Effect of peroxisome proliferator-activated receptor-α siRNA on hypertension and renal injury in the rat following nitric oxide withdrawal and high salt diet

Background Peroxisome proliferator-activated receptor (PPAR)-α has been implicated in the regulation of normal and pathological cellular functions, but the effect of specific gene silencing on PPARα-mediated function is not fully defined. Aim This study evaluated the role of PPARα in hypertensive renal injury induced by nitric oxide withdrawal and high salt (4% NaCl) diet [high salt/N^ω-nitro-_L-arginine ( _L-NNA)]. Methods Three PPARα siRNA clones, siRNA ^790-811, siRNA^974-995 or siRNA^1410-1431, directed at the DNA or ligand binding domain of PPARα mRNA or scrambled siRNA was cloned into plasmid expression vector and was injected (10 μg intravenously) in hypertensive rats. Twenty-four-hour readings of blood pressure and heart rate were taken in conscious rats using radiotelemetry. Kidney injury was evaluated by determining N-acetyl-β-glucosaminidase excretion, expression of kidney injury molecule-1 and histopathology. PPARα mRNA and protein expression were also determined. Results High salt/_L-NNA increased PPARα mRNA expression three-fold, and this was abolished in rats treated with PPARα siRNA^790-811, siRNA^974-995 or siRNA^1410-1431. High salt/_L-NNA also increased blood pressure but reduced heart rate without affecting pulse pressure. However, blood pressure was further increased in rats treated with PPARα siRNA ^790-811 (37 ±3%, P<0.05). High salt/_L-NNA also increased N-acetyl-β-glucosaminidase excretion and expression of kidney injury molecule-1. However, PPARα siRNA^790-811 did not affect N-acetyl-β-glucosaminidase excretion but reduced kidney injury molecule-1 expression. Histopathology of kidney tissues in high salt/_L-NNA- treated rats revealed global, fibrinoid and tubular interstitial necrosis that was blunted by PPARα siRNA^790-811. Conclusion These data suggest that increased PPARα expression is a protective mechanism in hypertensive renal injury induced by nitric oxide withdrawal/high salt diet and that siRNAs targeting the DNA-binding domain of PPARα gene elicited differential effects on hypertension and kidney injury.