摘要:Cells in vivo reside within a complex microenvironment that is rich in biological,chemical and mechanical cues,playing critical roles in regulating cellular activities(e.g.,proliferation,migration,differentiation)both spatially and temporally.Although it is well accepted that biochemical cues can significantly influence cell functions,accumulating evidence has also shown that mechanical feedback from the cell microenvironment(e.g.,stiffness of ECM,morphology,and tension force)also plays an important role in controlling cell fate.Disequilibrium of the mechanical microenvironment is associated with a series of diseases,such as cancer migration and tissue fibrosis.Thus,there is a pressing need to understand how cells transduce these mechanobiological cues.The cell cytoskeleton is linked to both the nuclear lamina via LINC complexes and to focal adhesions.This enables the intriguing possibility that forces directly transduced by the nucleus might in fact affect gene expression.Can force transmitted to nucleus and associated alterations to the special organization of genome inside the nucleus modulate gene expression programmes and change cell behaviors? This kind of putative mechanotransduction dominated by the nucleus is termed as nuclear mechanotransduction.Evidence shows that isolated nuclei regulate their stiffness to in response to force applied on nesprin with integrated nuclear lamina and emerin required.Another example is that the force applied on integrins in focal adhesions can be transmitted through actin filaments to the LINC complex and then stretch the chromatin directly through lamina-chromatin interactions.However,the mechanism of nuclear mechanotransduction is still unclear.Three hypotheses have been proposed.The first proposed mechanism is that the proteins on the nuclear lamina are phosphorylated induced by force and their special organization is changed to regulate downstream signal transduction.Transcription factors like YAP and calcium ions would enter the nucleus in the context of force stretching the nuclear lamina and opening nuclear pore complexes(NPC)and calcium channels.Another proposed hypothesis in this case is that force propagated through the cytoskeleton stretches,opens or condenses chromatin directly,leading to an entirely different genome organization.Nevertheless,due to the lack of research methods and instruments,researchers have not reached a consensus on how cells sense external forces and react specifically through nucleus.In this study,we used micropatterned techniques to modify poly(N-isopropyl-acrylamide)(PA)hydrogel surface with fibronectin(FN)which promote cell adhesion to shape-engineer the cells to investigate the effects of matrix stiffness on nuclear mechanotransduction.To illustrate the impact on nuclear shape induced by matrix stiffness,the nuclei were stained byDAPI and observed by a laser confocal microscopy with small step sizes.The nuclear shape index(NSI),which indicate the variation of projected nuclear shape was firstly researched thoroughly.Meanwhile,the nuclear height,width and volume were characterized in this study.To investigate the force transmitted to the nuclei in cells cultured on hydrogels with multiple stiffness,the cell traction force was measured and the cytoskeleton like actin cap was studied by pharmacological treatments.We also found that the impacts of matrix stiffness on nuclear mechanics,which indicated by the condensation of chromatin and the overexpression of Lamin A/C.