Abstract 303: Decreased Adrenomedullin and Interaction with NHE3 in Human GRK4γ142v Transgenic Mice
The expression of the human G protein-coupled receptor kinase 4γ (GRK4γ) 142V variant (hGRK4γ142V)in mice causes hypertension that is related to dysfunction of renal dopaminergic and renin-angiotensin systems. To determine if there are other dysfunctional systems in hGRK4γ142V mice, we quantified the expression of adrenomedullin (ADM), a natriuretic hormone, and components of its receptor, RAMP2 (receptor activity-modified protein2), CLCR (calcitonin-like calcitonin receptor), and ADMRL2 (ADM receptor L2) in the kidneys of hGRK4 γ142V and hGRK4γWT transgenic mice and non-transgenic (NT) littermates. Systolic blood pressure (measured under anesthesia) was elevated in hGRK4γ142V (129.3±10.4, mm Hg) but not in GRK4γWT mice (101.7±6.3), relative to NT littermates (99.8±1.8) (n=4/group). The sodium excretion and blood pressure plot in GRK4γ142V mice was shifted to the right of GRK4γWT mice. Protein expressions of ADM (37±4% of NT by immunoblotting and immunofluorescence) and RAMP2 (36±16%) were decreased in hGRK4γ142V mice but unchanged in GRK4γWT mice, relative to NT littermates. The protein expressions of CLCR and ADMRL2 were not altered in hGRK4γ142V andGRK4γWT. In the kidney ADM colocalized with NHE3 but not with NKCC2 and NCC. NHE3 protein expression in renal homogenates and brush border membranes was not altered in GRK4γ142V mice. However, the amount of NHE3 that coimmunoprecipitated with ADM was decreased in GRK4γ142V (77±3% of NT) mice; a similar decrease was also found in the reverse-coimmunoprecipitation of NHE3 with ADM. In vitro, human ADM inhibited apical sodium transport in polarized human renal proximal tubule cells (1 hr, n=5-6) at concentrations of 10 nM (84±4 % of vehicle) and 100 nM (81±3%), similar to that achieved with the NHE3 inhibitor EIPA (81±6%, 100 nM), suggesting that NHE3 activity was inhibited by ADM. Our data suggest that GRK4γ142V decreases ADM/RAMP2 expression in the kidney; the natriuretic effect of ADM may depend mainly on the inhibition of the activities of sodium transporters along the nephron (e.g., NHE3). The decreased ADM/NHE3 interaction and dysfunctional natriuretic and antinatriuretic factors may contribute to the impaired sodium excretion and increased blood pressure in GRK4γ142V transgenic mice.
Author Disclosures: D. Zhou: None. J. Jones: None. L. Asico: None. P.A. Jose: None. X. Wang: None.
- © 2014 by American Heart Association, Inc.