Distribution Of Neural Progenitor Cells And Neuroregeneration In Mouse Models Of Neurodegenerative Diseases

Last quite a long time, it was thought that once maturation, nerve cells in mammalian and human brain were no longer undergoing proliferation and differentiation, and only went to gradual degradation and death. However, a large number of recent studies show that neural stem cells also are found in adult brain, which can self-proliferate and differentiate to specific neuronal cells. Adult neural stem cells exist in brain ventricle and the subventricular zone (VZ and SVZ), ependymal and periventricular zone (subependymal zone), subgranular Zone (SGZ) in hippocampus dentate gyrus region. The discovery of stem cells in adult brain provides a broad prospect for treatment of neurodegenerative diseases with stem cell. In our experiments, mouse models of human neurodegenerative diseases for Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic Lateral Sclerosis (ALS) have been used to study neuron degeneration, distribution of neural stem/progenitor cells under the pathologic condition and neuroregeneration, which will be benefit to treatment of neurodegenerative diseases using neurogenesis in vivo and development of drugs.1. Neurogenic Responses to Amyloid-Beta Plaques in Alzheimer's Disease-Like MiceFormation and accumulation of beta-amyloid (Aβ) plaques are associated with declined memory and other neurocognitive function in AD patients. However, the effects of Aβplaques on neural progenitor cells (NPCs) and neurogenesis from NPCs remain largely unknown. The existing data on neurogenesis in AD patients and AD-like animal models remain controversial. For this reason, we utilized the nestin second-intron enhancer controlled LacZ reporter (pNes-LacZ) transgenic mice (pNes-Tg) and Bi-transgenic mice (Bi-Tg) containing both pPDGF-APPSw,Ind and pNes-LacZ transgenes to investigate the effects of Aβplaques on neurogenesis in the hippocampus and other brain regions of the AD–like mice. We chose transgenic mice at 2, 8 and 12 months of age, corresponding to the stages of Aβplaque free, plaque onset and plaque progression to analyze the effects of Aβplaques on the distribution and de novo neurogenesis of (from) NPCs. We demonstrated a slight increase in the number of NPCs in the hippocampal regions at the Aβplaque free stage, while a significant decrease in the number of NPCs at Aβplaque onset and progression stages. On the other hand, we showed that Aβplaques increase neurogenesis, but not gliogenesis from post-mitotic NPCs in the hippocampus of Bi-Tg mice compared with age-matched control pNes-Tg mice. In addition, the number of NPCs in cortex region increased first and then decreased from Aβplaque onset to progression stages. The number of NPCs in lateral ventricle increased at Aβfree stage, and decreased when Aβplaque began to form. The alteration of NPCs distribution and neurogenic responses of NPCs to Aβplaques suggest that experimental approaches to promote de novo neurogenesis may improve neurocognitive function and provide an effective therapy for AD.2. Protective Effect of MnSOD on Depletion and Effect on Regeneration of Dopaminergic Neurons in MPTP-PD Mice ModelPD is characterized by substantia nigra pars compacta (SNC) dopaminergic neurons injury, the number reduced, causing the dopamine content. PD etiology is not clear at present, but common perception is that the production of free-radical oxidation reaction and mitochondrial dysfunction and reduced glutathione levels, endogenous and exogenous factors such as toxicants lead to degeneration of the substantia nigra dopaminergic neurons. Mitochondrial dysfunction may play a leading role. Therefore, We used MPTP- PD mouse model of oxidative damage (normal mice), and transgenic mice ofβ-actin promoter driven human manganese superoxide dismutase (MnSOD) gene (MnSOD mice) to study the protective effect of MnSOD on depletion and effect on regeneration of dopaminergic neurons in SNC of MPTP-PD mice. We used three time points, namely D0 days, D10 days, D15 days, respectively on behalf of no MPTP, MPTP with consecutive injection for 10 and 15 days. The results showed that by two apoptosis pathway of AIF and Caspase3 dopaminergic neurons were undergoing apoptosis induced by MPTP, which led to the reduction in the number of dopaminergic neurons in SNC of normal mice. Especially after intraperitoneal injection of MPTP for 15days, dopaminergic neurons in normal mice markedly reduced; while overexpression of MnSOD inhibited these two apoptotic pathways and dopaminergic neurons only slightly reduced. MPTP inhibited the anti-apoptotic protein Bcl-2 expression, and MnSOD mice maintained Bcl2 expression. With MPTP treatment, expression of antioxidant substances such as cytochrome c, cytochrome c oxidase (COX IV), glutathione (GSH), glutathione peroxidase (GPX), manganese superoxide dismutase (MnSOD) in mitochondria of normal mice tended to decrease, and peroxidative products of lipid, protein, DNA increased dramatically. MnSOD mice were able to maintain high expression of these antioxidant substances, and significantly reduced peroxidative products in vivo like 4-hydroxy-2-nonenol (HNE), malondialdehyde (MDA), 8-hydroxy-2'-deoxyguanosine (8-OHG), 3-nitro tyrosine (3-NT). With injection of MPTP for 15 days, microglia cells in SNC of normal mice were activated in a large of amount. Astrocytes and Brdu immunoreactive cells in SNC of normal mice also presented significant increases. Furthermore, with injection of MPTP, nestin immunopositive neural stem / progenitor cells in SNR of both normal mice and MnSOD mice were increased. No regeneration of dopaminergic neurons was detected in SN. At the same time, nestin immunopositive neural stem / progenitor cells in DG of normal mouse hippocampus tended to decrease. At the D10 and D15, proliferate neural stem / progenitor cells represented by nestin staining can be detected. The protective effect of MnSOD on dopaminergic neuron injury caused by MPTP provides a basis for anti-PD drug design. And the alteration of NPCs distribution and proliferation of NPCs to dopaminergic neuron injury suggest that experimental approaches to promote de novo neurogenesis may improve motor function and provide an effective therapy for PD.3. Temporal Response of Neural Progenitor Cells to Disease Onset and Progression in ALS-Like Transgenic MiceRegenerative medicine through neural stem or neural progenitor cells (NPCs) has been proposed as an alterative avenue to restore neurological dysfunction in ALS. It is critical to understand the organization and distribution of endogenous adult NPCs in response to motor neuron degeneration before regenerative medicine can be applied for ALS therapy. For this reason, we analyzed the temporal response of NPCs to motor neuron degeneration in the spinal cord and brain using nestin enhancer driven LacZ reporter transgenic mice (pNes-Tg mice: control) and Bi-transgenic mice containing both nestin enhancer driven LacZ reporter gene and mutant G93A-SOD1 gene (Bi-Tg mice). We observed an increase of NPCs in the dorsal horns of the spinal cord at the disease onset and progression stages in the Bi-Tg mice compared with that of age-matched pNes-Tg control mice. In contrast, an increase of NPCs in the ventral horns was detected at the disease progression stage. Compared to control mice, the number of NPCs in lumbar region was much higher than those of cervical region and thoracic region.On the other hand, an increase of NPCs in the motor cortex at the disease onset stage, but not at the disease progression stage was detected. Furthermore, a decrease of NPCs in the lateral ventricle at the disease progression stage was observed, while no difference in the number of NPCs in the hippocampus was detected at the disease onset and progression stages. The organization and distribution of endogenous adult NPCs in the ALS-like transgenic mice at the disease onset and progression stages provide fundamental bases for consideration of regenerative therapy of ALS by increasing de novo neurogenesis.