Acute myocardial infarction induces sex-specific, time-dependent remodeling of the gut microbiome and intestinal immune compartment in retired breeder C57BL/6N mice.

Introduction: The gut microbiome influences cardiovascular health through metabolite production and immune modulation. Gut microbial dynamics and cardiovascular outcomes are also shaped by biological sex. However, sex-specific responses to myocardial infarction (MI) that involve the gut microbiome and intestinal milieu remain poorly defined, particularly in older hosts. Here, we characterize gut microbiome structure and function alongside physiological and immune responses to MI across multiple tissues in aging male and female mice. Methods: MI was induced by permanent LAD ligation and confirmed by echocardiography in C57BL/6N retired breeder mice. Sham surgery (SH) and no surgery (NoSx) groups served as controls. Gut microbiota and the cecal metabolome were characterized using 16S rRNA sequencing and untargeted UPLC-MS, respectively. Immune cells in the small intestine, heart, bone marrow, and spleen were quantified by flow cytometry, and small intestinal morphology was assessed on H&E-stained sections. Results: Sex-specific differences were evident at baseline. Following MI, pronounced time- and sex-specific differences in gut microbial and immune cell populations were observed, peaking on day 3 (D3) and absent in SH and NoSx controls. Early increases in Discussion: Convergence of peak physiological, immunological, and microbial responses on day 3 after MI reveals coordinated responses across the gut-heart axis that are fundamentally influenced by sex. Our findings highlight the need for personalized, sex-specific perioperative strategies and identify the gut microbiome as a potential therapeutic target to improve outcomes after MI.