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Regulation of Renal Hemodynamics and Function by RGS2.

Osei-Owusu P, Owens EA, Jie L, Reis JS, Forrester SJ, Kawai T, Eguchi S, Singh H, Blumer KJ - PLoS ONE (2015)

Bottom Line: RGS2 deficiency caused decreased sensitivity and magnitude of changes in RVR and RBF after a step increase in RPP.We conclude that RGS2 deficiency impairs renal function and autoregulation by increasing renal vascular resistance and reducing renal blood flow.These changes impair renal sodium handling by favoring sodium retention.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, 19102, United States of America.

ABSTRACT
Regulator of G protein signaling 2 (RGS2) controls G protein coupled receptor (GPCR) signaling by acting as a GTPase-activating protein for heterotrimeric G proteins. Certain Rgs2 gene mutations have been linked to human hypertension. Renal RGS2 deficiency is sufficient to cause hypertension in mice; however, the pathological mechanisms are unknown. Here we determined how the loss of RGS2 affects renal function. We examined renal hemodynamics and tubular function by monitoring renal blood flow (RBF), glomerular filtration rate (GFR), epithelial sodium channel (ENaC) expression and localization, and pressure natriuresis in wild type (WT) and RGS2 (RGS2-/-) mice. Pressure natriuresis was determined by stepwise increases in renal perfusion pressure (RPP) and blood flow, or by systemic blockade of nitric oxide synthase with L-NG-Nitroarginine methyl ester (L-NAME). Baseline GFR was markedly decreased in RGS2-/- mice compared to WT controls (5.0 ± 0.8 vs. 2.5 ± 0.1 μl/min/g body weight, p<0.01). RBF was reduced (35.4 ± 3.6 vs. 29.1 ± 2.1 μl/min/g body weight, p=0.08) while renal vascular resistance (RVR; 2.1 ± 0.2 vs. 3.0 ± 0.2 mmHg/μl/min/g body weight, p<0.01) was elevated in RGS2-/- compared to WT mice. RGS2 deficiency caused decreased sensitivity and magnitude of changes in RVR and RBF after a step increase in RPP. The acute pressure-natriuresis curve was shifted rightward in RGS2-/- relative to WT mice. Sodium excretion rate following increased RPP by L-NAME was markedly decreased in RGS2-/- mice and accompanied by increased translocation of ENaC to the luminal wall. We conclude that RGS2 deficiency impairs renal function and autoregulation by increasing renal vascular resistance and reducing renal blood flow. These changes impair renal sodium handling by favoring sodium retention. The findings provide a new line of evidence for renal dysfunction as a primary cause of hypertension.

No MeSH data available.


Related in: MedlinePlus

Analysis of renal tubular expression and distribution of sodium/proton exchanger-3 (NHE-3) and epithelial sodium channel (α-ENaC).A and D show representative images of expression and distribution of NHE-3 in wild type (RGS2+/+) and RGS2 knockout (RGS2-/-) renal tubules. B and E show representative images of α-ENaC expression and distribution. C and F are expanded inserts in B and E, respectively, showing a marked increase in luminal border localization of α-ENaC in RGS2-/- relative to wild type tubules. G, Frequency distribution of α-ENaC punctate size in the luminal border of renal tubules. H, average size of luminal α-ENaC granules. Values are mean ± SE. *P < 0.05 RGS2+/+ vs. RGS2-/- mice.
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pone.0132594.g007: Analysis of renal tubular expression and distribution of sodium/proton exchanger-3 (NHE-3) and epithelial sodium channel (α-ENaC).A and D show representative images of expression and distribution of NHE-3 in wild type (RGS2+/+) and RGS2 knockout (RGS2-/-) renal tubules. B and E show representative images of α-ENaC expression and distribution. C and F are expanded inserts in B and E, respectively, showing a marked increase in luminal border localization of α-ENaC in RGS2-/- relative to wild type tubules. G, Frequency distribution of α-ENaC punctate size in the luminal border of renal tubules. H, average size of luminal α-ENaC granules. Values are mean ± SE. *P < 0.05 RGS2+/+ vs. RGS2-/- mice.

Mentions: To determine whether the absence of RGS2 alters tubular sodium reabsorption, wild type and RGS2-/- mice were subjected to acute plasma volume expansion by continuous infusion of isotonic saline. To stimulate the excretion of excess water and sodium, arterial blood pressure was increased by systemic administration of the non-selective nitric oxide synthase inhibitor, L-NAME after baseline recordings. As expected, blood pressure, RVR and GFR increased whereas RBF decreased in both genotypes following L-NAME administration (Fig 6A–6D). Although sodium and potassium excretion rate increased in both genotypes following L-NAME injection, the natriuretic response was much more robust and reached significance only in wild type mice (Fig 6E and 6F), suggesting that sodium reabsorption was increased in RGS2-/- mice. To test this hypothesis, we determined whether RGS2 deficiency affected the expression and/or tissue distribution of Na+ channels in renal tubules. Tissue distribution (Fig 7A and 7D) and expression level of the proximal tubule sodium transporter, NHE-3, were unaffected by the absence of RGS2. In contrast, tubules from RGS2-/- mice showed increased luminal localization of ENaC, the distal tubule sodium transporter, whereas it was uniformly distributed in tubules from wild type animals (Fig 7B, 7C, 7E and 7F). Because ENaC can assemble and/or cluster in different stoichiometries and modular arrangements that can alter channel activity[44–48], we determined whether the absence of RGS2 affected the apparent size of luminal ENaC assemblies in renal tubules. As shown in Fig 7G, there was a heterogeneous population of luminal ENaC in the tubules of both genotypes. However, the average size of punctae of the highest frequency, determined from the frequency distribution plot (Fig 7G), was larger in RGS2-/- relative to those in wild type tubules (Fig 7H), suggesting a higher order arrangement or clustering in the absence of RGS2. These results together indicated that loss of RGS2 causes alterations in cellular distribution or assembly of ENaC that may promote sodium retention by the renal tubular system.


Regulation of Renal Hemodynamics and Function by RGS2.

Osei-Owusu P, Owens EA, Jie L, Reis JS, Forrester SJ, Kawai T, Eguchi S, Singh H, Blumer KJ - PLoS ONE (2015)

Analysis of renal tubular expression and distribution of sodium/proton exchanger-3 (NHE-3) and epithelial sodium channel (α-ENaC).A and D show representative images of expression and distribution of NHE-3 in wild type (RGS2+/+) and RGS2 knockout (RGS2-/-) renal tubules. B and E show representative images of α-ENaC expression and distribution. C and F are expanded inserts in B and E, respectively, showing a marked increase in luminal border localization of α-ENaC in RGS2-/- relative to wild type tubules. G, Frequency distribution of α-ENaC punctate size in the luminal border of renal tubules. H, average size of luminal α-ENaC granules. Values are mean ± SE. *P < 0.05 RGS2+/+ vs. RGS2-/- mice.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4508038&req=5

pone.0132594.g007: Analysis of renal tubular expression and distribution of sodium/proton exchanger-3 (NHE-3) and epithelial sodium channel (α-ENaC).A and D show representative images of expression and distribution of NHE-3 in wild type (RGS2+/+) and RGS2 knockout (RGS2-/-) renal tubules. B and E show representative images of α-ENaC expression and distribution. C and F are expanded inserts in B and E, respectively, showing a marked increase in luminal border localization of α-ENaC in RGS2-/- relative to wild type tubules. G, Frequency distribution of α-ENaC punctate size in the luminal border of renal tubules. H, average size of luminal α-ENaC granules. Values are mean ± SE. *P < 0.05 RGS2+/+ vs. RGS2-/- mice.
Mentions: To determine whether the absence of RGS2 alters tubular sodium reabsorption, wild type and RGS2-/- mice were subjected to acute plasma volume expansion by continuous infusion of isotonic saline. To stimulate the excretion of excess water and sodium, arterial blood pressure was increased by systemic administration of the non-selective nitric oxide synthase inhibitor, L-NAME after baseline recordings. As expected, blood pressure, RVR and GFR increased whereas RBF decreased in both genotypes following L-NAME administration (Fig 6A–6D). Although sodium and potassium excretion rate increased in both genotypes following L-NAME injection, the natriuretic response was much more robust and reached significance only in wild type mice (Fig 6E and 6F), suggesting that sodium reabsorption was increased in RGS2-/- mice. To test this hypothesis, we determined whether RGS2 deficiency affected the expression and/or tissue distribution of Na+ channels in renal tubules. Tissue distribution (Fig 7A and 7D) and expression level of the proximal tubule sodium transporter, NHE-3, were unaffected by the absence of RGS2. In contrast, tubules from RGS2-/- mice showed increased luminal localization of ENaC, the distal tubule sodium transporter, whereas it was uniformly distributed in tubules from wild type animals (Fig 7B, 7C, 7E and 7F). Because ENaC can assemble and/or cluster in different stoichiometries and modular arrangements that can alter channel activity[44–48], we determined whether the absence of RGS2 affected the apparent size of luminal ENaC assemblies in renal tubules. As shown in Fig 7G, there was a heterogeneous population of luminal ENaC in the tubules of both genotypes. However, the average size of punctae of the highest frequency, determined from the frequency distribution plot (Fig 7G), was larger in RGS2-/- relative to those in wild type tubules (Fig 7H), suggesting a higher order arrangement or clustering in the absence of RGS2. These results together indicated that loss of RGS2 causes alterations in cellular distribution or assembly of ENaC that may promote sodium retention by the renal tubular system.

Bottom Line: RGS2 deficiency caused decreased sensitivity and magnitude of changes in RVR and RBF after a step increase in RPP.We conclude that RGS2 deficiency impairs renal function and autoregulation by increasing renal vascular resistance and reducing renal blood flow.These changes impair renal sodium handling by favoring sodium retention.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, 19102, United States of America.

ABSTRACT
Regulator of G protein signaling 2 (RGS2) controls G protein coupled receptor (GPCR) signaling by acting as a GTPase-activating protein for heterotrimeric G proteins. Certain Rgs2 gene mutations have been linked to human hypertension. Renal RGS2 deficiency is sufficient to cause hypertension in mice; however, the pathological mechanisms are unknown. Here we determined how the loss of RGS2 affects renal function. We examined renal hemodynamics and tubular function by monitoring renal blood flow (RBF), glomerular filtration rate (GFR), epithelial sodium channel (ENaC) expression and localization, and pressure natriuresis in wild type (WT) and RGS2 (RGS2-/-) mice. Pressure natriuresis was determined by stepwise increases in renal perfusion pressure (RPP) and blood flow, or by systemic blockade of nitric oxide synthase with L-NG-Nitroarginine methyl ester (L-NAME). Baseline GFR was markedly decreased in RGS2-/- mice compared to WT controls (5.0 ± 0.8 vs. 2.5 ± 0.1 μl/min/g body weight, p<0.01). RBF was reduced (35.4 ± 3.6 vs. 29.1 ± 2.1 μl/min/g body weight, p=0.08) while renal vascular resistance (RVR; 2.1 ± 0.2 vs. 3.0 ± 0.2 mmHg/μl/min/g body weight, p<0.01) was elevated in RGS2-/- compared to WT mice. RGS2 deficiency caused decreased sensitivity and magnitude of changes in RVR and RBF after a step increase in RPP. The acute pressure-natriuresis curve was shifted rightward in RGS2-/- relative to WT mice. Sodium excretion rate following increased RPP by L-NAME was markedly decreased in RGS2-/- mice and accompanied by increased translocation of ENaC to the luminal wall. We conclude that RGS2 deficiency impairs renal function and autoregulation by increasing renal vascular resistance and reducing renal blood flow. These changes impair renal sodium handling by favoring sodium retention. The findings provide a new line of evidence for renal dysfunction as a primary cause of hypertension.

No MeSH data available.


Related in: MedlinePlus