Transcription Factor ChREBP Mediates High Glucose-Evoked Increase in HIF-1α Content in Epithelial Cells of Renal Proximal Tubules

Abstract

Hyperglycemia/diabetes appears to be accompanied by the state of hypoxia, which especially affects kidneys. The aim of the study was to elucidate the mechanism of high glucose action on HIF-1α expression in renal proximal tubule epithelial cells. The research hypotheses included: (1) the participation of transcription factor ChREBP; and (2) the involvement of the effects resulting from pseudohypoxia, i.e., lowered intracellular NAD+/NADH ratio. The experiments were performed on HK-2 cells and primary cells: D-RPTEC (Diseased Human Renal Proximal Tubule Epithelial Cells—Diabetes Type II) and RPTEC (Renal Proximal Tubule Epithelial Cells). Protein and mRNA contents were determined by Western blot and RT-qPCR, respectively. ChREBP binding to DNA was detected applying chromatin immunoprecipitation, followed by RT-qPCR. Gene knockdown was performed using siRNA. Sirtuin activity and NAD+/NADH ratio were measured with commercially available kits. It was found that high glucose in HK-2 cells incubated under normoxic conditions: (1) activated transcription of HIF-1 target genes, elevated HIF-1α and ChREBP content, and increased the efficacy of ChREBP binding to promoter region of HIF1A gene; and (2), although it lowered NAD+/NADH ratio, it affected neither sirtuin activity nor HIF-1α acetylation level. The stimulatory effect of high glucose on HIF-1α expression was not observed upon the knockdown of ChREBP encoding gene. Experiments on RPTEC and D-RPTEC cells demonstrated that HIF-1α content in diabetic proximal tubular cells was lower than that in normal ones but remained high glucose-sensitive, and the latter phenomenon was mediated by ChREBP. Thus, it is concluded that the mechanism of high glucose-evoked increase in HIF-1α content in renal proximal tubule endothelial cells involves activation of ChREBP, indirectly capable of HIF1A gene up-regulation.

Elevation of Circulating miR-210 Participates in the Occurrence and Development of Type 2 Diabetes Mellitus and Its Complications

“…During T2DM, HIF-1 signaling has been reported to participate in β cell dysfunction, thereby resulting in the occurrence of diabetic complications through regulating angiogenesis and apoptosis [ 44 ]. In addition, ChREBP is a critical regulatory factor for glycolysis and fat formation and is involved in the deregulation of HIF-1 signaling under high glucose condition [ 45 ]. Consistently, this study revealed that high glucose inhibited the expression of HIF-1 α and ChREBP.…”

Fetal Reprogramming of Nutrient Surplus Signaling, O-GlcNAcylation, and the Evolution of CKD

“…2,82 The activation of mTOR/HIF-1 α is particularly notable in the proximal renal tubule, where it drives glycolysis and the development of albuminuria and fibrosis in the renal cortex (Figure 1). 18,62,83,84 As SIRT1 in the proximal tubule declines during nutrient overload, 58 proximal tubular gluconeogenesis is suppressed, 85 presumably to minimize the likelihood that stress-induced SGLT2 upregulation 86 will activate nutrient surplus signaling and its attendant cytotoxic effects.…”

Special Issue: Cellular Oxygen Homeostasis

“…Some pathological states or diseases, such as hyperglycemia and diabetes induce a state of pseudohypoxia due to a decreased NAD+/NADH ratio. Owczarek et al [6] show that the transcription factor carbohydrate response element binding protein (ChREBP) is an important transcriptional regulator of HIF-1α expression in epithelial cells of renal proximal tubules in response to high glucose levels.…”