PCSK5 (proprotein convertase subtilisin/kexin type 5) is a serine endoprotease that cleaves proproteins at paired basic amino acids, recognizing the RXXX[KR]R consensus motif 1. The enzyme functions in both constitutive and regulated secretory pathways and plays essential roles in embryonic development. PCSK5 is critical for heart development, specifically required in early cranio-cardiac mesoderm for cardiogenesis 2. The protein activates precursor TGF-β to its mature form by binding the pro-TGF-β cleavage site, thereby promoting vascular fibrosis through TGF-β/SMAD2/3 pathway activation 1. Loss of PCSK5 function results in multiple developmental anomalies including cardiac malformations, caudal regression, and VACTERL association features 2. Genetic variants in PCSK5 show clinical significance: the rs6560480 polymorphism is associated with Takayasu arteritis development and increased vascular fibrosis 1, rs1110222 variants affect recurrent pregnancy loss risk 3, and germline mutations are linked to early-onset Alzheimer's disease age of onset 4. The gene maps to chromosome 9.3 5 and its expression alterations are observed in renal cell carcinoma, contributing to tumor microenvironment changes 6.