The molecular mechanism by which CTSB degrades FPN to disrupt macrophage iron homeostasis and promote the progression of atherosclerosis.

The incidence of atherosclerosis (AS) remains high, and iron-dependent cell death (termed ferroptosis) is thought to play a key role in the progression of AS. Studies have shown that cathepsin B (CTSB) is an important regulatory molecule in atherosclerosis. However, how CTSB regulates AS progression has not been reported, and whether it is related to ferroptosis is poorly studied. In the present study, we observed a significant upregulation of CTSB expression in two AS models, ApoE knockout mice and SD rats given a HFD. According to our findings, CTSB can promote development of the AS plaque region, while inhibition of CTSB showed a reduction of AS lesion area and lipid deposition. Single-cell transcriptome analysis of AS tissue from humans revealed that CTSB is primarily expressed in macrophages. Oxidized low-density lipoprotein (ox-LDL) significantly enhanced macrophage CTSB expression, and induced ferroptosis in vitro. Mechanistically, Ferroportin (FPN) is the binding target of CTSB. CTSB can negatively regulate the protein level of FPN and promote its degradation, which further leads to ferroptosis of macrophages. We confirmed that ferroptosis in macrophages could be effectively inhibited by knockdown or pharmacological inhibition of CTSB, which in turn slowed the progression of AS. In conclusion, our study suggests that CTSB disrupts iron homeostasis in macrophages by degrading FPN and induces ferroptosis, thereby exacerbating the development of AS. Targeting CTSB may become an important potential strategy for the treatment of AS.