Mechanical Trapping of the Cell Nucleus Into Microgroove Concavity But Not On Convexity Induces Cell Tissue Growth and Vascular Smooth Muscle Differentiation

Vascular smooth muscle cells (VSMCs) in the normal aortic wall regulate vascular contraction and dilation. VSMCs change their phenotype from contractile to synthetic and actively remodel the aortic wall under pathological conditions. Findings on the differentiation mechanism of VSMCs have been reported in many in vitro studies; however, the mechanical environments in vivo aortic walls are quite different from those of in vitro culture conditions: VSMCs in vivo exhibit an elongated shape and form a tissue that aligns with the circumferential direction of the walls, whereas VSMCs in vitro spread randomly and form irregular shapes during cultivation on conventional flat culture dishes and dedifferentiate into a synthetic phenotype. To clarify the mechanisms underlying the VSMC differentiation, it is essential to develop a cell culture model that considers the mechanical environment of in vivo aortic walls.

We fabricated a polydimethylsiloxane-based microgrooved substrate with 5, 10, and 20 μm of groove width and 5 μm of groove depth to induce VSMC elongation and alignment as observed in vivo. We established a coating method to control cell adhesion proteins only on the surface of groove concavities and investigated the effects of mechanical trapping of the cell nucleus in microgroove concavities on the morphology of intracellular nuclei, cell proliferation and motility, and VSMC differentiation.

We found that VSMCs adhering to the concavities formed a uniform cell tissue and allowed remarkable elongation. In particular, the microgrooves with 5 μm of groove width and depth facilitated a significant nuclear deformation and volume reduction of the nucleus due to a lateral compression by the side wall of the groove concavities that is relatively similar to a sandwich-like arrangement of in vivo elastic lamellae, resulting in the drastic inhibition of cell motility and proliferation, and the significant improvement of VSMC differentiation.

The results indicate that mechanical trapping of the cell nucleus into microgroove concavity but not on convexity induces cell tissue growth and VSMC differentiation. Our cell culture model with microgrooved substrates can be useful for studying the mechanisms of VSMC differentiation, considering the in vivo vascular mechanical environment.