Progeria, a model disease for the study of accelerated aging

Disease progression in Hutchinson-Gilford progeria syndrome: impact on growth and development

OBJECTIVES

Hutchinson-Gilford progeria syndrome is a rare and uniformly fatal segmental "premature aging" disease that affects a variety of organ systems. We sought to more clearly define the bone and weight abnormalities in patients with progeria as potential outcome parameters for prospective clinical trials.

PATIENTS AND METHODS

We collected and analyzed longitudinal medical information, both retrospectively and prospectively, from a total of 41 children with Hutchinson-Gilford progeria syndrome spanning 14 countries, from the Progeria Research Foundation Medical and Research Database at the Brown University Center for Gerontology.

RESULTS

In addition to a number of previously well-defined phenotypic findings in children with progeria, this study identified abnormalities in the eruption of secondary incisors lingually and palatally in the mandible and maxilla, respectively. Although bony structures appeared normal in early infancy, clavicular resorption, coxa valga, avascular necrosis of the femoral head, modeling abnormalities of long bones with slender diaphyses, flared metaphyses, and overgrown epiphyses developed. Long bones showed normal cortical thickness centrally and progressive focal demineralization peripherally. The most striking finding identified in the retrospective data set of 35 children was an average weight increase of only 0.44 kg/year, beginning at approximately 24 months of age and persisting through life, with remarkable intrapatient linearity. This rate is >2 SD below normal weight gain for any corresponding age and sharply contrasts with the parabolic growth pattern for normal age- and gender-matched children. This finding was also confirmed prospectively.

CONCLUSIONS

Our analysis shows evidence of a newly identified abnormal growth pattern for children with Hutchinson-Gilford progeria syndrome. The skeletal and dental findings are suggestive of a developmental dysplasia rather than a classical aging process. The presence of decreased and linear weight gain, maintained in all of the patients after the age of 2 years, provides the ideal parameter on which altered disease status can be assessed in clinical trials.

Accelerated telomere shortening and replicative senescence in human fibroblasts overexpressing mutant and wild-type lamin A

LMNA mutations are responsible for a variety of genetic disorders, including muscular dystrophy, lipodystrophy, and certain progeroid syndromes, notably Hutchinson-Gilford Progeria. Although a number of clinical features of these disorders are suggestive of accelerated aging, it is not known whether cells derived from these patients exhibit cellular phenotypes associated with accelerated aging. We examined a series of isogenic skin fibroblast lines transfected with LMNA constructs bearing known pathogenic point mutations or deletion mutations found in progeroid syndromes. Fibroblasts overexpressing mutant lamin A exhibited accelerated rates of loss of telomeres and shortened replicative lifespans, in addition to abnormal nuclear morphology. To our surprise, these abnormalities were also observed in lines overexpressing wild-type lamin A. Copy number variants are common in human populations; those involving LMNA, whether arising meiotically or mitotically, might lead to progeroid phenotypes. In an initial pilot study of 23 progeroid cases without detectable WRN or LMNA mutations, however, no cases of altered LMNA copy number were detected. Nevertheless, our findings raise a hypothesis that changes in lamina organization may cause accelerated telomere attrition, with different kinetics for overexpession of wild-type and mutant lamin A, which leads to rapid replicative senescence and progroid phenotypes.

Del(1)(q23) in a patient with Hutchinson-Gilford progeria

A 9-year-old patient with the classical clinical picture of Hutchinson-Gilford progeria (HGP) is described. The karyotype shows a 46,XY,del(1)(q23) constitution. Our findings suggest that the interval 1q23 may play a roll in the etiology of HGP. A perturbation in glycosylation in connective tissue has been demonstrated in patients with this condition. This abnormality may be due to a defect in the UDP-galactose:beta-N-acetylglucosamina-beta-1,4-galactosyltransferase 3 (B4GALT3) gene that has been mapped in the interval 1q21-23. The cytogenetical analyses of this patient suggest that the B4GALT3 gene could be involved in the pathogenesis of HGP.

Serum hyaluronic acid in Down's syndrome

In agreement with previous studies we show an age-related increase in serum levels of hyaluronic acid in healthy individuals. Levels in Down's syndrome persons were slightly higher, especially in those with hypothyroidism. This provides further evidence that the normal ageing process is accelerated in Down's syndrome.

Progeroid syndromes: probing the molecular basis of aging?

A valid method of studying age related degenerative pathologies is to study human genetic diseases that appear to accelerate many, though not necessarily all, features of the aging process. Such diseases are described as progeroid syndromes because of their possible relevance to many aspects of aging and age related disease. This article describes the recent progress made at the cellular and molecular levels in understanding the pathogenesis of one of the best characterised of these disorders, Werner's syndrome. These observations are related to some of the less well characterised progeroid syndromes within the context of the cell senescence hypothesis of aging, a theory formulated to explain the aging of regenerative tissue in normal individuals.

Serum hyaluronan as a disease marker

Hyaluronan is a connective tissue polysaccharide which has also been found in blood serum in concentrations < 100 micrograms/L (average 30-40 micrograms/L in middle-aged persons). The serum level is regulated by the influx of the polysaccharide from the tissues via lymph and its receptor-mediated clearance by liver endothelial cells. Markedly high serum levels are noted in certain liver diseases, especially in patients with cirrhosis, when the clearance is impaired. In these cases serum hyaluronan can be used to follow the development of the disease. Serum hyaluronan is also a sensitive marker for impending rejection of liver transplants. Patients with rheumatoid arthritis constitute another major group with increased serum hyaluronan, but in this case the level varies markedly during the day corresponding to physical activity. There are good indications that in these subjects the excess hyaluronan comes from the joints. Under stringent sampling conditions of serum it should be possible to extract interesting information on the inflammatory joint process. Increased hyaluronan levels are also seen in other inflammatory diseases and it is of special interest that high hyaluronan levels in patients with septic conditions is a sign of poor prognosis. Certain tumours, notably Wilms' tumour and mesothelioma, produce factors which activate synthesis of hyaluronan and increase its serum level. Rare hereditary diseases with disturbances of hyaluronan metabolism and elevated blood levels have also been discovered, e.g. Werner's syndrome and cutaneous hyaluronanosis. Information accumulated during the last decade regarding the metabolism of hyaluronan has made this polysaccharide an interesting clinical marker for a number of pathological conditions.

Elevated levels of glycoprotein gp200 in progeria fibroblasts

The glycosylation of proteins in fibroblasts from people with the premature ageing disease Hutchinson-Gilford Progeria Syndrome (progeria) was investigated. Protein was prepared from fibroblast cell lines established from skin biopsy taken from progeria patients and control donors. Glycoproteins were labelled by the covalent attachment of the steroid hapten digoxygenin to the sugar group. After separation of total protein by SDS-PAGE and electroblotting onto Immobilon-PTM, glycoproteins were detected by enzyme immunoassay. We have observed a glycoprotein of M(r) 200 kDa which is consistently present in protein preparations from progeria fibroblasts and which is absent, or markedly reduced, in preparations from control fibroblasts. This suggests that it may be useful as a marker for progeria. Similar analysis of progeria lymphoblast and control lymphoblast cultures did not show this altered pattern of glycosylated proteins, indicating that it may be cell-type specific. Glycoproteins were also detected by labelling fibroblasts in vitro with D-[6-3H]glucosamine hydrochloride followed by SDS-PAGE of isolated protein and subsequent fluorography. Profiles of glycoproteins from progeria and control fibroblasts were consistent with those obtained from labelling of carbohydrate groups with digoxygenin. Protease digestion of cell protein verified that the band at M(r) 200 kDa contains a protein core. Characteristic features of progeria primarily involve the connective tissue and include wrinkled and loose skin, loss of soft tissue, thin limbs and stiff joints. Death of progeria patients is usually a result of cardiovascular abnormalities. The most consistent manifestations thus involve the connective tissue. The glycoprotein of M(r) 200 kDa which we have observed in progeria fibroblasts in vitro could reflect a perturbation in glycosylation which may underly the connective tissue defects seen in progeria.

Proliferation-dependent regulation of DNA glycosylases in progeroid cells

The regulation of the base excision repair enzymes uracil DNA glycosylase and hypoxanthine DNA glycosylase was examined in 2 different progeroid cell strains. The immunoreactivity of the uracil DNA glycosylase in progeroid cells was examined by enzyme linked immunosorbent assay (ELISA) and by immunoblot analysis. The enzyme was recognized in a quantitative manner by 2 different anti-human uracil DNA glycosylase monoclonal antibodies in the ELISA. Western blot analysis identified a glycosylase protein of Mr = 37,000. In randomly proliferating progeroid cells, the uracil DNA glycosylase was enhanced 3-fold during cell growth. In synchronous cells, uracil DNA glycosylase and hypoxanthine DNA glycosylase were induced with an extent of induction (5-6-fold) comparable to that observed for normal human cells. Further, the activity of each base excision repair enzyme was enhanced with a comparable temporal sequence prior to the induction of DNA synthesis and DNA polymerase activity. These results indicate a normal cell cycle regulation of base excision repair in progeroid cells.

Cell-cycle defect of DNA repair in progeria skin fibroblasts

We examined the temporal regulation of DNA repair during synchronous cell proliferation in normal and progeroid human fibroblasts. Ultraviolet light-induced (254 nm, 20 J/m2) unscheduled DNA synthesis was measured at 4-h intervals after serum stimulation, for up to 32 h. Normal cells regulated DNA repair in a defined temporal sequence, showing a peak in the induction of DNA repair just before DNA synthesis. Progeroid skin fibroblasts failed to show an increase in nucleotide excision repair before scheduled DNA synthesis, but the background level of DNA repair was not significantly different from that in controls. Regulation of repair in progeroid human fibroblasts appeared similar, but not identical to that previously reported by Gupta and Sirover (1984b) for xeroderma pigmentosum complementation group C. Our results suggest that patients with Hutchinson-Gilford progeria may have a defect in DNA repair; the results offer nominal evidence that the average level of UV-induced DNA is decreased, and that individuals with this disease lack both the normal enhancement of DNA repair before scheduled DNA synthesis and the temporal control of DNA repair.

Hutchinson-Gilford progeria syndrome: report of a Libyan family and evidence of autosomal recessive inheritance

A Libyan family with the Hutchinson-Gilford progeria syndrome affecting three children of two sisters is described. The proband was ascertained because of repeated unhealing fractures. The pattern of inheritance appeared autosomal recessive.

Elevated c-myc expression in progeria fibroblasts

Protooncogene expression was determined in cultured human fibroblasts derived from donors diagnosed with Hutchinson-Gilford Syndrome (Progeria). An increased level of c-myc expression was noted in progeria cells compared to normal parental controls and unrelated, unaffected, age-matched controls. In two progeria cultures a 150% increase in c-myc expression was observed, while a third progeria culture, subsequently identified as a non-classic progeria showed a 45% increase in c-myc expression. Southern blot analysis did not indicate an amplification or translocation of the c-myc gene. No significant differences were found in the expression of the c-erbB or c-src protooncogenes.