Hypoxia/Reoxygenation of Rat Renal Arteries Impairs Vasorelaxation via Modulation of Endothelium-Independent sGC/cGMP/PKG Signaling

Abstract

Ischemia/reperfusion injury holds a key position in many pathological conditions such as acute kidney injury and in the transition to chronic stages of renal damage. We hypothesized that besides a reported disproportional activation of vasoconstrictor response, hypoxia/reoxygenation (H/R) adversely affects endothelial dilatory systems and impairs relaxation in renal arteries. Rat renal interlobar arteries were studied under isometric conditions. Hypoxia was induced by application of 95% N2, 5% CO2 for 60 min to the bath solution, followed by a 10 min period of reoxygenation (95% O2, 5% CO2). The effect of H/R on relaxation was assessed using various inhibitors of endothelial dilatory systems. mRNA expression of phosphodiesterase 5 (PDE5), NADPH oxidases (NOX), and nitric oxide synthase (NOS) isoforms were determined using qRT-PCR; cGMP was assayed with direct cGMP ELISA. Acetylcholine induced relaxation was impaired after H/R. Inhibition of the NOS isoforms with L-NAME, and cyclooxygenases (COXs) by indomethacin did not abolish the H/R effect. Moreover, blocking the calcium activated potassium channels KCa3.1 and KCa2.1, the main mediators of the endothelium-derived hyperpolarizing factor, with TRAM34 and UCL1684, respectively, showed similar effects in H/R and control. Arterial stiffness did not differ comparing H/R with controls, indicating no impact of H/R on passive vessel properties. Moreover, superoxide was not responsible for the observed H/R effect. Remarkably, H/R attenuated the endothelium-independent relaxation by sodium nitroprusside, suggesting endothelium-independent mechanisms of H/R action. Investigating the signaling downstream of NO revealed significantly decreased cGMP and impaired relaxation during PDE5 inhibition with sildenafil after H/R. Inhibition of PKG, the target of cGMP, did not normalize SNP-induced relaxation following H/R. However, the soluble guanylyl cyclase (sGC) inhibitor ODQ abolished the H/R effect on relaxation. The mRNA expressions of the endothelial and the inducible NOS were reduced. NOX and PDE5 mRNA were similarly expressed in H/R and control. Our results provide new evidence that impaired renal artery relaxation after H/R is due to a dysregulation of sGC leading to decreased cGMP levels. The presented mechanism might contribute to an insufficient renal reperfusion after ischemia and should be considered in its pathophysiology.

Supramolecular Nanofibers Containing Arginine-Glycine-Aspartate (RGD) Peptides Boost Therapeutic Efficacy of Extracellular Vesicles in Kidney Repair

“…The cells were grown at 37 °C in a humidified 5% CO 2 atmosphere. To mimic IRI in vitro , HK-2 cells were incubated in a humidified hypoxic/ischemic chamber at 37 °C for 6 h (5% CO 2 , 1% O 2 , and 94% N 2 atmosphere), as previously reported. , Subsequently, HK-2 cells were incubated in a reoxygenated environment with 95% air and 5% CO 2 for an additional 24 h, during which time cells were incubated with RGD hydrogels loaded with EVs without let-7a-5p (EV-inhibitor let‑7a‑5p ) or EV-inhibitor NC .…”

Nitric Oxide Signalling in Descending Vasa Recta after Hypoxia/Re-Oxygenation

“…Superoxide, a prominent representative of reactive oxygen species, does not only increase the Ang II response, since it is a part of the signalling, but also scavenges NO at the same time [37][38][39]. A similar increase in the Ang II response of DVR after H/R has also been observed in living kidney slices [40]. Taken together, functional changes in the outer medullary DVR seem to play a critical role in the disruption of medullary perfusion caused by ischaemia/re-perfusion.…”

Comparison of the Hypocalcemic Effects of Erythropoietin and U-74389G

“…Qian et al noticed that the downregulation [29] of IP3 receptors by IL-1ra attenuates Ca 2+ overload versus the dimethyl sulfoxide group and the systolic and diastolic dysfunctions of HR-injured CMs, which contributes to inhibition of apoptosis in IR-injured CMs and reduction of myocardial infarct size in vivo. Braun et al provided new evidence that blocking [30] the Ca activated potassium channels K Ca3.1 and K Ca2.1 , the main mediators of the endothelium-derived hyperpolarizing factor, with TRAM34 and UCL1684, respectively, showed similar effects in HR and control impaired renal artery relaxation. Yin et al significantly improved [31] the cell viability and decreased lactate dehydrogenase release, attenuated myocyte apoptosis, decreased [Ca 2+ ] i and Ca-sensing receptor (CaSR) expression, increased the ERK1/2 phosphorylation levels and inhibited the related apoptotic signaling pathways after pretreatment with Astragaloside IV (60 µmol/L) in rats with MIR injury.…”