Hepatic stellate cells secreting WFA⁺-M2BP: Its role in biological interactions with Kupffer cells

Background and Aim: Hepatic stellate cells (HSCs) play a central role in hepatic fibrosis and are regulated by Kupffer cells (KCs). Wisteria floribunda agglutinin-positive Mac-2 binding protein (WFA⁺-M2BP) was recently identified as a serum marker for hepatic fibrosis. Although WFA⁺-M2BP was identified as a ligand of Mac-2, the function of WFA⁺-M2BP in hepatic fibrosis remains unclear. Methods: Liver specimens were obtained from five patients with cirrhosis, five with chronic hepatitis, and five without hepatic fibrosis. WFA⁺-M2BP kinetics were evaluated histologically and in subpopulations of liver cells such as HSCs, KCs, endothelial cells, biliary epithelial cells, and hepatocytes in in vitro culture. The function of WFA⁺-M2BP in activated HSCs was evaluated using immunoblot analysis. Results: Numbers of WFA⁺-M2BP-positive cells in liver tissues increased with fibrosis stage. There were significant differences in WFA⁺-M2BP levels between fibrosis stages F0 and F1–2 (P = 0.012) and between fibrosis stages F1–2 and F3–4 (P < 0.001). HSCs were the source of WFA⁺-M2BP secretion in in vitro cultures of liver cells, as determined by sandwich immunoassay. Cells of the human HSC line LX-2 also secreted WFA⁺-M2BP. Histologically, tissue sections showed that WFA⁺-M2BP was located in Mac-2-expressing KCs. In vitro assays showed that exogenous WFA⁺-M2BP stimulation enhanced Mac-2 expression in KCs and that HSCs co-cultured with KCs increased α-smooth muscle actin expression. Finally, Mac-2-depleted KCs with short interfering RNA had reduced α-smooth muscle actin expression following co-culturing with HSCs. Conclusions: WFA⁺-M2BP from HSCs induces Mac-2 expression in KCs, which in turn activates HSCs to be fibrogenic.