Two-dimensional gel electrophoretic studies on the cellular aging: accumulation of alpha-2-macroglobulin in human fibroblasts with aging

Single-cell transcriptome of the mouse retinal pigment epithelium in response to a low-dose of doxorubicin

Cellular senescence of the retinal pigment epithelium (RPE) is thought to play an important role in vision-threatening retinal degenerative diseases, such as age-related macular degeneration (AMD). However, the single-cell RNA profiles of control RPE tissue and RPE tissue exhibiting cellular senescence are not well known. We have analyzed the single-cell transcriptomes of control mice and mice with low-dose doxorubicin (Dox)-induced RPE senescence (Dox-RPE). Our results have identified 4 main subpopulations in the control RPE that exhibit heterogeneous biological activities and play roles in ATP synthesis, cell mobility/differentiation, mRNA processing, and catalytic activity. In Dox-RPE mice, cellular senescence mainly occurs in the specific cluster, which has been characterized by catalytic activity in the control RPE. Furthermore, in the Dox-RPE mice, 6 genes that have not previously been associated with senescence also show altered expression in 4 clusters. Our results might serve as a useful reference for the study of control and senescent RPE.

Single cell transcriptomics pinpoints a cell subpopulation that could be involved in inducing cellular senescence of the retinal pigment epithelium, which in turn may construe retinal degenerative disease.

Integration of heterogeneous functional genomics data in gerontology research to find genes and pathway underlying aging across species

Understanding the biological mechanisms behind aging, lifespan and healthspan is becoming increasingly important as the proportion of the world's population over the age of 65 grows, along with the cost and complexity of their care. BigData oriented approaches and analysis methods enable current and future bio-gerontologists to synthesize, distill and interpret vast, heterogeneous data from functional genomics studies of aging. GeneWeaver is an analysis system for integration of data that allows investigators to store, search, and analyze immense amounts of data including user-submitted experimental data, data from primary publications, and data in other databases. Aging related genome-wide gene sets from primary publications were curated into this system in concert with data from other model-organism and aging-specific databases, and applied to several questions in genrontology using. For example, we identified Cd63 as a frequently represented gene among aging-related genome-wide results. To evaluate the role of Cd63 in aging, we performed RNAi knockdown of the C. elegans ortholog, tsp-7, demonstrating that this manipulation is capable of extending lifespan. The tools in GeneWeaver enable aging researchers to make new discoveries into the associations between the genes, normal biological processes, and diseases that affect aging, healthspan, and lifespan.

The effects of fucodian on senescence are controlled by the p16INK4a-pRb and p14Arf-p53 pathways in hepatocellular carcinoma and hepatic cell lines

Fucoidan is known to have various pharmacological effects, including antitumor activity. Although it has potential as a therapeutic agent for cancer cells, the anti-senescence effects and detailed mechanism of action remain poorly understood in normal hepatic cells. We investigated the anticancer functions of fucoidan using HepG2 cells as well as the mechanisms mediating the anti-senescent actions in Chang liver cells. Fucoidan effectively inhibited HepG2 cell viability and induced apoptosis. Also, fucoidan-induced G₁ phase arrest was caused by the activity of the p16(INK4a)-Rb and p14(Arf)-p53 pathways. Furthermore, upregulation of p16(INK4a) was critical to the antitumor activity of HepG2 cells treated with fucoidan and was correlated with inhibition of Cdk4 and pRb and upregulation of p21 expression. Our results suggest that fucoidan upregulates INK4a locus genes to induce apoptosis through p38 MAPK in HepG2 cells. Moreover, it prevents cellular senescence of Chang-L cells, by decreasing p14(Arf) expression as cells enter quiescence, with the reduction of p16(INK4a). Fucoidan treatment also downregulated the expression of α₂M. In conclusion, fucoidan can be considered a potential therapeutic agent against liver cancer that does not cause senescence in normal hepatic cells. Thus, it may be possible to use fucoidan therapeutically in both tumor suppression and aging.

Age-related and depot-specific changes in white adipose tissue of growth hormone receptor-null mice

Growth hormone receptor-null (GHR(-/-)) mice are dwarf, insulin sensitive, and long-lived in spite of increased adiposity. However, their adiposity is not uniform, with select white adipose tissue (WAT) depots enlarged. To study WAT depot-specific effects on insulin sensitivity and life span, we analyzed individual WAT depots of 12- and 24-month-old GHR(-) (/-) and wild-type (WT) mice, as well as their plasma levels of selected hormones. Adipocyte sizes and plasma insulin, leptin, and adiponectin levels decreased with age in both GHR(-) (/-) and WT mice. Two-dimensional gel electrophoresis proteomes of WAT depots were similar among groups, but several proteins involved in endocytosis and/or cytoskeletal organization (Ehd2, S100A10, actin), anticoagulation (S100A10, annexin A5), and age-related conditions (alpha2-macroglobulin, apolipoprotein A-I, transthyretin) showed significant differences between genotypes. Because Ehd2 may regulate endocytosis of Glut4, we measured Glut4 levels in the WAT depots of GHR(-) (/-) and WT mice. Inguinal WAT of 12-month-old GHR(-) (/-) mice displayed lower levels of Glut4 than WT. Overall, the protein changes detected in this study offer new insights into possible mechanisms contributing to enhanced insulin sensitivity and extended life span in GHR(-) (/-) mice.

α-2-Macroglobulin: a physiological guardian

Alpha macroglobulins are large glycoproteins which are present in the body fluids of both invertebrates and vertebrates. Alpha-2-macroglobulin (α2 M), a key member of alpha macroglobulin superfamily, is a high-molecular weight homotetrameric glycoprotein. α2 M has many diversified and complex functions, but it is primarily known by its ability to inhibit a broad spectrum of proteases without the direct blockage of the protease active site. α2 M is also known to be involved in the regulation, transport, and a host of other functions. For example, apart from inhibiting proteinases, it regulates binding of transferrin to its surface receptor, binds defensin and myelin basic protein, etc., binds several important cytokines, including basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), nerve growth factor (NGF), interleukin-1β (IL-1β), and interleukin-6 (IL-6), and modify their biological activity. α2 M also binds a number of hormones and regulates their activity. α2 M is said to protect the body against various infections, and hence, can be used as a biomarker for the diagnosis and prognosis of a number of diseases. However, this multipurpose antiproteinse is not "fail safe" and could be damaged by reactive species generated endogenously or exogenously, leading to various pathophysiological conditions.

Expression profiles of subtracted mRNAs during cellular senescence in human mesenchymal stem cells derived from bone marrow

Cellular senescence is an irreversible cell cycle arrest that limits the replicative lifespan of cells. Senescence suppresses development of tumors by regulating aging factors, such as cyclin dependent kinase inhibitor (CKI) and telomerase. Suppression subtractive hybridization (SSH) was used to identify genes that were differentially expressed between young human mesenchymal stem cells (Y-hMSCs) and senescent human mesenchymal stem cells (S-hMSCs). We selected positive clones that were functionally characterized by referring to public databases using NCBI BLAST tool. This search revealed that 19 genes were downregulated, and 43 genes were upregulated in S-hMSCs relative to Y-hMSCs. Among subtracted clones in Y-hMSCs, most of genes markedly were related to metabolic functions. These genes, PDIA3, WDR1, FSTL1, COPG1, LMAN1, and PDIA6, significantly downregulated. Conversely, genes for subtracted clones in S-hMSCs were mostly associated with cell adhesion. In particular, the expression levels of 9 genes, HSP90B1, EID1, ATP2B4, DDAH1, PRNP, RAB1A, PGS5, TM4SF1 and SSR3, gradually increased during senescence. These genes have not previously been identified as being related to cellular senescence, but they seemed to be potentially affected during cellular senescence.

Mass spectrometry identification of circulating alpha-1-B glycoprotein, increased in aged female C57BL/6 mice

In this study, we surveyed the profiles of mouse circulating proteins by 2-dimensional SDS-PAGE in different strains, sexes and ages. Among visible protein spots on 2-D gels with silver-staining, we identified a unique set of 7 seemingly-related proteins whose levels were consistently elevated in older C57BL/6 female mice. This set of 7 proteins was absent in C57BL/6 males or in BALB/c mice of either sex of any age. When C57BL/6 female mice were crossed with BALB/c males, the age-related increase of these proteins became sporadic and not linear in the F1 offspring. All 7 spots of this protein group were picked and subjected to identification by mass spectrometric analysis after tryptic digestion. The results showed that all 7 spots were different isoforms of alpha(1)B-glycoprotein with different degrees of post-translational modifications, such as phosphorylation. These results suggest that alpha(1)B-glycoprotein changes in mice in a sex and age dependent manner.

Cloning and characterization of cellular senescence-associated genes in human fibroblasts by suppression subtractive hybridization

Cellular senescence marks the end of the proliferative life span of normal cells in tissue culture and occurs after cells have undergone a certain number of population doublings (PDLs). It is accompanied by alterations in the pattern of gene expression. A specific human embryonic lung diploid fibroblast cell line, 2BS, has been studied as a model of senescence in our laboratory. Here, we report a set of cellular senescence-associated genes identified from suppression subtractive cDNA libraries from senescent and young 2BS cells. They include three novel genes and six previously identified genes of unknown function. The genes whose functions are known belong to various functional pathways that have been reported to change with the onset of senescence. These include three pre-mRNA splicing factors with reduced expression in senescent cells, indicating that the regulation of mRNA splicing is altered during cell senescence. In addition, the expression of the gene TOM1 (target of Myb 1), which has not previously been associated with cellular senescence, is shown to increase in senescent cells, and we demonstrate that the expression of antisense TOM1 gene in 2BS cells can delay the progress of senescence.

mRNA level of alpha-2-macroglobulin as an aging biomarker of human fibroblasts in culture

Cellular senescence is a well-established model system for studying the molecular basis of aging. To identify a reliable biomarker for cellular age and further study the gene expression of aging, we profiled the gene expression difference between aged and young cultured human embryonic lung fibroblasts by high-density complementary deoxyribonucleic acid (cDNA) arrays. Among the differentially expressed genes, alpha-2-macroglobulin (alpha(2)M) was selected for further study. Its gene expression level as a function of population doubling level (PDL) in cultured fibroblasts was determined by RT-PCR and northern hybridization. mRNA level of alpha(2)M showed a positive linear-correlation with cumulative PDL. Additional assays revealed that the levels of alpha(2)M increased in irreversible growth arrest induced by sublethal H(2)O(2), but not in quiescent state of cultured fibroblasts induced by serum-deprivation, and remained stable in Hela cells. These results suggest that mRNA level of alpha(2)M can be used as a biomarker of aging in cultured fibroblasts. mRNA level of alpha(2)M showed significant difference between newborn and old human leucocytes, which suggest that the mRNA level of alpha(2)M may be used as a biomarker of aging in vivo.

Proteomic analysis of adipocyte differentiation: Evidence that α2 macroglobulin is involved in the adipose conversion of 3T3 L1 preadipocytes

Adipogenesis is an important aspect of energy homeostasis. Here we have used a differential proteome mapping strategy to identify intracellular proteins that are differentially expressed during adipose conversion of 3T3 L1 preadipocytes. Two-dimensional gel electrophoresis analysis identified 8 proteins that are induced following hormone-evoked differentiation. In addition, we found that a alpha2 macroglobulin fragment was abundantly present in 3T3 L1 preadipocytes, but was virtually undetectable in fully differentiated adipocytes. Metabolic radiolabeling with (35S)methionine and Northern blot analysis indicated that the intracellular alpha2 macroglobulin fragment in preadipocytes was derived from the extracellular culture medium, not de novo synthesis. Incubation of preadipocytes with an antialpha2 macroglobulin polyclonal antibody caused depletion of the intracellular alpha2 macroglobulin fragments, and also enhanced spontaneous adipose conversion. These results suggest that intracellular alpha2 macroglobulin fragment inhibits adipocyte differentiation, and that hormone treatment induces differentiation at least in part by suppression of intracellular alpha2 macroglobulin activity in 3T3 L1 preadipocytes.

Blood-brain barrier damage induces release of alpha2-macroglobulin

Blood-brain barrier (BBB) failure occurs in many neurological diseases and is caused in part by activation of proinflammatory factors including matrix metalloproteinases. Counterbalancing, "BBB protective" cascades have recently been described, including NO-mediated interleukin 6 release by glia. Interleukin 6 has been shown to trigger production of matrix metalloproteinase inhibitors such as alpha2-macroglobulin (alpha2M). We hypothesized that BBB failure may result in increased alpha(2)M release by perivascular astrocytes. This was initially tested in patients undergoing iatrogenic BBB disruption by hyperosmotic mannitol for intra-arterial chemotherapy of brain tumors. Serum samples revealed significantly increased levels of alpha2M at 4 h after BBB disruption by hyperosmotic mannitol. In parallel in vitro experiments, we observed a similar increase of alpha2M release by astrocytes under conditions mimicking BBB failure and perivascular edema. For both experiments, protein analysis was initially performed by bidimensional gel electrophoresis and mass spectrometry followed by Western blotting immunodetection. We conclude that, in addition to proinflammatory changes, BBB failure may also trigger protective release of alpha2M by perivascular astrocytes as well as peripheral source.

Protein profiling of the human epidermis from the elderly reveals up-regulation of a signature of interferon-gamma-induced polypeptides that includes manganese-superoxide dismutase and the p85beta subunit of phosphatidylinositol 3-kinase

Aging of the human skin is a complex process that consists of chronological and extrinsic aging, the latter caused mainly by exposure to ultraviolet radiation (photoaging). Here we present studies in which we have used proteomic profiling technologies and two-dimensional (2D) PAGE database resources to identify proteins whose expression is deregulated in the epidermis of the elderly. Fresh punch biopsies from the forearm of 20 pairs of young and old donors (21-30 and 75-92 years old, respectively) were dissected to yield an epidermal fraction that consisted mainly of differentiated cells. One- to two-mm3 epidermal pieces were labeled with [35S]methionine for 18 h, lysed, and subjected to 2D PAGE (isoelectric focusing and non-equilibrium pH gradient electrophoresis) and phosphorimage autoradiography. Proteins were identified by matching the gels with the master 2D gel image of human keratinocytes (proteomics.cancer.dk). In selected cases 2D PAGE immunoblotting and/or mass spectrometry confirmed the identity. Quantitative analysis of 172 well focused and abundant polypeptides showed that the level of most proteins (148) remains unaffected by the aging process. Twenty-two proteins were consistently deregulated by a factor of 1.5 or more across the 20 sample pairs. Among these we identified a group of six polypeptides (Mx-A, manganese-superoxide dismutase, tryptophanyl-tRNA synthetase, the p85beta subunit of phosphatidylinositol 3-kinase, and proteasomal proteins PA28-alpha and SSP 0107) that is induced by interferon-gamma in primary human keratinocytes and that represents a specific protein signature for the effect of this cytokine. Changes in the expression of the eukaryotic initiation factor 5A, NM23 H2, cyclophilin A, HSP60, annexin I, and plasminogen activator inhibitor 2 were also observed. Two proteins exhibited irregular behavior from individual to individual. Besides arguing for a role of interferon-gamma in the aging process, the biological activities associated with the deregulated proteins support the contention that aging is linked with increased oxidative stress that could lead to apoptosis in vivo.