The Role of Proprotein Convertase Subtilisin/Kexin Type 9 in Nephrotic Syndrome-Associated Hypercholesterolemia

BACKGROUND: In nephrotic syndrome, damage to the podocytes of the kidney produces severe hypercholesterolemia for which novel treatments are urgently needed. PCSK9 (proprotein convertase subtilisin/kexin type 9) has emerged as an important regulator of plasma cholesterol levels and therapeutic target. Here, we tested the role of PCSK9 in mediating the hypercholesterolemia of nephrotic syndrome. METHODS: PCSK9 and plasma lipids were studied in nephrotic syndrome patients before and after remission of disease, mice with genetic ablation of the podocyte (Podocyte Apoptosis Through Targeted Activation of Caspase-8, Pod-ATTAC mice) and mice treated with nephrotoxic serum (NTS), which triggers immune-mediated podocyte damage. In addition, mice with hepatic deletion of Pcsk9 were treated with NTS to determine the contribution of PCSK9 to the dyslipidemia of nephrotic syndrome. RESULTS: Patients with nephrotic syndrome showed a decrease in plasma cholesterol and plasma PCSK9 on remission of their disease (P<0.05, n=47-50). Conversely, Pod-ATTAC mice and NTS-treated mice showed hypercholesterolemia and a 7- to 24-fold induction in plasma PCSK9. The induction of plasma PCSK9 appeared to be attributable to increased secretion of PCSK9 from the hepatocyte coupled with decreased clearance. Interestingly, knockout of Pcsk9ameliorated the effects of NTS on plasma lipids. Thus, in the presence of NTS, mice lacking hepatic Pcsk9 showed a 40% to 50% decrease in plasma cholesterol and triglycerides. Moreover, the ability of NTS treatment to increase the percentage of low-density lipoprotein-associated cholesterol (from 9% in vehicle-treated Flox mice to 47% after NTS treatment), was lost in mice with hepatic deletion of Pcsk9 (5% in both the presence and absence of NTS). CONCLUSIONS: Podocyte damage triggers marked inductions in plasma PCSK9, and knockout of Pcsk9 ameliorates dyslipidemia in a mouse model of nephrotic syndrome. These data suggest that PCSK9 inhibitors may be beneficial in patients with nephrotic syndrome-associated hypercholesterolemia.