Engineered haptoglobin β fusion protein targets myoglobin and ameliorates rhabdomyolysis-associated acute kidney injury

Rhabdomyolysis-induced acute kidney injury (RM-AKI) is mediated primarily by myoglobin (Mb) toxicity, yet effective targeted therapies remain unavailable. Through computational structural modeling, we uncovered that the haptoglobin β-subunit (Hpβ) can bind Mb, forming a structurally stable complex. We then engineered a 55 kDa recombinant GST-Hpβ fusion protein and demonstrated that this engineered construct exhibits robust binding affinity for free Mb (17.8 kDa), thereby generating a stable 72.8 kDa GST-Hpβ-Mb complex. Significantly, this complex surpasses the molecular size threshold of the glomerular filtration barrier (~69 kDa), thereby preventing Mb from being filtered into the renal tubules and inflicting subsequent pathological damage. Further analysis revealed that the GST-Hpβ-Mb complex is expeditiously eliminated via CD163-mediated macrophage phagocytosis. Employing well-established RM-AKI murine models, we demonstrated that a single intraperitoneal administration of the GST-Hpβ fusion protein markedly improves survival, ameliorates renal function, and alleviates kidney damage, with protective effects lasting beyond a two-week period. In sum, the GST-Hpβ fusion protein offers a novel and promising biotherapeutic agent that addresses the fundamental pathophysiology of RM-AKI.