PCSK9 inhibition mitigates vulnerable plaque formation induced by hyperhomocysteinemia through regulating lipid metabolism and inflammation

Atherosclerosis (AS) is a persistent inflammatory disorder marked by vulnerable plaques, which increase the likelihood of cardiovascular incidents. This study explored the involvement of proprotein convertase subtilisin/kexin type 9 (PCSK9) in the development of vulnerable plaques triggered by hyperhomocysteinemia (HHcy), with a focus on lipid metabolism, and inflammation. Apolipoprotein E knockout (ApoE^-/-) mice were fed a methionine-rich diet to induce HHcy. PCSK9 inhibition via SBC-115076 significantly improved plaque stability. HHcy upregulated PCSK9 levels, and hinder cholesterol efflux by downregulating the ATP-binding cassette transporters ABCA1 and ABCG1. In contrast, no significant effects were noted on low-density lipoprotein receptor (LDLR), cluster of differentiation 36 (CD36), or scavenger receptor class B type I (SR-BI). Inhibition of PCSK9 led to the restoration of ABCA1 and ABCG1, thereby facilitating an increase in cholesterol efflux. Furthermore, PCSK9 inhibition reduced HHcy-induced increase of proinflammatory cytokines, including interleukin-1beta (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and monocyte chemoattractant protein-1 (MCP-1). In vitro, mouse peritoneal macrophages (MPMs) exposed to HHcy presented reduced ABCA1 and ABCG1, whereas LDLR, CD36, and SR-BI remained unaffected. PCSK9 knockout reversed these changes. Additionally, HHcy upregulated expression of proinflammatory cytokines, along with the activation of Toll-like receptor 4 (TLR4) /nuclear factor kappa B (NF-κB) pathway. PCSK9 inhibition reduced the production of these cytokines and mitigated the activation of the TLR4/NF-κB pathway, confirming its role in macrophage inflammation. These findings reveal that PCSK9 exacerbates HHcy-related AS by impairing cholesterol efflux and promoting inflammation. PCSK9 inhibitors may offer a dual therapeutic approach for stabilizing plaques and reducing cardiovascular risk in patients with HHcy.