Fibronectin Peptides as Potential Regulators of Hepatic Fibrosis Through Apoptosis of Hepatic Stellate Cells

Abstract

The turnover of extracellular matrix (ECM) components can generate signals that regulate several cellular functions such as proliferation, differentiation, and apoptosis. During liver injury, matrix metalloproteases (MMPs) production is enhanced and increased levels of peptides derived from extracellular matrix proteins can be generated. Synthetic peptides with sequences present in extracellular matrix proteins were previously found to induce both stimulating and apoptotic effects on several cell types including the inflammatory cells monocytes/macrophages. Therefore, in inflammatory liver diseases, locally accumulated peptides could be also important in regulating hepatic fibrosis by inducing apoptosis of hepatic stellate cells (HSC), the primary cellular source of extracellular matrix components. Here, we describe the apoptotic effect of fibronectin peptides on the cell line of human hepatic stellate cells LX-2 based on oligonucleosomal DNA fragmentation, caspase-3 and -9 activation, Bcl-2 depletion, and accumulation of Bax protein. We also found that these peptides trigger the activation of Src kinase, which in turn mediated the increase of JNK and p38 activities. By the use of specific inhibitors we demonstrated the involvement of Src, JNK, and p38 in apoptosis induced by fibronectin peptides on HSC. Moreover, fibronectin peptides increased iNOS expression in human HSC, and specific inhibition of iNOS significantly reduced the sustained activity of JNK and the programmed cell death caused by these peptides. Finally, the possible regulatory effect of fibronectin peptides in liver fibrosis was further supported by the ability of these peptides to induce metalloprotease-9 (MMP-9) expression in human monocytes.

Metalloproteinases in liver fibrosis: current insights

“…86,87 In agreement with the mentioned role of TIMP-1 in HSC apoptosis, 71 MMP-2 can promote HSC apoptosis through cleavage of N-cadherin, 86 typical marker of activated myofibroblasts. Recently, the role of degradation products produced by MMPs in regulation of fibrosis has been proposed; cleaved fibronectin peptides induced apoptosis in HSC line and stimulated MMP-9 secretion from human monocytes.…”

“…Recently, the role of degradation products produced by MMPs in regulation of fibrosis has been proposed; cleaved fibronectin peptides induced apoptosis in HSC line and stimulated MMP-9 secretion from human monocytes. 87 Zbodakova et al Inflammation and regulation of TNFa signaling in liver injury ADAM17 was originally discovered as a protease effectively cleaving TNFa and is therefore also known as TNFaconverting enzymes. TNFa is pivotal in many pathological conditions of the liver and has a distinct effect on hepatocytes depending on the strength and duration of a signal.…”

Oxidation pathways underlying the pro-oxidant effects of apigenin

“…Cells were grown in MEM supplemented with 10% heat-inactivated FBS plus 1% penicillin and streptomycin and 1% non-essential amino acids. LX-2, (Lieming Xu-2) is a human non-tumoral immortalized cell line that was generously provided by Dr. Scott Friedman [29]. This cell line was generated by the immortalization of HSC with SV 40 large T antigen, followed by low serum conditions.…”

Expression of toll-like receptors in hepatic cirrhosis and hepatocellular carcinoma

“…It has been shown that the levels of IL-1 resulting from autocrine action in fibroblasts and paracrine action in Kupffer cells are positively associated with the severity of liver fibrosis. IL-1 also plays an important role in the synthesis and deposition of ECM materials through the upregulation of tissue inhibitor of metalloproteinases (TIMP) and the downregulation of matrix metalloproteinases (MMPs) (Mòdol et al, 2015). Kupffer cells also have multiple biological effects on hepatocytes, HSCs, and endothelial cells.…”