Sestrin-2 and BNIP3 regulate autophagy and mitophagy in renal tubular cells in acute kidney injury

Abstract

Autophagy is a cellular recycling process induced in response to many types of stress. However, little is known of the signaling pathways that regulate autophagy during acute kidney injury (AKI). Bcl-2/adenovirus E1B 19 kDa-interacting protein (BNIP)3 and sestrin-2 are the target proteins of hypoxia-inducible factor (HIF)-1␣ and p53, respectively. The aim of this study was to investigate the roles of BNIP3 and sestrin-2 in oxidative stressinduced autophagy during AKI. We used rat ischemia-reperfusion injury and cultured renal tubular (NRK-52E) cells as in vivo and in vitro models of AKI, respectively. Renal ischemia-reperfusion injury upregulated the expression of BNIP3 and sestrin-2 in the proximal tubules, as measured by immunohistochemical staining and Western blot analysis. In vitro, NRK-52E cells exposed to hypoxia showed increased expression of BNIP3 mRNA and protein in a HIF-1␣-dependent manner. In contrast, sestrin-2 mRNA and protein expression were upregulated in a p53-dependent manner after exposure to oxidative stress (exogenous H2O2). NRK-52E cells stably transfected with a fusion protein between green fluorescent protein and light chain 3 were used to investigate autophagy. Overexpression of BNIP3 or sestrin-2 in these cells induced light chain 3 expression and formation of autophagosomes. Interestingly, BNIP3-induced autophagosomes were mainly localized to the mitochondria, suggesting that this protein selectively induces mitophagy. These observations demonstrate that autophagy is induced in renal tubules by at least two independent pathways involving p53-sestrin-2 and HIF-1␣-BNIP3, which may be activated by different types of stress to protect the renal tubules during AKI.Bcl-2/adenovirus E1B 19 kDa-interacting protein-3; acute kidney injury; autophagy; mitophagy; sestrin-2 ISCHEMIA is the leading cause of acute kidney injury (AKI) in the adult population. Prominent morphological features of ischemic AKI include effacement and loss of the proximal tubule brush border, patchy loss of tubular cells, focal areas of proximal tubular dilation, and increased apoptosis (9). The mechanisms that dictate the survival or death of renal cells under oxidative stress must be more completely understood before novel therapeutic strategies for the treatment of ischemic AKI can be explored. Proximal renal tubular cells have high rates of ATP consumption and are very sensitive to hypoxia; thus, mitochondrial damage is one of the most important factors in determining the survival of these cells (1,43).Autophagy is one of the cellular processes that protect cells from genotoxic stress, oxidative stress, accumulation of misfolded proteins, and nutrient deprivation. We (20) have previously reported results from a study of autophagy in a mouse model of AKI. Autophagy plays roles in the pathogenesis of many diseases, and, in kidney disease, both beneficial and detrimental effects of autophagy have been reported (19 -22). Our understanding of autophagy has expanded greatly in recent years, largely due to the identification...

Expression of a novel stress-inducible protein, sestrin 2, in rat glomerular parietal epithelial cells

“…Just recently, increased expression of sestrin 2 was reported in renal proximal tubules in a model of renal ischemia-reperfusion injury (16). In addition, increased sestrin 2 expression was shown in cultured renal tubular cells (NRK-52E cells) exposed to oxidative stress (16). Taken together, the results of the present study show that in contrast to other cell types where sestrin 2 expression is related to stressors, sestrin 2 is constitutively expressed in normal adult PECs.…”

“…Sestrin 2 is a novel p53 target protein that accumulates in stressed cells (18). Just recently, increased expression of sestrin 2 was reported in renal proximal tubules in a model of renal ischemia-reperfusion injury (16). In addition, increased sestrin 2 expression was shown in cultured renal tubular cells (NRK-52E cells) exposed to oxidative stress (16).…”

SESN2/sestrin2 suppresses sepsis by inducing mitophagy and inhibiting NLRP3 activation in macrophages

“…Until now, the accumulating data has only shown that SESN2 expression can be upregulated in response to oxidative stress at the transcriptional level. 24,46,49,50 However, for the first time, we were able to demonstrate that Figure 10. SESN2 suppresses prolonged NLRP3 activation by preserving mitochondrial homeostasis through mitophagy induction.…”

Cellular and Molecular Mechanisms of AKI

“…Consistent with this concept, Ishihara et al have reported the involvement of autophagy molecules sestrin-2 and BNIP-3 in the acutely injured kidney. 37 Mitochondrial fusion is mediated by proteins including mitofusin 1, mitofusin 2 (Mfn2), and optic atrophy 1. Recent studies have demonstrated that deletion of Mfn2 selectively in renal epithelial cells leads to mitochondrial fragmentation and apoptosis after ATP depletion in vitro.…”