Question: 

EGFR plays an important role in proliferation, differentiation, survival of cells and can inhibit apoptosis. Mice with a constitutive deletion of EGFR in vascular smooth muscle cells (VSMCs) and a strong reduction in cardiomyocytes show an increased heart weight, hypertrophy, diastolic hypotension and a reduced lifespan (Schreier et al., Arterioscler Thromb Vasc Biol. 2011, 31(7):1643-52). Moreover EGFR seems to be involved in the formation of cardiovascular and renovascular diseases. As the importance of EGFR in VSMCs is poorly understood, we want to characterize the receptor in VSMCs to understand its physiological and pathophysiological role with regard to regulation of blood pressure, function of heart/ kidney and to vascular tissue.

Methodology: 

We generated an inducible knockout mouse model via Cre/loxP system by crossing EGFR flox/flox mice (kindly provided by Dr. Maria Sibilia, Insitute of Cancer research, Medical University of Vienna, Vienna, Austria) with SMMHC-Cre +/- mice (kindly provided by Dr. Stefan Offermanns, Department of Pharmacology, Max-Planck-Institute for Heart and Lung Research, Bad Nauheim, Germany). Cre recombinase is expressed under control of the SMMHC promoter and can be activated in VSMCs of mice by intraperitoneal injection of tamoxifen. Additionally we isolated VSMCs from aortas and induced the deletion of EGFR with 4-OH-tamoxifen.

Results: 

qRT-PCR confirms the successful deletion of EGFR in isolated, 4-OH-tamoxifen-treated VSMCs. Tamoxifen-induced EGFR deletion has no effect on the macroscopic mouse phenotype and the EGFR expression of heart, kidney, liver and muscle. In contrast to EGFR^{࢞/࢞VSMC&CM} heart weight was not affected. The heart rate is significantly reduced 21 days after tamoxifen. Tail cuff measurements show no significant changes of systolic blood pressure 28 days after tamoxifen treatment, similar to the results of the constitutive deletion model.

Conclusion: 

We could show that the Cre/loxP system works in vitro. First results with induced EGFR KO mice show that EGFR deletion in VSMC does not induce cardiac hypertrophy but affects heart rate to a similar extend as compared to mice with a deletion of EGFR in VSMCs and a strong reduction in cardiomyocytes. Thus, cardiac hypertrophy in the latter model was the result of reduced EGFR expression in cardiomyocytes.