Tracing G-Protein-Mediated Contraction and Relaxation in Vascular Smooth Muscle Cell Spheroids

Analyses of G-protein-mediated contraction and relaxation of vascular smooth muscle cells (VSMCs) are usually hampered by a rigid growth surface and culture conditions promoting cell proliferation and a less contractile phenotype. Our studies indicated that mouse aortic VSMCs cultured in three-dimensional spheroids acquire a quiescent contractile status while decreasing the baseline G-protein-dependent inositolphosphate formation and increasing the expression of endothelin receptor type A (Ednra). Endothelin-1 (ET-1) promoted inositolphosphate formation in VSMC spheroids, but not in VSMCs cultured under standard conditions. To trace ET-1-mediated contraction of VSMC spheroids, we developed an assay by adhering them to collagen hydrogels and recording structural changes by time-lapse microscopy. Under these conditions, mouse and human VSMC spheroids contracted upon treatment with ET-1 and potassium chloride or relaxed in response to caffeine and the prostacyclin analogue Iloprost. ET-1 activated AKT-, MKK1-, and MKK3/6-dependent signaling cascades, which were inhibited by an overexpressing regulator of G-protein signaling 5 (Rgs5) to terminate the activity of G alpha subunits. In summary, culture of VSMCs in three-dimensional spheroids lowers baseline G-protein activity and enables analyses of both contraction and relaxation of mouse and human VSMCs. This model serves as a simple and versatile tool for drug testing and investigating G-protein-depending signaling.