Dependency of deformation of cell nucleus on stretch direction of tissue: Relation to anisotropic response of aortic media to hypertension.

The deformation of the cell nucleus may cause dispersion of chromatin and eventually enhance transcription, translation, and protein expression. If this happens in the hypertensive artery, an excessive stretch of smooth muscle cell (SMC) nuclei caused by hypertension may provoke wall thickening. Here, we measured deformation of SMC nuclei in rabbit thoracic aortas stretched in different directions. Thin 0.2-mm-thick specimens were sliced in the direction perpendicular to their axial and circumferential directions, and stretched in the circumferential and axial directions, respectively. The deformation of the actin filament (AF) network was similar to that of the whole tissue, whereas the deformation of the nucleus was significantly smaller than the others. Notably, the nucleus seldom deformed when the tissue was stretched in the axial direction. A novel cell model in which the nucleus is connected to the extracellular matrix via the AF network successfully explained the relative unresponsiveness of the nucleus to the axial stretch. It has been pointed out that stress is maintained constant in the circumferential direction but not in the axial direction in the artery wall during hypertension. The relative unresponsiveness of the nucleus to the axial stretch represented in this study explains this phenomenon.