American journal of physiology. Renal physiology最新文献

Biological sex significantly influences disease presentation, progression, and therapeutic outcomes in chronic kidney disease and acute kidney injury. Sex hormones, including estrogen and testosterone, modulate key renal functions, including renal blood flow, glomerular filtration, and electrolyte transport, thereby affecting disease trajectory in a sex-specific manner. It is critical for researchers to understand why and how to integrate sex as a biological variable in data collection, analysis, and reporting. Integrating a sex-based perspective in kidney research will lead to more personalized and efficacious treatment strategies, optimizing therapeutic interventions for each sex. If addressed properly, the incorporation of sex as a biological variable (SABV) in renal research not only enhances the mechanistic understanding of renal disease, but also paves the way for precision medicine, promising improved clinical outcomes, and tailored treatment protocols for all patients. This paper is designed to serve as a guideline for researchers interested in rigorously incorporating sex as a biological variable in their studies.

The maintenance of fluid and electrolyte homeostasis by the kidney requires proper folding and trafficking of ion channels and transporters in kidney epithelia. Each of these processes requires a specific subset of a diverse class of proteins termed molecular chaperones. One such chaperone is GRP170, which is an Hsp70-like, endoplasmic reticulum (ER)-localized chaperone that plays roles in protein quality control and protein folding in the ER. We previously determined that loss of GRP170 in the mouse nephron leads to hypovolemia, electrolyte imbalance, and rapid weight loss. In addition, GRP170-deficient mice develop an acute kidney injury (AKI)-like phenotype, typified by tubular injury, elevation of kidney injury markers, and induction of the unfolded protein response (UPR). By using an inducible GRP170 knockout cellular model, we confirmed that GRP170 depletion induces the UPR, triggers apoptosis, and disrupts protein homeostasis. Based on these data, we hypothesized that UPR induction underlies hyponatremia and volume depletion in these rodents and that these and other phenotypes might be rectified by sodium supplementation. To test this hypothesis, control and GRP170 tubule-specific knockout mice were provided a diet containing 8% sodium chloride. We discovered that sodium supplementation improved electrolyte imbalance and kidney injury markers in a sex-specific manner but was unable to restore weight or tubule integrity. These results are consistent with UPR induction contributing to the kidney injury phenotype in the nephron-specific GR170 knockout model and indicate that GRP170 function in kidney epithelia is essential to both maintain electrolyte balance and ER homeostasis.NEW & NOTEWORTHY Loss of the endoplasmic reticulum chaperone, GRP170, results in widespread kidney injury and induction of the unfolded protein response (UPR). We now show that sodium supplementation is able to at least partially restore electrolyte imbalance and reduce kidney injury markers in a sex-dependent manner.

Approximately 30% of the patients with cancer experience kidney complications, which hinder optimal cancer management, imposing a burden on patients' quality of life and the healthcare system. The etiology of kidney complications in patients with cancer is often attributed to oncological therapies. However, the direct impact of cancer on kidney health is underestimated. Our previous study demonstrated that metastatic lung cancer adversely alters the kidney and exacerbates chemotherapy-induced nephrotoxicity, indicating lung cancer-kidney crosstalk. The current study examines whether this phenomenon is specific to the employed cancer model. Female and male mice of various strains were injected with different cell lines of remote organ cancer, and their kidney tissues were analyzed for toxicity and fibrosis. The impact of cancer on the kidney varied by cancer type. Breast cancer and specific subtypes of lung cancer, including KRAS- and epidermal growth factor receptor (EGFR)-mutant cancer, pathologically altered kidney physiology and function in a manner dependent on the metastatic potential of the cell line. This was independent of mouse strain, sex, and cancer cell line origin. Moreover, tumor DNA was not detected in the renal tissue, excluding metastases to the kidney as a causative factor for the observed pathological alterations. Lewis lung carcinoma and B16 melanoma did not cause nephrotoxicity, regardless of the tumor size. Our results confirm cancer-kidney crosstalk in specific cancer types. In the era of precision medicine, further research is essential to identify at-risk oncology populations, enabling early detection and management of renal complications.NEW & NOTEWORTHY Patients with cancer frequently experience kidney complications, often attributed to antineoplastic therapies. This emphasis on therapy-induced nephrotoxicity has led to the underestimation of the impact of cancer on the kidney. Our study demonstrates that distant organ cancer is sufficient to induce nephrotoxicity, highlighting the existence of cancer-kidney crosstalk. Our findings underscore a gap in our understanding of renal complications in patients with cancer and provide a rationale for identifying the underlying mechanisms for the development of nephroprotective agents.

Epithelial sodium channel (ENaC) represents a major route of Na⁺ reabsorption in the aldosterone-sensitive distal nephron where the bulk of ENaC activity is considered to occur in the cortical collecting duct (CCD). Relatively, ENaC activity in the medulla, especially the inner medulla, is often neglected. (Pro)renin receptor (PRR), also termed ATP6ap2, a newly characterized member of the renin-angiotensin system, has emerged as an important regulator of ENaC in the distal nephron. The ENaC regulatory action of PRR is largely mediated by the 28 kDa soluble PRR (sPRR). Although all three subunits of ENaC are under the control of aldosterone, sPRR only mediates the upregulation of α-ENaC but not the other two subunits. Furthermore, sPRR-dependent regulation of α-ENaC only occurs in the renal inner medulla but not in the cortex. sPRR also rapidly upregulates ENaC activity via Nox4-derived H₂O₂. Overall, sPRR has emerged as an important regulator of renal medullary Na⁺ reabsorption in the context of overactivation of the renin-angiotensin-aldosterone system.

Why fibroblast growth factor 23 (FGF23) levels increase markedly in chronic kidney disease (CKD) is unknown. Recently, we found that phosphate stimulates renal production of glycerol-3-phosphate (G-3-P), which circulates to the bone to trigger FGF23 production. To assess the impact of G-3-P on FGF23 production in CKD, we compared the effect of adenine-induced CKD in mice deficient in glycerol-3-phosphate dehydrogenase 1 (Gpd1), an enzyme that synthesizes G-3-P, along with wild-type littermates. We found that an adenine diet causes a similar degree of renal insufficiency across genotypes and that adenine-induced CKD increases blood G-3-P and FGF23 levels in wild-type mice. Furthermore, we found that the increases in both G-3-P and FGF23 are significantly attenuated, but not fully abrogated, in Gpd1^-/- compared with Gpd1^+/+ mice with CKD. There is no difference in blood phosphate or parathyroid hormone between Gpd1^-/- and Gpd1^+/+ mice on an adenine diet, but adenine-induced CKD causes greater cortical bone loss in Gpd1^-/- mice. In a separate cohort of rats fed an adenine or control diet, we confirmed that CKD causes an increase in blood G-3-P levels. Importantly, an acute phosphate load increases G-3-P production in both CKD and non-CKD rats, with a significant correlation between measured kidney phosphate uptake and blood G-3-P levels. Together, these findings establish a key role for G-3-P in mineral metabolism in CKD, although more work is required to parse the factors that regulate both Gpd1-dependent and Gpd1-independent G-3-P production in this context.NEW & NOTEWORTHY This study shows that glycerol-3-phosphate, a glycolytic by-product recently implicated in a kidney-to-bone signaling axis that regulates FGF23 production, increases in mice and rats with CKD. Furthermore, mice deficient in a key enzyme that synthesizes glycerol-3-phosphate have attenuated increases in both glycerol-3-phosphate and FGF23 in CKD, along with enhanced cortical bone loss. These studies identify glycerol-3-phosphate as a novel regulator of FGF23 and mineral metabolism in CKD.

Glomerular endothelial cell (GEnC) injury is a common feature across the wide spectrum of glomerular diseases. We recently reported that the endothelial-specific knockout of Krüppel-like factor 4 (Klf4) increases the susceptibility to GEnC injury and subsequent development of subacute thrombotic microangiopathy (TMA). However, the mechanism(s) mediating GEnCs response to injury in TMA are poorly understood. Single-nucleus RNA-sequencing demonstrated enrichment in pathways involved in angiogenesis, permeability, focal adhesion, dedifferentiation, and cytoskeletal organization in the endothelial cluster in mice with TMA. Plasmalemmal vesicle-associated protein (Plvap), a structural component of fenestral diaphragms, was highly enriched specifically in injured GEnCs. Induction of Plvap in cultured GEnCs increased proliferation, migration, and cell permeability with an accompanying loss of mature GEnC markers. Immunostaining for PLVAP in human kidney biopsies confirmed the increase in glomerular PLVAP in TMA, which correlated with a higher grade of glomerular injury. To date, this is the first study to show that the induction of Plvap in GEnCs shifts the cells to an immature state, which might exacerbate glomerular injury in TMA.NEW & NOTEWORTHY This study investigated the mechanism(s) underlying glomerular endothelial cell (GEnC) injury in thrombotic microangiopathy (TMA). We identified plasmalemmal vesicle-associated protein (PLVAP) as specifically upregulated in injured GEnCs in TMA, which was accompanied by pathways involved in angiogenesis and loss of differentiation. Induction of Plvap increased proliferation and migration of GEnCs. Human kidney biopsies with TMA demonstrated an increase in glomerular PLVAP, which correlated with histological markers of GEnC injury, confirming its pathologic role in TMA.

Kir5.1 encoded by Kcnj16 is an inwardly rectifying K⁺ channel subunit, and it possibly interacts with Kir4.2 subunit encoded by Kcnj15 for assembling a Kir4.2/Kir5.1 heterotetramer in the basolateral membrane of mouse proximal tubule. We now used patch clamp technique to examine basolateral K⁺ channels of mouse proximal tubule (PT) and an immunoblotting/immunofluorescence (IF) staining microscope to examine Kir4.2 expression in wild-type and Kir5.1-knockout mice. IF staining shows that Kir4.2 was exclusively expressed in the proximal tubule, whereas Kir5.1 was expressed in the proximal tubule and distal nephrons including distal convoluted tubule. Immunoblotting showed that the expression of Kir4.2 monomer was lower in Kir5.1-knockout mice than that in the wild-type mice. In contrast, Kir4.1 monomer expression was increased in Kir5.1 knockout mice. IF images further demonstrated that the basolateral membrane staining of Kir4.2 was significantly decreased in Kir5.1 knockout mice. This is in sharp contrast to Kir4.1, which also interacts with Kir5.1 in the distal nephron, and IF images show that Kir4.1 membrane expression was still visible and unchanged in Kir5.1 knockout mice. The single channel recording detected a 50-pS inwardly rectifying K⁺ channel, presumably a Kir4.2/Kir5.1 heterotetramer, in the basolateral membrane of the proximal tubule of Kir5.1 wild-type mice. However, this 50-pS K⁺ channel was completely absent in the basolateral membrane of the proximal tubule of Kir5.1 knockout mice. Moreover, the membrane potential of the proximal tubule was less negative in Kir5.1 knockout mice than wild-type mice. We conclude that Kir5.1 is essential for assembling basolateral 50-pS K⁺ channel in proximal tubule and that deletion of Kir5.1 decreased Kir4.2 expression in the proximal tubule thereby decreasing the basolateral K⁺ conductance and the membrane potentials.NEW & NOTEWORTHY Our study provides direct evidence for the notion that Kir5.1 is a key component of a 50-60 pS inwardly-rectifying-K⁺ channel, a main type K⁺ channel in the basolateral-membrane of PT. Also, we demonstrate that deletion of Kir5.1 decreased Kir4.2 protein expression including the basolateral-membrane in PT. Finally, depolarization of PT-membrane- potential in Kir5.1-knockout mice suggests that Kir4.2 alone is not able to sustain basolateral K⁺ conductance of the PT in the absence of Kir5.1.

Transcriptomic analysis of microdissected human glomeruli has suggested novel molecular signatures associated with membranous nephropathy (MN) by revealing several genes differentially upregulated in MN compared with other glomerular diseases. We focused on a novel protein, family with sequence similarity 114 member A1 (FAM114A1), that was identified as the top classifier gene in the dataset. To determine the localization of FAM114A1 within glomeruli, we performed immunofluorescence (IF) staining on normal human kidney specimens. The staining area was quantitated in human MN and rat passive Heymann nephritis (PHN). In addition, we analyzed the expression of FAM114A1 in cultured podocytes and C57BL/6N mice following lipopolysaccharide (LPS)-induced injury. In silico investigations were conducted to model the protein structure of FAM114A1. We knocked down FAM114A1 in cultured podocytes by siRNA transfection and conducted functional assays. To detect interacting proteins, an affinity pulldown assay was performed using FAM114A1-3XFLAG protein and human glomerular extract. IF studies demonstrated the majority of FAM114A1 staining localized to the primary and foot processes of podocytes. The expression of FAM114A1 was increased in human MN and rat PHN and with LPS-induced injury. In silico modeling revealed that FAM114A1 is an all-alpha protein with several conserved regions. In cultured podocytes, FAM114A1 colocalized with F-actin and focal adhesion molecules. Silencing FAM114A1 affected podocyte cytoskeletal development, podocyte cell migration, and cell attachment. Affinity pulldown screening revealed that FAM114A1 interacts with several cytoskeleton-associated proteins. These findings suggest that FAM114A1 is a novel podocyte cytoskeleton-associated protein whose expression is upregulated by glomerular injury.NEW & NOTEWORTHY Podocyte cytoskeletal proteins are crucial for podocyte integrity and maintenance of slit diaphragms as urinary filtration barriers. In this study, we focused on a novel protein, FAM114A1, that was the top classifier gene in MN in the gene expression study. We show that FAM114A1 is a podocyte-specific protein in the kidney and is upregulated in glomerular injury. FAM114A1 is associated with the podocyte cytoskeleton and silencing FAM114A1 affected podocyte cell morphology and functions.

(Pro)renin receptor (PRR) contains overlapping cleavage site for site-1 protease (S1P) and furin for generation of soluble PRR (sPRR). Although S1P-mediated cleavage mediates the release of sPRR, the functional implication of furin-mediated cleavage is unclear. Here we tested whether furin-mediated cleavage was required for the activity of sPRR in activating ENaC in cultured M-1 cells. M-1 cells were transfected with pcDNA3.4 containing full-length PRR with (Furin-site Mut) or without (WT) mutagenesis of the furin cleavage site. As compared with empty vector control (EM), Furin-site Mut showed the attenuation effect on WT-induced α-ENaC expression and amiloride-sensitive short circuit current. In a separate experiment, M-1 cells were transfected with pcDNA3.4 containing cDNA for sPRR with S1P cleavage (AA 1-282) (sPRR-S1P) or with furin cleavage (AA 1-279) (sPRR-furin), indicating overexpression of the two types of sPRR induced a significant and comparable increase in the release of sPRR, but only sPRR-furin showed an increase of ENaC activity. Single channel analysis of ENaC activity in Xenopus A6-2F3 cells confirms sPRR-furin activation of ENaC open probability. Lastly, HEK-293 cells were pretreated with furin inhibitor α1-antitrypsin Portland (α1-PDX) followed by transfection with EM, WT PRR. sPRR in the conditioned medium was enriched by using protein centrifugal filter devices and applied to M-1 cells followed by measurement of ENaC activity, demonstrating that pretreatment with α1-PDX attenuated ENaC-acting activity induced by overexpression of WT PRR. In summary, we conclude that furin-mediated modification is required for the activity of sPRR to increase ENaC-mediated Na⁺ transport in the CD cells.