (R8)-modified MITO-Porter, for efficient mitochondria deliv- org/10.18632/aging.100943 ery in both homogenates and living cells (Kawamura et al. Daubert MA, Yow E, Dunn G, Marchev S, Barnhart H, Douglas PS, O’Connor C, Goldstein S, Udelson JE, Sabbah HN (2017) Novel 2013). Another dual function conjugate is DFOSS02. It acts mitochondria-targeting peptide in heart failure treatment: a random- both as an antioxidant, inhibiting mitochondrial superoxide ized, placebo-controlled trial of Elamipretide. Circ Heart Fail 10: formation (as the SS02 parent peptide) and as a chelator for e004389. https://doi.org/10.1161/CIRCHEARTFAILURE.117. mitochondrial labile iron (a feature of the siderophore 004389 desferrioxamine (DFO) with high affinity for iron) (Alta Gong Z, Tasset I, Diaz A, Anguiano J, Tas E, Cui L, Kuliawat R, Liu H, Kühn B, Cuervo AM, Muzumdar R (2018) Humanin is an endoge- et al. 2017). The ongoing developments in targeting mito- nous activator of chaperone-mediated autophagy. J Cell Biol 217: chondria with bioactive molecules bound to synthetic peptide 635–647. https://doi.org/10.1083/jcb.201606095 vectors (like CPPs and MTPs) are directed towards the im- Han XJ, Hu YY, Yang ZJ, Jiang LP, Shi SL, Li YR, Guo MY, Wu HL, provement of their cellular uptake and mitochondrial Wan YY (2017) Amyloid β-42 induces neuronal apoptosis by targeting mitochondria. Mol Med Rep 16:4521–4528. https://doi. targeting. org/10.3892/mmr.2017.7203 Hashimoto Y, Niikura T, Tajima H, Yasukawa T, Sudo H, Ito Y, Kita Y, Kawasumi M, Kouyama K, Doyu M, Sobue G, Koide T, Tsuji S, Lang J, Kurokawa K, Nishimoto I (2001) A rescue factor abolishing Conclusions neuronal cell death by a wide spectrum of familial Alzheimer’s disease genes and Aβ. PNAS USA 98:6336–6341 Hashimoto Y, Nawa M, Kurita M, Tokizawa M, Iwamatsu A, Matsuoka 1. Figure 1 summarizes the state-of-art in mitochondrion- M (2013) Secreted calmodulin-like skin protein inhibits neuronal peptides relationship. death in cell-based Alzheimer’s disease models via the 2. The ongoing studies are focused on mitochondrial pep- heterotrimeric humanin receptor. Cell Death Dis 4:e555. https:// doi.org/10.1038/cddis.2013.80 tides exploitation in neurodegenerative diseases; howev- Hu W, Wang Z, Zheng H (2018) Mitochondrial accumulation of amyloid er, their potential in therapy is far from being entirely β (Aβ) peptides requires TOMM22 as a main Aβ receptor in yeast. uncovered. The design of novel cleavable linkers of J Biol Chem 293:12681–12689. https://doi.org/10.1074/jbc.RA118. cargoes and the refinement of their mitochondrial release 002713 are the most promising approaches. Jain A, Chugh A (2016) Mitochondrial transit peptide exhibits cell pen- 3. etration ability and efficiently delivers macromolecules to mitochon- This topic opens the question whether other dysfunctional dria. FEBS Lett 590:2896–28905. https://doi.org/10.1002/1873- intracellular organelles can/or cannot be targeted or ma- 3468.12329 nipulated by specific peptide conjugates; the answer re- Jean SR, Ahmed M, Lei EK, Wisnovsky SP, Kelley SO (2016) Peptide- mains to be explored. mediated delivery of chemical probes and therapeutics to mitochondria. Acc Chem Res 49:1893–1902 Compliance with ethical statements Kawamura E, Yamada Y, Harashima H (2013) Mitochondrial targeting functional peptides as potential devices for the mitochondrial delivery of a DF-MITO-Porter. Mitochondrion 13:610–614. https://doi. This mini review is a retrospective study on the recently published papers org/10.1016/j.mito.2013.08.010 related to the subject. My review did not require execution of novel Kim SJ, Mehta HH, Wan J, Kuehnemann C, Chen J, Hu JF, Hoffman AR, research involving human participants and/or animals. In this situation, Cohen P (2018) Mitochondrial peptides modulate mitochondrial formal consent is not necessary. function during cellular senescence. Aging (Albany NY) 10:1239– 1256. https://doi.org/10.18632/aging.101463 Conflict of interest The authors declare that they have no conflict of Klein LE, Cui L, Gong Z, Su K, Muzumdar R (2013) A humanin analog interest. decreases oxidative stress and preserves mitochondrial integrity in Cell Tissue Res (2019) 377:161–165 165

cardiac myoblasts. Biochem Biophys Res Commun 440:197–203. Sabbah HN, Gupta RC, Kohli S, Wang M, Hachem S, Zhang K (2016) https://doi.org/10.1016/j.bbrc.2013.08.055 Chronic therapy with elamipretide (MTP-131), a novel Kuang X, Zhou S, Guo W, Wang Z, Sun Y, Liu H (2017) SS-31 peptide mitochondria-targeting peptide, improves left ventricular and mito- enables mitochondrial targeting drug delivery: a promising thera- chondrial function in dogs with advanced heart failure. Circ Heart peutic alteration to prevent hair cell damage from aminoglycosides. Fail 9:e002206. https://doi.org/10.1161/CIRCHEARTFAILURE. Drug Deliv 24:1750–1761. https://doi.org/10.1080/10717544.2017. 115.002206 1402220 Sreekumar PG, Hinton DR, Kannan R (2017) Endoplasmic reticulum- Lee C, Yen K, Cohen P (2013) Humanin: a harbinger of mitochondrial- mitochondrial crosstalk: a novel role for the mitochondrial peptide derived peptides? Trends Endocrinol Metab 24:222–228. https://doi. humanin. Neural Regen Res 12:35–38. https://doi.org/10.4103/ org/10.1016/j.tem.2013.01.005 1673-5374.198970 Lee C, Zeng J, Drew BG, Sallam T, Martin-Montalvo A, Wan J, Kim SJ, Sweetwyne MT, Pippin JW, Eng DG, Hudkins KL, Chiao YA, Campbell Mehta H, Hevener AL, de Cabo R, Cohen P (2015) The MD, Marcinek DJ, Alpers CE, Szeto HH, Rabinovitch PS, mitochondrial-derived peptide MOTS-c promotes metabolic ho- Shankland SJ (2017) The mitochondrial-targeted peptide, SS-31, meostasis and reduces obesity and insulin resistance. Cell Metab improves glomerular architecture in mice of advanced age. Kidney 21:443–454. https://doi.org/10.1016/j.cmet.2015.02.009 Int 91:1126–1145. https://doi.org/10.1016/j.kint.2016.10.036 Lee C, Kim KH, Cohen P (2016) MOTS-c: a novel mitochondrial- de- Szeto HH (2018) Stealth peptides target cellular powerhouses to fight rare rived peptide regulating muscle and fat metabolism. Free Radic Biol and common age-related diseases. Protein Pept Lett. https://doi.org/ – Med 100:182 187. https://doi.org/10.1016/j.freeradbiomed.2016. 10.2174/0929866525666181101105209 05.015 Szeto HH, Liu S (2018) Cardiolipin-targeted peptides rejuvenate mito- Lei EK, Kelley SO (2017) Delivery and release of small-molecule probes – chondrial function, remodel mitochondria, and promote tissue re- in mitochondria using traceless linkers. Am Chem Soc. 139:9455 generation during aging. Arch Biochem Biophys 660:137–148. 9458. https://doi.org/10.1021/jacs.7b04415 https://doi.org/10.1016/j.abb.2018.10.013 Lin R, Zhang P, Cheetham AG, Walston J, Abadir P, Cui H (2015) Dual Taskin AA, Kücükköse C, Burger N, Mossmann D, Meisinger C, Vögtle peptide conjugation strategy for improved cellular uptake and mito- FN (2017) The novel mitochondrial matrix protease Ste23 is re- chondria targeting. Bioconjug Chem 26:71–77. https://doi.org/10. quired for efficient presequence degradation and processing. Mol 1021/bc500408p Biol Cell 28:997–1002. https://doi.org/10.1091/mbc.E16-10-0732 Mailloux RJ (2016) Application of mitochondria-targeted pharmaceuti- cals for the treatment of heart disease. Curr Pharm Des 22:4763– Teixeira PF, Masuyer G, Pinho CM, Branca RMM, Kmiec B, Wallin C, 4779 Wärmländer SKTS, Berntsson RP, Ankarcrona M, Gräslund A, Minasyan L, Sreekumar PG, Hinton DR, Kannan R (2017) Protective Lehtiö J, Stenmark P, Glaser E (2018) Mechanism of peptide bind- – ing and cleavage by the human mitochondrial peptidase neurolysin. mechanisms of the mitochondrial derived peptide humanin in – oxidative and endoplasmic reticulum stress in RPE cells. Oxid J Mol Biol 430:348 362. https://doi.org/10.1016/j.jmb.2017.11.011 Med Cell Longev 1675230. https://doi.org/10.1155/2017/1675230 Yamada Y, Furukawa R, Harashima HA (2016) Dual-ligand liposomal Nashine S, Cohen P, Chwa M, Lu S, Nesburn AB, Kuppermann BD, system composed of a cell-penetrating peptide and a mitochondrial Kenney MC (2017) Humanin G (HNG) protects age – related mac- RNA aptamer synergistically facilitates cellular uptake and mito- – ular degeneration (AMD) transmitochondrial ARPE-19cybrids from chondrial targeting. J Pharm Sci 105:1705 1713. https://doi.org/ mitochondrial and cellular damage. Cell Death Dis 8:e2951. https:// 10.1016/j.xphs.2016.03.002 doi.org/10.1038/cddis.2017.348 Zhang M, Zhao H, Cai J, Li H, Wu Q, Qiao T, Li K (2017) Chronic Nashine S, Cohen P, Nesburn AB, Kuppermann BD, Kenney MC (2018) administration of mitochondrion-targeted peptide SS-31 prevents Characterizing the protective effects of SHLP2, a mitochondrial- atherosclerotic development in ApoE knockout mice fed Western derived peptide, in macular degeneration. Sci Rep 8:15175. https:// diet. PLoS One 12:e0185688. https://doi.org/10.1371/journal. doi.org/10.1038/s41598-018-33,290-5 pone.0185688 eCollection 2017 Okada AK, Teranishi K, Lobo F, Isas JM, Xiao J, Yen K, Cohen P, ZhouS,SunY,KuangX,HouS,WangZ,QianZ,LiuH(2018) Langen R (2017) The mitochondrial-derived peptides, humanin Mitochondria-homing peptide functionalized nanoparticles S14G and small humanin-like peptide 2, exhibit chaperone-like ac- performing dual extracellular/intracellular roles to inhibit aminogly- tivity. Sci Rep 7:7802. https://doi.org/10.1038/s41598-017-08372-5 cosides induced ototoxicity. Artif Cells Nanomed Biotechnol 29:1– Pinho CM, Teixeira PF, Glaser E (2014) Mitochondrial import and deg- 10. https://doi.org/10.1080/21691401.2018.1457041 radation of amyloid-β peptide. Biochim Biophys Acta 1837:1069– 1074. https://doi.org/10.1016/j.bbabio.2014.02.007 Popov L-D (2017) Mitochondrial networking in diabetic left ventricle cardiomyocytes. Mitochondrion 34:24–31 Reddy PH, Manczak M, Yin X, Reddy AP (2018) Synergistic protective ’ effects of mitochondrial division inhibitor 1 and mitochondria- Publisher snoteSpringer Nature remains neutral with regard to targeted small peptide SS31 in Alzheimer’sdisease.JAlzheimers jurisdictional claims in published maps and institutional affiliations. Dis 62:1549–1565. https://doi.org/10.3233/JAD-170988