Renal excretion of water and major electrolytes exhibits a significant circadian rhythm. This functional periodicity is believed to result, at least in part, from circadian changes in secretion/reabsorption capacities of the distal nephron and collecting ducts. Here, we studied the molecular mechanisms underlying circadian rhythms in the distal nephron segments, i.e., distal convoluted tubule (DCT) and connecting tubule (CNT) and the cortical collecting duct (CCD). Temporal expression analysis performed on microdissected mouse DCT/CNT or CCD revealed a marked circadian rhythmicity in the expression of a large number of genes crucially involved in various homeostatic functions of the kidney. This analysis also revealed that both DCT/CNT and CCD possess an intrinsic circadian timing system characterized by robust oscillations in the expression of circadian core clock genes (clock, bma11, npas2, per, cry, nr1d1) and clock-controlled Par bZip transcriptional factors dbp, hlf, and tef. The clock knockout mice or mice devoid of dbp/hlf/tef (triple knockout) exhibit significant changes in renal expression of several key regulators of water or sodium balance (vasopressin V2 receptor, aquaporin-2, aquaporin-4, ␣ENaC). Functionally, the loss of clock leads to a complex phenotype characterized by partial diabetes insipidus, dysregulation of sodium excretion rhythms, and a significant decrease in blood pressure. Collectively, this study uncovers a major role of molecular clock in renal function.circadian rhythm ͉ homeostasis ͉ renal function R ecent evidence suggests that many if not all specific physiological functions are under the control of the circadian timing system. The mammalian circadian timing system is a hierarchically organized network of molecular oscillators driven by a central pacemaker located in the suprachiasmatic nucleus (SCN) of hypothalamus. This central pacemaker functions in a self-sustained fashion, but is reset each day by exposure to environmental synchronizers, mainly the light/dark cycle. The SCN masterclock drives the rest-activity cycle, which in turn imposes the feeding pattern [reviewed in (1, 2)]. The feeding time seems to be the dominant cue for circadian rhythms in the peripheral tissues (3, 4). Central and peripheral oscillators share a similar molecular core clock based on a set of self-autonomous transcriptional/ translational feedback loops. The key molecular components of these loops are the PAS domain transcriptional factors CLOCK, BMAL1, and NPAS2 and the feedback repressors PER1, PER2, CRY1, and CRY2. The orphan nuclear receptors NR1D1 and, probably, NR1D2 form an accessory feedback loop. The core oscillators confer circadian rhythmicity on a set of output genes underlying the tissue-specific functional rhythms. Current estimates indicate that up to 10% of the cellular transcriptome may follow a circadian expression pattern (5-7). Several recent studies have also demonstrated that the transcription of only a minority of these circadian genes is driven by systemic humoral or neurona...

Elevated plasma urate levels are associated with metabolic, cardiovascular, and renal diseases. Urate may also form crystals, which can be deposited in joints causing gout and in kidney tubules inducing nephrolithiasis. In mice, plasma urate levels are controlled by hepatic breakdown, as well as, by incompletely understood renal processes of reabsorption and secretion. Here, we investigated the role of the recently identified urate transporter, Glut9, in the physiological control of urate homeostasis using mice with systemic or liver-specific inactivation of the Glut9 gene. We show that Glut9 is expressed in the basolateral membrane of hepatocytes and in both apical and basolateral membranes of the distal nephron. Mice with systemic knockout of Glut9 display moderate hyperuricemia, massive hyperuricosuria, and an early-onset nephropathy, characterized by obstructive lithiasis, tubulointerstitial inflammation, and progressive inflammatory fibrosis of the cortex, as well as, mild renal insufficiency. In contrast, liver-specific inactivation of the Glut9 gene in adult mice leads to severe hyperuricemia and hyperuricosuria, in the absence of urate nephropathy or any structural abnormality of the kidney. Together, our data show that Glut9 plays a major role in urate homeostasis by its dual role in urate handling in the kidney and uptake in the liver.gout ͉ knockout ͉ nephrolithiasis ͉ uric acid

Calcium is vital to the normal functioning of multiple organ systems and its serum concentration is tightly regulated. Apart from CASR, the genes associated with serum calcium are largely unknown. We conducted a genome-wide association meta-analysis of 39,400 individuals from 17 population-based cohorts and investigated the 14 most strongly associated loci in ≤21,679 additional individuals. Seven loci (six new regions) in association with serum calcium were identified and replicated. Rs1570669 near CYP24A1 (P = 9.1E-12), rs10491003 upstream of GATA3 (P = 4.8E-09) and rs7481584 in CARS (P = 1.2E-10) implicate regions involved in Mendelian calcemic disorders: Rs1550532 in DGKD (P = 8.2E-11), also associated with bone density, and rs7336933 near DGKH/KIAA0564 (P = 9.1E-10) are near genes that encode distinct isoforms of diacylglycerol kinase. Rs780094 is in GCKR. We characterized the expression of these genes in gut, kidney, and bone, and demonstrate modulation of gene expression in bone in response to dietary calcium in mice. Our results shed new light on the genetics of calcium homeostasis.

No abstract

The circadian clock contributes to the control of BP, but the underlying mechanisms remain unclear. We analyzed circadian rhythms in kidneys of wild-type mice and mice lacking the circadian transcriptional activator clock gene. Mice deficient in clock exhibited dramatic changes in the circadian rhythm of renal sodium excretion. In parallel, these mice lost the normal circadian rhythm of plasma aldosterone levels. Analysis of renal circadian transcriptomes demonstrated changes in multiple mechanisms involved in maintaining sodium balance. Pathway analysis revealed the strongest effect on the enzymatic system involved in the formation of 20-HETE, a powerful regulator of renal sodium excretion, renal vascular tone, and BP. This correlated with a significant decrease in the renal and urinary content of 20-HETE in clockdeficient mice. In summary, this study demonstrates that the circadian clock modulates renal function and identifies the 20-HETE synthesis pathway as one of its principal renal targets. It also suggests that the circadian clock affects BP, at least in part, by exerting dynamic control over renal sodium handling. Recent evidence indicates that the circadian clock is involved in BP control. In mice, suppression or decrease of the circadian clock activity via deletion of the circadian transcriptional activators Bmal1, Clock, or Npas2 leads to low BP, whereas its constitutive activation via deletion of the circadian repressors Cry1 and Cry2 results in salt-sensitive hypertension. 1-4 Wang et al. have recently shown that mice simultaneously devoid of three prolineand acidic amino acid-rich basic leucine zipper circadian transcriptional factors Dbp, Hlf, and Tef exhibit a significant reduction in BP. 5 Maintaining BP within the normal range strongly depends on the capacity of the kidney to precisely regulate sodium content in the extracellular space. Thus, dysregulation of molecular mechanisms involved in renal sodium handling could be partially responsible for the elevated or decreased BP observed in mice with genetically altered clocks. This hypothesis is supported by evidence in humans suggesting that alteration of circadian rhythms of urinary sodium excretion is the primary cause of disease in several forms of hyper-or hypotension. For instance, a decreased renal capacity to excrete sodium during the daytime correlates with nocturnal hypertension, whereas increased sodium excretion during the nighttime contributes to the maintenance of orthostatic hypotension. 6,7 Of note, important changes in the amplitude or the circadian phase of urinary excretion of sodium can be provoked not only by a pathologic process but also by a misalignment between the endogenous circadian clock and the imposed rest-activity or feeding cycles, or by sleep disturbance. For instance, Kamperis et al. have shown that acute sleep deprivation in humans leads to excessive natriuresis and kaliuresis during the subjective night and attenuation of the

The functional interaction between fibroblast growth factor 23 and Klotho in the control of vitamin D and phosphate homeostasis is manifested by the largely overlapping phenotypes of Fgf23-and Klotho-deficient mouse models. However, to date,

Fibroblast growth factor 23 (FGF23) is a circulating factor secreted by osteocytes that is essential for phosphate homeostasis. In kidney proximal tubular cells FGF23 inhibits phosphate reabsorption and leads to decreased synthesis and enhanced catabolism of 1,25-dihydroxyvitamin D 3 (1,25[OH] 2 D 3 ). Excess levels of FGF23 cause renal phosphate wasting and suppression of circulating 1,25(OH) 2 D 3 levels and are associated with several hereditary hypophosphatemic disorders with skeletal abnormalities, including X-linked hypophosphatemic rickets (XLH) and autosomal recessive hypophosphatemic rickets (ARHR). Currently, therapeutic approaches to these diseases are limited to treatment with activated vitamin D analogues and phosphate supplementation, often merely resulting in partial correction of the skeletal aberrations. In this study, we evaluate the use of FGFR inhibitors for the treatment of FGF23-mediated hypophosphatemic disorders using NVP-BGJ398, a novel selective, pan-specific FGFR inhibitor currently in Phase I clinical trials for cancer therapy. In two different hypophosphatemic mouse models, Hyp and Dmp1-null mice, resembling the human diseases XLH and ARHR, we find that pharmacological inhibition of FGFRs efficiently abrogates aberrant FGF23 signaling and normalizes the hypophosphatemic and hypocalcemic conditions of these mice. Correspondingly, long-term FGFR inhibition in Hyp mice leads to enhanced bone growth, increased mineralization, and reorganization of the disturbed growth plate structure. We therefore propose NVP-BGJ398 treatment as a novel approach for the therapy of FGF23-mediated hypophosphatemic diseases. ß

Memo is a widely expressed 33-kDa protein required for heregulin (HRG)-, epidermal growth factor (EGF)-, and fibroblast growth factor (FGF)-induced cell motility. Studies in mouse embryonic fibroblasts, wild-type or knockout for Memo, were performed to further investigate the role of Memo downstream of FGFR. We demonstrated that Memo associates with the FGFR signalosome and is necessary for optimal activation of signaling. To uncover Memo's physiological role, Memo conditional-knockout mice were generated. These animals showed a reduced life span, increased insulin sensitivity, small stature, graying hair, alopecia, kyphosis, loss of subcutaneous fat, and loss of spermatozoa in the epididymis. Memo-knockout mice also have elevated serum levels of active vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D), and calcium compared to control littermates expressing Memo. In summary, the results from in vivo and in vitro models support the hypothesis that Memo is a novel regulator of FGFR signaling with a role in controlling 1,25(OH)2D production and normal calcium homeostasis.