Hepatocyte-derived small extracellular vesicles in the intrahepatic and liver-pancreas interactome in the context of non-alcoholic fatty liver disease

Resumen

Introduction and aims: The prevalence of non-alcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) are increasing rapidly worldwide, reaching epidemic proportions. Therapeutic strategies can address both diseases simultaneously, as they share pathophysiological mechanisms. Lipotoxicity increases the secretion of hepatocytederived small extracellular vesicles (Hep-sEV) that act locally and contribute to NAFLD progression (intrahepatic interactome) or reach the circulation and target other metabolic tissues involved in the control of whole-body glucose homeostasis such as the pancreas (liver-pancreas interactome), likely driving T2DM development. In this Doctoral Thesis, we have investigated whether Hep-sEV released under lipotoxic conditions cause liver and pancreas inflammation and the subsequent effects on insulin action and secretion. Materials and methods: Primary hepatocyte-released sEV (PH-sEV) from mice were purified by differential ultracentrifugation. In vitro and in vivo approaches were used to decipher the role of PH-sEV in inflammation-associated insulin resistance in the liver or βcell dysfunction in pancreatic islets. TLR4 contribution to PH-sEV-mediated effects in liver and pancreas was achieved by genetic deletion or pharmacological inhibition. Results: The lipotoxic NAFLD environment increased the release of PH-sEV enriched in saturated fatty acids (SFAs), highly proinflammatory lipid species. By combining in vitro and in vivo approaches we demonstrated the following: (1) Lipotoxic PH-sEV targeted tissueresident macrophages in the liver (Kupffer cells, KCs) and pancreatic islets (islet macrophages) inducing TLR4/NFκB-mediated inflammation. (2) The subsequent inflammatory secretome attenuated insulin signaling in hepatocytes and impaired β-cell insulin secretion in pancreatic islets. (3) Macrophage inflammation and subsequent hepatocyte insulin resistance were also induced by circulating sEV from mice and humans with NAFLD. (4) Chronic i.v. administration of lipotoxic PH-sEV in lean mice aggravated liver and pancreas inflammation through the recruitment of circulating immune cells and further induced fibrotic damage and hepatocyte injury in the liver, accompanied by other detrimental systemic effects such as dyslipidemia and inflammation. (5) Chronic i.v. administration of lipotoxic PH-sEV in lean mice induced hepatocyte insulin resistance without alterations in glucose tolerance due to compensatory insulin secretion by β-cells. (6) Pharmacological inhibition of TLR4 or its specific deletion in macrophages ameliorated PHsEV-mediated effects in the liver and pancreatic islets. Conclusions: We have identified Hep-sEV as transporters of SFAs targeting KCs in the liver and macrophages in pancreatic islets causing inflammation. These effects were mediated by TLR4 resulting in insulin resistance in hepatocytes and impaired insulin secretion by β-cells. Targeting TLR4-mediated effects of lipotoxic Hep-sEV would open new therapeutic opportunities for the early treatment of NAFLD and prevention of T2DM development