Review: Vascular effects of PPARs in the context of NASH.

BACKGROUND Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors known to regulate glucose and fatty acid metabolism, inflammation, endothelial function and fibrosis. PPAR isoforms have been extensively studied in metabolic diseases, including type 2 diabetes and cardiovascular diseases. Recent data extend the key role of PPARs to liver diseases coursing with vascular dysfunction, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). AIM This review summarises and discusses the pathobiological role of PPARs in cardiovascular diseases with a special focus on their impact and therapeutic potential in NAFLD and NASH. RESULTS AND CONCLUSIONS PPARs may be attractive for the treatment of NASH due to their liver-specific effects but also because of their efficacy in improving cardiovascular outcomes, which may later impact liver disease. Assessment of cardiovascular disease in the context of NASH trials is, therefore, of the utmost importance, both from a safety and efficacy perspective

Disfunció microcirculatòria sinusoïdal hepàtica en la cirrosi i dany per isquèmia/reperfusió: mecanismes involucrats i noves dianes terapèutiques

[cat] El sinusoide hepàtic és un llit vascular molt especialitzat. La comunicació autocrina i paracrina entre tots els tipus cel·lulars coordina els processos d’inflamació, trombosi i remodelat tissular i determina la correcta regulació del to vascular hepàtic, de manera que en resposta al dany, les cèl·lules sinusoïdals perden el seu fenotip característic i esdevenen pro-trombòtiques, pro- inflamatòries, pro-contràctils i pro-fibròtiques. En aquesta tesi doctoral hem estudiat els mecanismes de dany hepàtic i la regulació de les cèl·lules sinusoïdals durant la cirrosi i la isquèmia/reperfusió en resposta a dos fàrmacs diferents ja aprovats per a l’ús en humans: liraglutida i simvastatina. La liraglutida és un anàleg de la hormona incretina GLP-1 i és emprada en el tractament de la diabetis de tipus II. Estudis previs han demostrat els efectes antiinflamatoris d’aquest fàrmac en la malaltia de fetge gras d’origen no alcohòlic (NAFLD). Com que la inflamació és un factor implicat en l’inici i la progressió de la cirrosi hepàtica, la liraglutida podria tenir efectes protectors en aquest context, essent un fàrmac ràpidament aplicable a la pràctica clínica. Per tant, l’objectiu d’aquest estudi ha estat avaluar els efectes de la liraglutida sobre el fenotip de les cèl·lules estrellades hepàtiques (HSC), la funció microvascular i els seus efectes derivats en models pre-clínics de malaltia hepàtica crònica. Aquests efectes es van estudiar en diferents models de malaltia hepàtica crònica, tant en models de tractament in vitro en HSC cirròtiques aïllades de biòpsies hepàtiques humanes o de rata com en el tractament in vivo en models animals de malaltia hepàtica crònica. La liraglutida va millorar marcadament el fenotip de les HSC i en va reduir la proliferació. Les rates cirròtiques tractades amb liraglutida van mostrar una millora significativa de la funció microvascular, evidenciada per una menor pressió portal, una reducció en la resistència vascular intrahepàtica i millores marcades en la fibrosi, el fenotip de les HSC i la funció endotelial. Els efectes antifibròtics de la liraglutida es van confirmar en teixit humà i, tot i requerir més investigació, aquests efectes serien independents del receptor de GLP-1 i dependents de la via d’NF-kappaB – Sox9. D’altra banda, el factor de transcripció Krüppel-like factor 2 (KLF2), induïble amb simvastatina, confereix vasoprotecció endotelial. Considerant que estudis recents suggereixen que les estatines son capaces d’induir l’autofàgia (mecanisme de supervivència cel·lular), els objectius d’aquest segon estudi van ser: 1) caracteritzar la relació entre l’autofàgia i KLF2 a l’endotelil, 2) estudiar aquesta relació durant el dany hepàtic agut (isquèmia/reperfusió) i 3) estudiar els efectes de la modulació de KLF2-autofàgia in vitro i in vivo. Vam observar una retroalimentació positiva a l’endoteli entre l’autofàgia i KLF2: els activadors de KLF2, tant farmacològics (estatines, resveratrol, GGTI-298) com genètics (adenovirus codificant per KLF2) o fisiològics (estrès per fregament), van causar una sobreexpressió endotelial de KLF2 mitjançant un mecanisme depenent de Rac1-rab7-autofàgia, tant a l’endoteli sinusoïdal hepàtic (LSEC) com a les cèl·lules endotelials vasculars. Al seu torn, la inducció de KLF2 va promoure una activació de l’autofàgia. La isquèmia freda en solució de la Universitat de Wisconsin i la reperfusió van causar la inhibició de la fusió dels autofagosomes amb els lisosomes, mentre que el pretractament amb simvastatina va mantenir el flux autofàgic (incrementant els nivells de Rab7), resultant en la inducció de KLF2 i una millor viabilitat cel·lular i funció microvascular. En conjunt, els resultats obtinguts mostren el potencial prometedor de la liraglutida per al tractament de la cirrosi i ajuden a la comprensió dels mecanismes moleculars de la vasoprotecció mediada per estatines, permetent així proposar noves estratègies terapèutiques per al tractament de les malalties hepàtiques i extrahepàtiques.[eng] The hepatic sinusoid is a highly specialized vascular bed. Autocrine and paracrine communication between all hepatic cell types coordinate inflammation, thrombosis and tissue remodeling, determining the correct regulation of the hepatic vascular tone. As a response to injury, sinusoidal cells lose their characteristic phenotype and become pro-thrombotic, pro- inflammatory, pro-contractile and pro-fibrotic. In this thesis, we have studied the mechanisms of hepatic damage and sinusoidal cells regulation during cirrhosis and ischemia/reperfusion in response to two different drugs that are already approved for human administration: liraglutide and simvastatin. Liraglutide is an analogue of the incretin hormone GLP-1 with anti-inflammatory properties and used for the treatment of type II diabetes. In the first study, we describe for the first time that liraglutide improves the liver sinusoidal milieu in pre-clinical models of cirrhosis, including isolated human hepatic stellate cells or human precision cut liver slices. On the other hand, simvastatin is known for its cholesterol-independent vasoprotective effects which are mediated by induction of the transcription factor KLF2. In addition, simvastatin has recently been described to induce autophagy, which is a cell survival process. In the second study, we describe for the first time the complex autophagy-KLF2 relationship, modulating the phenotype and survival of the endothelium during ischemia/reperfusion. In conclusion, the obtained results show the promising potential of liraglutide for the treatment of cirrhosis and help in the comprehension of the molecular mechanisms of statin-mediated vasoprotection, thus proposing new therapeutic strategies for the treatment of hepatic and extrahepatic diseases

Advances in therapeutic options for portal hypertension

Portal hypertension represents one of the major clinical consequences of chronic liver disease, having a deep impact on patients’ prognosis and survival. Its pathophysiology defines a pathological increase in the intrahepatic vascular resistance as the primary factor in its development, being subsequently aggravated by a paradoxical increase in portal blood inflow. Although extensive preclinical and clinical research in the field has been developed in recent decades, no effective treatment targeting its primary mechanism has been defined. The present review critically summarizes the current knowledge in portal hypertension therapeutics, focusing on those strategies driven by the disease pathophysiology and underlying cellular mechanisms

Exercise attenuates the transition from fatty liver to steatohepatitis and reduces tumor formation in mice

Non-alcoholic fatty liver disease (NAFLD) leads to steatohepatitis (NASH), fibrosis, and hepatocellular carcinoma. For sedentary patients, lifestyle interventions combining exercise and dietary changes are a cornerstone of treatment. However, the benefit of exercise alone when dietary changes have failed is uncertain. We query whether exercise alone arrests the progression of NASH and tumorigenesis in a choline-deficient, high-fat diet (CD-HFD) murine model. Male C57Bl/6N mice received a control diet or CD-HFD for 12 weeks. CD-HFD mice were randomized further for 8 weeks of sedentariness (SED) or treadmill exercise (EXE). CD-HFD for 12 weeks produced NAFL. After 20 weeks, SED mice developed NASH and hepatic adenomas. Exercise attenuated the progression to NASH. EXE livers showed lower triglycerides and tumor necrosis factor-α expression, less fibrosis, less ballooning, and a lower NAFLD activity score than did SED livers. Plasma transaminases and triglycerides were lower. Exercise activated AMP-activated protein kinase (AMPK) with inhibition of mTORC1 and decreased S6 phosphorylation, reducing hepatocellular adenoma. Exercise activated autophagy with increased LC3-II/LC3-I and mitochondrial recruitment of phosphorylated PTEN-induced kinase. Therefore, exercise attenuates the transition from NAFL to NASH, improves biochemical and histological parameters of NAFLD, and impedes the progression of fibrosis and tumorigenesis associated with enhanced activation of AMPK signaling and favors liver autophagy. Our work supports the benefits of exercise independently of dietary changes

Impaired endothelial autophagy promotes liver fibrosis by aggravating the oxidative stress response during acute liver injury.

BACKGROUND & AIMS Endothelial dysfunction plays an essential role in liver injury, yet the phenotypic regulation of liver sinusoidal endothelial cells (LSECs) remains unknown. Autophagy is an endogenous protective system whose loss could undermine LSEC integrity and phenotype. The aim of our study was to investigate the role of autophagy in the regulation of endothelial dysfunction and the impact of its manipulation during liver injury. METHODS We analyzed primary isolated LSECs from Atg7 and Atg7 mice as well as rats after CCl induced liver injury. Liver tissue and primary isolated stellate cells were used to analyze liver fibrosis. Autophagy flux, microvascular function, nitric oxide bioavailability, cellular superoxide content and the antioxidant response were evaluated in endothelial cells. RESULTS Autophagy maintains LSEC homeostasis and is rapidly upregulated during capillarization in vitro and in vivo. Pharmacological and genetic downregulation of endothelial autophagy increases oxidative stress in vitro. During liver injury in vivo, the selective loss of endothelial autophagy leads to cellular dysfunction and reduced intrahepatic nitric oxide. The loss of autophagy also impairs LSECs ability to handle oxidative stress and aggravates fibrosis. CONCLUSIONS Autophagy contributes to maintaining endothelial phenotype and protecting LSECs from oxidative stress during early phases of liver disease. Selectively potentiating autophagy in LSECs during early stages of liver disease may be an attractive approach to modify the disease course and prevent fibrosis progression. LAY SUMMARY Liver endothelial cells are the first liver cell type affected after any kind of liver injury. The loss of their unique phenotype during injury amplifies liver damage by orchestrating the response of the liver microenvironment. Autophagy is a mechanism involved in the regulation of this initial response and its manipulation can modify the progression of liver damage