Abstract Body: Background: Following ischemic cardiac insult, the rapid infiltration of myeloid populations, such as neutrophils (Nu), monocytes, and macrophages (Mac), are pivotal for the transition from inflammation to tissue repair. While beta2-adrenergic receptor (β2AR) signaling is known to modulate leukocyte functions, its specific role in orchestrating myeloid cell-driven recovery after acute myocardial infarction (MI) remains unclear. Thus, we hypothesized that myeloid-specific β2AR signaling negatively regulates the resolution of cardiac inflammation by suppressing pro-efferocytosis pathways, and that its genetic deletion would accelerate injury resolution.
Methods: Myeloid cell-specific β2-adrenergic receptor knockout mice (LB2) and their control counterparts underwent myocardial infarction (MI), with or without prior bone marrow transplantation using shRNA-modified cells. The effects of myeloid-specific β2AR deletion along with the underlying mechanisms were evaluated through echocardiography, immunohistochemistry, flow cytometry, gene expression profiling, and efferocytosis assays.
Results: LB2 mice demonstrated preserved heart function and attenuated interstitial fibrosis post-MI compared to control group. While initial myeloid recruitment was equivalent across genotypes, LB2 hearts exhibited accelerated Nu clearance by day 4, characterized by an increased frequency of Mac-encapsulated Nu (efferocytosis). Supporting this phenotype the pro-efferocytic gene Anxa1 was upregulated in β2AR-deficient myeloid cells both in vivo and in vitro. Mechanistically, expression of several miRs known to target Anxa1 were elevated in response to β2AR stimulation, an effect absent with β2AR deletion, and miR-374b-5p mimic in particular was enough to decrease Anxa1 expression. Additionally, shRNA-mediated knockdown of Anxa1 in LB2 bone marrow reduced Nu efferocytosis in vitro and prevented the ameliorative effects on cardiac fibrosis and function observed with LB2 mice following MI in vivo. Furthermore, targeted β2AR deletion in cardiac-resident macrophages independently recapitulated the cardioprotective phenotype.
Conclusion: Myeloid-specific β2AR deletion abolishes miR-374b-5p–mediated repression of Anxa1, leading to enhanced efferocytosis-driven neutrophil clearance, which limits infarct expansion and improves cardiac function and fibrotic remodeling after acute injury.