Longwave UV Light Induces the Aging-Associated Progerin
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Figure 1
UVA induces progerin protein in young and aged fibroblasts. (a) Western blotting for Lamin A and C, which also detects splice variants of Lamin A, including progerin, demonstrates induction of progerin by UVA, but not by UVB, in young cells (neonatal fibroblasts with low population doublings; shown is a representative example of three repeat experiments with cells from the same donor). (b) Induction of progerin was also seen 2 weeks after five daily irradiations with a lower dose of UVA (shown are representative examples of three independent experiments), but only in cells aged in vitro (neonatal fibroblasts cultured for extended periods of time) and in cells aged in vivo (fibroblasts from older donors; shown here from a 50-year-old donor). (c) Immunocytochemistry with an anti-progerin antibody demonstrates a weakly enhanced signal for progerin in the nuclei of fibroblasts grown on glass cover slips following UVA irradiation. DAPI, 4',6-diamidino-2-phenylindole; HGPS, Hutchinson–Gilford progeria syndrome. Bar=10μm.
Figure 2
Repeated exposures to UVA induce Hutchinson–Gilford progeria syndrome (HGPS)-like abnormal nuclear shapes. (a) Staining of the nuclear membrane with an antibody directed against Lamin A/C showed some cells with abnormally shaped nuclei in cells grown on glass cover slips. UVA and UVB irradiations were repeated daily for 5 days and then cells were further incubated for 2 weeks. (b) Examples of cells with different degrees of abnormal shapes and the scoring that was used to quantitate the abnormalities observed in sham-, UVA-, or UVB-irradiated fibroblasts or fibroblasts from a HGPS patient. Using this scoring system, 100 cells from 10 different areas of the cover slips were scored: (c) young cells, (d) cells aged in vitro, and (e) cells aged in-vivo from a 50-year-old donor. Shown are average ratios±SD of three independent samples (two independent samples for 500Jm−2 UVB sample in d). *P<0.05; **P<0.01 (Student’s t-test). Bar=10μm.
Figure 3
UVA induces progerin mRNA in neonatal fibroblasts via generation of singlet oxygen. Shown are the ratios of progerin mRNA expressions against sham-irradiated samples, as determined by Taqman real-time quantitative PCR, from three to four independent samples per experiment (averages±SD). (a) Results of a representative example of three repeat experiments with young cells 8 and 24hours after irradiation. (b) The singlet oxygen quencher sodium azide (5mM in phosphate-buffered saline (PBS); EMD, added to cells 10minutes before and during irradiation, but not for the 24hours after irradiation) completely abrogates progerin induction in cells aged in vivo (50-year-old donor; representative example of two repeat experiments). *P<0.05; **P<0.01 (Student’s t-test).
Premature aging in Hutchinson–Gilford progeria syndrome (HGPS) is caused by a mutation of the LMNA gene that activates a cryptic splice site. This results in expression of a truncated form of Lamin A, called progerin. Accumulation of progerin in the nuclei of HGPS cells impairs nuclear functions and causes abnormal nuclear morphology. Progerin accumulation has not only been described in HGPS, but also during normal intrinsic aging. We hypothesized that accumulation of progerin with abnormal nuclear shapes may also be accelerated by UV and with that contribute to photoaging of the skin. We exposed neonatal or aged cultured fibroblasts to single or repeated doses of longwave or shortwave UV (UVA or UVB) and found that UVA, but not UVB, induces progerin expression and HGPS-like abnormal nuclear shapes in all cells, but more in aged cells. The induction of progerin is mediated by UVA-induced oxidative damage and subsequent alternative splicing of the LMNA transcript, as progerin induction was suppressed by the singlet oxygen quencher sodium azide, and as mRNA expression of LMNA was not induced by UVA. These data suggest a previously unreported pathway of photoaging and support the concept that photoaging is at least in part a process of damage-accelerated intrinsic aging.
The authors state no conflict of interest.
