Dongiovanni Paola, Meroni Marica, Baselli Guido Alessandro, Bassani Giulia Alessandra, Rametta Raffaela, Pietrelli Alessandro, Maggioni Marco, Facciotti Federica, Trunzo Valentina, Badiali Sara, Fargion Silvia, Gatti Stefano, Valenti Luca
Internal Medicine, Fondazione IRCCS Ca' Granda Ospedale Policlinico Milano, Milan, Italy
Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Milan, Italy.
Clin Sci (Lond). 2017 Jun 7;131(12):1301-1315. doi: 10.1042/CS20170175. Print 2017 Jun 1.
In patients with non-alcoholic fatty liver disease (NAFLD), insulin resistance (IR) associates with fibrosis progression independently of the hepatic inflammation, but the mechanisms are still unclear. We modeled the independent contribution of inflammation (non-alcoholic steatohepatitis: NASH) by exploiting the methionine-choline deficient (MCD) diet, and that of IR by insulin receptor (InsR) haploinsufficiency (InsR+/-) in the pathogenesis of liver fibrosis in C57BL/6 mice. We confirmed the study findings in 96 patients with NAFLD. InsR+/- enhanced hepatic fat content and impaired hepatic insulin signaling leading to Forkhead box protein O1 (FoxO1) accumulation in MCD-fed mice. Remarkably, despite reduced inflammation and hampered transdifferentiation of hepatic stellate cells (HSCs), InsR+/- promoted hepatic fibrosis accumulation, which correlated with the induction of the Lysyl Oxidase Like 2 (Loxl2), involved in matrix stabilization. Loxl2 up-regulation was not a cell autonomous property of insulin resistant HSCs, but was dependent on microparticles (MPs) released specifically by insulin resistant hepatocytes (HEPs) exposed to fatty acids. The mechanism entailed FoxO1 up-regulation, as FoxO1 silencing normalized Loxl2 expression reversing fibrosis in InsR+/- MCD-fed mice. Loxl2 up-regulation was similarly detected during IR induced by obesity, but not by lipogenic stimuli (fructose feeding). Most importantly, LOXL2 up-regulation was observed in NAFLD patients with type 2 diabetes (T2D) and LOXL2 hepatic and circulating levels correlated with histological fibrosis progression. IR favors fibrosis deposition independently of the classic 'inflammation - HSC transdifferentiation' pathway. The mechanism entails a cross-talk between enhanced lipotoxicity in insulin resistant HEPs and Loxl2 production by HSCs, which was confirmed in patients with diabetes, thereby facilitating extracellular matrix (ECM) stabilization.
在非酒精性脂肪性肝病（NAFLD）患者中，胰岛素抵抗（IR）与纤维化进展相关，且独立于肝脏炎症，但具体机制仍不清楚。我们通过利用蛋氨酸-胆碱缺乏（MCD）饮食模拟炎症（非酒精性脂肪性肝炎：NASH）的独立作用，并通过胰岛素受体（InsR）单倍体不足（InsR+/-）模拟IR在C57BL/6小鼠肝纤维化发病机制中的作用。我们在96例NAFLD患者中证实了该研究结果。在喂食MCD的小鼠中，InsR+/-增加了肝脏脂肪含量并损害了肝脏胰岛素信号传导，导致叉头框蛋白O1（FoxO1）积累。值得注意的是，尽管炎症减轻且肝星状细胞（HSC）的转分化受到阻碍，但InsR+/-促进了肝纤维化的积累，这与参与基质稳定的赖氨氧化酶样2（Loxl2）的诱导相关。Loxl2上调不是胰岛素抵抗的HSC的细胞自主特性，而是依赖于暴露于脂肪酸的胰岛素抵抗肝细胞（HEP）特异性释放的微粒（MP）。该机制涉及FoxO1上调，因为FoxO1沉默可使Loxl2表达正常化，从而逆转InsR+/-喂食MCD小鼠的纤维化。在肥胖诱导的IR过程中同样检测到Loxl2上调，但在生脂刺激（喂食果糖）过程中未检测到。最重要的是，在2型糖尿病（T2D）的NAFLD患者中观察到LOXL2上调，并且LOXL2在肝脏和循环中的水平与组织学纤维化进展相关。IR独立于经典的“炎症-HSC转分化”途径促进纤维化沉积。该机制涉及胰岛素抵抗的HEP中增强的脂毒性与HSC产生的Loxl2之间的相互作用，这在糖尿病患者中得到证实，从而促进细胞外基质（ECM）稳定。
