Ting Jia

Targeted Deletion of Klotho in Kidney Distal Tubule Disrupts Mineral Metabolism

Renal Klotho controls mineral metabolism by directly modulating tubular reabsorption of phosphate and calcium and by acting as a co-receptor for the phosphaturic and vitamin D-regulating hormone fibroblast growth factor-23 (FGF23). Klotho null mice have a markedly abnormal phenotype. We sought to determine effects of renal-specific and partial deletion of Klotho to facilitate investigation of its roles in health and disease. We generated a mouse model with partial deletion of Klotho in distal tubular segments (Ksp-KL(-/-)). In contrast to Klotho null mice, Ksp-KL(-/-) mice were fertile, had a normal gross phenotype, and did not have vascular or tubular calcification on renal histology. However, Ksp-KL(-/-) mice were hyperphosphatemic with elevated FGF23 levels and abundant expression of the sodium-phosphate cotransporter Npt2a at the brush border membrane. Serum calcium and 1,25-dihydroxyvitamin D(3) levels were normal but parathyroid hormone levels were decreased. TRPV5 protein was reduced with a parallel mild increase in urinary calcium excretion. Renal expression of vitamin D regulatory enzymes and vitamin D receptor was higher in Ksp-KL(-/-) mice than controls, suggesting increased turnover of vitamin D metabolites and a functional increase in vitamin D signaling. There was a threshold effect of residual renal Klotho expression on FGF23: deletion of >70% of Klotho resulted in FGF23 levels 30-250 times higher than in wild-type mice. A subgroup of Ksp-KL(-/-) mice with normal phosphate levels had elevated FGF23, suggesting a Klotho-derived renal-bone feedback loop. Taken together, renal FGF23-Klotho signaling, which is disrupted in CKD, is essential for homeostatic control of mineral metabolism.

Parathyroid-specific deletion of Klotho unravels a novel calcineurin-dependent FGF23 signaling pathway that regulates PTH secretion.

Klotho acts as a co-receptor for and dictates tissue specificity of circulating FGF23. FGF23 inhibits PTH secretion, and reduced Klotho abundance is considered a pathogenic factor in renal secondary hyperparathyroidism. To dissect the role of parathyroid gland resident Klotho in health and disease, we generated mice with a parathyroid-specific Klotho deletion (PTH-KL−/−). PTH-KL−/− mice had a normal gross phenotype and survival; normal serum PTH and calcium; unaltered expression of the PTH gene in parathyroid tissue; and preserved PTH response and sensitivity to acute changes in serum calcium. Their PTH response to intravenous FGF23 delivery or renal failure did not differ compared to their wild-type littermates despite disrupted FGF23-induced activation of the MAPK/ERK pathway. Importantly, calcineurin-NFAT signaling, defined by increased MCIP1 level and nuclear localization of NFATC2, was constitutively activated in PTH-KL−/− mice. Treatment with the calcineurin-inhibitor cyclosporine A abolished FGF23-mediated PTH suppression in PTH-KL−/− mice whereas wild-type mice remained responsive. Similar results were observed in thyro-parathyroid explants ex vivo. Collectively, we present genetic and functional evidence for a novel, Klotho-independent, calcineurin-mediated FGF23 signaling pathway in parathyroid glands that mediates suppression of PTH. The presence of Klotho-independent FGF23 effects in a Klotho-expressing target organ represents a paradigm shift in the conceptualization of FGF23 endocrine action.

A novel model of adenine-induced tubulointerstitial nephropathy in mice.

BackgroundIn vivo models of uremia are important tools to study numerous aspects of acute and chronic kidney disease. Mouse models are pivotal because most genetically engineered animal models are mice, which allow dissecting the impact of selected target genes in renal failure. Adenine-based protocols to induce renal failure are available in rats, but have not been adapted in mice due to their reluctance to consume adenine. In the current paper we developed a novel method for induction of renal failure through dietary delivery of adenine mixed in a casein-based diet.ResultsAfter an induction phase, a stable model of renal impairment was obtained (target urea range 80–100xa0mg/dL), mimicking several aspects of chronic kidney disease - mineral and bone disorder including secondary hyperparathyroidism, bone abnormalities and pathological elevation of FGF23. No deaths occurred and the level of uremia was adaptable through adjustments of the adenine content, providing significant advantages compared to existing models. In an 8-week proof-of-concept study, renal histology showed mainly a tubulointerstitial damage with infiltrating leukocytes, interstitial edema and widening of the Bownmans space. Fibrosis was present in most animals as defined by histology and gene expression changes of fibrosis markers. Parathyroid cell proliferation was markedly increased but without signs of glandular hypertrophy. Skeletal histology showed increased trabecular bone and bone marrow adiposity whereas bone biomarkers (CTX and PINP) suggested higher bone formation, but surprisingly, lower bone resorption and perturbations in mineral metabolism.ConclusionsWe present a novel, non-surgical method for induction of renal failure in mice. This is an important complement to existing uremic models for pathophysiological studies in acute and chronic kidney disease, especially in terms of tubulointerstitial lesions.

The complex role of adiponectin in chronic kidney disease.

Although adiponectin, an adipocytokine released from adipose tissue, is thought to have anti-atherogenic, anti-inflammatory, and insulin-sensitizing effects, it appears that high, rather than low, circulating levels of adiponectin predict increased mortality in chronic kidney disease (CKD) patients in whom the circulating levels may rise to about three times higher than the levels in healthy subjects. As it could be hypothesized that in the uremic milieu high adiponectin levels reflect protein-energy wasting, lower residual renal function and/or volume overload, this may explain, at least in part, the observed paradoxical link between hyperadiponectinemia and poor outcome in CKD. To determine the biological consequences of high circulating adiponectin levels on carbohydrate and insulin metabolism as well as relations with cardiovascular function and mortality in the uremic milieu, further studies need to take into account both high-, and low-molecular weight adiponectin moieties as well as the role of adiponectin receptors. This brief review summarizes some of the recent advances in our understanding of the complex and context-sensitive role of this elusive and intriguing adipokine in the uremic milieu.

Validation of insulin sensitivity surrogate indices and prediction of clinical outcomes in individuals with and without impaired renal function

As chronic kidney disease (CKD) progresses with abnormalities in glucose and insulin metabolism, commonly used insulin sensitivity indices (ISIs) may not be applicable in individuals with CKD. Here we sought to validate surrogate ISIs against the glucose disposal rate by the gold-standard hyperinsulinemic euglycemic glucose clamp (HEGC) technique in 1074 elderly men of similar age (70 years) of whom 495 had and 579 did not have CKD (estimated glomerular filtration rate (eGFR) under 60u2009ml/min per 1.73u2009m(2) (median eGFR of 46u2009ml/min per 1.73u2009m(2))). All ISIs provided satisfactory (weighted κ over 0.6) estimates of the glucose disposal rate in patients with CKD. ISIs derived from oral glucose tolerance tests (OGTTs) agreed better with HEGC than those from fasting samples (higher predictive accuracy). Regardless of CKD strata, all ISIs allowed satisfactory clinical discrimination between the presence and absence of insulin resistance (glucose disposal rate under 4u2009mg/kg/min). We also assessed the ability of both HEGC and ISIs to predict all-cause and cardiovascular mortality during a 10-year follow-up. Neither HEGC nor ISIs independently predicted mortality. Adjustment for renal function did not materially change these associations. Thus, ISIs can be applied in individuals with moderately impaired renal function for diagnostic purposes. For research matters, OGTT-derived ISIs may be preferred. Our data do not support the hypothesis of kidney function mediating insulin sensitivity (IS)-associated outcomes nor a role for IS as a predictor of mortality.

Dietary acid load, insulin sensitivity and risk of type 2 diabetes in community-dwelling older men

Aims/hypothesisWe tested the hypothesis that dietary acid load may increase the risk of type 2 diabetes, and studied the association between acid load and insulin sensitivity as a possible mechanism involved.MethodsAn observational survey with prospective follow-up including 911 non-diabetic Swedish men aged 70–71xa0years was carried out. The gold standard euglycaemic–hyperinsulinaemic clamp technique and the OGTT were used to determine insulin sensitivity and beta cell function, respectively. Diabetes incidence was assessed during 18xa0years of follow-up. Renal function was estimated from serum cystatin C concentrations. Dietary acid load was calculated as potential renal acid load (PRAL) and net endogenous acid production (NEAP) algorithms from 7xa0day food records. Adequate dietary reporters were identified by Goldberg cut-offs.ResultsPRAL and NEAP were not associated with insulin sensitivity or beta cell function. Underlying kidney function or consideration of dietary adequate reporters did not modify these null findings. During follow-up, 115 new cases of diabetes were validated. Neither PRAL nor NEAP was associated with diabetes incidence.Conclusions/interpretationOur results do not support the hypothesis that dietary acid load influences insulin sensitivity, beta cell function or diabetes risk. Interventional studies modifying acid–base dietary intake are needed to further elucidate a possible role of acid load in the development of type 2 diabetes.

IGF-1 and Survival in ESRD

BACKGROUND AND OBJECTIVESnIGF-1 deficiency links to malnutrition in CKD patients; however, it is not clear to what extent it associates with survival among these patients.nnnDESIGN, SETTING, PARTICIPANTS, & MEASUREMENTSnSerum IGF-1 and other biochemical, clinical (subjective global assessment), and densitometric (dual energy x-ray absorptiometry) markers of nutritional status and mineral and bone metabolism were measured in a cohort of 365 Swedish clinically stable CKD stage 5 patients (median age of 53 years) initiating dialysis between 1994 and 2009; in 207 patients, measurements were also taken after 1 year of dialysis. Deaths were registered during a median follow-up of 5 years. Associations of mortality with baseline IGF-1 and changes of IGF-1 after 1 year of dialysis were evaluated by Cox models.nnnRESULTSnAt baseline, IGF-1 concentrations associated negatively with age, diabetes mellitus, cardiovascular disease, poor nutritional status, IL-6, and osteoprotegerin and positively with body fat mass, bone mineral density, serum phosphate, calcium, and fibroblast growth factor-23. At 1 year, IGF-1 had increased by 33%. In multivariate regression, low age, diabetes mellitus, and high serum phosphate and calcium associated with IGF-1 at baseline, and in a mixed model, these factors, together with high fat body mass, associated with changes of IGF-1 during the first 1 year of dialysis. Adjusting for calendar year of inclusion, age, sex, diabetes mellitus, cardiovascular disease, IL-6, and poor nutritional status, a 1 SD higher level of IGF-1 at baseline associated with lower mortality risk (hazard ratio, 0.57; 95% confidence interval, 0.32 to 0.98). Persistently low or decreasing IGF-1 levels during the first 1 year on dialysis predicted worse survival (adjusted hazard ratio, 2.19; 95% confidence interval, 1.06 to 4.50).nnnCONCLUSIONnIn incident dialysis patients, low serum IGF-1 associates with body composition and markers of mineral and bone metabolism, and it predicts increased mortality risk.

Effect of Multi-Dimensional Education on Disease Progression in Pre-Dialysis Patients in China

Abstract Background: There is an increasing body of evidence showing that educational interventions aiming at empowering patients are successful in chronic disease management. The aim of this study was to conduct an evaluation of the systematic effectiveness of a multi-dimensional education intervention program in a group of pre-dialysis chronic kidney disease (CKD) patients. In addition, we investigated whether the outcome of the program was related with the amount of education. Methods: We collected data retrospectively from 302 patients with CKD stages 3, 4, and 5, who were followed up from February 2006 to March 2008. The patients were divided into long-time education group and short-time education group depending on the number of provided hours of education. Survival analysis was undertaken to see if the progression of the kidney function differed between these two groups. Results: The percentage of patients receiving long-time education was highest with severe degree of impairment of renal function (45.5%, 61.3%, and 66.7% in CKD stages 3, 4, and 5 groups, respectively). In a multivariate regression analysis, adjusting for age, gender, Charlson comorbidity index, and other traditional risk factors of renal failure, such as smoking, hypertension, and renal function (glomerular filtration rate), the length of time until a decline of renal function by 25% was noted and was significantly shorter in the short-time education group as compared to the long-time education group (p = 0.0334). Conclusion: Multi-component structured empowerment intervention is effective in pre-dialysis CKD patients and may lead to a delay in the progression of kidney disease.

Determinants and survival implications of low bone mineral density in end-stage renal disease patients.

BACKGROUNDnReduced bone mineral density (BMD) is common in end-stage renal disease (ESRD) patients and predicts outcomes. The chronic kidney disease-mineral bone disorder contributes to low BMD in ESRD; however, the impact of classical risk factors for osteoporosis in the general population, such as body weight and fat mass, remains less well defined in ESRD subjects.nnnMETHODSnBMD, body composition (dual-energy X-ray absorptiometry), nutritional status (subjective global assessment), hand grip strength and multiple biomarkers were investigated in 361 patients (218 males; 60.4%) starting on dialysis. The relations between BMD, body composition and biomarkers were analyzed at baseline, and the impact of BMD on mortality was analyzed prospectively.nnnRESULTSnIn univariate analysis, T-score correlated with fat mass (r = 0.308, p<0.001), lean body mass (r = 0.278, p<0.001), leptin (r = 0.124, p = 0.028) as well as the anabolic marker insulin-like growth factor-1 (IGF-1; r = 0.301, p<0.001), and its binding proteins IGFBP-1 (r = -0.342, p<0.001) and IGFBP-3 (0.231, p<0.001). BMD T-score was independently associated with age, total fat mass, intact parathyroid hormone and presence of wasting. During 5 years of follow-up, 87 deaths were recorded. Each unit of increase of T-score was associated with decreased all-cause mortality, which persisted after multivariate adjustment (hazard ratio = 0.824, 95% confidence interval, 0.681-0.996).nnnCONCLUSIONSnBMD is associated with body composition, especially total fat mass, nutritional status and mortality risk in ESRD patients.

Dietary acid load, kidney function, osteoporosis, and risk of fractures in elderly men and women

SummaryBecause kidney dysfunction reduces the ability to excrete dietary acid excess, we hypothesized that underlying kidney function may have confounded the mixed studies linking dietary acid load with the risk of osteoporosis and fractures in the community. In a relatively large survey of elderly men and women, we report that dietary acid load did neither associate with DEXA-estimated bone mineral density nor with fracture risk. Underlying kidney function did not modify these null findings. Our results do not support the dietary acid-base hypothesis of bone loss.IntroductionImpaired renal function reduces the ability to excrete dietary acid excess. We here investigate the association between dietary acid load and bone mineral density (BMD), osteoporosis, and fracture risk by renal function status.MethodsAn observational study was conducted in 861 community-dwelling 70-year-old men and women (49xa0% men) with complete dietary data from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS). The exposure was dietary acid load as estimated from 7-day food records by the net endogenous acid production (NEAP) and potential renal acid load (PRAL) algorithms. Renal function assessed by cystatin C estimated glomerular filtration rate was reduced in 21xa0% of the individuals. Study outcomes were BMD and osteoporosis state (assessed by DEXA) and time to fracture (median follow-up of 9.2xa0years).ResultsIn cross-section, dietary acid load had no significant associations with BMD or with the diagnosis of osteoporosis. During follow-up, 131 fractures were validated. Neither NEAP (adjusted hazard ratios (HR) (95xa0% confidence interval (CI)), 1.01 (0.85–1.21), per 1 SD increment) nor PRAL (adjusted HR (95xa0% CI), 1.07 (0.88–1.30), per 1 SD increment) associated with fracture risk. Further multivariate adjustment for kidney function or stratification by the presence of kidney disease did not modify these null associations.ConclusionsThe hypothesis that dietary acid load associates with reduced BMD or increased fracture risk was not supported by this study in community-dwelling elderly individuals. Renal function did not influence on this null finding.