Chaperone‐Mediated Autophagic Degradation of USP9X in Macrophages Exacerbates Postmyocardial Infarction Inflammation and Cardiac Dysfunction

ABSTRACT Excessive macrophage‐mediated inflammation following myocardial infarction (MI) exacerbates infarct expansion and impairs cardiac repair; however, the regulatory mechanisms remain poorly understood. Here, it is reported that ubiquitin‐specific peptidase 9 X‐linked (USP9X) was significantly downregulated in macrophages during early post‐MI inflammation. Macrophage‐specific deficiency of USP9X enhanced expression of pro‐inflammatory genes, thereby impeding cardiac functional recovery. Mechanistically, USP9X deubiquitinated and stabilized tumor necrosis factor receptor‐associated factor (TRAF)‐type zinc finger domain containing 1 (TRAFD1), a negative regulator of Toll‐like receptor (TLR) signaling, thereby restraining inflammatory responses. Moreover, inflammatory stimuli triggered acetylation of USP9X at K2414, exposing a latent KFERQ motif that promoted its recognition by the molecular chaperone heat shock cognate protein 70 (HSC70) and facilitated subsequent lysosomal degradation via chaperone‐mediated autophagy (CMA). Consistently, both genetic inhibition of HSC70 and pharmacological blockade of lysosomal degradation prevented USP9X degradation following inflammatory stimulation. Furthermore, a cell‐penetrating peptide mimicking the KFERQ sequence of USP9X that blocked its interaction with HSC70 and the subsequent CMA‐mediated degradation, thereby promoting inflammation resolution and cardiac repair post‐MI. Collectively, these findings establish the USP9X–TRAFD1 axis and its CMA‐mediated degradation as critical checkpoints in post‐MI inflammation, highlighting USP9X stabilization as a therapeutic strategy for ischemic heart disease.