Sustained increase in adult neurogenesis in the rat hippocampal dentate gyrus after transient brain ischemia

Expression and distribution of generated neurons and endogenous precursors in rat cerebral cortical venous ischemia

Neurogenesis in the subventricular zone (SVZ), subgranular zone (SGZ), and cerebral cortex is now a familiar event to confirm by cerebral arterial ischemia in rat models. However, it remains unclear whether cerebral venous ischemia (CVI) alone causes neurogenesis, and where that neurogenesis occurs. After creating CVI rat models via a two-vein occlusion (2-VO) method, neurogenesis was immunohistochemically evaluated by double-labeling 5-bromo-2'-deoxyuridine (BrdU)-positive cells with neuronal nuclei (NeuN) or doublecortin (DCX) antibody. Fifty Wistar rats were divided into two major groups (BrdU-NeuN and BrdU-DCX) and then separated into two subgroups (2-VO or sham). The total number of double-positive cells expressed inside a predefined region of interest (ROI) covering the ischemic area was compared between the two subgroups. Then, we divided the ROI into six sections to evaluate and compare the distribution of double-positive cells generated in each section between the two subgroups. The 2-VO subgroup presented more double-positive cells than the sham group in both BrdU-NeuN and BrdU-DCX groups, while the BrdU-DCX+2-VO group showed a characteristic distribution of double-positive cells in ROI 2 and ROI 3, suggesting areas of the ischemic core and penumbra, with a significant difference compared to the BrdU-DCX+sham group. This study demonstrates that CVI has the potential to induce endogenous neurogenesis, with significant numbers of both newly generated neurons and precursors observed in the ischemic area. The distribution of these cells suggests that the cortex could be the main origin of neurogenesis after cortical CVI.

Systemic Factors Trigger Vasculature Cells to Drive Notch Signaling and Neurogenesis in Neural Stem Cells in the Adult Brain

It is well documented that adult neural stem cells (NSCs) residing in the subventricular zone (SVZ) and the subgranular zone (SGZ) are induced to proliferate and differentiate into new neurons after injury such as stroke and hypoxia. However, the role of injury‐related cues in driving this process and the means by which they communicate with NSCs remains largely unknown. Recently, the coupling of neurogenesis and angiogenesis and the extensive close contact between vascular cells and other niche cells, known as the neurovascular unit (NVU), has attracted interest. Further facilitating communication between blood and NSCs is a permeable blood‐brain‐barrier (BBB) present in most niches, making vascular cells a potential conduit between systemic signals, such as vascular endothelial growth factor (VEGF), and NSCs in the niche, which could play an important role in regulating neurogenesis. We show that the leaky BBB in stem cell niches of the intact and stroke brain can respond to circulating VEGF₁₆₅ to drive induction of the Notch ligand DLL4 (one of the most important cues in angiogenesis) in endothelial cells (ECs), pericytes, and further induce significant proliferation and neurogenesis of stem cells. Stem Cells2019;37:395–406

Peroxynitrite enhances self-renewal, proliferation and neuronal differentiation of neural stem/progenitor cells through activating HIF-1α and Wnt/β-catenin signaling pathway

Hypoxic/ischemic stimulation could mediate growth and differentiation of neural stem/progenitor cells (NSCs) into mature neurons but its underlying mechanisms are largely unclear. Peroxynitrite formation is considered as a crucial pathological process contributing to cerebral ischemia-reperfusion injury. In the present study, we tested the hypothesis that peroxynitrite at low concentration could function as redox signaling to promote the growth of NSCs under hypoxic/ischemic conditions. Increased NSCs proliferation was accompanied by peroxynitrite production in the rat brains with 1 h of ischemia plus 7 days of reperfusion in vivo. Cell sorting experiments revealed that endogenous peroxynitrite level affected the capacity of proliferation and self-renewal in NSCs in vitro. Hypoxia stimulated peroxynitrite production and promoted NSCs self-renewal, proliferation and neuronal differentiation whereas treatments of peroxynitrite decomposition catalysts (PDCs, FeTMPyP and FeTPPS) blocked the changes in NSCs self-renewal, proliferation and neuronal differentiation. Exogenous peroxynitrite treatment revealed similar effects to promote NSCs proliferation, self-renewal and neuronal differentiation. Furthermore, the neurogenesis-promoting effects of peroxynitrite were partly through activating HIF-1α correlated with enhanced Wnt/β-catenin signaling pathway. In conclusion, peroxynitrite could be a cellular redox signaling for promoting NSCs proliferation, self-renewal and neuronal differentiation and peroxynitrite production could contribute to neurogenesis in ischemic/hypoxic NSCs.

Non-invasive remote ischemic postconditioning stimulates neurogenesis during the recovery phase after cerebral ischemia

Ischemic postconditioning (IPostC) has been reported to have neuroprotection against ischemic diseases, and one cycle of IPostC induces neurogenesis when treated nearby. To expanding these effects, we explored the effects of repetitively remote IPostC (NRIPostC) on neurogenesis in the subgranular zone (SGZ) and subentricular zone (SVZ) during stroke recovery. Animals underwent transient cerebral ischemia were treated with vehicle or NRIPostC immediately after reperfusion. Neurological severity scores, infarct size, neurogenesis, and protein expression levels of nestin and GFAP were quantified at 3d, 7d, 14d, 21d and 28d post-ischemia. Results showed that NRIPostC significantly reduced acute infarction and improved neurological outcomes during the recovery phase. Meanwhile, NRIPostC significantly increased the number of BrdU⁺/nestin⁺ cells in SGZ on day 14 and in the SVZ on days 3, 7 and 14 respectively, and the number of DCX⁺ cells from days 3 to 14. There were significant increments in the number of BrdU⁺/NeuN⁺ and BrdU⁺/GFAP⁺ cells in the SGZ and SVZ during the stroke recovery. The changing tendency of the protein expression of nestin and GFAP in DG was consistent with the result mentioned above. In conclusion, NRIPostC reduced acute infarction and improved functional outcomes up to 28d, and it induced neurogenesis both in the SGZ and SVZ.

Neural Stem Cell Plasticity: Advantages in Therapy for the Injured Central Nervous System

The physiological and pathological properties of the neural germinal stem cell niche have been well-studied in the past 30 years, mainly in animals and within given limits in humans, and knowledge is available for the cyto-architectonic structure, the cellular components, the timing of development and the energetic maintenance of the niche, as well as for the therapeutic potential and the cross talk between neural and immune cells. In recent years we have gained detailed understanding of the potentiality of neural stem cells (NSCs), although we are only beginning to understand their molecular, metabolic, and epigenetic profile in physiopathology and, further, more can be invested to measure quantitatively the activity of those cells, to model in vitro their therapeutic responses or to predict interactions in silico. Information in this direction has been put forward for other organs but is still limited in the complex and very less accessible context of the brain. A comprehensive understanding of the behavior of endogenous NSCs will help to tune or model them toward a desired response in order to treat complex neurodegenerative diseases. NSCs have the ability to modulate multiple cellular functions and exploiting their plasticity might make them into potent and versatile cellular drugs.

Bumetanide promotes neural precursor cell regeneration and dendritic development in the hippocampal dentate gyrus in the chronic stage of cerebral ischemia

Bumetanide has been shown to lessen cerebral edema and reduce the infarct area in the acute stage of cerebral ischemia. Few studies focus on the effects of bumetanide on neuroprotection and neurogenesis in the chronic stage of cerebral ischemia. We established a rat model of cerebral ischemia by injecting endothelin-1 in the left cortical motor area and left corpus striatum. Seven days later, bumetanide 200 µg/kg/day was injected into the lateral ventricle for 21 consecutive days with a mini-osmotic pump. Results demonstrated that the number of neuroblasts cells and the total length of dendrites increased, escape latency reduced, and the number of platform crossings increased in the rat hippocampal dentate gyrus in the chronic stage of cerebral ischemia. These findings suggest that bumetanide promoted neural precursor cell regeneration, dendritic development and the recovery of cognitive function, and protected brain tissue in the chronic stage of ischemia.

Postischemic Anhedonia Associated with Neurodegenerative Changes in the Hippocampal Dentate Gyrus of Rats

Poststroke depression is one of the major symptoms observed in the chronic stage of brain stroke such as cerebral ischemia. Its pathophysiological mechanisms, however, are not well understood. Using the transient right middle cerebral artery occlusion- (MCAO-, 90 min) operated rats as an ischemia model in this study, we first observed that aggravation of anhedonia spontaneously occurred especially after 20 weeks of MCAO, and it was prevented by chronic antidepressants treatment (imipramine or fluvoxamine). The anhedonia specifically associated with loss of the granular neurons in the ipsilateral side of hippocampal dentate gyrus and was also prevented by an antidepressant imipramine. Immunohistochemical analysis showed increased apoptosis inside the granular cell layer prior to and associated with the neuronal loss, and imipramine seemed to recover the survival signal rather than suppressing the death signal to prevent neurons from apoptosis. Proliferation and development of the neural stem cells were increased transiently in the subgranular zone of both ipsi- and contralateral hippocampus within one week after MCAO and then decreased and almost ceased after 6 weeks of MCAO, while chronic imipramine treatment prevented them partially. Overall, our study suggests new insights for the mechanistic correlation between poststroke depression and the delayed neurodegenerative changes in the hippocampal dentate gyrus with effective use of antidepressants on them.

Scorpion venom heat-resistant peptide (SVHRP) enhances neurogenesis and neurite outgrowth of immature neurons in adult mice by up-regulating brain-derived neurotrophic factor (BDNF)

Scorpion venom heat-resistant peptide (SVHRP) is a component purified from Buthus martensii Karsch scorpion venom. Although scorpions and their venom have been used in Traditional Chinese Medicine (TCM) to treat chronic neurological disorders, the underlying mechanisms of these treatments remain unknown. We applied SVHRP in vitro and in vivo to understand its effects on the neurogenesis and maturation of adult immature neurons and explore associated molecular mechanisms. SVHRP administration increased the number of 5-bromo-2’-dexoxyuridine (BrdU)-positive cells, BrdU- positive/neuron-specific nuclear protein (NeuN)-positive neurons, and polysialylated-neural cell adhesion molecule (PSA-NCAM)-positive immature neurons in the subventricular zone (SVZ) and subgranular zone (SGZ) of hippocampus. Furthermore immature neurons incubated with SVHRP-pretreated astrocyte-conditioned medium exhibited significantly increased neurite length compared with those incubated with normal astrocyte-conditioned medium. This neurotrophic effect was further confirmed in vivo by detecting an increased average single area and whole area of immature neurons in the SGZ, SVZ and olfactory bulb (OB) in the adult mouse brain. In contrast to normal astrocyte-conditioned medium, higher concentrations of brain-derived neurotrophic factor (BDNF) but not nerve growth factor (NGF) or glial cell line-derived neurotrophic factor (GDNF) was detected in the conditioned medium of SVHRP-pretreated astrocytes, and blocking BDNF using anti-BDNF antibodies eliminated these SVHRP-dependent neurotrophic effects. In SVHRP treated mouse brain, more glial fibrillary acidic protein (GFAP)-positive cells were detected. Furthermore, immunohistochemistry revealed increased numbers of GFAP/BDNF double-positive cells, which agrees with the observed changes in the culture system. This paper describes novel effects of scorpion venom-originated peptide on the stem cells and suggests the potential therapeutic values of SVHRP.

Cux2 activity defines a subpopulation of perinatal neurogenic progenitors in the hippocampus

The hippocampus arises from the medial region of the subventricular (SVZ) within the telencephalon. It is one of two regions in the postnatal brain that harbors neural progenitors (NPs) capable of giving rise to new neurons. Neurogenesis in the hippocampus is restricted to the subgranular zone (SGZ) of the dentate gyrus (DG) where it contributes to the generation of granule cell layer (gcl) neurons. It is thought that SGZ progenitors are heterogeneous, differing in their morphology, expression profiles, and developmental potential, however it is currently unknown whether they display differences in their developmental origins and cell fate-restriction in the DG. Here we demonstrate that Cux2 is a marker for SGZ progenitors and nascent granule cell neurons in the perinatal brain. Cux2 was expressed in the presumptive hippocampal forming region of the embryonic forebrain from E14.5 onwards. At fetal stages, Cux2 was expressed in early-forming Prox1⁺ granule cell neurons as well as the SVZ of the DG germinal matrix. In the postnatal brain, Cux2 was expressed in several types of progenitors in the SGZ of the DG, including Nestin/Sox2 double-positive radial glia, Sox2⁺ cells that lacked a radial glial process, DCX⁺ neuroblasts, and Calretinin-expressing nascent neurons. Another domain characterized by a low level of Cux2 expression emerged in Calbindin⁺ neurons of the developing DG blades. We used Cux2-Cre mice in genetic fate-mapping studies and showed almost exclusive labeling of Calbindin-positive gcl neurons, but not in any progenitor cell types or astroglia. This suggests that Cux2⁺ progenitors directly differentiate into gcl neurons and do not self-renew. Interestingly, developmental profiling of cell fate revealed an outside-in formation of gcl neurons in the DG, likely reflecting the activity of Cux2 in the germinative matrices during DG formation and maturation. However, DG morphogenesis proceeded largely normally in hypomorphic Cux2 mutants lacking Cux2 expression. Taken together we conclude that Cux2 expression reflects hippocampal neurogenesis and identifies non-self-renewing NPs in the SGZ.

Direct stimulation of adult neural stem/progenitor cells in vitro and neurogenesis in vivo by salvianolic acid B

BACKGROUND

Small molecules have been shown to modulate the neurogenesis processes. In search for new therapeutic drugs, the herbs used in traditional medicines for neurogenesis are promising candidates.

METHODOLOGY AND PRINCIPAL FINDINGS

We selected a total of 45 natural compounds from Traditional Chinese herbal medicines which are extensively used in China to treat stroke clinically, and tested their proliferation-inducing activities on neural stem/progenitor cells (NSPCs). The screening results showed that salvianolic acid B (Sal B) displayed marked effects on the induction of proliferation of NSPCs. We further demonstrated that Sal B promoted NSPCs proliferation in dose- and time-dependent manners. To explore the molecular mechanism, PI3K/Akt, MEK/ERK and Notch signaling pathways were investigated. Cell proliferation assay demonstrated that Ly294002 (PI3K/Akt inhibitor), but neither U0126 (ERK inhibitor) nor DAPT (Notch inhibitor) inhibited the Sal B-induced proliferation of cells. Western Blotting results showed that stimulation of NSPCs with Sal B enhanced the phosphorylation of Akt, and Ly294002 abolished this effect, confirming the role of Akt in Sal B mediated proliferation of NSPCs. Rats exposed to transient cerebral ischemia were treated for 4 weeks with Sal B from the 7th day after stroke. BrdU incorporation assay results showed that exposure Sal B could maintain the proliferation of NSPCs after cerebral ischemia. Morris water maze test showed that delayed post-ischemic treatment with Sal B improved cognitive impairment after stroke in rats.

SIGNIFICANCE

Sal B could maintain the NSPCs self-renew and promote proliferation, which was mediated by PI3K/Akt signal pathway. And delayed post-ischemic treatment with Sal B improved cognitive impairment after stroke in rats. These findings suggested that Sal B may act as a potential drug in treatment of brain injury or neurodegenerative diseases.

Caveolin-1 plays a crucial role in inhibiting neuronal differentiation of neural stem/progenitor cells via VEGF signaling-dependent pathway

In the present study, we aim to elucidate the roles of caveolin-1(Cav-1), a 22 kDa protein in plasma membrane invaginations, in modulating neuronal differentiation of neural progenitor cells (NPCs). In the hippocampal dentate gyrus, we found that Cav-1 knockout mice revealed remarkably higher levels of vascular endothelial growth factor (VEGF) and the more abundant formation of newborn neurons than wild type mice. We then studied the potential mechanisms of Cav-1 in modulating VEGF signaling and neuronal differentiation in isolated cultured NPCs under normoxic and hypoxic conditions. Hypoxic embryonic rat NPCs were exposed to 1% O₂ for 24 h and then switched to 21% O₂ for 1, 3, 7 and 14 days whereas normoxic NPCs were continuously cultured with 21% O₂. Compared with normoxic NPCs, hypoxic NPCs had down-regulated expression of Cav-1 and up-regulated VEGF expression and p44/42MAPK phosphorylation, and enhanced neuronal differentiation. We further studied the roles of Cav-1 in inhibiting neuronal differentiation by using Cav-1 scaffolding domain peptide and Cav-1-specific small interfering RNA. In both normoxic and hypoxic NPCs, Cav-1 peptide markedly down-regulated the expressions of VEGF and flk1, decreased the phosphorylations of p44/42MAPK, Akt and Stat3, and inhibited neuronal differentiation, whereas the knockdown of Cav-1 promoted the expression of VEGF, phosphorylations of p44/42MAPK, Akt and Stat3, and stimulated neuronal differentiation. Moreover, the enhanced phosphorylations of p44/42MAPK, Akt and Stat3, and neuronal differentiation were abolished by co-treatment of VEGF inhibitor V1. These results provide strong evidence to prove that Cav-1 can inhibit neuronal differentiation via down-regulations of VEGF, p44/42MAPK, Akt and Stat3 signaling pathways, and that VEGF signaling is a crucial target of Cav-1. The hypoxia-induced down-regulation of Cav-1 contributes to enhanced neuronal differentiation in NPCs.

Synergistic effects of sodium butyrate, a histone deacetylase inhibitor, on increase of neurogenesis induced by pyridoxine and increase of neural proliferation in the mouse dentate gyrus

We previously observed that pyridoxine (vitamin B(6)) significantly increased cell proliferation and neuroblast differentiation without any neuronal damage in the hippocampus. In this study, we investigated the effects of sodium butyrate, a histone deacetylase (HDAC) inhibitor which serves as an epigenetic regulator of gene expression, on pyridoxine-induced neural proliferation and neurogenesis induced by the increase of neural proliferation in the mouse dentate gyrus. Sodium butyrate (300 mg/kg, subcutaneously), pyridoxine (350 mg/kg, intraperitoneally), or combination with sodium butyrate were administered to 8-week-old mice twice a day and once a day, respectively, for 14 days. The administration of sodium butyrate significantly increased acetyl-histone H3 levels in the dentate gyrus. Sodium butyrate alone did not show the significant increase of cell proliferation in the dentate gyrus. But, pyridoxine alone significantly increased cell proliferation. Sodium butyrate in combination with pyridoxine robustly enhanced cell proliferation and neurogenesis induced by the increase of neural proliferation in the dentate gyrus, showing that sodium butyrate treatment distinctively enhanced development of neuroblast dendrites. These results indicate that an inhibition of HDAC synergistically promotes neurogenesis induced by a pyridoxine and increase of neural proliferation.