Nuclear membrane ruptures underlie the vascular pathology in a mouse model of Hutchinson-Gilford progeria syndrome
Paul H. Kim, Natalie Y. Chen, Patrick J. Heizer, Yiping Tu, Thomas A. Weston, Jared L.-C. Fong, Navjot Kaur Gill, Amy C. Rowat, Stephen G. Young, Loren G. Fong
Paul H. Kim, Natalie Y. Chen, Patrick J. Heizer, Yiping Tu, Thomas A. Weston, Jared L.-C. Fong, Navjot Kaur Gill, Amy C. Rowat, Stephen G. Young, Loren G. Fong
View: Text | PDF
Research Article Vascular biology

Nuclear membrane ruptures underlie the vascular pathology in a mouse model of Hutchinson-Gilford progeria syndrome

Abstract

The mutant nuclear lamin protein (progerin) produced in Hutchinson-Gilford progeria syndrome (HGPS) results in loss of arterial smooth muscle cells (SMCs), but the mechanism has been unclear. We found that progerin induces repetitive nuclear membrane (NM) ruptures, DNA damage, and cell death in cultured SMCs. Reducing lamin B1 expression and exposing cells to mechanical stress — to mirror conditions in the aorta — triggered more frequent NM ruptures. Increasing lamin B1 protein levels had the opposite effect, reducing NM ruptures and improving cell survival. Remarkably, raising lamin B1 levels increased nuclear compliance in cells and was able to offset the increased nuclear stiffness caused by progerin. In mice, lamin B1 expression in aortic SMCs is normally very low, and in mice with a targeted HGPS mutation (LmnaG609G), levels of lamin B1 decrease further with age while progerin levels increase. Those observations suggest that NM ruptures might occur in aortic SMCs in vivo. Indeed, studies in LmnaG609G mice identified NM ruptures in aortic SMCs, along with ultrastructural abnormalities in the cell nucleus that preceded SMC loss. Our studies identify NM ruptures in SMCs as likely causes of vascular pathology in HGPS.

Authors

Paul H. Kim, Natalie Y. Chen, Patrick J. Heizer, Yiping Tu, Thomas A. Weston, Jared L.-C. Fong, Navjot Kaur Gill, Amy C. Rowat, Stephen G. Young, Loren G. Fong

×

Figure 4

Lamin B1 decreases nuclear stiffness.

Options: View larger image (or click on image) Download as PowerPoint
Lamin B1 decreases nuclear stiffness. (A) Microscopy images of a live SM...
(A) Microscopy images of a live SMC (arrow) expressing Nuc-GFP (green) and increased amounts of lamin B1 (see Supplemental Video 4). Scale bar: 20 μm. (B) Microscopy images of Hoechst-stained nuclei in suspended cells expressing lamin B1 (B1), nf-lamin B1 (nf-B1), or lamin B2 (B2) before (left) and after (right) compressing the cells with a glass coverslip. Scale bar: 10 μm. Nuclear lamin expression was induced with Dox (see Supplemental Figure 4A). (C) Inducing lamin B1 expression (+Dox) increases nuclear area (mean ± SD, numbers of cells examined are reported above each bar; Student’s t test, *P < 0.001). (D) Lamin B1 (B1) decreases nuclear stiffness (Young’s modulus) in SMCs, as measured by AFM (mean ± SEM, n = 5 experiments). Measurements were compared with noninduced SMCs by ANOVA (*P < 0.002, **P < 0.0001). (E) Lamin B1 increases nuclear size (spreading) in PreA-SMCs and Progerin-SMCs. Nuclei size was measured as in C (mean ± SD; Student’s t test, *P < 0.001). (F) Progerin (Prog) but not nf-Prog increases nuclear stiffness in SMCs (mean ± SEM, n = 5 experiments). Expression data are shown in Supplemental Figure 4F. All measurements were compared with control SMCs (Con) by ANOVA (*P < 0.0001). (G) Western blot showing increased expression of lamin B1 (B1) and nf-B1 in SMCs examined in H. (H) Increasing lamin B1 expression but not nf-B1 reduces nuclear stiffness in Prog-SMCs (mean ± SEM, n = 3 experiments). Measurements were compared with SMCs expressing progerin by ANOVA (*P < 0.0001). (I) Disrupting the LINC complex with KASH2 (blue bars) reduces nuclear stiffness in Prog-SMCs (mean ± SEM; n = 3 experiments). Nuclear stiffness was compared with cells expressing the inactive mutant KASH2ext (white bars) by the Student’s t test (*P < 0.01).