Region-Specific Characteristics of Astrocytes and Microglia: A Possible Involvement in Aging and Diseases

Long-term Treatment with a 5-Alpha-Reductase Inhibitor AlleviatesDepression-like Behavior in Obese Male Rats

Several studies have reported side effects of finasteride (FIN), such as anxiety/depression in young men. Obesity is also positively associated with anxiety/depression symptoms; however, the impacts of long-term FIN treatment and FIN withdrawal in young obese individuals are still elusive. The present study aimed to investigate the effect of long-term treatment and its withdrawal on anxiety/depression and brain pathologies in lean and obese adult male rats. Forty-eight male Wistar rats were equally divided into two groups and fed either a normal or high-fat diet. At age 13 weeks, rats in each dietary group were divided into three subgroups: 1) the control group receiving drinking water, 2) the long-term treatment group receiving FIN orally at 5mg/kg/day for 6 weeks, and 3) the withdrawal group receiving FIN orally at 5mg/kg/day for 2 weeks followed by a 4-week withdrawal period. Anxiety/depression-like behaviors, biochemical analysis, brain inflammation, oxidative stress, neuroactive steroids, brain metabolites, and microglial complexity were tested. The result showed that lean rats treated with long-term FIN and its withdrawal exhibited metabolic disturbances, depressive-like behavior, and both groups showed increased neurotoxic metabolites and reduced microglial complexity. Obesity itself led to metabolic disturbances and brain pathologies, including increased inflammation, oxidative stress, and quinolinic acid, as well as reduced microglial complexity, resulting in increased anxiety- and depression-like behaviors. Interestingly, the long-term FIN treatment group in obese rats showed attenuation of depressive-like behaviors, brain inflammation, and oxidative stress, along with increased brain antioxidants, suggesting the possible benefits of FIN in obese conditions.

Old age alters inflammation and autophagy signaling in the brain, leading to exacerbated neurological outcomes after spinal cord injury in male mice

Older patients with spinal cord injury (SCI) have different features with regard to neurological characteristics after injury. Recent large-scale longitudinal population-based studies showed that individuals with SCI are at a higher risk of developing dementia than non-SCI patients, indicating that SCI is a potential risk factor for dementia. Aging is known to potentiate inflammation and neurodegeneration at the injured site leading to impaired recovery from SCI. However, no research has been aimed at studying the mechanisms of SCI-mediated cognitive impairment in the elderly. The present study examined neurobehavioral and molecular changes in the brain and the underlying mechanisms associated with brain dysfunction in aged C57BL/6 male mice using a contusion SCI model. At 2 months post-injury, aged mice displayed worse performance in locomotor, cognitive and depressive-like behavioral tests compared to young adult animals. Histopathology in injured spinal cord tissue was exacerbated in aged SCI mice. In the brain, transcriptomic analysis with NanoString neuropathology panel identified activated microglia and dysregulated autophagy as the most significantly altered pathways by both age and injury. These findings were further validated by flow cytometry, which demonstrated increased myeloid and lymphocytes infiltration at both the injured site and brain of aged mice. Moreover, SCI in aged mice altered microglial function and dysregulated autophagy in microglia, resulting in worsened neurodegeneration. Taken together, our data indicate that old age exacerbates neuropathological changes in both the injured spinal cord and remote brain regions leading to poorer functional outcomes, at least in part, through altered inflammation and autophagy function.

Human pluripotent stem cell (hPSC)-derived microglia for the study of brain disorders. A comprehensive review of existing protocols

Microglia, resident immune cells of the brain that originate from the yolk sac, play a critical role in maintaining brain homeostasis by monitoring and phagocytosing pathogens and cellular debris in the central nervous system (CNS). While they share characteristics with myeloid cells, they are distinct from macrophages. In response to injury, microglia release pro-inflammatory factors and contribute to brain homeostasis through activities such as synapse pruning and neurogenesis. To better understand their role in neurological disorders, the generation of in vitro models of human microglia has become essential. These models, derived from patient-specific induced pluripotent stem cells (iPSCs), provide a controlled environment to study the molecular and cellular mechanisms underlying microglia-mediated neuroinflammation and neurodegeneration. The incorporation or generation of microglia into three-dimensional (3D) organoid cultures provides a more physiologically relevant environment that offers further opportunities to study microglial dynamics and disease modeling. This review describes several protocols that have been recently developed for the generation of human-induced microglia. Importantly, it highlights the promise of these in vitro models in advancing our understanding of brain disorders and facilitating personalized drug screening.

Diabetic Retinopathy: New Treatment Approaches Targeting Redox and Immune Mechanisms

Diabetic retinopathy (DR) represents a severe complication of diabetes mellitus, characterized by irreversible visual impairment resulting from microvascular abnormalities. Since the global prevalence of diabetes continues to escalate, DR has emerged as a prominent area of research interest. The development and progression of DR encompass a complex interplay of pathological and physiological mechanisms, such as high glucose-induced oxidative stress, immune responses, vascular endothelial dysfunction, as well as damage to retinal neurons. Recent years have unveiled the involvement of genomic and epigenetic factors in the formation of DR mechanisms. At present, extensive research explores the potential of biomarkers such as cytokines, molecular and cell therapies, antioxidant interventions, and gene therapy for DR treatment. Notably, certain drugs, such as anti-VEGF agents, antioxidants, inhibitors of inflammatory responses, and protein kinase C (PKC)-β inhibitors, have demonstrated promising outcomes in clinical trials. Within this context, this review article aims to introduce the recent molecular research on DR and highlight the current progress in the field, with a particular focus on the emerging and experimental treatment strategies targeting the immune and redox signaling pathways.

Microglia activity in the human basal ganglia is altered in alcohol use disorder and reversed with remission from alcohol

Alcohol use disorder (AUD) is characterized by cycles of abuse, withdrawal, and relapse. Neuroadaptations in the basal ganglia are observed in AUD; specifically in the putamen, globus pallidus (GP), and ventral pallidum (VP). These regions are associated with habit formation, drug-seeking behaviors, and reward processing. While previous studies have shown the crucial role of glial cells in drug seeking, it remains unknown whether glial cells in the basal ganglia are altered in AUD. Glial cells in the putamen, GP, and VP were examined in human post-mortem tissue of AUD and alcohol remission cases. Immunohistochemistry was performed to analyze cell count, staining intensity, and morphology of microglia and astrocytes, using markers Iba-1 and GFAP. Morphological analysis revealed a significant decrease in microglia cell size and process retraction, indicating activation or a dystrophic microglia phenotype in individuals with AUD compared to controls. Microglia staining intensity was also higher in the GP and VP in AUD cases, whereas microglia staining intensity and cell size in remission cases were not different to control cases. In contrast, no astrocyte changes were observed in examined brain regions for both AUD and remission cases compared to controls. These results suggest alcohol exposure alters microglia, potentially contributing to dysfunctions in the basal ganglia that maintain addiction, and abstinence from alcohol may reverse microglia changes and associated dysfunctions. Overall, this study further characterizes AUD neuropathology and implicates microglia in the putamen, GP, and VP as a potential target for therapy.

Astroglial Cells: Emerging Therapeutic Targets in the Management of Traumatic Brain Injury

Traumatic Brain Injury (TBI) represents a significant health concern, necessitating advanced therapeutic interventions. This detailed review explores the critical roles of astrocytes, key cellular constituents of the central nervous system (CNS), in both the pathophysiology and possible rehabilitation of TBI. Following injury, astrocytes exhibit reactive transformations, differentiating into pro-inflammatory (A1) and neuroprotective (A2) phenotypes. This paper elucidates the interactions of astrocytes with neurons, their role in neuroinflammation, and the potential for their therapeutic exploitation. Emphasized strategies encompass the utilization of endocannabinoid and calcium signaling pathways, hormone-based treatments like 17β-estradiol, biological therapies employing anti-HBGB1 monoclonal antibodies, gene therapy targeting Connexin 43, and the innovative technique of astrocyte transplantation as a means to repair damaged neural tissues.

TAM receptors in phagocytosis: Beyond the mere internalization of particles

TYRO3, AXL, and MERTK constitute the TAM family of receptor tyrosine kinases, activated by their ligands GAS6 and PROS1. TAMs are necessary for adult homeostasis in the immune, nervous, reproductive, skeletal, and vascular systems. Among additional cellular functions employed by TAMs, phagocytosis is central for tissue health. TAM receptors are dominant in providing phagocytes with the molecular machinery necessary to engulf diverse targets, including apoptotic cells, myelin debris, and portions of live cells in a phosphatidylserine-dependent manner. Simultaneously, TAMs drive the release of anti-inflammatory and tissue repair molecules. Disruption of the TAM-driven phagocytic pathway has detrimental consequences, resulting in autoimmunity, male infertility, blindness, and disrupted vascular integrity, and which is thought to contribute to neurodegenerative diseases. Although structurally and functionally redundant, the TAM receptors and ligands underlie complex signaling cascades, of which several key aspects are yet to be elucidated. We discuss similarities and differences between TAMs and other phagocytic pathways, highlight future directions and how TAMs can be harnessed therapeutically to modulate phagocytosis.

Microglia-Astrocyte Interaction in Neural Development and Neural Pathogenesis

The interaction between microglia and astrocytes exhibits a relatively balanced state in order to maintain homeostasis in the healthy central nervous system (CNS). Disease stimuli alter microglia-astrocyte interaction patterns and elicit cell-type-specific responses, resulting in their contribution to various pathological processes. Here, we review the similarities and differences in the activation modes between microglia and astrocytes in various scenarios, encompassing different stages of neural development and a wide range of neural disorders. The aim is to provide a comprehensive understanding of their roles in neural development and regeneration and guiding new strategies for restoring CNS homeostasis.

Cocaine Regulates NLRP3 Inflammasome Activity and CRF Signaling in a Region- and Sex-Dependent Manner in Rat Brain

Cocaine, one of the most abused drugs worldwide, is capable of activating microglia in vitro and in vivo. Several neuroimmune pathways have been suggested to play roles in cocaine-mediated microglial activation. Previous work showed that cocaine activates microglia in a region-specific manner in the brains of self-administered mice. To further characterize the effects of cocaine on microglia and neuroimmune signaling in vivo, we utilized the brains from both sexes of outbred rats with cocaine self-administration to explore the activation status of microglia, NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activity, corticotropin-releasing factor (CRF) signaling, and NF-κB levels in the striatum and hippocampus (HP). Age-matched rats of the same sex (drug naïve) served as controls. Our results showed that cocaine increased neuroinflammation in the striatum and HP of both sexes with a relatively higher increases in male brains. In the striatum, cocaine upregulated NLRP3 inflammasome activity and CRF levels in males but not in females. In contrast, cocaine increased NLRP3 inflammasome activity in the HP of females but not in males, and no effects on CRF signaling were observed in this region of either sex. Interestingly, cocaine increased NF-κB levels in the striatum and HP with no sex difference. Taken together, our results provide evidence that cocaine can exert region- and sex-specific differences in neuroimmune signaling in the brain. Targeting neuroimmune signaling has been suggested as possible treatment for cocaine use disorders (CUDs). Our current results indicate that sex should be taken into consideration when determining the efficacy of these new therapeutic approaches.

Role of Senescent Astrocytes in Health and Disease

For many decades after their discovery, astrocytes, the abundant glial cells of the brain, were believed to work as a glue, supporting the structure and metabolic functions of neurons. A revolution that started over 30 years ago revealed many additional functions of these cells, including neurogenesis, gliosecretion, glutamate homeostasis, assembly and function of synapses, neuronal metabolism with energy production, and others. These properties have been confirmed, limited however, to proliferating astrocytes. During their aging or following severe brain stress lesions, proliferating astrocytes are converted into their no-longer-proliferating, senescent forms, similar in their morphology but profoundly modified in their functions. The changed specificity of senescent astrocytes is largely due to their altered gene expression. The ensuing effects include downregulation of many properties typical of proliferating astrocytes, and upregulation of many others, concerned with neuroinflammation, release of pro-inflammatory cytokines, dysfunction of synapses, etc., specific to their senescence program. The ensuing decrease in neuronal support and protection by astrocytes induces the development, in vulnerable brain regions, of neuronal toxicity together with cognitive decline. Similar changes, ultimately reinforced by astrocyte aging, are also induced by traumatic events and molecules involved in dynamic processes. Senescent astrocytes play critical roles in the development of many severe brain diseases. The first demonstration, obtained for Alzheimer's disease less than 10 years ago, contributed to the elimination of the previously predominant neuro-centric amyloid hypothesis. The initial astrocyte effects, operating a considerable time before the appearance of known Alzheimer's symptoms evolve with the severity of the disease up to their proliferation during the final outcome. Involvement of astrocytes in other neurodegenerative diseases and cancer is now intensely investigated.

Secreted phosphoprotein 1 slows neurodegeneration and rescues visual function in mouse models of aging and glaucoma

Aging causes an irreversible, cumulative decline in neuronal function. Using the visual system as a model, we show that astrocytes play a critical role in maintaining retinal ganglion cell health and that deletion of SPP1 (secreted phosphoprotein 1, or osteopontin) from astrocytes leads to increased vulnerability of ganglion cells to age, elevated intraocular pressure, and traumatic optic nerve damage. Overexpression of SPP1 slows the age-related decline in ganglion cell numbers and is highly protective of visual function in a mouse model of glaucoma. SPP1 acts by promoting phagocytosis and secretion of neurotrophic factors while inhibiting production of neurotoxic and pro-inflammatory factors. SPP1 up-regulates transcription of genes related to oxidative phosphorylation, functionally enhances mitochondrial respiration, and promotes the integrity of mitochondrial microstructure. SPP1 increases intracellular ATP concentration via up-regulation of VDAC1.