Repetitive head injury promotes free radical dependent degradation of the glia limitans superficialis -a crucial structural barrier that protects the brain parenchyma.

Tauopathies, which include frontotemporal dementia, Alzheimer's disease, and chronic traumatic encephalopathy, are a class of neurological disorders resulting from pathogenic tau aggregates. These aggregates disrupt neuronal health and function leading to the cognitive and physical decline of tauopathy patients. Genome‐wide association studies and clinical evidence have brought to light the large role of the immune system in inducing and driving tau‐mediated pathology. More specifically, innate immune genes are found to harbor tauopathy risk alleles, and innate immune pathways are upregulated throughout the course of disease. Experimental evidence has expanded on these findings by describing pivotal roles for the innate immune system in the regulation of tau kinases and tau aggregates. In this review, we summarize the literature implicating innate immune pathways as drivers of tauopathy.

IntroductionMutations in INPP5D, which encodes for the SH2‐domain‐containing inositol phosphatase SHIP‐1, have recently been linked to an increased risk of developing late‐onset Alzheimer's disease. While INPP5D expression is almost exclusively restricted to microglia in the brain, little is known regarding how SHIP‐1 affects neurobiology or neurodegenerative disease pathogenesis.MethodsWe generated and investigated 5xFAD Inpp5dfl/flCx3cr1Ert2Cre mice to ascertain the function of microglial SHIP‐1 signaling in response to amyloid beta (Aβ)‐mediated pathology.ResultsSHIP‐1 deletion in microglia led to substantially enhanced recruitment of microglia to Aβ plaques, altered microglial gene expression, and marked improvements in neuronal health. Further, SHIP‐1 loss enhanced microglial plaque containment and Aβ engulfment when compared to microglia from Cre‐negative 5xFAD Inpp5dfl/fl littermate controls.DiscussionThese results define SHIP‐1 as a pivotal regulator of microglial responses during Aβ‐driven neurological disease and suggest that targeting SHIP‐1 may offer a promising strategy to treat Alzheimer's disease.Highlights Inpp5d deficiency in microglia increases plaque‐associated microglia numbers. Loss of Inpp5d induces activation and phagocytosis transcriptional pathways. Plaque encapsulation and engulfment by microglia are enhanced with Inpp5d deletion. Genetic ablation of Inpp5d protects against plaque‐induced neuronal dystrophy.