Non-alcoholic fatty liver disease (NAFLD) patients have multiple metabolic disturbances, with markedly elevated levels of lactate. Lactate accumulations play pleiotropic roles in disease progression through metabolic rearrangements and epigenetic modifications. Monocarboxylate transporter 4 (MCT4) is highly expressed in hepatocytes and responsible for transporting intracellular lactate out of the cell. To explore whether elevated MCT4 levels played any role in NAFLD development, we overexpressed and silenced MCT4 in hepatocytes and performed a comprehensive in vitro and in vivo analysis. Our results revealed that MCT4 overexpression down-regulated the genes for lipid synthesis while up-regulating the genes involved in lipid catabolism. Conversely, silencing MCT4 expression or inhibiting MCT4 expression led to the accumulation of intracellular lipid and glucose metabolites, resulting in hepatic steatosis. In a mouse model of NAFLD, we found that exogenous MCT4 overexpression significantly reduced lipid metabolism and alleviated hepatocellular steatosis. Mechanistically, MCT4 alleviated hepatic steatosis by regulating a group of hub genes such as Arg2, Olr1, Cd74, Mmp8, Irf7, Spp1, and Apoe, which in turn impacted multiple pathways involved in lipid metabolism and inflammatory response, such as PPAR, HIF-1, TNF, IL-17, PI3K-AKT, Wnt, and JAK-STAT. Collectively, our results strongly suggest that MCT4 may play an important role in regulating lipid metabolism and inflammation and thus serve as a potential therapeutic target for NAFLD.

Recombinant adenovirus (rAdV) is a commonly used vector system for gene transfer. Efficient initial packaging and subsequent production of rAdV remains time-consuming and labor-intensive, possibly attributable to rAdV infection-associated oxidative stress and reactive oxygen species (ROS) production. Here, we show that exogenous GAPDH expression mitigates adenovirus-induced ROS-associated apoptosis in HEK293 cells, and expedites adenovirus production. By stably overexpressing GAPDH in HEK293 (293G) and 293pTP (293GP) cells, respectively, we demonstrated that rAdV-induced ROS production and cell apoptosis were significantly suppressed in 293G and 293GP cells. Transfection of 293G cells with adenoviral plasmid pAd-G2Luc yielded much higher titers of Ad-G2Luc at day 7 than that in HEK293 cells. Similarly, Ad-G2Luc was amplified more efficiently in 293G than in HEK293 cells. We further showed that transfection of 293GP cells with pAd-G2Luc produced much higher titers of Ad-G2Luc at day 5 than that of 293pTP cells. 293GP cells amplified the Ad-G2Luc much more efficiently than 293pTP cells, indicating that exogenous GAPDH can further augment pTP-enhanced adenovirus production. These results demonstrate that exogenous GAPDH can effectively suppress adenovirus-induced ROS and thus accelerate adenovirus production. Therefore, the engineered 293GP cells represent a superfast rAdV production system for adenovirus-based gene transfer and gene therapy.

Liver is an important organ for regulating glucose and lipid metabolism. Recent studies have shown that bone morphogenetic proteins (BMPs) may play important roles in regulating glucose and lipid metabolism. In our previous studies, we demonstrated that BMP4 significantly inhibits hepatic steatosis and lowers serum triglycerides, playing a protective role against the progression of non-alcoholic fatty liver disease (NAFLD). However, the direct impact of BMP4 on hepatic glucose metabolism is poorly understood. Here, we investigated the regulatory roles of BMP4 in hepatic glucose metabolism. Through a comprehensive analysis of the 14 types of BMPs, we found that BMP4 was one of the most potent BMPs in promoting hepatic glycogen accumulation, reducing the level of glucose in hepatocytes and effecting the expression of genes related to glucose metabolism. Mechanistically, we demonstrated that BMP4 reduced the hepatic glucose levels through the activation of mTORC2 signaling pathway in vitro and in vivo. Collectively, our findings strongly suggest that BMP4 may play an essential role in regulating hepatic glucose metabolism. This knowledge should aid us to understand the molecular pathogenesis of NAFLD, and may lead to the development of novel therapeutics by exploiting the inhibitory effects of BMPs on hepatic glucose and lipid metabolism.