American Journal of Physiology-renal Physiology最新文献

Acute kidney injury (AKI) is deadly and expensive, and specific, effective therapy remains a large unmet need. We have demonstrated the beneficial effects of transplanted adult tubular cells and extracellular vesicles (EVs; exosomes) derived from those renal cells on experimental ischemic AKI, even when administered after renal failure is established. To further examine the mechanisms of benefit with renal EVs, we tested the hypothesis that EVs from other epithelia or platelets (a rich source of EVs) might be protective, using a well-characterized ischemia-reperfusion model. When given after renal failure was present, renal EVs, but not those from skin or platelets, markedly improved renal function and histology. The differential effects allowed us to examine the mechanisms of benefit with renal EVs. We found significant decreases in oxidative stress postischemia in the renal EV-treated group with preservation of renal superoxide dismutase and catalase as well as increases in anti-inflammatory interleukin-10. In addition, we propose a novel mechanism of benefit: renal EVs enhanced nascent peptide synthesis following hypoxia in cells and in postischemic kidneys. Although EVs have been used therapeutically, these results serve as "proof of principle" to examine the mechanisms of injury and protection.NEW & NOTEWORTHY Acute kidney injury is common and deadly, yet the only approved treatment is dialysis. Thus, a better understanding of injury mechanisms and potential therapies is needed. We found that organ-specific, but not extrarenal, extracellular vesicles improved renal function and structure postischemia when given after renal failure occurred. Oxidative stress was decreased and anti-inflammatory interleukin-10 increased with renal, but not skin or platelet, exosomes. We also propose enhanced nascent peptide synthesis as a novel protective mechanism.

Infiltrating T cells in the kidney amplify salt-sensitive (SS) hypertension and renal damage, but the mechanisms are not known. Genetic deletion of T cells (SS^CD247-/-) or of the p67^phox subunit of NADPH oxidase 2 (NOX2; SS^p67phox-/-) attenuates SS hypertension in the Dahl SS rat. We hypothesized that reactive oxygen species produced by NOX2 in T cells drive the SS phenotype and renal damage. T cells were reconstituted by adoptively transferring splenocytes (∼10 million) from the Dahl SS (SS→CD247) rat, the SS^p67phox-/- rat (p67^phox→CD247), or only PBS (PBS→CD247) into the SS^CD247-/- rat on postnatal day 5. Animals were instrumented with radiotelemeters and studied at 8 wk of age. There were no detectable differences in mean arterial pressure (MAP) or albuminuria between groups when rats were maintained on a low-salt (0.4% NaCl) diet. After 21 days of high-salt diet (4.0% NaCl), MAP and albuminuria were significantly greater in SS→CD247 rats compared with p67^phox→CD247 and PBS→CD247 rats. Interestingly, there was no difference between p67^phox→CD247 and PBS→CD247 rats in albuminuria or MAP after 21 days. The lack of CD3⁺ cells in PBS→CD247 rats and the presence of CD3⁺ cells in rats that received the T cell transfer demonstrated the effectiveness of the adoptive transfer. No differences in the number of CD3⁺, CD4⁺, or CD8⁺ cells were observed in the kidneys of SS→CD247 and p67^phox→CD247 rats. These results indicate that reactive oxygen species produced by NOX2 in T cells participates in the amplification of SS hypertension and renal damage.NEW & NOTEWORTHY Our current work used the adoptive transfer of T cells that lack functional NADPH oxidase 2 into a genetically T cell-deficient Dahl salt-sensitive (SS) rat model. The results demonstrated that reactive oxygen species produced by NADPH oxidase 2 in T cells participate in the amplification of SS hypertension and associated renal damage and identifies a potential mechanism that exacerbates the salt-sensitive phenotype.

High K⁺ supplementation is correlated with a lower risk of the composite of death, major cardiovascular events, and ameliorated blood pressure, but the exact mechanisms have not been established. Inwardly rectifying K⁺ (K_ir) channels expressed in the basolateral membrane of the distal nephron play an essential role in maintaining electrolyte homeostasis. Mutations in this channel family have been shown to result in strong disturbances in electrolyte homeostasis, among other symptoms. K_ir7.1 is a member of the ATP-regulated subfamily of K_ir channels. However, its role in renal ion transport and its effect on blood pressure have yet to be established. Our results indicate the localization of K_ir7.1 to the basolateral membrane of aldosterone-sensitive distal nephron cells. To examine the physiological implications of K_ir7.1, we generated a knockout of K_ir7.1 (Kcnj13) in Dahl salt-sensitive (SS) rats and deployed chronic infusion of a specific K_ir7.1 inhibitor, ML418, in the wild-type Dahl SS strain. Knockout of Kcnj13 (Kcnj13^-/-) resulted in embryonic lethality. Heterozygous Kcnj13^+/- rats revealed an increase in K⁺ excretion on a normal-salt diet but did not exhibit a difference in blood pressure development or plasma electrolytes after 3 wk of a high-salt diet. Wild-type Dahl SS rats exhibited increased renal K_ir7.1 expression when dietary K⁺ was increased. K⁺ supplementation also demonstrated that Kcnj13^+/- rats excreted more K⁺ on normal salt. The development of hypertension was not different when rats were challenged with high salt for 3 wk, although Kcnj13^+/- rats excrete less Na⁺. Interestingly, chronic infusion of ML418 significantly increased Na⁺ and Cl^- excretion after 14 days of high salt but did not alter salt-induced hypertension development. Here, we found that reduction of K_ir7.1 function, either through genetic ablation or pharmacological inhibition, can influence renal electrolyte excretion but not to a sufficient degree to impact the development of SS hypertension.NEW & NOTEWORTHY To investigate the role of the K_ir7.1 channel in salt-sensitive hypertension, its function was examined using complementary genetic and pharmacological approaches. The results revealed that although reducing K_ir7.1 expression had some impact on maintaining K⁺ and Na⁺ balance, it did not lead to a significant change in the development or magnitude of salt-induced hypertension. Hence, it is probable that K_ir7.1 works in conjunction with other basolateral K⁺ channels to fine-tune membrane potential.

Tubular epithelial cell fate following exposure to various types of injurious stimuli can be decided at distinct cell cycle checkpoints. One such checkpoint occurs during mitosis, known as the spindle assembly checkpoint, and is tightly regulated through the actions of cell division cycle protein 20 (CDC20). Due to our paucity of knowledge about the role of CDC20 in the kidney, the present study was designed to investigate the expression levels and distribution of CDC20 within the kidney and how pharmacological inhibition of CDC20 function affects kidney recovery using various rodent models of kidney injury. CDC20 is normally detected in distal tubules, but upon injury by either cisplatin administration or ureter obstruction, CDC20 accumulation is considerably elevated. Blockade of CDC20 activity using a selective pharmacological inhibitor, Apcin, lowered serum creatinine, tubular damage, and DNA injury following acute kidney injury compared with vehicle-treated mice. In unilateral ureteral obstruction, Apcin reduced tissue kidney injury molecule-1 levels, sirius red staining, and tubulointerstitial α-smooth muscle actin staining in the tissue. The findings in the present study demonstrated that elevations in CDC20 levels in the kidney are associated with kidney injury and that inhibition of CDC20 can alleviate and reverse some of the pathological effects on the architecture and function of kidney.NEW & NOTEWORTHY To our knowledge, this is the first study to characterize the expression and localization of cell division cycle 20 protein (CDC20) in normal and acute, and chronically injured kidneys. Tubular epithelial cell damage was markedly reduced through the administration of a selective inhibitor of CDC20, Apcin. This study provides new evidence that CDC20 can be induced in damaged kidney cells and negatively impact the recovery of the kidney following acute kidney injury.

The impact of chronic dietary K⁺ loading on proximal tubule (PT) function was measured using free-flow micropuncture along with measurements of overall kidney function, including urine volume, glomerular filtration rate, and absolute and fractional Na⁺ and K⁺ excretion in the rat. Feeding animals a diet with 5% KCl [high K⁺ (HK)] for 7 days reduced glomerular filtration rate by 29%, increased urine volume by 77%, and increased absolute K⁺ excretion by 202% compared with rats on a 1% KCl [control K⁺ (CK)] diet. HK did not change absolute Na⁺ excretion but significantly increased fraction excretion of Na⁺ (1.40% vs. 0.64%), indicating that fractional Na⁺ absorption is reduced by HK. PT reabsorption was assessed using free-flow micropuncture in anesthetized animals. At 80% of the accessible length of the PT, measurements of inulin concentration indicated volume reabsorption of 73% and 54% in CK and HK, respectively. At the same site, fractional PT Na⁺ reabsorption was 66% in CK animals and 37% in HK animals. Fractional PT K⁺ reabsorption was 66% in CK and 37% in HK. To assess the role of Na⁺/H⁺ exchanger isoform 3 (NHE3) in mediating these changes, we measured NHE3 protein expression in total kidney microsomes as well as surface membranes using Western blots. We found no significant changes in protein in either cell fraction. Expression of the Ser⁵⁵² phosphorylated form of NHE3 was also similar in CK and HK animals. Reduction in PT transport may facilitate K⁺ excretion and help balance Na⁺ excretion by shifting Na⁺ reabsorption from K⁺-reabsorbing to K⁺-secreting nephron segments.NEW & NOTEWORTHY In rats fed a diet rich in K⁺, proximal tubules reabsorbed less fluid, Na⁺, and K⁺ compared with those in animals on a control diet. Glomerular filtration rates also decreased, probably due to glomerulotubular feedback. These reductions may help to maintain balance of the two ions simultaneously by shifting Na⁺ reabsorption to K⁺-secreting nephron segments.

The high prevalence of inadequate hydration (e.g., hypohydration and underhydration) is concerning given that extreme heat increases excess hospitalizations for fluid/electrolyte disorders and acute kidney injury (AKI). Inadequate hydration may also be related to renal and cardiometabolic disease development. This study tested the hypothesis that prolonged mild hypohydration increases the urinary AKI biomarker product of insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2 ([IGFBP7·TIMP-2]) compared with euhydration. In addition, we determined the diagnostic accuracy and optimal cutoffs of hydration assessments for discriminating positive AKI risk ([IGFBP·TIMP-2] >0.3 (ng/mL)²/1,000). In a block-randomized crossover design, 22 healthy young adults (11 females and 11 males) completed 24 h of fluid deprivation (hypohydrated group) or 24 h of normal fluid consumption (euhydrated group) separated by ≥72 h. Urinary [IGFBP7·TIMP-2] and other AKI biomarkers were measured following the 24-h protocols. Diagnostic accuracy was assessed via receiver operating characteristic curve analysis. Urinary [IGFBP7·TIMP-2] [1.9 (95% confidence interval: 1.0-2.8) vs. 0.2 (95% confidence interval: 0.1-0.3) (ng/mL)²/1,000, P = 0.0011] was markedly increased in hypohydrated versus euhydrated groups. Urine osmolality (area under the curve: 0.91, P < 0.0001) and urine specific gravity (area under the curve: 0.89, P < 0.0001) had the highest overall performance for discriminating positive AKI risk. Optimal cutoffs with a positive likelihood ratio of 11.8 for both urine osmolality and specific gravity were 952 mosmol/kgH₂O and 1.025 arbitrary units. In conclusion, prolonged mild hypohydration increased urinary [IGFBP7·TIMP-2] in males and females. Urinary [IGFBP7·TIMP-2] corrected to urine concentration was elevated in males only. Urine osmolality and urine specific gravity may have clinical utility for discriminating positive AKI risk following prolonged mild hypohydration.NEW & NOTEWORTHY This study found that prolonged mild hypohydration in healthy young adults increased the Food and Drug Administration approved acute kidney injury (AKI) biomarker urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2 [IGFBP7·TIMP-2]. Urine osmolality and specific gravity demonstrated an excellent ability to discriminate positive AKI risk. These findings emphasize the importance of hydration in protecting renal health and lend early support for hydration assessment as an accessible tool to assess AKI risk.

Urothelial cells, which play an essential role in barrier function, are also thought to play a sensory role in bladder physiology by releasing signaling molecules in response to sensory stimuli that act upon adjacent sensory neurons. However, it is challenging to study this communication due to the overlap in receptor expression and proximity of urothelial cells to sensory neurons. To overcome this challenge, we developed a mouse model where we can directly stimulate urothelial cells using optogenetics. We crossed a uroplakin II (UPK2) cre mouse with a mouse that expresses the light-activated cation channel channelrhodopsin-2 (ChR2) in the presence of cre expression. Optogenetic stimulation of urothelial cells cultured from UPK2-ChR2 mice initiates cellular depolarization and release of ATP. Cystometry recordings demonstrated that optical stimulation of urothelial cells increases bladder pressure and pelvic nerve activity. Increases in bladder pressure persisted, albeit to a lesser extent, when the bladder was excised in an in vitro preparation. The P2X receptor antagonist PPADS significantly reduced optically evoked bladder contractions in vivo and ex vivo. Furthermore, corresponding nerve activity was also inhibited with PPADS. Our data suggest that urothelial cells can initiate robust bladder contractions via sensory nerve signaling or contractions through local signaling mechanisms. These data support a foundation of literature demonstrating communication between sensory neurons and urothelial cells. Importantly, with further use of these optogenetic tools, we hope to scrutinize this signaling mechanism, its importance for normal micturition and nociception, and how it may be altered in pathophysiological conditions.NEW & NOTEWORTHY Urothelial cells play a sensory role in bladder function. However, it has been particularly challenging to study this communication as both sensory neurons and urothelial cells express similar sensory receptors. Here we demonstrate using an optogenetic technique, that specific urothelial stimulation alone resulted in bladder contractions. This approach will have a long-lasting impact on how we study urothelial-to-sensory neuron communication and the changes that occur under disease conditions.

Renal nerves have been an attractive target for interventions aimed at lowering blood pressure; however, the specific roles of renal afferent (sensory) versus efferent sympathetic nerves in mediating hypertension are poorly characterized. A number of studies have suggested that a sympathoexcitatory signal conveyed by renal afferents elicits increases in blood pressure, whereas other studies identified sympathoinhibitory afferent pathways. These sympathoinhibitory pathways have been identified as protective against salt-sensitive increases in blood pressure through endothelin B (ET_B) receptor activation. We hypothesized that ET_B-deficient (ET_B-def) rats, which are devoid of functional ET_B receptors except in adrenergic tissues, lack appropriate sympathoinhibition and have lower renal afferent nerve activity following a high-salt diet compared with transgenic controls. We found that isolated renal pelvises from high salt-fed ET_B-def animals lack a response to a physiological stimulus, prostaglandin E₂, compared with transgenic controls but respond equally to a noxious stimulus, capsaicin. Surprisingly, we observed elevated renal afferent nerve activity in intact ET_B-def rats compared with transgenic controls under both normal- and high-salt diets. ET_B-def rats have been previously shown to have heightened global sympathetic tone, and we also observed higher total renal sympathetic nerve activity in ET_B-def rats compared with transgenic controls under both normal- and high-salt diets. These data indicate that ET_B receptors are integral mediators of the sympathoinhibitory renal afferent reflex (renorenal reflex), and, in a genetic rat model of ET_B deficiency, the preponderance of sympathoexcitatory renal afferent nerve activity prevails and may contribute to hypertension.NEW & NOTEWORTHY Here, we found that endothelin B receptors are an important contributor to renal afferent nerve responsiveness to a high-salt diet. Rats lacking endothelin B receptors have increased afferent nerve activity that is not responsive to a high-salt diet.

Diabetic kidney disease (DKD) is one of the most devastating complications of diabetes mellitus, where currently there is no cure available. Several important mechanisms contribute to the pathogenesis of this complication, with oxidative stress being one of the key factors. The past decades have seen a large number of publications with various aspects of this topic; however, the specific details of redox regulation in DKD are still unclear. This is partly because redox biology is very complex, coupled with a complex and heterogeneous organ with numerous cell types. Furthermore, often times terms such as "oxidative stress" or reactive oxygen species are used as a general term to cover a wide and rich variety of reactive species and their differing reactions. However, no reactive species are the same, and not all of them are capable of biologically relevant reactions or "redox signaling." The goal of this review is to provide a biochemical background for an array of specific reactive oxygen species types with varying reactivity and specificity in the kidney as well as highlight some of the advances in redox biology that are paving the way to a better understanding of DKD development and risk.

Hypertension is among the most prevalent medical conditions globally and a major contributor to chronic kidney disease, cardiovascular disease, and death. Prevention through nonpharmacological, population-level interventions is critically needed to halt this worldwide epidemic. However, there are ongoing disagreements as to where public policy efforts should focus. Recently the Salt Substitute and Stroke Study demonstrated the efficacy of substituting table salt with potassium salt to reduce the risk of stroke, major cardiovascular events, and death. However, this sparked debate over whether sodium or potassium should be prioritized in countries where table salt substitution was less feasible. In this commentary, we summarize arguments in favor of either strategy: reduced sodium or increased potassium intake. Moreover, we discuss evidence and policy approaches related to either or combined approaches relevant to cultural context. Ultimately, there is an urgent need for policies that both reduce sodium and increase potassium intake; however, identifying a strategy that fits cultural context will be key to improve population-wide blood pressures.