P2Y12 receptor (P2Y12-R) signaling is mediated through Gi, ultimately reducing cellular cAMP levels. Because cAMP is a central modulator of arginine vasopressin (AVP)-induced water transport in the renal collecting duct (CD), we hypothesized that if expressed in the CD, P2Y12-R may play a role in renal handling of water in health and in nephrogenic diabetes insipidus. We found P2Y12-R mRNA expression in rat kidney, and immunolocalized its protein and aquaporin-2 (AQP2) in CD principal cells. Administration of clopidogrel bisulfate, an irreversible inhibitor of P2Y12-R, significantly increased urine concentration and AQP2 protein in the kidneys of Sprague-Dawley rats. Notably, clopidogrel did not alter urine concentration in Brattleboro rats that lack AVP. Clopidogrel administration also significantly ameliorated lithium-induced polyuria, improved urine concentrating ability and AQP2 protein abundance, and reversed the lithium-induced increase in free-water excretion, without decreasing blood or kidney tissue lithium levels. Clopidogrel administration also augmented the lithium-induced increase in urinary AVP excretion and suppressed the lithium-induced increase in urinary nitrates/nitrites (nitric oxide production) and 8-isoprostane (oxidative stress). Furthermore, selective blockade of P2Y12-R by the reversible antagonist PSB-0739 in primary cultures of rat inner medullary CD cells potentiated the expression of AQP2 and AQP3 mRNA, and cAMP production induced by dDAVP (desmopressin). In conclusion, pharmacologic blockade of renal P2Y12-R increases urinary concentrating ability by augmenting the effect of AVP on the kidney and ameliorates lithium-induced NDI by potentiating the action of AVP on the CD. This strategy may offer a novel and effective therapy for lithium-induced NDI.

Lithium (Li) administration causes deranged expression and function of renal aquaporins and sodium channels/transporters resulting in nephrogenic diabetes insipidus (NDI). Extracellular nucleotides (ATP/ADP/UTP), via P2 receptors, regulate these transport functions. We tested whether clopidogrel bisulfate (CLPD), an antagonist of ADP-activated P2Y(12) receptor, would affect Li-induced alterations in renal aquaporins and sodium channels/transporters. Adult mice were treated for 14 days with CLPD and/or Li and euthanized. Urine and kidneys were collected for analysis. When administered with Li, CLPD ameliorated polyuria, attenuated the rise in urine prostaglandin E2 (PGE2), and resulted in significantly higher urinary arginine vasopressin (AVP) and aldosterone levels as compared to Li treatment alone. However, urine sodium excretion remained elevated. Semi-quantitative immunoblotting revealed that CLPD alone increased renal aquaporin 2 (AQP2), Na-K-2Cl cotransporter (NKCC2), Na-Cl cotransporter (NCC), and the subunits of the epithelial Na channel (ENaC) in medulla by 25-130 %. When combined with Li, CLPD prevented downregulation of AQP2, Na-K-ATPase, and NKCC2 but was less effective against downregulation of cortical α- or γ-ENaC (70 kDa band). Thus, CLPD primarily attenuated Li-induced downregulation of proteins involved in water conservation (AVP-sensitive), with modest effects on aldosterone-sensitive proteins potentially explaining sustained natriuresis. Confocal immunofluorescence microscopy revealed strong labeling for P2Y(12)-R in proximal tubule brush border and blood vessels in the cortex and less intense labeling in medullary thick ascending limb and the collecting ducts. Therefore, there is the potential for CLPD to be directly acting at the tubule sites to mediate these effects. In conclusion, P2Y(12)-R may represent a novel therapeutic target for Li-induced NDI.

COX-2/mPGES-1/PGE2 cascade plays critical roles in modulating many physiological and pathological actions in different organs. In the kidney, this cascade is of high importance in regulating fluid metabolism, blood pressure, and renal hemodynamics. Under some disease conditions, this cascade displays various actions in response to the different pathological insults. In the present review, the roles of this cascade in the pathogenesis of kidney injuries including diabetic and nondiabetic kidney diseases and acute kidney injuries were introduced and discussed. The new insights from this review not only increase the understanding of the pathological role of the COX-2/mPGES-1/PGE2 pathway in kidney injuries, but also shed new light on the innovation of the strategies for the treatment of kidney diseases.

Diabetic nephropathy (DN) is a severe complication of diabetes and serves as the leading cause of chronic renal failure. In the past decades, angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin II receptor blockers (ARBs) based first-line therapy can slow but cannot stop the progression of DN, which urgently requests the innovation of therapeutic strategies. Thiazolidinediones (TZDs), the synthetic exogenous ligands of nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ), had been thought to be a promising candidate for strengthening the therapy of DN. However, the severe adverse effects including fluid retention, cardiovascular complications, and bone loss greatly limited their use in clinic. Recently, numerous novel PPARγ agonists involving the endogenous PPARγ ligands and selective PPARγ modulators (SPPARMs) are emerging as the promising candidates of the next generation of antidiabetic drugs instead of TZDs. Due to the higher selectivity of these novel PPARγ agonists on the regulation of the antidiabetes-associated genes than that of the side effect-associated genes, they present fewer adverse effects than TZDs. The present review was undertaken to address the advancements and the therapeutic potential of these newly developed PPARγ agonists in dealing with diabetic kidney disease. At the same time, the new insights into the therapeutic strategies of DN based on the PPARγ agonists were fully addressed.

Kishore BK, Ecelbarger CM. Impaired natriuretic response to highNaCl diet plus aldosterone infusion in mice overexpressing human CD39, an ectonucleotidase (NTPDase1). Am J Physiol Renal Physiol 308: F1398 -F1408, 2015. First published April 15, 2015 doi:10.1152/ajprenal.00125.2014.-Extracellular nucleotides acting through P2 receptors facilitate natriuresis. To define how purinergic mechanisms are involved in sodium homeostasis, we used transgenic (TG) mice that globally overexpress human CD39 (hCD39, NTPDase1), an ectonucleotidase that hydrolyzes extracellular ATP/ADP to AMP, resulting in an altered extracellular purine profile. On a high-sodium diet (HSD, 3.5% Na ϩ ), urine volume and serum sodium were significantly higher in TG mice but sodium excretion was unaltered. Furthermore, TG mice showed an attenuated fall in urine aldosterone with HSD. Western blot analysis revealed significantly lower densities (ϳ40%) of the ␤-subunit of the epithelial sodium channel (ENaC) in medulla, and the major band (85-kDa) of ␥-ENaC in TG mice cortex. To evaluate aldosterone-independent differences, in a second experiment, aldosterone was clamped by osmotic minipump at 20 g/day, and mice were fed either an HSD or a low-sodium diet (LSD, 0.03% Na ϩ ). Here, no differences in urine volume or osmolality, or serum aldosterone were found, but TG mice showed a modest, yet significant impairment in late natriuresis (days 3 and 4). Several major sodium transporters or channel subunits were differentially expressed between the genotypes. HSD caused a downregulation of Na-Cl cotransporter (NCC) in both genotypes; and had higher cortical levels of NCC, Na-K-ATPase (␣-1 subunit), and ␣-and ␥-ENaC. The Na-K-2Cl cotransporter (NKCC2) was downregulated by HSD in wild-type mice, but it increased in TG mice. In summary, our data support the concept that extracellular nucleotides facilitate natriuresis; they also reveal an aldosterone-independent downregulation of major renal sodium transporters and channel subunits by purinergic signaling. purinergic receptors; extracellular nucleotides; ectonucleotidases; nucleoside triphosphate diphosphohydrolase-1; aldosterone; sodium transporters EXTRACELLULAR NUCLEOTIDES (ATP/ADP/UTP), acting through type-2 purinergic receptors (P2), potentially regulate renal tubular transport of water and sodium, and thereby urinary concentrating ability (5,7,11,18,19,23,25,26,28,29,33,39). P2 receptor signal modulation is controlled by a narrow range of extracellular concentrations of ATP and related nucleotides, which are mediated through regulated release from cells and rapidly hydrolyzed by ectonucleotidases (10). Several types of ectonucleotidases exist, such as nucleoside triphosphate diphosphohydrolases (NTPDases), ectonucleotide pyrophosphatases (E-NPPs), alkaline phosphatases, and ecto-5=-nucelotidase (CD73) (24, 34).NTPDases are a family of membrane-bound enzymes that sequentially hydrolyze extracellular nucleotides and thus limit P2 receptor activities and desensitization. NTPDase1 is the same as CD39, a pu...

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