Hypothalamic lipid-laden astrocytes induce microglia migration and activation

LncRNA SNHG5 enhances astrocytes and microglia viability via upregulating KLF4 in spinal cord injury

This study aims to explore the role and mechanism of lncRNA SNHG5 in spinal cord injury (SCI). The interaction between SNHG5 and Krüppel-like factor 4 (KLF4) was verified by RNA pull-down and RNA immunoprecipitation (RIP) assay. Rat neural function was evaluated by BBB and BMS scores. Results showed that GFAP and Iba-1 (specific proteins for astrocytes and microglia respectively) were upregulated in spinal cord of SCI rats. Simultaneously, spinal cord also expressed substantially higher levels of SNHG5, KLF4 and eNOS (endothelial Nitric Oxide Synthase) than sham group. In traumatically injured astrocytes and microglia, SNHG5 overexpression increased cells viability, which was significantly inhibited by SNHG5 knockdown. KLF4 is a directly target for SNHG5 and is positively regulated by SNHG5. The knockdown of KLF4 effectively decreased astrocytes and microglia viability induced by SHNG5 overexpression and attenuated the pcDNA-SNHG5-mediated repression of the apoptosis. In SCI rats, the injection of Lenti-SNHG5 reduced BBB and BMS scores and also enhanced the protein expression of KLF4, eNOS, GFAP and Iba-1. In summary, our data suggested that SNHG5 promotes SCI via increasing the viability of astrocytes and microglia. The mechanism by which SNHG5 works is its directive interaction to KLF4 and contribution to eNOS upregulation.

Microglia-Astrocyte Crosstalk: An Intimate Molecular Conversation

Microglia-astrocyte crosstalk has recently been at the forefront of glial research. Emerging evidence illustrates that microglia- and astrocyte-derived signals are the functional determinants for the fates of astrocytes and microglia, respectively. By releasing diverse signaling molecules, both microglia and astrocytes establish autocrine feedback and their bidirectional conversation for a tight reciprocal modulation during central nervous system (CNS) insult or injury. Microglia, the constant sensors of changes in the CNS microenvironment and restorers of tissue homeostasis, not only serve as the primary immune cells of the CNS but also regulate the innate immune functions of astrocytes. Similarly, microglia determine the functions of reactive astrocytes, ranging from neuroprotective to neurotoxic. Conversely, astrocytes through their secreted molecules regulate microglial phenotypes and functions ranging from motility to phagocytosis. Altogether, the microglia-astrocyte crosstalk is fundamental to neuronal functions and dysfunctions. This review discusses the current understanding of the intimate molecular conversation between microglia and astrocytes and outlines its potential implications in CNS health and disease.

The possible factors affecting microglial activation in cases of obesity with cognitive dysfunction

Obesity has reached epidemic proportions in many countries around the world. Several studies have reported that obesity can lead to the development of cognitive decline. There is increasing evidence to demonstrate that microglia play a crucial role in cognitive decline in cases of obesity, Alzheimer's disease and also in the aging process. Although there have been several studies into microglia over the past decades, the mechanistic link between microglia and cognitive decline in obese models is still not fully understood. In this review, the current available evidence from both in vitro and in vivo investigations regarding the association between the alteration in microglial activity in different obese models with respect to cognition are included. The metabolite profiles from obesity, adiposity, dietary and hormone affected microglial activation and its function in the brain are comprehensively summarized. In addition, the possible roles of microglial activation in relation to cognitive dysfunction are also presented and discussed. To ensure a balanced perspective controversial reports regarding these issues are included and discussed.

LncRNA MALAT1 promotes high glucose-induced inflammatory response of microglial cells via provoking MyD88/IRAK1/TRAF6 signaling

Although a large number of studies have confirmed from multiple levels that diabetes mellitus (DM) promotes cerebral ischemic reperfusion (I/R) injury, but the precise mechanism is still unclear. A cerebral I/R injury model in diabetic rats was established. The neurological deficit scores and brain edema were monitored at 24 and 72 hours after injury. The peri-infarct cortical tissues of rats were isolated for molecular biology detection. The rat primary microglia and microglia line HAPI were cultured to establish the cell model of DM-I/R by high glucose (HG) and hypoxia-reoxygenation (H/R). The endogenous expression of MALAT1 and MyD88 was regulated by the transfection with pcDNA-MALAT1, si-MALAT1 and si-MyD88, respectively. The cerebral I/R injury model in diabetic rats had more severe neuronal injury as shown by the significantly higher neurological deficit scores and an obvious increasing brain edema at 24 and 72 hours after injury. Moreover, the microglia were activated and induced a large number of inflammatory cytokines TNF-α, IL-1β and IL-6 in the peri-infarct cortical tissues during cerebral I/R injury associated with DM. The expression of MALAT1, MyD88, IRAK1 and TRAF6 protein were significantly up-regulated by DM-I/R in vitro and in vivo. Furthermore, the HG-H/R-induced MALAT1 promoted the inflammatory response in microglia via MyD88/IRAK1/TRAF6 signaling. Our results suggested that MALAT1 mediated the exacerbation of cerebral I/R injury induced by DM through triggering the inflammatory response in microglia via MyD88 signaling.

The involvement of 4-1BB/4-1BBL signaling in glial cell-mediated hypothalamic inflammation in obesity

Obesity‐induced inflammation occurs not only in peripheral tissues but also in areas of the central nervous system. Glial cells such as astrocytes and microglia play crucial roles in obesity‐related hypothalamic inflammation, leading to the derangement of energy metabolism and neurodegenerative pathologies. Here, we show that the interaction of 4‐1BB/4‐1BBL between lipid‐laden astrocytes/microglia promotes hypothalamic inflammation in obesity. Stimulation of 4‐1BB, a member of the TNF receptor superfamily, and/or its ligand 4‐1BBL on astrocytes and/or microglia with a specific agonist resulted in activation of the inflammatory signaling pathway and enhanced production of inflammatory mediators. Contact coculture of lipid‐laden astrocytes and microglia increased the production of inflammatory mediators, and blockade of the 4‐1BB/4‐1BBL interaction reduced the inflammatory response. Moreover, deficiency of 4‐1BB reduced hypothalamic inflammation in obese mice fed an high‐fat diet. These findings suggest that 4‐1BBL/4‐1BB signaling enhances the glial cell‐mediated inflammatory cross talk and participates in obesity‐induced hypothalamic inflammation.