The Outcomes of Maternal Immune Activation Induced with the Viral Mimetic Poly I:C on Microglia in Exposed Rodent Offspring.

Maternal immune activation (MIA) can result from a variety of maternal inflammatory factors, including metabolic disorders, nutritional deficits, infections, and psychosocial stress. MIA has been consistently recognized as a major risk factor for neurodevelopmental disorders, and this association seems to be especially important for viral infections as viral exposure during pregnancy was associated with a higher risk of developing neurodevelopmental disorders, such as schizophrenia. In MIA, the gestational parent's inflammatory response to an immune stimulus alters or interrupts fetal development, triggering neurodevelopmental consequences. As MIA can occur in any pregnancy, it is important to understand the many factors at play that contribute to altered brain development in the offspring, especially considering recent global events such as the COVID-19 pandemic. The underlying mechanisms by which MIA results in deleterious outcomes are not yet clear, but due to the inflammatory response it initiates, it is becoming apparent that microglia are critically involved. Through investigation of MIA animal models, the role of microglia in this field is becoming more evident. Compelling evidence from animal models indicates that MIA can disrupt synaptic pruning, neuronal progenitor cell proliferation/differentiation, oligodendrogenesis, and more. Microglia appear as an active player, assisting these neural-related functions during healthy development but also mediating MIA-induced disturbances in these critical processes when neurodevelopment is challenged. The present review illustrates this complex web by reviewing recent literature, focusing on the outcomes of MIA resulting from viral mimetic polyinosinic-polycytidylic acid in rodents, to provide a clear description of how MIA impacts microglial functions and what this means for the offspring's neurodevelopment. Moreover, we discuss the possible implications of the COVID-19 pandemic on the neurodevelopment of the current and next generations in the frame of MIA models and propose some putative pharmacological and non-pharmacological approaches to prevent or attenuate MIA consequences.

All roads lead to heterogeneity: The complex involvement of astrocytes and microglia in the pathogenesis of Alzheimer's disease.

In recent years, glial cells have been acknowledged as key players in the pathogenesis of Alzheimer's disease (AD), a neurodegenerative condition in which an accumulation of intracellular neurofibrillary tangles and extracellular fibrillar amyloid beta is notably observed in the central nervous system. Genome-wide association studies have shown, both in microglia and astrocytes, an increase in gene variants associated with a higher risk of developing late-onset AD. Microglia, the resident innate immune cells of the brain, and astrocytes, glial cells crucial for vascular integrity and neuronal support, both agglomerate near amyloid beta plaques and dystrophic neurites where they participate in the elimination of these harmful parenchymal elements. However, their role in AD pathogenesis has been challenging to resolve due to the highly heterogeneous nature of these cell populations, i.e., their molecular, morphological, and ultrastructural diversity, together with their ever-changing responsiveness and functions throughout the pathological course of AD. With the recent expansions in the field of glial heterogeneity through innovative advances in state-of-the-art microscopy and -omics techniques, novel concepts and questions arose, notably pertaining to how the diverse microglial and astrocytic states interact with each other and with the AD hallmarks, and how their concerted efforts/actions impact the progression of the disease. In this review, we discuss the recent advances and findings on the topic of glial heterogeneity, particularly focusing on the relationships of these cells with AD hallmarks (e.g., amyloid beta plaques, neurofibrillary tangles, synaptic loss, and dystrophic neurites) in murine models of AD pathology and post-mortem brain samples of patients with AD.