Throughout adulthood, neurons are continuously replaced by new cells in the dentate gyrus (DG) of the hippocampus, and this neurogenesis is increased by various neuronal injuries including ischemic stroke and seizure. While several mechanisms of this injury-induced neurogenesis have been elucidated, the initiation factor remains unclear. Here, we investigated which signal(s) triggers ischemia-induced cell proliferation and neurogenesis in the hippocampal DG region. We found that early apoptotic cell death of the immature neurons occurred in the DG region following transient forebrain ischemia/reperfusion. Moreover, early immature neuronal death in the DG initiated transient forebrain ischemia/reperfusion-induced neurogenesis through glycogen synthase kinase-3?/?-catenin signaling, which was mediated by microglia-derived insulin-like growth factor-1 (IGF-1). Additionally, we observed that the blockade of immature neuronal cell death, early microglial activation, or IGF-1 signaling attenuated ischemia-induced neurogenesis. These results suggest that early immature neuronal cell death initiates ischemia-induced neurogenesis through microglial IGF-1.
Mesenchymal stem cells (MSCs) are effective vectors in delivering a gene of interest into degenerating brain. In ex vivo gene therapy, viability of transplanted MSCs is correlated with the extent of functional recovery. It has been reported that BDNF facilitates survival of MSCs but dividing MSCs do not express the BDNF receptor, TrkB. In this study, we found that the expression of TrkB is upregulated in human MSCs by the addition of forskolin (Fsk), an activator of adenylyl cyclase. To increase survival rate of MSCs and their secretion of tropic factors that enhance regeneration of endogenous cells, we pre-exposed hMSCs with Fsk and transduced with BDNF-adenovirus before transplantation into the brain of memory deficient rats, a degenerating brain disease model induced by ibotenic acid injection. Viability of MSCs and expression of a GABA synthesizing enzyme were increased. The pre-treatment improved learning and memory, as detected by the behavioral tests including Y-maze task and passive avoidance test. These results suggest that TrkB expression of hMSCs elevates the neuronal regeneration and efficiency of BDNF delivery for treating degenerative neurological diseases accompanying memory loss.
Soy (Glycine Max Merr, family Leguminosae) has been reported to possess anti-cancer, anti-lipidemic, estrogen-like, and memory-enhancing effects. We investigated the memory-enhancing effects and the underlying mechanisms of soyasaponin I (soya-I), a major constituent of soy. Impaired learning and memory were induced by injecting ibotenic acid into the entorhinal cortex of adult rat brains. The effects of soya-I were evaluated by measuring behavioral tasks and neuronal regeneration of memory-deficient rats. Oral administration of soya-I exhibited significant memory-enhancing effects in the passive avoidance, Y-maze, and Morris water maze tests. Soya-? also increased BrdU incorporation into the dentate gyrus and the number of cell types (GAD67, ChAT, and VGluT1) in the hippocampal region of memory-deficient rats, whereas the number of reactive microglia (OX42) decreased. The mechanism underlying memory improvement was assessed by detecting the differentiation and proliferation of neural precursor cells (NPCs) prepared from the embryonic hippocampus (E16) of timed-pregnant Sprague-Dawley rats using immunocytochemical staining and immunoblotting analysis. Addition of soya-? in the cultured NPCs significantly elevated the markers for cell proliferation (Ki-67) and neuronal differentiation (NeuN, TUJ1, and MAP2). Finally, soya-I increased neurite lengthening and the number of neurites during the differentiation of NPCs. Soya-? may improve hippocampal learning and memory impairment by promoting proliferation and differentiation of NPCs in the hippocampus through facilitation of neuronal regeneration and minimization of neuro-inflammation.
Berberine is an isoquinoline alkaloid isolated from goldenthread, Coptidis Rhizoma and shown to have many biological and pharmacological effects. We previously reported that berberine promotes cell survival and differentiation of neural stem cells. To examine whether berberine has survival promoting effect on damaged neuronal cells, we generated a cellular model under oxidative stress and an neonatal animal model of degenerating brain disease by injecting MK-801. MK801, a noncompetitive antagonist of N-methyl-d-aspartate (NMDA) receptors, acts as a neurotoxin in developing rats by inhibiting NMDA receptors and induce neuronal cell death. We found that the survival rate of the SH-SY5Y cells under oxidative stress was increased by 287% and 344%, when treated with 1.5 and 3.0µg/ml berberine, respectively. In the developing rats injected by MK801, we observed that TUNEL positive apoptotic cells were outspread in entire brain. The cell death was decreased more than 3 fold in the brains of the MK-801-induced neurodegenerative animal model when berberine was treated to the model animals. This suggests that berberine promotes activity dependent cell survival mediated by NMDA receptor because berberine is known to activate neurons by blocking K(+) current or lowering the threshold of the action potential. Taken together, berberine has neuroprotective effect on damaged neurons and neurodegenerating brains of neonatal animal model induced by MK-801 administration.
Neuregulin 1 (NRG1) and epidermal growth factor receptor (ErbB) signaling pathways control Schwann cells during axonal regeneration in an injured peripheral nervous system. We investigated whether a persistent supply of recombinant NRG1 to the injury site could improve axonal growth and recovery of sensory and motor functions in rats during nerve regeneration. We generated a recombinant adenovirus expressing a secreted form of EGF-like domain from Heregulin? (sHRG?E-Ad). This virus, sHRG?E-Ad allowed for the secretion of 30-50 ng of small sHRG?E peptides per 10(7-8) virus particle outside cells and was able to phosphorylate ErbB receptors. Transduction of the concentrated sHRG?E-Ad into an axotomy model of sciatic nerve damage caused an effective promotion of nerve regeneration, as shown by histological features of the axons and Schwann cells, as well as increased expression of neurofilaments, GAP43 and S100 in the distal stump of the injury site. This result is consistent with longer axon lengths and thicker calibers observed in the sHRG?E-Ad treated animals. Furthermore, sensory and motor functions were significantly improved in sHRG?E-Ad treated animals when evaluated by a behavioral test. These results suggest a therapeutic potential for sHRG?E-Ad in treatment of peripheral nerve injury.
Berberine, an isoquinoline alkaloid component of Coptidis Rhizoma (goldenthread) extract, has been reported to have therapeutic potential for central nervous system disorders such as Alzheimers disease, cerebral ischemia, and schizophrenia. We have previously shown that berberine promotes the survival and differentiation of hippocampal precursor cells. In a memory-impaired rat model induced by ibotenic acid injection, the survival of pyramidal and granular cells was greatly increased in the hippocampus by berberine administration. In the present study, we investigated the effects of berberine on neurite outgrowth in the SH-SY5Y neuronal cell line and axonal regeneration in the rat peripheral nervous system (PNS). Berberine enhanced neurite extension in differentiating SH-SY5Y cells at concentrations of 0.25-3??g/mL. In an injury model of the rat sciatic nerve, we examined the neuroregenerative effects of berberine on axonal remyelination by using immunohistochemical analysis. Four weeks after berberine administration (20?mg/kg i.p. once per day for 1 week), the thickness of remyelinated axons improved approximately 1.4-fold in the distal stump of the injury site. Taken together, these results indicate that berberine promotes neurite extension and axonal regeneration in injured nerves of the PNS.
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