Lamin B1 overexpression increases nuclear rigidity in autosomal dominant leukodystrophy fibroblasts

Abstract

The architecture and structural mechanics of the cell nucleus are defined by the nuclear lamina, which is formed by A- and B-type lamins. Recently, gene duplication and protein overexpression of lamin B1 (LB1) have been reported in pedigrees with autosomal dominant leukodystrophy (ADLD). However, how the overexpression of LB1 affects nuclear mechanics and function and how it may result in pathology remain unexplored. Here, we report that in primary human skin fibroblasts derived from ADLD patients, LB1, but not other lamins, is overexpressed at the nuclear lamina and specifically enhances nuclear stiffness. Transient transfection of LB1 in HEK293 and neuronal N2a cells mimics the mechanical phenotype of ADLD nuclei. Notably, in ADLD fibroblasts, reducing LB1 protein levels by shRNA knockdown restores elasticity values to those indistinguishable from control fibroblasts. Moreover, isolated nuclei from ADLD fibroblasts display a reduced nuclear ion channel open probability on voltage-step application, suggesting that biophysical changes induced by LB1 overexpression may alter nuclear signaling cascades in somatic cells. Overall, the overexpression of LB1 in ADLD cells alters nuclear mechanics and is linked to changes in nuclear signaling, which could help explain the pathogenesis of this disease.—Ferrera, D., Canale, C., Marotta, R., Mazzaro, N., Gritti, M., Mazzanti, M., Capellari, S., Cortelli, P., Gasparini, L. Lamin B1 overexpression increases nuclear rigidity in autosomal dominant leukodystrophy fibroblasts.

Squish and squeeze — the nucleus as a physical barrier during migration in confined environments

“…In addition to regulating nuclear shape and stiffness [27,39–42], they play important roles in chromatin organization, DNA damage repair, and transcriptional regulation [37,43,44]. Cell-stretching and micropipette aspiration experiments indicate that A-type lamins have a larger impact on nuclear stiffness than B-type lamins—nuclear stiffness strongly scales with expression of lamins A/C [39–42], although increased expression of lamin B1 can also increase nuclear rigidity [45]. Consistent with the ‘nuclear barrier’ hypothesis, recent studies found that cells with reduced levels of lamins A/C have more deformable nuclei and migrate faster through tight spaces than control cells with normal lamin A/C levels [18,46].…”

Bursting the Bubble – Nuclear Envelope Rupture as a Path to Genomic Instability?

“…The major component in regulating the structure and integrity of the NE are lamins [24, 36], with reduced levels of lamin A/C resulting in more deformable nuclei that are more prone to NE rupture [7, 10, 24, 36–38]. While the B-type lamins, lamins B1 and B2, have a less pronounced effect on nuclear stiffness [36, 39], loss of B-type lamins increases the likelihood of nuclear bleb formation and NE rupture [6, 7, 9, 40]. Even in cells expressing B-type lamins, nuclear membrane blebs form at sites with openings in the lamin B-network [7, 8].…”

Causes and consequences of nuclear envelope alterations in tumour progression

“…Accordingly, cells migrating in 3D collagen matrices show extensive nuclear deformation when MMP activity is inhibited, and sufficiently small pore sizes can lead to complete stalling of cell movement as the nucleus becomes ‘trapped’ in the dense network (Wolf et al, 2013). The deformability of the nucleus is largely determined by expression of A-type lamins (Lammerding et al, 2006; Lammerding et al, 2004; Pajerowski et al, 2007; Schape et al, 2009), although changes in B-type lamin expression can also impact nuclear elasticity (Ferrera et al, 2014; Swift et al, 2013). As a result, cells with decreased lamin A/C levels migrate significantly faster through narrow constrictions in microfluidics devices and transwell plates with 3 µm pore sizes (Davidson et al, 2014; Harada et al, 2014; Shin et al, 2013).…”