Distal Convoluted Tubule Cells Research Articles

Irisin mitigates salt-sensitive hypertension via regulating renal AMPK-Rac1 pathway

ABSTRACT Background Irisin, as a myokine, plays a protective role against cardiovascular disease, including myocardial infarction, atherosclerosis and hypertension. However, whether irisin attenuates salt-sensitive hypertension and the related underlying mechanisms is unknown. Methods Male Dahl salt-resistant (DSR) and Dahl salt-sensitive (DSS) (12 weeks) rats were fed a high salt diet (8% NaCl) with or without irisin treatment by intraperitoneal injection for 8 weeks. Results Compared with DSR rats, DSS rats showed higher systolic blood pressure (SBP), impaired natriuresis and diuresis and renal dysfunction. In addition, it was accompanied by downregulation of renal p-AMPKα and upregulation of renal RAC1 and nuclear mineralocorticoid receptor (MR). Irisin intervention could significantly up-regulated renal p-AMPKα level and down-regulated renal RAC1-MR signal, thereby improving renal sodium excretion and renal function, and ultimately reducing blood pressure in DSS rats. Ex vivo treatment with irisin reduced the expression of RAC1 and nuclear MR in primary renal distal convoluted tubule cells from DSS rats and the effects of irisin were abolished by cotreatment of compound C (AMPK inhibitor), indicating that the regulation of RAC1-MR signals by irisin depended on the activation of AMPK. Conclusions Irisin administration lowered salt-sensitive hypertension through regulating RAC1-MR signaling via activation of AMPK, which may be a promising therapeutic approach for salt-sensitive hypertension.

Single-Nucleus RNA Sequencing Reveals Loss of Distal Convoluted Tubule 1 Renal Tubules in HIV Viral Protein R Transgenic Mice

Hyponatremia and salt wasting is a common occurance in patients with HIV/AIDS, however, the understanding of its contributing factors is limited. HIV viral protein R (Vpr) contributes to HIV-associated nephropathy. To investigate the effects of Vpr on the distal tubules and on the expression level of the Slc12a3 gene, encoding the Na-Cl cotransporter, which is responsible for sodium reabsorption in distal nephron segments, single-nucleus RNA sequencing was performed on kidney cortices from three wild-type (WT) and three Vpr-transgenic (Vpr Tg) mice. The results showed that the percentage of distal convoluted tubule (DCT) cells was significantly lower in Vpr Tg mice compared with WT mice (P < 0.05), and that in Vpr Tg mice, Slc12a3 expression was not significantly different in DCT cells. The Pvalb+ DCT1 subcluster had fewer cells in Vpr Tg mice compared with WT mice (P < 0.01). Immunohistochemistry demonstrated fewer Slc12a3+Pvalb+ DCT1 segments in Vpr Tg mice. Differential gene expression analysis between Vpr Tg and WT in the DCT cluster showed downregulation of Ier3 gene, which is an inhibitor of apoptosis. The in vitro knockdown of Ier3 by siRNA transfection induced apoptosis in mouse DCT cells. These observations suggest that the salt-wasting effect of Vpr in Vpr Tg mice is likely mediated by Ier3 downregulation in DCT1 cells and loss of Slc12a3+Pvalb+ DCT1 segments.

Transcript Deconvolution Reveals Heterogeneous Cell Populations in Microdissected Nephron Segments of the Rat Kidney

Introduction: The kidney tubule comprises distinct segments with specialized epithelium, including proximal tubules (PT) subsegments S1, S2, and S3, descending (DTL) and ascending (ATL) thin limbs, thick ascending limb (TAL) medullary (MTAL) and cortical (CTAL) subsegments, distal convoluted tubule (DCT), connecting tubule (CNT), and collecting ducts (CD) containing principal (PC) and intercalated (IC) cells. Single-cell RNA sequencing (scRNAseq) is a crucial tool in kidney research. However, it assigns cells to nephron segments based on transcriptome similarity, disregarding anatomical context and spatial information, critical for kidney function. Hypothesis: We hypothesized that cellular deconvolution of microdissected tubule segment transcriptomes would identify mixed cell populations coexisting on different parts of the nephron. Methods: We employed CibersortX to estimate cell proportions in microdissected rat nephron segment transcriptomes (GSE56743), using rat kidney epithelial cell transcriptomes from a scRNAseq dataset (GSE137869) as reference. Raw sequencing files from the Sequence Read Archive (SRA) were downloaded and reprocessed. The number of detected genes was 34,322 for bulk RNAseq and 15,282 for scRNAseq, with a shared gene space of 13,373 used for deconvolution. Results: We discovered that PT.S1 segments primarily consist of S1 cells (81%) and some S2 cells (12%). Microdissected PT.S2 segments contain a mix of S1 (18%), S2 (58%), and S3 (19%) cells. PT.S3 segments were primarily composed of S3 cells (75%). DTL and ATL segments displayed a high percentage of the corresponding cell type. Microdissected MTAL segments were a mix of MTAL (25%) and CTAL (69%) cells, while microdissected CTAL segments were almost exclusively composed of MTAL cells (95%). DCT segments exhibited 80% DCT cells with some principal (2%) and intercalated (1%) cells. In CNT, CCD, and OMCD, we observed a continuous increase in PC abundance (58%, 72%, and 78%, respectively) along with a decrease in IC (32%, 23%, and 11%, respectively). Microdissected IMCD contained PC (58%), IC (4%), and 18% of a distinct cell type with IC characteristics not found in other segments. Conclusions: Our analysis supports the well-established cell heterogeneity in connecting tubules and the collecting duct system, including the existence of a specialized IMCD cell. Additionally, we identified mixed cell populations in the S2 segment of the proximal tubule and the medullary thick ascending limb. In the case of S2, the high proportion of cells from adjacent S1 and S3 segments suggests a differentiation continuum from S1 to S3 with diffused anatomical boundaries. We identified two different TAL cell types, the MTAL phenotype restricted to the MTAL and the CTAL phenotype present in higher abundance in both subsegments. These cell types may correspond to the medullary "rough surface" and cortical "smooth surface" cells described in rat TAL. In summary, the terminology used in scRNAseq cluster assignment referring to specific nephron segments is misleading, as it encompasses anatomical regions with multiple coexisting cell types. This highlights the need for caution when interpreting such data. This work was supported in part by CWRU BGT670107 and NIH-NIDDK DK128304 grants to AGV. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Epithelial Na+ Channel Is a Zn2+ Sensitive Renal Na+ Reabsorption Pathway that Mediates Zn2+ Deficiency-induced Hypertension

Background: Zinc (Zn2+) deficiency (ZnD) is comorbid with many chronic diseases including kidney disease and diabetes. Individuals in these vulnerable populations have a higher prevalence of hypertension. Recently, we reported that ZnD induces hypertension by promoting renal Na+ reabsorption. However, the renal Na+ reabsorption mechanisms involved continue to be identified. The renal epithelial Na+ channel (ENaC) plays an essential role in regulating whole-body Na+ and water balance and is involved in hypertension. We hypothesize that ENaC is a Zn2+-sensitive channel that mediates ZnD-induced hypertension. Experimental Design: To establish the role of ENaC in ZnD-induced hypertension, WT C57Bl/6 mice were switched from a Zn2+ adequate to a Zn2+ deficient diet for 10 weeks. During weeks 9 and 10, mice were treated with benzamil, an ENaC inhibitor. Systolic blood pressure (BP) was monitored by tail-cuff plethysmography; Renal ENaC expression was examined by immunohistochemistry and Western blot. To authenticate the Zn2+ sensitivity of ENaC, mouse distal convoluted tubule cells (mDCT) were treated with a Zn2+ chelator (TPEN) or vehicle (ethanol) for 24 hours. A subset of TPEN-treated cellular monolayers were supplemented with Zn2+ for 24 hours to replete intracellular Zn2+. Cellular ENaC expression was examined by Western blot analysis. Results: 1) Blood pressure: Compared to Zn2+ adequate mice (101.4 mm Hg ± 4.225), Zn2+ deficient mice had increased BP (154.6 mm Hg ± 2.422). However, benzamil treatment lowered BP (115.0 mm Hg ± 4.626) of Zn2+ deficient mice. 2)Immunohistochemistry: Next, Zn2+ effects on ENaC expression were examined. In Zn2+ deficient mice, αENaC protein abundance significantly increased compared with Zn2+ adequate mice. 3) Western blot analysis: To directly investigate Zn2+effects on ENaC expression, in vitro studies were performed using mDCT cells. Western blot analysis showed that TPEN-induced ZnD stimulated both αENaC and βENaC protein expression. Conclusion: Collectively, our findings reveal that (1) ENaC is a Zn2+ sensitive renal Na+ reabsorption pathway and (2) ENaC mediates ZnD-induced hypertension. Significance: Understanding the renal mechanisms by which Zn2+ regulates blood pressure may have an important therapeutic impact on hypertension. Funding: R21 DK119879, R01 DK-133698 (National Institute of Diabetes and Digestive and Kidney Diseases); R25DK078381 (NIH NIDDK STEP-UP program);1742339 (National Science Foundation ASK Program). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Comprehensive molecular and cellular characterization of endoplasmic reticulum stress-related key genes in renal ischemia/reperfusion injury.

Renal ischemia-reperfusion injury (RIRI) is an inevitable complication in the process of kidney transplantation and lacks specific therapy. The study aims to determine the underlying mechanisms of RIRI to uncover a promising target for efficient renoprotection. Four bulk RNA-seq datasets including 495 renal samples of pre- and post-reperfusion were collected from the GEO database. The machine learning algorithms were utilized to ascertain pivotal endoplasmic reticulum stress genes. Then, we incorporated correlation analysis and determined the interaction pathways of these key genes. Considering the heterogeneous nature of bulk-RNA analysis, the single-cell RNA-seq analysis was performed to investigate the mechanisms of key genes at the single-cell level. Besides, 4-PBA was applied to inhibit endoplasmic reticulum stress and hence validate the pathological role of these key genes in RIRI. Finally, three clinical datasets with transcriptomic profiles were used to assess the prognostic role of these key genes in renal allograft outcomes after RIRI. In the bulk-RNA analysis, endoplasmic reticulum stress was identified as the top enriched pathway and three endoplasmic reticulum stress-related genes (PPP1R15A, JUN, and ATF3) were ranked as top performers in both LASSO and Boruta analyses. The three genes were found to significantly interact with kidney injury-related pathways, including apoptosis, inflammatory response, oxidative stress, and pyroptosis. For oxidative stress, these genes were more strongly related to oxidative markers compared with antioxidant markers. In single-cell transcriptome, the three genes were primarily upregulated in endothelium, distal convoluted tubule cells, and collecting duct principal cells among 12 cell types of renal tissues in RIRI. Furthermore, distal convoluted tubule cells and collecting duct principal cells exhibited pro-inflammatory status and the highest pyroptosis levels, suggesting their potential as main effectors of three key genes for mediating RIRI-associated injuries. Importantly, inhibition of these key genes using 4-phenyl butyric acid alleviated functional and histological damage in a mouse RIRI model. Finally, the three genes demonstrated highly prognostic value in predicting graft survival outcomes. The study identified three key endoplasmic reticulum stress-related genes and demonstrated their prognostic value for graft survival, providing references for individualized clinical prevention and treatment of postoperative complications after renal transplantation.

Heterogeneity of Distal Convoluted Tubule Cells.

Heterogeneity of Distal Convoluted Tubule Cells.

Enriched Single-Nucleus RNA-Sequencing Reveals Unique Attributes of Distal Convoluted Tubule Cells.

High-resolution single-nucleus RNA-sequencing data indicate a clear separation between primary sites of calcium and magnesium handling within distal convoluted tubule (DCT). Both DCT1 and DCT2 express Slc12a3, but these subsegments serve distinctive functions, with more abundant magnesium-handling genes along DCT1 and more calcium-handling genes along DCT2. The data also provide insight into the plasticity of the distal nephron-collecting duct junction, formed from cells of separate embryonic origins. By focusing/changing gradients of gene expression, the DCT can morph into different physiological cell states on demand. The distal convoluted tubule (DCT) comprises two subsegments, DCT1 and DCT2, with different functional and molecular characteristics. The functional and molecular distinction between these segments, however, has been controversial. To understand the heterogeneity within the DCT population with better clarity, we enriched for DCT nuclei by using a mouse line combining "Isolation of Nuclei Tagged in specific Cell Types" and sodium chloride cotransporter-driven inducible Cre recombinase. We sorted the fluorescently labeled DCT nuclei using Fluorescence-Activated Nucleus Sorting and performed single-nucleus transcriptomics. Among 25,183 DCT cells, 75% were from DCT1 and 25% were from DCT2. In addition, there was a small population (<1%) enriched in proliferation-related genes, such as Top2a , Cenpp , and Mki67 . Although both DCT1 and DCT2 expressed sodium chloride cotransporter, magnesium transport genes were predominantly expressed along DCT1, whereas calcium, electrogenic sodium, and potassium transport genes were more abundant along DCT2. The transition between these two segments was gradual, with a transitional zone in which DCT1 and DCT2 cells were interspersed. The expression of the homeobox genes by DCT cells suggests that they develop along different trajectories. Transcriptomic analysis of an enriched rare cell population using a genetically targeted approach clarifies the function and classification of distal cells. The DCT segment is short, can be separated into two subsegments that serve distinct functions, and is speculated to derive from different origins during development.

Single-cell RNA-seq analysis decodes the kidney microenvironment induced by polystyrene microplastics in mice receiving a high-fat diet

In recent years, the environmental health issue of microplastics has aroused an increasingly significant concern. Some studies suggested that exposure to polystyrene microplastics (PS-MPs) may lead to renal inflammation and oxidative stress in animals. However, little is known about the essential effects of PS-MPs with high-fat diet (HFD) on renal development and microenvironment. In this study, we provided the single-cell transcriptomic landscape of the kidney microenvironment induced by PS-MPs and HFD in mouse models by unbiased single-cell RNA sequencing (scRNA-seq). The kidney injury cell atlases in mice were evaluated after continued PS-MPs exposure, or HFD treated for 35 days. Results showed that PS-MPs plus HFD treatment aggravated the kidney injury and profibrotic microenvironment, reshaping mouse kidney cellular components. First, we found that PS-MPs plus HFD treatment acted on extracellular matrix organization of renal epithelial cells, specifically the proximal and distal convoluted tubule cells, to inhibit renal development and induce ROS-driven carcinogenesis. Second, PS-MPs plus HFD treatment induced activated PI3K-Akt, MAPK, and IL-17 signaling pathways in endothelial cells. Besides, PS-MPs plus HFD treatment markedly increased the proportions of CD8+ effector T cells and proliferating T cells. Notably, mononuclear phagocytes exhibited substantial remodeling and enriched in oxidative phosphorylation and chemical carcinogenesis pathways after PS-MPs plus HFD treatment, typified by alterations tissue-resident M2-like PF4+ macrophages. Multispectral immunofluorescence and immunohistochemistry identified PF4+ macrophages in clear cell renal cell carcinoma (ccRCC) and adjacent normal tissues, indicating that activate PF4+ macrophages might regulate the profibrotic and pro-tumorigenic microenvironment after renal injury. In conclusion, this study first systematically revealed molecular variation of renal cells and immune cells in mice kidney microenvironment induced by PS-MPs and HFD with the scRNA-seq approach, which provided a molecular basis for decoding the effects of PS-MPs on genitourinary injury and understanding their potential profibrotic and carcinogenesis in mammals.Graphical

Single-cell transcriptomics and chromatin accessibility profiling elucidate the kidney-protective mechanism of mineralocorticoid receptor antagonists.

Mineralocorticoid excess commonly leads to hypertension (HTN) and kidney disease. In our study, we used single-cell expression and chromatin accessibility tools to characterize the mineralocorticoid target genes and cell types. We demonstrated that mineralocorticoid effects were established through open chromatin and target gene expression, primarily in principal and connecting tubule cells and, to a lesser extent, in segments of the distal convoluted tubule cells. We examined the kidney-protective effects of steroidal and nonsteroidal mineralocorticoid antagonists (MRAs), as well as of amiloride, an epithelial sodium channel inhibitor, in a rat model of deoxycorticosterone acetate, unilateral nephrectomy, and high-salt consumption-induced HTN and cardiorenal damage. All antihypertensive therapies protected against cardiorenal damage. However, finerenone was particularly effective in reducing albuminuria and improving gene expression changes in podocytes and proximal tubule cells, even with an equivalent reduction in blood pressure. We noted a strong correlation between the accumulation of injured/profibrotic tubule cells expressing secreted posphoprotein 1 (Spp1), Il34, and platelet-derived growth factor subunit b (Pdgfb) and the degree of fibrosis in rat kidneys. This gene signature also showed a potential for classifying human kidney samples. Our multiomics approach provides fresh insights into the possible mechanisms underlying HTN-associated kidney disease, the target cell types, the protective effects of steroidal and nonsteroidal MRAs, and amiloride.

MiR-125a-5p/miR-125b-5p contributes to pathological activation of angiotensin II-AT1R in mouse distal convoluted tubule cells by the suppression of Atrap

The renin-angiotensin system plays a crucial role in the regulation of blood pressure. Activation of the angiotensin II (Ang II)-Ang II type 1 receptor (AT1R) signaling pathway contributes to the pathogenesis of hypertension and subsequent organ damage. AT1R-associated protein (ATRAP) has been identified as an endogenous inhibitory protein of the AT1R pathological activation. We have shown that mouse Atrap (Atrap) represses various Ang II-AT1R-mediated pathologies, including hypertension in mice. The expression of human ATRAP (ATRAP)/Atrap can be altered in various pathological states in humans and mice, such as Ang II stimulation and serum starvation. However, the regulatory mechanisms of ATRAP/Atrap are not yet fully elucidated. miRNAs are 21 to 23 nucleotides of small RNAs that post-transcriptionally repress gene expression. Single miRNA can act on hundreds of target mRNAs, and numerous miRNAs have been identified as the Ang II-AT1R signaling-associated disease phenotype modulator, but nothing is known about the regulation of ATRAP/Atrap. In the present study, we identified miR-125a-5p/miR-125b-5p as the evolutionarily conserved miRNAs that potentially act on ATRAP/Atrap mRNA. Further analysis revealed that miR-125a-5p/miR-125b-5p can directly repress both ATRAP and Atrap. In addition, the inhibition of miR-125a-5p/miR-125b-5p resulted in the suppression of the Ang II-AT1R signaling in mouse distal convoluted tubule cells. Taken together, miR-125a-5p/miR-125b-5p activates Ang II-AT1R signaling by the suppression of ATRAP/Atrap. Our results provide new insights into the potential approaches for achieving the organ-protective effects by the repression of the miR-125 family associated with the enhancement of ATRAP/Atrap expression.

Early Transcriptional Changes in Distal Convoluted Tubule Cells Are Evident in PKD1 (Polycystin 1) Mutant Mice Prior to Cyst Development

Early Transcriptional Changes in Distal Convoluted Tubule Cells Are Evident in PKD1 (Polycystin 1) Mutant Mice Prior to Cyst Development

Proteomic Profiling of a Novel Immortalised Human Distal Convoluted Tubule Cell Line

Proteomic Profiling of a Novel Immortalised Human Distal Convoluted Tubule Cell Line

Analysis of distal convoluted tubule (DCT) cell de-differentiation due to COP9 signalosome (CSN) dysfunction via enriched DCT single-nucleus RNA-sequencing

Cullin-RING-ligases (CRLs) are a group of E3 ubiquitin ligases that mediate the regulated degradation of proteins. All CRLs are regulated by the COP9 signalosome (CSN), which interacts with the CRL and turns off ubiquitin ligase activity. To investigate the role of impaired CSN dysfunction in the kidney, we inactivated the CSN by deleting Jab1 (the key CSN catalytic subunit) along the entire nephron. Even though the CSN is expressed all along the nephron, these mice showed remodeling only along the distal nephron, with shortening of the distal convoluted tubule (DCT) and a large reduction in DCT-specific proteins. The DCT is known to remodel due to changes in dietary salt intaked, drug administration, and human disease. Yet, the cellular and molecular basis for this plasticity is unclear. We hypothesized that CSN dysfunction causes de-differentiation of DCT cells leading to DCT remodeling. To test our hypothesis, inducible DCT-specific NCC-Cre-ERT2 mice were bred to INTACT (Isolation of Nuclei TAgged in specific Cell Types, which fluorescently labels nuclei) and Jab1 floxed mice to generate DCT-INTACT- Jab1 -/- mice. One adult male DCT-INTACT- Jab1 -/- mouse and one DCT-INTACT control mouse were treated with tamoxifen to induce nuclear GFP expression and to induce deletion of Jab1 only in DCT cells. Six-weeks post treatment, nuclei from one kidney cortex was isolated and the DCT was enriched using Fluorescence-Activated Nuclei Sorting (FANS). GFP-positive nuclei were used for single-nucleus RNA-sequencing (NovaSeq). Initial results showed that unbiased clustering and UMAP visualization revealed 7 clusters with most cells from the DCT (99.0% for control and 97.6% for Jab1 -/- mice), indicating that the enrichment process was highly successful. Both the control and Jab1 -/- mouse had similar proportions of DCT1 and DCT2 cells; however, we identified two specialized cell types (dDCT1 and dDCT2) which comprised a much larger proportion of the cells in the Jab1 -/- mouse (dDCT1: 2.9% in control vs 41.1% in Jab1 -/- ; dDCT2: 2.0% in control vs 13.9% in Jab1 -/- ). These cells were highly de-differentiated with lower expression of the canonical DCT identifier genes such as Egf and Umod for DCT1, Calb1 and S100g for DCT2, as well as Slc12a3. Both dDCT1 and dDCT2 cell populations had induced expression of the disease- or carcinoma-related genes Ano3, Nrg1, and Pvt1. In conclusion, Jab1 deletion causes de-differentiation of a population of DCT cells. Further examination of CSN dysfunction via DCT-enriched single-nucleus RNA-sequencing could lead to a better understanding of the molecular mechanisms involved in DCT remodeling. NIH K01DK120790, NIH R01DK51496, Foundation LeDucq: Transatlantic Network of Excellence 17CVD05 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

FBLN2 Abates Epigenetic-mediated Salt-sensitive Hypertension Through Regulation of NCC Trafficking

Epigenetics play a role in the development of hypertension. However, the precise mechanisms of how histone modification in renal tubule cells regulates blood pressure is largely undiscovered. In this study, we investigated the role of renal Kdm6a in salt-sensitive hypertension using a kidney tubular cell-specific Kdm6a gene knockout (Kdm6a cKO) mouse model. First, we demonstrated that knockout of Kdm6a in the renal tubular cells resulted in an increase of H3K27me3 associated with the development of hypertension in both male and female Kdm6a cKO mice. To explore the mechanism of H3K27me3-mediated hypertension, we performed a ChIP seq to identify the target genes of H3K27me3 in the renal tubular cells. Data showed that H3K27me3 regulated several physiological pathways in the renal tubular cells, including sodium transport in proximal convoluted tubule (PCT), and blood pressure regulation in distal convoluted tubule (DCT). Indeed, we found that the expressions of NCC, NKCC2, and AQP2 were upregulated in kidneys of Kdm6a cKO mice. Furthermore, ChIP seq data reveals that FBLN2, an extracellular matrix protein, appears to be a target of H3K27me3, which was downregulated in the kidney of Kdm6a cKO mice determined by real-time PCR, Western, and IHC. Notably, we demonstrated that FBLN2 abated high salt-induced hypertension through downregulation of NCC, NKCC2, and AQP2 in the tubular cells of Kdm6a cKO mice. Interestingly, pre-treatment of FBLN2 prevented salt-sensitive hypertension in these mice. Additionally, we have provided evidence that FBLN2 may regulate blood pressure through mediating the NCC cell membrane trafficking. Using a super high-resolution microscopy, we demonstrated that FBLN2 reduced levels of cell surface NCC in DCT cells cultured in hypotonic medium. Here, we have first demonstrated that FBLN2 may be a target gene of H3K27me3 in epigenetic-mediated hypertension. FBLN2 treatment may prevent and treat salt-sensitive hypertension. NIH This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Resolving the thiazide-induced hypocalciuria conundrum using single cell transcriptomics

Thiazide diuretics lower urinary calcium excretion and are used to prevent calcium stone recurrence. Thiazides inhibit the NaCl cotransporter (NCC) in the distal convoluted tubule (DCT). Hypocalciuria also occurs in Gitelman syndrome, caused by mutations in SLC12A3, encoding NCC. The mechanism by which loss of NCC function affects calcium handling remains very controversial. The two prevailing hypotheses invoked are 1) hypocalciuria results from volume-dependent increases in proximal tubule reabsorption; 2) thiazides activate calcium reabsorption along the DCT. Here we combined single nucleus RNA sequencing with physiologic analysis to unravel the causes of hypocalciuria.Eight to 10-week old male mice were given 50 mg/kg/day metolazone (MTZ) orally in food for 4 days. Littermates receiving only vehicle were used as controls. As DCT cells comprise a small percentage of the kidney mass, we used the NCC-Cre +/- - INTACT +/- mouse line to enrich for DCT via Cre-dependent GFP expression in DCT nuclei. After nuclei isolation, GFP+ events (DCT nuclei) were enriched by fluorescence assisted nuclei sorting. The purified DCT nuclei were sequenced using 10X Chromium controller. Reads were then analyzed using a standard transcriptomic bioinformatics pipeline with Seurat.The MTZ-treated mice showed lower urinary calcium excretion compared to controls recapitulating thiazide-induced hypocalciuria. Our snRNAseq integrated dataset contained 51,876 mapped genes across 45,953 samples from 3 MTZ-treated and 3 control mice. Roughly 99% of the nuclei were singlets expressing Slc12a3 showing successful enrichment for the DCT. Dimensional reduction analysis and projection confirmed two clusters, DCT1 and DCT2, based on canonical segment markers consistent with previously published transcriptomic atlases. Gene expression analysis showed the DCT2 contained a calcium cassette consisting of the known calciotropic genes Trpv5, Calb1, S100g, Slc8a1, Ryr2, Vdr, Casr, and Atp2b1. These genes were also expressed in the connecting tubule (CNT), as documented using the Calb1-Cre-INTACT system. From this set of genes, we defined a calcium score computed from the pooled average expression of all these genes in a single cell. Although all calcium cassette genes, and the average calcium score, were lower in the MTZ-treated group, the proportion of DCT2/DCT1 cells increased (0.27 ± 0.03 vs 0.35 ± 0.03; p = 0.027). These data suggest that lower calcium delivery to the DCT reduces calcium cassette expression per cell, but that distal fractional reabsorption is nonetheless increased owing to hypertrophy and elongation of the calcium transporting segments, DCT2 and CNT.We propose a modified mechanism to account for thiazide -induced hypocalciuria: 1) volume-dependent increase in proximal tubule reabsorption; 2) increased fractional (not absolute) DCT2 reabsorption owing to structural remodeling of DCT2 and CNT providing more surface area for calcium reabsorption. Funding: NIH DK51496, NIH DK054983, VA 1I01BX002228, LeDucq Foundation, DOST-PCHRD-ASTHRDP This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Renal CD81 interacts with sodium potassium 2 chloride cotransporter and sodium chloride cotransporter in rats with lipopolysaccharide-induced preeclampsia.

The kidney regulates blood pressure through salt/water reabsorption affected by tubular sodium transporters. Expanding our prior research on placental cluster of differentiation 81 (CD81), this study explores the interaction of renal CD81 with sodium transporters in preeclampsia (PE). Effects of renal CD81 with sodium transporters were determined in lipopolysaccharide (LPS)-induced PE rats and immortalized mouse renal distal convoluted tubule cells. Urinary exosomal CD81, sodium potassium 2 chloride cotransporter (NKCC2), and sodium chloride cotransporter (NCC) were measured in PE patients. LPS-PE rats had hypertension from gestational days (GD) 6 to 18 and proteinuria from GD9 to GD18. Urinary CD81 in both groups tented to rise during pregnancy. Renal CD81, not sodium transporters, was higher in LPS-PE than controls on GD14. On GD18, LPS-PE rats exhibited higher CD81 in kidneys and urine exosomes, higher renal total and phosphorylated renal NKCC2 and NCC with elevated mRNAs, and lower ubiquitinated NCC than controls. CD81 was co-immunoprecipitated with NKCC2 or NCC in kidney homogenates and co-immunostained with NKCC2 or NCC in apical membranes of renal tubules. In plasma membrane fractions, LPS-PE rats had greater amounts of CD81, NKCC2, and NCC than controls with enhanced co-immunoprecipitations of CD81 with NKCC2 or NCC. In renal distal convoluted tubule cells, silencing CD81 with siRNA inhibited NCC and prevented LPS-induced NCC elevation. Further, PE patients had higher CD81 in original urines, urine exosomes and higher NKCC2 and NCC in urine exosomes than controls. Thus, the upregulation of renal CD81 on NKCC2 and NCC may contribute to the sustained hypertension observed in LPS-PE model. Urine CD81 with NKCC2 and NCC may be used as biomarkers for PE.

S-27-6: ADAPTIVE IMMUNITY REGULATES RENAL SALT-RETENTION AND BLOOD PRESSURE

Hypertension is a major public health problem, which contributes to a plethora of other cardiovascular diseases. A long-time postulate is that a defect in the kidney plays a key role in the development of hypertension. Years of intense research have confirmed that distal nephron plays important role in excessive salt retention, which contributes to the pathogenesis of hypertension. Yet the precise identity of this kidney defect and the downstream signaling mechanisms that impair sodium handling remain unclear. In the past decade, T cells, in particular CD8+ T cells (CD8Ts), have garnered attention as an important contributor to hypertension. T cells infiltrate into the kidneys of hypertensive animals, possibly driven by elevated perfusion pressure. Subsequently elevation of blood pressure and salt content stimulate T cell-activation and cytokine production. We recently reported a new mechanism by which renal infiltrated CD8Ts contribute to salt retention and hypertension: CD8Ts upregulate the sodium-chloride cotransporter (NCC) in the renal distal tubules, resulting in excessive salt retention via direct interactions between CD8Ts and renal distal convoluted tubule cells (DCTs) (Image in enclosed figure). This finding raises the exciting prospect that kidney-accumulation of CD8Ts and their interactions with DCTs represent one kidney defect in the pathogenesis of salt-sensitive hypertension. Although blocking NCC using thiazide temporarily lowered blood pressure in hypertensive animals, it failed to diminish T cell-homing to the kidneys, and hypertension returned after withdrawal of thiazide. Thus, in order to design effective therapeutics for salt-sensitive hypertension which interrupt the initial stimuli that trigger renal sodium retention, it is critical for us to define mechanisms of T cell-homing to the kidney and identify the key molecules mediating the CD8T-DCT interaction. Here, we further identified critical molecular players and demonstrated their roles in augmenting the CD8T-DCT interaction leading to salt-sensitive hypertension. We found that activated CD8Ts exhibit enhanced interaction with DCTs via IFNγ-induced upregulation of MHC-I and PDL1 in DCTs, thereby stimulating higher expression of NCC in DCTs to cause excessive salt retention and progressive elevation of blood pressure. Eliminating IFNγ or renal tubule-specific knockdown of PDL1 prevented T cell homing into the kidney, thereby attenuating hypertension in two different mouse models. These findings provide a new mechanism for T cell involvement in the pathogenesis of hypertension and reveal novel therapeutic targets.

Abstract 15468: Cd81 Interacts With Sodium Chloride Cotransporter in Lps-Induced Preeclampsia Rats and in Cultured Mouse Renal Distal Convoluted Tubule Cells

Kidney regulates blood pressure mainly through salt/water reabsorption affected by sodium transport proteins along nephron. We have reported that placental CD81 plays an important role in the pathogenesis of preelampsia. In order to explore the connection between CD81 and renal sodium transport proteins in preelampsia, we studied their interactions in vivo and in vitro. On the gestation day 18 of lipopolysaccharide-induced preeclamsia model rats with hypertension and albuminuria, the renal protein abundances of NKCC2 (150±14,% of control, n=5-6/group, mean±SE, t-test, same as below), p-NKCC2(567±70%), NCC (254±41) and WNK4 (196±12) were increased together with an increase of CD81 in kidney (225±46) and urinary exosomes(396±100). Renal NCC (215±30) was elevated while NKCC2 tended to increase at 17000g pellet in LPS group. There was no change of both NKCC2 and NCC at 200,000g pellet. In kidney homogenates, CD81 was coimmunoprecipitated with NKCC2, NCC, not NHE3 while NKCC2, NCC were coimmunoprecipitated with CD81 not CD63. In renal plasma-membrane-enriched fraction NCC, not NKCC2, was also increased in preeclampsia rats. In the apical membrane of renal tubules CD81 was colocalized with NCC while minimum colocalization was found between CD81 and NKCC2. In cultured mouse distal convoluted tubule cells, CD81 was colocalized with NCC while CD81 deletion with siRNA decreased NCC and partially reversed lipopolysaccharide-induced increase of NCC. Furthermore, CD81 was detected only in the urinary exosomes from preeclampsia patients along with increases in NKCC2 (6063±811) and NCC(1085±191)relative to normal pregnant women (n=6/group, t-test). Those findings suggest that CD81 interacts with renal NCC in vivo and in vitro and the increase of renal CD81 may up-regulate NCC, possibly NKCC2 as well, and contribute to the increased blood pressure in preeclampsia.

Phenotypic Characterisation of Novel Immortalised Human Distal Convoluted Tubule Cells

Phenotypic Characterisation of Novel Immortalised Human Distal Convoluted Tubule Cells

Abstract 071: Hypertension Rewrites The Kidney Transcriptome And Drives Nephropathy

Hypertensive nephropathy is a commonly diagnosed form of chronic kidney disease (CKD), but the biological processes underlying disease initiation are poorly understood. Here, we explore if non-malignant hypertension (HTN) is sufficient to initiate kidney damage and seek to identify pathways that drive disease development. We created a genetically defined hypertensive mouse by introducing activating mutations in the Ste20p-related proline alanine-rich kinase (SPAK) that are solely expressed in distal convoluted tubule cells. These constitutively active SPAK mice (CA-SPAK) develop salt-sensitive HTN due to hyperactivation of the thiazide-sensitive sodium chloride cotransporter (NCC). For these studies, CA-SPAK and control mice were fed either control salt (0.74% NaCl, CSD) or high salt diets (2% NaCl, HSD) for 24 weeks, and renal function and blood pressure were evaluated. RNASeq was performed to assess changes in the kidney transcriptional profile, the results of which were used for pathway enrichment analysis. CA-SPAK mice fed CSD develop HTN and show declining renal function starting at 26 weeks old and progresses over the next 10 weeks until they develop azotemia (BUN 30.8 vs 21.5 mg/dl; PCr - 0.42 vs 0.25 mg/dl, n=8) and albuminuria (5.2 vs 1.8 mg/day; n=8). HSD exacerbates HTN in CA-SPAK and initiates the same decline of renal function after only 8 weeks (20 weeks old). To identify changes in renal gene expression associated with the onset of function decline, we performed RNASeq on cortical tissue from both genotypes fed HSD for 8 weeks. We identified 3568 deferentially expressed genes in CA-SPAK. Pathway enrichment analysis found 3 biological processes associated with the early decline in CA-SPAK renal function that includes alterations of the filtration barrier (e.g. decreased nephrin, podocalyxin, synaptopodin, CD2AP, collagen 4a3, laminin B2), albuminuria associated genes (e.g. decreased cubilin, megalin, mucin 1), and immune system activation (e.g. increased MHC class II, T and B lymphocytes markers). Our findings from CA-SPAK mice demonstrate that non-malignant HTN can induce altered renal gene expression, the consequence of which is sufficient to disrupt kidney function resulting in the onset of hypertensive nephropathy.