Extracellular matrix regulates the hepatocellular heat shock response

Background. Cirrhosis is characterized by the accumulation of collagen with in the extracellular matrix (ECM) of the liver and progressive hepatocellul ar dysfunction. Since recent studies have shown that the ECM can modulate c ellular function, we examined whether the ECM could contribute to hepatocel lular dysfunction. To address this question we examined hepatocyte behavior in two different ECM environments. Materials and methods. Primary rat hepatocytes were cultured as a monolayer on collagen or as multicellular aggregates (spheroids) within a laminin-ri ch ECM. Hepatocytes were then compared for viability, response to proinflam matory cytokines, and their capacity to activate a heat shock response and adopt a thermotolerant phenotype. In addition, we compared the ability of p rior heat shock exposure to protect hepatocytes from tumor necrosis factor (TNF) alpha/actinomycin-D-induced apoptosis in the two different ECM enviro nments. Results. Hepatocytes cultured as a monolayer on collagen exhibited decrease d viability, underwent spontaneous apoptosis, and displayed an attenuated c ytokine-stimulated nitric oxide production compared to hepatocytes cultured as spheroids. In response to heat, hepatocytes in both ECM environments ex pressed inducible heat shock protein 70 (hsp72). But, only the hepatocyte s pheroids exhibited thermotolerance in response to a subsequent thermal chal lenge. In contrast to previous reports, induction of the heat shock respons e failed to protect hepatocytes against TNF alpha-induced apoptosis. Conclusions. These data demonstrate that the ECM can play an integral role in specific hepatocellular behaviors. Furthermore, the progressive depositi on of collagen within the ECM, which is characteristic of fibrotic liver di seases, may directly contribute to the progressive hepatocellular dysfuncti on observed in cirrhosis. Hepatocellular viability, response to proinflamma tory cytokines, heat shock response, and thermotolerance were all altered d epending on the composition of the ECM. In contrast, TNF alpha-induced apop tosis was independent of the composition of the ECM. (C) 2000 Academic Pres s.