Role of Hepatocyte nuclear factor 4A in the Kidney

Abstract

In this study we wanted to investigate the role of the transcriptional factor HNF4A in the normal and diseased status of kidney . We proceeded with this objective by studying the expression of HNF4A in a range of kidney diseases. Diabetic nephropathy, Acute renal rejection, IgA nephropathy, Minimal change kidney disease, Acute tubular injury, Interstitial fibrosis and tubular atrophy (IFTA) were included in this study. We found by immunostaining that HNF4A is upregulated in all disease conditions except IFTA. HNF4A is known to regulate a wide range of genes involved in metabolic pathways, cell proliferation etc. Hence HNF4A upregulation could be responsible for the complex molecular changes that occur during these disease conditions contributing to the severity of the disease. After having shown that HNF4A is upregulated in a range of disease conditions, we wanted to focus our attention on diabetic nephropathy. We were interested in studying which target genes of HNF4A could be upregulated in diabetic nephropathy. We thought that Acyl Coenzyme A dehydrogenase Very long chain(ACADVL) could be a target of HNF4A as it has been previously shown that ACADVL is upregulated in HEK293 cells overexpressing HNF4A. ACADVL is involved in the oxidation of fatty acids. We showed that ACADVL is upregulated in a type 2 diabetic mouse model and in human diabetic nephropathy. This could lead to increased fatty acid oxidation in diabetes which can eventually lead to increased ketoacidosis, which is a serious complication in diabetes. After having shown that ACADVL is upregulated together with HNF4A in diabetes, we wanted to show that ACADVL is a direct target of HNF4A. For this purpose we investigated the genomic sequence of ACADVL for HNF4A response elements. Three possible response elements were analyzed. By dual luciferase reporter assay we showed that only one of the response elements for HNF4A is biologically active. This novel HNF4A response element is situated +370bp downstream of the translation start site of ACADVL. We also sought to investigate the mechanism by which HNF4A and its target genes are upregulated in diabetes. We found by luciferase reporter assay that hyperglycemia in diabetes activates HNF4A promoter and target genes. Furthermore, we showed that HNF4A over expression increases high glucose induced cell death. HEK293 cells stably over expressing HNF4A was seen to have reduced cell survival under high glucose conditions compared to the control cells. This can have important implications for diabetic nephropathy where there is a high glucose environment present. Hence increased HNF4A expression in diabetic nephropathy would lead to reduced cell survival HNF4A is known to play a role in cellular and metabolic processes. Hence the upregulation of HNF4A can have important consequences for these disease conditions. For example in diabetes, increase in HNF4A levels could lead to upregulation of gluconeogenic enzymes such as Phosphoenol Pyruvate Carboxy Kinase(PEPCK). This could lead to increased gluconeogenesis in diabetes, which can lead to worsening of the diabetic condition.

Our finding that HNF4A and some of its target genes such as ACADVL is upregulated in the kidney diseases offers some possibilities for therapeutic intervention to alleviate the disease condition. We hypothesize that some metabolic and cellular changes in these disease conditions are due to HNF4A upregulation. Therefore if we could suppress HNF4A expression or use a potent inhibitor against HNF4A, it would be possible to lessen the severity of the disease. We intend to carry out in vitro screening for HNF4A inhibitors for this purpose.