Topological morphology descriptors reveal sex-dependent changes in microglial morphology across AD neuropathologic change

Alzheimer’s disease (AD) shows marked sex differences in prevalence and clinical course, potentially driven by differential microglial activation. Since microglial morphologic changes may coincide with diverse activation states, thereby potentially serving as a morphologic proxy for underlying functional reactivity, this study characterizes differential microglial morphologic changes across AD neuropathology (ADNC) and biologic sex using novel topological morphology descriptor (TMD) methodology applied to whole-slide images. Individuals with CNS autopsies of no (N = 12), intermediate (N = 12), and high ADNC (N = 12) were identified from the Mayo Clinic Study of Aging and Alzheimer’s Disease Research Center. After diagnostic neuropathologic evaluation, single immunohistochemistry for pan-microglial marker IBA1 was performed on sections of the dorsolateral prefrontal cortex and scanned at 40X (Leica GT450). Skeletonized microglial tracings collected from cortical regions of interest were converted to TMDs, then persistence images, and bootstrapped without replacement to reduce intragroup cellular variability. High-dimensional bootstrapped datapoints were pooled and underwent dimensionality reduction and visualization. Comparisons were made by ADNC, sex, and cognitive status. Analyses to compare TMDs to standard morphometric approaches were additionally performed. A total of 63,872 cell skeletons were traced from 180 ROIs across 36 postmortem brains. Microglial morphologies clustered by ADNC level with minimal sex differences at no pathology, converged at intermediate ADNC, and diverged at high ADNC. Analysis with TMDs outperformed the tested conventional morphometric approaches, including Sholl analysis. These findings validate TMD-based methodology for human microglia whole slide analysis, a methodology that had been previously applied to 3D constructed images and further suggests sexually dimorphic microglial trajectories across AD progression, supporting a potential role for microglial reactivity in sex-specific AD risk.