Soft-tissue calcification is a prominent feature in both chronic kidney disease (CKD) and experimental Klotho deficiency, but whether Klotho deficiency is responsible for the calcification in CKD is unknown. Here, wild-type mice with CKD had very low renal, plasma, and urinary levels of Klotho. In humans, we observed a graded reduction in urinary Klotho starting at an early stage of CKD and progressing with loss of renal function. Despite induction of CKD, transgenic mice that overexpressed Klotho had preserved levels of Klotho, enhanced phosphaturia, better renal function, and much less calcification compared with wild-type mice with CKD. Conversely, Klotho-haploinsufficient mice with CKD had undetectable levels of Klotho, worse renal function, and severe calcification. The beneficial effect of Klotho on vascular calcification was a result of more than its effect on renal function and phosphatemia, suggesting a direct effect of Klotho on the vasculature. In vitro, Klotho suppressed Na ϩ -dependent uptake of phosphate and mineralization induced by high phosphate and preserved differentiation in vascular smooth muscle cells. In summary, Klotho is an early biomarker for CKD, and Klotho deficiency contributes to soft-tissue calcification in CKD. Klotho ameliorates vascular calcification by enhancing phosphaturia, preserving glomerular filtration, and directly inhibiting phosphate uptake by vascular smooth muscle. Replacement of Klotho may have therapeutic potential for CKD.

Klotho is an antiaging substance with pleiotropic actions including regulation of mineral metabolism. It is highly expressed in the kidney and is present in the circulation and urine but its role in acute kidney injury (AKI) is unknown. We found that ischemia–reperfusion injury (IRI) in rodents reduced Klotho in the kidneys, urine, and blood, all of which were restored upon recovery. Reduction in kidney and plasma Klotho levels were earlier than that of neutrophil gelatinase-associated lipocalin (NGAL), a known biomarker of kidney injury. Patients with AKI were found to have drastic reductions in urinary Klotho. To examine whether Klotho has a pathogenic role, we induced IRI in mice with different endogenous Klotho levels ranging from heterozygous Klotho haploinsufficient, to wild-type (WT), to transgenic mice overexpressing Klotho. Klotho levels in AKI were lower in haploinsufficient and higher in transgenic compared with WT mice. The haploinsufficient mice had more extensive functional and histological alterations compared with WT mice, whereas these changes were milder in overexpressing transgenic mice, implying that Klotho is renoprotective. Rats with AKI given recombinant Klotho had higher Klotho protein, less kidney damage, and lower NGAL than rats with AKI given vehicle. Hence, AKI is a state of acute reversible Klotho deficiency, low Klotho exacerbates kidney injury and its restoration attenuates renal damage and promotes recovery from AKI. Thus, endogenous Klotho not only serves as an early biomarker for AKI but also functions as a renoprotective factor with therapeutic potential.

Synthetic antibody libraries harbor tremendous potential for a variety of biomedical and clinical applications. Using such a reagent, we furnish data in support of αKlotho deficiency in human CKD, and we set the foundation for the development of diagnostic and therapeutic applications of anti-αKlotho antibodies.

In 40 of 50 US states, scheduled dialysis is withheld from undocumented immigrants with end-stage renal disease (ESRD); instead, they receive intermittent emergency-only dialysis to treat life-threatening manifestations of ESRD. However, the comparative effectiveness of scheduled dialysis vs emergency-only dialysis and the influence of treatment on health outcomes, utilization, and costs is uncertain. OBJECTIVE To compare the effectiveness of scheduled vs emergency-only dialysis with regard to health outcomes, utilization, and costs in undocumented immigrants with ESRD. DESIGN, SETTING, AND PARTICIPANTS Observational cohort study of 181 eligible adults with ESRD receiving emergency-only dialysis in Dallas, Texas, who became newly eligible and applied for private commercial health insurance in February 2015; 105 received coverage and were enrolled in scheduled dialysis; 76 were not enrolled in insurance for nonclinical reasons (eg, lack of capacity at a participating outpatient dialysis center) and remained uninsured, receiving emergency-only dialysis. We examined data on eligible persons during a 6-month period prior to enrollment (baseline period,

Adenosine is an autacoid that regulates renal Na

We postulate the following: (1) DA modifies NHE-3 phosphorylation by activating PKA through DA1 and by other kinases/phosphatases via DA2. (2) DA1 is sufficient to inhibit NHE-3, while DA2 is insufficient but plays a synergistic role by altering NHE-3 phosphorylation.

The intrarenal autocrine-paracrine dopamine (DA) system is critical for Na(+) homeostasis. l-Dihydroxyphenylalanine (l-DOPA) uptake from the glomerular filtrate and plasma provides the substrate for DA generation by the renal proximal tubule. The transporter(s) responsible for proximal tubule l-DOPA uptake has not been characterized. Renal cortical poly-A(+) RNA injected into Xenopus laevis oocytes induced l-DOPA uptake in a time- and dose-dependent fashion with biphasic K(m)s in the millimolar and micromolar range and independent of inward Na(+), K(+), or H(+) gradients, suggesting the presence of low- and high-affinity l-DOPA carriers. Complementary RNA from two amino acid transporters yielded l-DOPA uptake significantly above water-injected controls the rBAT/b(0,+)AT dimer (rBAT) and the LAT2/4F2 dimer (LAT2). In contradistinction to renal cortical poly-A(+), l-DOPA kinetics of rBAT and LAT2 showed classic Michaelis-Menton kinetics with K(m)s in the micromolar and millimolar range, respectively. Sequence-specific antisense oligonucleotides to rBAT or LAT2 (AS) caused inhibition of rBAT and LAT2 cRNA-induced l-DOPA transport and cortical poly-A(+)-induced arginine and phenylalanine transport. However, the same ASs only partially blocked poly-A(+)-induced l-DOPA transport. In cultured kidney cells, silencing inhibitory RNA (siRNA) to rBAT significantly inhibited l-DOPA uptake. We conclude that rBAT and LAT2 can mediate apical and basolateral l-DOPA uptake into the proximal tubule, respectively. Additional l-DOPA transport mechanisms exist in the renal cortex that remain to be identified.

mine is a potent natriuretic paracrine/autocrine hormone that is central for mammalian sodium homeostasis. In the renal proximal tubule, dopamine induces natriuresis partly via inhibition of the sodium/ proton exchanger NHE3. The signal transduction pathways and mechanisms by which dopamine inhibits NHE3 are complex and incompletely understood. This manuscript describes the role of the serine/ threonine protein phosphatase 2A (PP2A) in the regulation of NHE3 by dopamine. The PP2A regulatory subunit B56␦ (coded by the Ppp2r5d gene) directly associates with more than one region of the carboxy-terminal hydrophilic putative cytoplasmic domain of NHE3 (NHE3-cyto), as demonstrated by yeast-two-hybrid, coimmunoprecipitation, blot overlay, and in vitro pull-down assays. Phosphorylated NHE3-cyto is a substrate for purified PP2A in an in vitro dephosphorylation reaction. In cultured renal cells, inhibition of PP2A by either okadaic acid or by overexpression of the simian virus 40 (SV40) small T antigen blocks the ability of dopamine to inhibit NHE3 activity and to reduce surface NHE3 protein. Dopamineinduced NHE3 redistribution is also blocked by okadaic acid ex vivo in rat kidney cortical slices. These studies demonstrate that PP2A is an integral and critical participant in the signal transduction pathway between dopamine receptor activation and NHE3 inhibition. natriuresis; sodium transport; signal transduction THE INTRARENAL AUTOCRINE/PARACRINE dopamine natriuretic system is critical for mammalian sodium homeostasis (5,8,28,29,37,39,47,49,53). The dopamine precursor 3,4-dihydroxy-Lphenylalanine (L-DOPA) is taken up from the glomerular filtrate and plasma into the proximal tubule (48, 50), decarboxylated to dopamine by the action of the cytoplasmic aromatic amino acid decarboxylase (61), and dopamine is extruded into the urinary lumen as well as the interstitial space (43,51,58). Dopamine locally controls multiple aspects of renal function including renal blood flow, glomerular filtration rate, the setting of tubuloglomerular feedback, renin release, and Na ϩ absorption by the renal tubules (5, 37). Quantitatively, the most important mechanism by which dopamine induces natriuresis is direct suppression of Na ϩ absorption by the renal tubular epithelium (9,20,27,40). Inhibition of proximal Na ϩ absorption translates into effective whole kidney natriuresis because downstream of the proximal tubule, dopamine also inhibits Na ϩ absorption in the thick ascending loop of Henle, tubuloglomerular feedback, and Na ϩ transporters in the distal nephron (37). In the proximal tubule, dopamine inhibits the two principal Na ϩ transporters: the apical membrane Na ϩ /H ϩ exchanger NHE3 (7,23,26,33,59,60) and the basolateral Na ϩ -K ϩ -ATPase (4, 12, 13). Inhibition of NHE3 by dopamine involves reduced transport activity and increased endocytosis (7,33,59) and is associated with NHE3 phosphorylation (33, 64). Two PKA phosphorylation sites (serines 552 and 605 in rat NHE3) are necessary but not sufficient for PKA-mediated NHE3 regulation ...