Astrocyte-to-microglia communication via Sema4B-Plexin-B2 modulates injury-induced reactivity of microglia

Microglia modulate integrity of myelin and proliferation of oligodendrocyte precursor cells in murine model of bone cancer pain

Cancer pain, a frequent complication in patients with cancer, adversely affects quality of life and survival rates. Microglia promote nociceptive information transmission by modulating myelin integrity during pain perception. However, the specific mechanisms by which microglia regulate myelin in the context of cancer pain remain poorly understood. In this study, we developed a bone cancer pain model to examine the interactions among microglia, myelin, and oligodendrocyte precursor cells and their roles in cancer pain. Our study found that mice with bone cancer pain had oligodendrocyte differentiation defects and myelin loss, and that promoting myelination did not relieve pain. In addition, we observed that reactive microglia and inflammatory cytokines increased and microglia phagocytosed myelin in mice with bone cancer pain. Inhibition of microglia not only alleviated pain behaviors in mice with bone cancer but also mitigated myelin phagocytosis and the proliferation of oligodendrocyte precursor cells. Our study suggests that microglia-mediated myelin loss and oligodendrocyte precursor cell proliferation may be one of the pathological mechanisms underlying pain in mice with bone cancer.

Akkermansia mono-colonization modulates microglia and astrocytes in a strain specific manner

Microglia and astrocytes are the primary glial cells in the central nervous system (CNS) and their function is shaped by multiple factors. Regulation of CNS glia by the microbiota have been reported, although the role of specific bacteria has not been identified. We colonized germ-free mice with the type strain Akkermansia muciniphila (AmT) and a novel A. muciniphila strain BWH-H3 (Am-H3) isolated from a subject with multiple sclerosis and compared to mice colonized with Bacteroides cellulosilyticus strain BWH-E5 (Bc) isolated from a healthy control subject. We then investigated the effect of these bacteria on microglia and astrocyte gene expression by RNA sequencing. We found altered gene expression profiles in brain microglia, with Akkermansia downregulating genes related to antigen presentation and cell migration. Furthermore, we observed strain specific effects, with Akkermansia H3 upregulating histone and protein binding associated genes and downregulating channel and ion transport genes. Astrocyte pathways that were altered by Akkermansia H3 mono-colonization included upregulation of proliferation pathways and downregulation in cytoskeletal associated genes. Furthermore, animals colonized with type strain Akkermansia and strain H3 had effects on the immune system including elevated splenic γδ-T cells and increased IFNγ production in CD4 + T cells. We also measured intestinal short chain fatty acids and found that both A. muciniphila strains produced proprionate while B. cellulosilyticus produced acetate, proprionate, and isovalerate. Taken together, our study shows that specific members of the intestinal microbiota influence both microglial and astroyctes which may be mediated by changes in short chain fatty acids and peripheral immune signaling.

Plexins: Navigating through the neural regulation and brain pathology

Plexins are a family of transmembrane receptors known for their diverse roles in neural development, axon guidance, neuronal migration, synaptogenesis, and circuit formation. Semaphorins are a class of secreted and membrane proteins that act as primary ligands for plexin receptors. Semaphorins play a crucial role in central nervous system (CNS) development by regulating processes such as axonal growth, neuronal positioning, and synaptic connectivity. Various types of semaphorins like sema3A, sema4A, sema4C, sema4D, and many more have a crucial role in developing brain diseases. Likewise, various evidence suggests that plexin receptors are of four types: plexin A, plexin B, plexin C, and plexin D. Plexins have emerged as crucial regulators of neurogenesis and neuronal development and connectivity. When bound to semaphorins, these receptors trigger two major networking cascades, namely Rho and Ras GTPase networks. Dysregulation of plexin networking has been implicated in a myriad of brain disorders, including autism spectrum disorder (ASD), Schizophrenia, Alzheimer's disease (AD), Parkinson's disease (PD), and many more. This review synthesizes findings from molecular, cellular, and animal model studies to elucidate the mechanisms by which plexins contribute to the pathogenesis of various brain diseases.

Glia-glia crosstalk via semaphorins: Emerging implications in neurodegeneration

The central nervous system (CNS) is wired by a complex network of integrated glial and neuronal signals, which is critical for its development and homeostasis. In this context, glia-glia communication is a complex and dynamic process that is essential for ensuring optimal CNS function. Semaphorins, which include secreted and transmembrane molecules, and their receptors, mainly found in the plexin and neuropilin families, are expressed in a wide range of cell types, including glia. In the CNS, semaphorin signalling is involved in a spectrum of processes, including neurogenesis, neuronal migration and wiring, and glial cell recruitment. Recently, semaphorins and plexins have attracted intense research aimed at elucidating their roles in instructing glial cell behavior during development or in response to inflammatory stimuli. In this review, we provide an overview of the multifaceted role of semaphorins in glia-glia communication, highlighting recent discoveries about semaphoring-dependent regulation of glia functions in healthy conditions. We also discuss the mechanisms of gliaglia crosstalk mediated by semaphorins under pathological conditions, and how these interactions may provide potential avenues for therapeutic intervention in neuroinflammation-mediated neurodegeneration.

Loss of microglial Arid1a exacerbates microglial scar formation via elevated CCL5 after traumatic brain injury

Traumatic brain injury (TBI) is an acquired insult to the brain caused by an external mechanical force, potentially resulting in temporary or permanent impairment. Microglia, the resident immune cells of the central nervous system, are activated in response to TBI, participating in tissue repair process. However, the underlying epigenetic mechanisms in microglia during TBI remain poorly understood. ARID1A (AT-Rich Interaction Domain 1 A), a pivotal subunit of the multi-protein SWI/SNF chromatin remodeling complex, has received little attention in microglia, especially in the context of brain injury. In this study, we generated a Arid1a cKO mouse line to investigate the potential roles of ARID1A in microglia in response to TBI. We found that glial scar formation was exacerbated due to increased microglial migration and a heightened inflammatory response in Arid1a cKO mice following TBI. Mechanistically, loss of ARID1A led to an up-regulation of the chemokine CCL5 in microglia upon the injury, while the CCL5-neutralizing antibody reduced migration and inflammatory response of LPS-stimulated Arid1a cKO microglia. Importantly, administration of auraptene (AUR), an inhibitor of CCL5, repressed the microglial migration and inflammatory response, as well as the glial scar formation after TBI. These findings suggest that ARID1A is critical for microglial response to injury and that AUR has a therapeutic potential for the treatment of TBI.