Pathobiology of renal-specific oxidoreductase/myo-inositol oxygenase in diabetic nephropathy: its implications in tubulointerstitial fibrosis

Abstract

Xie P, Sun L, Oates PJ, Srivastava SK, Kanwar YS. Pathobiology of renal-specific oxidoreductase/myo-inositol oxygenase in diabetic nephropathy: its implications in tubulointerstitial fibrosis. Am J Physiol Renal Physiol 298: F1393-F1404, 2010. First published March 24, 2010 doi:10.1152/ajprenal.00137.2010.-Renal-specific oxido-reductase/myoinositol oxygenase (RSOR/MIOX) is expressed in renal tubules. It catabolizes myo-inositol and its expression is increased in diabetic mice and in LLC-PK 1 cells under high-glucose ambience. Aldose reductase (AR) is another aldo-keto reducase that is expressed in renal tubules. It regulates the polyol pathway and plays an important role in glucose metabolism, osmolyte regulation, and ECM pathobiology via the generation of advanced glycation end products, reactive oxygen species, and activation of transforming growth factor (TGF)-␤. In view of the similarities between AR and RSOR/MIOX, the pathobiology of RSOR/MIOX and some of the cellular pathways affected by its overexpression were investigated. An increased expression of fibronectin was noted by transfection of LLC-PK 1 cells with pcDNA3.1-RSOR/MIOX. Similar changes were observed in LLC-PK 1 cells under high-glucose ambience, and they were notably lessened by RSOR/MIOX-small interfering (si) RNA treatment. The changes in tubulointerstitial fibronectin expression were also observed in the kidneys of db/db mice having high levels of RSOR. The pcDNA3.1-RSOR/MIOX transfectants had an increased NADH/NAD ϩ ratio, PKC and TGF-␤ activity, Raf1:Ras association, and p-ERK phosphorylation. These changes were significantly reduced by the inhibitors of PKC, aldose reductase, Ras farnesylation, and MEK1. Similar increases in various the above-noted parameters were observed under high-glucose ambience. Such changes were partially reversed with RSOR-siRNA treatment. Expression of Ecadherin and vimentin paralleled in cells overexpressing RSOR/ MIOX or subjected to high-glucose ambience. These studies suggest that RSOR/MIOX modulates various downstream pathways affected by high-glucose ambience, and conceivably it plays a role in the pathobiology of tubulointerstitium in diabetic nephropathy.fibronectin; db/db mice; sorbinil DIABETES MELLITUS IS A COMMON metabolic disorder in which hyperglycemia afflicts injury on multiple organ systems in humans, and frequent lesions that have been well described include diabetic microangiopathy, neuropathy, retinopathy, and nephropathy (6,33,47,54). The changes in the kidney occur in more than one-third of the patients with diabetes mellitus, and they have been exhaustively described in the literature (27,46,51,53,57,62). The hyperglycemia-induced renal changes may be acute and reversible or chronic and irreversible in nature, and these kidney lesions may serve as a prototypical example that would be applicable to other mammalian organ systems. The acute metabolic changes include increased activity of the polyol pathway, altered redox state of pyridine nucleotides (NADPH:NADP ϩ and NADH:NAD ϩ ratios), pert...

Disruption of Renal Tubular Mitochondrial Quality Control by Myo-Inositol Oxygenase in Diabetic Kidney Disease

“…MIOX, a tubular enzyme, is upregulated during HG ambience, and its critical involvement in the pathogenesis of DKD has been shown. [15][16][17][18] During hyperglycemia, MIOX induces redox imbalance and mitochondrial dysfunction that could result in tubular oxidative injury and apoptosis. 17,18 In view of this contention, the underlying mechanisms by which MIOX may cause mitochondrial dysfunction and tubular cell injury were delineated.…”

“…[15][16][17][18] During hyperglycemia, MIOX induces redox imbalance and mitochondrial dysfunction that could result in tubular oxidative injury and apoptosis. 17,18 In view of this contention, the underlying mechanisms by which MIOX may cause mitochondrial dysfunction and tubular cell injury were delineated. As shown in Figure 10, under HG ambience, MIOX is upregulated in tubular cells, [16][17][18] and then, it modulates mitochondrial dynamics through two conceivable pathways.…”

“…17,18 In view of this contention, the underlying mechanisms by which MIOX may cause mitochondrial dysfunction and tubular cell injury were delineated. As shown in Figure 10, under HG ambience, MIOX is upregulated in tubular cells, [16][17][18] and then, it modulates mitochondrial dynamics through two conceivable pathways. In the first pathway, MIOX increases intracellular ROS generation through transcriptional mechanisms, 18 which would then activate cytosolic Drp1 and promote its mitochondrial translocation, leading to mitochondrial fragmentation.…”

“…16,17 A porcine MIOX cDNA was generated by RT-PCR and cloned into pcDNA3.1 (Life Technologies). The plasmid constructs and empty vector (control) were then transfected into LLC-PK1 cells, and stable transfectants were selected by growing cells in the presence of Geneticin and maintained.…”

“…15,16 Previously, we had shown that the upregulation of MIOX during hyperglycemia could modulate redox imbalance by transcriptional mechanisms and also, conceivably, induce mitochondrial-dependent apoptosis, which inevitably may lead to tubulointerstitial injury and fibrosis. [16][17][18] With respect to the amelioration of such an injury, D-glucaric acid, an anticancer drug, may serve as a potential pharmacologic inhibitor of MIOX. 19 Interestingly, a derivative of this drug is believed to have a renoprotective effect in DKD by a yet to be defined mechanism.…”