Mitochondria and renal microvascular dysfunction following ischemia-reperfusion in rats

Abstract

The pathophysiological mechanisms underlying ischemia-reperfusion (IR) induced acute kidney injury (AKI) remain poorly understood. Preglomerular microvessels (PGMV), specifically afferent arterioles, possess an intrinsic autoregulatory ability that is vital for ensuring stable renal hemodynamics. Our recent study indicates that renal autoregulation is impaired in IR rats due to reactive oxygen species (ROS) accumulation. We hypothesized that mitochondria-derived ROS (mtROS) in preglomerular microvessels contribute to renal autoregulatory impairment in IR rats. Blood-perfused juxtamedullary nephron experiments were performed on kidneys of male Sprague-Dawley rats 24 hours after IR induction (60-min, bilateral renal artery clamping). Afferent arteriolar autoregulation was assessed as perfusion pressure (PP) was increased from 65 to 170 mmHg in 15 mmHg increments. Afferent arterioles of sham-operated control rats (n=7) established pressure-mediated autoregulatory responses. Baseline diameter (100 mmHg) averaged 13.2±0.4 μm and increased to 114±4% of baseline when PP decreased from 100 to 65 mmHg. Diameter decreased to 65±3% of baseline when PP increased to 170 mmHg. In contrast, afferent arterioles from IR rats lost autoregulatory capability and remained between 90 and 100% of baseline diameter over 65-170 mmHg (n=8). Addition of Mito-Tempo (mitochondria-targeted antioxidant, 0.1 mM, n=3) to the perfusate restored autoregulation in IR rats at lower PP (65-125 mmHg, P>0.05 vs sham) and partially restored it over 140-170 mmHg. Superfusion with oligomycin (ATP synthase inhibitor, 2.5 μM) in normal kidneys evoked vasodilation to 178±13% baseline and blunting of autoregulatory reactivity. Renal autoregulation is linked to ATP-sensitive P2X1-receptor signaling. Changes in ATP-induced intracellular calcium concentration ([Ca2+]i) were assessed in isolated PGMV myocytes using Fura-2 fluorescent dye. IR markedly attenuated [Ca2+]i responses to 10 and 100 μM ATP by 46±11% and 57±15%, respectively (P<0.05, n=3-4 rats/group), and blunted ATP-induced afferent arteriolar vasoconstriction ( P<0.05 vs. sham, n=3/group). IR markedly increased the fluorescence intensity of mitoROS (MitoSOX™ kit) in PGMV compared to sham rats. Mitochondrial respiratory function was assessed using High Resolution Respirometry in freshly isolated PGMV (n=3/group). IR significantly reduced basal respiration (20±4 vs. 58±9 pmol/s·ml in sham, P<0.05) and oxidative phosphorylation capacity (51±10 vs. 219±37 pmol/s·ml in sham, P<0.05). The percentage of ATP-linked respiration was also reduced in PGMV of IR (60±2% vs. 75±2% in sham, P<0.05). In conclusion, mitochondria of PGMV are involved in regulating renal microvascular tone and autoregulation. IR leads to autoregulatory dysfunction by causing mitochondrial dysfunction in PGMV, increased mtROS production and suppression of ATP-dependent calcium signaling. This study is supported by grants R01DK106500. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.