Neprilysin-neuropeptide Y axis as target for treatment of liver fibrosis and portal hypertension

Background and aims Chronic liver injury induces fibrosis and contraction of hepatic stellate cells (HSC) leading to fibrosis. Importantly, the angiotensin converting enzyme (ACE) and angiotensin-II levels are involved in these processes. Neprilysin (NEP) is a neutral endopeptidase that cleaves neuropeptide Y (NPY), a 36 amino acid peptide described as a co-transmiter for contraction. Our aim is to study the effects of NPY and its cleavage mediated by NEP on fibrosis.

Methods Portal, hepatic, central and peripheral venous blood was collected from patients receiving transjugular intrahepatic portosystemic stent (TIPS) and analyzed for circulating levels of NPY. NEP expression was correlated with collagen1a1 expression in human fibrotic liver. In silico docking experiments reveals the effect of full-length NPY or the short NPY fragments cleaved by NEP on NPY type 1 receptor (Y1R). Liver fibrosis and portal hypertension (PH) was induced in wild type (WT) and Nep^-/- mice using bile duct ligation (BDL; 2 weeks) and carbon tetrachloride

(CCl₄; 4 weeks) and hemodynamic changes were measured in vivo. Hepatic protein and mRNA expression were analyzed in these animals. In vitro analysis of primary HSC from WT and Nep^-/- mice were incubated with NPY. In addition, fibrotic Nep^-/- mice (BDL/CCl₄) were treated with AT1R blocker (losartan) or ACE inhibitor (captopril) for 2 weeks/4 weeks respectively.

Results NPY levels increased in cirrhosis in humans and originates largely from portal vein. Hepatic NEP increases also with the severity of the disease but only in HSC. NEP deficiency in mice showed less fibrosis but higher hepatic NPY levels which induced PH. In vitro, full-length NPY induces contraction of HSC by activation of Y1R but its fragments derived from NEP proteolysis, blocked Y1R and increased fibrosis in HSC. Molecular docking of NPY fragments to the receptor confirmed that NPY short peptides act as antagonist of the Y1R and act profibrotic. AT1R blockage (losartan) or ACE inhibition (captopril) in NEP deficiency mice, decreased fibrosis and portal pressure.

Conclusions The link between fibrosis and contraction relay on the NEP/NPY axis. Dual NEP inhibition with AT1R blockade should be evaluated as a treatment to decrease fibrosis and PH in humans.

Publication History

Article published online:
08 September 2020