Transcript ppt
Neurogenesis and Cell Death Mechanisms Neurogenesis: History • Old Dogma: no new neurons after infancy • 1960’s: (Altman) Cell proliferation in olfactory bulb and hippocampus • 1980’s: (Nottebohm) Neurogenesis in adult canaries • 1990’s: Neurogenesis occurs throughout life span in many species Adult Neurogenesis Hagg T, TINS 28 (2005) Adult Hippocampal Neurogenesis Christie and Cameron, Hippocampus 16 (:2006) Methods to Study Neural Precursor Cells In Vivo • Mitotic Labeling: Thymidine or BrdU – Problems: DNA repair, apoptosis • Mitotic Staining (IHC): Ki67 and PCNA – Variable expression during cell cycle phases (Ki67) and expression in early postmitotic cells (PCNA • Retroviral Labeling: reporter gene expression – Advantages: cell identification for electrophysiology, no dilution of marker – Disadvantages: tissue damage, infection rates are low and variable, fewer cells and differentiation markers @ long survival times Methods to Study Neural Precursor Cells In Vivo • Electrophysiology and Retrograde Axonal Labeling – Function and integration – Neuronal identity • Phenotypic Identification & Progression of Differentiation Double and triple staining methods Stem Cell markers (nestin/GFAP) Glia versus neurons Early(DCX, PSA-NCAM; Tuj1 and mature (NeuN) neurons – Neurotransmitter phenotype – – – – Neurogenesis in the Adult Human Brain? NeuN BrdU BrdU Adult Neurogenesis Positive Regulation (Proliferation/Survival) – Environmental Enrichment – Exercise – Memory Formation – Dietary restriction – Trophic Factors (shh, IGF-1, bFGF, HB-EGF, VEGF, BDNF) – 5-HT (Antidepressants) – Hormones (Estrogen, Thyroid) – Pathological Conditions (Stroke, Seizure, Disease Models) Adult Neurogenesis Negative Regulation (Proliferation/Survival) – Aging – Inflammation – Depression – Stress – Glucocorticoids – Neurotransmitters: Glumatate, ACh, DA – Chemotherapy – Methamphetamine – Opiates Evidence for Neurogenesis in the Human Brain • Huntington’s Disease: – PCNA/GFAP/Tuj1 – Increased cell birth in subependymal zone – More pronounced with increasing severity • Alzheimer’s Disease – PSA-NCAM, DCX, TUC-4 – Elevated numbers of immature neurons in subgranular zone, granule cell layer, CA1 • Stroke – Cell cycle (Ki67, PCNA) and lineage restricted makers (Tuj1, DCX,PSA-NCAM, TUC-4) – Increased expression in ischemic tissue surrounding infarcts (perivascular areas) Neuronal Phenotype of New Born Cells Following Stroke in Human CNS DCX/GFAP DCX/Ki67 TuJ1 TuJ1/Ki67 Jin, Kunlin et al. (2006) Proc. Natl. Acad. Sci. USA 103, 13198-13202 Caveats of Human Neurogenesis Studies • Sources of cells are unclear • Integration and Function have not been addressed • Few cells are generated and in limited sites • A potential endogenous source for repair? – Therapeutic targets: environment and drugs? Remaining Questions Regarding Adult Neurogenesis… • How do different extracellular signaling cascades cooperate to affect signaling within the neural precursors? • Is there a link between neurotransmitters and growth factors? • Which molecules induce specific neuronal phenotypes? Remaining Questions Regarding Adult Neurogenesis… • Which molecules regulate axonal and dendritic growth, and functional integration of the new neurons? • Are the molecular regulators in humans the same as in rodents, and how do neurological disorders affect these? NGF withdrawal Scheme summarizing proposed mechanisms used by Ras to protect SCG neurons from apoptosis. Xue L et al. J. Biol. Chem. 2000;275:8817-8824