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

Area of Science:

• Neuroscience
• Immunology
• Genomics

Background:

• Postmortem tissue is essential for studying human microglia, but postmortem delay (PMD) effects are unclear, especially in aging.
• Aging microglia exhibit primed states, and understanding PMD's influence on these states is critical.

Purpose of the Study:

• To investigate the impact of PMD on microglial gene expression and morphology in young and aged mice.
• To determine if PMD confounds aging-associated microglial signatures and to validate findings in human datasets.

Main Methods:

• Bulk RNA sequencing of Dectin-1-high (primed) and Dectin-1-low microglia after 0, 6, and 12-hour PMDs in young and aged mice.
• Morphological analysis of cortical microglia.
• Reanalysis of human single-cell and single-nucleus RNA sequencing datasets.

Main Results:

• PMD consistently altered microglial gene expression, upregulating mitochondrial, heat-shock, and apoptosis pathways, and downregulating actin cytoskeleton regulation.
• These PMD effects varied between young and aged animals and between primed and non-primed microglia.
• PMD reduced microglial cell shape complexity in young mice, mimicking aged morphology, while aged microglia morphology was unaffected by PMD. PMD-associated signatures correlated with human data.

Conclusions:

• Postmortem delay introduces subtle but consistent transcriptional and morphological changes in microglia.
• These changes can confound the interpretation of aging- and disease-related microglial phenotypes.
• Controlling for PMD is vital for accurate analysis of human postmortem brain tissue studies.