Indoxyl sulfate-induced epithelial-to-mesenchymal transition and apoptosis of renal tubular cells as novel mechanisms of progression of renal disease

Abstract

Indoxyl sulfate (IS), one of the uremic toxins, is regarded to have a substantial role in the progression of chronic kidney disease (CKD). Epithelial-to-mesenchymal transition (EMT) and apoptosis of renal tubular cells are known to be the critical mechanisms of the development and aggravation of CKD. We investigated the effect of IS on EMT and apoptosis in renal proximal tubular cells, NRK-52E cells. IS significantly inhibited cell proliferation and induced cell migration with a morphological transition from cuboidal epithelial cells to spindle-shaped scattered fibroblast-like cells. IS downregulated the expressions of zonula occluden-1 and E-cadherin, whereas upregulated a-SMA expression at 48 h, which was blocked by a pretreatment of the organic anion transporter, probenecid. IS also induced apoptosis of NRK cells from a concentration of 25 mg/ml with an activation of ERK1/2 and p38 MAP kinase (MAPK). Pretreatment of ERK1/2 or p38 MAPK inhibitors, PD98059 or SB203580, resulted in no significant effect on IS-induced EMT, whereas it ameliorated IS-induced apoptosis of NRK cells. These findings suggested phenotypic transition and apoptosis as potential mechanisms of IS-induced renal damage and the differential role of MAPK activation in IS-induced EMT and apoptosis of renal tubular cells. KEYWORDS: apoptosis; chronic kidney disease; epithelial-to-mesenchymal transition; indoxyl sulfate; MAPKinase Indoxyl sulfate (IS) is one of the protein-bound uremic solutes derived from tryptophan, which is converted to indole and subsequently undergoes sulfate conjugation in hepatocytes to form IS.1 It is taken by organic anion transporters (OATs) at the basolateral membrane of proximal tubular cells, and excreted mostly into urine through tubular secretion.2 Therefore, IS accumulates in patients with chronic kidney disease (CKD), 3 demonstrated as an increase in serum level and positive immunostaining area of IS in the kidneys. 4 Although IS is regarded as a marker of renal dysfunction, recent data have revealed that IS also has a substantial role in the progression of CKD.5 Indole, the precursor of IS, caused glomerular sclerosis in uremic rats, 6 and oral administration of IS increased serum creatinine and decreased inulin clearance in uremic rats.3 In a clinical study, patients with urinary IS levels 490 mg/day showed faster progression rate of CKD than did those with urinary IS o30 mg/day.7 Furthermore, the administration of oral adsorbent of IS resulted in a decrease in glomerular sclerosis and interstitial fibrosis in uremic rats associated with a decrease in plasma and urinary IS levels.3 Lowering IS also resulted in an improvement of renal function and a delay in the initiation of dialysis in CKD patients. 8 In a multicenter, randomized clinical study, Schulman et al 9 showed that an administration of AST-120, oral adsorbent of IS, ameliorated uremic symptoms in a dose-dependent manner with a decrease in serum IS and a stable maintenance of serum creatinine. The mechanism of IS-induced renal progression has been expla...

Podocyte Injury Caused by Indoxyl Sulfate, a Uremic Toxin and Aryl-Hydrocarbon Receptor Ligand

“…The decreased cell number of podocytes following indoxyl sulfate exposure may reflect cell death or detachment from the culture substratum. In fact, apoptosis and altered adherens junctions have been reported in indoxyl sulfate-exposed endothelial cells and renal tubular cells [49], [50], and our microarray results for indoxyl sulfate-exposed human podocytes also showed decreased expression of integrins, which facilitate podocyte adhesion to the extracellular matrix [25], [39], [51].…”

The Kidney and Uremic Toxin Removal: Glomerulus or Tubule?

“…38,98,99 It is well documented that several uremic toxins can induce apoptosis in a variety of cell types, such as smooth muscle cells, neutrophils, and proximal tubule cells. [100][101][102] However, only a few studies have reported a direct effect of uremic solutes on cell metabolism, including mitochondrial functioning. Mitochondria are Figure 3.…”

Effects of dexamethasone on the TGF-β1-induced epithelial-to-mesenchymal transition in human peritoneal mesothelial cells

“…16 The filters were immersed overnight in 130 mg/ml matrigel (10 mg/ml; Becton Dickenson, Franklin Lakes, NJ, USA) in PBS at 4 1C. The HPMCs were seeded onto the top of the transwell filter with the addition of DEXA (10 mM) to the lower chamber under serum-free conditions.…”