Human Hutchinson-Gilford Progeria Syndrome Research Articles

Ghrelin delays premature aging in Hutchinson-Gilford progeria syndrome.

Hutchinson-Gilford progeria syndrome (HGPS) is a rare and fatal genetic condition that arises from a single nucleotide alteration in the LMNA gene, leading to the production of a defective lamin A protein known as progerin. The accumulation of progerin accelerates the onset of a dramatic premature aging phenotype in children with HGPS, characterized by low body weight, lipodystrophy, metabolic dysfunction, skin, and musculoskeletal age-related dysfunctions. In most cases, these children die of age-related cardiovascular dysfunction by their early teenage years. The absence of effective treatments for HGPS underscores the critical need to explore novel safe therapeutic strategies. In this study, we show that treatment with the hormone ghrelin increases autophagy, decreases progerin levels, and alleviates other cellular hallmarks of premature aging in human HGPS fibroblasts. Additionally, using a HGPS mouse model (LmnaG609G/G609G mice), we demonstrate that ghrelin administration effectively rescues molecular and histopathological progeroid features, prevents progressive weight loss in later stages, reverses the lipodystrophic phenotype, and extends lifespan of these short-lived mice. Therefore, our findings uncover the potential of modulating ghrelin signaling offers new treatment targets and translational approaches that may improve outcomes and enhance the quality of life for patients with HGPS and other age-related pathologies.

Abstract 11821: Telomerase Therapy Reverses Vascular Senescence and Extends Lifespan in Progeria Mice

Background: Hutchinson-Gilford Progeria Syndrome (HGPS) is an accelerated aging syndrome associated with premature vascular disease and death due to heart attack and stroke. In HGPS a mutation in lamin A (progerin), alters nuclear morphology and gene expression. Current therapy increases the lifespan of these children only modestly. Thus, greater understanding of the underlying mechanisms of HGPS is required to improve therapy. Endothelial cells (ECs) differentiated from induced pluripotent stem cells (iPSCs) derived from these patients exhibit hallmarks of senescence including replication arrest, DNA damage, increased expression of inflammatory markers and telomere erosion. We hypothesized that correction of shortened telomeres may reverse these measures of vascular aging. Methods: We generated ECs from iPSCs belong to children with HGPS and their unaffected parents. Telomerase mRNA (hTERT) was used to treat HGPS ECs. Endothelial morphology and functions were assessed, as well as proteomic and transcriptional profiles with attention to inflammatory markers, DNA damage and EC identity genes. In a mouse model of HGPS, we assessed the effects of lentiviral transfection of mTERT on measures of senescence, focusing on the EC phenotype in various organs. Results: hTERT treatment of human HGPS ECs improved replicative capacity; restored endothelial functions such as nitric oxide generation, acLDL uptake and angiogenesis; and reduced the elaboration of inflammatory cytokines. In addition, hTERT treatment improved cellular and nuclear morphology, in association with a normalization of the transcriptional profile, effects which may be mediated in part by a reduction in progerin expression and an increase in SIRT1. Progeria mice treated with mTERT Lentivirus manifested similar improvements, with a reduction in inflammatory and DNA damage markers and increased SIRT1 in their vasculature and other organs. Furthermore, mTERT therapy increased the lifespan of HGPS mice. Conclusion: Vascular rejuvenation using telomerase mRNA is a promising approach for progeria and other age-related diseases.

Genomic instability in the naturally and prematurely aged myocardium

Genomic instability, the unresolved accumulation of DNA variants, is hypothesized as one of the contributors to the natural aging process. We assessed the frequency of unresolved DNA damage reaching the transcriptome of the murine myocardium during the course of natural aging and in hearts from four distinct mouse models of premature aging with established aging-related cardiac dysfunctions. RNA sequencing and variant calling based on total RNA sequencing was compared between hearts from naturally aging mice, mice with cardiomyocyte-specific deficiency of Ercc1, a component of the DNA repair machinery, mice with reduced mitochondrial antioxidant capacity, Tert-deficient mice with reduced telomere length, and a mouse model of human Hutchinson-Gilford progeria syndrome (HGPS). Our results demonstrate that no enrichment in variants is evident in the naturally aging murine hearts until 2 y of age from the HGPS mouse model or mice with reduced telomere lengths. In contrast, a dramatic accumulation of variants was evident in Ercc1 cardiomyocyte-specific knockout mice with deficient DNA repair machinery, in mice with reduced mitochondrial antioxidant capacity, and in the intestine, liver, and lung of naturally aging mice. Our data demonstrate that genomic instability does not evidently contribute to naturally aging of the mouse heart in contrast to other organs and support the contention that the endogenous DNA repair machinery is remarkably active to maintain genomic integrity in cardiac cells throughout life.

Telomerase therapy reverses vascular senescence and extends lifespan in progeria mice.

Hutchinson-Gilford progeria syndrome (HGPS) is an accelerated ageing syndrome associated with premature vascular disease and death due to heart attack and stroke. In HGPS a mutation in lamin A (progerin) alters nuclear morphology and gene expression. Current therapy increases the lifespan of these children only modestly. Thus, greater understanding of the underlying mechanisms of HGPS is required to improve therapy. Endothelial cells (ECs) differentiated from induced pluripotent stem cells (iPSCs) derived from these patients exhibit hallmarks of senescence including replication arrest, increased expression of inflammatory markers, DNA damage, and telomere erosion. We hypothesized that correction of shortened telomeres may reverse these measures of vascular ageing. We generated ECs from iPSCs belonging to children with HGPS and their unaffected parents. Telomerase mRNA (hTERT) was used to treat HGPS ECs. Endothelial morphology and functions were assessed, as well as proteomic and transcriptional profiles with attention to inflammatory markers, DNA damage, and EC identity genes. In a mouse model of HGPS, we assessed the effects of lentiviral transfection of mTERT on measures of senescence, focusing on the EC phenotype in various organs. hTERT treatment of human HGPS ECs improved replicative capacity; restored endothelial functions such as nitric oxide generation, acetylated low-density lipoprotein uptake and angiogenesis; and reduced the elaboration of inflammatory cytokines. In addition, hTERT treatment improved cellular and nuclear morphology, in association with a normalization of the transcriptional profile, effects that may be mediated in part by a reduction in progerin expression and an increase in sirtuin 1 (SIRT1). Progeria mice treated with mTERT lentivirus manifested similar improvements, with a reduction in inflammatory and DNA damage markers and increased SIRT1 in their vasculature and other organs. Furthermore, mTERT therapy increased the lifespan of HGPS mice. Vascular rejuvenation using telomerase mRNA is a promising approach for progeria and other age-related diseases.

Baricitinib, a JAK-STAT Inhibitor, Reduces the Cellular Toxicity of the Farnesyltransferase Inhibitor Lonafarnib in Progeria Cells.

Hutchinson–Gilford progeria syndrome (HGPS) is an ultra-rare multisystem premature aging disorder that leads to early death (mean age of 14.7 years) due to myocardial infarction or stroke. Most cases have a de novo point mutation at position G608G within exon 11 of the LMNA gene. This mutation leads to the production of a permanently farnesylated truncated prelamin A protein called “progerin” that is toxic to the cells. Recently, farnesyltransferase inhibitor (FTI) lonafarnib has been approved by the FDA for the treatment of patients with HGPS. While lonafarnib treatment irrefutably ameliorates HGPS disease, it is however not a cure. FTI has been shown to cause several cellular side effects, including genomic instability as well as binucleated and donut-shaped nuclei. We report that, in addition to these cellular stresses, FTI caused an increased frequency of cytosolic DNA fragment formation. These extranuclear DNA fragments colocalized with cGAs and activated the cGAS-STING-STAT1 signaling axis, upregulating the expression of proinflammatory cytokines in FTI-treated human HGPS fibroblasts. Treatment with lonafarnib and baricitinib, a JAK-STAT inhibitor, not only prevented the activation of the cGAS STING-STAT1 pathway, but also improved the overall HGPS cellular homeostasis. These ameliorations included progerin levels, nuclear shape, proteostasis, cellular ATP, proliferation, and the reduction of cellular inflammation and senescence. Thus, we suggest that combining lonafarnib with baricitinib might provide an opportunity to reduce FTI cellular toxicity and ameliorate HGPS symptoms further than lonafarnib alone.

Impact of Progerin Expression on Adipogenesis in Hutchinson-Gilford Progeria Skin-Derived Precursor Cells.

Hutchinson–Gilford progeria syndrome (HGPS) is a segmental premature aging disease caused by a mutation in LMNA. The mutation generates a truncated and farnesylated form of prelamin A, called progerin. Affected individuals develop several features of normal aging, including lipodystrophy caused by the loss of general subcutaneous fat. To determine whether premature cellular senescence is responsible for the altered adipogenesis in patients with HGPS, we evaluated the differentiation of HGPS skin-derived precursor stem cells (SKPs) into adipocytes. The SKPs were isolated from primary human HGPS and normal fibroblast cultures, with senescence of 5 and 30%. We observed that the presence of high numbers of senescent cells reduced SKPs’ adipogenic differentiation potential. Treatment with baricitinib, a JAK–STAT inhibitor, ameliorated the ability of HGPS SKPs to differentiate into adipocytes. Our findings suggest that the development of lipodystrophy in patients with HGPS may be associated with an increased rate of cellular senescence and chronic inflammation.

Arterial stiffness and cardiac dysfunction in Hutchinson-Gilford Progeria Syndrome corrected by inhibition of lysyl oxidase.

Arterial stiffening and cardiac dysfunction are hallmarks of premature aging in Hutchinson-Gilford Progeria Syndrome (HGPS), but the molecular regulators remain unknown. Here, we show that the LaminAG609G mouse model of HGPS recapitulates the premature arterial stiffening and early diastolic dysfunction seen in human HGPS. Lysyl oxidase (LOX) is up-regulated in the arteries of these mice, and treatment with the LOX inhibitor, β-aminopropionitrile, improves arterial mechanics and cardiac function. Genome-wide and mechanistic analysis revealed reduced expression of the LOX-regulator, miR-145, in HGPS arteries, and forced expression of miR-145 restores normal LOX gene expression in HGPS smooth muscle cells. LOX abundance is also increased in the carotid arteries of aged wild-type mice, but its spatial expression differs from HGPS and its up-regulation is independent of changes in miR-145 abundance. Our results show that miR-145 is selectively misregulated in HGPS and that the consequent up-regulation of LOX is causal for premature arterial stiffening and cardiac dysfunction.

Cytoskeleton stiffness regulates cellular senescence and innate immune response in Hutchinson-Gilford Progeria Syndrome.

Hutchinson–Gilford progeria syndrome (HGPS) is caused by the accumulation of mutant prelamin A (progerin) in the nuclear lamina, resulting in increased nuclear stiffness and abnormal nuclear architecture. Nuclear mechanics are tightly coupled to cytoskeletal mechanics via lamin A/C. However, the role of cytoskeletal/nuclear mechanical properties in mediating cellular senescence and the relationship between cytoskeletal stiffness, nuclear abnormalities, and senescent phenotypes remain largely unknown. Here, using muscle‐derived mesenchymal stromal/stem cells (MSCs) from the Zmpste24 −/− (Z24 −/−) mouse (a model for HGPS) and human HGPS fibroblasts, we investigated the mechanical mechanism of progerin‐induced cellular senescence, involving the role and interaction of mechanical sensors RhoA and Sun1/2 in regulating F‐actin cytoskeleton stiffness, nuclear blebbing, micronuclei formation, and the innate immune response. We observed that increased cytoskeletal stiffness and RhoA activation in progeria cells were directly coupled with increased nuclear blebbing, Sun2 expression, and micronuclei‐induced cGAS‐Sting activation, part of the innate immune response. Expression of constitutively active RhoA promoted, while the inhibition of RhoA/ROCK reduced cytoskeletal stiffness, Sun2 expression, the innate immune response, and cellular senescence. Silencing of Sun2 expression by siRNA also repressed RhoA activation, cytoskeletal stiffness and cellular senescence. Treatment of Zmpste24− / − mice with a RhoA inhibitor repressed cellular senescence and improved muscle regeneration. These results reveal novel mechanical roles and correlation of cytoskeletal/nuclear stiffness, RhoA, Sun2, and the innate immune response in promoting aging and cellular senescence in HGPS progeria.

Long term breeding of the Lmna G609G progeric mouse: Characterization of homozygous and heterozygous models.

The transgenic LmnaG609G progeric mouse represents an outstanding animal model for studying the human Hutchinson-Gilford Progeria Syndrome (HGPS) caused by a mutation in the LMNA gene, coding for the nuclear envelope protein Lamin A/C, and, as an important, more general scope, for studying the complex process governing physiological aging in humans. Here we give a comprehensive description of the peculiarities related to the breeding of LmnaG609G mice over a prolonged period of time, and of many features observed in a large colony for a 2-years period. We describe the breeding and housing conditions underlining the possible interference of the genetic background on the phenotype expression. This information represents a useful tool when planning and interpreting studies on the LmnaG609G mouse model, complementing any specific data already reported in the literature about this model since its production. It is also particularly relevant for the heterozygous mouse, which mirrors the genotype of the human pathology however requires an extended time to manifest symptoms and to be carefully studied.

Dysfunction of iPSC-derived endothelial cells in human Hutchinson–Gilford progeria syndrome

ABSTRACT Children with Hutchinson–Gilford progeria syndrome (HGPS) succumb to myocardial infarction and stroke in their teen years. Endothelial dysfunction is an early event in more common forms of atherosclerosis. Endothelial pathobiology may contribute to HGPS, but a comprehensive characterization of endothelial function in HGPS has not been performed. iPSCs derived from fibroblasts of HGPS patients or unaffected relatives were differentiated into endothelial cells (ECs). Immunofluorescent signal of the pluripotent stem cell markers SSEA4, Oct4, Sox2 and TRAI-60 was similar in HGPS or control iPSCs. Following the differentiation, FACS analysis and immunocytochemistry for CD31 and CD144 revealed a smaller percentage of ECs from HGPS iPSCs. Immunostaining for Lamin A revealed nuclear dysmorphology in HGPS iPSC-ECs. Furthermore, these cells were significantly larger and rounded, and they proliferated less, features which are typical of senescent endothelial cells. HGPS iPSC-ECs manifested less Dil-Ac-LDL uptake; less DAF-2DA staining for nitric oxide generation and formed fewer networks in matrigel in vitro. In immunodeficient mice injected with iPSC-ECs, HGPS iPSC-ECs generated a sparser vascular network compared to the control, with reduced capillary number. Telomere length (T/S ratio) of HGPS iPSC-EC was reduced as assessed by mmqPCR. iPSC-ECs derived from HGPS patients have dysmorphic appearance, abnormal nuclear morphology, shortened telomeres, reduced replicative capacity and impaired functions in vitro and in vivo. Targeting the endothelial abnormality in patients with HGPS may provide a new therapeutic avenue for the treatment of this condition. Abbreviations: HGPS: Hutchinson–Gilford progeria syndrome; ZMPSTE24: Zinc metallopeptidase STE24; FTI: Farnesyltransferase inhibitors; VSMCs: Vascular smooth muscle cells; iPSC: Induced pluripotent stem cells; EC: Endothelial cells; hTERT: Human telomerase reverse transcriptase; VEGF: vascular endothelial growth factor; DAF-FM DA: 3-Amino, 4-aminomethyl-2’,7’-difluorofluorescein diacetate; BMP4: Bone Morphogenetic Protein 4; mmqPCR: mono chrome multiplex PCR; SCG: single-copy gene; CSI: Cell shape index.

Abstract QS18: Adipose Derived Stem Cells Isolated from Premature Aging Mice Show Sustained Stemness: Implications for Regenerative Medicine

PURPOSE: Exhaustion of functional stem cells in tissues may be caused by the effects of aging and stem cell senescence, which may ultimately lead to decreased rejuvenation and increased age progression. Adipose tissues and mature adipocytes may become dysfunctional and acquire a pro-inflammatory, senescent-like phenotype with aging, but the influence of the aging process on adipose stem cells is not well understood. Mice deficient in Zmpste24 (Zmpste24-/-or Z24-/-), a zinc metalloproteinase involved in the formation of mature lamin A for the nuclear membrane, demonstrate premature onset of age-related changes and have been studied as a model for human Hutchinson-Gilford Progeria Syndrome (HGPS). Using this mouse model, our current study is focused on investigating the characteristics and rejuvenative potential of ASCs from Z24-/- premature mice in vitro with implications for regenerative medicine. METHODS: Subcutaneous adipose tissues were harvested from Z24-/- and age-matched wild-type (WT) control mice and adipose tissue was minced, enzymatically digested for 1 hr at 37°C and ASCs were separated by centrifugation. ASCs were cultured in adipocyte growth medium. We compared the culture characteristics of Z24-/- and WT (wild-type) ASCs, and performed qPCR to determine senescence and quiescent properties of ASCs. Co-cultured ASCs with muscle progenitor cells (MPCs) in a Transwell system for 2 days to determine the potential influence of Z24-/- ASCs on Z24-/- muscle progenitor cells and eventual rescuing and rejuvenation of defective phenotypes. RESULTS:Z24-/- ASCs grew much slower rate than WT ASCs, but cell senescence-associated β-galactosidase (SA-β-Gal) staining showed <5% in Z24-/- ASCs. RT-qPCR results showed mTORC1 (cell senescence-promoting factor) down-regulation and p21 (negative cell cycle regulator) upregulation with decreased proliferation potential of Z24-/- ASCs. These results suggest that Z24-/- ASCs are more quiescent but not more senescent. Furthermore, TGF-β1expression was upregulated and pro-inflammatory factors (IL-1β and IL-6) were downregulated, suggesting that Z24-/- ASCs may exhibit decreased pro-inflammatory potential. VEGF gene expression was upregulated, suggesting sustained regenerative potential of Z24-/- ASCs. Co-culture of WT or Z24-/- ASCs with Z24-/- MPCs in a Transwell system for 2 days showed that Z24-/- ASCs rescued the defective phenotypes of Z24-/- MPCs in a manner comparable to that of WT ASCs. WT ASCs as well as Z24-/- ASCs were able to repress the expression of pro-inflammatory factors and pro-fibrogenic factors, and increase the expression of anti-inflammatory factors and energy metabolism factors. CONCLUSION: Our preliminary results showed that ASCs from Z24-/- prematurely aged mice were not as defective as MPCs and exhibited rejuvenative potential comparable to WT ASCs. Z24-/- ASCs were generally not senescent, but may be more quiescent compared to WT ASCs. Both WT and Z24-/- ASCs were able to repress pro-inflammatory and pro-fibrogenic factors, and promoted anti-inflammatory and energy metabolism factors. We believe that ASCs may show sustained stemness and lower senescence, in which ASCs could perform better in anti-aging therapy and tissue rejuvenation, with greater implications for regenerative medicine. S.K. Ravuri: None. X. Mu: None. W. Chen: None. J. Huard: None.

Interruption of progerin-lamin A/C binding ameliorates Hutchinson-Gilford progeria syndrome phenotype.

Hutchinson-Gilford progeria syndrome (HGPS) is a rare autosomal dominant genetic disease that is caused by a silent mutation of the LMNA gene encoding lamins A and C (lamin A/C). The G608G mutation generates a more accessible splicing donor site than does WT and produces an alternatively spliced product of LMNA called progerin, which is also expressed in normal aged cells. In this study, we determined that progerin binds directly to lamin A/C and induces profound nuclear aberrations. Given this observation, we performed a random screening of a chemical library and identified 3 compounds (JH1, JH4, and JH13) that efficiently block progerin-lamin A/C binding. These 3 chemicals, particularly JH4, alleviated nuclear deformation and reversed senescence markers characteristic of HGPS cells, including growth arrest and senescence-associated β-gal (SA-β-gal) activity. We then used microarray-based analysis to demonstrate that JH4 is able to rescue defects of cell-cycle progression in both HGPS and aged cells. Furthermore, administration of JH4 to LmnaG609G/G609G-mutant mice, which phenocopy human HGPS, resulted in a marked improvement of several progeria phenotypes and an extended lifespan. Together, these findings indicate that specific inhibitors with the ability to block pathological progerin-lamin A/C binding may represent a promising strategy for improving lifespan and health in both HGPS and normal aging.

Molecular mechanisms of normal and pathological aging

We have recently defined nine molecular and cellular hallmarks that represent common denominators of aging in different organisms. These hallmarks are: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient-sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. On the other hand, parallel studies of our laboratory on accelerated aging syndromes, including Hutchinson-Gilford Progeria Syndrome (HGPS) and Nestor-Guillermo Progeria Syndrome (NGPS), have provided relevant information about these hallmarks of aging. HGPS is caused by a point mutation in the LMNA gene that yields a truncated form of prelamin A called progerin, which is also produced during normal aging. Over the last years, the generation of mouse models of HGPS and other progeroid laminopathies has shed light on the molecular alterations functionally involved in these diseases. Thus, knock-out mice deficient in Zmpste24 metalloproteinase implicated in prelamin A maturation, mosaic mice containing Zmpste24-deficient and Zmpste24-proficient cells, and knock-in mice carrying the human HGPS mutation which causes progerin accumulation, have allowed us to demonstrate that progeroid laminopathies result from the combined action of both cell-autonomous and systemic factors. Accordingly, we have shown that nuclear envelope defects causative of these complex diseases lead to alterations in stem cell functionality, epigenetic abnormalities, perturbations in cell senescence pathways, metabolic changes and chronic activation of inflammatory responses. We have also demonstrated that the genetic or pharmacological blockade of these altered pathways prevents the development of many age-associated features of these progeroid mice and extends their longevity. On this basis, we have developed therapeutic strategies for progeroid laminopathies which are now in clinical trials coordinated by Pr. Nicolas Levy for the treatment of HGPS patients. These findings illustrate the importance of mouse models for designing therapeutic strategies to treat rare and dramatic progeroid syndromes as well as for improving our knowledge of the universal and complex process of human aging.

Reversal of age-dependent nuclear morphology by inhibition of prenylation does not affect lifespan in Caenorhabditis elegans

Fibroblasts derived from Hutchinson-Gilford progeria syndrome (HGPS) patients and dermal cells derived from healthy old humans in culture display age-dependent progressive changes in nuclear architecture due to accumulation of farnesylated lamin A. Treating human HGPS cells or mice expressing farnesylated lamin A with farnesyl transferase inhibitors (FTIs) reverses nuclear phenotypes and extends lifespan. Aging adult Caenorhabditis elegans show changes in nuclear architecture resembling those seen in HGPS fibroblasts, as well as a decline in motility, phenotypes which are also inhibited by the FTI gliotoxin. However, it was not clear whether these effects were due to loss of farnesylation or to side effects of this drug. Here, we used a different FTI, manumycin, or downregulated polyprenyl synthetase with RNAi to test the roles of farnesylation in C. elegans aging. Our results show that the age-dependent changes in nuclear morphology depend on farnesylation. We also demonstrate that inhibition of farnesylation does not affect motility or lifespan, suggesting that the effects of blocking protein prenylation on nuclear morphology could be separated from their effects on motility and lifespan. These results provide further understanding of the role of lamin and farnesylation in the normal aging process and in HGPS.

Mesenchymal Stem Cells Ameliorate Murine Progeria Phenotype

Our goal is to test mesenchymal stem cell therapy in a mouse model of Hutchinson-Gilford Progeria Syndrome (HGPS), a lethal childhood disorder for which no definitive therapy is available. HGPS patients have failure to thrive, lipodystrophy, skeletal dysplasia, sclerotic skin, alopecia, and occlusive vascular disease that results in premature death from myocardial infarction or stroke in early teens. In HGPS, the accumulation of incompletely processed nuclear architectural protein lamin A (a farnesylated version of prelamin A, termed progerin) results in dysfunction of multiple organ systems, particularly those of mesenchymal origin. Consistent with this, progerin has been shown to interfere with the proliferation and differentiation of mesenchymal stem cells (MSCs). Furthermore, MSC depletion is thought to account for the specific segmental nature of human progeria. The identification of HGPS-specific MSC dysfunction, and emerging evidence about the plasticity and paracrine effects of MSCs have prompted us to test the hypothesis that MSCs might be coaxed into becoming cells able to correct widespread pathology in HGPS. To determine whether MSCs can be used to rescue progeria phenotype, MSCs from wild-type donors were tested. First, donor MSCs (0.5 × 106 per recipient) were stably transfected to express the red fluoroform DsRed2, which permitted donor cell tracking in tissues post mortem. Next, to achieve wide biodistribution DsRed2+ MSCs were injected intra-arterially into 2-week-old ZMPSTE24−/− mutant mice. Like HGPS cells, ZMPSTE24−/− mutant mice accumulate progerin and the mice exhibit many progeria-like signs, including alopecia, micrognathia, dental abnormalities, osteolytic lesions in bones, osteoporosis, retarded growth, muscle weakness, and shortened lifespan. Therefore, survival, growth (measured by weight gain), and muscle weakness (measured by grip strength) were analyzed. MSC-treated (n = 13) versus untreated (n = 23) ZMPSTE24−/− mice had significantly increasedsurvival (65% versus 100%),weight gain after 6 weeks of life, andgrip strength (judged by the ability to hang onto an upside–down grid).These data are consistent with the hypothesis that the transfer of wild-type MSCs reduces the severity of the lamin A defect. To investigate whether the benefits associated with MSC infusion were attributable to persistent tissue engraftment or to a transient paracrine effect of donor MSCs, all mice were electively harvested at 20 weeks of age. Because dermal lipodystrophy, cardiac arteriosclerosis, and skeletal myopathy are prominent pathological findings in both human and murine progeria, post-mortem analyses focused on donor cell engraftment and progerin expression in corresponding organs of pathology (skin, liver, and skeletal muscle). Donor cells were identified in skin, liver, and skeletal muscle specimens with a frequency of 1%–5%, indicating that donor MSCs can repopulate tissue niches presumed to be dysfunctional in progeria. Experiments are ongoing to evaluate tissue levels of prelamin A and mature lamin A, abnormalities in nuclear shape, and pertubations in intracellular signaling pathway genes known to be dysregulated in human progeria. Collectively, these data demonstrate the proof of principle of MSC transfer for phenotypic reversion of lamin A defect in murine progeria. This may offer a valuable approach for treatment of human HGPS with human MSCs, which are already in clinical use.

Involvement of xeroderma pigmentosum group A (XPA) in progeria arising from defective maturation of prelamin A.

Cellular accumulation of DNA damage has been widely implicated in cellular senescence, aging, and premature aging. In Hutchinson-Gilford progeria syndrome (HGPS) and restrictive dermopathy (RD), premature aging is linked to accumulation of DNA double-strand breaks (DSBs), which results in genome instability. However, how DSBs accumulate in cells despite the presence of intact DNA repair proteins remains unknown. Here we report that the recruitment of DSB repair factors Rad50 and Rad51 to the DSB sites, as marked by gamma-H2AX, was impaired in human HGPS and Zmpste24-deficient cells. Consistently, the progeria-associated DSBs appeared to be unrepairable although DSBs induced by camptothecin were efficiently removed in the progeroid cells. We also found that these progeroid cells exhibited nuclear foci of xeroderma pigmentosum group A (XPA), a unique nucleotide excision repair protein. Strikingly, these XPA foci colocalized with the DSB sites in the progeroid cells. This XPA-DSB association was further confirmed and found to be mediated by DNA, using a modified chromatin immunoprecipitation assay and coimmunoprecipitation. RNA interference (RNAi) knockdown of XPA in HGPS cells partially restored DSB repair as evidenced by Western blot analysis, immunofluorescence and comet assays. We propose that the uncharacteristic localization of XPA to or near DSBs inhibits DSB repair, thereby contributing to the premature aging phenotypes observed in progeria arising from genetic defects in prelamin A maturation.

A farnesyltransferase inhibitor improves disease phenotypes in mice with a Hutchinson-Gilford progeria syndrome mutation

Hutchinson-Gilford progeria syndrome (HGPS) is caused by the production of a truncated prelamin A, called progerin, which is farnesylated at its carboxyl terminus. Progerin is targeted to the nuclear envelope and causes misshapen nuclei. Protein farnesyltransferase inhibitors (FTI) mislocalize progerin away from the nuclear envelope and reduce the frequency of misshapen nuclei. To determine whether an FTI would ameliorate disease phenotypes in vivo, we created gene-targeted mice with an HGPS mutation (LmnaHG/+) and then examined the effect of an FTI on disease phenotypes. LmnaHG/+ mice exhibited phenotypes similar to those in human HGPS patients, including retarded growth, reduced amounts of adipose tissue, micrognathia, osteoporosis, and osteolytic lesions in bone. Osteolytic lesions in the ribs led to spontaneous bone fractures. Treatment with an FTI increased adipose tissue mass, improved body weight curves, reduced the number of rib fractures, and improved bone mineralization and bone cortical thickness. These studies suggest that FTIs could be useful for treating humans with HGPS.

Inhibiting farnesylation of progerin prevents the characteristic nuclear blebbing of Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disorder that is characterized by dramatic premature aging and accelerated cardiovascular disease. HGPS is almost always caused by a de novo point mutation in the lamin A gene (LMNA) that activates a cryptic splice donor site, producing a truncated mutant protein termed "progerin." WT prelamin A is anchored to the nuclear envelope by a farnesyl isoprenoid lipid. Cleavage of the terminal 15 aa and the farnesyl group releases mature lamin A from this tether. In contrast, this cleavage site is deleted in progerin. We hypothesized that retention of the farnesyl group causes progerin to become permanently anchored in the nuclear membrane, disrupting proper nuclear scaffolding and causing the characteristic nuclear blebbing seen in HGPS cells. Also, we hypothesized that blocking farnesylation would decrease progerin toxicity. To test this hypothesis, the terminal CSIM sequence in progerin was mutated to SSIM, a sequence that cannot be farnesylated. SSIM progerin relocalized from the nuclear periphery into nucleoplasmic aggregates and produced no nuclear blebbing. Also, blocking farnesylation of authentic progerin in transiently transfected HeLa, HEK 293, and NIH 3T3 cells with farnesyltransferase inhibitors (FTIs) restored normal nuclear architecture. Last, treatment of both early- and late-passage human HGPS fibroblasts with FTIs resulted in significant reductions in nuclear blebbing. Our results suggest that treatment with FTIs represents a potential therapy for patients with HGPS.

Blocking protein farnesyltransferase improves nuclear shape in fibroblasts from humans with progeroid syndromes

Defects in the biogenesis of lamin A from its farnesylated precursor, prelamin A, lead to the accumulation of prelamin A at the nuclear envelope, cause misshapen nuclei, and result in progeroid syndromes. A deficiency in ZMPSTE24, a protease involved in prelamin A processing, leads to prelamin A accumulation, an absence of mature lamin A, misshapen nuclei, and a lethal perinatal progeroid syndrome: restrictive dermopathy (RD). Hutchinson-Gilford progeria syndrome (HGPS) is caused by a mutant prelamin A that cannot be processed to lamin A. The hallmark cellular abnormality in RD and HGPS is misshapen nuclei. We hypothesized that the farnesylation of prelamin A is important for its targeting to the nuclear envelope in RD and HGPS and that blocking farnesylation would ameliorate the nuclear shape abnormalities. Indeed, when RD fibroblasts were treated with a farnesyltransferase inhibitor (FTI), prelamin A was partially mislocalized away from the nuclear envelope, and the frequency of nuclear shape abnormalities was reduced (P < 0.0001). A FTI also mislocalized prelamin A and improved nuclear shape in Zmpste24-deficient mouse embryonic fibroblasts (P < 0.0001) and improved nuclear shape in human HGPS fibroblasts (P < 0.0001). Most remarkably, a FTI significantly improved nuclear shape in two fibroblast cell lines from atypical progeria patients with lamin A missense mutations in the absence of prelamin A accumulation (P = 0.0003 and P < 0.0001). These findings establish a paradigm for ameliorating the most obvious cellular pathology in lamin-related progeroid syndromes and suggest a potential strategy for treating these diseases.