Frank Murphy

Inhibition of Apoptosis of Activated Hepatic Stellate Cells by Tissue Inhibitor of Metalloproteinase-1 Is Mediated via Effects on Matrix Metalloproteinase Inhibition IMPLICATIONS FOR REVERSIBILITY OF LIVER FIBROSIS

The activated hepatic stellate cell (HSC) is central to liver fibrosis as the major source of collagens I and III and the tissue inhibitors of metalloproteinase-1 (TIMP-1). During spontaneous recovery from liver fibrosis, there is a decrease of TIMP expression, an increase in collagenase activity, and increased apoptosis of HSC, highlighting a potential role for TIMP-1 in HSC survival. In this report, we use tissue culture and in vivomodels to demonstrate that TIMP-1 directly inhibits HSC apoptosis. TIMP-1 demonstrated a consistent, significant, and dose-dependent antiapoptotic effect for HSC activated in tissue culture and stimulated to undergo apoptosis by serum deprivation, cycloheximide exposure, and nerve growth factor stimulation. A nonfunctional mutated TIMP-1 (T2G mutant) in which all other domains are conserved did not inhibit apoptosis, indicating that inhibition of apoptosis was mediated through MMP inhibition. Synthetic MMP inhibitors also inhibited HSC apoptosis. Studies of experimental liver cirrhosis demonstrated that persistent expression of TIMP-1 mRNA determined by PCR correlated with persistence of activated HSC quantified by α smooth muscle actin staining, while in fibrosis, loss of activated HSC correlated with a reduction in TIMP-1 mRNA. We conclude that TIMP-1 inhibits apoptosis of activated HSC via MMP inhibition.

Active matrix metalloproteinase-2 promotes apoptosis of hepatic stellate cells via the cleavage of cellular N-cadherin

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.

N-Cadherin cleavage during activated hepatic stellate cell apoptosis is inhibited by tissue inhibitor of metalloproteinase-1

Apoptosis of hepatic stellate cells (HSC) has previously been shown to occur during spontaneous resolution of experimental liver fibrosis. TIMP-1 has also been shown to have a key role because of its ability to inhibit apoptosis of HSC via matrix metalloproteinase (MMP) inhibition. This has led to further study of novel substrates for MMPs that might impact on HSC survival. N-Cadherin is known to mediate cell-cell contacts in fibroblasts. In this study we demonstrate that N-Cadherin is expressed by activated rat HSC. Furthermore, during apoptosis of HSC, the N-Cadherin is cleaved into smaller fragments. Apoptosis of HSC may be inhibited by TIMP-1. This is associated with reduced fragmentation of N-Cadherin. N-Cadherin may have an important role in supporting HSC survival while N-Cadherin cleavage may play a part in promoting HSC apoptosis in recovery from liver fibrosis.

Developing strategies for liver fibrosis treatment

Liver fibrosis represents a major worldwide healthcare burden. Current therapy is limited to removing the causal agent. This approach is successful in some diseases; particularly haemochromatosis and chronic viral hepatitis. However, for many patients treatment is not possible, while other patients present to medical attention at an advanced stage of fibrosis. There is therefore a great need for novel therapies for liver fibrosis. The hepatic stellate cell has been recognised to be responsible for most of the excess extracellular matrix observed in chronic liver fibrosis. The detailed understanding of hepatic stellate cell biology has allowed the rational design of novel antifibrotic therapies. This review describes for the general reader the novel emerging therapies for liver fibrosis.

Tissue Inhibitor of Metalloproteinase-1 Inhibits Apoptosis of Rat and Human Hepatic Stellate Cells In Vitro

INTRODUCTION. Liver fibrosis represents the final common pathway for the majority of chronic liver insults (alcohol, autoimmune or viral injury). Current evidence indicates that the central mediator of fibrosis is the hepatic stellate cell (HSC). During fibrotic injury, these retinoid rich cells proliferate and undergo a phenotypic transformation to myofibroblast-like cells, a process termed activation. Previous work by the our group has demonstrated that activated HSC also express the powerful tissue inhibitors of metalloproteinases (TIMPs) 1 and 2, suggesting that matrix degradation is inhibited during fibrogenesis. This hypothesis is supported by findings that spontaneous recovery from liver fibrosis is associated with a diminution of TIMP expression and an increase in collagenase activity with consequent matrix degradation (1). A further finding in this study is that sustained apoptosis of HSC accompanies recovery from fibrosis. This has highlighted the role of TIMP-1 and -2 in HSC proliferation, survival and apoptosis.