Peripheral Infusion of IGF-I Selectively Induces Neurogenesis in the Adult Rat Hippocampus
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The Journal of Neuroscience, April 15, 2000, 20(8):2896–2903 Peripheral Infusion of IGF-I Selectively Induces Neurogenesis in the Adult Rat Hippocampus Maria A. I. Åberg,1 N. David Åberg,1 Helena Hedba¨ cker,1 Jan Oscarsson,2 and Peter S. Eriksson1 1Institute of Clinical Neuroscience, Sahlgrenska University Hospital, and 2Department of Physiology and Pharmacology, Go¨ teborg University, Go¨ teborg, Sweden In several species, including humans, the dentate granule cell progeny, we characterized the colocalization of BrdU- layer (GCL) of the hippocampus exhibits neurogenesis through- immunolabeled cells with cell-specific markers. In animals out adult life. The ability to regulate adult neurogenesis phar- treated with IGF-I for 20 d, BrdU-positive cells increased sig- macologically may be of therapeutic value as a mechanism for nificantly. Furthermore, the fraction of newly generated neurons replacing lost neurons. Insulin-like growth factor-I (IGF-I) is a in the GCL increased, as evaluated by the neuronal markers growth-promoting peptide hormone that has been shown to Calbindin D28K , microtubule-associated protein-2, and NeuN. have neurotrophic properties. The relationship between IGF-I There was no difference in the fraction of newly generated and adult hippocampal neurogenesis is to date unknown. The astrocytes. Thus, our results show that peripheral infusion of aim of this study was to investigate the effect of the peripheral IGF-I increases progenitor cell proliferation and selectively in- administration of IGF-I on cellular proliferation in the dentate duces neurogenesis in the progeny of adult neural progenitor subgranular proliferative zone, which contains neuronal pro- cells. This corresponds to a 78 Ϯ 17% ( p Ͻ 0.001) increase in genitor cells, and on the subsequent migration and differentia- the number of new neurons in IGF-I-treated animals compared tion of progenitor cells within the GCL. Using bromodeoxyuri- with controls. dine (BrdU) labeling, we found a significant increase of BrdU- immunoreactive progenitors in the GCL after6dofperipheral Key words: brain; rat; IGF-I; insulin-like growth factor-I; stem IGF-I administration. To determine the cell fate in progenitor cell; progenitor cell; hippocampus; neurogenesis; stereology Most CNS neurons are terminally differentiated and are, thus, not ing neurons (Suhonen et al., 1996). Proliferation and differentia- replaced after neuronal cell death. However, self-renewing cells tion of adult neural stem cells are affected by age, growth factors, with multilineage potential, designated stem cells or progenitor excitatory input, adrenal steroids, seizures, and enrichment of the cells, have been identified in the adult mammalian brain (Reyn- environment (Cameron and Gould, 1994; Palmer et al., 1995; olds and Weiss, 1992; Richards et al., 1992; Craig et al., 1996; Craig et al., 1996; Kuhn et al., 1996; Bengzon et al., 1997; Gould Suhonen et al., 1996; McKay, 1997; Temple and Alvarez-Buylla, et al., 1997; Kempermann et al., 1997; McKay, 1997; Nilsson et al., 1999). Neural stem cells generate new neurons throughout life in 1999). However, there are to our knowledge no known exogenous the dentate gyrus of the hippocampus in several species, including substances that selectively induce neurogenesis in the adult mam- humans (Altman and Das, 1965; Kuhn et al., 1996; Eriksson et al., malian CNS in vivo. 1998). Progenitor cells isolated from this region have demon- Insulin-like growth factor-I (IGF-I) is a growth-promoting pep- strated the capacity for self-renewal in vitro; when grafted back tide that is important during development of the brain (Sara and into the adult brain, they have the potential to develop into Carlsson-Skwirut, 1988; Bozyczko-Coyne et al., 1993; Giacobini mature neurons with the phenotypic characteristics of surround- et al., 1995; Dentremont et al., 1999). Overexpression of IGF-I, both peripherally and centrally, in transgenic mice results in an Received Oct. 21, 1999; revised Feb. 7, 2000; accepted Feb. 7, 2000. increase in brain size and myelin content (Carson et al., 1993). This study was supported by grants from the Swedish Medical Research Council Conversely, the number of granule cells in the hippocampus, the (project no. 12X-12535), the Faculty of Medicine of the University of Go¨teborg, the oligodendrocyte and neuron density within the olfactory bulbs, John and Brit Wennerstro¨ms Foundation for Neurological Research, the Rune and Ulla Amlo¨vs Foundation for Neurological and Rheumatological Research, Stiftelsen and total brain size are reduced in knock-out mice (Beck et al., Go¨teborgs MS fo¨renings forsknings och byggnadsfond, Stiftelsen Handlanden Hjal- 1995; Cheng et al., 1998). mar Svenssons Forskningsfond, the Swedish Society of Medicine, Go¨teborgs There are two potential pathways by which IGF-I may affect the La¨karesa¨llskap, the Edit Jacobssons Foundation, Stiftelsen Thure Carlssons Minne, Stiftelsen Lars Hiertas Minne, the Novo Nordisk Foundation, the Åke Wiberg hippocampus. IGF-I receptors expressed in the adult dentate Foundation, the Magnus Bergvalls Foundation, Axel Linders stiftelse, and the Tore gyrus (Lesniak et al., 1988) may be reached by IGF-I either from Nilssons Foundation. We appreciate the technical advice of Ann-Marie Alborn and the periphery (by crossing the blood–brain barrier) (Duffy et al., the assistance of Barbro Eriksson with coding slides. We also want to thank Maria Wågberg and Knut Pettersson at Astra Ha¨ssle Gothenburg for kindly letting us use 1988; Reinhardt and Bondy, 1994) or locally by paracrine IGF-I their microscope. Recombinant human IGF-I was a kind gift from Genentech (South (Breese et al., 1996). In the present study we wanted to assess the San Francisco, CA). We are grateful to Dr. Tommy Johnson at the Department of Statistics (Go¨teborg University, Go¨teborg, Sweden) for the statistical advice and to impact of peripheral, normally liver-derived, IGF-I. Proper English (Alfta, Sweden) for proofreading of this manuscript in English. It is possible that the reported alterations in hippocampal Correspondence should be addressed to Dr. Peter S. Eriksson, Institute of granule cell number in animals with supranormal or subnormal Clinical Neuroscience, Go¨teborg University, Blå Stråket 7, SE-413 45 Go¨teborg, Sweden. E-mail: [email protected]. IGF-I levels occur in part as a result of a perturbation in the Copyright © 2000 Society for Neuroscience 0270-6474/00/202896-08$15.00/0 proliferation of endogenous neural progenitor cells. This hypoth- Åberg et al. • IGF-I Stimulation of Adult Progenitor Stem Cells J. Neurosci., April 15, 2000, 20(8):2896–2903 2897 esis led us to investigate the proliferation and differentiation of Mannheim, Mannheim, Germany), or rabbit anti-GFAP (1:500; Dako, progenitor cells in the adult dentate gyrus in hypophysectomized Glostrup, Denmark) and rat anti-BrdU antibody (1:200; Harlan, Lough- borough, United Kingdom) overnight at 4°C. GFAP and Calbindin D28K (hx) rats treated with peripheral administration of IGF-I. The hx were detected with Texas Red-conjugated anti-rabbit IgG (1:200 for rat is widely used as a model of somatic IGF-I deficiency because GFAP and 1:100 for Calbindin D28K; Jackson ImmunoResearch, West hx animals have low circulating levels of IGF-I (Schoenle et al., Grove, PA), Calbindin D28K was also detected with Cy5-conjugated 1982; Sjo¨berg et al., 1994). We used bromodeoxyuridine (BrdU) anti-rabbit IgG (1:150; Jackson ImmunoResearch), NeuN and MAP2 labeling to monitor proliferation and double or triple immuno- were detected with Texas Red-conjugated anti-mouse IgG (1:100; Jack- son ImmunoResearch), and BrdU was labeled with an FITC-conjugated fluorescent labeling for BrdU and cell-specific markers to deter- anti-rat IgG (1:150; Jackson ImmunoResearch) for 2 hr at 37°C. Immu- mine the phenotype of the progenitor progeny. nofluorescence was detected and processed with a Nikon Diaphot fluo- rescence microscope and confocal laser-scanning microscopy using a Bio-Rad 1024 system (Hercules, CA). MATERIALS AND METHODS Quantification. For each animal, the number of BrdU-positive cells in the granule cell layer (GCL; including the subgranular layer) and in the Animals and hormonal treatment. We used hx rats, which have low hilus and their corresponding sample volumes were determined in 12 circulating levels of IGF-I (Schoenle et al., 1982; Sjo¨berg et al., 1994). immunoperoxidase-stained, 40-m-thick coronal sections taken 240 m The effect of IGF-I treatment was shown by comparing the weight gain apart. Area estimations were obtained by planimetry, using a Lucivid in treated versus untreated (control) hx rats (data not shown) (Schoenle device (MicroBrightField, Colchester, VT) attached to a Leica micro- et al., 1982; Fielder et al., 1996). Female Sprague Dawley rats (Mølle- scope. The section thickness of 40 m (microtome setting) was used in gaard Breeding Center, Ejby, Denmark) were hypophysectomized at the dissector estimation of volume. The number of BrdU-positive cells 50 d of age at the Møllegaard Breeding Center. Weight-matched female was counted within the GCL and two cell diameters below the GCL, normal (non-hx) rats were also investigated. All rats were maintained ignoring the cells in the uppermost focal plane and focusing through the under standard conditions of temperature (24–26°C) and humidity (50– thickness of the section to avoid errors caused by oversampling [for a 60%) and with lights on between 05:00 and 19:00 hr. The rats had access discussion of the optical dissector principle, see Gundersen et al. (1988); to water and standard laboratory chow ad libitum. Hormonal treatment West (1993); Coggeshall and Lekan (1996)]. Pictures were taken under a started 7–10 d after hypophysectomy. All hx rats received subcutaneous Nikon microscope equipped with a video camera. The results are ex- injections of cortisol phosphate (400 g/kg per d; Solu-Cortef, Upjohn, pressed as BrdU-positive cells per sample volume per section. We deter- Puurs, Belgium) and L-thyroxine (10 g/kg per d; Nycomed Pharma, mined the total number of BrdU-positive cells in the GCL and in the Oslo, Norway) diluted in saline (08:00 hr) (Sjo¨berg et al., 1994).