Rap1b GTPase Ameliorates Glucose-Induced Mitochondrial Dysfunction

Abstract

The role of tubular injury in diabetic nephropathy is relatively unknown, despite that apoptosis of tubular epithelial cells is commonly observed in human renal biopsies. The GTPase Ras-proximate-1 (Rap1b) is upregulated in the hyperglycemic state and is known to increase B-Raf, an antiapoptotic effector protein.In this study, the effects of high glucose on renal tubular apoptosis and the potential ability for Rap1b to ameliorate these effects were investigated. In the kidneys of diabetic mice, apoptotic tubular cells and dysmorphic mitochondria were observed, Bcl-2 expression was decreased, and Bax expression was increased. Total Rap1b expression was slightly increased, but its associated GTPase activity was significantly decreased. In vitro, high extracellular glucose led to decreased Bcl-2 expression, reduced Rap1b GTPase activity, and increased levels of both Bax and GTPase activating protein in a proximal tubular cell line (HK-2). These changes were accompanied by increased DNA fragmentation, decreased high molecular weight mitochondrial DNA, altered mitochondrial morphology and function, disrupted Bcl-2-Bax and Bcl-2-Rap1b interactions, and reduced cell survival. Overexpression of Rap1b partially prevents these abnormalities. Furthermore, the BH4 domain of Bcl-2 was found to be required for successful protein-protein interaction between Bcl-2 and Rap1b. In summary, these data suggest that Rap1b ameliorates glucose-induced mitochondrial dysfunction in renal tubular cells.

myo-Inositol Oxygenase Overexpression Accentuates Generation of Reactive Oxygen Species and Exacerbates Cellular Injury following High Glucose Ambience

“…Assessment of Cellular Distribution of Cytochrome c-Confocal microscopy was employed to delineate the distribution of cytochrome c, as described previously (41). Cells were incubated with 25 nM Mitotracker dye (Mitotracker Red, Molecular Probes, Inc.) at 37°C for 10 min.…”

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

“…The features of tubulointerstitial histopathology include inflammation and apoptosis, which are not necessarily secondary to glomerular lesions. 7,[24][25][26] In addition, tubular injury alone is believed to be closely correlate with clinical manifestations of DKD, including the extent albumin excretion and its degradation in tubules. The latter may serve as a primary key site for the development of DKD, because tubular injury has been described to be a better predictor in the progression of the renal disease.…”

“…5,6 Although the pathogenesis of DKD still remains unclear, recent studies in animals and humans have led to an emerging concept that mitochondrial dysfunctions, which are pivotal events, lead to activation of various cellular processes and aberrant signaling in different cell types of the kidney. [7][8][9] Mitochondria are dynamic organelles that constantly undergo fusion and fission cycles to maintain a balance of cellular reticular network and mitochondrial turnover. 10 Their dynamics are regulated by profission proteins (Drp1 and Fis1) and profusion mediators (Mfn1/2 and OPA1).…”

Association between Mitochondrial DNA Copy Number in Peripheral Blood and Incident CKD in the Atherosclerosis Risk in Communities Study

“…29 In addition, diabetic mouse models and in vitro studies have demonstrated that hyperglycemia induced mitochondrial fragmentation in podocytes, endothelial cells, and renal tubular cells. 7,30 Finally, WBCs are involved in the kidney's response to injury as evidenced by leukocyte infiltration in kidney tissues of patients with CKD and in experimental models. [31][32][33] Lower mtDNA copy number might alter the role of WBCs and platelets in injury response.…”

“…[3][4][5] Molecules that target mitochondrial function, including thiazolidinediones, have been proposed as therapeutic agents for protecting kidney function. [6][7][8][9] However, studies on measures of mitochondrial dysfunction and CKD at the population level have been limited.…”