American Journal of Physiology-renal Physiology最新文献

Sheep develop sepsis-associated acute kidney injury (SA-AKI) during experimental sepsis despite normal to increased renal oxygen delivery. A disturbed relation between oxygen consumption (V̇o₂) and renal Na⁺ transport has been demonstrated in sheep and in clinical studies of AKI, which could be explained by mitochondrial dysfunction. We investigated the function of isolated renal mitochondria compared with renal oxygen handling in an ovine hyperdynamic model of SA-AKI. Anesthetized sheep were randomized to either an infusion of live Escherichia coli with resuscitative measures (sepsis group; n = 13 animals) or served as controls (n = 8 animals) for 28 h. Renal V̇o₂ and Na⁺ transport were repeatedly measured. Live cortical mitochondria were isolated at baseline and at the end of the experiment and assessed in vitro with high-resolution respirometry. Sepsis markedly reduced creatinine clearance, and the relation between Na⁺ transport and renal V̇o₂ was decreased in septic sheep compared with control sheep. Cortical mitochondrial function was altered in septic sheep with a reduced respiratory control ratio (6.0 ± 1.5 vs. 8.2 ± 1.6, P = 0.006) and increased complex II-to-complex I ratio during state 3 (1.6 ± 0.2 vs. 1.3 ± 0.1, P = 0.0014) mainly due to decreased complex I-dependent state 3 respiration (P = 0.016). However, no differences in renal mitochondrial efficiency or mitochondrial uncoupling were found. In conclusion, renal mitochondrial dysfunction composed of a reduction of the respiratory control ratio and an increased complex II/complex I relation in state 3 was demonstrated in an ovine model of SA-AKI. However, the disturbed relation between renal V̇o₂ and renal Na⁺ transport could not be explained by a change in renal cortical mitochondrial efficiency or uncoupling.NEW & NOTEWORTHY We studied the function of renal cortical mitochondria in relation to oxygen consumption in an ovine model of sepsis with acute kidney injury. We demonstrated changes in the electron transport chain induced by sepsis consisting of a reduced respiratory control ratio mainly by a reduced complex I-mediated respiration. Neither an increase in mitochondrial uncoupling nor a reduction in mitochondrial efficiency was demonstrated and cannot explain why oxygen consumption was unaffected despite reduced tubular transport.

Chronic kidney disease (CKD) is a major health problem. Kidney fibrosis is a hallmark and final common pathway of CKD. The Hippo/yes-associated protein (YAP) pathway regulates organ size, inflammation, and tumorigenesis. Our previous study demonstrated tubular YAP activation by tubule-specific double knockout of mammalian STE20-like protein kinase 1/2 (Mst1/2) induced CKD in mice, but the underlying mechanisms remain to be fully elucidated. Activator protein (AP)-1 activation was found to promote tubular atrophy and tubulointerstitial fibrosis. Therefore, we studied whether YAP regulates AP-1 expression in the kidney. We found that expression of various AP-1 components was induced in kidneys subjected to unilateral ureteric obstruction and in Mst1/2 double knockout kidneys, and these inductions were blocked by deletion of Yap in tubular cells, with Fosl1 being most affected compared with other AP-1 genes. Inhibition of Yap also most highly suppressed Fosl1 expression among AP-1 genes in HK-2 and IMCD3 renal tubular cells. YAP bound to the Fosl1 promoter and promoted Fosl1 promoter-luciferase activity. Our results suggest that YAP controls AP-1 expression and that Fosl1 is the primary target of YAP in renal tubular cells.NEW & NOTEWORTHY Yes-associated protein (YAP) activation leads to tubular injury, renal inflammation, and fibrosis, but the underlying mechanisms are not fully understood. We now provide genetic evidence that YAP promotes activator protein-1 expression and that Fosl1 is the primary target of YAP in renal tubular cells.

Renal ischemia-reperfusion (RIR)-induced acute kidney injury (AKI) is a common renal functional disorder with high morbidity and mortality. Stimulator of interferon (IFN) genes (STING) is the cytosolic DNA-activated signaling pathway that mediates inflammation and injury. Our recent study showed that extracellular cold-inducible RNA-binding protein (eCIRP), a newly identified damage-associated molecular pattern, activates STING and exacerbates hemorrhagic shock. H151 is a small molecule that selectively binds to STING and inhibits STING-mediated activity. We hypothesized that H151 attenuates eCIRP-induced STING activation in vitro and inhibits RIR-induced AKI in vivo. In vitro, renal tubular epithelial cells incubated with eCIRP showed increased levels of IFN-β, STING pathway downstream cytokine, IL-6, tumor necrosis factor-α, and neutrophil gelatinase-associated lipocalin, whereas coincubation with eCIRP and H151 diminished those increases in a dose-dependent manner. In vivo, 24 h after bilateral renal ischemia-reperfusion, glomerular filtration rate was decreased in RIR-vehicle-treated mice, whereas glomerular filtration rate was unchanged in RIR-H151-treated mice. In contrast to sham, serum blood urea nitrogen, creatinine, and neutrophil gelatinase-associated lipocalin were increased in RIR-vehicle, but in RIR-H151, these levels were significantly decreased from RIR-vehicle. In contrast to sham, kidney IFN-β mRNA, histological injury score, and TUNEL staining were also increased in RIR-vehicle, but in RIR-H151, these levels were significantly decreased from RIR-vehicle. Importantly, in contrast to sham, in a 10-day survival study, survival decreased to 25% in RIR-vehicle, but RIR-H151 had a survival of 63%. In conclusion, H151 inhibits eCIRP-induced STING activation in renal tubular epithelial cells. Therefore, STING inhibition by H151 can be a promising therapeutic intervention for RIR-induced AKI.NEW & NOTEWORTHY Renal ischemia-reperfusion (RIR)-induced acute kidney injury (AKI) is a common renal functional disorder with a high morbidity and mortality rate. Stimulator of interferon genes (STING) is the cytosolic DNA-activated signaling pathway responsible for mediating inflammation and injury. Extracellular cold-inducible RNA-binding protein (eCIRP) activates STING and exacerbates hemorrhagic shock. H151, a novel STING inhibitor, attenuated eCIRP-induced STING activation in vitro and inhibited RIR-induced AKI. H151 shows promise as a therapeutic intervention for RIR-induced AKI.

The gut microbiome impacts host gene expression not only in the colon but also at distal sites including the liver, white adipose tissue, and spleen. The gut microbiome also influences the kidney and is associated with renal diseases and pathologies; however, a role for the gut microbiome to modulate renal gene expression has not been examined. To determine if microbes modulate renal gene expression, we used whole organ RNA sequencing to compare gene expression in C57Bl/6 mice that were germ free (lacking gut microbiota) versus conventionalized (gut microbiota reintroduced using an oral gavage of a fecal slurry composed of mixed stool). 16S sequencing showed that male and female mice were similarly conventionalized, although Verrucomicrobia was higher in male mice. We found that renal gene expression was differentially regulated in the presence vs. absence of microbiota and that these changes were largely sex specific. Although microbes also influenced gene expression in the liver and large intestine, most differentially expressed genes (DEGs) in the kidney were not similarly regulated in the liver or large intestine. This demonstrates that the influence of the gut microbiota on gene expression is tissue specific. However, a minority of genes (n = 4 in males and n = 6 in females) were similarly regulated in all three tissues examined, including genes associated with circadian rhythm (period 1 in males and period 2 in females) and metal binding (metallothionein 1 and metallothionein 2 in both males and females). Finally, using a previously published single-cell RNA-sequencing dataset, we assigned a subset of DEGs to specific kidney cell types, revealing clustering of DEGs by cell type and/or sex.NEW & NOTEWORTHY It is unknown whether the microbiome influences host gene expression in the kidney. Here, we utilized an unbiased, bulk RNA-sequencing approach to compare gene expression in the kidneys of male and female mice with or without gut microbiota. This report demonstrates that renal gene expression is modulated by the microbiome in a sex- and tissue-specific manner.

Leptin regulates energy balance via leptin receptors expressed in central and peripheral tissues, but little is known about leptin-sensitive kidney genes and the role of the tubular leptin receptor (Lepr) in response to a high-fat diet (HFD). Quantitative RT-PCR analysis of Lepr splice variants A, B, and C revealed a ratio of ∼100:10:1 in the mouse kidney cortex and medulla, with medullary levels being ∼10 times higher. Leptin replacement in ob/ob mice for 6 days reduced hyperphagia, hyperglycemia, and albuminuria, associated with normalization of kidney mRNA expression of molecular markers of glycolysis, gluconeogenesis, amino acid synthesis, and megalin. Normalization of leptin for 7 h in ob/ob mice did not normalize hyperglycemia or albuminuria. Tubular knockdown of Lepr [Pax8-Lepr knockout (KO)] and in situ hybridization revealed a minor fraction of Lepr mRNA in tubular cells compared with endothelial cells. Nevertheless, Pax8-Lepr KO mice had lower kidney weight. Moreover, while HFD-induced hyperleptinemia, increases in kidney weight and glomerular filtration rate, and a modest blood pressure lowering effect were similar compared with controls, they showed a blunted rise in albuminuria. Use of Pax8-Lepr KO and leptin replacement in ob/ob mice identified acetoacetyl-CoA synthetase and gremlin 1 as tubular Lepr-sensitive genes that are increased and reduced by leptin, respectively. In conclusion, leptin deficiency may increase albuminuria via systemic metabolic effects that impinge on kidney megalin expression, whereas hyperleptinemia may induce albuminuria by direct tubular Lepr effects. Implications of Lepr variants and the novel tubular Lepr/acetoacetyl-CoA synthetase/gremlin 1 axis remain to be determined.NEW & NOTEWORTHY This study provides new insights into kidney gene expression of leptin receptor splice variants, leptin-sensitive kidney gene expression, and the role of the leptin receptor in renal tubular cells for the response to diet-induced hyperleptinemia and obesity including albuminuria.

The objective of this study was to understand the response of mice lacking insulin-regulated aminopeptidase (IRAP) to an acute water load. For mammals to respond appropriately to acute water loading, vasopressin activity needs to decrease. IRAP degrades vasopressin in vivo. Therefore, we hypothesized that mice lacking IRAP have an impaired ability to degrade vasopressin and, thus, have persistent urinary concentration. Age-matched 8- to 12-wk-old IRAP wild-type (WT) and knockout (KO) male mice were used for all experiments. Blood electrolytes and urine osmolality were measured before and 1 h after water load (∼2 mL sterile water via intraperitoneal injection). Urine was collected from IRAP WT and KO mice for urine osmolality measurements at baseline and after 1 h administration of the vasopressin type 2 receptor antagonist OPC-31260 (10 mg/kg ip). Immunofluorescence and immunoblot analysis were performed on kidneys at baseline and after 1 h acute water load. IRAP was expressed in the glomerulus, thick ascending loop of Henle, distal tubule, connecting duct, and collecting duct. IRAP KO mice had elevated urine osmolality compared with WT mice due to higher membrane expression of aquaporin 2 (AQP2), which was restored to that of controls after administration of OPC-31260. IRAP KO mice developed hyponatremia after an acute water load because they were unable to increase free water excretion due to increased surface expression of AQP2. In conclusion, IRAP is required to increase water excretion in response to an acute water load due to persistent vasopressin stimulation of AQP2.NEW & NOTEWORTHY Insulin-regulated aminopeptidase (IRAP) degrades vasopressin, but its role in urinary concentration and dilution is unknown. Here, we show that IRAP-deficient mice have a high urinary osmolality at baseline and are unable to excrete free water in response to water loading. These results reveal a novel regulatory role for IRAP in urine concentration and dilution.

The Ca²⁺-permeable transient receptor potential vanilloid type 4 (TRPV4) channel serves as the sensor of tubular flow, thus being well suited to govern mechanosensitive K⁺ transport in the distal renal tubule. Here, we directly tested whether the TRPV4 function is significant in affecting K⁺ balance. We used balance metabolic cage experiments and systemic measurements with different K⁺ feeding regimens [high (5% K⁺), regular (0.9% K⁺), and low (<0.01% K⁺)] in newly created transgenic mice with selective TRPV4 deletion in the renal tubule (TRPV4^fl/fl-Pax8Cre) and their littermate controls (TRPV4^fl/fl). Deletion was verified by the absence of TRPV4 protein expression and lack of TRPV4-dependent Ca²⁺ influx. There were no differences in plasma electrolytes, urinary volume, and K⁺ levels at baseline. In contrast, plasma K⁺ levels were significantly elevated in TRPV4^fl/fl-Pax8Cre mice on high K⁺ intake. K⁺-loaded knockout mice exhibited lower urinary K⁺ levels than TRPV4^fl/fl mice, which was accompanied by higher aldosterone levels by day 7. Moreover, TRPV4^fl/fl-Pax8Cre mice had more efficient renal K⁺ conservation and higher plasma K⁺ levels in the state of dietary K⁺ deficiency. H⁺-K⁺-ATPase levels were significantly increased in TRPV4^fl/fl-Pax8Cre mice on a regular diet and especially on a low-K⁺ diet, pointing to augmented K⁺ reabsorption in the collecting duct. Consistently, we found a significantly faster intracellular pH recovery after intracellular acidification, as an index of H⁺-K⁺-ATPase activity, in split-opened collecting ducts from TRPV4^fl/fl-Pax8Cre mice. In summary, our results demonstrate an indispensable prokaliuretic role of TRPV4 in the renal tubule in controlling K⁺ balance and urinary K⁺ excretion during variations in dietary K⁺ intake. NEW & NOTEWORTHY The mechanoactivated transient receptor potential vanilloid type 4 (TRPV4) channel is expressed in distal tubule segments, where it controls flow-dependent K⁺ transport. Global TRPV4 deficiency causes impaired adaptation to variations in dietary K⁺ intake. Here, we demonstrate that renal tubule-specific TRPV4 deletion is sufficient to recapitulate the phenotype by causing antikaliuresis and higher plasma K⁺ levels in both states of K⁺ load and deficiency.