Journal Article

HFD and HFD-provoked hepatic hypoxia act as reciprocal causation for NAFLD via HIF-independent signaling

Wei, Wenjing, Yang, Shuyu, Liu, Suhuan, Zhang, Xiaofang, Shangguan, Zhaoshui, Liu, Yijie, Li, Xuejun, Huang, Caoxin

2020

Overview

Background The occurrence of non-alcoholic fatty liver disease (NAFLD) is found to be higher in patients with obstructive sleep apnea (OSA), which is characterized by intermittent hypoxia. Activation of hypoxia-inducible factors has been shown in the development and progression of NAFLD, implying a cause and effects relationship between NAFLD and hypoxia. The present study was designed to investigate the interaction of lipotoxicity and hypoxia in the pathogenesis of NAFLD using mice model with high-fat diet (HFD) feeding or hypoxic treatment. Methods NAFLD model was induced in mice by HFD feeding, and in cultured primary hepatocytes by administration of palmitate acid. Mouse hypoxic model was produced by placing the mice in a Animal incubator with oxygen concentration at 75% followed by a 21% oxygen supplement. Hypoxic condition was mimicked by treating the hepatocytes with cobalt chloride (CoCl 2 ) or 1% oxygen supply. Pimonidazole assay was conducted to evaluate hypoxia. Lipid metabolic genes were measured by real-time polymerase-chain reaction. HIF-1α and HIF-2α genes were silenced by siRNA. Results HFD feeding and palmitate acid treatment provoked severe hepatic hypoxia along with TG accumulation in mice and in cultured primary hepatocytes respectively. Conversely, hypoxia induced hepatic TG accumulation in mice and in cultured primary hepatocytes. Hypoxic treatment inhibited the expression of lipolytic genes, while increased the expression of lipogenicgenes in mice. Although both lipotoxicity and hypoxia could activate hepatic hypoxia-induced factor 1α and 2α, while neither lipotoxicity- nor hypoxia- induced hepatic steatosis was affected when HIF was knocked down. Conclusions HFD resulted in hepatic TG accumulation and concomitant hypoxia. Conversely, hypoxia induced hepatic TG accumulation in mice and in cultured heptocytes. Thus lipotoxicity and hypoxia might work as reciprocal causation and orchestrate to promote the development of NAFLD.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Acids / Animals / Anoxia / Apnea / Causes of / Cobalt / Cobalt chloride / Complications and side effects / Development and progression / Diet, High-Fat - adverse effects / Fatty liver / Gastroenterology / Gene expression / Gene silencing / Genetic aspects / Health aspects / Hepatocytes / Hepatology / HIF / High fat diet / Humans / Hypoxia / Hypoxia-inducible factor 1a / Hypoxia-inducible factors / Internal Medicine / Laboratory animals / Lipids / Liver / Liver diseases / Medicine / Medicine & Public Health / Metabolism / Mice / Mice, Inbred C57BL / NAFLD / Non-alcoholic Fatty Liver Disease - etiology / Nutrition and metabolism / Oxygen / Palmitic acid / Pathogenesis / Proteins / Research Article / siRNA / Sleep / Sleep disorders / Steatosis / Transcription factors