Differential effects of cyclic and static stretch on expression of tyrosine kinase receptors in microvascular endothelial cells

Abstract

Mechanical stretch, an important stimulus for vascular growth, results not only from pulsatile blood flow (cyclic stretch, CS), but also from tissue expansion during growth (constant static stretch, SS). In order to investigate whether both types of stretch provide similar or dissimilar stimuli for growth factor receptor up-regulation, rat coronary microvascular endothelial cells were cultured in Bioflex culture plates coated with collagen and exposed to CS or SS. The CS was generated by a computerized Flexercell Strain Unit with 10% elongation at 30 cycles/min, while the SS was induced at the same elongation but with constant stretch without relaxation. Controls consisted of cells seeded on the culture plates but not subjected to stretch. The protein level of tyrosine kinase receptor was assessed with Western blotting. The levels of Flk-1 protein increased in a time dependent manner following CS or SS. Maximal levels of Flk-1 reached 3.2 ± 0.54 fold at 6 hours after CS and 3.4 ± 0.75 fold at 18 hours after SS, respectively. SS enhanced protein level of Flt-1, peaked (2.1 ± 0.51 fold over the control value) by 18 hr. In contrast, CS did not alter the flt-1 expression. Both CS and SS caused up-regulation of Tie-2 protein after only 1 hour, however, CS affected relatively higher and longer expression of Tie-2, which remained elevated up to 18 hr of stretch (1.8 ± 0.23), while SS-induced up-regulation of Tie-2 returned to normal levels after 6 hr. Our study is the first to distinguish between the effects of the two types of stretch on key tyrosine kinase receptor expression. These results suggest that endothelial cell responses to two types of stretch display both differences and similarities with regard to receptor expression. Supported by NIH grant HL075446.