Abstract
Background & aims:
Aging and alcohol misuse independently alter monocyte (MO) and macrophage (MØ) function, leading to impaired antimicrobial responses. However, how alcohol misuse contributes to impaired MO/MØ function during aging remains unclear.
Methods:
We compared the transcriptomes of MOs and MØs from alcohol-modulated niches (liver, brain, and bone marrow [BM]) in young (3-month-old) and old (20-24-month-old) female C57BL/6N mice (n = 4-6 per group). Statistical significance was determined using two-way ANOVA.
Results:
MO/MØ transcriptomes showed unique organ-specific responses to aging and alcohol. Aging elicited a common deregulation of pathogen-responsive pathways, while alcohol misuse commonly inhibited IFN signaling in the aged populations. Our studies on intercellular communication using ligand-receptor interactions revealed that BM MOs were the least communicative and liver MØs were the most communicative. Alcohol misuse specifically increased MO/MØ communication in aging. We also identified and validated specific pathways driving inter-organ MO/MØ crosstalk in alcohol misuse during aging, including APOE-TREM2 signaling from the liver to microglia and the NRXN2 and SPP1 pathways.
Conclusion:
Our results provide a unique insight into the heterogeneity of the MO/MØ transcriptome and define the inter-organ crosstalk between BM, liver, and brain during aging and alcohol misuse.
Impact and implications:
Aging and alcohol misuse are linked to immune dysfunction, systemic inflammation, and altered innate immune responses. Here, we examined monocyte/macrophage responses in the liver, brain, and bone marrow of young and aged mice under alcohol exposure at the transcriptomic level. We observed that aging and alcohol predominantly elicited organ-specific changes in gene expression, with minimal overlap between the monocyte/macrophage populations across different tissues. However, aging commonly upregulated pathogen response pathways while alcohol misuse inhibited interferon signaling. We also assessed cell-cell communication by analyzing ligand-receptor expression in the different monocyte/macrophage populations and identified candidate molecules (APOE, TREM2, NRXN2, SPP1) from the top pathways guiding inter-organ signaling specifically in aging and alcohol misuse. Our findings have generated a unique repository and provide novel insights on how aging and alcohol impact tissue-specific monocytes/macrophages and their crosstalk.