Rescue of cGMP kinase I knockout mice by smooth muscle-specific expression of either isozyme

Abstract

Smooth muscle expresses the Iα and the Iβ isoforms of cGMP-dependent protein kinase I (cGKI). Inactivation of the murine cGKI gene prkg1 leads to multiple phenotypes and premature death at ap;6 weeks. We reconstituted mice with the cGKIα or -Iβ isozyme to test which isozyme was needed to support basic smooth muscle functions. Mice were generated by gene targeting. The cGKIα or the -Iβ coding sequences were placed under the control of the SM22α promoter to express either isoform selectively in smooth muscle cells (SM-Iα or SM-Iβ transgene). To generate smooth muscle-specific cGKIα or cGKIβ rescue mice, the SM-Iα or SM-Iβ transgenes were crossed on a cGKI genetic background. The levels of cGKIα or -Iβ expression were comparable to endogenous cGKI expression in wild-type aortic and intestinal smooth muscles. In cGKIα or -Iβ rescue mice, expression of the isozymes was not detectable in non-smooth muscle tissues and cells. Median survival time of the Iα and Iβ rescue mice was 52 weeks. Both isozymes mediated the 8-bromo-cGMP-induced relaxation of precontracted jejunum and aorta muscle strips. Activation of both isozymes reduced hormone- or K-induced [Ca]i levels. The cGKIα and cGKIβ rescue mice did not show a significant difference in intestinal passage time of BaSO4 in comparison with wild-type animals. Telemetric blood pressure measurements in conscious freely moving animals did not show differences between rescues and control mice in basal blood pressure and its regulation by DETA-NO, sodium nitroprusside, carbachol, or Y-27632. These results show that cGKI in smooth muscle is essential and that either cGKI isozyme alone can rescue basic vascular and intestinal smooth muscle functions. © 2007 American Heart Association, Inc.