Mechanosensing Defects in Nuclear Envelope Related Disorders

Abstract

Recent data indicate that mutations in nuclear envelope genes cause both defects in mechanotransduction signaling and force transmission across the nuclear envelop. A central role in this mechanosensory process has been attributed to A-type lamins, which together with the LInker of the Nucleoskeleton and Cytoskeleton (LINC)-complex enables force transmission across the nuclear envelop. Whereas a basic picture is that extracellular mechanical forces are transmitted from outside the cell to the nucleus, we hypothesize that mutations in A-type lamin (LMNA) or in nesprin can affect the mechanical transmission from the nuclear envelop to the extracellular matrix. Human myoblasts with either LMNA or nesprin-1 mutations were cultured on soft substrates (12 kPa) and compared to control (WT) myoblasts. On soft surface, LMNA and nesprin-1 mutated myoblasts exhibited enlarged and increased number of focal adhesions, increased stress fibers and enlarged cell spreading area compared with WT. Further, nesprin-1 mutant exerted significantly higher traction forces on the substrate compared with WT myoblasts. These abnormalities were greatly reduced after treatment with Y27632, or SU6656, which inhibit Rho-associated protein kinase or the Src family kinase respectively, suggesting an abnormal activation of Rho-dependent Src pathway in mutant cells. Treatment with the MLCK inhibitor ML7 also significantly reduced the spreading area in mutant cells but without modifying the number and distribution of perinuclear actin stress fibers. We concluded that the integrity of the LINC complex and the lamina is required for proper regulation of the cytoplasmic actin contractility in soft substrates, through an apparent Src-dependent ROCK pathway.