Image-based elastography of heterochromatin and euchromatin domains in the deforming cell nucleus

Abstract

Chromatin of the eukaryotic cell nucleus comprises of microscopically dense heterochromatin and loosely packed euchromatin domains, each with distinct transcriptional ability and roles in cellular mechanotransduction. While recent methods have been developed to characterize the nucleus, measurement of intranuclear mechanics remains largely unknown. Here, we describe the development of nuclear elastography, which combines microscopic imaging and computational modeling to quantify the relative elasticity of the heterochromatin and euchromatin domains.Using contracting murine embryonic cardiomyocytes, nuclear elastography reveals that the heterochromatin is almost four times stiffer than the euchromatin at peak deformation. The relative elasticity between the two domains changes rapidly during the active deformation of the cardiomyocyte in the normal physiological condition but progresses more slowly in cells cultured in a mechanically stiff environment, although the relative stiffness at peak deformation does not change. Further, we found that the disruption of the LINC complex in cardiomyocytes compromises the intranuclear elasticity distribution resulting in elastically similar heterochromatin and euchromatin. These results provide insight into the elastography dynamics of heterochromatin and euchromatin domains, and provide a non-invasive framework to further investigate the mechanobiological function of subcellular and subnuclear domains limited only by the spatiotemporal resolution of the image acquisition method.

Stiffness and Aging in Cardiovascular Diseases: The Dangerous Relationship between Force and Senescence

“…Although senolityc, epigenetic, and cytoskeleton-interfering drugs represent a promising and novel therapeutic approach, it is necessary to proceed with a deeper understanding of the molecular pathways, potentially establishing the tight association between cell-based mechano-sensing and cellular senescence. Novel interdisciplinary approaches integrating measurements of the forces actually developed by the cells [ 85 ] along with determination of the nuclear topology [ 86 ] and chromatin rheological features [ 87 ] will open novel avenues to resolve the problem of cellular senescence and retard the onset of aging-related diseases.…”

The LINC Between Mechanical Forces and Chromatin

“…A more recent study using isolated nuclei from HeLa cells demonstrated that in nuclei stretched at a physiologically relevant speed of 50 nm/s, lamin A/C levels modulate the nuclear stiffness primarily in response to more than 3 µm of stretch, whereas euchromatin/heterochromatin levels mainly control nuclear stiffening at less than 3 µm stretch (Stephens et al, 2017). Moreover, disruption of the LINC complex abrogates the difference between heterochromatin and euchromatin elasticities/stiffnesses at the peak nuclear deformation induced by CM contraction (Ghosh et al, 2021), suggesting that an intact LINC complex is also necessary for maintaining chromatin stiffness. Chromatin decondensation further results in an increased movement of chromatin, while inhibition of myosin II and decoupling the nucleus from the cytoskeleton decreases chromatin mobility in HUVEC cells (Spagnol and Noel Dahl, 2014), further supporting the notion that the intact actomyosin apparatus and the LINC complex are critical factors for the mechanical signal transmission to chromatin.…”

Nuclear envelope mechanobiology: linking the nuclear structure and function

“…Optical microscopy-based [170][171][172] elastography is a powerful potential method to measure the distribution of mechanical properties noninvasively within the nucleus. Based on techniques like deformable image registration and inverse finite element methods, image-based elastography of heterochromatin and euchromatin domains in the deforming cell nucleus is now possible [173,174].…”