Resumen de Alcoholic liver disease: Contribution of hypoxia signaling and translational relevance in a humanized liver mouse model
ALD is a major concern worldwide as it is one of the most prevalent liver diseases in Europe and USA (Blachier et al., 2013; Pimpin et al., 2018; Rehm et al., 2013). In addition, despite most patients with alcoholic fatty liver and early stages of alcoholic steatohepatitis (ASH) can recover after cessation ofdrinking, current treatment for more advanced stages as alcoholic cirrhosis and alcoholic hepatitis (AH) is limited and have undergone a minimal innovation with respect to the first description of the potential benefits of corticosteroid therapy. Thus, the recommendation for patients with advanced ALD is currently liver transplantation (Sanyal et al., 2018), suggesting the urgent need for new therapeutic targets. Although the main features of the different stages of the disease have been described, severalunderlying mechanismsstill remain unknown, which could be the key for developing new therapies. For instance, the role of hypoxic pathway in ALD is still controversial, as opposite roles for the master regulator of hypoxia (HIF-1α) have been described using the same experimental model of ALD (Nath et al., 2011; Nishiyama et al., 2011). In this doctoral thesishepatocyte specific deletion of VHL has been used as a model to stabilize HIF-α and study its contribution to acute-on-chronic model of ALD. In this context, a synergistic effect of VHL deletion and ethanol intake has been characterized, in which livers presented severe steatosis and fibrosis, as well as increased cholesterol trafficking to mitochondria, which completely impaired mitochondrial respiration. Our results suggestthe direct implication of hypoxic pathway in fibrosis, fat accumulation and cholesterol transport with a subsequent impact in respiration decline, proposing a new mechanistic pathway for the metabolic switch in hypoxic environment and progression to more severe stages of ALD. ALD is studied using a wide variety of models that are performed mainly in rodents. However, the animal models that are used to study many aspects of human disease cannot replicate some very important features of human biology. To overcome this limitation, previous reports used human knock-in models with the expression of human genes (as CYP2E1 (Lu et al., 2010) and CIDEC (Xu et al., 2015) in ALD. Although these models have been useful, these reports only apply to the impact of a single gene. Therefore, we approached this issue using a humanized model with humanized mice. The humanization process takes advantage of immune deficient mice, creating chimeric animals that harbor human tissues and cells, including hepatocytes. In this regard, the “humanized liver” model can be used to mimic human metabolism in the liver and further study the human disease in a more physiological environment, which allows us to compare the differences in ALD to murine versus humanized livers.Our results in this doctoral thesis suggest a clear difference between hepatocytes from different species. In fact, human hepatocytes displayed basal reduced expression of ER stress or oxidative stress markers compared to murine hepatocytes, as well as an increased antioxidant defense (GSH). Despite this, we observed an enhanced susceptibility of human hepatocytes upon acute-on-chronic model of alcohol intake compared to murine hepatocytes as all stress parameters significantly induced,whereasonly a slight increase was observed in murine hepatocytes. Overall, this doctoralthesis presents new insights of the differences between species upon the same insult, increasing the awareness on the research of ALD using rodents as animal models.
