Citations

We previously showed that the Drosophila Malpighian tubule (MT) can model the formation of calcium oxalate (CaOx) kidney stones. Two epithelial cell types, stellate cells (SC) and principal cells (PC) comprise MTs, with each transporting different solutes from the hemolymph to MT lumen. Prestin, Neat and Ndae1 contribute to transepithelial ox2-, HCO 3 - transport and fluid secretion. Neat (2HCO 3 - /ox2- exchange) and NDAE1 (Na + ,2HCO 3 - /Cl - exchange) functionally combine to takeup hemolymph ox2-, can also facilitate HCO 3 - uptake. Prestin then secretes ox2- via Cl - / ox2-exchange to create luminal MT CaOx crystals, but it can also exchange Cl - /HCO 3 - . This study examines transepithelial ion secretion by Prestin (Slc26a6, apical), Neat (Slc26a1-like, basal) and Ndae1 (Slc4a8-like, basal). We use a functionally similar, simple genetic model (Drosophila Malpighian tubules, MT) to measure renal CaOx crystallization (NaOx feeding), membrane transport (pHi, fluorescent pH sensors) and fluid secretion (Ramsey assay) to: (1) compare cell-specific gene knockdown (KD) vs gene knockout, (2) quantify CaOx crystallization and intracellular pH (pHi) regulation by CO 2 /HCO 3 - , and (3) humanize these transporters by replacing them with human homologs. We hypothesize that humanizing individual transporters will restore MT physiology. Candidate transporter genes are tested for transepithelial ox2-and HCO 3 - secretion with gene-specific knockdown or knockout, using CRIMIC (CRISPR-Mediated Integration Cassette) alleles, in MTs due to comparable function to mammalian nephrons. Neat and NDAE1 work together to take-up hemolymph ox2- or HCO 3 - then Prestin secretes ox2- or HCO 3 - into the MT lumen. Prestin, Neat or NDAE1 knockdowns in principal cells decrease CaOx crystals. NDAE1 but not Neat knockdown in SC increases CaOx crystals like AQP (Drip, Prip)-knockdowns while either KD enhance HCO 3 - transport. Ndae1-SC-KD reduces fluid secretion like AQP-KD. Each CRIMIC allele must be physiologically compared to PC/SC-KDs because Ndae1-KO but not Neat-KO mirrors PC rather than SC function. Ndae1-SC-KD shows that HCO 3 - and Cl - secretion cause fluid secretion. Human homolog replacements are on-going. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Immune checkpoint inhibitors (ICIs) can cause immune-related adverse events (irAEs), with acute interstitial nephritis (ICI-AIN) being the most common irAE. While the exact mechanism remains unclear, upregulation of IFN-γ and TNF-α pathways has been implicated. This study used a humanized chimeric PD-1/PD-L1 mouse model to assess renal effects of ICIs, alone or combined with proinflammatory cytokines, and to test if selective TNF-α blockade could prevent ICI-AIN. Mice were randomly divided into 4 experimental groups: Control, ICI-Only, ICI-Cytokines (ICI-Cyt), and ICI-Block (ICI-TNF-α blockade). Renal function and cytokine profiles were assessed, while kidney tissue was analyzed using microscopy and single-cell RNA-seq. Histology revealed increased renal infiltration of CD4 + /CD8 + T cells in ICI-treated groups and decreased TNF-α expression following TNF-α blockade. Additionally, kidney tissue ELISA demonstrated reduced IFN-γ levels following TNF-α blockade. Plasma IL-6, MCP-1, and TNF-α were lower in ICI-Block mice. Single-cell RNA-seq revealed shifts in immune cell populations and genes of interest including Bcl2a1 , Icos , Il18r1 , Ccr2 , and Jaml . This humanized model replicates ICI-AIN key features, revealing a synergistic role of ICIs and proinflammatory cytokines. TNF-α blockade demonstrated protective effects, supporting its potential role in mitigating the risk of ICI-AIN.

Key Points Fibroblast growth factor 23 and 24,25-dihydroxyvitamin D are positively correlated and are significantly lower in Dent disease than in idiopathic calcium kidney stones patients. Dent patients with low 24,25-dihydroxyvitamin D had greater hypercalciuria and proteinuria, and, among adults, higher 1,25-dihydroxyvitamin D concentrations. Moderate phosphate supplementation mitigates hypercalciuria. Background Hypercalciuria is a prominent characteristic in Dent disease type 1 (DD1) and is associated with kidney stones and nephrocalcinosis. The objectives of this study were to assess fibroblast growth factor 23 (FGF23) and 24,25-dihydroxyvitamin D (24,25(OH) 2 D) in DD1 patients and investigate the effects of phosphate supplementation on urinary calcium excretion. Methods Serum and 24-hour urine assessments from adult and pediatric DD1 patients ( N =10 adults; N =9 pediatrics) were compared with adult control subjects with a history of idiopathic calcium kidney stones and hypercalciuria ( N =9). Adult DD1 patients and control participants completed an oral phosphate supplementation intervention (1 g/d×14 days) with reassessment immediately after intervention. Results FGF23 was significantly lower in DD1 than in the control cohort (adults, P = 0.006) and positively correlated with 24,25(OH) 2 D across all study cohorts. The concentrations of 24,25(OH) 2 D were low with conversion ratios (25-hydroxyvitamin D: 24,25(OH) 2 D) exceeding the clinical reference limit for five of 10 adults and six of 9 pediatric DD1 patients. The DD1 cohorts were then stratified by the 24,25(OH) 2 D ratio into “normal” and “low” 24,25(OH) 2 D. Adult DD1 patients with low 24,25(OH) 2 D ( n =5) had lower FGF23, higher 1,25-dihydroxyvitamin D, greater urine calcium, and greater urine protein. Pediatric stratified data mirrored that in adults with the exception of no difference in serum 1,25-dihydroxyvitamin D. Phosphate supplementation was effective in decreasing urine calcium in both adult DD1 and control adult cohorts. Conclusions Clinical measurement of 24,25(OH) 2 D is a novel and useful analysis for evaluating the severity of calcium and protein dysregulation in DD1. In addition, moderate phosphate supplementation effectively mitigates urine calcium excretion in DD1 adult patients. Clinical Trial registry name and registration number: ClinicalTrials.gov, NCT02016235.

The glomerular filtration rate (GFR) is a key indicator of kidney function, yet no ideal method exists for its direct measurement. This two-part review examines the development of GFR measurement techniques, focusing on their physiologic basis, performance characteristics, and clinical applications. Part 1 reviews endogenous markers used to estimate GFR (eGFR), including creatinine- and cystatin C-based equations, with emphasis on their derivation, limitations, and clinical use. Part 2 addresses exogenous filtration markers and measured GFR (mGFR) methodologies, highlighting comparative performance and specific uses. Emphasis is placed on innovation in marker development, highlighting the need for continued development and standardization to enhance accuracy and clinical utility.

Measured glomerular filtration rate (mGFR) remains the reference standard for precise assessment of kidney function when estimated approaches are insufficient. This second part of a two-part series reviews exogenous filtration markers used to obtain mGFR, including inulin, iothalamate, iohexol, and radionuclide-based tracers, with emphasis on their physiologic handling, analytic methods, accuracy, and clinical applicability. The review further examines emerging fluorescent and near-infrared tracers coupled with transcutaneous monitoring technologies that enable rapid or continuous assessment of GFR. Together, these approaches illustrate the evolution of mGFR measurement toward methods that are more practical, scalable, and responsive to dynamic changes in kidney function, while maintaining analytical accuracy.

Radiation exposure to the eye during cancer treatment can lead to ocular radiation injury (ORI), a devastating condition that can have a profound and permanent impact on vision-related quality of life. Rodent models do not have adequate ocular anatomy to accurately simulate human ORI, and modeling in non-human primates is limited by logistical and ethical concerns. To improve future translational research investigating ways to treat or prevent ORI, we developed protocols for a tree shrew model of ORI. Northern tree shrews (Tupaia belangeri) were obtained by our laboratory. Custom housing and handling methods were developed, including custom body suits to maintain the tree shrew’s body temperature during procedures. Radiation delivery was optimized to accurately deliver radiation, and imaging was performed to observe fundus changes from ORI. Optimization of tree shrew handling, housing, anesthesia approaches, radiation delivery, and clinically-relevant ocular imaging permitted successful induction and assessment of ORI in tree shrews. With these protocols, tree shrews can be used as a highly relevant model organism with key anatomic features similar to humans to study ORI.

SLC26A9 is a Cl - channel and electrogenic Cl - -HCO 3 ‑ exchanger found in several human epithelia, including the lung, intestine / GI tract, and kidney. SLC26 proteins are defined by a C-terminal, cytoplasmic sulfate transporter / anti-σ-domain (STAS). In mammals, several STAS domains have protein-protein interactions with the regulatory-region of CFTR (R-CFTR), the Cl - channel associated with cystic fibrosis. However, the functional consequences, i.e., regulatory effects (up/downregulation), of STAS-to-R-CFTR binding seem to differ by SLC26 member. Our prior work showed that the SLC26A9:CFTR interaction decreases SLC26A9 channel and exchange activity. If SLC26A9-STAS was replaced with SLC26A6-STAS, no inhibition of SLC26A9 conductance occurred when interacting with R-CFTR (PMID 19643730). Complete deletion of SLC26A9-STAS removed Cl - conductance. Thus, we hypothesized that a disordered loop within STAS is the likely interaction area, and therefore deleted this STAS-disordered loop (ΔLoop) to test this region’s functionality. We used a voltage clamp to measure Cl - currents (IV; conductance G calculated) in Xenopus laevis oocytes (n=10 / construct) injected with cRNA of ΔLoop and subcomponent areas of SLC26A9. Each construct contained a 3xFLAG tag such that stained oocytes from these constructs allowed determination of membrane expression. ΔLoop has three subregions: K/R rich, Middle, S/T rich. Both ΔLoop and ΔLoop(K/R) increase Cl - currents (and conductance) by 5x greater comparted to wild-type SLC26A9. Five amino acid extension of ΔLoop (N- or C-terminal) produces Cl - currents equivalent to ΔLoop deletion. However, 10 amino acid extension of ΔLoop (N- or C- direction) produces currents equivalent to WT-SLC26A9. Membrane localization indicates that ΔLoop and regional deletion constructs have similar membrane abundance to WT, while boundary deletions inhibit channel trafficking to the membrane. As ΔLoop(S/T) slightly increased conductance, the ordered S/T-rich motif [T 620 SVSYITFS 628 ] was examined for possible phosphorylation effects by serial alanine substitution. Each alanine substitution in the S/T-rich motif decrease SLC26A9 Cl - conductance vs WT-SLC26A9. However, for S623A the conductance decrease was due to minimal plasma membrane expression rather than apparent change of channel activity. Together these data suggest that the disordered loop is multifaceted and can maintain low conductance (autoinhibition) or by potential phosphorylation. As cystic fibrosis (CF) results from loss-of-function, trafficking or degradation mutations, the robust Cl - conductance from elimination of SLC26A9 autoinhibitory, disordered loop, presents an opportunity to supplement or replace Cl - conductance in CF tissues and potentially patients. R25-DK101405 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

The urethra is considered a passive conduit for urine. Here, we reveal a surprising multicellular signaling pathway guiding the urethra’s dynamic response to an invading pathogen. Using a genetic approach in female mice, we deposited uropathogenic Escherichia coli into the distal urethra to establish a model of ascending urinary tract infection that progresses to the bladder within 4 h. We show that urethral neuroendocrine cells (UNECs), and the serotonin they synthesize, protect the bladder from bacterial colonization. We tested the hypothesis that serotonin initiates urethral contraction to expel ascending bacteria. We identified transient receptor potential cation channel subfamily A member 1, a noncanonical lipopolysaccharide receptor, in human and mouse UNECs and localized the serotonin receptors (HTR) 2B and 3, as well as the calcium-activated chloride channel anoctamin 1 (ANO1) to the pacemaker cells of the human and mouse urethra, the interstitial cells of Cajal (ICCs). HTR2B or ANO1 activation is sufficient for urethral contraction and is required for serotonin-induced mouse urethral contraction. Our results support the hypothesis that the urethra actively surveils its environment and responds to an ascending pathogen by evoking UNECs and ICC to induce urethral contraction and pathogen expulsion.