Strikingly conserved gene expression changes of polyamine regulating enzymes among various forms of acute and chronic kidney injury

The polyamines spermidine and spermine and their common precursor molecule putrescine are involved in tissue injury and repair. Here, we test the hypothesis that impaired polyamine homeostasis contributes to various kidney pathologies in mice during experimental models of ischemia-reperfusion, transplantation, rhabdomyolysis, cyclosporine treatment, arterial hypertension, diabetes, unilateral ureteral obstruction, high oxalate feeding, and adenine-induced injuries. We found a remarkably similar pattern in most kidney pathologies with reduced expression of enzymes involved in polyamine synthesis together with increased expression of polyamine degrading enzymes. Transcript levels of amine oxidase copper-containing 1 (Aoc1), an enzyme which catalyzes the breakdown of putrescine, were barely detectable by in situ mRNA hybridization in healthy kidneys. Aoc1 was highly expressed upon various experimental kidney injuries resulting in a significant reduction of kidney putrescine content. Kidney levels of spermine were also significantly reduced, whereas spermidine was increased in response to ischemia-reperfusion injury. Increased Aoc1 expression in injured kidneys was mainly accounted for by an Aoc1 isoform that harbors 22 additional amino acids at its N-terminus and shows increased secretion. Mice with germline deletion of Aoc1 and injured kidneys showed no decrease of kidney putrescine content; although they displayed no overt phenotype, they had fewer tubular casts upon ischemia-reperfusion injury. Hyperosmotic stress stimulated AOC1 expression at the transcriptional and post-transcription levels in metanephric explants and kidney cell lines. AOC1 expression was also significantly enhanced after kidney transplantation in humans. These data demonstrate that the kidneys respond to various forms of injury with down-regulation of polyamine synthesis and activation of the polyamine breakdown pathway. Thus, an imbalance in kidney polyamines may contribute to various etiologies of kidney injury.

Piezo1 Mediates Vasodilation Induced by Acute Hyperglycemia in Mouse Renal Arteries and Microvessels

BACKGROUND

Acute hyperglycemia is a risk factor for developing acute kidney injury and poor renal outcome in critically ill patients, whereby the role of renal vasculature remains unclear. We hypothesize that hyperglycemia-associated hyperosmolarity facilitates vasodilation through Piezo1-mediated eNOS (endothelial NO synthase) activation.

METHODS

Vasoreactivity was analyzed using wire myography in isolated mouse mesenteric arteries and renal interlobar, and using microvascular perfusion in renal afferent arterioles and efferent arterioles, and vasa recta. Immunofluorescence and Western blot were used for molecular analyses of isolated mouse blood vessels and human umbilical vein endothelial cells.

RESULTS

Pretreatment with hyperglycemia (44 mmol/L glucose; 4 hours) increased acetylcholine-induced relaxation in interlobar arteries and mesenteric arteries, which was prevented by eNOS inhibition using Nω-nitro-L-arginine methylester hydrochloride. Hyperosmotic mannitol solution had a similar effect. Hyperglycemia induced an immediate, Nω-nitro-L-arginine methylester hydrochloride-inhibitable dilation in afferent arterioles, efferent arterioles, and vasa recta, whereby stronger dilation in afferent arterioles compared to efferent arterioles. Hyperglycemia also increased glomerular filtration rate in mice. In human umbilical vein endothelial cells, hyperglycemia, and the Piezo1 activator Yoda-1 increased levels of Piezo1 protein, p-CaMKII (phosphorylated Ca²⁺/Calmodulin-dependent protein kinase type II), Akt, and p-eNOS (phosphorylated eNOS). The hyperglycemia effect could be prevented by inhibiting Piezo1 using GsMTx4 (Grammostola spatulata mechanotoxin 4) and CaMKII using KN93. Furthermore, in arteries and microvessels, inhibition of Piezo1 using GsMTx4 prevented the hyperglycemia -effect, while Yoda-1 caused relaxation and dilation, respectively.

CONCLUSIONS

Results reveal that Piezo1 mediates renal vasodilation induced by hyperosmolarity in acute hyperglycemia. This mechanism may contribute to the pathogenesis of renal damage by acute hyperglycemia.

Age Impairs Soluble Guanylyl Cyclase Function in Mouse Mesenteric Arteries

Endothelial dysfunction (ED) comes with age, even without overt vessel damage such as that which occurs in atherosclerosis and diabetic vasculopathy. We hypothesized that aging would affect the downstream signalling of the endothelial nitric oxide (NO) system in the vascular smooth muscle (VSM). With this in mind, resistance mesenteric arteries were isolated from 13-week (juvenile) and 40-week-old (aged) mice and tested under isometric conditions using wire myography. Acetylcholine (ACh)-induced relaxation was reduced in aged as compared to juvenile vessels. Pretreatment with L-NAME, which inhibits nitrix oxide synthases (NOS), decreased ACh-mediated vasorelaxation, whereby differences in vasorelaxation between groups disappeared. Endothelium-independent vasorelaxation by the NO donor sodium nitroprusside (SNP) was similar in both groups; however, SNP bolus application (10⁻⁶ mol L⁻¹) as well as soluble guanylyl cyclase (sGC) activation by runcaciguat (10⁻⁶ mol L⁻¹) caused faster responses in juvenile vessels. This was accompanied by higher cGMP concentrations and a stronger response to the PDE5 inhibitor sildenafil in juvenile vessels. Mesenteric arteries and aortas did not reveal apparent histological differences between groups (van Gieson staining). The mRNA expression of the α1 and α2 subunits of sGC was lower in aged animals, as was PDE5 mRNA expression. In conclusion, vasorelaxation is compromised at an early age in mice even in the absence of histopathological alterations. Vascular smooth muscle sGC is a key element in aged vessel dysfunction.

The Aza-Analogous Benzo[c]phenanthridine P8-D6 Acts as a Dual Topoisomerase I and II Poison, thus Exhibiting Potent Genotoxic Properties

The benzo[c]phenanthridine P8-D6 was recently found to suppress the catalytic activity of both human topoisomerase (Topo) I and II. Concomitantly, potent cytotoxic activity was observed in different human tumor cell lines, raising questions about the underlying mechanisms in vitro. In the present study, we addressed the question of whether P8-D6 acts as a so-called Topo poison, stabilizing the covalent Topo-DNA intermediate, thus inducing fatal DNA strand breaks in proliferating cells. In HT-29 colon carcinoma cells, fluorescence imaging revealed P8-D6 to be taken up by the cells and to accumulate in the perinuclear region. Confocal microscopy demonstrated that the compound is partially located inside the nuclei, thus reaching the potential target. In the "in vivo complex of enzyme" (ICE) bioassay, treatment of HT-29 cells with P8-D6 for 1 h significantly enhanced the proportion of Topo I and II covalently linked to the DNA in concentrations ≥1 µM, indicating effective dual Topo poisoning. Potentially resulting DNA damage was analyzed by single-cell gel electrophoresis ("comet assay"). Already at 1 h of incubation, significant genotoxic effects were observed in the comet assay in concentrations as low as 1 nM. Taken together, the present study demonstrates the high Topo-poisoning and genotoxic potential of P8-D6 in human tumor cells.