[Neural stem cells and Notch signalling]

Role of brahma-related gene 1/brahma-associated factor subunits in neural stem/progenitor cells and related neural developmental disorders

Different fates of neural stem/progenitor cells (NSPCs) and their progeny are determined by the gene regulatory network, where a chromatin-remodeling complex affects synergy with other regulators. Here, we review recent research progress indicating that the BRG1/BRM-associated factor (BAF) complex plays an important role in NSPCs during neural development and neural developmental disorders. Several studies based on animal models have shown that mutations in the BAF complex may cause abnormal neural differentiation, which can also lead to various diseases in humans. We discussed BAF complex subunits and their main characteristics in NSPCs. With advances in studies of human pluripotent stem cells and the feasibility of driving their differentiation into NSPCs, we can now investigate the role of the BAF complex in regulating the balance between self-renewal and differentiation of NSPCs. Considering recent progress in these research areas, we suggest that three approaches should be used in investigations in the near future. Sequencing of whole human exome and genome-wide association studies suggest that mutations in the subunits of the BAF complex are related to neurodevelopmental disorders. More insight into the mechanism of BAF complex regulation in NSPCs during neural cell fate decisions and neurodevelopment may help in exploiting new methods for clinical applications.

The paradigm of amyloid precursor protein in amyotrophic lateral sclerosis: The potential role of the 682YENPTY687 motif

Neurodegenerative diseases are characterized by the progressive decline of neuronal function in several brain areas, and are always associated with cognitive, psychiatric, or motor deficits due to the atrophy of certain neuronal populations. Most neurodegenerative diseases share common pathological mechanisms, such as neurotoxic protein misfolding, oxidative stress, and impairment of autophagy machinery. Amyotrophic lateral sclerosis (ALS) is one of the most common adult-onset motor neuron disorders worldwide. It is clinically characterized by the selective and progressive loss of motor neurons in the motor cortex, brain stem, and spinal cord, ultimately leading to muscle atrophy and rapidly progressive paralysis. Multiple recent studies have indicated that the amyloid precursor protein (APP) and its proteolytic fragments are not only drivers of Alzheimer's disease (AD) but also one of the earliest signatures in ALS, preceding or anticipating neuromuscular junction instability and denervation. Indeed, altered levels of APP peptides have been found in the brain, muscles, skin, and cerebrospinal fluid of ALS patients. In this short review, we discuss the nature and extent of research evidence on the role of APP peptides in ALS, focusing on the intracellular C-terminal peptide and its regulatory motif ₆₈₂YENPTY₆₈₇, with the overall aim of providing new frameworks and perspectives for intervention and identifying key questions for future investigations.

Notch Signalling in the Hippocampus of Patients With Motor Neuron Disease

Introduction

The Notch signalling pathway regulates neuronal survival. It has some similarities with the APP signalling pathway, and competes with the latter for α- and γ-secretase proteolytic complexes. The objective of this study was to study the Notch signalling pathway in the hippocampi of patients with motor neuron disease.

Methods

We studied biological material from the autopsies of 12 patients with motor neuron disease and 4 controls. We analysed the molecular markers of the Notch and APP signalling pathways, TDP43, tau, and markers of neurogenesis.

Results and Conclusion

Low NICD expression suggests Notch signalling pathway inactivation in neurons. Inactivation of the pathway despite increased Notch1 expression is associated with a lack of α-secretase expression. We observed increased β-secretase expression associated with activation of the amyloid cascade of APP, leading to increases in amyloid-β and AICD peptides and decreased levels of Fe65. Inactivation of the Notch signalling pathway is an important factor in decreased neurogenic response in the hippocampi of patients with amyotrophic lateral sclerosis.

The role of neuro-epithelial-like and radial-glial stem and progenitor cells in development, plasticity, and repair

Neural stem and progenitor cells (NSPCs) are the primary source of new neurons in the brain and serve critical roles in tissue homeostasis and plasticity throughout life. Within the vertebrate brain, NSPCs are located within distinct neurogenic niches differing in their location, cellular composition, and proliferative behaviour. Heterogeneity in the NSPC population is hypothesized to reflect varying capacities for neurogenesis, plasticity and repair between different neurogenic zones. Since the discovery of adult neurogenesis, studies have predominantly focused on the behaviour and biological significance of adult NSPCs (aNSPCs) in rodents. However, compared to rodents, who show lifelong neurogenesis in only two restricted neurogenic niches, zebrafish exhibit constitutive neurogenesis across multiple stem cell niches that provide new neurons to every major brain division. Accordingly, zebrafish are a powerful model to probe the unique cellular and molecular profiles of NSPCs and investigate how these profiles govern tissue homeostasis and regenerative plasticity within distinct stem cell populations over time. Amongst the NSPC populations residing in the zebrafish central nervous system (CNS), proliferating radial-glia, quiescent radial-glia and neuro-epithelial-like cells comprise the majority. Here, we provide insight into the extent to which these distinct NSPC populations function and mature during development, respond to experience, and contribute to successful CNS regeneration in teleost fish. Together, our review brings to light the dynamic biological roles of these individual NSPC populations and showcases their diverse regenerative modes to achieve vertebrate brain repair later in life.

Influence of isoflurane exposure in pregnant rats on the learning and memory of offsprings

Background

About 2% of pregnant women receive non-obstetric surgery under general anesthesia each year. During pregnancy, general anesthetics may affect brain development of the fetus. This study aimed to investigate safe dosage range of isoflurane.

Methods

Forty-eight SpragueDawley (SD) pregnant rats were randomly divided into 3 groups and inhaled 1.3% isoflurane (the Iso1 group), 2.0% isoflurane (the Iso2 group) and 50% O₂ alone (the control group) for 3 h, respectively. Their offsprings were subjected to Morris water maze at day 28 and day 90 after birth to evaluate learning and memory. The expression of cAMP-response element binding protein (CREB) and phosphorylated cAMP-response element binding protein (p-CREB) was detected in the hippocampus dentate gyrus.

Results

Less offsprings of Iso2 group were able to cross the platform than that of the control group (P < 0.05). Accordingly, the Iso2 offsprings expressed p-CREB mainly in the subgranular zone in contrast to the whole granular cell layer of hippocampus dentate gyrus as detected in the Iso1 and control offsprings; the expression level of pCREB was also lower in the Iso2 than Iso1 or control offsprings (P < 0.05).

Conclusion

Inhalation of isoflurane at 1.3% during pregnancy has no significant influence on learning and memory of the offspring; exposure to isoflurane at 2.0% causes damage to spatial memory associated with inhibition of CREB phosphorylation in the granular cell layer of hippocampus dentate gyrus.

Notch1 signaling in melanoma cells promoted tumor-induced immunosuppression via upregulation of TGF-β1

Background

The receptors of Notch family play an important role in controlling the development, differentiation, and function of multiple cell types. The aim of this study is to investigate the role of Notch1 signaling upon immune suppression induced by melanoma cells.

Methods

Melanoma cell line B16 cells were transfected by lentivirus containing mouse Notch1 gene or Notch1 shRNA to generate B16 cell line that highly or lowly expressed Notch1. Notch1 in anti-tumor immune response was comprehensively appraised in murine B16 melanoma tumor model in immunocompetent and immunodeficient mice. The ratios of CD3⁺CD8⁺ cytotoxic T cells, CD49b⁺NK cells, CD4⁺CD25⁺FoxP3⁺ Tregs and Gr1⁺CD11b⁺ MDSCs in tumor-DLN or spleen were examined by flow cytometry. After the co-culture of B16 cells and CD8⁺ T cells, the effects of Notch1 on the proliferation and activation of T cells were assessed by CCK8 assay, CFSE dilution and Chromium-release test. The mRNA expression and supernatant secretion of immunosuppressive cytokines, TGF-β1, VEGF, IL-10 and IFN-γ were measured by RT-PCR and ELISA, respectively.

Results

Downregulation or overexpression of Notch1 in B16 melanoma cells inhibited or promoted tumor growth in immunocompetent mice, respectively. Notch1 expression in B16 melanoma cells inhibited the infiltration of CD8+ cytotoxic T lymphocytes and NK cells and reduced IFN-γ release in tumor tissue. It could also enhance B16 cell-mediated inhibition of T cell proliferation and activation, and upregulate PD-1 expression on CD4⁺ and CD8⁺ T cells. The percentage of CD4⁺CD25⁺FoxP3⁺ Tregs and Gr1⁺CD11b⁺MDSCs were significantly increased in tumor microenvironment, and all these were attributed to the upregulation of TGF-β1.

Conclusion

These findings suggested that Notch1 signaling in B16 melanoma cells might inhibit antitumor immunity by upregulation of TGF-β1.

BLOS2 negatively regulates Notch signaling during neural and hematopoietic stem and progenitor cell development

Notch signaling plays a crucial role in controling the proliferation and differentiation of stem and progenitor cells during embryogenesis or organogenesis, but its regulation is incompletely understood. BLOS2, encoded by the Bloc1s2 gene, is a shared subunit of two lysosomal trafficking complexes, biogenesis of lysosome-related organelles complex-1 (BLOC-1) and BLOC-1-related complex (BORC). Bloc1s2^-/- mice were embryonic lethal and exhibited defects in cortical development and hematopoiesis. Loss of BLOS2 resulted in elevated Notch signaling, which consequently increased the proliferation of neural progenitor cells and inhibited neuronal differentiation in cortices. Likewise, ablation of bloc1s2 in zebrafish or mice led to increased hematopoietic stem and progenitor cell production in the aorta-gonad-mesonephros region. BLOS2 physically interacted with Notch1 in endo-lysosomal trafficking of Notch1. Our findings suggest that BLOS2 is a novel negative player in regulating Notch signaling through lysosomal trafficking to control multiple stem and progenitor cell homeostasis in vertebrates.