Nuclear Mechanics within Intact Cells Is Regulated by Cytoskeletal Network and Internal Nanostructures

Abstract

The mechanical properties of the cellular nucleus are extensively studied as they play a critical role in important processes, such as cell migration, gene transcription, and stem cell differentiation. While the mechanical properties of the isolated nucleus have been tested, there is a lack of measurements about the mechanical behavior of the nucleus within intact cells and specifically about the interplay of internal nuclear components with the intracellular microenvironment, because current testing methods are based on contact and only allow studying the nucleus after isolation from a cell or disruption of cytoskeleton. Here, all‐optical Brillouin microscopy and 3D chemomechanical modeling are used to investigate the regulation of nuclear mechanics in physiological conditions. It is observed that the nuclear modulus can be modulated by epigenetic regulation targeting internal nuclear nanostructures such as lamin A/C and chromatin. It is also found that nuclear modulus is strongly regulated by cytoskeletal behavior through a robust mechanism conserved in different culturing conditions. Given the active role of cytoskeletal modulation in nearly all cell functions, this work will enable to reveal highly relevant mechanisms of nuclear mechanical regulations in physiological and pathological conditions.

Dorsoventral polarity directs cell responses to migration track geometries

“…Our Brillouin microscopy measurements reveal that vertical, but not lateral, confinement increases nuclear Brillouin shift relative to 2D cells, suggesting increased nuclear stiffness in these channels. Brillouin microscopy has recently emerged as a promising technique for investigating cellular and nuclear mechanical properties in a contact-free manner (26,36). Although the Brillouin-derived longitudinal modulus is not directly related to traditionally measured elastic modulus, a strong correlation between the two moduli appears in cells (26), indicating that these two moduli change in the same direction in many physiological and pathologic processes.…”

The relative densities of cell cytoplasm, nucleoplasm, and nucleoli are robustly conserved during cell cycle and drug perturbations

“…The effects of the nuclear and cytoplasmic mass densities on their mechanical properties, and vice versa, is still unexplored, primarily due to the lack of practical techniques to measure local mechanical properties inside cells. There are emerging non-invasive optical microscopic techniques to probe the mechanical properties of biological samples including Brillouin microscopy (52,73,74), fluorescence lifetime imaging (FLIM) (75,76), and time-lapse quantitative phase microscopy (77). In the future, combining ODT with such other microscopic modalities can reveal the interaction between the mass density and mechanical properties of nucleus and cytoplasm.…”

“…4 g. We also revealed that the mass density difference across the nuclear membrane of cytochalasin D-and nocodazole-treated cells was 8.8  0.4 mg/ml and 7.1  0.4 mg/ml, which are slightly lower than that of control cells as 10.2  0.3 mg/ml. It may imply that cytoskeletal perturbation may induce a subtle force imbalance between the osmotic pressure gradient across the nuclear membrane and the force exerted by the cytoskeleton (50)(51)(52).…”

Nuclear Mechanotransduction in Skeletal Muscle

“…The cytoskeletal components relevant for force transmission to the nucleus include actin filaments (F-actin), microtubules (MTs) and intermediate filaments (IFs), whose structural and functional organization, including assembly sites, dynamics, turnover and integration with other cell components, determine function [39][40][41]. The perinuclear cytoskeleton provides a structural network to transmit and focus pushing or pulling forces onto the nucleus [40,42] through specialized proteins that comprise the LINC complex [43][44][45].…”