Cathepsin B ablation alleviates VSMC phenotypic switching by modulating alternative macrophage polarization through the NLRP3 signaling pathway.

Introduction: The classical activation of pro-inflammatory macrophages contributes to neointimal hyperplasia by driving the excessive accumulation of phenotypically switched vascular smooth muscle cells (VSMCs), a process that underlies occlusive disorders such as atherosclerosis and restenosis. However, the impact of Cathepsin B (CTSB) on the regulation of macrophage polarization remains unclear. Methods and Results: Analysis of the Gene Expression Omnibus (GEO) database revealed a significant upregulation of CTSB in advanced human atherosclerotic plaques. Furthermore, a time-dependent increase in CTSB expression was observed in carotid arteries following vascular injury. At the cellular level, CTSB expression was markedly elevated in pro-inflammatory M1 macrophages but suppressed in resolving M2 macrophages. A loss-of-function approach, utilizing AdshCTSB-transfected bone marrow-derived macrophages (BMDMs), demonstrated that CTSB knockdown promotes a shift in polarization, repressing M1 markers while inducing those characteristic of the M2 phenotype. This CTSB-mediated polarization switch subsequently attenuated the proliferation and migration of VSMCs while promoting their differentiation. Mechanistically, we identified NLRP3 as a direct target of CTSB. Knockdown of CTSB suppressed the NLRP3 inflammasome, an effect mediated through the cGAS-STING signaling pathway. The functional significance of this pathway was confirmed, as the STING agonist DMXAA abolished the polarizing effects of CTSB silencing. Discussion: In conclusion, our findings suggest that CTSB inhibition represents a promising therapeutic strategy for mitigating intimal hyperplasia. This approach operates by favoring alternative macrophage polarization, which in turn attenuates VSMC phenotypic switching, a process that is partially mediated by the inactivation of the cGAS-STING-NLRP3 axis.