Role of mitochondria in paricalcitol-mediated cytoprotection during obstructive nephropathy

Abstract

Vitamin D slows the progression of chronic kidney disease. Furthermore, activators of vitamin D receptors (VDR) have suppressant effects on the renin-angiotensin system, as well as anti-inflammatory and antifibrotic actions. This study aimed to evaluate the cytoprotective effects of paricalcitol, a VDR activator, at the mitochondrial level using an obstructive nephropathy model [unilateral ureteral obstruction (UUO)]. Rats subjected to UUO and controls were treated daily with vehicle or paricalcitol. The control group underwent a sham surgery. The treatment was done for 15 days (30 ng/kg). The following were determined: biochemical parameters; fibrosis; apoptosis; mitochondrial morphology; VDR, AT(1) receptor, and NADPH oxidase 4 expression; and NADPH oxidase activity (in total and in mitochondrial fractions from the renal cortex). VDR activation prevented fibrosis (20 ± 5 vs. 60 ± 10%) and the number of TUNEL-positive apoptotic cells (10 ± 3 vs. 25 ± 4) in UUO. Biochemical, histological, and molecular studies suggest mitochondrial injury. Electron microscopy revealed in UUO electronically luminous material in the nucleus. Some mitochondria were increased in size and contained dilated crests and larger than normal spaces in their interiors. These changes were not present with paricalcitol treatment. Additionally, high AT(1)-receptor mRNA and NADPH activity was reverted in mitochondrial fractions from obstructed paricalcitol-treated animals (0.58 ± 0.06 vs. 0.95 ± 0.05 relative densitometry units and 9,000 ± 800 vs. 15,000 ± 1,000 relative fluorescence units·μg protein(-1)·min(-1), respectively). These changes were consistent with an improvement in VDR expression (0.75 ± 0.05 vs. 0.35 ± 0.04 relative densitometry units). These results suggest that paricalcitol confers a protective effect and reveal, as well, a possible AT(1) receptor-dependent protective effect that occurs at the mitochondrial level.

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“…Further evidence for RAS/VDR signaling interactions was provided by our study in rats subjected to obstructive nephropathy (a model of RAS upregulation) and treated with the VDR activator paricalcitol, where VDR activation attenuated renal fibrosis, apoptosis, and mitochondrial injury, accompanied by reduction of mitochondrial AT 1 R mRNA contents and VDR upregulation (147). In SHR, the same renal protective effects were brought about by 4 mo paricalcitol, enalapril, or combined paricalcitol-enalapril treatments.…”

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“…In this context, we show that mitochondrial injury linked to AT 1 /VDR uncoupling was improved when paricalcitol, enalapril, or, better still, the combination of both was used. This finding is feasible taking into consideration recent contributions that reported the identification and characterization of a functional mitochondrial RAS (Abadir et al 2011), the mitochondrial localization of VDR (García et al 2012 andSilvagno et al 2010), and ultrastructural mitochondrial improvement as a consequence of recovery in mitochondrial VDR expression linked to poor AT 1 and NADPH oxidase activity during obstructive nephropathy. Moreover, a ligand-independent mitochondrial import of VDR through the permeability transition pore (PTP) was reported (Silvagno et al 2013); and since functional and structural changes in mitochondria are caused by the opening of the mitochondrial PTP and by the mitochondrial generation of ROS, this finding open new perspectives on PTP function as transporter and on VDR role in mitochondria.…”

“…A standard point counting method (Hruska et al 2000;Morrissey et al 2002) was used to quantitate the fibrosis of the renal interstitium. The fibrosis of the renal cortical interstitium was determined as previously reported (García et al 2012), and the results were expressed as a percentage of the measured area.…”

“…Mitochondrial isolation from tissue as well as purity was performed according to our previous reports (García et al 2012). The values were expressed as relative fluorescence units (RFU) per microgram of protein and per min of incubation.…”

“…Previously, we have demonstrated that paricalcitol (19-nor-1, 25-dihydroxyvitamin D 2 , an inducer of vitamin D receptors) was able to ameliorate renal interstitial fibrosis in obstructive nephropathy by means of a possible AT 1 receptordependent protective effect that occurs at the mitochondrial level (García et al 2012). …”