Bacterial Infections Shape Cardiac Macrophages' Response to Ischemia

Area of Science:

• Cardiovascular immunology
• Innate immunity
• Myocardial ischemia

Background:

• Bacterial infections elevate cardiovascular event risk.
• The role of cardiac innate immune cell adaptation post-infection is unclear.
• This study investigates chronic cardiac myeloid cell changes after bacterial insult and their impact on myocardial ischemia.

Purpose of the Study:

• To explore chronic adaptations of cardiac myeloid cells following bacterial infection.
• To determine the implications of these adaptations for subsequent myocardial ischemia.
• To investigate the origin and characteristics of cardiac macrophages post-infection.

Main Methods:

• Flow cytometry for immune cell analysis (cardiac, peripheral, bone marrow, spleen).
• Genetic fate-mapping to trace cardiac macrophage origins after bacteremia.
• Single-cell RNA sequencing for cardiac leukocyte heterogeneity analysis.
• Nanoparticle-mediated RNA interference to target macrophages in vivo.

Main Results:

• Bacteremia led to persistent increases and subset alterations in cardiac macrophages.
• Local origin was identified as the primary source of cardiac macrophages post-infection.
• Two novel macrophage subpopulations with distinct metabolic and chemotactic properties were identified.
• Targeting macrophage inflammatory activity reduced subsequent ischemic inflammation.

Conclusions:

• Bacteremia induces enduring alterations in cardiovascular innate immune cell composition.
• These changes can exacerbate myocardial inflammation following subsequent ischemic injury.
• Modulating cardiac macrophage inflammatory responses may mitigate post-infection cardiovascular risks.