Cell-Free Hemoglobin Drives CD163+ Macrophage Reprogramming and Drp1-Dependent Mitochondrial Transfer to Promote Septic Cardiac Dysfunction

Background Severe trauma is commonly accompanied by secondary infection and multiple organ dysfunction, wherein sepsis and SIMD constitute predominant determinants of fatal outcomes. Despite this, the mechanistic connection between systemic hemolysis and cardiac immune remodeling has yet to be defined. Accordingly, this study was designed to determine whether CFH drives septic cardiac injury and to elucidate the cellular and molecular basis underlying this process. Methods Clinical samples from patients with sepsis, cecal ligation and puncture (CLP) mouse models, single-cell RNA sequencing, metabolomic profiling, high-resolution live-cell imaging, and genetic manipulation were integrated to characterize CFH-mediated cardiac remodeling. Intercellular mitochondrial transfer was dynamically tracked using fluorescence imaging and super-resolution microscopy. A hemoglobin-targeting nanoparticle (HbAb-NP) was developed to evaluate the therapeutic potential of CFH scavenging. Results Circulating CFH was markedly elevated in septic patients and CLP mice and was associated with myocardial hemoglobin deposition, endothelial barrier disruption, cardiac dysfunction, and poor survival. CFH exposure was associated with an increased relative proportion of a metabolically reprogrammed CD163+ macrophage subset through activation of the glycolysis–NF-κB1 signaling axis. These macrophages exhibited mitochondrial dysfunction and transferred damaged mitochondria to endothelial cells via tunneling nanotubes (TNTs), resulting in oxidative stress, impaired mitochondrial respiration, endothelial barrier disruption, and reduced angiogenic capacity. Mechanistically, Drp1 facilitated TNT formation by activating the Cdc42/Rac1–cofilin/profilin pathway to drive actin cytoskeletal remodeling. Therapeutically, HbAb-NP efficiently scavenged circulating CFH, suppressed CD163+ macrophage activation, alleviated endothelial injury, improved cardiac function, and prolonged survival in septic mice. Conclusions This study identifies circulating CFH as a previously unrecognized upstream regulator linking systemic hemolysis to cardiac immune microenvironment remodeling during sepsis. CFH-induced CD163+ macrophage reprogramming and Drp1-dependent pathological mitochondrial transfer establish a macrophage–mitochondria–endothelial injury axis that drives SIMD. Targeting circulating CFH represents a promising therapeutic strategy for sepsis-associated cardiac dysfunction.