Background and aims: Hepatic stellate cells (HSC) are known to synthesise excess matrix that characterises liver fibrosis and cirrhosis. Activated HSC express the matrix-degrading matrix metalloproteinase enzymes (MMPs) and their tissue inhibitors (TIMPs). During spontaneous recovery from experimental liver fibrosis, the expression of TIMP-1 declines and hepatic collagenolytic activity increases. This is accompanied by HSC apoptosis. In this study, we examine a potential mechanism whereby MMP activity might induce HSC apoptosis by cleaving N-cadherin at the cell surface.
Results: N-cadherin expression was upregulated in human HSC during activation in culture. Addition of function-blocking antibodies or a peptide targeting the extracellular domain of N-cadherin, to cultured HSC, promoted apoptosis. During apoptosis, there was cleavage of N-cadherin into 20-100 kDa fragments. MMP-2 became activated early during HSC apoptosis and directly cleaved N-cadherin in vitro. Addition of activated MMP-2 to HSCs in culture resulted in enhanced apoptosis and loss of N-cadherin.
Conclusions: Together, these studies identify a role for both N-cadherin and MMP-2 in mediating HSC apoptosis, where N-cadherin works to provide a cell survival stimulus and MMP-2 promotes HSC apoptosis concomitant with N-cadherin degradation.