Abstract
Premature aging disorders provide an opportunity to study the mechanisms that drive aging. In Hutchinson-Gilford progeria syndrome (HGPS), a mutant form of the nuclear scaffold protein lamin A distorts nuclei and sequesters nuclear proteins. We sought to investigate protein homeostasis in this disease. Here, we report a widespread increase in protein turnover in HGPS-derived cells compared to normal cells. We determine that global protein synthesis is elevated as a consequence of activated nucleoli and enhanced ribosome biogenesis in HGPS-derived fibroblasts. Depleting normal lamin A or inducing mutant lamin A expression are each sufficient to drive nucleolar expansion. We further show that nucleolar size correlates with donor age in primary fibroblasts derived from healthy individuals and that ribosomal RNA production increases with age, indicating that nucleolar size and activity can serve as aging biomarkers. While limiting ribosome biogenesis extends lifespan in several systems, we show that increased ribosome biogenesis and activity are a hallmark of premature aging.
Highlights
Our data are consistent with the model (Fig. 7a) that progerin acts as a dominant negative mutant to prevent the previously unappreciated role of lamin A in organizing nucleoli and limiting ribosome biogenesis
Since both lamin A depletion (Fig. 6) and ectopic expression of progerin (Fig. 5) rapidly induce nucleolar expansion, it is likely that the lamin network is directly involved in regulating nucleolar activity
We propose that as progerin disrupts the global heterochromatin environment[12, 14] (Supplementary Fig. 1d, f), repressive marks normally found on inactive rDNA loci are lost
Summary
Goat anti-lamin A/C N-18(sc-6215), rabbit anti-LAP2a (sc-28541), and mouse anti-UBF1(sc-13125) were purchased from Santa Cruz Biotechnology. Nucleolin(#14574), phospho (Ser 235/236) S6(#4858), Histone H3 (#4499), LC3B(#3868), PARP(#9532), 4EBP1(#9644), S6, phospho(Ser 1108) eIF4G (#2441),, and phospho (Ser65) 4EBP1(#9451) rabbit antibodies were purchased from Cell Signaling. Primary human dermal fibroblasts AG16409, AG04386, AG04457, AG05413, AG02974, AG05274, AG3257, AG3258, AG22153, AG21753, AG05247, AG10884, and AG07725 (wild type) and AG11513, AG11498 (HGPS, LMNA G608G splice site mutation) were obtained from Coriell Cell Research (https:// catalog.coriell.org). Human dermal fibroblasts HGFDFN168 (wild type) and HGADFN167 (HGPS, LMNA G608G splice site mutation) were obtained from the Progeria Research Foundation. Human dermal fibroblasts 22RC, 23 VA, 25MH, 62MP, 64JW, and 67LR were prepared from 4 mm skin biopsies obtained from human donors. Fibroblast cultures began to grow out from tissue approximately 1 week after seeding
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