American journal of physiology. Renal physiology最新文献

Chronic kidney disease (CKD) is one of the leading causes of global morbidity, and early diagnosis is essential to prevent complications. Estimated glomerular filtration rate (eGFR) is a key biomarker for assessing renal function. However, its value is influenced by various factors, including circadian variations. Previous studies have documented a circadian rhythm in eGFR, but population-level investigations using the cosinor method have not been conducted. We conducted a retrospective study in two hospitals in Spain (Toledo and Lorca) between 2017 and 2019. The circadian rhythm of eGFR was studied by fitting it to a cosine function, analyzing the effects of age and CKD stage. The results showed a statistically significant circadian rhythm in both populations, with the acrophase occurring at the beginning of the active phase of the day. The amplitude of the rhythm decreased in older patients (70-85 yr), whereas patients with advanced CKD had lost their circadian rhythm entirely. This study, for the first time, uses the cosinor method to demonstrate the existence of a population-level circadian rhythm of eGFR. The cosinor analysis was performed on different CKD stages and ages, revealing the existence of significant rhythms, although none at advanced ages or post-G1 CKD stage. The loss of circadian variability in advanced CKD emphasizes the importance of considering these rhythms in clinical practice to improve the diagnosis and management of kidney disease.NEW & NOTEWORTHY This study, for the first time, uses the cosinor method to demonstrate the existence of a population-level circadian rhythm of estimated glomerular filtration rate, which is influenced both by age and the progression of chronic kidney disease.

NaCl restriction upregulates pendrin, in part, through increased circulating aldosterone and the intercalated cell (IC) mineralocorticoid receptor (MR). Since 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) enhances aldosterone binding to this receptor in other cells, we asked if pendrin abundance is reduced in NaCl-restricted 11β-HSD2 knockout (KO) rats. However, pendrin abundance was greater in 11β-HSD2 KOs than in controls, possibly from enhanced glucocorticoid MR activation. Moreover, the MR antagonist, spironolactone, reduced pendrin abundance in mice that do not produce aldosterone (aldosterone synthase KO). IC MR gene ablation also reduced pendrin protein abundance in corticosterone-treated, adrenalectomized mice. Therefore, the MR regulates pendrin independently of aldosterone. As such, we asked whether glucocorticoids, the other MR ligands, change pendrin abundance and/or subcellular distribution in adrenalectomized wild-type mice. We observed that corticosterone upregulated pendrin in a dose-dependent manner through both increased total protein abundance and subcellular redistribution. At higher doses, corticosterone increased pendrin abundance from greater pendrin-positive cell number within the late distal convoluted tubule 2 (DCT2) rather than increased pendrin abundance per cell. Finally, we asked whether pendrin contributes to the hypertension seen in rodent models of Cushing syndrome. Although corticosterone increased blood pressure in wild-type mice, it had no effect in pendrin KOs. In conclusion, glucocorticoids upregulate pendrin by increasing pendrin total protein abundance through an MR-dependent pathway and subcellular redistribution. Glucocorticoids increase pendrin abundance by increasing the number of pendrin-positive cells within the DCT2. In doing so, pendrin contributes to the hypertension seen in rodent models of Cushing syndrome.NEW & NOTEWORTHY Pendrin participates in the hypertension seen in Cushing syndrome.

Obesity and sex influence the salt-sensitivity of blood pressure, but it is unknown whether this also affects tissue electrolyte accumulation. We hypothesized that obese female rats exhibit greater salt-sensitivity of blood pressure with higher nonosmotic sodium accumulation in skin compared with obese male or lean female rats. To investigate this, male and female lean and obese ZSF1 rats received either a deoxycorticosterone acetate (DOCA) pellet plus a high-salt diet (6% NaCl) or a placebo pellet plus normal salt diet at 19 wk of age. Systolic blood pressure (SBP) and 24-h sodium excretion were measured biweekly from 12 to 26 wk. At 26 wk, sodium and potassium content in the skin was measured. SBP was higher in obese than in lean rats within the DOCA + high-salt groups. Lean female rats showed no SBP increase in response to the DOCA + high-salt diet. Analysis of pressure-natriuresis curves confirmed that obesity increased the salt-sensitivity of blood pressure. Furthermore, there was a significant interaction between sex and obesity on salt-sensitivity of blood pressure: lean female rats were completely salt-resistant, whereas obese female rats showed the greatest salt-sensitivity of blood pressure. Similar trends were observed in males, but the effects were less pronounced. Despite differences in salt-sensitivity of blood pressure, there were no differences in skin electrolytes. In conclusion, obesity enhances salt-sensitive hypertension more in female than in male rats, independent of skin electrolytes.NEW & NOTEWORTHY In the presence of obesity, salt-sensitivity of blood pressure was greater in female than in male ZSF1 rats, whereas in the absence of obesity, female rats were salt-resistant. Interestingly, these differences occurred without changes in sodium or potassium accumulation in the skin. These findings highlight that obesity leads to loss of female advantage in salt-sensitive hypertension and call into question the role of nonosmotic sodium storage in salt-sensitivity of blood pressure.

We examine the role of mTORc2 in mediating overnight-high-K⁺-(HK)-intake-induced stimulation of renal outer medullary K⁺ channels (ROMK) in late distal-convoluted-tubule (DCT2)/early connecting-tubule (early-CNT). Also, we explore whether mTORc2 simultaneously inhibits Kir4.1/Kir5.1 and stimulates ROMK/epithelial Na⁺ channel (ENaC) during overnight-HK. We performed patch-clamp experiments, immunoblotting, metabolic cage, and in vivo measurement of urinary K⁺ excretion in kidney tubule-specific RICTOR (rapamycin insensitive companion of mTOR) knockout mice (Ks-RICTOR-KO) and Rictor^flox/flox mice (wild type). Ks-RICTOR-KO mice had a lower urinary K⁺-excretion and higher plasma K⁺ concentration than Rictor^flox/flox mice. Moreover, overnight HK intake further increased plasma K⁺ level in Ks-RICTOR-KO mice but not in Rictor^flox/flox mice. Ks-RICTOR-KO mice had higher basolateral Kir4.1/Kir5.1 activity in the DCT than in Rictor^flox/flox mice. In contrast, tertiapin-Q (TPNQ)-sensitive K⁺ currents (ROMK) were lower in both DCT2/early-CNT and cortical-collecting-duct (CCD) of Ks-RICTOR-KO mice than in Rictor^flox/flox mice. Amiloride-sensitive Na⁺ currents (ENaC) were significantly lower in DCT2/CNT in Ks-RICTOR-KO mice than in wild type. Overnight HK intake decreased Kir4.1/Kir5.1 activity of DCT and increased amiloride-sensitive Na⁺ currents and TPNQ-sensitive K⁺ currents in DCT2/early-CNT and in the CCD in Rictor^flox/flox mice. However, these effects of overnight-HK were absent in Ks-RICTOR-KO mice. Finally, in vivo measurement of urinary K⁺ excretion showed that urinary K⁺ excretion in Ks-RICTOR-KO mice on overnight-HK was lower than in Rictor^flox/flox mice. In summary, mTORc2 plays a role in maintaining baseline activity of Kir4.1/Kir5.1, ROMK, and ENaC and it mediates the effect of overnight-HK on ENaC and ROMK in aldosterone-sensitive distal nephron (ASDN). We conclude that mTORc2 plays a key role in stimulating renal K⁺ excretion during high-K⁺-loading by inhibiting Kir4.1/Kir5.1 in the DCT and stimulating ENaC and ROMK in ASDN.NEW & NOTEWORTHY Our study has two novel findings. First, we demonstrate that mTORc2 plays a key role in mediating high-K⁺-intake-induced stimulation of ENaC/ROMK activity in late DCT. Second, we demonstrate that overnight-HK-induced stimulation of kidney K⁺ excretion is achieved by simultaneously stimulating ENaC and ROMK in the late DCT, CNT, and CCD, and inhibiting Kir4.1/Kir5.1 in the DCT. Thus, we have illustrated an integrated mechanism by which mTORc2 regulates kidney K⁺ excretion.

Despite advances in drug delivery technologies, there is still an unmet demand for non-invasive kidney-targeted drug delivery systems that enhance therapeutic efficacy while minimizing systemic side effects. In the present study, we conducted a proof-of-concept study to evaluate the feasibility and effectiveness of intravesical delivery as a kidney-targeting strategy in mice. We demonstrated that intravesical infusion could retrogradely deliver molecules with a size up to 500 kDa to both the medulla and cortex of the kidney. In particular, empagliflozin, an antagonist of sodium-glucose cotransporter 2 (SGLT2), could effectively target the uppermost segment of the renal tubular system, i.e., the proximal tubules, when administered via the intravesical route, thereby promoting glucose excretion. In an orthotopic renal carcinoma model, intravesical delivery of a chemotherapeutic agent achieved superior tumor suppression with markedly reduced adverse effects on extrarenal organs, compared with systemic administration at an equivalent dose. This improvement was attributed to a higher renal drug concentration and substantially lower systemic exposure achieved by intravesical delivery, demonstrating its kidney-targeting specificity. Thus, these findings indicated that the intravesical delivery route offers a promising strategy for kidney-targeted therapy and related translational research.

Atonal BHLH transcription factor 8 (ATOH8) is a basic helix-loop-helix (bHLH) transcription factor; however, its role in glomerular epithelial cells (podocytes) remains unclear. This study aimed to elucidate the function of ATOH8 in podocytes. First, ATOH8 expression in the mouse kidney was confirmed in podocytes by immunofluorescence staining and in situ hybridization. In cultured human podocytes, transforming growth factor-beta (TGF-β) treatment significantly reduced ATOH8 mRNA expression. To examine the functional consequences of ATOH8 downregulation, ATOH8 expression was knocked down using shRNA. Subsequent RNA sequencing analysis of ATOH8-knockdown podocytes revealed increased extracellular matrix gene expression and activation of TGF-β signaling. ATOH8-knockdown podocytes also showed SMAD2/3 nuclear translocation, increased SMAD transcriptional activity, as determined by a luciferase assay, and upregulated TGFB1 mRNA even without TGF-β stimulation, consistent with TGF-β signaling activation. In vivo, C57BL/6 Atoh8-deficient mice showed no renal abnormalities at baseline. However, in an adriamycin (ADR)-induced focal segmental glomerulosclerosis (FSGS) model, Atoh8-deficient mice developed significantly more severe glomerulosclerosis than wild-type mice, with higher renal cortical Tgfb1 and Col4a1 mRNA levels. Reduced ATOH8 expression was also observed in ADR-induced nephropathy in mice and rats and in various human glomerular diseases. These findings suggest that ATOH8 downregulation enhances TGF-β signaling and glomerulosclerosis progression, indicating a protective role for ATOH8 in maintaining podocyte i 77 ntegrity and preventing kidney injury.

Epigenetic regulation through histone modifications plays a crucial role in driving cellular state transitions. Regulating gene transcription through bivalency, the co-occurrence of activating H3K4me3 and repressive H3K27me3 histone marks, drives cell fate in development; however, its role in kidney injury is not known. Here, we investigated bivalent gene activation in the adult male Mus musculus kidney following ischemia-reperfusion injury (IRI). We developed and validated a novel per-gene scoring method for identifying bivalent domains from CUT&RUN data. Our analysis revealed that bivalent genes in the mature kidney substantially overlap with known embryonic bivalent domains. Following IRI, a subset of bivalent genes became activated, defined by a loss of H3K27me3, enrichment of H3K4me3, and a corresponding increase in gene transcription. Activated bivalent genes were differentially expressed in kidney epithelial cells and strongly enriched for pathways involving inflammation and fibrosis. To uncover the regulatory mechanism associated with activated bivalent genes, we identified key transcription factors linking these genes which converged on the pioneer transcription factor Spi1 (PU.1). We demonstrated that Spi1 targets are differentially expressed in both mouse and human kidney epithelial cells after injury and preferentially depleted of H3K27me3 and gain H3K4me3 enrichment after IRI, supporting its role in mediating the epigenetic switch. Our findings reveal a common epigenetic mechanism where transcription factors, acting on bivalent chromatin, contribute to inflammatory and fibrotic responses to kidney injury. This suggests that the progression from acute to chronic kidney injury is an active, transcriptionally driven failure of repair that is epigenetically mediated by histone modifications.

We investigated the interplay between the mineralocorticoid aldosterone and a mutation mimicking Liddle syndrome in the control of the processing of the epithelia Na⁺ channel (ENaC) in mouse kidneys. Rates of processing were assessed by the appearance of the cleaved form of the γENaC subunit. Cleaved γENaC increased with decreasing dietary Na intake and with administration of aldosterone. Measurements taken from isolated tubules indicated that enhanced processing was similar in connecting tubules and in late distal convoluted tubules. In a mouse model with a truncated βENaC subunit (Liddle mice), levels of cleaved γENaC were similar in wild-type (WT) and Liddle animals. The amounts of the full-length form of the subunit were lower in the Liddle mice on control and high-Na diets. Infusion of a low dose of aldosterone produced similar increases in cleaved γENaC in WT and Liddle mice, while with maximal doses, levels in Liddle animals were 35% higher than in WT. Acute Na repletion of Na-depleted mice decreased cleaved γENaC with a time constant of 5 hours. Rates of decrease were similar in WT and Liddle genotypes. The Liddle's mutation produces modest changes in ENaC processing, and a major effect of the mutation is on the activation of processed channels.

Podocytes are highly specialized terminally differentiated visceral epithelial cells that are critical for the maintenance of the glomerular filtration barrier. In subtypes of glomerulonephritis and focal segmental glomerulosclerosis (FSGS), injured podocytes trigger the activation and proliferation of neighboring parietal epithelial cells (PECs) which line Bowman's capsule. Mechanisms by which injured podocytes trigger the activation of PECs remain poorly understood. In three independent murine models of proliferative glomerulopathy, we observed that rapid podocyte loss triggered the formation of novel intercellular bridges (or tunneling nanotubes) extending between podocytes and PECs. Immunofluorescence staining of a coculture of mouse podocytes and PECs also revealed the presence of vesicle-like structures within intercellular bridges. In addition, these vesicle-like structures stained positive for RAB11A, a RabGTPase involved in the regulation of vesicle transport, and cytoplasmic dynein 1 heavy chain 1, a critical motor protein involved in cargo transport. Finally, we identified intercellular bridges in human kidney biopsies with subtypes of glomerulonephritis and collapsing FSGS, suggesting relevance to human disease.

The Dahl Salt-Sensitive (SS) rat is an established model of hypertensive kidney injury, where the gut microbiota has been shown to causally contribute to disease progression. Gut bacteria-derived metabolites serve as mechanistic links between the microbiota and disease, with dietary fiber providing a critical source of protective metabolites such as short-chain fatty acids (SCFAs). The current study hypothesized that the substitution of non-fermentable fiber cellulose with the fermentable fiber inulin would attenuate hypertension and renal damage in SS rats via increased circulating SCFAs. Male and female SS rats were placed on the 0.4% NaCl (LS) inulin diet for one week prior to the switch to a 4.0% NaCl (HS) inulin diet for 4 weeks. Controls were maintained on diets containing cellulose. Rats consuming inulin had a reduction in mean arterial pressure (MAP) compared to cellulose, though the antihypertensive effect was more robust in females. The inulin diet significantly protected both sexes from albuminuria, medullary protein cast formation, and renal immune cell infiltration, and was associated with specific changes to the fecal microbiota. Assessed by mass spectrometry, inulin consumption resulted in increased circulating propionate and butyrate, and the administration of these SCFAs revealed a protective effect of propionate against salt-sensitive hypertension and kidney damage in males, which coincided with an expansion of renal T regulatory cells. In conclusion, substitution of cellulose for the fermentable fiber inulin lowered blood pressure and significantly attenuated salt-induced renal damage in both sexes, which may be attributed to greater production of the protective, anti-inflammatory SCFA propionate.