Karima Djabali

The Mutant Form of Lamin A that Causes Hutchinson-Gilford Progeria Is a Biomarker of Cellular Aging in Human Skin

Hutchinson-Gilford progeria syndrome (HGPS, OMIM 176670) is a rare disorder characterized by accelerated aging and early death, frequently from stroke or coronary artery disease. 90% of HGPS cases carry the LMNA G608G (GGC>GGT) mutation within exon 11 of LMNA, activating a splice donor site that results in production of a dominant negative form of lamin A protein, denoted progerin. Screening 150 skin biopsies from unaffected individuals (newborn to 97 years) showed that a similar splicing event occurs in vivo at a low level in the skin at all ages. While progerin mRNA remains low, the protein accumulates in the skin with age in a subset of dermal fibroblasts and in a few terminally differentiated keratinocytes. Progerin-positive fibroblasts localize near the basement membrane and in the papillary dermis of young adult skin; however, their numbers increase and their distribution reaches the deep reticular dermis in elderly skin. Our findings demonstrate that progerin expression is a biomarker of normal cellular aging and may potentially be linked to terminal differentiation and senescence in elderly individuals.

Cardiovascular Pathology in Hutchinson-Gilford Progeria: Correlation With the Vascular Pathology of Aging

Objective—Children with Hutchinson-Gilford progeria syndrome (HGPS) exhibit dramatically accelerated cardiovascular disease (CVD), causing death from myocardial infarction or stroke between the ages of 7 and 20 years. We undertook the first histological comparative evaluation between genetically confirmed HGPS and the CVD of aging. Methods and Results—We present structural and immunohistological analysis of cardiovascular tissues from 2 children with HGPS who died of myocardial infarction. Both had features classically associated with the atherosclerosis of aging, as well as arteriolosclerosis of small vessels. In addition, vessels exhibited prominent adventitial fibrosis, a previously undescribed feature of HGPS. Importantly, although progerin was detected at higher rates in the HGPS coronary arteries, it was also present in non-HGPS individuals. Between the ages of 1 month and 97 years, progerin staining increased an average of 3.34% per year (P<0.0001) in coronary arteries. Conclusion—We find concordance among many aspects of cardiovascular pathology in both HGPS and geriatric patients. HGPS generates a more prominent adventitial fibrosis than typical CVD. Vascular progerin generation in young non-HGPS individuals, which significantly increases throughout life, strongly suggests that progerin has a role in cardiovascular aging of the general population.

A lamin A protein isoform overexpressed in Hutchinson–Gilford progeria syndrome interferes with mitosis in progeria and normal cells

Hutchinson–Gilford progeria syndrome (HGPS) is a rare genetic disorder characterized by dramatic premature aging. Classic HGPS is caused by a de novo point mutation in exon 11 (residue 1824, C → T) of the LMNA gene, activating a cryptic splice donor and resulting in a mutant lamin A (LA) protein termed “progerin/LAΔ50” that lacks the normal cleavage site to remove a C-terminal farnesyl group. During interphase, irreversibly farnesylated progerin/LAΔ50 anchors to the nuclear membrane and causes characteristic nuclear blebbing. Progerin/LAΔ50s localization and behavior during mitosis, however, are completely unknown. Here, we report that progerin/LAΔ50 mislocalizes into insoluble cytoplasmic aggregates and membranes during mitosis and causes abnormal chromosome segregation and binucleation. These phenotypes are largely rescued with either farnesyltransferase inhibitors or a farnesylation-incompetent mutant progerin/LAΔ50. Furthermore, we demonstrate that small amounts of progerin/LAΔ50 exist in normal fibroblasts, and a significant percentage of these progerin/LAΔ50-expressing normal cells are binucleated, implicating progerin/LAΔ50 as causing similar mitotic defects in the normal aging process. Our findings present evidence of mitotic abnormality in HGPS and may shed light on the general phenomenon of aging.

Defective Lamin A-Rb Signaling in Hutchinson-Gilford Progeria Syndrome and Reversal by Farnesyltransferase Inhibition

Hutchinson-Gilford Progeria Syndrome (HGPS) is a rare premature aging disorder caused by a de novo heterozygous point mutation G608G (GGC>GGT) within exon 11 of LMNA gene encoding A-type nuclear lamins. This mutation elicits an internal deletion of 50 amino acids in the carboxyl-terminus of prelamin A. The truncated protein, progerin, retains a farnesylated cysteine at its carboxyl terminus, a modification involved in HGPS pathogenesis. Inhibition of protein farnesylation has been shown to improve abnormal nuclear morphology and phenotype in cellular and animal models of HGPS. We analyzed global gene expression changes in fibroblasts from human subjects with HGPS and found that a lamin A-Rb signaling network is a major defective regulatory axis. Treatment of fibroblasts with a protein farnesyltransferase inhibitor reversed the gene expression defects. Our study identifies Rb as a key factor in HGPS pathogenesis and suggests that its modulation could ameliorate premature aging and possibly complications of physiological aging.

Dermal fibroblasts in Hutchinson-Gilford progeria syndrome with the lamin A G608G mutation have dysmorphic nuclei and are hypersensitive to heat stress

BackgroundHutchinson-Gilford progeria syndrome (HGPS, OMIM 176670) is a rare sporadic disorder with an incidence of approximately 1 per 8 million live births. The phenotypic appearance consists of short stature, sculptured nose, alopecia, prominent scalp veins, small face, loss of subcutaneous fat, faint mid-facial cyanosis, and dystrophic nails. HGPS is caused by mutations in LMNA, the gene that encodes nuclear lamins A and C. The most common mutation in subjects with HGPS is a de novo single-base pair substitution, G608G (GGC>GGT), within exon 11 of LMNA. This creates an abnormal splice donor site, leading to expression of a truncated protein.ResultsWe studied a new case of a 5 year-old girl with HGPS and found a heterozygous point mutation, G608G, in LMNA. Complementary DNA sequencing of RNA showed that this mutation resulted in the deletion of 50 amino acids in the carboxyl-terminal tail domain of prelamin A. We characterized a primary dermal fibroblast cell line derived from the subjects skin. These cells expressed the mutant protein and exhibited a normal growth rate at early passage in primary culture but showed alterations in nuclear morphology. Expression levels and overall distributions of nuclear lamins and emerin, an integral protein of the inner nuclear membrane, were not dramatically altered. Ultrastructural analysis of the nuclear envelope using electron microscopy showed that chromatin is in close association to the nuclear lamina, even in areas with abnormal nuclear envelope morphology. The fibroblasts were hypersensitive to heat shock, and demonstrated a delayed response to heat stress.ConclusionDermal fibroblasts from a subject with HGPS expressing a mutant truncated lamin A have dysmorphic nuclei, hypersensitivity to heat shock, and delayed response to heat stress. This suggests that the mutant protein, even when expressed at low levels, causes defective cell stability, which may be responsible for phenotypic abnormalities in the disease.

Epidermal expression of the truncated prelamin A causing Hutchinson–Gilford progeria syndrome: effects on keratinocytes, hair and skin

Hutchinson-Gilford progeria syndrome (HGPS) is an accelerated aging disorder caused by point mutation in LMNA encoding A-type nuclear lamins. The mutations in LMNA activate a cryptic splice donor site, resulting in expression of a truncated, prenylated prelamin A called progerin. Expression of progerin leads to alterations in nuclear morphology, which may underlie pathology in HGPS. We generated transgenic mice expressing progerin in epidermis under control of a keratin 14 promoter. The mice had severe abnormalities in morphology of skin keratinocyte nuclei, including nuclear envelope lobulation and decreased nuclear circularity not present in transgenic mice expressing wild-type human lamin A. Primary keratinocytes isolated from these mice had a higher frequency of nuclei with abnormal shape compared to those from transgenic mice expressing wild-type human lamin A. Treatment with a farnesyltransferase inhibitor significantly improved nuclear shape abnormalities and induced the formation of intranuclear foci in the primary keratinocytes expressing progerin. Similarly, spontaneous immortalization of progerin-expressing cultured keratinocytes selected for cells with normal nuclear morphology. Despite morphological alterations in keratinocyte nuclei, mice expressing progerin in epidermis had normal hair grown and wound healing. Hair and skin thickness were normal even after crossing to Lmna null mice to reduce or eliminate expression of normal A-type lamins. Although progerin induces significant alterations in keratinocyte nuclear morphology that are reversed by inhibition of farnesyltransferasae, epidermal expression does not lead to alopecia or other skin abnormalities typically seen in human subjects with HGPS.

Sulforaphane enhances progerin clearance in Hutchinson-Gilford progeria fibroblasts.

Hutchinson–Gilford progeria syndrome (HGPS, OMIM 176670) is a rare multisystem childhood premature aging disorder linked to mutations in the LMNA gene. The most common HGPS mutation is found at position G608G within exon 11 of the LMNA gene. This mutation results in the deletion of 50 amino acids at the carboxyl‐terminal tail of prelamin A, and the truncated protein is called progerin. Progerin only undergoes a subset of the normal post‐translational modifications and remains permanently farnesylated. Several attempts to rescue the normal cellular phenotype with farnesyltransferase inhibitors (FTIs) and other compounds have resulted in partial cellular recovery. Using proteomics, we report here that progerin induces changes in the composition of the HGPS nuclear proteome, including alterations to several components of the protein degradation pathways. Consequently, proteasome activity and autophagy are impaired in HGPS cells. To restore protein clearance in HGPS cells, we treated HGPS cultures with sulforaphane (SFN), an antioxidant derived from cruciferous vegetables. We determined that SFN stimulates proteasome activity and autophagy in normal and HGPS fibroblast cultures. Specifically, SFN enhances progerin clearance by autophagy and reverses the phenotypic changes that are the hallmarks of HGPS. Therefore, SFN is a promising therapeutic avenue for children with HGPS.

Induced Pluripotent Stem Cells Reveal Functional Differences Between Drugs Currently Investigated in Patients With Hutchinson-Gilford Progeria Syndrome

Hutchinson‐Gilford progeria syndrome is a rare congenital disease characterized by premature aging in children. Identification of the mutation and related molecular mechanisms has rapidly led to independent clinical trials testing different marketed drugs with a preclinically documented impact on those mechanisms. However, the extensive functional effects of those drugs remain essentially unexplored. We have undertaken a systematic comparative study of the three main treatments currently administered or proposed to progeria‐affected children, namely, a farnesyltransferase inhibitor, the combination of an aminobisphosphonate and a statin (zoledronate and pravastatin), and the macrolide antibiotic rapamycin. This work was based on the assumption that mesodermal stem cells, which are derived from Hutchinson‐Gilford progeria syndrome‐induced pluripotent stem cells expressing major defects associated with the disease, may be instrumental to revealing such effects. Whereas all three treatments significantly improved misshapen cell nuclei typically associated with progeria, differences were observed in terms of functional improvement in prelamin A farnesylation, progerin expression, defective cell proliferation, premature osteogenic differentiation, and ATP production. Finally, we have evaluated the effect of the different drug combinations on this cellular model. This study revealed no additional benefit compared with single‐drug treatments, whereas a cytostatic effect equivalent to that of a farnesyltransferase inhibitor alone was systematically observed. Altogether, these results reveal the complexity of the modes of action of different drugs, even when they have been selected on the basis of a similar mechanistic hypothesis, and underscore the use of induced pluripotent stem cell derivatives as a critical and powerful tool for standardized, comparative pharmacological studies.

De novo mutations in monilethrix

Abstract: Mutations in the hair keratins hHb1 and hHb6 have been recently reported to cause monilethrix, an autosomal dominant hair shaft disorder, characterized by variable degrees of hair fragility and follicular hyperkeratosis. We found 10 families with monilethrix in which the parents were not clinically affected, and sequenced the hair keratin hHb1, hHb3 and hHb6 genes in seven patients. In five patients no mutations were found, while in two patients we identified de novo germline missense mutations at the helix termination motif: E402K (hHb6) and E413K (hHb1).

Naive adult stem cells from patients with Hutchinson-Gilford progeria syndrome express low levels of progerin in vivo.

Summary Hutchinson-Gilford progeria syndrome (HGPS, OMIM 176670) is a rare disorder characterized by segmental accelerated aging and early death from coronary artery disease or stroke. Nearly 90% of HGPS sufferers carry a G608G mutation within exon 11 of LMNA, producing a truncated form of prelamin A, referred to as “progerin”. Here, we report the isolation of naïve multipotent skin-derived precursor (SKP) cells from dermal fibroblast cultures from HGPS donors. These cells form spheres and express the neural crest marker, nestin, in addition to the multipotent markers, OCT4, Sox2, Nanog and TG30; these cells can self-renew and differentiate into smooth muscle cells (SMCs) and fibroblasts. The SMCs derived from the HGPS-SKPs accumulate nuclear progerin with increasing passages. A subset of the HGPS-naïve SKPs express progerin in vitro and in situ in HGPS skin sections. This is the first in vivo evidence that progerin is produced in adult stem cells, and implies that this protein could induce stem cells exhaustion as a mechanism contributing to aging. Our study provides a basis on which to explore therapeutic applications for HGPS stem cells and opens avenues for investigating the pathogenesis of other genetic diseases.