NF-κB plays an important role in indoxyl sulfate-induced cellular senescence, fibrotic gene expression, and inhibition of proliferation in proximal tubular cells

Abstract

We previously demonstrated that indoxyl sulfate induces senescence and dysfunction of proximal tubular cells by activating p53 expression. However, little is known about the role of nuclear factor (NF)-κB in these processes. The present study examines whether activation (phosphorylation) of NF-κB by indoxyl sulfate promotes senescence and dysfunction in human proximal tubular cells (HK-2 cells). Indoxyl sulfate induced phosphorylation of NF-κB p65 on Ser-276, which was suppressed by N-acetylcysteine, an antioxidant. Furthermore, indoxyl sulfate induced NF-κB p65 expression. Inhibitors of NF-κB (pyrrolidine dithiocarbamate and isohelenin) and NF-κB p65 small interfering RNA (siRNA) suppressed indoxyl sulfate-induced senescence-associated β-galactosidase activity and expression of p53, transforming growth factor (TGF)-β1, and α-smoothe muscle actin (SMA). The induction of p53 expression and p53 promoter activity by indoxyl sulfate were inhibited by pifithrin-α, p-nitro, an inhibitor of p53, whereas p53-transfected cells showed enhanced p53 promoter activity. NF-κB inhibitors suppressed indoxyl sulfate-induced p21 expression, whereas NF-κB p65 siRNA enhanced its expression. NF-κB inhibitors partially alleviated indoxyl sulfate-induced inhibition of cellular proliferation. NF-κB p65 siRNA-transfected cells showed less proliferation in the presence of indoxyl sulfate than control cells. Phosphorylated NF-κB p65 was expressed and colocalized with p53, p21, β-galactosidase, TGF-β1, and α-SMA in the kidneys of chronic renal failure (CRF) rats. AST-120, which reduces serum indoxyl sulfate level, suppressed their expression in the CRF rat kidneys. Taken together, NF-κB plays an important role in indoxyl sulfate-induced cellular senescence, fibrotic gene expression, and inhibition of proliferation in proximal tubular cells. More notably, indoxyl sulfate accelerates proximal tubular cell senescence with progression of CRF through reactive oxygen species-NF-κB-p53 pathway.

Cardiorenal Syndrome

“…One study demonstrated that an antioxidant can suppress IS-induced NF-κB activation in proximal tubular cells, and inhibition of NF-κB in turn suppressed TGF-β1 protein expression in uremic rats. 130 The authors in this study concluded that the ROS/NF-κB/TGF-β1 pathway is likely involved in adverse renal effects induced by IS.…”

“…148 Collectively, it is suggested that: IS is likely to be at least partly responsible for the development of cardiac fibrosis in the CKD setting; the reduction of cardiac fibrosis by AST-120 treatment is partially directly because of its IS-lowering effect and not secondary to improved renal function; and IS-induced cardiac fibrosis may be mediated via the proposed ROS/NF-κB/TGF-β1 pathway of IS-induced renal fibrosis. 130 However, further investigation is needed to confirm this mechanistic pathway. Specifically, increased ROS production caused by IS has been demonstrated in mesangial cells 140 and in endothelial cells 81 but has not yet been demonstrated in cardiac cells.…”

“…The kidney, specifically the renal tubular cells, is most likely to be the first target of injury caused by retention of IS. [129][130][131] IS accelerates the progression of CKD mainly because of its profibrotic and oxidative stress-inducing effects.…”

“…The authors 170 suggested that intrarenal RAAS activation is most likely because of CKD-associated oxidative stress, which has been shown to be enhanced by IS. 130 Interestingly, a superior renoprotective effect of combined RAAS blocker and AST-120 therapy compared with AST-120 treatment alone has been reported in CKD patients. 154 Thus, it is of importance to investigate whether neurohormonal pathways activated in CRS are involved in IS-induced cardiac fibrosis because their pharmacological blockade is readily available.…”

Iindoxyl Sulfate, A Tryptophan Metabolite, Induces Nephro-Vascular Toxicity

“…Further, we have demonstrated that NF-κB plays an important role in indoxyl sulfate-induced cellular senescence, fibrotic gene expression and inhibition of proliferation in proximal tubular cells (42). More notably, indoxyl sulfate accelerates proximal tubular cell senescence with progression of CKD through ROS-NF-κB-p53 pathway (42).…”