Age-related decline in the synthesis of glycosaminoglycans by cultured human fibroblasts (WI-38)

4-Methylumbeliferone Treatment at a Dose of 1.2 g/kg/Day Is Safe for Long-Term Usage in Rats

4-methylumbelliferone (4MU) has been suggested as a potential therapeutic agent for a wide range of neurological diseases. The current study aimed to evaluate the physiological changes and potential side effects after 10 weeks of 4MU treatment at a dose of 1.2 g/kg/day in healthy rats, and after 2 months of a wash-out period. Our findings revealed downregulation of hyaluronan (HA) and chondroitin sulphate proteoglycans throughout the body, significantly increased bile acids in blood samples in weeks 4 and 7 of the 4MU treatment, as well as increased blood sugars and proteins a few weeks after 4MU administration, and significantly increased interleukins IL10, IL12p70 and IFN gamma after 10 weeks of 4MU treatment. These effects, however, were reversed and no significant difference was observed between control treated and 4MU-treated animals after a 9-week wash-out period.

Remodeling of the Aged and Emphysematous Lungs: Roles of Microenvironmental Cues

Aging is a slow process that affects all organs, and the lung is no exception. At the alveolar level, aging increases the airspace size with thicker and stiffer septal walls and straighter and thickened collagen and elastic fibers. This creates a microenvironment that interferes with the ability of cells in the parenchyma to maintain normal homeostasis and respond to injury. These changes also make the lung more susceptible to disease such as emphysema. Emphysema is characterized by slow but progressive remodeling of the deep alveolar regions that leads to airspace enlargement and increased but disorganized elastin and collagen deposition. This remodeling has been attributed to ongoing inflammation that involves inflammatory cells and the cytokines they produce. Cellular senescence, another consequence of aging, weakens the ability of cells to properly respond to injury, something that also occurs in emphysema. These factors conspire to make alveolar walls more prone to mechanical failure, which can set emphysema in motion by driving inflammation through immune stimulation by protein fragments. Both aging and emphysema are influenced by microenvironmental conditions such as local inflammation, chemical makeup, tissue stiffness, and mechanical stresses. Although aging and emphysema are not equivalent, they have the potential to influence each other in synergistic ways; aging sets up the conditions for emphysema to develop, while emphysema may accelerate cellular senescence and thus aging itself. This article focuses on the similarities and differences between the remodeled microenvironment of the aging and emphysematous lung, with special emphasis on the alveolar septal wall. © 2022 American Physiological Society. Compr Physiol 12:3559-3574, 2022.

Age associated communication between cells and matrix: a potential impact on stem cell-based tissue regeneration strategies

A recent paper demonstrated that decellularized extracellular matrix (DECM) deposited by synovium-derived stem cells (SDSCs), especially from fetal donors, could rejuvenate human adult SDSCs in both proliferation and chondrogenic potential, in which expanded cells and corresponding culture substrate (such as DECM) were found to share a mutual reaction in both elasticity and protein profiles (see ref. (1) ). It seems that young DECM may assist in the development of culture strategies that optimize proliferation and maintain "stemness" of mesenchymal stem cells (MSCs), helping to overcome one of the primary difficulties in MSC-based regenerative therapies. In this paper, the effects of age on the proliferative capacity and differentiation potential of MSCs are reviewed, along with the ability of DECM from young cells to rejuvenate old cells. In an effort to highlight some of the potential molecular mechanisms responsible for this phenomenon, we discuss age-related changes to extracellular matrix (ECM)'s physical properties and chemical composition.

Preferential reduction of the α-2-6-sialylation from cell surface N-glycans of human diploid fibroblastic cells by in vitro aging

Human diploid fibroblastic cell line, TIG-3, has a finite life span of about 80 population doubling levels (PDL), and is used for in vitro aging studies. Young cells (PDL 23) grew to higher cell densities at a higher growth rate than aged cells (PDL 77). When the electrophoretic mobility of cells was determined, the negative surface charge of the aged cells decreased significantly when compared to that of young cells. Lectin blot analysis of membrane glycoproteins showed that the alpha-2-6-sialylation but not the alpha-2-3-sialylation of N-glycans decreases markedly in the aged cells when compared to the young cells. In support of this observation, the cDNA microarray assay and reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the gene expression of the alpha-2,6-sialyltransferase I (ST6Gal I), which transfers sialic acid to galactose residues of N-glycans, decreases in the aged cells. These results indicate that the concordant decrease of the alpha-2,6-sialylation of N-glycans with the ST6Gal I gene expression is induced in TIG-3 cells by in vitro aging.

Stimulation of cell proliferation by hyaluronidase during in vitro aging of human skin fibroblasts

The effect of the degradation of extracellular hyaluronan on the proliferation of human skin fibroblasts in serial cultures during in vitro aging was investigated. Human skin fibroblasts at different time intervals from 3rd to 36th passages were exposed after plating to bovine testicular hyaluronidase. The enzyme treatment resulted in an increase in cell proliferation (cell number vs. time) as compared to the untreated control fibroblasts. The effect was dose dependent, reversible, and was independent of the type of the glycosidic linkage cleaved in hyaluronan. The increased proliferation was observed at all passages when untreated cells underwent mitosis. The degradation of hyaluronan induced cell proliferation up to the presenescent phase. Depletion of hyaluronan did not induce proliferation of postmitotic fibroblasts. The incorporation of 3H-glucosamine into hyaluronan decreased with increasing cell passages (increase of the number of population doublings). Twenty-fourth passage fibroblasts accumulated about two time less hyaluronan in the medium than ninth passage cultures. Following hyaluronidase treatment, the amount of newly synthesized, labeled hyaluronan increased in the medium. Accordingly, the fibroblasts restored the degraded hyaluronan even in the declining phase of proliferation (phase III according to Hayflick).

Cellular ageing related proteins secreted by human fibroblasts

Fibroblast secreted proteins participate in the formation of extracellular matrix. Extracellular matrix affects growth factor action, mediates cell adhesion and supports cell growth. Structural and quantitative characteristics of secreted proteins are modified in a similar manner, during both in vivo and in vitro cellular ageing. Such ageing related modifications may either be directly controlled by primary ageing causes, or evolve from a reformation of the extracellular matrix induced by a few ageing defects in key proteins such as fibronectin. They may result in the further inhibition of cell adhesion, cell stimulation by growth factors and, eventually, of cell proliferative ability.

Changes in the cell surface of human diploid fibroblasts during cellular aging

The electrophoretic mobility of 13 human diploid cell strains, TIG-1, TIG-2, TIG-3, TIG-7, WI-38, IMR-90, MRC-5, MRC-9, TIG-1H, TIG-1L, TIG-2M, TIG-2B, and TIG-3S, which were established from different tissues of human embryos, was studied at different passages. The net negative surface charge of the cells was characteristic for each cell strain and decreased significantly during the in vitro aging of the cells. The decrease in the net negative charge of the cells correlated well with the decrease in cell density throughout the life span of the cells. A strict linear correlation between the electrophoretic mobility and the number of cells harvested at each passage was obtained for all the human diploid cell strains. Moreover, almost the same linear regression coefficient of the cells was obtained among these cell strains. Therefore, the net negative surface charge of human diploid cell strains could serve as a cell surface marker for in vitro cellular aging.

Cellular ageing of Alzheimer's disease and Down syndrome cells in culture

In Alzheimer's disease, the typical clinical symptoms and the pathological findings are restricted to the nervous system. Nevertheless, like in some other neurologic-metabolic disorders, several alterations are found in peripheral tissues. The aim of this study was to examine whether cellular properties which can be studied in vitro on skin fibroblast cultures obtained from Alzheimer's disease patients differ from those of age-matched controls. Down syndrome patients were also included, since the same neuropathological findings are present in nearly 100% of Down syndrome patients. Since Alzheimer's disease is an age-related disorder, we examined the growth characteristics of skin fibroblast cultures. The in vitro senescence of cultured fibroblasts is widely accepted as a model for in vivo ageing. Normal growth properties were found. We can conclude that there is no premature ageing in Alzheimer's disease nor in Down syndrome and that the abnormalities found in peripheral tissues are related to the disease itself. The beta amyloid precursor protein (beta APP) has been shown to have adhesive interactions. We therefore investigated several parameters of adhesion in the skin fibroblast cultures: adhesion to a fibronectin coat, adhesion to extracellular matrix of Alzheimer's disease cultures and semi-quantification of adhesion-related molecules (beta 1-integrin, cell surface proteoglycans, extracellular matrix proteoglycans, extracellular matrix fibronectin). No significant difference was found in the parameters examined.

In vitro cultures of trabecular meshwork cells of the human eye as a model system for the study of cellular aging

Cells from the human trabecular meshwork providing a drainage system for the outflow of aqueous humour in the eye were isolated and propagated in monolayer culture. Following serial subcultivation of the primary cultures, there was a gradual decline in the fraction of dividing cells with increasing population doubling level (PDL) resulting finally in growth cessation and disintegration of these 'senescent' cultures. The number of population doublings was at most 20. Senescent cultures revealed reduced glycosaminoglycan synthesis rates (as measured by [14C]glucosamine incorporation) with a relative decrease of hyaluronic acid and increase of heparan sulfate. Medium-supplied (exogenous) hyaluronic acid enhanced hyaluronic acid synthesis of trabecular meshwork cells cultured in a defined, serum-free medium. Ascorbic acid (25-200 micrograms/ml), which is found in very high concentration in the ocular aqueous humour, stimulated hyaluronic acid synthesis of confluent cultures, also. The functional significance of decreased hyaluronic acid (and elevated heparan sulfate) synthesis in the process of cellular aging in vitro (and in vivo?), as well as the importance of hyaluronic acid for the structural integrity and functional activity of the trabecular meshwork were discussed.

Changes in negative surface charge of human diploid fibroblasts, TIG-1, during in vitro aging

The electrophoretic mobility of human diploid fibroblasts, TIG-1, was studied at different passages. The net negative surface charge of the cells decreased from -1.658 +/- 0.108 micron/s/V/cm at an early passage (15 population doublings, PD) to -1.173 +/- 0.116 at the final passage (67 PD) in 1/15 M phosphate buffer supplemented with 5.4% glucose. The decrease was slow at 15-45 PD, but was rapid at 45-67 PD. The net negative surface charge of small cells in the late passage populations was not different from that of larger cells in this population, and was significantly lower than that of small cells in the middle passage populations. The distribution of the mobilities of cells in each passage was independent of the size of the individual cells, and the mean value was distinct for the passage number. The viability of the cells was retained during the assay of electrophoretic mobility under these conditions. These results indicate that the net negative surface charge of human diploid fibroblasts represents a cell surface maker for in vitro cellular age in the population.

Modulation of WI-38 cell proliferation by elevated levels of CaCl2

Elevating the level of extracellular calcium (CaEx2+) increases the saturation density achieved by the normal human diploid cell line, WI-38, but does not change the growth rate. Day 7 cell yields remain unchanged when [CaEx2+] is between 0.5 mM and 3.0 mM, decrease when [CaEx2+] less than 0.5 mM, and increase when [CaEx2+] greater than 3.0 mM. Combining hydrocortisone with additional CaCl2 results in an additive effect on the saturation density relative to that obtained with each treatment separately. The stimulatory effect of elevated [CaCl2] is independent of serum concentration but is lost when WI-38 cells are grown in conditioned medium. Stimulation is recovered when conditioned medium is diluted with serum-free medium. In the case of young cultures grown in conditioned medium, stimulation can also be recovered when higher than usual levels of additional CaCl2 are used (2-3 mM). A glutamine supplementation to the conditioned medium potentiates cell response to elevated [CaCl2]. These results indicate that the loss of an enhanced saturation density when cells are grown in conditioned medium is not due to serum depletion but is more likely the effect of metabolites and/or nutrient depletion. When older or less vigorously growing cultures are grown in conditioned medium, additions of up to 3 mM CaCl2 only lead to inhibition, suggesting an age-related change in proliferative regulation. Elevated levels of CaEx2+ also enhance the proliferative response of quiescent monolayers to serum stimulation. This finding, along with the increase in saturation density of Ca2+-treated cultures, suggests that an elevated level of CaEx2+ affects cell entry into and exit from quiescence brought on by density-dependent inhibition.

Proteoglycans synthesized by gingival fibroblasts derived from human donors of different ages

The proteoglycans synthesized by fibroblasts derived from human donors of ages ranging from 12 years to 68 years have been studied. In addition, the in vitro proliferation rates of the various cell strains were studied and demonstrated that increasing donor age correlated with a decrease in proliferative activity. The incorporation of [35S]-sulfate into proteoglycans decreased with increasing donor age with cells from the oldest donor demonstrating a 50% reduction compared with cells from the youngest donor. Analysis on Sepharose CL-4B of isolated [35S]-labeled proteoglycans for molecular size distribution revealed few differences between the cell-layer-associated proteoglycans of all cell strains studied. However, analysis of the medium-associated [35S]-labeled proteoglycans demonstrated an increase in the amount of small molecular size proteoglycans with increasing age. More specific analysis of the glycosaminoglycan composition revealed an increase in heparan sulfate from 52% to 73% in the cell-layer-associated proteoglycans of cells from the youngest and oldest donors, respectively. Accompanying this increase was a relative decrease in dermatan and chondroitin sulfate content from 24% to 13% and 25% to 16%, respectively, with increasing donor age. Additionally, the degree of N-sulfation of cell layer heparan sulfate increased with age. Heparan sulfate levels increased in the medium as well with increasing age, with a concomitant decrease in chondroitin sulfate. The quantity of medium-derived dermatan sulfate remained relatively evenly distributed throughout the various ages studied. The various differences noted are considered to reflect the general metabolic changes associated with aging. In particular the increase in heparan sulfate content with age is considered to be related to the decreased proliferative activity of the fibroblasts with increasing age.

Synthesis and composition of glycosaminoglycans by explant cultures of human ciliary body and ciliary processes in serum-containing and serum-free defined media

Freshly isolated ciliary body explants and tips of ciliary processes derived from human eyes were cultured in serum-containing or serum-free defined medium. These cultures synthesized tissue-bound and medium-released ("excreted") glycosaminoglycans (GAGs), as evidenced by the incorporation of 14C-glucosamine and enzymatic characterization of these labelled GAGs (hyaluronic acid, heparan sulphate, chondroitin sulphate, dermatan sulphate). The GAG synthesis and excretion rate was enhanced by serum. It is suggested that ciliary epithelium performs this function of GAG synthesis also under in vivo conditions.

Altered glycosaminoglycan production in cultured osteogenesis-imperfecta skin fibroblasts

Collagen and glycosaminoglycan syntheses were studied in skin fibroblasts cultured from patients with osteogenesis imperfecta (OI) and from age-matched controls. Collagen synthesis (measured as protein-bound [3H]hydroxyproline) was decreased in all four OI cell lines studied in the present experiments, comprising 16-24% of total protein synthesis (40% in normal cells). Hyaluronic acid production in OI skin fibroblasts per cell was higher than in age-matched controls, but the production of sulphated glycosaminoglycans was at the normal level. Thus the ratio of the hyaluronic acid and sulphated-glycosaminoglycan radioactivities was markedly higher in OI cultures than in control cultures, especially at the exponential phase of growth where the synthesis of hyaluronic acid was highest. Hyaluronic acid in OI had a normal molecular weight when determined by gel filtration on Sepharose 2B. The removal of high-molecular-weight hyaluronic acid from the medium by hyaluronidase had no effect on the rate of collagen secretion in OI cell line 1 (A.T.C.C. 1262), in which the rate of collagen secretion was lowest.

DNA repair by articular chondrocytes. I. Unscheduled DNA synthesis following ultraviolet irradiation in monolayer culture

The hypothesis that aging of articular chondrocytes at a cellular level results from loss of DNA repair capability was studied by measuring unscheduled DNA synthesis (UDS). Cultured rabbit and human articular chondrocytes were irradiated with 254 nm ultraviolet light (20 J/m2) following treatment with 10 mM hydroxyurea. Neither the "in vitro senescence" nor spontaneous transformation that developed during serial passage of rabbit chondrocytes was accompanied by diminution of UDS. Synthesis of sulfated glycosaminoglycans declined more rapidly than the ability of the cells to divide. Levels of UDS by chondrocytes from old donors, rabbit or human, were comparable to those of younger individuals. UDS was greater in human than rabbit chondrocytes. Similar data have been reported previously for dermal fibroblasts but do not necessarily indicate that there is a direct or causative relationship between UDS capability and the longevity of mammalian species. X-Irradiation of rabbit chondrocytes or cartilage explants, in doses up to 40 000 rads, yielded no measurable UDS.

Comparison between proliferative changes and nuclear events during ageing of human fibroblasts in vitro

Age-related alterations in nucleoproteins were examined in resting human embryonic fibroblasts at various population doubling levels (PDL) with three techniques for electron microscopy. Conventional glutaraldehyde fixation showed nuclear modifications consistent with previously published studies. Miller's technique permitted the detection of transcription complexes in young as well as in old cells. The technique involving the ultrathin sectioning of partially loosened nucleoproteins revealed at high PDL a marked rarefaction of the chromatin threads and the appearance of large parts of the lamina densa devoid of attached threads. In addition, the nucleolar filamentous masses were considerably less tufty than at earlier PDL, suggesting a decrease in the ribosomal transcriptional activity. These changes in nucleoprotein organization were rare before the 40th PDL, then increased to about 5% of the nuclei when the percentage of cells initiating DNA during the first 24 h remained at low levels. They were the rule for the last 6 to 7 PDL and coincided with the time when the maximal densities started to fall rapidly. They appeared after treatment with a loosening medium at neutral and at alkaline pH.

Synthesis and composition of glycosaminoglycans by cultured human trabecular meshwork cells

A human trabecular meshwork cell line with a limited number of population doublings was established in monolayer culture. All cultures produced hyaluronic acid, heparan sulfate, chondroitin sulfate, and dermatan sulfate. Following [14C]-glucosamine incorporation into proliferating (phase II) cultures, 70%--80% of the medium glycosaminoglycan label was found in hyaluronic acid and 8%--14% in heparin sulfate. About 60% of the cell-bound activity was associated with hyaluronic acid and 30% with heparan sulfate. Long-term cultivation under nondividing ("senescent") conditions resulted in a change of the pattern of synthesized and excreted (medium) [14C]-glucosamine-labeled glycosaminoglycans with a relative decrease of hyaluronic acid and a relative increase of heparan sulfate.

A re-evaluation of the changes in proliferation in human fibroblasts during ageing in vitro

Previously published studies concerning the proliferative changes, during ageing in vitro, of human embryonic fibroblasts, have been reappraised. The data suggest that the changes occur through shifts in a whole spectrum of cells between two extremes: complete inhibition and a normal division cycle. Reversion from the non-dividing to the dividing state becomes increasingly difficult and random. Ageing is the result of a long chain of events that hinder the transit of cells through the division cycle, mainly through interference with the G1 but also with the G2 period. Some metabolic events at the very end of the lifespan could support the terminal differentiation hypothesis.

Distribution of DNA between sister cells during serial subcultivation of human fibroblasts

The segregation of DNA at the time of cell division was analysed by measuring the DNA contents of cells in mitosis and the incorporation of tritiated thymidine (3H-TdR) on each half of anaphases and telophases. Results suggest that the spreads in the 2C and 4C DNA contents are due to quantitative differences which could originate during semi-conservative DNA synthesis, chromosome assembly and chromosome segregation. This continuous rearrangement of the genome could lead either to a degenerative process or to a differentiation program.

Werner's syndrome: a review of recent research with an analysis of connective tissue metabolism, growth control of cultured cells, and chromosomal aberrations

Werner's syndrome is a rare, autosomal recessive condition with multiple progeroid features, but it is an imitation of aging rather than accelerated or premature senescence. Somatic chromosome aberrations occur in multiple tissues in vivo and in vitro, and there is an increased incidence of neoplasia. Thus. Werner's syndrome can be classified in the group of chromosome instability syndromes. Recent findings provide additional support for the concept that there is an aberration of connective tissue metabolism in Werner's syndrome, but it is unclear whether this is a primary or secondary manifestation of the underlying genetic defect. Abnormal growth characteristics are observed in cultured skin fibroblast-like cells and this provides another avenue for current research. Identification of the basic genetic defect in Werner's syndrome might clarify our understanding of the normal aging process in general, or might elucidate specific aspects such as the development of neoplasia, atherosclerosis, diabetes, or osteoporosis.

Loss of organized fibronectin matrix from the surface of aging diploid fibroblasts (IMR-90)

Indirect immunofluorescence was used to investigate the production of a fibrillar fibronectin matrix by human diploid fibroblasts (IMR-90) as cells progress through their in vitro lifespan. Early and mid-passage cultures displayed a prominent fibrillar reticulum over the cell layer which formed within 24 hours of seeding. Even sparsely seeded early-passage cells exhibited fibrils of fibronectin on external surfaces. In contrast, fibrillar fibronectin was reduced or absent on surfaces of late-passage cells. However, the larger, non-proliferating, late-passage cells were producing fibronectin, 1h determined by radioimmunoassay of the medium.

Cell culture aging

Cellular research in aging has been stimulated by the observation that human diploid cells have a limited number of cell divisions in culture. This loss of cellular proliferation (in vitro senescence) has been extensively studied by biochemical, clonal, and genetic analysis. Studies of human skin fibroblast cultures have revealed that in vitro senescense is related to in vivo human cellular aging. Recently differentiated cells have been proposed for aging studies. These cells may provide additional information on aging since alterations of in vitro cellular functions may be related to the in vivo behavior of specific differented cell types.

Glycosaminoglycan synthesis and composition in human fibroblasts during in vitro cellular aging (IMR-90)

The synthesis and turnover of sulfate-labeled glycosaminoglycans(35S-GAGs) has been investigated in diploid human embryo fibroblasts during in vitro cellular aging. With progressive subcultivation, there was a decreased incorporation of Na2(35)SO4 into 35S-GAGs released to the medium, but not into those accumulated at the cell surface. The composition of 35S-GAGs found in extracellular medium, cell surface (removable by gentle proteolysis), and intracellular compartments of the culture after 48-hr labeling did not change significantly with progressive subcultivation. Pulse-labeled 35S-GAGs moved from intracellular to surface and extracellular compartments more slowly in late-passage cultures. Addition of 1 mM beta-xyloside to both early- and late-passage cultures produced a ten-fold enhancement of extracellular 35S-GAG production without a concomitant increase in surface-associated 35S-GAG. We interpret the data of this study to mean that secreted and cell-surface glycosaminoglycans represent different pools and that cellular aging has its effect primarily upon the secreted pool of glycosaminoglycans. Late-passage fibroblasts demonstrate marked decreases in proliferation, culture density, fibronectin matrix, and gap-junction formation. Our results suggest that glycosaminoglycan synthesis and composition are not intimately related to these parameters.

Age-related changes in the distribution pattern of glycosaminoglycans synthesized by cultured human diploid fibroblasts (WI-38)

A gradual decline in the synthesis of glycosaminoglycans, as evidenced by reduced rates of incorporation of [35S] sulfate and [14C] glucosamine into cellular and medium glycosaminoglycans, was observed during the last (about 5) population doublings before phase-out. The decline was accompanied by a change in the distribution pattern of individual glycosaminoglycans with a relative decrease in the incorporation rate of [14C] glucosamine into cellular and medium hyaluronic acid. The incorporation rate of [14D] glucosamine and [35S] sulfate into cellular and medium heparan sulfate continually increased during the last population doublings ("senescence"). The possibility of a coupling between cell growth and hyaluronic acid synthesis or an involvement of hyaluronic acid in the adhesion of cells (among one another or/and to the substratum), and the functional significance of heparan sulfate as a growth inhibitor were discussed.

Changes in cell-surface glycosaminoglycans in human diploid fibroblasts during in vitro aging

Changes in glycosaminoglycans during in vitro aging were investigated in human diploid fibroblasts. The cells were found to produce predominantly hyaluronate and smaller amounts of chondroitin 4-sulfate, chondroitin 6-sulfate, dermatan sulfate and heparan sulfate. Accumulation of heparan sulfate on the cell surface was notable during aging. Total glycosaminoglycan production in preconfluent culture did not change with population doubling level (PDL), while in confluent culture a decline in glycosaminoglycan production was observed. In contrast with this, heparan sulfate on the cell surface increased as a function of PDL in both confluent and preconfluent cultures. The distribution pattern of heparan sulfate in medium and cell surface indicated that the increase in heparan sulfate on the cell surface could be attributed to an increased accumulation on the cell surface, but not to an elevated production. Thus, we conclude that the increased accumulation of heparan sulfate on the cell surface might be involved in an age-related alteration in the cell membrane.

Aging in vitro and D-glucose uptake kinetics of diploid human fibroblasts

By use of a rapid technique, initial rates of D-glucose transport were obtained during the lifespan in vitro of a commercially available strain of human embryo lung fibroblasts (Flow 2000). The apparent Km of the D-glucose carrier did not change during senescence in vitro: x = 1.8 mM (range 1.3-2.3) in phase II, x = 1.8 mM (range 1.5-2.2) in phase III. Transport rates remained constant in stationary phase II cultures, which had completed between 30% and 80% of their replicative lifespan. A wide variation, however, was observed in terminally differentiated cells (phase III), which showed a two- to threefold increase in average cell size and protein content. In some senescent cultures, glucose transport calculated on a per cell basis was also two- to threefold increased, while it was strongly decreased (-75%) in others. When calculated per unit of cell water, protein, and surface area, respectively, transport rates in phase III cultures ranged from values established for stationary phase II cultures down to very low values. Detaching cells flushed off from senescent cultures did not show measurable rates of glucose transport into the inulin impermeable cell space. Present evidence argues against the idea that an impairment of D-glucose transport might precede loss of replicative potential in aging human fibroblasts. Instead our data indicate that the transport capacity of cell membrane finally decreases during postreplicative senescence in terminally differentiated cells.

Effect of short- or long-term treatment with exogenous glycosaminoglycans on growth and glycosaminoglycan synthesis of human fibroblasts (WI-38) in culture

Short-term (several days) or long-term (several weeks and months) treatment of cultured human diploid fibroblasts (WI-38; phase II) with heparin at 20--500 micrograms/ml inhibited cell proliferation and stimulated glycosaminoglycan synthesis (as measured by the incorporation rates of [35S] sulfate and [14C] glucosamine into cellular and medium glycosaminoglycans). Characterization of the individual glycosaminoglycan types revealed an increased portion of incorporated radioactivity in the heparan sulfate and hyaluronic acid fractions of heparin-treated cells. Treatment with chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate of hyaluronic acid at concentrations up to 500 micrograms/ml exhibited no or slightly inhibitory (especially in the case of hyaluronic acid) effects on growth and glycosaminoglycan synthesis. The average cellular protein and RNA content of short- or long-term heparin (100 micrograms/ml)-treated cells was elevated by about 70--80%. "Senescent" (phase III) WI-38 cells exhibited a relative increase of [35S] sulfate and [14C] glucosamine incorporation into cell-bound and medium heparan sulfate. Possible mechanisms for the action of heparin (for example, interaction with specific cell-surface sites) and a potential role of heparan sulfate in the regulation of cell growth are discussed.

Age-related cell surface changes in human diploid fibroblasts revealed by lectin-mediated red blood cell adsorption assay: a lectin survey

Two types of age-related cell surface changes could be demonstrated in human diploid fibroblasts with the two methods of the lectin-mediated red blood cell (RBC) adsorption assay: the fibroblast coating method (in which RBCs are adsorbed to lectin-coated fibroblasts) and the RBC coating method (in which lectin-coated RBCs are adsorbed to fibroblasts). With the fibroblast coating method, concanavalin A and agglutinin L from Phaseolus vulgaris gave a change in RBC adsorption which did not occur throughout the phase II period, but increased with the advance of the phase III period (type I). With the RBC coating method, these lectins gave another type of change in RBC adsorption which increased continuously from early phases of cell passage up through cell senescence (type II). Ricinus communis agglutinin 120 also gave the type I change in RBC adsorption with the fibroblast coating method. On the other hand, even with the fibroblast coating method, Phaseolus vulgaris agglutinin E and wheat-germ agglutinin gave the type II change in RBC adsorption. Soy bean agglutinin and Bauhinia purpurea agglutinin gave only a restricted amount of RBC adsorption. Lens culinaris agglutin, pokeweed mitogen, Dolichos biflorus agglutinin, Lotus tetragonolobus agglutinin, Limulus polyhemus agglutinin and divalent succinylated concanavalin A did not give any RBC adsorption throughout the life span of human diploid fibroblasts.