Premature aging syndromes often result from mutations in nuclear proteins involved in the maintenance of genomic integrity. Lamin A is a major component of the nuclear lamina and nuclear skeleton. Truncation in lamin A causes Hutchinson-Gilford progerial syndrome (HGPS), a severe form of early-onset premature aging. Lack of functional Zmpste24, a metalloproteinase responsible for the maturation of prelamin A, also results in progeroid phenotypes in mice and humans. We found that Zmpste24-deficient mouse embryonic fibroblasts (MEFs) show increased DNA damage and chromosome aberrations and are more sensitive to DNA-damaging agents. Bone marrow cells isolated from Zmpste24-/- mice show increased aneuploidy and the mice are more sensitive to DNA-damaging agents. Recruitment of p53 binding protein 1 (53BP1) and Rad51 to sites of DNA lesion is impaired in Zmpste24-/- MEFs and in HGPS fibroblasts, resulting in delayed checkpoint response and defective DNA repair. Wild-type MEFs ectopically expressing unprocessible prelamin A show similar defects in checkpoint response and DNA repair. Our results indicate that unprocessed prelamin A and truncated lamin A act dominant negatively to perturb DNA damage response and repair, resulting in genomic instability which might contribute to laminopathy-based premature aging.

Perlecan, a modular proteoglycan carrying primary heparan sulfate (HS) side chains, is a major component of blood vessel basement membranes. It sequesters growth factors such as fibroblast growth factor 2 (FGF-2) and regulates the ligand-receptor interactions on the cell surface, and thus it has been implicated in the control of angiogenesis. Both stimulatory and inhibitory effects of perlecan on FGF-2 signaling have been reported. To understand the in vivo function of HS carried by perlecan, the perlecan gene heparan sulfate proteoglycan 2 (Hspg2) was mutated in mouse by gene targeting. The HS at the NH 2 terminus of perlecan was removed while the core protein remained intact. Perlecan HS-deficient (Hspg2 ⌬3/⌬3 ) mice survived embryonic development and were apparently healthy as adults. However, mutant mice exhibited significantly delayed wound healing, retarded FGF-2-induced tumor growth, and defective angiogenesis. In the mouse corneal angiogenesis model, FGF-2-induced neovascularization was significantly impaired in Hspg2 ⌬3/⌬3 mutant mice. Our results suggest that HS in perlecan positively regulates the angiogenesis in vivo.

A de novo G608G mutation in LMNA gene leads to Hutchinson–Gilford progeria syndrome. Mice lacking the prelamin A-processing metalloprotease, Zmpste24, recapitulate many of the progeroid features of Hutchinson–Gilford progeria syndrome. Here we show that A-type lamins interact with SUV39H1, and prelamin A/progerin exhibits enhanced binding capacity to SUV39H1, protecting it from proteasomal degradation and, consequently, increasing H3K9me3 levels. Depletion of Suv39h1 reduces H3K9me3 levels, restores DNA repair capacity and delays senescence in progeroid cells. Remarkably, loss of Suv39h1 in Zmpste24−/− mice delays body weight loss, increases bone mineral density and extends lifespan by ∼60%. Thus, increased H3K9me3 levels, possibly mediated by enhanced Suv39h1 stability in the presence of prelamin A/progerin, compromise genome maintenance, which in turn contributes to accelerated senescence in laminopathy-based premature aging. Our study provides an explanation for epigenetic alterations in Hutchinson–Gilford progeria syndrome and a potential strategy for intervention by targeting SUV39H1-mediated heterochromatin remodelling.

The nuclear lamins are essential for various molecular events in the nucleus, such as chromatin organization, DNA replication, and provision of mechanical support. A specific point mutation in the LMNA gene creates a truncated prelamin A termed progerin, causing Hutchinson-Gilford progeria syndrome (HGPS). SIRT6 deficiency leads to defective genomic maintenance and accelerated aging similar to HGPS, suggesting a potential link between lamin A and SIRT6. Here, we report that lamin A is an endogenous activator of SIRT6 and facilitates chromatin localization of SIRT6 upon DNA damage. Lamin A promotes SIRT6-dependent DNA-PKcs (DNA-PK catalytic subunit) recruitment to chromatin, CtIP deacetylation, and PARP1 mono-ADP ribosylation in response to DNA damage. The presence of progerin jeopardizes SIRT6 activation and compromises SIRT6-mediated molecular events in response to DNA damage. These data reveal a critical role for lamin A in regulating SIRT6 activities, suggesting that defects in SIRT6 functions contribute to impaired DNA repair and accelerated aging in HGPS.