Transcriptional regulation of adult neural stem/progenitor cells: tales from the subventricular zone

Transcriptomic analysis of CNTF-treated mouse subventricular zone-derived neurosphere culture reveals key transcription factor genes related to adult neurogenesis

Neural Stem Progenitor Cells (NSPCs) maintenance and neuronal cell differentiation are the two key aspects of sustained neurogenesis in the adult mammalian brain. Transcription factors (TFs) are known to regulate these biological processes under the influence of various neurotrophic factors. Understanding the role of key TF genes in regulating adult neurogenesis is essential for determining the functional complexity and neuronal diversity seen in the adult mammalian brain. Although several molecular mechanisms leading to adult neurogenesis have been reported, details on its transcriptional regulation are still limited. Our initial results showed that Ciliary Neurotrophic Factor (CNTF) induced neuronal differentiation in SVZ-derived NSPC cultures. To investigate further the role of CNTF in inducing the expression of TF genes related to adult neurogenesis and the potential pathways involved, whole transcriptome RNA-sequencing (RNA-seq) analysis was done in CNTF-treated Sub-ventricular Zone derived neurosphere cultures from the mouse brain. The study revealed 483 differentially expressed genes (DEGs), among which 33 DEGs were identified as coding for transcription factors (TFs). Kyoto Encyclopedia of Gene and Genomes (KEGG) analysis revealed MAPK, PI3K-Akt, and FoxO as the significantly enriched signaling pathways. Gene co-expression network analysis identified five upregulated TF genes related to adult neurogenesis (Runx1, Hmga2, Fos, ID2, and Prrx1) in a single cluster, interacting with each other, and was also validated by quantitative PCR. Our data suggest several potential TFs that may act as critical regulators in the intrinsic transcriptional networks driving the adult neurogenesis process. Further investigation into these molecular regulators may yield a homogeneous population of neuronal progenitors for translational stem cell studies in the future.

Increased oligodendrogenesis and myelination in the subventricular zone of aged mice and gray mouse lemurs

The adult rodent subventricular zone (SVZ) generates neural stem cells (NSCs) throughout life that migrate to the olfactory bulbs (OBs) and differentiate into olfactory interneurons. Few SVZ NSCs generate oligodendrocyte precursor cells (OPCs). We investigated how neurogliogenesis is regulated during aging in mice and in a non-human primate (NHP) model, the gray mouse lemur. In both species, neuronal commitment decreased with age, while OPC generation and myelin content unexpectedly increased. In the OBs, more tyrosine hydroxylase interneurons in old mice, but fewer in lemurs, marked a surprising interspecies difference that could relate to our observation of a continuous ventricle in lemurs. In the corpus callosum, aging promoted maturation of OPCs into mature oligodendrocytes in mice but blocked it in lemurs. The present study highlights similarities and dissimilarities between rodents and NHPs, revealing that NHPs are a more relevant model than mice to study the evolution of biomarkers of aging.

Dexmedetomidine alleviates olfactory cognitive dysfunction by promoting neurogenesis in the subventricular zone of hypoxic-ischemic neonatal rats

Background: Hypoxic-ischemic brain damage (HIBD) is the main cause of neurological dysfunction in neonates. Olfactory cognitive function is important for feeding, the ability to detect hazardous situations and social relationships. However, only a few studies have investigated olfactory cognitive dysfunction in neonates with HIBD; furthermore, the specific mechanisms involved are yet to be elucidated. It has been reported that neurogenesis in the subventricular zone (SVZ) is linked to olfactory cognitive function. Recently, dexmedetomidine (DEX) has been shown to provide neuroprotection in neonates following HIBD. In the present study, we investigated whether DEX could improve olfactory cognitive dysfunction in neonatal rats following HIBD and attempted to determine the underlying mechanisms.

Methods: We induced HIBD in rats using the Rice–Vannucci model, and DEX (25 μg/kg, i.p.) was administered immediately after the induction of HIBD. Next, we used triphenyl tetrazolium chloride (TTC) staining and the Zea-longa score to assess the success of modelling. The levels of BDNF, TNF-α, IL-1β and IL-6 were determined by western blotting. Immunofluorescence staining was used to detect microglial activation and microglial M1/M2 polarization as well as to evaluate the extent of neurogenesis in the SVZ. To evaluate the olfactory cognitive function, the rats in each group were raised until post-natal days 28–35; then, we performed the buried food test and the olfactory memory test.

Results: Analysis showed that HIBD induced significant brain infarction, neurological deficits, and olfactory cognitive dysfunction. Furthermore, we found that DEX treatment significantly improved olfactory cognitive dysfunction in rat pups with HIBD. DEX treatment also increased the number of newly formed neuroblasts (BrdU/DCX) and neurons (BrdU/NeuN) in the SVZ by increasing the expression of BDNF in rat pups with HIBD. Furthermore, analysis showed that the neurogenic effects of DEX were possibly related to the inhibition of inflammation and the promotion of M1 to M2 conversion in the microglia.

Conclusion: Based on the present findings, DEX treatment could improve olfactory cognitive dysfunction in neonatal rats with HIBD by promoting neurogenesis in the SVZ and enhancing the expression of BDNF in the microglia. It was possible associated that DEX inhibited neuroinflammation and promoted M1 to M2 conversion in the microglia.

Genetic Regulation of Vertebrate Forebrain Development by Homeobox Genes

Forebrain development in vertebrates is regulated by transcription factors encoded by homeobox, bHLH and forkhead gene families throughout the progressive and overlapping stages of neural induction and patterning, regional specification and generation of neurons and glia from central nervous system (CNS) progenitor cells. Moreover, cell fate decisions, differentiation and migration of these committed CNS progenitors are controlled by the gene regulatory networks that are regulated by various homeodomain-containing transcription factors, including but not limited to those of the Pax (paired), Nkx, Otx (orthodenticle), Gsx/Gsh (genetic screened), and Dlx (distal-less) homeobox gene families. This comprehensive review outlines the integral role of key homeobox transcription factors and their target genes on forebrain development, focused primarily on the telencephalon. Furthermore, links of these transcription factors to human diseases, such as neurodevelopmental disorders and brain tumors are provided.

Repurposed anti-cancer epidermal growth factor receptor inhibitors: mechanisms of neuroprotective effects in Alzheimer's disease

Numerous molecular mechanisms are being examined in an attempt to discover disease-modifying drugs to slow down the underlying neurodegeneration in Alzheimer’s disease. Recent studies have shown the beneficial effects of epidermal growth factor receptor inhibitors on the enhancement of behavioral and pathological sequelae in Alzheimer’s disease. Despite the promising effects of epidermal growth factor receptor inhibitors in Alzheimer’s disease, there is no irrefutable neuroprotective evidence in well-established animal models using epidermal growth factor receptor inhibitors due to many un-explored downstream signaling pathways. This caused controversy about the potential involvement of epidermal growth factor receptor inhibitors in any prospective clinical trial. In this review, the mystery beyond the under-investigation of epidermal growth factor receptor in Alzheimer’s disease will be discussed. Furthermore, their molecular mechanisms in neurodegeneration will be explained. Also, we will shed light on SARS-COVID-19 induced neurological manifestations mediated by epidermal growth factor modulation. Finally, we will discuss future perspectives and under-examined epidermal growth factor receptor downstream signaling pathways that warrant more exploration. We conclude that epidermal growth factor receptor inhibitors are novel effective therapeutic approaches that require further research in attempts to be repositioned in the delay of Alzheimer’s disease progression.

Programmed cell death in stem cell-based therapy: Mechanisms and clinical applications

Stem cell-based therapy raises hopes for a better approach to promoting tissue repair and functional recovery. However, transplanted stem cells show a high death percentage, creating challenges to successful transplantation and prognosis. Thus, it is necessary to investigate the mechanisms underlying stem cell death, such as apoptotic cascade activation, excessive autophagy, inflammatory response, reactive oxygen species, excitotoxicity, and ischemia/hypoxia. Targeting the molecular pathways involved may be an efficient strategy to enhance stem cell viability and maximize transplantation success. Notably, a more complex network of cell death receives more attention than one crucial pathway in determining stem cell fate, highlighting the challenges in exploring mechanisms and therapeutic targets. In this review, we focus on programmed cell death in transplanted stem cells. We also discuss some promising strategies and challenges in promoting survival for further study.

Mitogen and Stress-activated Protein Kinase 1 Negatively Regulates Hippocampal Neurogenesis

Neurogenesis in the subgranular zone (SGZ) of the adult hippocampus can be stimulated by a variety of means, including via exposure of experimental animals to an enriched environment that provides additional sensory, social, and motor stimulation. Tangible health and cognitive benefits accrue in enriched animals, including the amelioration of signs modelling psychiatric, neurological and neurodegenerative conditions that affect humans, which may in part be due to enhanced production of neurons. A key factor in the neuronal response to enrichment is the release of brain-derived neurotrophic factor (BDNF) and the activation of the Mitogen-Activated Protein Kinase (MAPK) cascade, which can lead to the stimulation of neurogenesis. Mitogen- and Stress-Activated protein Kinase 1 (MSK1) is a nuclear enzyme downstream of BDNF and MAPK that regulates transcription. MSK1 has previously been implicated in both basal and stimulated neurogenesis on the basis of studies with mice lacking MSK1 protein. In the present study, using mice in which only the kinase activity of MSK1 is lacking, we show that the rate of cellular proliferation in the SGZ (Ki-67 staining) is unaffected by the MSK1 kinase-dead (KD) mutation, and no different from controls levels after five weeks of enrichment. However, compared to wild-type mice, the number of doublecortin (DCX)-positive cells was greater in both standard-housed and enriched MSK1 KD mice. These observations suggest that, while MSK1 does not influence the basal rate of proliferation of neuronal precursors, MSK1 negatively regulates the number of cells destined to become neurons, potentially as a homeostatic control on the number of new neurons integrating into the dentate gyrus.