Interaction Between Hepatocytes and Proximal Tubular Epithelial Cells in Hypoxia-induced Lipotoxicity

Hypoxia is one of the main pathogenetic factors in liver, an organ that exhibits lower oxygen pressure than that in other organs. Liver hepatocytes have an approximately 10-fold higher oxygen demand than other cells for homeostatic metabolism. Moreover, several clinical studies have indicated that liver diseases might aggravate some kidney diseases. Therefore, it is critical to develop in vitro models for investigating diseases resulting from the interaction of liver and kidney under hypoxia. In this study, transwell plates were used to evaluate the interaction between proximal tubular epithelial cells and hepatocytes under hypoxia, which was induced using a mixture of sodium sulfite and cobalt chloride. Increased relative lactate dehydrogenase release was not observed in single cultures of proximal tubular epithelial cells and hepatocytes under hypoxic conditions. Compared to single cultures of proximal tubular epithelial cells and hepatocytes, relative lactate dehydrogenase releases were 1.70 and 1.50 times higher in co-cultures of proximal tubular epithelial cells and hepatocytes, respectively. Gene expressions of several markers such as serine palmitoyltransferase light chain 1 and ceramide synthetase 2 were analyzed to examine lipotoxicity under hypoxia. In addition, treatment with myriocin, a well-known ceramide inhibitor, reduced cytotoxicity in proximal tubular epithelial cells. The results of this study suggest that hypoxia might not be cytotoxic in separate monolayer cultures of proximal epithelial cells and hepatocytes. However, it might be cytotoxic due to interactions between these cell types, possibly due to an accumulation of ceramide, a result that can be described as lipotoxicity.