Astrocytes, emerging stars of energy homeostasis

Astrocytes as Drivers and Disruptors of Behavior: New Advances in Basic Mechanisms and Therapeutic Targeting

Astrocytes are emerging as key regulators of cognitive function and behavior. This review highlights some of the latest advances in the understanding of astrocyte roles in different behavioral domains across lifespan and in disease. We address specific molecular and circuit mechanisms by which astrocytes modulate behavior, discuss their functional diversity and versatility, and highlight emerging astrocyte-targeted treatment strategies that might alleviate behavioral and cognitive dysfunction in pathologic conditions. Converging evidence across different model systems and manipulations is revealing that astrocytes regulate behavioral processes in a precise and context-dependent manner. Improved understanding of these astrocytic functions may generate new therapeutic strategies for various conditions with cognitive and behavioral impairments.

Autism Spectrum Disorder: A Neuro-Immunometabolic Hypothesis of the Developmental Origins

Fetal neuroinflammation and prenatal stress (PS) may contribute to lifelong neurological disabilities. Astrocytes and microglia, among the brain's non-neuronal "glia" cell populations, play a pivotal role in neurodevelopment and predisposition to and initiation of disease throughout lifespan. One of the most common neurodevelopmental disorders manifesting between 1-4 years of age is the autism spectrum disorder (ASD). A pathological glial-neuronal interplay is thought to increase the risk for clinical manifestation of ASD in at-risk children, but the mechanisms remain poorly understood, and integrative, multi-scale models are needed. We propose a model that integrates the data across the scales of physiological organization, from genome to phenotype, and provides a foundation to explain the disparate findings on the genomic level. We hypothesize that via gene-environment interactions, fetal neuroinflammation and PS may reprogram glial immunometabolic phenotypes that impact neurodevelopment and neurobehavior. Drawing on genomic data from the recently published series of ovine and rodent glial transcriptome analyses with fetuses exposed to neuroinflammation or PS, we conducted an analysis on the Simons Foundation Autism Research Initiative (SFARI) Gene database. We confirmed 21 gene hits. Using unsupervised statistical network analysis, we then identified six clusters of probable protein-protein interactions mapping onto the immunometabolic and stress response networks and epigenetic memory. These findings support our hypothesis. We discuss the implications for ASD etiology, early detection, and novel therapeutic approaches. We conclude with delineation of the next steps to verify our model on the individual gene level in an assumption-free manner. The proposed model is of interest for the multidisciplinary community of stakeholders engaged in ASD research, the development of novel pharmacological and non-pharmacological treatments, early prevention, and detection as well as for policy makers.

Cardiac sympathetic afferent ablation to prevent ventricular arrhythmia complicating acute myocardial infarction by inhibiting activated astrocytes

Enhanced cardiac sympathetic afferent reflex (CSAR) contributes to ventricular arrhythmia (VA) after acute myocardial infarction (AMI). However, central regulation mechanisms remain unknown. The aim of this study was to investigate whether local cardiac sympathetic afferent ablation (LCSAA) could reduce VA by inhibiting activated astrocytes in the hypothalamus paraventricular (PVN) in an AMI rat model. The rats were randomly divided into AMI, AMI + BD (baroreceptor denervation), AMI + LCSAA and AMI + BD+ LCSAA groups. Before the generation of AMI, BD and (or) LCSAA were performed. At 24 h after AMI, the incidence and duration of VA in AMI + LCSAA group and AMI + BD + LCSAA group were significantly reduced than AMI group (P < 0.05). Furthermore, LCSAA significantly reduced GFAP (a marker for activated astrocytes) positive cells and their projections as well as the level of TNF‐α and IL‐6 in the PVN of AMI + LCSAA group and AMI + BD+ LCSAA group, along with the decrease of neuronal activation in PVN and sympathetic nerve activity (P < 0.05). but BD had no obvious difference between AMI + LCSAA and AMI + BD + LCSAA group (P > 0.05). Therefore, LCSAA could decrease sympathoexcitation and VA occurrence in AMI rats by inhibiting astrocyte and neuronal activation in the PVN. Our study demonstrates that activated astrocytes may play an important role on CSAR in AMI.

The ventromedial hypothalamic nucleus: watchdog of whole-body glucose homeostasis

The brain, particularly the ventromedial hypothalamic nucleus (VMH), has been long known for its involvement in glucose sensing and whole-body glucose homeostasis. However, it is still not fully understood how the brain detects and responds to the changes in the circulating glucose levels, as well as brain-body coordinated control of glucose homeostasis. In this review, we address the growing evidence implicating the brain in glucose homeostasis, especially in the contexts of hypoglycemia and diabetes. In addition to neurons, we emphasize the potential roles played by non-neuronal cells, as well as extracellular matrix in the hypothalamus in whole-body glucose homeostasis. Further, we review the ionic mechanisms by which glucose-sensing neurons sense fluctuations of ambient glucose levels. We also introduce the significant implications of heterogeneous neurons in the VMH upon glucose sensing and whole-body glucose homeostasis, in which sex difference is also addressed. Meanwhile, research gaps have also been identified, which necessities further mechanistic studies in future.

Astrocyte Bioenergetics and Major Psychiatric Disorders

Ongoing research continues to add new elements to the emerging picture of involvement of astrocyte energy metabolism in the pathophysiology of major psychiatric disorders, including schizophrenia, mood disorders, and addictions. This review outlines what is known about the energy metabolism in astrocytes, the most numerous cell type in the brain, and summarizes the recent work on how specific perturbations of astrocyte bioenergetics may contribute to the neuropsychiatric conditions. The role of astrocyte energy metabolism in mental health and disease is reviewed on the organism, organ, and cell level. Data arising from genomic, metabolomic, in vitro, and neurobehavioral studies is critically analyzed to suggest future directions in research and possible metabolism-focused therapeutic interventions.

Regulation of the Fructose Transporter Gene Slc2a5 Expression by Glucose in Cultured Microglial Cells

Microglia play a role in the regulation of metabolism and pathogenesis of obesity. Microglial activity is altered in response to changes in diet and the body’s metabolic state. Solute carrier family 2 member 5 (Slc2a5) that encodes glucose transporter 5 (GLUT5) is a fructose transporter primarily expressed in microglia within the central nervous system. However, little is known about the nutritional regulation of Slc2a5 expression in microglia and its role in the regulation of metabolism. The present study aimed to address the hypothesis that nutrients affect microglial activity by altering the expression of glucose transporter genes. Murine microglial cell line SIM-A9 cells and primary microglia from mouse brain were exposed to different concentrations of glucose and levels of microglial activation markers and glucose transporter genes were measured. High concentration of glucose increased levels of the immediate-early gene product c-Fos, a marker of cell activation, Slc2a5 mRNA, and pro-inflammatory cytokine genes in microglial cells in a time-dependent manner, while fructose failed to cause these changes. Glucose-induced changes in pro-inflammatory gene expression were partially attenuated in SIM-A9 cells treated with the GLUT5 inhibitor. These findings suggest that an increase in local glucose availability leads to the activation of microglia by controlling their carbohydrate sensing mechanism through both GLUT5-dependent and –independent mechanisms.

The infundibular peptidergic neurons and glia cells in overeating, obesity, and diabetes

Dysfunctional regulation of energy homeostasis results in increased bodyweight and obesity, eventually leading to type 2 diabetes mellitus. The infundibular nucleus (IFN) of the hypothalamus is the main regulator of energy homeostasis. The peptidergic neurons and glia cells of the IFN receive metabolic cues concerning energy state of the body from the circulation. The IFN can monitor hormones like insulin and leptin and nutrients like glucose and fatty acids. All these metabolic cues are integrated into an output signal regulating energy homeostasis through the release of neuropeptides. These neuropeptides are released in several inter- and extrahypothalamic brain regions involved in regulation of energy homeostasis. This review will give an overview of the peripheral signals involved in the regulation of energy homeostasis, the peptidergic neurons and glial cells of the IFN, and will highlight the main intra-hypothalamic projection sites of the IFN.

Serotonin receptor 4 regulates hippocampal astrocyte morphology and function

Astrocytes are an important component of the multipartite synapse and crucial for proper neuronal network function. Although small GTPases of the Rho family are powerful regulators of cellular morphology, the signaling modules of Rho-mediated pathways in astrocytes remain enigmatic. Here we demonstrated that the serotonin receptor 4 (5-HT₄ R) is expressed in hippocampal astrocytes, both in vitro and in vivo. Through fluorescence microscopy, we established that 5-HT₄ R activation triggered RhoA activity via Gα₁₃ -mediated signaling, which boosted filamentous actin assembly, leading to morphological changes in hippocampal astrocytes. We investigated the effects of these 5-HT₄ R-mediated changes in mixed cultures and in acute slices, in which 5-HT₄ R was expressed exclusively in astrocytes. In both systems, 5-HT₄ R-RhoA signaling changed glutamatergic synaptic transmission: It increased the frequency of miniature excitatory postsynaptic currents (mEPSCs) in mixed cultures and reduced the paired-pulse-ratio (PPR) of field excitatory postsynaptic potentials (fEPSPs) in acute slices. Overall, our present findings demonstrate that astrocytic 5-HT₄ R-Gα₁₃ -RhoA signaling is a previously unrecognized molecular pathway involved in the functional regulation of excitatory synaptic circuits.

Clinical - pathological significance of leptin receptor (LEPR) expression in squamous cell carcinoma of the skin

Adipokine leptin functions through its transmembrane receptors (LEPR). In many malignant tumors it stimulates the growth, migration and invasion of malignant cells. The aim of our work is to examine the effect of LEPR expression on the clinical-morphological properties of squamous cell carcinoma of the skin (cSCC). The biopsy material obtained by excision of squamous cell skin cancer was used. The test group consisted of excision biopsies of squamous cell carcinoma of the skin (n = 62), and the control group (n = 62) consisted of excision biopsies of non-tumor tissue of the skin (from the tumor environment) from an operative preparation delivered to the Pathohistology Department. After routine processing and paraffin molding, histochemical Hematoxylin-Eosin and immunohistochemical ABC method with anti LEPR and Ki67 antibodies were applied at 4 μm sections. The statistical software package SPSS for Windows (26.0) was used to analyze obtained results. Intracytoplasmic and intramembranous LEPR expression was found in 100 % of examined cSCCs. LEPR expression was statistically significantly associated with proliferation index and histologic grade of tumors. Pronounced LEPR expression was associated with a high proliferation index in 66.7 % of cases and with poorly differentiated cSCC in 94.4 %. Multivariate regression analysis showed that cSCCs with pronounced LEPR expression were seven times more often poorly differentiated than tumors with moderate or LEPR expression in trace. Our results indicate that LEPR expression is a predictor of the malignant potential of cSCC, so that based on LEPR expression, it is possible to identify an aggressive cSCC phenotype, which provides the possibility of individualizing anti-tumor treatment using LEPR antagonists.