Distribution Pattern of Activated Psrc and Its Relation with the Cell Cycle State of Endothelial Cells during Capillary Morphogenesis

Lery O. Álvarez-Lugo, University of Puerto Rico, Mayagüez, PR 00680 and Carlos E. Semino, Massachusetts Institute of Technology, Cambridge, MA 02139.

It has been previously demonstrated that physiological values of interstitial fluid flow normal to an endothelial cell monolayer in combination with VEGF induced capillary morphogenesis by promoting cell sprouting. Evidence suggests that at these interstitial flow values a maximum of the activated form of the mechanical transducer Src (pSrc, phosphorylated-Src) can be observed. In addition, we found that under these conditions the length of the capillary structures and cell proliferation rate presented a maximum, suggesting that the transduction pathway in charge of “sensing” the mechanical stimuli operates at the cell cycle level inducing cell division. We also observed that BrdU labeled cells were not detected in the capillary-like structures, indicating cells undergoing S phase do not participate in capillary development. In this work, we studied the pattern of distribution of pSrc on the monolayer in early stages of capillary morphogenesis. First, we found that cells undergoing capillary morphogenesis (early sprouting) presented high levels of pSrc and were restricted to G1 stage (expressing Cdk6). Second, we observed that independently of fluid flow or VEGF two defined cell clusters types where detected: 1, cells containing pSrc and 2, cells deficient in pSrc. We propose that the endothelial monolayer presents pre-determined pSrc zones which under optimal conditions engage G1-stage cells in capillary morphogenesis.