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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ajog.2005.12.050 Byline: Carl P. Weiner (a), Clifford Mason (b), Gentzon Hall (c), Usma Ahmad (d), Peter Swaan (b), Irina A. Buhimschi (d) Abstract: Coupled to hundreds of receptors, G-proteins modulate signal transduction pathways and are important hormonal targets. The first objective was to determine the effect of pregnancy and estradiol on myometrial guanosine triphosphatase activity. The second objective was to begin dissecting the molecular mechanism(s) underlying alterations in guanosine triphosphatase activity. Author Affiliation: (a) Departments of Obstetrics and Gynecology, University of Kansas School of Medicine, Kansas City, KS (b) Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy (c) Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Maryland School of Medicine Baltimore, MD (d) Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, CT Article History: Received 3 October 2005; Revised 9 December 2005; Accepted 22 December 2005 Article Note: (footnote) Supported by Grants HL49041 (to C.P.W.), HD049185 (to C.P.W.), and U01-DP000187 (to C.P.W.) from the United States Public Health Service.

The effect of pregnancy and estradiol on myometrical guanosine triphosphatase activity is determined. Results reveal that basal myometrial guanosine triphospahatase activity is increased with pregnant compared with nonpregnant animals.

Nephrotic syndrome (NS) is a clinicopathological entity characterized by proteinuria, hypoalbuminemia, peripheral edema, and hyperlipidemia. It is the most common cause of glomerular disease in children and adults. Although the molecular pathogenesis of NS is not completely understood, data from the study of familial NS suggest that it is a “podocytopathy.” Virtually all of the genes mutated in hereditary NS localize to the podocyte or its secreted products and the slit diaphragm. Since the completion of human genome sequence and the advent of next generation sequencing, at least 29 causes of single-gene NS have been identified. However, these findings have not been matched by therapeutic advances owing to suboptimal in vitro and in vivo models for the study of human glomerular disease and podocyte injury phenotypes. Multidisciplinary collaboration between clinicians, geneticists, cell biologists, and molecular physiologists has the potential to overcome this barrier and thereby speed up the translation of genetic findings into improved patient care.

Selective modulation of Rho GTPase activity in podocytes recapitulates characteristic features of human nephrosis. Using a mouse model, Robins et al.found that high levels of Rac1 activation in podocytes caused podocyte detachment and glomerulosclerosis. Podocyte Rac1 activity was enhanced in biopsy specimens from patients with nephrosis, and serum from this patient population activated Rac1 in cultured podocytes. These data provide a causal link between podocyte Rac1 activation and human nephrotic diseases.

The emerging role of the transient receptor potential cation channel isotype 6 (TRPC6) as a central contributor to various pathological processes affecting podocytes has generated interest in the development of therapeutics to modulate its function. Recent insights into the regulation of TRPC6 have revealed PKG as a potent negative modulator of TRPC6 conductance and associated signaling via its phosphorylation at two highly conserved amino acid residues: Thr69/Thr70(Thr69in mice and Thr70in humans) and Ser321/Ser322(Ser321in mice and Ser322in humans). Here, we tested the role of PKG in modulating TRPC6-dependent responses in primary and conditionally immortalized mouse podocytes. TRPC6 was phosphorylated at Thr69in nonstimulated podocytes, but this declined upon ANG II stimulation or overexpression of constitutively active calcineurin phosphatase. ANG II induced podocyte motility in an in vitro wound assay, and this was reduced 30–60% in cells overexpressing a phosphomimetic mutant TRPC6 (TRPC6T70E/S322E) or activated PKG (P< 0.05). Pretreatment of podocytes with the PKG agonists S-nitroso-N-acetyl-dl-penicillamine (nitric oxide donor), 8-bromo-cGMP, Bay 41–2772 (soluble guanylate cyclase activator), or phosphodiesterase 5 (PDE5) inhibitor 4-{[3′,4′-(methylenedioxy)benzyl]amino}[7]-6-methoxyquinazoline attenuated ANG II-induced Thr69dephosphorylation and also inhibited TRPC6-dependent podocyte motility by 30–60%. These data reveal that PKG activation strategies, including PDE5 inhibition, ameliorate ANG II-induced podocyte dysmotility by targeting TRPC6 in podocytes, highlighting the potential therapeutic utility of these approaches to treat hyperactive TRPC6-dependent glomerular disease.