Region-specific features of early glial activation and Aquaporin-4 dysregulation in conditional mouse models of TDP-43 proteinopathies.

INTRODUCTION: Aggregation and cytoplasmic mislocalization of TDP-43 are key features of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Neuroinflammatory processes mediated by glial cells play crucial roles in the pathophysiology of these and other diseases, defined as TDP-43 proteinopathies. Here, we characterized region-specific glial activation in two conditional mouse models: hTDP-43-WT (overexpressing nuclear wild-type human TDP-43) and hTDP-43-ΔNLS (expressing cytoplasmic TDP-43 with altered nuclear localization signal) following 1 month of transgene expression.

METHODS AND RESULTS: Immunofluorescence analysis revealed distinct patterns of microglial activation across brain regions. hTDP-43-WT mice exhibited significant microgliosis in motor (MC) and somatosensory (SSC) cortices and hippocampal dentate gyrus (DG) with pronounced morphological alterations (i.e. increased soma size). Sholl analysis demonstrated reduced branching length and complexity in MC, SSC, and hippocampal subfields. hTDP-43-ΔNLS mice displayed more pronounced microglial activation in hippocampal regions (CA1, DG) compared to cortical areas, with significant increases in microglial density. Additionally, we observed region-specific cortical astrocytosis in both models, suggesting coordinated glial reactivity. hTDP-43-ΔNLS mice showed decreased polarization of astrocytic water channel Aquaporin-4 (AQP4) around vascular structures in SSC and hippocampal CA1/DG. The changes in AQP4 localization, which is critical for glymphatic function, support the hypothesis that this waste clearance system for the brain is altered in TDP-43 proteinopathies.

CONCLUSION: These findings demonstrate that these different animal models of ALS/FTD induce distinct neuroinflammatory signatures, potentially contributing to the region-specific vulnerability observed in these diseases. Our data provide insights into early glial-mediated pathogenic mechanisms that could guide targeted therapeutic strategies for TDP-43 proteinopathies.