Dysregulated UPR and ER Stress Related to a Mutation in the Sdf2l1 Gene Are Involved in the Pathophysiology of Diet-Induced Diabetes in the Cohen Diabetic Rat.

The Cohen Diabetic rat is a model of type 2 diabetes mellitus that consists of the susceptible (CDs/y) and resistant (CDr/y) strains. Diabetes develops in CDs/y provided diabetogenic diet (DD) but not when fed regular diet (RD) nor in CDr/y given either diet. We recently identified in CDs/y a deletion in Sdf2l1, a gene that has been attributed a role in the unfolded protein response (UPR) and in the prevention of endoplasmic reticulum (ER) stress. We hypothesized that this deletion prevents expression of SDF2L1 and contributes to the pathophysiology of diabetes in CDs/y by impairing UPR, enhancing ER stress, and preventing CDs/y from secreting sufficient insulin upon demand. We studied SDF2L1 expression in CDs/y and CDr/y. We evaluated UPR by examining expression of key proteins involved in both strains fed either RD or DD. We assessed the ability of all groups of animals to secrete insulin during an oral glucose tolerance test (OGTT) over 4 weeks, and after overnight feeding (postprandial) over 4 months. We found that SDF2L1 was expressed in CDr/y but not in CDs/y. The pattern of expression of proteins involved in UPR, namely the PERK (EIF2α, ATF4 and CHOP) and IRE1 (XBP-1) pathways, was different in CDs/y DD from all other groups, with consistently lower levels of expression at 4 weeks after initiation of DD and coinciding with the development of diabetes. In CDs/y RD, insulin secretion was mildly impaired, whereas in CDs/y DD, the ability to secrete insulin decreased over time, leading to the development of the diabetic phenotype. We conclude that in CDs/y DD, UPR participating proteins were dysregulated and under-expressed at the time point when the diabetic phenotype became overt. In parallel, insulin secretion in CDs/y DD became markedly impaired. Our findings suggest that under conditions of metabolic load with DD and increased demand for insulin secretion, the lack of SDF2L1 expression in CDs/y is associated with UPR dysregulation and ER stress which, combined with oxidative stress previously attributed to the concurrent Ndufa4 mutation, are highly likely to contribute to the pathophysiology of diabetes in this model.

Minimal Change Disease Following the Pfizer-BioNTech COVID-19 Vaccine.

We report on the development of minimal change disease (MCD) with nephrotic syndrome and acute kidney injury (AKI), shortly after first injection of the BNT162b2 COVID-19 vaccine (Pfizer-BioNTech). A 50-year-old previously healthy man was admitted to our hospital following the appearance of peripheral edema. Ten days earlier, he had received the first injection of the vaccine. Four days after injection, he developed lower leg edema, which rapidly progressed to anasarca. On admission, serum creatinine was 2.31 mg/dL and 24-hour urinary protein excretion was 6.9 grams. As kidney function continued to decline over the next days, empirical treatment was initiated with prednisone 80 mg/d. A kidney biopsy was performed and the findings were consistent with MCD. Ten days later, kidney function began to improve, gradually returning to normal. The clinical triad of MCD, nephrotic syndrome, and AKI has been previously described under a variety of circumstances, but not following the Pfizer-BioNTech COVID-19 vaccine. The association between the vaccination and MCD is at this time temporal and by exclusion, and by no means firmly established. We await further reports of similar cases to evaluate the true incidence of this possible vaccine side effect.

Interleukin-6 contributes to the increase in fibroblast growth factor 23 expression in acute and chronic kidney disease.

The high serum fibroblast growth factor 23 (FGF23) levels in patients with acute kidney injury (AKI) and chronic kidney disease (CKD) are associated with increased morbidity and mortality. Mice with folic acid-induced AKI had an increase in bone FGF23 mRNA expression together with an increase in serum FGF23 and several circulating cytokines including interleukin-6 (IL-6). Dexamethasone partially prevented the increase in IL-6 and FGF23 in the AKI mice. IL-6 knock-out mice fed an adenine diet to induce CKD failed to increase bone FGF23 mRNA and had a muted increase in serum FGF23 levels, compared with the increases in wild-type mice with CKD. Therefore, IL-6 contributes to the increase in FGF23 observed in CKD. Hydrodynamic tail injection of IL-6/soluble IL-6 receptor (sIL-6R) fusion protein hyper IL-6 (HIL-6) plasmid increased serum FGF23 levels. Circulating sIL-6R levels were increased in both CKD and AKI mice, suggesting that IL-6 increases FGF23 through sIL-6R-mediated trans-signaling. Renal IL-6 mRNA expression was increased in mice with either AKI or CKD, suggesting the kidney is the source for the increased serum IL-6 levels in the uremic state. HIL-6 also increased FGF23 mRNA in calvaria organ cultures and osteoblast-like UMR106 cells in culture, demonstrating a direct effect of IL-6 on FGF23 expression. HIL-6 increased FGF23 promoter activity through STAT3 phosphorylation and its evolutionarily conserved element in the FGF23 promoter. Thus, IL-6 increases FGF23 transcription and contributes to the high levels of serum FGF23 in both acute and chronic kidney disease.

The fibroblast growth factor receptor mediates the increased FGF23 expression in acute and chronic uremia.

Serum FGF23 is markedly elevated in chronic kidney disease and has been associated with poor long-term outcomes. FGF23 expression is increased by activation of the FGF receptor 1 (FGFR1) in rats with normal renal function and in vitro in bone-derived osteoblast-like cells. We studied the regulation of FGF23 by FGFR1 in vivo in acute and chronic uremia in mice and rats. Folic acid-induced acute kidney injury increased calvaria FGF23 mRNA and serum FGF23 and parathyroid hormone (PTH) levels at 6 h. The FGFR1 receptor inhibitor PD173074 prevented the folic acid-induced increase in both FGF23 mRNA and serum levels but had no effect on serum PTH levels. A more prolonged uremia due to an adenine high-phosphorus diet for 14 days resulted in high levels of FGF23 mRNA and serum FGF23 and PTH. PD173074 decreased serum FGF23 and mRNA levels with no effect on PTH in the adenine high phosphorus-induced uremic rats. Therefore, a derangement in FGF23 regulation starts early in the course of acute kidney injury, is in part independent of the increase in serum PTH, and involves activation of FGFR1. It is possible that FGFR1 in the osteocyte is activated by locally produced canonical FGFs, which are increased in uremia. This is the first demonstration that activation of FGFR1 is essential for the high levels of FGF23 in acute and chronic experimental uremia.

Deletion of the vitamin D receptor specifically in the parathyroid demonstrates a limited role for the receptor in parathyroid physiology.

1,25(OH)2D3 decreases parathyroid hormone (PTH) gene transcription through the vitamin D receptor (VDR). Total body VDR(-/-) mice have high PTH levels, hypocalcemia, hypophosphatemia, and bone malformations. To investigate PTH regulation by the VDR specifically in the parathyroid, we generated parathyroid-specific VDR knockout mice (PT-VDR(-/-)). In both strains, there was a decrease in parathyroid calcium receptor (CaR) levels. The number of proliferating parathyroid cells was increased in the VDR(-/-) mice but not in the PT-VDR(-/-) mice. Serum PTH levels were moderately but significantly increased in the PT-VDR(-/-) mice with normal serum calcium levels. The sensitivity of the parathyroid glands of the PT-VDR(-/-) mice to calcium was intact as measured by serum PTH levels after changes in serum calcium. This indicates that the reduced CaR in the PT-VDR(-/-) mice enables a physiologic response to serum calcium. Serum C-terminal collagen crosslinks, a marker of bone resorption, were increased in the PT-VDR(-/-) mice with no change in the bone formation marker, serum osteocalcin, consistent with a resorptive effect due to the increased serum PTH levels in the PT-VDR(-/-) mice. Therefore, deletion of the VDR specifically in the parathyroid decreases parathyroid CaR expression and only moderately increases basal PTH levels, suggesting that the VDR has a limited role in parathyroid physiology.

Vitamin D supplementation after renal transplantation: how much vitamin D should we prescribe?

Vitamin D deficiency is common in patients with chronic kidney disease after renal transplantation. Vitamin D, essential for mineral and bone metabolism, also has myriad beneficial autocrine effects on intact immune responses and defense against infection, as well as suppression of malignant changes. Supplementation with oral parental vitamin D could correct this problem. Courbebaisse et al. define how much oral vitamin D to prescribe to renal allograft recipients.

A novel mutation in the NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4 (Ndufa4) gene links mitochondrial dysfunction to the development of diabetes in a rodent model.

The mechanisms underlying diabetes remain unresolved. The Cohen diabetic rat represents a model of diet-induced diabetes, in which the disease is induced after exposure to a diabetogenic diet (DD) in the diabetes-sensitive (CDs/y) but not in the -resistant (CDr/y) strain. Diet imposes a metabolic strain that leads to diabetes in the appropriate genetic background. We previously identified, through whole-genome linkage analysis, a diabetes-related quantitative trait locus on rat chromosome 4 (RNO4), which incorporates NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4 (Ndufa4), a nuclear gene that affects mitochondrial function. Here, we sequenced the gene and found a major deletion in CDs/y that leads to lack of expression of the NDUFA4 protein that has been reported to be involved in the activities of mitochondrial complexes I and IV. In the absence of NDUFA4 in the diabetic CDs/y on DD, complex I activity is reduced in comparison to that in nondiabetic CDs/y on regular diet and CDr/y on either diet; complex IV activity is reduced in both strains provided DD, and thus as a result of diet and unrelated to the gene mutation. ATP fails to increase in diabetic CDs/y in response to DD, in comparison to nondiabetic CDr/y on DD. Plasma malondialdehyde levels are elevated in CDs/y on DD, whereas SOD1 and SOD2 levels fail to increase, indicating increased oxidative stress and inability of the pancreas to generate an appropriate antioxidative stress response. These findings suggest that the Ndufa4 mutation in CDs/y on DD is directly associated with mitochondrial dysfunction, which we attribute to the lack of expression of NDUFA4 and to diet, and which prevents the anticipated increase in ATP production. The resulting enhanced oxidative stress impairs the ability of the pancreas to secrete insulin, leading to the development of diabetes. This is the first demonstration of an inherited mutation in a nuclear gene that adversely affects mitochondrial function and promotes diet-induced diabetes.

The gut-kidney axis in chronic renal failure: A new potential target for therapy.

Evidence is accumulating to consider the gut microbiome as a central player in the gut-kidney axis. Microbiome products, such as advanced glycation end products, phenols, and indoles, are absorbed into the circulation but are cleared by normal-functioning kidneys. These products then become toxic and contribute to the uremic load and to the progression of chronic kidney failure. In this review, we discuss the gut-kidney interaction under the state of chronic kidney failure as well as the potential mechanisms by which a change in the gut flora (termed gut dysbiosis) in chronic kidney disease (CKD) exacerbates uremia and leads to further progression of CKD and inflammation. Finally, the potential therapeutic interventions to target the gut microbiome in CKD are discussed.

The protein phosphatase calcineurin determines basal parathyroid hormone gene expression.

Calcium and phosphate regulate PTH mRNA stability through differences in binding of parathyroid (PT) proteins to a minimal 63-nucleotide (nt) cis-acting instability element in its 3'-untranslated region. One of these proteins is adenosine-uridine-rich binding factor (AUF1), whose levels are not regulated in PT extracts from rats fed the different diets. However, two-dimensional gels showed posttranslational modification of AUF1 that included phosphorylation. There is no PT cell line, but in HEK 293 cells the 63-nt element is recognized as an instability element, and RNA interference for AUF1 decreased human PTH secretion in cotransfection experiments. Stably transfected cells with a chimeric GH gene containing the PTH 63-nt cis-acting element were used to study the signal transduction pathway that regulates AUF1 modification and chimeric gene mRNA stability. Cyclosporine A, the calcineurin inhibitor, regulated AUF1 posttranslationally, and this correlated with an increase in the stability of GH-PTH 63-nt mRNA but not of the control GH mRNA. Mice with genetic deletion of the calcineurin Abeta gene had markedly increased PTH mRNA levels that were still regulated by low calcium and phosphorus diets. Therefore, calcineurin regulates AUF1 posttranslationally in vitro and PTH gene expression in vivo but still allows its physiological regulation by calcium and phosphate.

Regulation of PTH synthesis and secretion relevant to the management of secondary hyperparathyroidism in chronic kidney disease.

Regulation of PTH synthesis and secretion relevant to the management of secondary hyperparathyroidism in chronic kidney disease. Small decreases in serum Ca(++) and more prolonged increases in serum phosphate (P) stimulate the parathyroid (PT) to secrete parathyroid hormone (PTH), while 1,25(OH)(2)-vitamin D(3) decreases PTH synthesis and secretion. A prolonged decrease in serum Ca(++) and 1,25(OH)(2)D(3), or increase in serum P, such as in patients with chronic renal failure, leads to the appropriate secondary increase in serum PTH. This secondary hyperparathyroidism involves increases in PTH gene expression, synthesis, and secretion, and, if chronic, to proliferation of the parathyroid cells. A low serum Ca(++) leads to an increase in PTH secretion, PTH mRNA stability, and parathyroid cell proliferation. Pi also regulates the parathyroid in a similar manner. The effect of Ca(++) on the parathyroid is mediated by a membrane Ca(2+) receptor (CaR). 1,25(OH)(2)D(3) decreases PTH gene transcription. Ca(2+) and P regulate the PTH gene post-transcriptionally by regulating the binding of parathyroid cytosolic proteins, trans factors, to a defined cis sequence in the PTH mRNA 3'-untranslated region (UTR), thereby determining the stability of the transcript. The parathyroid trans factors and cis elements have been defined.

Implementation of guidelines for metabolic syndrome control in kidney transplant recipients: results at a single center.

BACKGROUND: Cardiovascular disease is a leading cause of death among kidney transplant recipients. Metabolic syndrome increases the risk for cardiovascular events and decreases graft survival. Lately, guidelines for management of the metabolic syndrome, primarily hypertension, diabetes mellitus (DM) and hypercholesterolemia have dramatically changed in an attempt to decrease cardiovascular risks among kidney transplant recipients. In the present study we examined whether these guideline changes had impact on our management of post-transplantation patients and the subsequent treatment outcomes for these diseases. METHODS: Data were obtained from kidney transplant clinic files from two follow-up (FU) periods-between 1994-1997 and between 2008-2011. Demographic data, monitoring and screening frequency for cardiovascular risk factors, immunosuppression regimen, treatment for hypertension, diabetes and hyperlipidemia, treatment outcomes and graft function changes were compared between the two follow-up periods. RESULTS: There was a significant increase in the percentage of patients undergoing transplantation due to renal failure secondary to diabetes and/or hypertension. Patient monitoring and screening during the second FU period were less frequent, but more targeted, reflecting changes in clinic routines. Blood pressure was better controlled in the second FU period (p < 0.01), as was hypercholesterolemia (p < 0.001). High fasting glucose levels were more prevalent among patients in the second group (p < 0.005), although more patients received treatment for DM (p < 0.001). Significantly, fewer patients experienced deterioration of kidney functions during the second FU period (p < 0.001). CONCLUSIONS: We found that guideline changes had impact on clinical practice, which translated to better control of the metabolic syndrome. DM control is challenging. Overall, stability of kidney function improved.

Carbapenem-resistant Klebsiella pneumoniae is associated with poor outcome in hemodialysis patients.

BACKGROUND: Hemodialysis (HD) units have become a source of resistant bacteria. One of the most alarming developments is the emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP). Risk factors and outcomes of CRKP isolation in HD patients have not been previously studied. METHODS: A nested case-control study was conducted in maintenance HD patients between January 1st 2006 and June 30th 2009. CRKP-positive patients were matched with randomly selected CRKP-negative HD patients. Demographics, clinical and laboratory data were collected for 24 months prior to the specimen collection. Multivariate analyses identified independent risk factors for CRKP. A prospective follow-up determined CRKP-associated outcome. RESULTS: Demographics associated with CRKP acquisition in HD patients were age between 65 and 75 and having no living offspring. Clinical conditions associated with CRKP were previous hospitalization, temporary HD catheter and previous isolation of vancomycin-resistant enterococcus. CRKP-related outcome was poor: median survival of one month and a hazard ratio [95% CI] of 5.9 [3.2-11.0] for mortality. CONCLUSIONS: Temporary HD catheters and previous treatment for VRE may predict subsequent CRKP isolation. A microbiological diagnosis of CRKP in HD patients is highly associated with imminent mortality. Meticulous measures to control the spread of CRKP bacteria among HD patients appear particularly warranted.

Increased parathyroid hormone gene expression in secondary hyperparathyroidism of experimental uremia is reversed by calcimimetics: correlation with posttranslational modification of the trans acting factor AUF1.

Most patients with chronic kidney disease develop secondary hyperparathyroidism with disabling systemic complications. Calcimimetic agents are effective tools in the management of secondary hyperparathyroidism, acting through allosteric modification of the calcium-sensing receptor (CaR) on the parathyroid gland (PT) to decrease parathyroid hormone (PTH) secretion and PT cell proliferation. This study showed that rats that were fed an adenine high-phosphorus diet had increased serum PTH and PTH mRNA levels at 7 and 21 d. For studying the effect of activation of the CaR by the calcimimetics R-568 on PTH gene expression, R-568 was given by gavage to uremic rats for the last 4 d of a 7-d adenine high-phosphorus diet. R-568 decreased both PTH mRNA and serum PTH levels. The effect of the calcimimetic on PTH gene expression was posttranscriptional and correlated with differences in protein-RNA binding and posttranslational modifications of the trans acting factor AUF1 in the PT. The AUF1 modifications as a result of uremia were reversed by treatment with R-568 to those of normal rats. Therefore, uremia and activation of the CaR mediated by calcimimetics modify AUF1 posttranslationally. These modifications in AUF1 correlate with changes in protein-PTH mRNA binding and PTH mRNA levels.

Pathogenesis of parathyroid dysfunction in end-stage kidney disease.

Small decreases in serum calcium (Ca(2+)) and more-prolonged increases in serum phosphate (Pi) stimulate the parathyroid (PT) to secrete parathyroid hormone (PTH). 1,25-Dihydroxyvitamin D(3) [1,25(OH)(2) D(3)] decreases PTH synthesis and secretion. The prolonged decrease in serum Ca(2+) and 1,25(OH)(2) D(3), or increase in serum Pi, observed in patients with chronic renal failure leads to a secondary increase in serum PTH. This secondary hyperparathyroidism involves increases in PTH gene expression, synthesis, and secretion and, if chronic, to proliferation of the PT cells. A low serum Ca(2+) leads to an increase in PTH secretion, PTH mRNA stability, and PT cell proliferation. Pi also regulates the PT in a similar manner. The effect of Ca(2+) on the PT is mediated by a membrane Ca(2+) receptor. 1,25(OH)(2) D(3) decreases PTH gene transcription. Ca(2+) and Pi regulate the PTH gene post transcriptionally by regulating the binding of PT cytosolic proteins, trans factors, to a defined cis sequence in the PTH mRNA 3'-untranslated region, thereby determining the stability of the transcript. The PT trans factors and cis elements have been defined.

Calcineurin Abeta is central to the expression of the renal type II Na/Pi co-transporter gene and to the regulation of renal phosphate transport.

The sensing and response to extracellular phosphate (Pi) concentration is preserved from prokaryotes to mammals and ensures an adequate supply of Pi in the face of large differences in its availability. In mammals, the kidneys are central to Pi homeostasis. Renal Pi reabsorption is mediated by a Na/Pi co-transporter that is regulated by a renal Pi sensing system and humoral factors. The signal transduction by which Pi regulates type II Na/Pi activity is largely unknown. It is shown that calcineurin inhibitors specifically and dramatically decrease type II Na/Pi gene expression in a proximal tubule cell line and in vivo. Mice with genetic deletion of the calcineurin Abeta gene had a marked decrease in type II Na/Pi mRNA levels and remarkably did not show the expected increase in type II Na/Pi mRNA levels after the challenge of a low-Pi diet. In contrast, the regulation of renal 25(OH)-vitamin D 1alpha-hydroxylase gene expression by Pi was intact. This is the first demonstration that calcineurin has a crucial role in the signal transduction pathway regulating renal Pi homeostasis both in vitro and in vivo. These results suggest that the use of calcineurin inhibitors contributes to the renal Pi wasting seen in renal transplant patients.