Extracellular matrix components indicate remodelling activity in different fibrosis stages of human non-alcoholic fatty liver disease

Aims: The composition of several important extracellular matrix components (ECM) has not yet been elucidated in human non-alcoholic fatty liver disease (NAFLD). We aim to investigate the proportion of hepatic stellate cells (IISCs) and activity of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) in human NAFLD liver tissue with respect to severity of inflammation and fibrosis. Methods and results: Histopathological features were quantified by NAFLD activity score and grading assignment. The collagen proportionate area (CPA) was measured. Slides were stained with alpha-smooth muscle actin (alpha-SMA), as a marker of activated HSCs, and alpha-SMA was quantified digitally. Zymography was performed to measure the proteolytic activity of MMP-2 and MMP-9. TIMP-1 and TIMP-2 protein concentration was measured with enzyme-linked immunosorbent assay (ELISA). alpha-SMA was higher in severe fibrosis (6.3%, interquartile range 2.9-13.1) than mild and no fibrosis (median 1.1 and 0.9%, P < 0.001) and correlated strongly with CPA (Rs = 0.870, P < 0.001). ProMMP-2 activity in severe (4.1%, IQR 2.6-16.2) and mild fibrosis (2.7%, IQR 1.9-3.9) was higher than in no fibrosis (1.5%, (IQR 0.95-2.1); P = 0.001 and P = 0.046) and showed a moderate positive correlation with CPA (Rs = 0.495, P - 0.001). TIMP-1 and TIMP-2 were significantly higher in severe fibrosis than mild or no fibrosis. Both showed moderate correlation with CPA (TIMP-1: Rs = 0.471, P = 0.002 and TIMP-2: Rs = 0.325, P = 0.036). MMP-9 correlated as the only ECM component to inflammation severity. Conclusions: Advanced human NAFLD-fibrosis has a distinct ECM composition with increased HSCs and increased TIMP inhibition, but there is also ongoing remodelling activity of MMP-2.