The 2.3 kb smooth muscle myosin heavy chain promoter directs gene expression into the vascular system of transgenic mice and rabbits.

BACKGROUND: Smooth muscle cells (SMC) are a preferential target for gene therapeutic approaches in atherosclerosis and restenosis. However, the undesirable expression of putative therapeutic genes in tissues other than the vascular wall is a considerable safety limitation for clinical trials, thus requiring the identification of a smooth-muscle-specific promoter sequence. Since the 2.3 kb rabbit Smooth Muscle Myosin Heavy Chain (SMHC) promoter was shown to be transcriptionally active in primary vascular but not visceral or other non-SMC in vitro, this fragment was chosen for in vivo analysis. METHODS AND RESULTS: Transgenic mice and rabbits were established expressing a luciferase reporter gene under control of the 2.3 kb rabbit SMHC promoter. In contrast to the endogenous expression pattern of the SMHC gene both species revealed light emission predominantly in the arterial system including coronary arteries. Low activities were measured in large veins and the gastrointestinal system. In situ hybridization of murine embryos using a luciferase riboprobe confirmed reporter gene expression in large arteries with no detectable mRNA in the viscera. Unlike adult animals, ectopic luciferase activities were found in ventricular myocardium during murine development ceasing 1 week post partum. CONCLUSIONS: In two animal species, the 2.3 kb SMHC promoter appeared to be effective in discriminating between the pathways regulating vascular and visceral smooth muscle gene expression. The vascular-specific expression profile of the 2.3 kb SMHC promoter suggests that the 2.3 kb SMHC promoter contains the regulatory elements necessary for selective gene targeting into vascular SMC of large arteries including coronary arteries in vivo.

Transgenic animal models: new avenues in cardiovascular physiology.

Application of molecular genetic tools to inherited cardiovascular disorders has provided important insights into the molecular mechanisms underlying cardiomyopathies, arrhythmias, blood pressure regulation, and atherosclerosis. In addition, alteration of gene expression has been observed under common cardiovascular conditions such as cardiac hypertrophy and heart failure. Recent advances in transgenic and gene-targeting approaches allow a sophisticated manipulation of the mouse genome by gene addition, gene deletion, or gene modifications. These transgenic models enable the dissection of in vivo pathways responsible for these complex disease phenotypes. This review describes tissue-specific promoters suitable for targeting candidate genes to the cardiovascular system as well as a number of valuable transgenic animal models of blood pressure regulation, atherogenesis, defects in the coagulation system, cardiac hypertrophy, myocarditis, cardiomyopathies, and heart failure. Limitations and difficulties associated with these transgenic approaches are discussed. Animal models which may provide a basis for future gene therapy of cardiovascular diseases are introduced. Finally, methods are described to regulate the spatial and temporal expression level of a transgene, to inactivate a target gene in a tissue-specific manner, and to introduce specific mutations into the genome. These recent advances in transgenic technology are expected to have a considerable impact on cardiovascular research in the near future.