The direct effect of fibroblast growth factor 23 on vascular smooth muscle cell phenotype and function.

BACKGROUND: In chronic kidney disease (CKD) patients, increased levels of fibroblast growth factor 23 (FGF23) are associated with cardiovascular mortality. The relationship between FGF23 and heart hypertrophy has been documented, however, it is not known whether FGF23 has an effect on vasculature. Vascular smooth muscle cells VSMCs may exhibit different phenotypes; our hypothesis is that FGF23 favours a switch from a contractile to synthetic phenotype that may cause vascular dysfunction. Our objective was to determine whether FGF23 may directly control a change in VSMC phenotype. METHODS: This study includes in vitro, in vivo and ex vivo experiments and evaluation of patients with CKD stages 2-3 studying a relationship between FGF23 and vascular dysfunction. RESULTS: In vitro studies show that high levels of FGF23, by acting on its specific receptor FGFR1 and Erk1/2, causes a change in the phenotype of VSMCs from contractile to synthetic. This change is mediated by a downregulation of miR-221/222, which augments the expression of MAP3K2 and PAK1. miR-221/222 transfections recovered the contractile phenotype of VSMCs. Infusion of recombinant FGF23 to rats increased vascular wall thickness, with VSMCs showing a synthetic phenotype with a reduction of miR-221 expression. Ex-vivo studies on aortic rings demonstrate also that high FGF23 increases arterial stiffening. In CKD 2-3 patients, elevation of FGF23 was associated with increased pulse wave velocity and reduced plasma levels of miR-221/222. CONCLUSION: In VSMCs, high levels of FGF23, through the downregulation of miR-221/222, causes a change to a synthetic phenotype. This change in VSMCs increases arterial stiffening and impairs vascular function, which might ultimately worsen cardiovascular disease.

TWEAK Signaling Pathway Blockade Slows Cyst Growth and Disease Progression in Autosomal Dominant Polycystic Kidney Disease.

BACKGROUND: In autosomal dominant polycystic kidney disease (ADPKD), cyst development and enlargement lead to ESKD. Macrophage recruitment and interstitial inflammation promote cyst growth. TWEAK is a TNF superfamily (TNFSF) cytokine that regulates inflammatory responses, cell proliferation, and cell death, and its receptor Fn14 (TNFRSF12a) is expressed in macrophage and nephron epithelia. METHODS: To evaluate the role of the TWEAK signaling pathway in cystic disease, we evaluated Fn14 expression in human and in an orthologous murine model of ADPKD. We also explored the cystic response to TWEAK signaling pathway activation and inhibition by peritoneal injection. RESULTS: Meta-analysis of published animal-model data of cystic disease reveals mRNA upregulation of several components of the TWEAK signaling pathway. We also observed that TWEAK and Fn14 were overexpressed in mouse ADPKD kidney cysts, and TWEAK was significantly high in urine and cystic fluid from patients with ADPKD. TWEAK administration induced cystogenesis and increased cystic growth, worsening the phenotype in a murine ADPKD model. Anti-TWEAK antibodies significantly slowed the progression of ADPKD, preserved renal function, and improved survival. Furthermore, the anti-TWEAK cystogenesis reduction is related to decreased cell proliferation-related MAPK signaling, decreased NF-κB pathway activation, a slight reduction of fibrosis and apoptosis, and an indirect decrease in macrophage recruitment. CONCLUSIONS: This study identifies the TWEAK signaling pathway as a new disease mechanism involved in cystogenesis and cystic growth and may lead to a new therapeutic approach in ADPKD.

Inflammation both increases and causes resistance to FGF23 in normal and uremic rats.

Fibroblast growth factor 23 (FGF23) increases phosphorus excretion and decreases calcitriol (1,25(OH)2D) levels. FGF23 increases from early stages of renal failure. We evaluated whether strict control of phosphorus intake in renal failure prevents the increase in FGF23 and to what extent inflammation impairs regulation of FGF23. The study was performed in 5/6 nephrectomized (Nx) Wistar rats fed diets containing 0.2-1.2% phosphorus for 3 or 15 days. FGF23 levels significantly increased in all Nx groups in the short-term (3-day) experiment. However, at 15 days, FGF23 increased in all Nx rats except in those fed 0.2% phosphorus. In a second experiment, Nx rats fed low phosphorus diets (0.2 and 0.4%) for 15 days received daily intraperitoneal lipopolysaccharide (LPS) injections to induce inflammation. In these rats, FGF23 increased despite the low phosphorus diets. Thus, higher FGF23 levels were needed to maintain phosphaturia and normal serum phosphorus values. Renal Klotho expression was preserved in Nx rats on a 0.2% phosphorus diet, reduced on a 0.4% phosphorus diet, and markedly reduced in Nx rats receiving LPS. In ex vivo experiments, high phosphorus and LPS increased nuclear ß-catenin and p65-NFκB and decreased Klotho. Inhibition of inflammation and Wnt signaling activation resulted in decreased FGF23 levels and increased renal Klotho. In conclusion, strict control of phosphorus intake prevented the increase in FGF23 in renal failure, whereas inflammation independently increased FGF23 values. Decreased Klotho may explain the renal resistance to FGF23 in inflammation. These effects are likely mediated by the activation of NFkB and Wnt/ß-catenin signaling.

PGC-1α deficiency causes spontaneous kidney inflammation and increases the severity of nephrotoxic AKI.

PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1α, PPARGC1A) regulates the expression of genes involved in energy homeostasis and mitochondrial biogenesis. Here we identify inactivation of the transcriptional regulator PGC-1α as a landmark for experimental nephrotoxic acute kidney injury (AKI) and describe the in vivo consequences of PGC-1α deficiency over inflammation and cell death in kidney injury. Kidney transcriptomic analyses of WT mice with folic acid-induced AKI revealed 1398 up- and 1627 downregulated genes. Upstream transcriptional regulator analyses pointed to PGC-1α as the transcription factor potentially driving the observed expression changes with the highest reduction in activity. Reduced PGC-1α expression was shared by human kidney injury. Ppargc1a-/- mice had spontaneous subclinical kidney injury characterized by tubulointerstitial inflammation and increased Ngal expression. Upon AKI, Ppargc1a-/- mice had lower survival and more severe loss of renal function, tubular injury, and reduction in expression of mitochondrial PGC-1α-dependent genes in the kidney, and an earlier decrease in mitochondrial mass than WT mice. Additionally, surviving Ppargc1a-/- mice showed higher rates of tubular cell death, compensatory proliferation, expression of proinflammatory cytokines, NF-κB activation, and interstitial inflammatory cell infiltration. Specifically, Ppargc1a-/- mice displayed increased M1 and decreased M2 responses and expression of the anti-inflammatory cytokine IL-10. In cultured renal tubular cells, PGC-1α targeting promoted spontaneous cell death and proinflammatory responses. In conclusion, PGC-1α inactivation is a key driver of the gene expression response in nephrotoxic AKI and PGC-1α deficiency promotes a spontaneous inflammatory kidney response that is magnified during AKI. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Epigenetic Modifiers as Potential Therapeutic Targets in Diabetic Kidney Disease.

Diabetic kidney disease is one of the fastest growing causes of death worldwide. Epigenetic regulators control gene expression and are potential therapeutic targets. There is functional interventional evidence for a role of DNA methylation and the histone post-translational modifications-histone methylation, acetylation and crotonylation-in the pathogenesis of kidney disease, including diabetic kidney disease. Readers of epigenetic marks, such as bromodomain and extra terminal (BET) proteins, are also therapeutic targets. Thus, the BD2 selective BET inhibitor apabetalone was the first epigenetic regulator to undergo phase-3 clinical trials in diabetic kidney disease with an endpoint of kidney function. The direct therapeutic modulation of epigenetic features is possible through pharmacological modulators of the specific enzymes involved and through the therapeutic use of the required substrates. Of further interest is the characterization of potential indirect effects of nephroprotective drugs on epigenetic regulation. Thus, SGLT2 inhibitors increase the circulating and tissue levels of ß-hydroxybutyrate, a molecule that generates a specific histone modification, ß-hydroxybutyrylation, which has been associated with the beneficial health effects of fasting. To what extent this impact on epigenetic regulation may underlie or contribute to the so-far unclear molecular mechanisms of cardio- and nephroprotection offered by SGLT2 inhibitors merits further in-depth studies.

Calcimimetics maintain bone turnover in uremic rats despite the concomitant decrease in parathyroid hormone concentration.

Calcimimetics decrease parathyroid hormone (PTH) secretion in patients with secondary hyperparathyroidism. The decrease in PTH should cause a reduction in bone turnover; however, the direct effect of calcimimetics on bone cells, which express the calcium-sensing receptor (CaSR), has not been defined. In this study, we evaluated the direct bone effects of CaSR activation by a calcimimetic (AMG 641) in vitro and in vivo. To create a PTH "clamp," total parathyroidectomy was performed in rats with and without uremia induced by 5/6 nephrectomy, followed by a continuous subcutaneous infusion of PTH. Animals were then treated with either the calcimimetic or vehicle. Calcimimetic administration increased osteoblast number and osteoid volume in normal rats under a PTH clamp. In uremic rats, the elevated PTH concentration led to reduced bone volume and increased bone turnover, and calcimimetic administration decreased plasma PTH. In uremic rats exposed to PTH at 6-fold the usual replacement dose, calcimimetic administration increased osteoblast number, osteoid surface, and bone formation. A 9-fold higher dose of PTH caused an increase in bone turnover that was not altered by the administration of calcimimetic. In an osteosarcoma cell line, the calcimimetic induced Erk1/2 phosphorylation and the expression of osteoblast genes. The addition of a calcilytic resulted in the opposite effect. Moreover, the calcimimetic promoted the osteogenic differentiation and mineralization of human bone marrow mesenchymal stem cells in vitro. Thus, calcimimetic administration has a direct anabolic effect on bone that counteracts the decrease in PTH levels.

Differential regulation of renal Klotho and FGFR1 in normal and uremic rats.

In renal failure, hyperphosphatemia occurs despite a marked elevation in serum fibroblast growth factor (FGF)-23. Abnormal regulation of the FGFR1-Klotho receptor complex may cause a resistance to the phosphaturic action of FGF23. The purpose of the present study was to investigate the regulation of renal Klotho and FGF receptor (FEFR)-1 in healthy and uremic rats induced by 5/6 nephrectomy. In normal rats, the infusion of rat recombinant FGF23 enhanced phosphaturia and increased renal FGFR1 expression; however, Klotho expression was reduced. Uremic rats on a high-phosphate (HP) diet presented hyperphosphatemia with marked elevation of FGF23 and an increased fractional excretion of phosphate (P) that was associated with a marked reduction of Klotho expression and an increase in FGFR1. After neutralization of FGF23 by anti-FGF23 administration, phosphaturia was still abundant, Klotho expression remained low, and the FGFR1 level was reduced. These results suggest that the expression of renal Klotho is modulated by phosphaturia, whereas the FGFR1 expression is regulated by FGF23. Calcitriol (CTR) administration prevented a decrease in renal Klotho expression. In HEK293 cells HP produced nuclear translocation of ß-catenin, together with a reduction in Klotho. Wnt/ß-catenin inhibition with Dkk-1 prevented the P-induced down-regulation of Klotho. The addition of CTR to HP medium was able to recover Klotho expression. In summary, high FGF23 levels increase FGFR1, whereas phosphaturia decreases Klotho expression through the activation of Wnt/ß-catenin pathway.-Muñoz-Castañeda, J. R., Herencia, C., Pendón-Ruiz de Mier, M. V., Rodriguez-Ortiz, M. E., Diaz-Tocados, J. M., Vergara, N., Martínez-Moreno, J. M., Salmerón, M. D., Richards, W. G., Felsenfeld, A., Kuro-O, M., Almadén, Y., Rodríguez, M. Differential regulation of renal Klotho and FGFR1 in normal and uremic rats.

Dietary magnesium supplementation prevents and reverses vascular and soft tissue calcifications in uremic rats.

Although magnesium has been shown to prevent vascular calcification in vitro, controlled in vivo studies in uremic animal models are limited. To determine whether dietary magnesium supplementation protects against the development of vascular calcification, 5/6 nephrectomized Wistar rats were fed diets with different magnesium content increasing from 0.1 to 1.1%. In one study we analyzed bone specimens from rats fed 0.1%, 0.3%, and 0.6% magnesium diets, and in another study we evaluated the effect of intraperitoneal magnesium on vascular calcification in 5/6 nephrectomized rats. The effects of magnesium on established vascular calcification were also evaluated in uremic rats fed on diets with either normal (0.1%) or moderately increased magnesium (0.6%) content. The increase in dietary magnesium resulted in a marked reduction in vascular calcification, together with improved mineral metabolism and renal function. Moderately elevated dietary magnesium (0.3%), but not high dietary magnesium (0.6%), improved bone homeostasis as compared to basal dietary magnesium (0.1%). Results of our study also suggested that the protective effect of magnesium on vascular calcification was not limited to its action as an intestinal phosphate binder since magnesium administered intraperitoneally also decreased vascular calcification. Oral magnesium supplementation also reduced blood pressure in uremic rats, and in vitro medium magnesium decreased BMP-2 and p65-NF-κB in TNF-α-treated human umbilical vein endothelial cells. Finally, in uremic rats with established vascular calcification, increasing dietary magnesium from 0.1% magnesium to 0.6% reduced the mortality rate from 52% to 28%, which was associated with reduced vascular calcification. Thus, increasing dietary magnesium reduced both vascular calcification and mortality in uremic rats.

High phosphate induces a pro-inflammatory response by vascular smooth muscle cells and modulation by vitamin D derivatives.

In chronic kidney disease patients, high phosphate (HP) levels are associated with cardiovascular disease, the major cause of morbidity and mortality. Since serum phosphate has been independently correlated with inflammation, the present study aimed to investigate an independent direct effect of HP as a pro-inflammatory factor in VSMCs. A possible modulatory effect of vitamin D (VitD) was also investigated. The study was performed in an in vitro model of human aortic smooth muscle cells (HASMCs). Incubation of cells in an HP (3.3 mM) medium caused an increased expression of the pro-inflammatory mediators intercellular adhesion molecule 1 (ICAM-1), interleukins (ILs) IL-1ß, IL-6, IL-8 and tumour necrosis factor α (TNF-α) (not corroborated at the protein levels for ICAM-1), as well as an increase in reactive oxygen/nitrogen species (ROS/RNS) production. This was accompanied by the activation of nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) signalling as demonstrated by the increase in the nuclear translocation of nuclear factor κ-light-chain-enhancer of activated B cells protein 65 (p65-NF-κΒ) assessed by Western blotting and confocal microscopy. Since all these events were attenuated by an antioxidant pre-incubation with the radical scavenger Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP), it is suggested that the inflammatory response is upstream mediated by the ROS/RNS-induced activation of NF-κΒ. Addition of paricalcitol (PC) 3·10-8 M to cells in HP prevented the phosphate induced ROS/RNS increase, the activation of NF-κΒ and the cytokine up-regulation. A bimodal effect was observed, however, for different calcitriol (CTR) concentrations, 10-10 and 10-12 M attenuated but 10-8 M stimulated this phosphate induced pro-oxidative and pro-inflammatory response. Therefore, these findings provide novel mechanisms whereby HP may directly favour vascular dysfunctions and new insights into the protective effects exerted by VitD derivatives.

Vitamin D modulates tissue factor and protease-activated receptor 2 expression in vascular smooth muscle cells.

Clinical and epidemiologic studies reveal an association between vitamin D deficiency and increased risk of cardiovascular disease. Because vascular smooth muscle cell (VSMC)-derived tissue factor (TF) is suggested to be critical for arterial thrombosis, we investigated whether the vitamin D molecules calcitriol and paricalcitol could reduce the expression of TF induced by the proinflammatory cytokine TNF-α in human aortic VSMCs. We found that, compared with controls, incubation with TNF-α increased TF expression and procoagulant activity in a NF-κB-dependent manner, as deduced from the increased nuclear translocation of nuclear factor κ-light-chain-enhancer of activated B cells protein 65 (p65-NF-κB) and direct interaction of NF-κB to the TF promoter. This was accompanied by the up-regulation of TF signaling mediator protease-activated receptor 2 (PAR-2) expression and by the down-regulation of vitamin D receptor expression in a miR-346-dependent way. However, addition of calcitriol or paricalcitol blunted the TNF-α-induced TF expression and activity (2.01 ± 0.24 and 1.32 ± 0.14 vs. 3.02 ± 0.39 pmol/mg protein, P < 0.05), which was associated with down-regulation of NF-κB signaling and PAR-2 expression, as well as with restored levels of vitamin D receptor and enhanced expression of TF pathway inhibitor. Our data suggest that inflammation promotes a prothrombotic state through the up-regulation of TF function in VSMCs and that the beneficial cardiovascular effects of vitamin D may be partially due to decreases in TF expression and its activity in VSMCs.

Magnesium modulates parathyroid hormone secretion and upregulates parathyroid receptor expression at moderately low calcium concentration.

BACKGROUND: The interest on magnesium (Mg) has grown since clinical studies have shown the efficacy of Mg-containing phosphate binders. However, some concern has arisen for the potential effect of increased serum Mg on parathyroid hormone (PTH) secretion. Our objective was to evaluate the direct effect of Mg in the regulation of the parathyroid function; specifically, PTH secretion and the expression of parathyroid cell receptors: CaR, the vitamin D receptor (VDR) and FGFR1/Klotho. METHODS: The work was performed in vitro by incubating intact rat parathyroid glands in different calcium (Ca) and Mg concentrations. RESULTS: Increasing Mg concentrations from 0.5 to 2 mM produced a left shift of PTH-Ca curves. With Mg 5 mM, the secretory response was practically abolished. Mg was able to reduce PTH only if parathyroid glands were exposed to moderately low Ca concentrations; with normal-high Ca concentrations, the effect of Mg on PTH inhibition was minor or absent. After 6-h incubation at a Ca concentration of 1.0 mM, the expression of parathyroid CaR, VDR, FGFR1 and Klotho (at mRNA and protein levels) was increased with a Mg concentration of 2.0 when compared with 0.5 mM. CONCLUSIONS: Mg reduces PTH secretion mainly when a moderate low calcium concentration is present; Mg also modulates parathyroid glands function through upregulation of the key cellular receptors CaR, VDR and FGF23/Klotho system.

Calcium deficiency reduces circulating levels of FGF23.

Fibroblast growth factor (FGF) 23 inhibits calcitriol production, which could exacerbate calcium deficiency or hypocalcemia unless calcium itself modulates FGF23 in this setting. In Wistar rats with normal renal function fed a diet low in both calcium and vitamin D, the resulting hypocalcemia was associated with low FGF23 despite high parathyroid hormone (PTH) and high calcitriol levels. FGF23 correlated positively with calcium and negatively with PTH. Addition of high dietary phosphorus to this diet increased FGF23 except in rats with hypocalcemia despite high PTH levels. In parathyroidectomized rats, an increase in dietary calcium for 10 days increased serum calcium, with an associated increase in FGF23, decrease in calcitriol, and no change in phosphorus. Also in parathyroidectomized rats, FGF23 increased significantly 6 hours after administration of calcium gluconate. Taken together, these results suggest that hypocalcemia reduces the circulating concentrations of FGF23. This decrease in FGF23 could be a response to avoid a subsequent reduction in calcitriol, which could exacerbate hypocalcemia.

Dietary Mg Supplementation Decreases Oxidative Stress, Inflammation, and Vascular Dysfunction in an Experimental Model of Metabolic Syndrome with Renal Failure.

BACKGROUND: Metabolic syndrome (MetS) and chronic kidney disease (CKD) are commonly associated with cardiovascular disease (CVD) and in these patients Mg concentration is usually decreased. This study evaluated whether a dietary Mg supplementation might attenuate vascular dysfunction through the modulation of oxidative stress and inflammation in concurrent MetS and CKD. METHODS: A rat model of MetS (Zucker strain) with CKD (5/6 nephrectomy, Nx) was used. Nephrectomized animals were fed a normal 0.1%Mg (MetS+Nx+Mg0.1%) or a supplemented 0.6%Mg (MetS+Nx+Mg0.6%) diet; Sham-operated rats with MetS receiving 0.1%Mg were used as controls. RESULTS: As compared to controls, the MetS+Nx-Mg0.1% group showed a significant increase in oxidative stress and inflammation biomarkers (lipid peroxidation and aortic interleukin-1b and -6 expression) and Endothelin-1 levels, a decrease in nitric oxide and a worsening in uremia and MetS associated pathology as hypertension, and abnormal glucose and lipid profile. Moreover, proteomic evaluation revealed changes mainly related to lipid metabolism and CVD markers. By contrast, in the MetS+Nx+Mg0.6% group, these parameters remained largely similar to controls. CONCLUSION: In concurrent MetS and CKD, dietary Mg supplementation reduced inflammation and oxidative stress and improved vascular function.

In vascular smooth muscle cells paricalcitol prevents phosphate-induced Wnt/ß-catenin activation.

The present study investigates the differential effect of two vitamin D receptor agonists, calcitriol and paricalcitol, on human aortic smooth muscle cells calcification in vitro. Human vascular smooth muscle cells were incubated in a high phosphate (HP) medium alone or supplemented with either calcitriol 10(-8)M (HP + CTR) or paricalcitol 3·10(-8) M (HP + PC). HP medium induced calcification, which was associated with the upregulation of mRNA expression of osteogenic factors such as bone morphogenetic protein 2 (BMP2), Runx2/Cbfa1, Msx2, and osteocalcin. In these cells, activation of Wnt/ß-catenin signaling was evidenced by the translocation of ß-catenin into the nucleus and the increase in the expression of direct target genes as cyclin D1, axin 2, and VCAN/versican. Addition of calcitriol to HP medium (HP + CTR) further increased calcification and also enhanced the expression of osteogenic factors together with a significant elevation of nuclear ß-catenin levels and the expression of cyclin D1, axin 2, and VCAN. By contrast, the addition of paricalcitol (HP + PC) not only reduced calcification but also downregulated the expression of BMP2 and other osteoblastic phenotype markers as well as the levels of nuclear ß-catenin and the expression of its target genes. The role of Wnt/ß-catenin on phosphate- and calcitriol-induced calcification was further demonstrated by the inhibition of calcification after addition of Dickkopf-related protein 1 (DKK-1), a specific natural antagonist of the Wnt/ß-catenin signaling pathway. In conclusion, the differential effect of calcitriol and paricalcitol on vascular calcification appears to be mediated by a distinct regulation of the BMP and Wnt/ß-catenin signaling pathways.

Development of parathyroid gland hyperplasia without uremia: role of dietary calcium and phosphate.

Background. Many experimental studies have demonstrated that parathyroid cell proliferation is induced by uremia and further aggravated by hypocalcemia, phosphorus retention and vitamin D deficiency. However, these factors may also promote parathyroid growth without uremia. In the present study, we examined the onset and progression of parathyroid hyperplasia regardless of the uremic setting, a situation that might occur soon during the early renal disease. Thus, the novelty of this work resides in the close examination of the time course for the expected changes in proliferation rates and their association with parathyroid hormone (PTH) release in normal rats under the physiological demands of a high-phosphate diet (HPD) or a low-calcium diet (LCD). Methods. We evaluated the functional response of the parathyroid glands in normal rats to different physiological demands an HPD 0.6% Ca, 1.2% P) and LCD 0.2% Ca, 0.6% P) and compared it with that of uremic rats. Furthermore, we also evaluated the time course for the reversal of high-P and low-Ca-induced parathyroid cell growth and PTH upon normalization of dietary Ca and P intake (0.6% Ca, 0.6% P). Proliferation was measured by flow cytometry and calcium receptor (CaR) and vitamin D receptor (VDR) expression were assessed by qRT-PCR. Results. The pattern in the development of parathyroid hyperplasia by the two dietary models was different. The HPD produced a stronger stimulus than the number of proliferating cells doubled after only 1 day, while the LCD required 5 days to induce an increase; the elevated calcitriol might be a mitigating factor. The increase in cell proliferation was accompanied by a transient down-regulation of VDR expression (higher in the HPD); the expression of CaR was not affected by either diet. Cell proliferation and VDR mRNA levels were restored to control values by Day 15; it is as though the gland had attained a sufficient level of hyperplasia to respond to the PTH challenge. Compared to normal rats, the response of uremic rats to the HPD showed sustained and much higher rates of PTH secretion and cell proliferation and sustained down-regulation of both VDR mRNA and CaR mRNA. Finally, the recovery from the HPD or LCD to a control diet resulted in a rapid restoration of PTH values (1 to 2 days), but the reduction in cell proliferation was delayed (3 to 5 days). Conclusions. Regardless of uremia, a physiological demand to increase the PTH secretion driven either by a high P or a low Ca intake is able to induce a different pattern of parathyroid hyperplasia, which might be aggravated by the down-regulation of VDR expression. The recovery from the HPD or LCD to a control diet results in a more rapid reduction in PTH than in cell proliferation.

Molecular pathways driving omeprazole nephrotoxicity.

Omeprazole, a proton pump inhibitor used to treat peptic ulcer and gastroesophageal reflux disease, has been associated to chronic kidney disease and acute interstitial nephritis. However, whether omeprazole is toxic to renal cells is unknown. Omeprazole has a lethal effect over some cancer cells, and cell death is a key process in kidney disease. Thus, we evaluated the potential lethal effect of omeprazole over tubular cells. Omeprazole induced dose-dependent cell death in human and murine proximal tubular cell lines and in human primary proximal tubular cell cultures. Increased cell death was observed at the high concentrations used in cancer cell studies and also at lower concentrations similar to those in peptic ulcer patient serum. Cell death induced by omeprazole had features of necrosis such as annexin V/7-AAD staining, LDH release, vacuolization and irregular chromatin condensation. Weak activation of caspase-3 was observed but inhibitors of caspases (zVAD), necroptosis (Necrostatin-1) or ferroptosis (Ferrostatin-1) did not prevent omeprazole-induced death. However, omeprazole promoted a strong oxidative stress response affecting mitochondria and lysosomes and the antioxidant N-acetyl-cysteine reduced oxidative stress and cell death. By contrast, iron overload increased cell death. An adaptive increase in the antiapoptotic protein BclxL failed to protect cells. In mice, parenteral omeprazole increased tubular cell death and the expression of NGAL and HO-1, markers of renal injury and oxidative stress, respectively. In conclusion, omeprazole nephrotoxicity may be related to induction of oxidative stress and renal tubular cell death.

The Contribution of Histone Crotonylation to Tissue Health and Disease: Focus on Kidney Health.

Acute kidney injury (AKI) and chronic kidney disease (CKD) are the most severe consequences of kidney injury. They are interconnected syndromes as CKD predisposes to AKI and AKI may accelerate CKD progression. Despite their growing impact on the global burden of disease, there is no satisfactory treatment for AKI and current therapeutic approaches to CKD remain suboptimal. Recent research has focused on the therapeutic target potential of epigenetic regulation of gene expression, including non-coding RNAs and the covalent modifications of histones and DNA. Indeed, several drugs targeting histone modifications are in clinical use or undergoing clinical trials. Acyl-lysine histone modifications (e.g. methylation, acetylation, and crotonylation) have modulated experimental kidney injury. Most recently, increased histone lysine crotonylation (Kcr) was observed during experimental AKI and could be reproduced in cultured tubular cells exposed to inflammatory stress triggered by the cytokine TWEAK. The degree of kidney histone crotonylation was modulated by crotonate availability and crotonate supplementation protected from nephrotoxic AKI. We now review the functional relevance of histone crotonylation in kidney disease and other pathophysiological contexts, as well as the implications for the development of novel therapeutic approaches. These studies provide insights into the overall role of histone crotonylation in health and disease.

Ferroptosis and kidney disease.

Cell death is a finely regulated process occurring through different pathways. Regulated cell death, either through apoptosis or regulated necrosis offers the possibility of therapeutic intervention. Necroptosis and ferroptosis are among the best studied forms of regulated necrosis in the context of kidney disease. We now review the current evidence supporting a role for ferroptosis in kidney disease and the implications of this knowledge for the design of novel therapeutic strategies. Ferroptosis is defined functionally, as a cell modality characterized by peroxidation of certain lipids, constitutively suppressed by GPX4 and inhibited by iron chelators and lipophilic antioxidants. There is functional evidence of the involvement of ferroptosis in diverse forms of kidneys disease. In a well characterized nephrotoxic acute kidney injury model, ferroptosis caused an initial wave of death, triggering an inflammatory response that in turn promoted necroptotic cell death that perpetuated kidney dysfunction. This suggests that ferroptosis inhibitors may be explored as prophylactic agents in clinical nephrotoxicity or ischemia-reperfusion injury such as during kidney transplantation. Transplantation offers the unique opportunity of using anti-ferroptosis agent ex vivo, thus avoiding bioavailability and in vivo pharmacokinetics and pharmacodynamics issues.

Engineering parathyroid cells to treat secondary hyperparathyroidism.

Kanai et al. used antisense technology to reduce excessive PTH production. The authors have overcome technical difficulties to demonstrate that, by strategies of RNA interference, a steady reduction of PTH secretion can be induced in cultured parathyroid-cell spheroids and in athymic nude mice with hyperplastic parathyroid cells transplanted from patients with secondary hyperparathyroidism.

Mangiferin protects against adverse skeletal muscle changes and enhances muscle oxidative capacity in obese rats.

Obesity-related skeletal muscle changes include muscle atrophy, slow-to-fast fiber-type transformation, and impaired mitochondrial oxidative capacity. These changes relate with increased risk of insulin resistance. Mangiferin, the major component of the plant Mangifera indica, is a well-known anti-inflammatory, anti-diabetic, and antihyperlipidemic agent. This study tested the hypothesis that mangiferin treatment counteracts obesity-induced fiber atrophy and slow-to-fast fiber transition, and favors an oxidative phenotype in skeletal muscle of obese rats. Obese Zucker rats were fed gelatin pellets with (15 mg/kg BW/day) or without (placebo group) mangiferin for 8 weeks. Lean Zucker rats received the same gelatin pellets without mangiferin and served as non-obese and non-diabetic controls. Lesser diameter, fiber composition, and histochemical succinic dehydrogenase activity (an oxidative marker) of myosin-based fiber-types were assessed in soleus and tibialis cranialis muscles. A multivariate discriminant analysis encompassing all fiber-type features indicated that obese rats treated with mangiferin displayed skeletal muscle phenotypes significantly different compared with both lean and obese control rats. Mangiferin significantly decreased inflammatory cytokines, preserved skeletal muscle mass, fiber cross-sectional size, and fiber-type composition, and enhanced muscle fiber oxidative capacity. These data demonstrate that mangiferin attenuated adverse skeletal muscle changes in obese rats.