Phosphate Transporter Regulator That Prevents Abnormal Hyperphosphatemia.

Renal type II sodium-dependent inorganic phosphate (Pi) transporters NaPi2a and NaPi2c cooperate with other organs to strictly regulate the plasma Pi concentration. A high Pi load induces the phosphaturic hormones parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23), enhances urinary Pi excretion and prevents the onset of hyperphosphatemia. How FGF23 is induced from the bones by a high Pi load and the setpoint of the plasma Pi concentration, however, are unclear. Here, we investigated the role of transporter-associated protein (TRAP), found in gene co-expression networks in NaPi2a and NaPi2c function. TRAP is localized in the renal proximal tubules and interacts with NaPi2a. In TRAP-knockout (KO) mice, the serum FGF23 concentration was markedly increased but increased Pi excretion and hypophosphatemia were not observed. In addition, TRAP-KO mice exhibit reduced NaPi2a responsiveness to FGF23 and PTH administration. Furthermore, a dietary Pi load causes marked hyperphosphatemia and abnormal NaPi2a regulation in TRAP-KO mice. Thus, TRAP is thought to be associated with FGF23 induction in bones and the regulation of NaPi2a to prevent an increase in the plasma Pi concentration due to a high Pi load and kidney injury.

Redefining the Role of ADAM17 in Renal Proximal Tubular Cells and Its Implications in an Obese Mouse Model of Pre-Diabetes

Acute and chronic kidney lesions induce an increase in A Disintegrin And Metalloproteinase domain 17 (ADAM17) that cleaves several transmembrane proteins related to inflammatory and fibrotic pathways. Our group has demonstrated that renal ADAM17 is upregulated in diabetic mice and its inhibition decreases renal inflammation and fibrosis. The purpose of the present study was to analyze how Adam17 deletion in proximal tubules affects different renal structures in an obese mice model. Tubular Adam17 knockout male mice and their controls were fed a high-fat diet (HFD) for 22 weeks. Glucose tolerance, urinary albumin-to-creatinine ratio, renal histology, and pro-inflammatory and pro-fibrotic markers were evaluated. Results showed that wild-type mice fed an HFD became obese with glucose intolerance and renal histological alterations mimicking a pre-diabetic condition; consequently, greater glomerular size and mesangial expansion were observed. Adam17 tubular deletion improved glucose tolerance and protected animals against glomerular injury and prevented podocyte loss in HFD mice. In addition, HFD mice showed more glomerular macrophages and collagen accumulation, which was prevented by Adam17 deletion. Galectin-3 expression increased in the proximal tubules and glomeruli of HFD mice and ameliorated with Adam17 deletion. In conclusion, Adam17 in proximal tubules influences glucose tolerance and participates in the kidney injury in an obese pre-diabetic murine model. The role of ADAM17 in the tubule impacts on glomerular inflammation and fibrosis.

Evaluation of the Role of Na+/ K+ ATPase Ion Transporters and Na+/K+/ 2Cl and Na+/H+ Exchanger Cotransporters in Nephrons of Periophthalmus Waltoni Using Immunohistochemistry and Histology

Kidneys play an important role in regulating the balance of water and ions in freshwater and seawater fish. However, complex kidney structures impair a comprehensive understanding of kidney function. In this study, in addition to renal histology, Na+/K+/ATPase ion transporter proteins and Na+/K+/2Cl− and NHE3 cotransporters were located in Priophthalmus waltoni kidney tissue to evaluate the ion regulation abilities of epithelial cells in various parts of nephrons. The renal tubules are composed of proximal tubules and distal tubules, followed by collecting tubes and finally collecting ducts. Light microscope immunohistochemistry was utilized to locate Na+/ K+-ATPase along renal tubules and collecting ducts. However, the distribution of the Na+/K+-ATPase immune response varies in different sections. Na+/K+/CL− cotransporter positioning was reported only in collecting tubes and collecting ducts, and proximal tubes and distal tubes did not respond to Na+/K+/Cl− cotransporter immunolocalization. Immunohistochemical response for NHE3 localization was detected only at the apex of epithelial cells of proximal tubules and collecting tubes. The distal tubes showed negative reaction and the collecting ducts showed a weak response to NHE3 safety immunolocalization.

Proximal Tubule p53 in Cold Storage/Transplantation-Associated Kidney Injury and Renal Graft Dysfunction

Kidney injury associated with cold storage/transplantation is a primary factor for delayed graft function and poor outcome of renal transplants. p53 contributes to both ischemic and nephrotoxic kidney injury, but its involvement in kidney cold storage/transplantation is unclear. Here, we report that p53 in kidney proximal tubules plays a critical role in cold storage/transplantation kidney injury and inhibition of p53 can effectively improve the histology and function of transplanted kidneys. In a mouse kidney cold storage/transplantation model, we detected p53 accumulation in proximal tubules in a cold storage time-dependent manner, which correlated with tubular injury and cell death. Pifithrin-α, a pharmacologic p53 inhibitor, could reduce acute tubular injury, apoptosis and inflammation at 24 h after cold storage/transplantation. Similar effects were shown by the ablation of p53 from proximal tubule cells. Notably, pifithrin-α also ameliorated kidney injury and improved the function of transplanted kidneys in 6 days when it became the sole life-supporting kidney in recipient mice. in vitro, cold storage followed by rewarming induced cell death in cultured proximal tubule cells, which was accompanied by p53 activation and suppressed by pifithrin-α and dominant-negative p53. Together, these results support a pathogenic role of p53 in cold storage/transplantation kidney injury and demonstrate the therapeutic potential of p53 inhibitors.

GATA3 Is a Useful Immunohistochemical Marker to Differentiate Variants of Renal Tubular Lesions from Different Segments of Renal Tubules

Introduction/Objective GATA3 is found in glomerular mesangial cells, and the distal tubules & collecting ducts in metanephros and eventual kidneys, but not associated with the proximal tubules and loops of Henle. We hypothesize that GATA3 can be used as a marker to identify the origin of tubular differentiation in most renal tumors. Methods/Case Report Ten negative controls and 43 renal mass lesions (RCC, papillary, clear cell papillary, and chromophobe carcinomas, oncocytoma, and polycystic kidney disease). GATA3 nuclear stain was graded as negative (absent stain), equivocal and positive (< 5 and > 5% cells, respectively). Details of their GATA3 nuclear expression was analyzed for identifying their tubular segmental origins. Results (if a Case Study enter NA) In 10 normal renal parenchyma, GATA3 was positive in mesangial cells, distal tubules, and collecting ducts, but was negative in the proximal tubules and loop of Henle. The cystic lining of glomerulocystic renal disease was stained negatively for GATA3 (proximal tubular origin), whereas pediatric and adult variants of polycystic kidney diseases was positive for GATA3 staining (distal tubular origin). 1/10 ten clear cell RCC and papillary RCC showed focal positive GATA3 stain. GATA3 showed weakly positive staining in some oncocytomas (4/11) and some chromophobe RCC (4/11), indicating that they might be derived from the junctional segment between the loop of Henle and the distal tubules. By contrast, all clear cell papillary RCC (distal tubule origin) were diffusely positive. Conclusion Our results indicate that GATA3 is a useful immunohistochemical marker to determine the developmental origin in the specific renal tubular segment for the majority of renal mass lesions. Thus, it may be useful for routine differential diagnosis of these lesions.

Abstract 17: Genetic Deletion Of Angiotensin Ii AT 1a Receptors Selectively In The Proximal Tubules Of The Kidney Attenuates Two-kidney, One-clip Goldblatt Hypertension In Pt- Agtr1a -/- Mice

The activation of the renin-angiotensin system (RAS) in the clipped kidney plays a critical role in the development of two-kidney, one-clip Goldblatt hypertension (2K1C), but the roles of angiotensin II (Ang II) and AT 1a receptors in the proximal tubules has not been determined previously. The present study tested the hypothesis that genetic deletion of AT 1a receptors selectively in the proximal tubules attenuates the development of 2K1C Goldblatt hypertension via AT 1a receptor-mediated, Na + /H + exchanger 3 (NHE3)-dependent mechanisms. To test the hypothesis, 2K1C Goldblatt hypertension was induced by placing a silver clip, 0.2 mm internal diameter, on the left renal artery for 4 weeks in adult male wild-type (WT), global AT 1a receptor knockout ( Agtr1a -/- ), proximal tubule (PT)-specific Agtr1a -/- (PT- Agtr1a -/- ), or PT- Nhe3 -/- mice, respectively. In WT mice, systolic blood pressure increased in a time-dependent manner reaching a maximal response by Week 3 (Basal: 112 ± 2 vs. 2K1C: 149 ± 4 mmHg, n=12, P <0.01). 2K1C Goldblatt hypertension in WT mice was associated with significant increases in renin mRNA expression in the clipped kidney (Control: 2366 ± 255 vs. Clipped: 3144 ± 569 copies/ng RNA, P <0.01) and decreases in renin mRNA expression in the nonclipped kidney (1738 ± 341 copies/ng RNA, P <0.05). Plasma Ang II levels were significantly increased in WT mice with 2K1C Goldblatt hypertension (Control: 50.2 ± 7.2 vs. 2K1C: 109.7 ± 17.2 pg/ml, P <0.05). Glomerular and tubulointerstitial fibrotic responses were also significantly increased in the clipped kidney ( P <0.01). In contrast to WT mice, the development of 2K1C hypertension was completely attenuated in Agtr1a -/- (Basal: 88 ± 4 vs. 2K1C: 92 ± 2 mmHg, n=9, n.s .), PT- Agtr1a -/- mice (Basal: 101 ± 2 vs. 2K1C: 104 ± 3 mmHg, n=12, n.s .) and PT- Nhe3 -/- mice (Basal: 103 ± 3 vs. 109 ± 5 mmHg, n=12, n.s .). Renin mRNA expression was not different in clipped and nonclipped kidney of Agtr1a -/- mice, but it was decreased in the nonclipped kidney of PT- Agtr1a -/- mice ( P <0.05). Taken together, these data suggest that genetic deletion of AT 1a receptors selectively in the proximal tubules attenuates the development of 2K1C Goldblatt hypertension via AT 1a receptor-mediated, Na + /H + exchanger 3 (NHE3)-dependent mechanisms.

Reduced Expression of Metallothionein-I/II in Renal Proximal Tubules Is Associated with Advanced Chronic Kidney Disease

Chronic kidney disease (CKD) is a commonly occurring complex renal syndrome that causes overall mortality in many diseases. The clinical manifestations of CKD include renal tubulointerstitial fibrosis and loss of renal function. Metallothionein-I/II (MT-I/II) is potentially expressed in the liver and kidney, and possesses antioxidant and metal detoxification properties. However, whether MT-I/II expression is associated with the prognosis of nephropathy remains unknown. In this study, we investigated the MT-I/II level in human CKD, using immunohistochemistry. MT-I/II is located on the proximal tubules and is notably reduced in patients with CKD. MT-I/II expression was significantly correlated with the functional and histological grades of CKD. In an aristolochic acid (AAI)-induced nephropathy mouse model, MT-I/II was abundantly increased after AAI injection for 7 days, but decreased subsequently compared to that induced in the acute phase when injected with AAI for 28 days. Furthermore, we found that ammonium pyrrolidinedithiocarbamate (PDTC) restored AAI-induced MT-I/II reduction in HK2 cells. The injection of PDTC ameliorated AAI-induced renal tubulointerstitial fibrosis and reduced the concentrations of blood urea nitrogen and creatinine in mouse sera. Taken together, our results indicate that MT-I/II reduction is associated with advanced CKD, and the retention of renal MT-I/II is a potential therapeutic strategy for CKD.

Connexin mRNA distribution in adult mouse kidneys

Kidneys are thought to express eight different connexin isoforms (i.e., Cx 26, 30, 32, 37, 40, 43, 45, and 46), which form either hemichannels or gap junctions serving to intercellular communication and functional synchronization. Proper function of connexins has already been shown to be crucial for regulation of renal hemodynamics and renin secretion, and there is also growing evidence for connexins to play a role in pathologic conditions such as renal fibrosis or diabetic nephropathy. Therefore, exact intrarenal localization of the different connexin isoforms gains particular interest. Until now intrarenal expression of connexins has mainly been examined by immunohistochemistry, which in part generated conflicting results depending on antibodies and fixation protocols used. In this work, we used fluorescent RNAscope as an alternative technical approach to localize renal connexin mRNAs in healthy mouse kidneys. Addition of RNAscope probes for cell type specific mRNAs was used to assign connexin mRNA signals to specific cell types. We hereby found Cx26 mRNA strongly expressed in proximal tubules, Cx30 mRNA was selectively detected in the urothelium, and Cx32 mRNA was found in proximal tubules and to a lesser extent also in collecting ducts. Cx37 mRNA was mainly associated with vascular endothelium, Cx40 mRNA was largely found in glomerular mesangial and less in vascular endothelial cells, Cx43 mRNA was sparsely expressed by interstitial cells of all kidney zones, and Cx45 mRNA was predominantly found in smooth muscle cell layers of both blood vessels and ureter as well as in mesangial and interstitial (fibroblastic) cells. Cx46 mRNA could not be detected. In summary our results essentially confirm previous data on connexin expression in the renal vasculature and in glomeruli. In addition, they demonstrate strong connexin gene expression in proximal tubules, and they suggest significant connexin expression in resident tubulointerstitial cells.

Intratubular, Intracellular, and Mitochondrial Angiotensin II/AT1 (AT1a) Receptor/NHE3 Signaling Plays a Critical Role in Angiotensin II-Induced Hypertension and Kidney Injury

Hypertension is well recognized to be the most important risk factor for cardiovascular diseases, stroke, and end-stage kidney failure. A quarter of the world’s adult populations and 46% of the US adults develop hypertension and currently require antihypertensive treatments. Only 50% of hypertensive patients are responsive to current antihypertensive drugs, whereas remaining patients may continue to develop cardiovascular, stroke, and kidney diseases. The mechanisms underlying the poorly controlled hypertension remain incompletely understood. Recently, we have focused our efforts to uncover additional renal mechanisms, pathways, and therapeutic targets of poorly controlled hypertension and target organ injury using novel animal models or innovative experimental approaches. Specifically, we studied and elucidated the important roles of intratubular, intracellular, and mitochondrial angiotensin II (Ang II) system in the development of Ang II-dependent hypertension. The objectives of this invited article are to review and discuss our recent findings that (a) circulating and intratubular Ang II is taken up by the proximal tubules via the (AT1) AT1a receptor-dependent mechanism, (b) intracellular administration of Ang II in proximal tubule cells or adenovirus-mediated overexpression of an intracellular Ang II fusion protein selectively in the mitochonria of the proximal tubules induces blood pressure responses, and (c) genetic deletion of AT1 (AT1a) receptors or the Na+/H+ exchanger 3 selectively in the proximal tubules decreases basal blood pressure and attenuates Ang II-induced hypertension. These studies provide a new perspective into the important roles of the intratubular, intracellular, and mitochondrial angiotensin II/AT1 (AT1a) receptor signaling in Ang II-dependent hypertensive kidney diseases.