Autophagy and apoptosis in tubular cells following unilateral ureteral obstruction are associated with mitochondrial oxidative stress

Abstract

Tubular epithelial loss has been shown to be responsible for the formation of atubular glomeruli leading to nephron decomposition and interstitial fibrosis in obstructive uropathy. Cells undergoing apoptosis and autophagic cell death play an important role in this process, yet the mechanisms are not fully understood. In this study, we aimed to investigate whether autophagy cooperating with apoptosis is associated with mitochondrial damage and whether oxidative stress plays an important role in the loss of tubular epithelium following unilateral ureteral obstruction. In this model, we demonstrated that there is coexistence of autophagy and apoptosis with tubular atrophy in obstructed proximal tubules. After unilateral ureteral obstruction (UUO), autophagy in proximal tubular cells was enhanced steadily up to 7 days in the obstructed kidney and declined thereafter, while apoptosis was induced in a time-dependent manner from 3 to 14 days. Mitochondrial structure and number also changed during UUO. Lipid peroxidation products, NOX4, and NADPH oxidase activity were also increased in the obstructed renal cortex, and peaked at 7 days. In vitro, we showed that H2O2 induced mitochondrial injury leading to autophagy and apoptosis through the Beclin 1 pathway and interference with Bcl-2 expression. Thus, our data demonstrate that oxidative stress leading to mitochondrial damage and driven autophagy-dependent cell death and apoptosis are important mechanisms of tubular decomposition in obstructive nephropathy.

Persistent activation of autophagy in kidney tubular cells promotes renal interstitial fibrosis during unilateral ureteral obstruction

“…Although it is uncertain whether or not this persistent autophagy can directly cause tubular cell death, recent studies have consistently demonstrated that UUO-induced autophagy in proximal tubules (14 d of duration) may act in concert with apoptosis to induce tubular atrophy and nephron loss that is associated with the progression of interstitial fibrosis. 28,29,31 In this study, when autophagy was impaired in PT-Atg7 KO mice, UUO-induced tubular atrophy and nephron loss was significantly reversed (Fig. 5E to G), further suggesting a role for persistent induction of autophagy in tubular degeneration during renal fibrosis.…”

“…[28][29][30][31][32]35 Using pharmacological and genetic inhibitory approaches, our study has determined the regulation of renal interstitial fibrosis by autophagy in the in vivo model of UUO and in vitro model of TGFB1-treated proximal tubular cells. The results show that blockade of autophagy by pharmacological inhibitors (choloroquine and 3-methyladenine) or conditional Atg7 deletion from proximal tubules suppressed renal interstitial fibrosis during UUO.…”

“…[28][29][30][31][32] The techniques for analyzing autophagy in vivo in those studies mainly include electron microscopy profile of autophagic vesicles, immunohistochemical staining of LC3, GFP-LC3 fluorescent puncta, and conversion of LC3-I to LC3-II. These methods can monitor autophagy at steady-state levels, but they do not reveal the dynamic nature of autophagy.…”

“…23 In the kidney, autophagy appears to occur in the UUO model of kidney fibrosis. [28][29][30][31][32] Also, TGFB1 activates autophagy in renal tubules in mice and in cultured renal tubular and mesangial cells. [33][34][35] Under these conditions, however, the role(s) of autophagy in renal interstitial fibrosis is poorly understood.…”

“…36 On the one hand, autophagy has been suggested to induce tubular atrophy and decomposition to promote fibrosis. 28,29,31,35 On the other hand, autophagy may contribute to the degradation of COL1/collagen I and active TGFB1 to inhibit kidney fibrosis. 32,34 Thus, autophagy regulation in renal fibrosis may be multifaceted and cell-specific.…”