Proximal Tubule Research Articles

Hereditary Rickets: A Quick Guide for the Pediatrician.

With the increased discovery of genes implicated in vitamin D metabolism and the regulation of calcium and phosphate homeostasis, a growing number of genetic forms of rickets are now recognized. These are categorized into calciopenic and phosphopenic rickets. Calciopenic forms of hereditary rickets are caused by genetic mutations that alter the enzymatic activity in the vitamin D activation pathway or impair the vitamin D receptor action. Hereditary forms of phosphopenic rickets, on the other hand, are caused by genetic mutations that lead to increased expression of FGF23 hormone or that impair the absorptive capacity of phosphate at the proximal renal tubule. Due to the clinical overlap between acquired and genetic forms of rickets, identifying children with hereditary rickets can be challenging. A clear understanding of the molecular basis of hereditary forms of rickets and their associated biochemical patterns allow the health care provider to assign the correct diagnosis, avoid non-effective interventions and shorten the duration of the diagnostic journey in these children. In this mini-review, known forms of hereditary rickets listed on the Online Mendelian Inheritance in Man database are discussed. Further, a clinical approach to identify and diagnose children with hereditary forms of rickets is suggested.

A new era in the treatment of kidney diseases: NLRP3 inflammasome and cytokine-targeted therapies.

The kidneys are crucial for filtering blood, managing overall body water, electrolyte, and acid-base balance, and regulating blood pressure. They remove metabolic waste products, toxins, and drugs. In addition, they limit inflammation by clearing cytokines and reduce immune cell activation by removing bacterial components. Dendritic cells (DCs) in the kidney maintain peripheral tolerance. About 85% of filtered water is reabsorbed by the proximal tubule, exposing distal nephron cells to high concentrations of low molecular weight antigens. These antigens are captured by DCs, helping to inactivate potentially autoreactive T cells and maintain tolerance to circulating antigens. In kidney failure, immune function is severely compromised due to the retention of toxins and cytokines, which activate immune cells and increase systemic inflammation. The kidneys are also vulnerable to immune-mediated diseases. Loss of immune homeostasis, characterized by over- or under-activity of the immune response, can adversely affect kidney function. With advances in immunology and cellular biology, biologic therapies targeting various pathways involved in the pathophysiology of kidney diseases are being developed. In this review, the immunologic aspects of kidney diseases and focus on cytokine-based therapies that may hold promise for the treatment of kidney diseases in the future will be presented.

Mesenchymal Stem Cell-conditioned Medium Protecting Renal Tubular Epithelial Cells by Inhibiting Hypoxia-inducible Factor-1α and Nuclear Receptor Coactivator-1.

Acute kidney injury (AKI) is characterized by inflammatory infiltration and damage and death of renal tubular epithelial cells (RTECs), in which hypoxia plays an important role. Deferoxamine (DFO) is a well-accepted chemical hypoxia-mimetic agent. Mesenchymal stem cell-conditioned medium (MSC-CM) can reduce local inflammation and repair tissue. In this study, we explored the effect and molecular mechanism of MSC-CM-mediated protection of RTECs under DFO-induced hypoxia. Rat renal proximal tubule NRK-52E cells were treated with different concentrations of DFO for 24 hours, followed by evaluation of RTEC injury, using a Cell Counting Kit-8 (CCK-8) to detect cell viability and western blotting to evaluate the expression of transforming growth factor- beta 1 (TGF-β1), α-smooth muscle actin (α-SMA), and hypoxia-inducible factor-1 alpha (HIF-1α) in NRK-52E cells. Then, three groups of NRK-52E cells were used in experiments, including normal control (NC), 25 μM DFO, and 25 μM DFO + MSC-CM. MSC-CM was obtained from the human umbilical cord. MSC-CM was used to culture cells for 12 hours before DFO treatment, then fresh MSC-CM and 25 μM DFO were added, and cells were cultured for another 24 hours before analysis. Western blotting and cellular immunofluorescence staining showed culture of NRK-52E cells in 25 μM DFO for 24 hours induced HIF-1α and nuclear receptor coactivator-1 (NCoA-1), simulating hypoxia. MSC-CM could inhibit the DFO-induced up-regulation of α-SMA, TGF-β1, HIF-1α and NCoA-1. Our results suggest that MSC-CM has a protective effect on RTECs by down-regulating HIF-1α and NCoA-1, which may be the harmful factors in renal injury.

Axial heterogeneity of superficial proximal tubule paracellular transport in mice.

A considerable amount of NaCl reabsorption in proximal tubules (PTs) occurs via the paracellular transport regulated by the tight junction proteins claudins (Cldns). However, the paracellular transport properties in mouse superficial PTs remain unclear. We characterized these properties in superficial PT S1-S3 segments from mice expressing [wild-type (WT, WTS1-WTS3)] or lacking claudin-2 [knockout (KO, KOS1-KOS3)]. We isolated and perfused segments with symmetrical solutions in the presence of bath ouabain and measured the diffusion potential upon changing the salt composition of the lumen or bath. Based on the diffusion potential corrected for the liquid junction potential (dVT), we calculated the paracellular Na+ over Cl- permeability (PNa/PCl) ratio. The PNa/PCl values upon reducing luminal NaCl averaged 1.27, 1.04, and 0.85 in WTS1, WTS2, and WTS3 and 0.34, 0.55, and 0.80 in KOS1, KOS2, and KOS3, respectively. The dVT values exhibited a symmetrical response to bidirectional NaCl concentration gradients in WTS1-WTS3 and KOS1-KOS3. WTS1 and WTS3 were monovalent cation-selective, with WTS1 demonstrating stronger cation selectivity. The order of permeabilities relative to Cl- was K+ > Rb+ > Na+ > Li+, whereas both KOS1 and KOS3 exhibited monovalent cation selectivity loss and consequently enhanced anion selectivity, especially in KOS1. Protamine addition to the lumen and bath similarly decreased PNa/PCl values upon reduced luminal NaCl in the order of WTS1 > WTS3 > KOS3 > KOS1. Therefore, this study presents evidence of axial heterogeneity in paracellular transport across superficial PTs in mice.

Renal Semaphorin 3C mediates cardiac adaptive response

Abstract Cardiorenal syndrome, characterized by reciprocal heart-kidney interactions that progressively promote dysfunction in both organs, is associated with a high mortality rate. However, the mechanisms linking the two organs are insufficiently understood. Here we report that semaphorin 3C (SEMA3C) is a novel cardioprotective mediator secreted from the kidney. SEMA3C was highly expressed in the renal proximal tubules in mice. Renal Sema3c expression and circulating SEM3C were reduced by the left ventricular pressure overload that induced renal remodeling. Proximal tubule-specific secretory Sema3c deletion exacerbated cardiac hypertrophy, fibrosis and dysfunction after the pressure overload, suggesting renal SEMA3C is important for the proper cardiac adaptive response. Mechanistically, SEMA3C inhibits pathological cardiac remodeling at least partly by inhibiting Akt, ERK and Wnt/β-catenin signaling in cardiomyocytes. In heart failure patients, the plasma SEMA3C level was decreased and the low plasma SEMA3C was associated with poor cardiac outcomes. Collectively, our results show that SEMA3C produced by the kidney pivotally contributes to the cardiac stress response and its reduction contributes to the progression of heart failure. SEMA3C signaling appears to be an attractive therapeutic and diagnostic target for cardiorenal syndrome.

Prostate-specific Membrane Antigen (PSMA): A Diagnostic and Therapeutic Target in Advanced Prostate Cancer

Prostate cancer is among the most prevalent malignant conditions globally, and both incidence and mortality are expected to increase markedly over the next two decades. Recently, the diagnostic and treatment landscape for managing this disease underwent remarkable advances that led to the incorporation of innovative approaches, such as prostate-specific membrane antigen (PSMA) theranostics. PSMA, which is also known as folate hydroxylase or glutamate carboxypeptidase, is a transmembrane protein 100- to 1000-fold overexpressed by prostate cancer cells compared to healthy cells found in the benign prostate gland, salivary glands, proximal renal tubules, small intestine mucosa, and hepatocytes, amongst others. Since its discovery over 30 years ago (see Figure 1 for this and other milestones), PSMA has caught the attention of the scientific community as a potential therapeutic target, and for the past two decades many efforts have been undertaken to identify and develop PSMA ligands and antibodies that could be exploited as prostate cancer therapeutics. This review aims to provide an overview of available PSMA ligands, their mechanisms of action, diagnostic and therapeutic applications, and future perspectives of PSMA-targeted therapeutic approaches within the field of radioligand therapy (RLT).

Multifunctional extracellular vesicles and edaravone-loaded scaffolds for kidney tissue regeneration by activating GDNF/RET pathway

With the severity of chronic kidney disease worldwide, strategies to recover renal function via tissue regeneration provide alternatives to kidney replacement therapy. To exclude side effects from direct cell transplantation, extracellular vesicles (EVs) are great substitutes representing paracrine cell signaling. To build three-dimensional structures for implantation into the 5/6 nephrectomy model by incorporating bioactive materials, including multifunctional EVs (mEVs), porous PMEZE/mEV scaffolds were developed in combination with edaravone (EDV; E) and mEV based on PMEZ scaffolds with PLGA (P), MH-RA (M), ECM (E), ZnO-ALA (Z). The oxygen free radical scavenger EDV was incorporated to induce tubular regeneration. mEVs were engineered to serve regenerative activities with a combination of two EVs from SDF-1α overexpressed tonsil-derived mesenchymal stem cells (sEVs) and intermediate mesoderm (IM) cells during differentiation into kidney progenitor cells (dEVs). mEVs displayed beneficial effects on regeneration by facilitating migration and inducing differentiation of surrounding stem cells, and EDV improved kidney function by regulating the GDNF/RET pathway and their downstream genes. The promotion of MSC recruitment was confirmed with sEV particles number dependently, and the regulation of the GDNF/RET pathway by the effect of EDV and its enhanced effect by mEVs were elucidated using in vitro analysis. The regeneration of tubules was additionally demonstrated through the increased expression of aquaporin-1 (AQP-1) and cadherin-16 (CDH16) for proximal tubules, and calbindin and PAX2 for distal tubules in the renal defect model. With these, structural regeneration and functional recovery were achieved with kidney regeneration in the 5/6 nephrectomy mice model.Graphical abstract

Handling the sugar rush: The role of the renal proximal tubule.

Blood glucose homeostasis is critical to ensure the proper functioning of the human body. Through the processes of filtration, reabsorption, secretion, and metabolism, much of this task falls to the kidneys. With a rise in glucose and other added sugars, there is an increased burden on this organ, mainly the proximal tubule which is responsible for all glucose reabsorption. In this review, we focus on the current physiological and cell biological functions of the renal proximal tubule as it works to reabsorb and metabolize glucose and fructose. We also highlight the physiological adaptations that occur within the proximal tubule as sugar levels rise under pathophysiological conditions including diabetes. This includes the detrimental impacts of an excess glucose load that leads to glucotoxicity. Finally, we explore some of the emerging therapeutics that modulate renal glucose handling and the systemic protection that can be realized by targeting the reabsorptive properties of the kidney.

Exploring the Cardiorenal Benefits of SGLT2i: A Comprehensive Review

The history of sodium-glucose cotransporter 2 inhibitors (SGLT2i) is so long and started in 1835 when Petersen extracted a compound called phlorizin from apple tree bark. About fifty years later, von Mering discovered its glucosuric properties. In the 1980s, it was discovered that the glucosuria resulted from inhibition by phlorizin of glucose reabsorption by the renal tubules, which lowered blood glucose levels in diabetic rats. Nowadays, beyond their glucose-lowering effects, growing evidence suggests significant cardiorenal benefits associated with SGLT2i therapy. Indeed, several clinical trials, including landmark studies such as EMPA-REG OUTCOME, CANVAS Program, and DECLARE-TIMI 58, have demonstrated robust reductions in cardiovascular events, particularly heart failure hospitalizations and cardiovascular mortality, among patients treated with SGLT2i. However, subsequent trials showed that SGLT2i benefits extend beyond the diabetic population, encompassing individuals with and without diabetes. Additionally, SGLT2i exhibit nephroprotective effects, manifesting as a slowing of the progression of chronic kidney disease and a reduction in the risk of end-stage kidney disease. The mechanisms underlying the cardiorenal benefits of SGLT2i are multifactorial and include improvements in glycemic control, reduction in arterial stiffness, modulation of inflammation and oxidative stress, reduction of intraglomerular pression and promotion of natriuresis and diuresis through inhibition of SGLT2 in the luminal brush border of the first segments of the proximal kidney tubule. This narrative review aims to explore the cardiorenal outcomes of SGLT2i, encompassing their mechanisms of action, clinical evidence, safety profile, and implications for clinical practice.

Active immunological participation and metabolic shutdown of kidney structural cells during kidney transplant rejection

Contrary to immune cells, the response of the kidney structural cells in rejection is less established. We performed single-cell RNA sequencing on 18 kidney transplant biopsies from 14 recipients.Single-cell RNA sequencing identified cells from the major compartments of the kidney, next to infiltrated immune cells. Endothelial cells from the glomerulus, peritubular capillaries and vasa recta showed upregulation of class I and II HLA genes, adhesion molecules and cytokines and chemokines, suggesting an active participation in the alloimmune process, with compartment-specific differences. Epithelial cells including proximal tubular, loop of Henle and collecting duct cells, also showed increased expression of immune genes. Strikingly, in proximal tubule cells a strong downregulation of energy metabolism upon inflammation was observed. There was a large overlap between the cell-specific expression changes upon alloimmune inflammation and those observed in two large micro-array biopsy cohorts.In conclusion, the kidney structural cells, being the main target of the alloimmune process, appear to actively contribute herein, enhancing the damaging effects of the infiltrating immune cells. In epithelial cells, a profound shutdown of metabolism was seen upon inflammation, which associated with poor kidney function. These observations highlight the critical role of the graft in triggering and sustaining rejection after transplantation.

Reconstitution of Rab11-FIP4 Expression Rescues Cellular Homeostasis in Cystinosis.

Rab11 family interacting protein 4 (Rab11-FIP4) regulates endocytic trafficking. A possible role for Rab11-FIP4 in the regulation of lysosomal function has been proposed, but its precise function in the regulation of cellular homeostasis is unknown. By mRNA array and protein analysis, we found that Rab11-FIP4 is downregulated in the lysosomal storage disease cystinosis, which is caused by genetic defects in the lysosomal cystine transporter, cystinosin. Rescue of Rab11-FIP4 expression in Ctns-/- fibroblasts re-established normal autophagosome levels and decreased LC3B-II expression in cystinotic cells. Furthermore, Rab11-FIP4 reconstitution increased the localization of the chaperone-mediated autophagy receptor LAMP2A at the lysosomal membrane. Treatment with genistein, a phytoestrogen that upregulates macroautophagy, or the CMA activator QX77 (CA77) restored Rab11-FIP4 expression levels in cystinotic cells supporting a cross-regulation between two independent autophagic mechanisms, lysosomal function and Rab11-FIP4. Improved cellular homeostasis in cystinotic cells rescued by Rab11-FIP4 expression correlated with decreased endoplasmic reticulum stress, an effect that was potentiated by Rab11 and partially blocked by expression of a dominant negative Rab11. Restoring Rab11-FIP4 expression in cystinotic proximal tubule cells increased the localization of the endocytic receptor megalin at the plasma membrane, suggesting that Rab11-FIP4 reconstitution has the potential to improve cellular homeostasis and function in cystinosis.

Circulating proteins linked to apoptosis processes and fast development of end-stage kidney disease in diabetes.

Many circulating proteins are associated with risk of ESKD, but their source and the biological pathways/disease processes they represent are unclear. Using OLINK proteomics platform, concentrations of 455 proteins were measured in plasma specimens obtained at baseline from 399 individuals with diabetes. Elevated concentrations of 46 circulating proteins were associated (P < 1 × 10-5) with development of ESKD (n = 143) during 7-15 years of follow-up. Twenty of these proteins enriched apoptosis/TNF receptor signaling pathways. A subset of 20 proteins (5-7 proteins), summarized as an apoptosis score, together with clinical variables accurately predicted risk of ESKD. Expression of genes encoding the 46 proteins in peripheral WBCs showed no difference between cells from individuals who did or did not develop ESKD. In contrast, plasma concentration of many of the 46 proteins differed by this outcome. In single-nucleus RNA-Seq analysis of kidney biopsies, the majority of genes encoding for the 20 apoptosis/TNF receptor proteins were overexpressed in injured versus healthy proximal tubule cells. Expression of these 20 genes also correlated with the overall index of apoptosis in these cells. Elevated levels of circulating proteins flagging apoptotic processes/TNF receptor signaling pathways - and likely originating from kidney cells, including injured/apoptotic proximal tubular cells - preceded the development of ESKD.

Potential protection of resveratrol-tempeh against nephrotoxic and hepatotoxic histological damage in mice induced by aluminum

Aluminum is a widely distributed metal that, while generally safe at low levels, can become toxic when accumulated in the body. Its exposure is daily through various sources, including food, water, and medications. High levels of aluminum have been shown to adversely affect the kidneys and liver, leading to significant organ damage. Resveratrol-tempeh is a safe protective agent against organ damage caused by aluminum. Here, we investigated the impact of resveratrol on liver and kidney toxicity and Al-induced levels of catalase and malondialdehyde. The mice group was the control group, Al-group, Al+REST5-group, and Al+REST10-group. Aluminum and resveratrol were administered intraperitoneally to mice for four weeks, but resveratrol was administered one hour after exposure to aluminum. Mice were killed by cervical dislocation; the liver and kidney were isolated for slide, and the level of an antioxidant enzyme of catalase and oxidant of malondialdehyde was measured. The results showed that administration of aluminum at a dose of 200 mg/kg body weight caused glomerular shrinkage and proximal tubule degeneration in the kidneys. In addition, it also caused liver tissue damage, with hepatocytes undergoing degeneration, sinusoids dilating, and decreased body weight in the mice. Administration of resveratrol-tempeh tended to decrease malondialdehyde levels and increase catalase activity, although the changes were not significant. It seems that resveratrol-tempeh can repair liver and kidney damage and restore them to normal conditions. Conclusion: Aluminum at 200 mg/kg is toxic to mice. Resveratrol-tempeh can be considered a potential candidate to protect kidney and liver damage caused by aluminum chloride toxicity.

Beyond hemoglobin: Critical role of 2,3-bisphosphoglycerate mutase in kidney function and injury.

2,3-bisphosphoglycerate mutase (BPGM) is traditionally recognized for its role in modulating oxygen affinity to hemoglobin in erythrocytes. Recent transcriptomic analyses, however, have indicated a significant upregulation of BPGM in acutely injured murine and human kidneys, suggesting a potential renal function for this enzyme. Here we aim to explore the physiological role of BPGM in the kidney. A tubular-specific, doxycycline-inducible Bpgm-knockout mouse model was generated. Histological, immunofluorescence, and proteomic analyses were conducted to examine the localization of BPGM expression and the impact of its knockout on kidney structure and function. Invitro studies were performed to investigate the metabolic consequences of Bpgm knockdown under osmotic stress. BPGM expression was localized to the distal nephron and was absent in proximal tubules. Inducible knockout of Bpgm resulted in rapid kidney injury within 4 days, characterized by proximal tubular damage and tubulointerstitial fibrosis. Proteomic analyses revealed involvement of BPGM in key metabolic pathways, including glycolysis, oxidative stress response, and inflammation. Invitro, Bpgm knockdown led to enhanced glycolysis, decreased reactive oxygen species elimination capacity under osmotic stress, and increased apoptosis. Furthermore, interactions between nephron segments and immune cells in the kidney suggested a mechanism for propagating stress signals from distal to proximal tubules. BPGM fulfills critical functions beyond the erythrocyte in maintaining glucose metabolism in the distal nephron. Its absence leads to metabolic imbalances, increased oxidative stress, inflammation, and ultimately kidney injury.

Nanoparticle Transport in Proximal Tubules with Rhabdomyolysis‐induced Necrosis

Renal‐clearable engineered nanoparticles are being explored for their potential to deliver therapeutic agents for kidney disease treatment. A fundamental understanding of how these nanoparticles accumulate in diseased kidneys at the cellular level is essential to enhance their effectiveness and minimize side effects on adjacent healthy tissues. Herein, we report that the accumulation of glutathione‐coated, near‐infrared emitting gold nanoparticles (GS‐AuNPs) correlates strongly with the necrotic stages of injured proximal tubular cells. Using a rhabdomyolysis‐induced acute kidney injury (AKI) mouse model, we observed that GS‐AuNPs were significantly accumulated in the extracellular lumen of proximal tubular epithelial cells (PTECs) at advanced necrotic stage, where cellular debris and released intracellular contents impeded their clearance. In contrast, during early necrosis, GS‐AuNPs were still cleared through the open lumen. Additionally, intracellular uptake of GS‐AuNPs was significantly reduced across all necrotic stages. These findings underscore the need for new strategies to design nanoparticles that can effectively target and be taken up by the diseased tubular cells before extensive necrosis occurs; so that nanoparticle‐mediated drug delivery for kidney disease treatment can be achieved with desired efficacy and precision.

Nanoparticle Transport in Proximal Tubules with Rhabdomyolysis-induced Necrosis.

Renal-clearable engineered nanoparticles are being explored for their potential to deliver therapeutic agents for kidney disease treatment. A fundamental understanding of how these nanoparticles accumulate in diseased kidneys at the cellular level is essential to enhance their effectiveness and minimize side effects on adjacent healthy tissues. Herein, we report that the accumulation of glutathione-coated, near-infrared emitting gold nanoparticles (GS-AuNPs) correlates strongly with the necrotic stages of injured proximal tubular cells. Using a rhabdomyolysis-induced acute kidney injury (AKI) mouse model, we observed that GS-AuNPs were significantly accumulated in the extracellular lumen of proximal tubular epithelial cells (PTECs) at advanced necrotic stage, where cellular debris and released intracellular contents impeded their clearance. In contrast, during early necrosis, GS-AuNPs were still cleared through the open lumen. Additionally, intracellular uptake of GS-AuNPs was significantly reduced across all necrotic stages. These findings underscore the need for new strategies to design nanoparticles that can effectively target and be taken up by the diseased tubular cells before extensive necrosis occurs; so that nanoparticle-mediated drug delivery for kidney disease treatment can be achieved with desired efficacy and precision.

Empagliflozin protects the kidney by reducing toxic ALB (albumin) exposure and preventing autophagic stagnation in proximal tubules

ABSTRACT The renoprotective effects of SLC5A2/SGLT2 (solute carrier 5 (sodium/glucose cotransporter), member 2) inhibitors have recently been demonstrated in non-diabetic chronic kidney disease (CKD), even without overt albuminuria. However, the mechanism underlying this renoprotection is largely unclear. We investigated the renoprotective mechanisms of the SLC5A2 inhibitor empagliflozin with a focus on ALB (albumin) reabsorption and macroautophagy/autophagy in proximal tubules using wild-type or drug-inducible lrp2/Megalin or atg5 knockout mice with high-fat diet (HFD)-induced obesity or 5/6 nephrectomy that elevated intraglomerular pressure without overt albuminuria. Empagliflozin treatment of HFD-fed mice reduced several hallmarks of lipotoxicity in the proximal tubules, such as phospholipid accumulation in the lysosome, inflammation and fibrosis. Empagliflozin, which decreases intraglomerular pressure, not only reduced the HFD-induced increase in ALB reabsorption via LRP2 in the proximal tubules (i.e. total nephron ALB filtration), as assessed by urinary ALB excretion caused by genetic ablation of Lrp2, but also ameliorated the HFD-induced imbalance in circulating ALB-bound fatty acids. Empagliflozin alleviated the HFD-induced increase in autophagic demand and successfully prevented autophagic stagnation in the proximal tubules. Similarly, empagliflozin decreased ALB exposure and autophagic demand in 5/6 nephrectomized mice. Finally, empagliflozin reduced HFD-induced vulnerability to ischemia–reperfusion injury, whereas LRP2 blockade and atg5 ablation separately diminished this effect. Our findings indicate that empagliflozin reduces ALB exposure and prevents autophagic stagnation in the proximal tubules even without overt albuminuria. Autophagy improvement may be critical for the renoprotection mediated by SLC5A2 inhibition.

SARS-CoV-2 infection causes a decline in renal megalin expression and affects vitamin D metabolism in the kidney of K18-hACE2 mice

Patients with coronavirus disease 2019 (COVID-19) often experience acute kidney injury, linked to disease severity or mortality, along with renal tubular dysfunction and megalin loss in proximal tubules. Megalin plays a crucial role in kidney vitamin D metabolism. However, the impact of megalin loss on vitamin D metabolism during COVID-19 is unclear. This study investigated whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection reduces megalin expression in proximal tubules and its subsequent effect on vitamin D metabolism in mice expressing human angiotensin converting enzyme 2 (K18-hACE2 mice). Histological and immunohistochemical staining analyses revealed glomerular and capillary congestion, and elevated renal neutrophil gelatinase-associated lipocalin levels, indicative of acute kidney injury in K18-hACE2 mice. In SARS-CoV-2-infected mice, immunohistochemical staining revealed suppressed megalin protein levels. Decreased vitamin D receptor (VDR) localization in the nucleus and increased mRNA expression of VDR, CYP27B1, and CYP24A1 were observed by quantitative PCR in SARS-CoV-2-infected mice. Serum vitamin D levels remained similar in infected and vehicle-treated mice, but an increase in tumor necrosis factor-alpha and a decrease in IL-4 mRNA expression were observed in the kidneys of the SARS-CoV-2 group. These findings suggest that megalin loss in SARS-CoV-2 infection may impact the local role of vitamin D in kidney immunomodulation, even when blood vitamin D levels remain unchanged.

A Novel Role for FERM Domain-Containing Protein 3 (FRMD3) in CKD.

Currently there are limited methods to link disease severity and risk of disease progression in Chronic Kidney Disease (CKD). To better understand this potential relationship, we interrogated the renal transcriptomic profile of individuals with CKD with measures of CKD severity and identified FERM-domain containing protein 3 (FRMD3) as a candidate gene for follow-up study. RNA-seq was used to profile the transcriptome of CKD biopsies from the North Dublin Renal BioBank the results of which were correlated with clinical parameters. The potential function of FRMD3 was explored by interrogating the FRMD3 interactome and assessing the impact of lentiviral mediated FRMD3 knock down on human renal proximal tubule epithelial cells by assessing cell viability, metabolic activity, and structural markers. We identified a subset of 93 genes which are significantly correlated with estimated glomerular filtration rate and percentage tubulointerstitial fibrosis at time of biopsy and with CKD progression 5 years post-biopsy. These results were validated against transcriptomic data from an external cohort of 432 nephrectomy samples. One of the top-ranking genes from this subset, FRMD3, has previously been associated with the risk of developing diabetic kidney disease. Interrogating the interactome of FRMD3 in tubule epithelial cells revealed interactions with cytoskeletal components of cell-cell junctions. Knockdown of FRMD3 expression in tubule epithelial cells resulted in increased pro-apoptotic activity within the cells as well as dysregulation of E-Cadherin. We have identified a panel of kidney-specific transcripts correlated with severity and progression of kidney disease, and from this have identified a possible role for FRMD3 in tubule cell structure and health.

Genetic testing, a challenge to kidney biopsy? A case report

The field of genetic testing has experienced significant growth in medical practice since 1956, when the first genetic analysis was introduced. Persistent proteinuria has long been considered a strong risk factor for the progression of chronic renal failure, though, paradoxically, it can also be a benign process, as seen in individuals with mutations in the cubilin (CUBN) protein, specifically the C-terminal. CUBN is a peripheral protein that plays a crucial role in the receptor-mediated endocytotic reabsorption of albumin in the proximal tubule. In the past, there have been misinterpretations of CUBN variants with isolated proteinuria as glomerular injury, leading to unnecessary kidney biopsies and ineffective treatments. This paper discusses two siblings with a homozygous variant of (p.Tyr3018Ser) in the C-terminal of the CUBN protein, inherited from both heterozygous carrier parents. This case presents an opportunity to question our typical approach to proteinuria in an effort to avoid unnecessary kidney biopsies and the subsequent side effects of treatments, particularly for those with proteinuria.