Impaired natriuretic response to high-NaCl diet plus aldosterone infusion in mice overexpressing human CD39, an ectonucleotidase (NTPDase1)

Abstract

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...

Clopidogrel attenuates lithium-induced alterations in renal water and sodium channels/transporters in mice

“…Conversely, one can deduce that the same purinergic signaling may play a significant role in the development of clinical conditions in which the sensitivity of the kidney to AVP or aldosterone is altered, such as acquired nephrogenic diabetes insipidus (NDI) or aldosterone escape. In fact, reports from our and other laboratories support this concept [3,[9][10][11][12][13][14][15].…”

Extracellular Nucleotides and P2 Receptors in Renal Function

“…Confirming the natriuretic potential of extracellular ATP, mice overexpressing human CD39, an ectonucleotidase that hydrolyzes extracellular ATP/ADP to AMP (see sect. IIB and FIGURE 1), showed evidence for an impaired natriuretic response to a high-salt diet and concomitant aldosterone infusion, including potential dysregulation in the expression of NKCC2 and NCC (586). Proposed dysregulation of NKCC2 is reminiscent of enhanced renal NKCC2 expression observed in P2Y 2 Ϫ/Ϫ mice (431,578).…”

“…Pressure natriuresis plays an important role in regulating salt homeostasis (231). In addition to hemodynamic factors such as medullary blood flow and renal interstitial hydrostatic pressure, the underlying mechanism includes inhibi-tory effects on proximal and distal tubular transport, in part mediated by paracrine factors, including extracellular nucleotides (586). Microdialysis experiments indicated a positive relationship between renal artery perfusion pressure and the concentration of ATP in the interstitial fluid of the kidney cortex (357,382).…”

CD39-adenosinergic axis in renal pathophysiology and therapeutics

“…In recent years, it has been established that extracellular nucleotides, acting through P2Y 2 and P2Y 12 receptors, also play significant roles in the transport of water and sodium in the kidney, mainly by opposing the actions of one or both hormones on the kidney [13,16,18,20,21,23]. We used a transgenic (TG) mouse model globally overexpressing hCD39 including in the kidney, which had elevated tissue and blood levels of adenosine [53] and showed that these mice manifest defective water and sodium handling [42,54]. Under basal conditions, TG mice exhibited impaired urinary concentrating ability despite normal AVP levels and had impaired AVP release in response to water deprivation.…”

“…However, as shown in Fig. 1, the released ATP is sequentially hydrolyzed to ADP and AMP by CD39 or NTPDase1 (nucleoside triphosphate diphosphohydrolase-1), which is expressed in vascular and tubular structures of the kidney [40][41][42]. ATP can also be directly hydrolyzed to AMP by nucleotide pyrophosphatases (NPPs), expressed in the kidney [41].…”