PCSK9 and rheumatoid arthritis: Dysregulated lipid metabolism in RA is characterized by elevated low-density lipoprotein Cholesterol (LDL-C), impaired high-density lipoprotein cholesterol (HDL-C) function, and abnormal proprotein convertase subtilisin/kexin Type 9 (PCSK9) accumulation, which directly drive inflammation and immune dysregulation.