Altered regulation of platelet-derived growth factor A-chain and c-fos gene expression in senescent progeria fibroblasts

Identification of hub genes, key pathways, and therapeutic agents in Hutchinson-Gilford Progeria syndrome using bioinformatics analysis

BACKGROUND

Hutchinson-Gilford Progeria syndrome (HGPS) is a rare lethal premature and accelerated aging disease caused by mutations in the lamin A/C gene. Nevertheless, the mechanisms of cellular damage, senescence, and accelerated aging in HGPS are not fully understood. Therefore, we aimed to screen potential key genes, pathways, and therapeutic agents of HGPS by using bioinformatics methods in this study.

METHODS

The gene expression profile of GSE113648 and GSE41751 were retrieved from the gene expression omnibus database and analyzed to identify the differentially expressed genes (DEGs) between HGPS and normal controls. Then, gene ontology and the Kyoto encyclopedia of genes and genomes pathway enrichment analysis were carried out. To construct the protein-protein interaction (PPI) network, we used STRING and Cytoscape to make module analysis of these DEGs. Besides, the connectivity map (cMAP) tool was used as well to predict potential drugs.

RESULTS

As a result, 180 upregulated DEGs and 345 downregulated DEGs were identified, which were significantly enriched in pathways in cancer and PI3K-Akt signaling pathway. The top centrality hub genes fibroblast growth factor 2, decorin, matrix metallopeptidase2, and Fos proto-oncogene, AP-1 transcription factor subunit were screened out as the critical genes among the DEGs from the PPI network. Dexibuprofen and parthenolide were predicted to be the possible agents for the treatment of HGPS by cMAP analysis.

CONCLUSION

This study identified key genes, signal pathways and therapeutic agents, which might help us improve our understanding of the mechanisms of HGPS and identify some new therapeutic agents for HGPS.

Loss of Serum Response Factor Activity Is the Basis of Reduced C-FOS Expression in Aging Human Fibroblasts

Les fibroblastes diploïdes humains subissent un nombre limité de dédoublements de population in vitro et sont largement utilisés comme modèle de vieillissement cellulaire. Malgré l'évidence grandissante que le vieillissement cellulaire est dû à une modification de l'expression du gène, l'activité des facteurs de transcription des cellules âgées est encore mal connue. Ici, nous rapportons que la réduction dramatique de l'expression du facteur de transcription fos durant le vieillissement cellulaire semble due à l'incapacité d'un autre facteur de transcription, le facteur réponse de sérum (FRS), de se lier à son site de reconnaissance appelé élément de réponse du sérum (ERS). Ce site est situé en amont de plusieurs gènes comprenant le gène humain c-fos. À l'opposé, les activités des protéines liées à la boîte TATA de la polymérase ARN ainsi qu'à l'élément réponse AMPc sont conservées chez les fibroblastes humains vieillissants. Nous présentons l'évidence que l'hyperphosphorilation du FRS induit une baisse du pouvoir de liaison observée au cours des dernières divisions cellulaires comme ceci a été précédemment suggéré pour la protéine fos.

Polo-like kinase 3 functions as a tumor suppressor and is a negative regulator of hypoxia-inducible factor-1 alpha under hypoxic conditions

Polo-like kinase 3 (Plk3) is an important mediator of the cellular responses to genotoxic stresses. In this study, we examined the physiologic function of Plk3 by generating Plk3-deficient mice. Plk3(-/-) mice displayed an increase in weight and developed tumors in various organs at advanced age. Many tumors in Plk3(-/-) mice were large in size, exhibiting enhanced angiogenesis. Plk3(-/-) mouse embryonic fibroblasts were hypersensitive to the induction of hypoxia-inducible factor-1 alpha (HIF-1 alpha) under hypoxic conditions or by nickel and cobalt ion treatments. Ectopic expression of the Plk3-kinase domain (Plk3-KD), but not its Polo-box domain or a Plk3-KD mutant, suppressed the nuclear accumulation of HIF-1 alpha induced by nickel or cobalt ions. Moreover, hypoxia-induced HIF-1 alpha expression was tightly associated with a significant down-regulation of Plk3 expression in HeLa cells. Given the importance of HIF-1 alpha in mediating the activation of the "survival machinery" in cancer cells, these studies strongly suggest that enhanced tumorigenesis in Plk3-null mice is at least partially mediated by a deregulated HIF-1 pathway.

Aggrecan expression is substantially and abnormally upregulated in Hutchinson–Gilford Progeria Syndrome dermal fibroblasts

Hutchinson-Gilford Progeria syndrome (HGPS) is a rare genetic disorder that displays features of segmental aging. It is manifested predominantly in connective tissue, with most prominent histological changes occurring in the skin, cartilage, bone and cardiovascular tissues. Detailed quantitative real time reverse-transcription polymerase chain reaction studies confirmed the previous observation that platelet-derived growth factor A-chain transcripts are consistently elevated 11+/-2- to 13+/-2-fold in two HGPS dermal fibroblast lines compared with age-matched controls. Furthermore, we identified two additional genes with substantially altered transcript levels. Nucleotide pyrophosphatase transcription was virtually shut down with decreased expression of 13+/-3- to 59+/-3-fold in HGPS, whereas aggrecan mRNA was elevated to 24+/-5 times to 41+/-4 times that of chronologically age-matched controls. Aggrecan, normally a component of cartilage and not always detectable in normal fibroblasts cultures, was secreted by HGPS fibroblast lines and was produced as a proteoglycan. This demonstrates that elevated aggrecan expression and its secretion are aberrant features of HGPS. We conclude that HGPS cells can display massively altered transcript levels leading to the secretion of inappropriate protein species.

Altered levels of primary antioxidant enzymes in progeria skin fibroblasts

Free radicals are involved in the aging process. In this study, the profile of primary antioxidant enzymes that scavenge reactive oxygen species (ROS) was examined for the first time in human skin fibroblasts from progeria, a premature aging disease. Altered levels of antioxidant enzymes were found in progeria cells. Basal levels of MnSOD were decreased in progeria cells as well as a blunted induction in response to chronic stress. This change may contribute to the accelerated aging process in progeria cells. In contrast, the levels of CuZnSOD showed no progeria-related change. Two H2O2 removing enzymes demonstrated a significant reduction in progeria cells: only 50% of normal CAT activity and 30% of normal GPX activity can be detected in progeria cells. This diminished H2O2 removing capacity in progeria cells may lead to an imbalance of intracellular ROS and therefore may play an important role in the development of progeria.

Signals controlling the expression of PDGF

PDGF is an important polypeptide growth factor that plays an essential role during early vertebrate development and is associated with tissue repair and wound healing in the adult vertebrate. Moreover, PDGF is thought to play a role in a variety of pathological phenomena, such as cancer, fibrosis and atherosclerosis. PDGF is expressed as a dimer of A and/or B chains, the precursors of which are encoded by two single copy genes. Although the PDGF genes are expressed coordinately in a number of cell types, they are independently expressed in a majority of cell types. The expression of either PDGF gene can be affected by very diverse extracellular stimuli and the type of response is dependent on the cell type that is exposed to the stimulus. Expression of the PDGF chains can be modulated at every imaginable level: by regulating accessibility of the transcription start site, by varying the transcription initiation rate, by using alternative transcription start sites, by alternative splicing, by using alternative polyadenylation signals, by varying mRNA decay rates, by regulating efficiency of translation, by protein modification, and by regulating secretion. Even upon secretion, the activity of PDGF can be modulated by non-specific or specific PDGF-binding proteins. This review provides an overview of the cell types in which the PDGF genes are expressed, of the factors that are known to affect the expression of PDGF, and of the various levels at which the expression of PDGF genes can be regulated.

Production and secretion of platelet-derived growth factor AB by cultured human keratinocytes: regulatory effects of phorbol 12-myristate 13-acetate, etretinate, 1,25-dihydroxyvitamin D3, and several cytokines

Platelet-derived growth factor (PDGF) is a potent mitogen for several mesenchymal cells and plays an important role in wound repair. Three PDGF isoforms, PDGF-AA, PDGF-BB, and PDGF-AB, have been found to be generated in various tissues. PDGF-AB production by normal human keratinocytes (NHKs), by human squamous cell carcinoma cell line (HSC-1) cells, and by human dermal fibroblasts (HDFs) was studied in the presence of agents which influence cell growth. Both NHKs and HSC-1 cells spontaneously produced and secreted PDGF-AB. NHKs grown in keratinocyte growth medium produced more PDGF-AB than did those grown in keratinocyte basic medium. Phorbol 12-myristate 13-acetate inhibited PDGF-AB production in NHKs but promoted its production in HSC-1 cells. 1,25-dihydroxyvitamin D3 up-regulated PDGF-AB production, whereas etretinate did not. High levels of calcium in the culture medium induced little change in cellular PDGF-AB levels. Prostaglandin E1 slightly inhibited PDGF-AB production, transforming growth factor beta 1 promoted PDGF-AB production and interferon-gamma, interleukin-1 alpha, and tumor necrosis factor-alpha failed to exert any influence at all. Cultured HDFs did not produce any detectable PDGF-AB. These results suggest that keratinocytes are a major source of cutaneous PDGF and that this factor may therefore play an important role in wound repair and in certain proliferative skin diseases.

Hutchinson-Gilford progeria types defined by differential binding of lectin DSA

Hutchinson-Gilford Progeria Syndrome (progeria) is an extremely rare childhood disorder characterized by precocious senility which presents features similar to those seen in human aging. We have previously described a consistent increase of the glycoprotein gp200 in progeria skin fibroblasts in vitro. Here we extend these glycosylation studies and present evidence for the existence of two types of progeria skin fibroblasts. These two forms, called D- and D+, are distinguished by their response to the lectin DSA. In the D- group, DSA bound glycoproteins from progeria fibroblast strains AG03513B and AG10750 with markedly lower affinities compared with glycoproteins from three control fibroblast strains. In the D+ group, DSA binding to glycoproteins from four other progeria strains AG01972A, AG06297A, AG06917 and AG03198, was comparable to controls. Discrimination by DSA is the most distinctive feature of the D- and D+ groups, in contrast to binding of lectins Con A, GNA, PHA-L, RCA120, AAA and PNA which show no such selectivity. The data are consistent with a model of altered glycosylation in the D- type of progeria fibroblasts.

Loss of serum response element-binding activity and hyperphosphorylation of serum response factor during cellular aging

Human diploid fibroblasts undergo a limited number of population doublings in vitro and are used widely as a model of cellular aging. Despite growing evidence that cellular aging occurs as a consequence of altered gene expression, little is known about the activity of transcription factors in aging cells. Here, we report a dramatic reduction in the ability of proteins extracted from the nuclei of near-senescent fibroblasts to bind the serum response element which is necessary for serum-induced transcription of the c-fos gene. In contrast, the activities of proteins binding to the RNA polymerase core element, TATA, as well as to the cyclic AMP response element were maintained during cellular aging. While no major differences in the expression of the serum response factor (SRF) that binds the serum response element were seen between early-passage and late-passage cells, hyperphosphorylation of SRF was observed in near-senescent cells. Furthermore, removal of phosphatase inhibitors during the isolation of endogenous nuclear proteins restored the ability of SRF isolated from old cells to bind the SRE. These data, therefore, indicate that hyperphosphorylation of SRF plays a role in altering the ability of this protein to bind to DNA and regulate gene expression in senescent cells.

Loss of serum response element-binding activity and hyperphosphorylation of serum response factor during cellular aging

Human diploid fibroblasts undergo a limited number of population doublings in vitro and are used widely as a model of cellular aging. Despite growing evidence that cellular aging occurs as a consequence of altered gene expression, little is known about the activity of transcription factors in aging cells. Here, we report a dramatic reduction in the ability of proteins extracted from the nuclei of near-senescent fibroblasts to bind the serum response element which is necessary for serum-induced transcription of the c-fos gene. In contrast, the activities of proteins binding to the RNA polymerase core element, TATA, as well as to the cyclic AMP response element were maintained during cellular aging. While no major differences in the expression of the serum response factor (SRF) that binds the serum response element were seen between early-passage and late-passage cells, hyperphosphorylation of SRF was observed in near-senescent cells. Furthermore, removal of phosphatase inhibitors during the isolation of endogenous nuclear proteins restored the ability of SRF isolated from old cells to bind the SRE. These data, therefore, indicate that hyperphosphorylation of SRF plays a role in altering the ability of this protein to bind to DNA and regulate gene expression in senescent cells.

Familial co-segregation of the elastin phenotype in skin fibroblasts from Hutchinson-Gilford progeria

Elastin and type IV collagen production are markedly elevated in fibroblasts derived from the skin of patients with Hutchinson-Gilford progeria (HGP). Fibroblasts from three affected children and their parents were compared to normal human skin fibroblasts with respect to elastin production as a function of different concentrations of calf serum and the cytokines, transforming growth factor-beta and basic fibroblast growth factor (TGF-beta 1, bFGF). In cultured fibroblasts from the parents of probands that were very high elastin producers (> 10(5) molecular equivalents/cell per h), at least one parent (mother) presented the same phenotype. Overproduction of elastin in culture could have been due to increased sensitivity of HGP strains to stimuli present in serum; however, relative stimulation of elastin production by calf serum in cell strains from HGP elastin over-producers was less than half the control strain. In most of the cultures examined, the responsiveness of elastin production to TGF-beta 1 was almost absent when compared to the response of normal fibroblasts. HGP strains with high elastin production modified conditioned medium to enhance elastin production in normal cells. These results suggest the presence, in HGP skin fibroblasts, of inheritance of high elastin production that is associated with accelerated aging.

Kinetics of 125I-PDGF binding and down-regulation of PDGF receptor in arterial smooth muscle cells derived from patients with moyamoya disease

Progressive stenosis or occlusion of bilateral internal carotid arteries by fibrocellular intimal thickening results in cerebral ischemia in moyamoya disease. We recently found that cultured smooth muscle cells (SMC) derived from arteries of patients with moyamoya disease responded poorly to serum mitogens, especially to platelet-derived growth factor (PDGF). In the present study, we investigated further the binding and processing of 125I-PDGF, as well as down-regulation of the PDGF receptor in arterial SMC derived from patients with moyamoya disease. The specific binding sites of 125I-PDGF were reduced significantly at both 4 degrees C and 22 degrees C on SMC from moyamoya disease compared with those from control (4.78 vs. 11.92 x 10(4)/cell at 4 degrees C), though the apparent dissociation constant (Kd) were the same. Kinetics of 125I-PDGF binding at 37 degrees C in cells from moyamoya disease showed fewer binding sites (less than 1/3 of controls) and lower degradation per cell than in those from controls, though no difference was observed in either internalization or degradation of each receptor. When SMC were exposed to lower concentrations of nonlabeled PDGF at 37 degrees C, the percentage of remaining binding sites on cells from moyamoya disease was significantly less than that from controls. This excess down-regulation of PDGF receptor in SMC from moyamoya disease may be interpreted as insufficient recycling or a decreased intracellular pool of the PDGF receptor. These results are closely correlated with the diminished proliferation responses to PDGF in SMC from moyamoya disease and provide evidence that functional alterations in vascular cells are involved in the mechanism of development of intimal thickening in moyamoya disease.

Altered genetic response to beta-adrenergic receptor activation in late passage C6 glioma cells

Previous studies have demonstrated variability in the phenotype of rat C6 glioma cells. In the present study, we compared morphology, growth rate, and beta-adrenergic regulation of gene expression in early (P39-47) and late (P55-90) passage C6 cells. Morphological changes were observed in five independently derived, late passage populations. In four of the five, the untreated cells were more polygonal than the fibroblast-like parental cells, and only a small fraction exhibited process outgrowth after dbcAMP treatment. Untreated cells from the fifth late passage population had longer cytoplasmic processes than parental cells and responded to dbcAMP with further process outgrowth. All late passage populations had shorter generation times than the parental cells. In early passage cells, treatment with the beta-adrenergic agonist, isoproterenol (IPR), resulted in an increase in c-fos mRNA and a decrease in c-jun mRNA (Gu-bits RM, Yu H: J Neurosci Res, 30:625-630, 1991). Both of these immediate early gene responses were irreversibly lost between P50 and P55. Additional differences in basal or IPR-induced mRNA levels were observed for beta-APP, GFAP, NGF, and PPE, but not for a number of other mRNAs. These results are discussed in relationship to previously described differences in the ability of early and late passage C6 cells to accumulate cAMP (Mallorga P, et al.: Biochim Biophys Acta 678:221-229, 1981).

Altered cellular responsiveness during ageing

The capacity of cells and organisms to respond to external stimuli and to maintain stability in order to survive decreases progressively during ageing. The mitogenic and stimulatory effects of growth factors, hormones and other agents are reduced significantly during cellular ageing. The sensitivity of ageing cells to toxic agents including antibiotics, phorbol esters, radiations and heat shock increases. This failure of homeostasis during cellular ageing does not appear to be due to any quantitative and qualitative defects in the receptor systems. Instead, metabolic defects in the pathways of macromolecular synthesis may be the basis of altered cellular responsiveness during ageing.

Homoeostatic imbalance during cellular ageing: altered responsiveness

The inability of normal cells to maintain themselves for ever is a reflection of homoeostatic imbalance and a progressive failure of maintenance. Ageing cells respond less to growth stimulants whereas they show increased sensitivity to toxic agents including antibiotics, phorbol esters, radiation and other physical stresses. No major quantitative and qualitative defects in the receptor systems have been detected that could explain the reasons for altered responsiveness during ageing. Random metabolic defects in the processes involved in maintaining homoeostasis may be critical for causing homoeostatic imbalance, cellular ageing and death.

Insulin receptor gene expression is reduced in cells from a progeric patient

We have studied a 15-year-old girl (P1) suffering from the Hutchinson-Gilford syndrome (progeria) associated with a severe insulin resistance. Insulin binding activity to P1 erythrocytes was 85% reduced when compared to that measured in ten normal controls matched for sex and age. This finding was confirmed in Epstein-Barr virus (EBV)-transformed lymphoblasts and depends on a reduction in insulin receptor number. Also the amount of total insulin receptors, [35S]methionine labeled and immunoprecipitated, was 90% reduced in P1 lymphoblasts when compared to controls. Next, we measured insulin receptor mRNA levels and we found undetectable levels of insulin receptor transcript in P1 EBV-transformed lymphoblasts, in the absence of any rearrangement of insulin receptor gene as evaluated by Southern blot analysis. The marked reduction in insulin receptor gene expression probably accounts for the severe insulin resistance presented by the patient. Despite extensive studies, the molecular basis of progeria is still unknown. The near complete absence of a molecule crucial in the transduction of cell growth and differentiation signals could be involved in the accelerated aging of the patient.