Tenascin-C: A Crucial Proinflammatory Mediator in Macrosteatotic Liver Ischemia and Reperfusion Injury.

Abstract

A shortage of organ donors has led to an increased use of steatotic livers in transplantation; however, marginal livers have higher susceptibility to ischemia and reperfusion injury (IRI). Tenascin-C (Tnc) is an extracellular matrix protein (ECM) involved in various aspects of immunity, including liver injury. Here, we dissect the functional significance of high levels of Tnc in steatotic hepatic IRI. Methods: Tnc deficient (Tnc -/-) knockout (KO) mice (C57BL/6N-TgH) and matched wild-type (WT) control littermates were fed with a high-fat diet (60% total-kilocalories); mice with about 50% macrovesicular steatosis (MaS) were submitted to 60% of partial warm ischemia, followed by reperfusion. Results: While Tnc is not normally expressed in adult tissues, it was readily detected in naïve steatotic livers and further upregulated in MaS-WT livers post-IRI. Compared to MaS-WT mice, MaS-Tnc-/-mice showed significantly reduced liver damage; Tnc ablation resulted in decreased AST levels (IU/L) at 6h (4,920±1,974 vs. 7,698±1,124 p<0.05) and 24h (990±801 vs. 6,665±3,485, p<0.05) post-IRI. Moreover, histological damage was selectively sheltered in Tnc-KO livers, which showed reduced periportal congestion and necrosis compared to MaS-WT controls. The recruitment of Ly6G (6h: 50.9±13.8 vs. 106.0±39.0; 24h:74.1±28.3 vs. 215.4±24.5; p<0.05) and Mac-1 (6h:48.5±25.7 vs. 82.9±17.4; 24h:84.7±30.7 vs. 132.8±33.8;p<0.05) leukocytes was significantly decreased in MaS Tnc KO livers. MaS-Tnc KO livers were also characterized by decreased expression of pro-inflammatory TNF-α (p<0.05) and IL-1β (p<0.05), compared to MaS-WT controls. Next, we performed a series of in vitro studies, which identified hepatic stellate cells (HSCs) as primary sources of Tnc in our settings and provided evidence of a fat-dependent mechanism for Tnc upregulation by these cells. Indeed, the incubation of HSCs in conditioned medium from steatotic hepatocytes resulted in the upregulation of Tnc expression (˜4-fold-increase), compared with HSCs cultured in medium from non-steatotic hepatocytes. Conclusion: Our results evidence a critical role for Tnc expression in the pathogenesis of steatotic hepatic IRI. They also support the view that studies aimed at further understanding how ECM molecules, such as Tnc, participate in steatotic liver injury will likely contribute to the successful utilization of marginal steatotic livers in transplantation.