Pathologic TDP43 Associated Tri‐Glial Dysfunction in Amnestic and Non‐amnestic Clinical Dementia Syndromes: A Multiplexed Immunofluorescence Study

Background Alzheimer’s disease (AD) is a substantial cause of death and disability. In addition to the plaques and tangles classically observed in AD, other co‐existing brain lesions also contribute to the development of cognitive impairment, such as pathologic trans‐active response DNA‐binding protein 43 (pTDP43). TDP43 is ubiquitously expressed in the brain and mechanistic studies suggest potential roles for TDP43 in maintaining normal physiologic conditions in glia (astrocytes, microglia, oligodendrocytes) (Bulgiani, 2022). Effective glial functioning and signaling are crucial to maintaining functional connectivity and pTDP43 is strongly associated with lower cognitive performance (Flanagan, 2018). However, pTDP43’s role in tri‐glial dysfunction remains unclear. We hypothesize that nuclear astrocytic TDP43 loss alters astrocyte‐to‐microglial signaling, and results in tri‐glial dysfunction. Here we examine glial pTDP43 subtypes in amnestic and non‐amnestic clinical dementia syndromes with matched AD pathology. Method Paraffin embedded autopsy samples (hippocampus and middle frontal cortex) were stained using multiplexed immunofluorescence (Pu.1: microglia, GLUL: astrocytes, total TDP43), and imaged. Indica Labs Halo software was used to perform quantitative analyses on whole slide images. Cases were matched for AD pathology (low and high) (Montine, 2012). Students’ t‐tests were performed to compare cell counts between groups. Kolmogorov–Smirnov test was performed to check approximate normality before applying t‐test and all measurements passed it. Clinical phenotypes (AD dementia vs. behavioral variant frontotemporal dementia (bvFTD)) and pTDP43 status were compared (n = 50). Spatial localization plots, NSInC colocalization indices, and Box plot comparisons were used to assess the impact of glial pTDP43 on the microenvironment. Result Hippocampal astrocyte counts are lowest in the AD dementia setting with the highest AD pathology burden, and presence of co‐existing pTDP43. Cases with high AD pathology had lower astrocyte counts when co‐existing pTDP43 was present when comparing both AD dementia with pTDP43 vs. AD dementia without pTDP43 (p = 0.03), and AD dementia with pTDP43 vs. bvFTD without pTDP43 (p = 0.05). Conclusion Contradictory to studies showing increased GFAP in mutant TDP43 mice (Yan, 2014), the lowest astrocyte counts were found in individuals with AD dementia, highest burden of AD pathology, and presence of pTDP43. Results support the role