Cells Of Renal Proximal Convoluted Tubules Research Articles

Proximal convoluted tubule cells-derived exosomes attenuate aging-related vascular dysfunction

Aging is an identified risk factor for cardiovascular disease. Aging is associated with increased prevalence of endothelial dysfunction and arterial stiffening. Exosomes are bi-lipid nanoscale vesicles that play important roles in intercellular communications. The purpose of this study was to determine whether administration of renal proximal convoluted tubule cells (PCT)-derived exosomes affects vascular and renal function in aging mice. Aging (24 months old) and young mice (3 months old) were treated with PCT-derived exosomes via non-invasive injection into the kidney 3 times a week for 2 weeks. Administration of PCT-derived exosomes did not affect blood pressure or urinary Na+, K+, and Ca2+ excretions, indicating that PCT-derived exosomes did not affect kidney function. Pulse wave velocity (PWV) was increased in aging mice, indicating arterial stiffening. Interestingly, treatment with PCT-exosomes effectively reduced aging-associated arterial stiffening. In addition, aortic endothelium-dependent relaxing (EDR) responses to acetylcholine (Ach) were reduced in aging mice, indicating endothelial dysfunction. Treatment with PCT-derived exosomes rescued aging-associated aortic endothelial dysfunction. Mechanistically, aortic expression of VCAM1, ICAM1, TNFα, and MCP-1 was upregulated in aging mice, indicating vascular inflammation. Notably, aging-associated vascular inflammation was largely attenuated by delivery of PCT-derived exosomes. Our results suggest that PCT-derived exosomes improves aging-associated arterial stiffening and vascular dysfunction partly via inhibiting vascular inflammation. The findings may help develop novel therapeutic strategies for aging-associated vascular dysfunction using PCT-derived exosomes. This work is supported by NIH research grants R01 HL154147 and AG062375. 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.

XBP1-mediated transcriptional regulation of SLC5A1 in human epithelial cells in disease conditions

BackgroundSodium-Glucose cotransporter 1 and 2 (SGLT1/2) belong to the family of glucose transporters, encoded by SLC5A1 and SLC5A2, respectively. SGLT2 is almost exclusively expressed in the renal proximal convoluted tubule cells. SGLT1 is expressed in the kidneys but also in other organs throughout the body. Many SGLT inhibitor drugs have been developed based on the mechanism of blocking glucose (re)absorption mediated by SGLT1/2, and several have gained major regulatory agencies’ approval for treating diabetes. Intriguingly these drugs are also effective in treating diseases beyond diabetes, for example heart failure and chronic kidney disease. We recently discovered that SGLT1 is upregulated in the airway epithelial cells derived from patients of cystic fibrosis (CF), a devastating genetic disease affecting greater than 70,000 worldwide.ResultsIn the present work, we show that the SGLT1 upregulation is coupled with elevated endoplasmic reticulum (ER) stress response, indicated by activation of the primary ER stress senor inositol-requiring protein 1α (IRE1α) and the ER stress-induced transcription factor X-box binding protein 1 (XBP1), in CF epithelial cells, and in epithelial cells of other stress conditions. Through biochemistry experiments, we demonstrated that the spliced form of XBP1 (XBP1s) acts as a transcription factor for SLC5A1 by directly binding to its promoter region. Targeting this ER stress → SLC5A1 axis by either the ER stress inhibitor Rapamycin or the SGLT1 inhibitor Sotagliflozin was effective in attenuating the ER stress response and reducing the SGLT1 level in these cellular model systems.ConclusionsThe present work establishes a causal relationship between ER stress and SGLT1 upregulation and provides a mechanistic explanation why SGLT inhibitor drugs benefit diseases beyond diabetes.

Mitochondrial Superoxide Dismutase in Cisplatin-Induced Kidney Injury.

Cisplatin is a chemotherapy agent commonly used to treat a wide variety of cancers. Despite the potential for both severe acute and chronic side effects, it remains a preferred therapeutic option for many malignancies due to its potent anti-tumor activity. Common cisplatin-associated side-effects include acute kidney injury (AKI) and chronic kidney disease (CKD). These renal injuries may cause delays and potentially cessation of cisplatin therapy and have long-term effects on renal function reserve. Thus, developing mechanism-based interventional strategies that minimize cisplatin-associated kidney injury without reducing efficacy would be of great benefit. In addition to its action of cross-linking DNA, cisplatin has been shown to affect mitochondrial metabolism, resulting in mitochondrially derived reactive oxygen species (ROS). Increased ROS formation in renal proximal convoluted tubule cells is associated with cisplatin-induced AKI and CKD. We review the mechanisms by which cisplatin may induce AKI and CKD and discuss the potential of mitochondrial superoxide dismutase mimetics to prevent platinum-associated nephrotoxicity.

TMEM33 regulates intracellular calcium homeostasis in renal tubular epithelial cells

Mutations in the polycystins cause autosomal dominant polycystic kidney disease (ADPKD). Here we show that transmembrane protein 33 (TMEM33) interacts with the ion channel polycystin-2 (PC2) at the endoplasmic reticulum (ER) membrane, enhancing its opening over the whole physiological calcium range in ER liposomes fused to planar bilayers. Consequently, TMEM33 reduces intracellular calcium content in a PC2-dependent manner, impairs lysosomal calcium refilling, causes cathepsins translocation, inhibition of autophagic flux upon ER stress, as well as sensitization to apoptosis. Invalidation of TMEM33 in the mouse exerts a potent protection against renal ER stress. By contrast, TMEM33 does not influence pkd2-dependent renal cystogenesis in the zebrafish. Together, our results identify a key role for TMEM33 in the regulation of intracellular calcium homeostasis of renal proximal convoluted tubule cells and establish a causal link between TMEM33 and acute kidney injury.

Erratum: In colchicine-treated rats, cellular distribution of AQP-1 in convoluted and straight proximal tubule segments is differently affected

In cells along the nephron, the recycling of various components between the plasma membrane and intracellular organelles by vesicle trafficking depends on intact microtubules (MT). Previous studies of rats treated with the MT-disrupting drug colchicine showed that some brush-border membrane (BBM) transporters in renal proximal convoluted tubule cells (PCTC) become internalized in numerous vesicles randomly scattered in the cytoplasm. In this study, we compare the intracellular distribution of MT and several BBM proteins [megalin, vacuolar (V)-ATPase, water channel aquaporin-1 (AQP-1)] as well as endocytosis of the in-vivo-injected fluorescent marker FITC-dextran in PCTC and proximal straight tubule cells (PSTC) in control and colchicine-treated rats. Immunoblotting and immunocytochemical data show that in the PCTC and PSTC colchicine treatment causes: (1) disappearance of MT, (2) strongly diminished endocytosis of FITC-dextran, and (3) marked loss of megalin and V-ATPase from the BBM and their redistribution into intracellular vesicles. Similar pattern was observed for the distribution of AQP-1 in the PCTC. However, in the PSTC, the staining intensity of AQP-1 in the BBM, as well as its intracellular distribution remained unaffected by colchicine treatment. We conclude that in the PSTC, either MT play a minor role in the recycling of AQP-1 between the BBM and intracellular vesicles or BBM AQP-1 turns over much more slowly than in the PCTC.

Clinical experience with cidofovir in the treatment of cytomegalovirus retinitis.

Cidofovir (Vistide, HPMPC) is a nucleotide analogue with potent in vitro activity against cytomegalovirus (CMV) that was recently licensed for treatment of patients with acquired immunodeficiency syndrome (AIDS) and CMV retinitis. Cidofovir's prolonged intracellular half-life permits dosing once every 2 weeks for maintenance treatment. The treatment-limiting toxicity of cidofovir is dose- and schedule-dependent nephrotoxicity affecting renal proximal convoluted tubule cells. A treatment regimen that includes concomitant administration of oral probenecid, intravenous hydration, and careful preinfusion evaluation of renal function with conservative dose modification has reduced cidofovir-associated nephrotoxicity. Preliminary results of clinical studies of cidofovir in AIDS patients with newly diagnosed and relapsing CMV retinitis are described.

Diverse modulations of chloride channels in renal proximal tubules

Cl- selective channels were detected and characterized in apical membranes of cultured rat renal proximal convoluted tubule cells (PCT) using patch-clamping methods. Subpopulations of Cl- channels modulated by cyclic nucleotides, Ca2+, or voltage were identified. Two different 30-pS, voltage-independent, Cl- channels modulated by adenosine 3',5'-cyclic monophosphate (cAMP) or Ca2+ were seen most frequently. The cAMP-dependent channel was activated by membrane-permeable analogues of cAMP, dibutyryl-cAMP or 8-bromo-cAMP. Catalytic subunit of protein kinase A (PKA) applied to detached inside-out patches, activated the channel as well, suggesting activation via phosphorylation. Channel activity was blocked by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, by 4,4-dinitrostilbene-2,2-disulfonic acid, and by SCN-. Permeability sequence for different halides was Cl- > I > F with a Cl(-)-to-cation permeability ratio (PCl/Pcation) of 7:1. The Ca(2+)-sensitive channel was not activated by cAMP nor by PKA. A third anionic selective channel encountered infrequently is voltage dependent and has a unitary conductance of 145 pS, with a PCl/Pcation value of 9:1. This diversity of Cl- channels may underlie the rich repertoire of physiological functions attributed to Cl- channels.

IGF-II/Man-6-P receptors in rat kidney: Apical localization in proximal tubule cells

The present study was performed to determine the localization of insulin-like growth factor II (IGF-II) binding in the rat nephron and, furthermore, to determine directly the distribution of the IGF-II/Man-6-P receptor in the proximal tubule. The IGF-II/Man-6-P receptor was visualized by immunohisto- and cytochemical techniques, and the binding of IGF-II was shown by light and electron microscope autoradiography applying 125I-IGF-II directly on cryosections. The tubular uptake of IGF-II was studied by autoradiography after in vivo injection of 125I-IGF-II. The light microscope immunolabeling was confined to a relatively narrow band in the apical part of the proximal tubule cells just below the brush border, and was strongest in the first portion of the proximal tubule, segment 1 (S1), with decreasing intensity in segment 2 (S2) and weaker in segment 3 (S3). Several cytoplasmic bodies were labeled but no label was observed in the basolateral part of the cells. We did not detect any labeling of glomeruli or other segments of the nephron. Electron microscope immunocytochemistry in the proximal tubule revealed a strong labeling in apical endocytic invaginations, small endocytic vacuoles, and large endocytic vacuoles, weaker in lysosomes and dense apical tubules. Light microscope autoradiography after incubation of cryosections with labeled IGF-II demonstrated an intense labeling just beneath the brush border, especially in S1 of the proximal tubule, and, in addition, the corresponding electron microscope autoradiography revealed an intense labeling over large endocytic vacuoles and lysosomes. These results were confirmed and extended by competitive binding experiments and quantitative immunocytochemistry. After i.v. injection of 125I-IGF-II autoradiographic grains were almost exclusively observed in the electronmicroscope over endocytic vacuoles and lysosomes in the S1 of the proximal tubule. The present study shows that the IGF-II/Man-6-P receptor is located in components of the vacuolar system in the apical cytoplasm of rat renal proximal convoluted tubule cells, mainly in S1. This localization was seen to be consistent using various immunolabeling and autoradiographic techniques in vivo and in vitro.

A Cl- channel activated by parathyroid hormone in rabbit renal proximal tubule cells.

Previous data suggested an active Cl- conductance in the renal proximal convoluted tubule, although single channel conductance and regulation were not found. We have investigated the presence and regulation of the Cl- channel in proximal convoluted tubules by patch clamp analysis. The current-voltage relationship of whole cells with 130 mM NaCl in the pipette was nonlinear. The addition of 1-34 PTH (10(-8) M), forskolin, or cAMP significantly increased whole cell Cl- conductance. We found a single Cl- channel in excised apical membranes possessing conductance of 33 picosiemens (pS) at positive and 22.5 pS at negative potential, which was blocked by 4,4'-diisothiocyanostilbene-2,2'- disulfonic acid (10(-4) M) and was selective to Cl- (Cl/Na = 10). The channel was activated by prolonged membrane depolarization, by a catalytic subunit of protein kinase A (PKA), or by purified kinase C (PKC), but not by Ca2+ (1 microM) inside the membrane. During cell-attached patch clamping, the channel was similarly activated by PTH, phorbol ester, or dibutyryl cAMP in a dose-dependent manner. To investigate second messenger contributions to the PTH-action, the PTH-evoked channels were modified further by the subsequent addition of several blockers of the second messengers. This suggested that PKA and PKC were involved in Cl- channel activation. We therefore conclude that renal proximal convoluted tubule cells possess an apical Cl- channel activated by PTH via the PKA and PKC pathways.

Distribution of lead in renal proximal convoluted tubules of lead‐poisoned rats

AbstractIntranuclear inclusions have been found in epithelial cells of renal proximal convoluted tubules (RPCT) in lead poisoned animals. It has been suggested previously that the inclusions contained lead. The present report gives evidence to the contrary. Samples of renal cortex were taken from adult rats fed laboratory chow containing 2% lead acetate for 1 month. Under the electron microscope (EM), intranuclear inclusions were observed in epithelial cells of RPCT. They were round or ovoid, and not delineated by a membrane. They consisted of two parts: Peripheral and central. Lysosomes increased in number, and many myelin figures appeared in the cytoplasm. In the lumen of the tubules, high electron‐dense concretions were found. By x‐ray microranalysis, neither the central part nor the peripheral part of the intranuclear inclusions produced a lead peak in the spectrum. Lysosomes and the cytoplasmic matrix also showed no lead peak. However, when the electron beam was focused on the concretion in the lumen of the RPCT, the Lα peak of lead (10.551 keV) and Kα peak of calcium (3.691 keV) were evident. From these findings it is suggested that intranuclear inclusions in the cells of RPCT are not lead deposits. Rather, it is the concretions found in the lumen of tubule that contain lead.

Enflurane nephrotoxicity and pre-existing renal dysfunction.

This study provides the first morphological evidence of significant structural damage following high doses of enflurane alone and confirms previous findings of transient renal functional abnormalities following high dosage enflurane. The study also indicates that enflurane may have a greater potential for renal toxicity in the presence of renal impairment. Treatment of Fischer 344 rats with a nephrotoxic dose of gentamicin prior to six hours of enflurane (GE) anaesthesia at 1 MAC resulted in increased serum concentration of the enflurance metabolite inorganic fluoride (GE, 43.9 +/- 1.5; E, 34.5 +/- 1.8 mu mol/L), increased urine flow rate and a greater degree of structural damage in renal proximal convoluted tubule cells than was observed with either gentamicin (G) or enflurane (E) alone. Treatment with gentamicin prior to enflurane also resulted in reduced urinary osmolality compared to enflurane or gentamicin alone (GE, 742 +/- 57; E, 1709 +/- 66; G, 985 +/- 32 m0sm/kg).

THE ETIOLOGY OF METHOXYFLURANE NEPHROTOXICITY

COUSINS, M. J.; MAZZE, R. I.; KOSEK, J. C.; HITT, B. A.; LOVE, F. V. Author Information