Apical and Basal Stress Fibers have Different Roles in Mechanical Regulation of the Nucleus in Smooth Muscle Cells Cultured on a Substrate

摘要

Actin stress fibers (SFs) play important roles in cellular mechanotransduction and in regulation of various cellular functions. Stress fibers generate internal tension and contribute to physical interactions between cells and extracellular matrices. We recently found that SFs in vascular smooth muscle cells (SMCs) cultured on a two-dimensional substrate mechanically interact with cell nucleus via nuclear membrane proteins, and that the internal tension of SFs is transmitted directly to the nucleus. However, SFs exist on both the apical side and the basal side of adherent cells on a substrate, and it remains unclear whether these two types of SFs play different roles on the mechanical environment around the nucleus. Here, we investigated differences between the apical and basal stress fibers (BSFs) in SMCs by using a laser nano-scissor technique. We microdissected apical SFs running across the top surface of nucleus (actin cap fibers: ACFs) or BSFs underneath the nucleus by using a laboratory-built laser nano-scissor and observed the subsequent mechanical responses of the SFs and the nucleus. Shortening of the dissected fibers was significantly greater in the ACFs than in the BSFs. Nuclei also moved in the direction of retraction of the dissected fibers, and displacement and local deformation of the nucleus was more remarkable after the dissection of the ACFs than after that of the BSFs. ACFs mostly aligned in the major axis of the nucleus, whereas BSFs showed a weak alignment with asymmetry: the direction of BSFs was rotated clockwise by similar to 10A degrees from the major axis of the nucleus. These results indicate that ACFs and BSFs play different roles in mechanical regulation of the nucleus, and that intracellular tension is transmitted to the nucleus more efficiently by ACFs. ACFs may play significant roles in controlling the intranuclear distribution of DNA through intracellular orientation and positioning of the nucleus.