Post‐Mortem Delay Induces Distinct Transcriptional and Morphological Changes in Microglia With Age‐Specific Patterns

microglia, correlate with PMD in human datasets and display similar enrichment patterns. Morphological analysis in fixed brain tissue from the same animals revealed that postmortem delay reduced the cell shape complexity of cortical microglia in young mice, mimicking morphological changes in the aged brain. In contrast, the morphology of aged microglia remained unchanged by postmortem delay. Taken together, these findings suggest that postmortem delay introduces subtle yet consistent transcriptional and morphological changes in microglia that can confound the interpretation of aging- and disease-related phenotypes. These results highlight the importance of controlling for postmortem effects in studies using human postmortem tissue.