Reduced mRNA and protein content of rho guanine nucleotide exchange factor (RhoGEF) in Bartter's and Gitelman's syndromes: relevance for the pathophysiology of hypertension.

BACKGROUND: Activation of RhoA/Rho kinase (ROK) pathway by angiotensin II (Ang II) is involved in the pathophysiology of hypertension and remodeling. In Bartter's and Gitelman's syndrome (BS/GS), the short-term and long-term signaling of Ang II are blunted. The BS/GS have also reduced expression and response on Ang II challenge of ROK, which indicate downregulation of RhoA/ROK pathway. As causes for RhoA/ROK downregulation in BS/GS, we hypothesized an alteration at the level of the upstream regulators of RhoA such as reduced expression of Rho guanine nucleotide exchange factor (RhoGEF), which links activation of G protein-coupled receptors to RhoA/ROK signaling or increased guanine nucleotide dissociation inhibitor (RhoGDI), which inhibits dissociation of GDP from GDI maintaining RhoA in an inactive state.

METHODS: In mononuclear cells of 9 BS/GS and 9 healthy controls (C), we looked at gene and protein expression (reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot) of RhoA, RhoGEF, and RhoGDI.

RESULTS: In BS/GS RhoA gene and protein expression were not different from C. Also RhoGDI mRNA and protein levels were not different. On the contrary, p115RhoGEF mRNA and protein levels were reduced in BS/GS.

CONCLUSIONS: Reduced p115RhoGEF may explain the downregulation of RhoA/ROK pathway in BS/GS. This is the first report of upstream regulators of RhoA level in BS/GS, a human clinical condition characterized by reduced vascular tone regulation. Because BS/GS represent the mirror image of derangements involved in hypertension, the reduced RhoGEF expression in BS/GS underlines a major impact of RhoA/ROK pathway on blood pressure regulation and confirms BS/GS as a good human model for exploring mechanisms involved in the pathophysiology of hypertension and remodeling.