Abstract

PDHα۱ gene encodes catalytic subunit PDHE1α of pyruvate dehydrogenase (PDH) complex. Based on previous studies, it is hypothesized that inhibition of PDH activity prevents the entry of glycolytic pyruvate into TCA cycle, while promotes fatty acid oxidation and reduces liver triglyceride (TG) level, thereby alleviating nonalcoholic fatty liver disease (NAFLD). In this study, an in vitro model for NAFLD was established with medical fat emulsion; the most effective siRNA for PDHα۱ gene was screened out by qPCR technology; the alterations in metabolism of glucose and lipid, and structure & function of mitochondria in the NAFLD cells were primarily evaluated after transfecting PDHα۱ siRNA. As the results showed, after inhibiting the expression of PDHα۱ gene, glucose level in culture medium was time-dependently increased, and LDH activity in the cells was moderately elevated after 24 h of transfection and then returned to the normal level after 48 h; intracellular TG level was decreased while LPS activity was increased in a time-dependent manner; no significant change in mitochondrial structure was observed with or without siRNA transfection, and ATP content was obviously reduced after 24 h of transfection, followed by restoration after 48 h. It can be concluded that inhibiting PDHα۱ gene in fatty liver cells enhances lipid degradation, and represses the utilization of glucose to an extent, thus reducing TG level without impacting energy generation required for cell survival.

Introduction

Nonalcoholic fatty liver disease (NAFLD) is a continuous spectrum of diseases characterized by excessive deposition of fat in the liver accompanied with diffuse hepatic cell bullous steatosis caused by the factors other than alcohol and other known liver injury-related factors (Farrell et al., 2007, Targher and Byrne, 2017). In turn, hepatic steatosis further aggravates liver metabolic disorders, or even develops into liver fibrosis and cirrhosis, exacerbating liver damage if not given proper treatment (Monteillet et al., 2018).

Nowadays, it has been widely accepted that intrahepatic lipid accumulation caused by various factors (excessive liver fat synthesis, insulin resistance, inflammation, mitochondrial dysfunction, gut microbiota and adipokines), together with the increased de novo fatty acid synthesis, the reduced fatty acid oxidation (FAO) and the blocked liver lipid efflux ultimately cause the occurrence of fatty liver disease (Ratziu et al., 2016, Matsumoto et al., 2018). Obviously, the formation of fatty liver is closely related with the abnormality of lipid metabolism. Accordingly, how to improve the degradation and transportation of intrahepatic lipid is of great significance in preventing the occurrence of fatty liver. It is noteworthy that mitochondria, also called powerhouses of the cells, play an important role in the regulation of fat metabolism and inflammatory response (Ni et al., 2015). As an example, it has been found that adding MitoQ, one mitochondrial-targeted antioxidant, could strongly rescue mitochondrial function and attenuate the development of fatty liver disease by decreasing pathogenic alterations of cardiolipin content, an unique mitochondrial phospholipid playing a key role in mitochondrial bioenergetics (Fouret et al., 2015).

Conclusions

Based on above findings, inhibiting PDHα۱ gene expression could attenuate glucose utilization by the cells, while facilitate lipid degradation which was mainly reflected by the elevated glucose level in the medium and the increased LPS activity, respectively; whereas the cellular energy produced by lipid degradation after interfering the expression of this gene might be not enough to compensate for the decrease of ATP level caused by the reduced glycolysis, which might be the reason for the short-time decrease of energy production.