Fibroblast growth factor can substitute for platelet factor to sustain the growth of Balb/3T3 cells in the presence of plasma

Sarcopenia: Aging-Related Loss of Muscle Mass and Function

Sarcopenia is a loss of muscle mass and function in the elderly that reduces mobility, diminishes quality of life, and can lead to fall-related injuries, which require costly hospitalization and extended rehabilitation. This review focuses on the aging-related structural changes and mechanisms at cellular and subcellular levels underlying changes in the individual motor unit: specifically, the perikaryon of the α-motoneuron, its neuromuscular junction(s), and the muscle fibers that it innervates. Loss of muscle mass with aging, which is largely due to the progressive loss of motoneurons, is associated with reduced muscle fiber number and size. Muscle function progressively declines because motoneuron loss is not adequately compensated by reinnervation of muscle fibers by the remaining motoneurons. At the intracellular level, key factors are qualitative changes in posttranslational modifications of muscle proteins and the loss of coordinated control between contractile, mitochondrial, and sarcoplasmic reticulum protein expression. Quantitative and qualitative changes in skeletal muscle during the process of aging also have been implicated in the pathogenesis of acquired and hereditary neuromuscular disorders. In experimental models, specific intervention strategies have shown encouraging results on limiting deterioration of motor unit structure and function under conditions of impaired innervation. Translated to the clinic, if these or similar interventions, by saving muscle and improving mobility, could help alleviate sarcopenia in the elderly, there would be both great humanitarian benefits and large cost savings for health care systems.

Inhibition of serum and transforming growth factor beta (TGF-beta1)-induced DNA synthesis in confluent airway smooth muscle by heparin

1. Airway remodelling occurs in asthma and involves an increase in airway smooth muscle mass through cell proliferation and hypertrophy. Increased eosinophil density in the airways is a feature of asthma. Eosinophils exhibiting activation in the airways of asthmatics also exhibit increased expression of transforming growth factor beta (TGF-beta1). We have examined the capacity of TGF-beta1 and epidermal growth factor (EGF) to influence airway smooth muscle division and the effect of heparin on TGF-beta1. EGF and serum-induced smooth muscle DNA synthesis in confluent airway smooth muscle cells (ASMC) as an indication of entry into S phase preceding mitogenesis. 2. ASMC were obtained from cell populations growing out from explanted bovine trachealis muscle sections. Cell division was monitored in sparse plated cells by direct cell counting following nuclear staining. Cell DNA synthesis in confluent cells was monitored by uptake of [3H]-thymidine. 3. TGF-beta1 (100 microM) inhibited FBS (10%)-induced smooth muscle division in sparsely plated cells (40%). TGF-beta1 (100 pM) increased cell DNA synthesis (200%) in confluent cells in the presence of bovine serum albumin (BSA, 0.25%). EGF (0.7 nM) also increased airway smooth muscle DNA synthesis (69%) in the presence of BSA (0.25%). The facilitatory effect of TGF-beta1 was observed between 1-100 pM, while that of EGF was observed between 20 200 pM. 4. Heparin inhibited serum and TGF-beta1-induced DNA synthesis in confluent ASMC (55%), consistent with our previous observation of inhibition of division in sparsely populated ASMC (Kilfeather et al., 1995a). This action of heparin was observed between concentrations of 1-100 microg ml(-1). Heparin did not inhibit DNA synthesis in response to EGF. An anti-mitogenic effect of heparin was also observed against responses to combined exposure to TGF-beta1 and EGF. 5. There was a clear inhibitory effect of heparin in absolute terms against serum-induced division in cells plated at 10, 20 and 45 x 10(3) cells cm(-2). The inhibitory effect of heparin was also observed at a plating density of 45,000 cells cm(-2) when responses to serum were expressed as fold-stimulation of basal DNA synthesis. 6. These findings demonstrate a potential role of TGF-beta1, EGF and heparin-related molecules in regulation of airway smooth muscle division.

A form of basic fibroblast growth factor is secreted into the adluminal fluid of the rat coagulating gland

Rat coagulating gland and its secreted fluid contain a mitogenic substance that, by numerous criteria, appears to be similar to basic fibroblast growth factor (basic FGF). It is a potent competence factor in the BALB/c3T3 mouse embryo fibroblast assay, elutes from heparin-agarose at concentrations of NaCl greater than 1.0 M, and has an isoelectric point (pI) between 8 and 9. In coagulating gland fluid, its molecular weight was 20,000 +/- 5,000, as indicated by gel filtration on Sephadex G-200. Western blot analysis of purified factor from coagulating gland cytosol and fluid, respectively, revealed immunoreactive bands of 16,000 and 17,000 relative molecular weight similar to that of purified bovine basic FGF.

Inhibition by pertussis toxin of fibroblast growth factor-stimulated hexose transport in Swiss 3T3 cells

Addition of fibroblast growth factor to quiescent cultures of Swiss 3T3 cells stimulated the membrane transport of 2-deoxyglucose. Treatment of the cells with pertussis toxin (islet-activating protein) inhibited fibroblast growth factor-stimulated hexose transport. 5'-Guanylyl imidodiphosphate (p[NH]ppG), a non hydrolyzable analogue of GTP, increased the number of hexose carriers in the plasma membrane of saponin-permeabilized cells. These results suggest that guanine nucleotide binding protein may be involved in the regulation of hexose transport system by fibroblast growth factor in Swiss 3T3 cells.

Induction of protein kinase C activation and Ca2+ mobilization by fibroblast growth factor in Swiss 3T3 cells

Addition of fibroblast growth factor (FGF) to quiescent cultures of Swiss 3T3 cells rapidly induced diacylglycerol formation, protein kinase C activation and Ca2+ mobilization. Protein kinase C-activating agents such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and 1-oleoyl-2-acetylglycerol (OAG) mimicked the action of FGF and stimulated DNA synthesis in the presence of insulin. Prolonged treatment of the cells with phorbol-12,13-dibutyrate (PDBu) led to the down-regulation and complete disappearance of protein kinase C. In these cells, TPA and OAG did not induce DNA synthesis any more. FGF still elicited Ca2+ mobilization and DNA synthesis, but the magnitude of DNA synthesis was reduced to almost half as compared with that in the control cells. These results clearly indicate that both diacylglycerol and Ca2+ may serve as second messengers for FGF and suggest that these messengers may be involved in the mitogenic action of this growth factor.

Factors controlling the DNA-synthesis in 3T3 and EAT cells

Beta globulins, (Cohn Fr. III), are a major source of molecules affecting the DNA-synthesis of 3T3 and EAT cells. Growth inhibitors for both cell types, chromatograph at the same position, corresponding to a mol. wt of about 50,000. A very basic, (pI 10.1), factor is isolated by gel electrofocusing, which stimulates the DNA-synthesis of 3T3 and EAT cells. Because of its extremely high cationic charge and its adsorption on gels, the estimation of the exact molecular weight and its preparative isolation, becomes very difficult. Some of the above mentioned molecules are heat-stable and express their action even after boiling for 10 min at pH 3.

A model of cell cycle control: sequential events regulated by growth factors

PDGF is a potent mitogen that initiates the proliferation of quiescent fibroblastic cells. EGF and somatomedin C (or insulin) can replace the requirement for plasma to function synergistically with PDGF to stimulate DNA synthesis. PDGF, EGF and somatomedin C control discrete cellular events in the cell cycle. Cyclic AMP can potentiate the effects of polypeptide mitogens. The down-regulation of EGF receptors by PDGF and cyclic AMP brings about a loss of the requirement for exogenous EGF. The transient treatment of density-arrested fibroblasts with PDGF allows better study of synergistic actions of PDGF and plasma-derived factors. These synergistic interactions are important to understand in determining how multiple growth factors regulate cellular proliferation.

Epidermal growth factor (EGF) is required only during the traverse of early G1 in PDGF stimulated density-arrested BALB/c-3T3 cells

Density-arrested BALB/c-3T3 cells that had received a transient exposure to PDGF and were then transferred to medium containing only EGF and somatomedin C (Sm-C) began DNA synthesis after the G0/G1 lag. Supraphysiological concentrations of insulin could be employed to replace the Sm-C requirement. This G0/G1 lag phase was bisected by the requirement for the exogenous presence of EGF. Our data indicated that EGF was required during the traverse of only the first half of G0/G1 phase (6 h) and not during the traverse of late G1. Subphysiological serum concentrations of Sm-C were also necessary to be present with EGF for progression through early G0/G1; however, traverse of the final half of G0/G1 and commitment to DNA synthesis required the presence of Sm-C. It was found that physiological concentrations of Sm-C were required for the traverse late G1. The requirement for Sm-C for G0/G1 traverse of BALB/c-3T3 cells as opposed to human fibroblasts or glial cells may be due to a difference in endogenous synthesis of an insulin-like growth factor. Our data are in close agreement with previous reports that EGF is only required for approximately the first 8 h during traverse of the G0/G1 phase. The requirement for EGF to be present for the first 6 h of G0/G1 could result from a continued or repetitious event or by more than one distinct EGF-requiring event.

Active proliferation of Rous sarcoma virus-infected, but not normal, chicken heart mesenchymal cells in culture medium of physiological composition

Normal as well as Rous sarcoma virus-infected chicken pectoral and chicken embryo fibroblasts proliferate actively in a plasma containing medium of physiological ion concentrations (Ca2+, 1.2 mM; Mg2+, 0.7 mM). Reduction of medium calcium and magnesium concentrations is necessary to achieve selective quiescence of normal fibroblasts in these cell systems. By contrast, normal chicken heart mesenchymal cells proliferate only sluggishly (one doubling or less during a 6-day period) in a plasma containing medium of physiologic ion concentrations, whereas Rous sarcoma virus-infected heart mesenchymal cells proliferate actively (more than four doublings during an initial 2-day phase of exponential growth). The chicken heart mesenchymal cell system therefore has great potential for studies of the mechanism that initiates cell replication and of the failure in cellular regulatory processes that is responsible for the autonomous initiation of replication of neoplastic cells. From comparison of the chicken heart mesenchymal cell system to dialyzed plasma-based systems in which 3T3 cells tend to proliferative quiescence, it is argued that this proliferative quiescence of 3T3 cells is a result of cell starvation and is not physiologically meaningful.

Effects of hydrocortisone on the adrenaline-adenylate cyclase system of the skin

Using pig skin slices, we investigated the effects of hydrocortisone on the adenylate cyclase system of the skin. In short-term experiments, hydrocortisone, when added singly or in combination with other stimulators of adenylate cyclase in the skin (adrenaline or histamine), had no effect on cyclic AMP accumulation. However, when skin slices were incubated with hydrocortisone for more than 6 h, the response to adrenaline differed, with a greater accumulation of cyclic AMP in the hydrocortisone-treated skin. This effect was seen at a concentration of more than I micrometer hydrocortisone and was most marked 48 h later, while responses to adrenaline in control skin gradually decreased and remained low. Histamine, which is another stimulator of adenylate cyclase of the skin, did not cause a greater cyclic AMP accumulation in response to this hydrocortisone treatment. There was no significant difference in either low Km or high Km cyclic AMP phosphodiesterase activities as a result of this hydrocortisone treatment. Hydrocortisone seems to act by protecting the adrenaline-adenylate cyclase system of the skin.

Sarcoma growth factor (SGF): specific binding to epidermal growth factor (EGF) membrane receptors

Cells transformed by murine sarcoma viruses (MSV) produce and release into their tissue culture media several polypeptide growth stimulating factors. One of these has been partially purified using Bio-Gel P-60 column chromatography followed by DEAE-cellulose chromatography. This growth factor was assigned the name sarcoma growth factor (SGF), and is here shown to require the epidermal growth factor (EGF) receptor in order to function as a growth factor. DEAE-cellulose chromatography yielded a product that was several-fold purer than the material present in the Bio-Gel P-60 column pool II. The biologically active material from the DEAE-cellulose column, when labeled with 125I, showed specific binding to EGF membrane receptors. The specific binding could be prevented with the addition of either unlabeled EGF or SGF. Both radiolabeled SGF and EGF will bind to live or fixed cells. We were able to bind 125I-SGF as well as 125I-EGF to fixed cells and elute the bound material from fixed receptors. The eluted SGF showed a greater than 25-fold increase in specific binding. The biological activities of EGF and SGF could be bound to and eluted from fixed receptors. The eluted SGF showed a greater than 25-fold increase in specific binding. The biological activities of EGF and SGF could be bound to and eluted from fixed cells. A 3T3 clone lacking EGF receptors was unable to respond to either EGF or SGF, whereas it responded well to serum and several other purified growth factors. The SGF isolated using DEAE-cellulose chromatography was unable to compete in a radioimmune assay using 125I-EGF and antibody to purified mouse submaxillary gland EGF; it also was not precipitated by anti-EGF antibody. From these studies it appears that the SGF produced and released by these MSV-transformed cells combines with and requires the EGF receptor in order to exert its biological effects. The peptide, however, is antigenically distinct from mouse submaxillary gland EGF.

Regulation of the cell cycle of 3T3 cells in culture by a surface membrane-enriched cell fraction

Addition of a suspension of a surface membrane enriched fraction prepared from confluent 3T3 cells to sparse 3T3 cells in culture results in a concentration dependent and saturable decrease in the rate of DNA synthesis. The inhibition of cell growth by membranes resembles the inhibition of cell growth observed at confluent cell densities by a number of criteria: 1) In both cases the cells are arrested in the G1 portion of the cell cycle; 2) the inhibition by membranes or by high local cell density can to a large extent be compensated for by raising the serum concentration or by addition of fibroblast growth factor plus dexamethasone. Membranes prepared from sparse cultures inhibit less well than membranes from confluent cultures in a manner which suggests that binding of membranes to cells is not by itself sufficient to cause inhibition of cell growth. The inhibitory activity has a subcellular distribution similar to phosphodiesterase (a plasma membrane marker) and appears to reside in one or more intrinsic membrane components. Maximally, membranes can arrest about 40% of the cell population in each cell cycle. Plasma membranes obtained from sparse 3T3 cells are less inhibitory than membranes obtained from confluent cells. This suggests either that the inhibitory component(s) in the plasma membrane responsible for growth inhibition may be in part induced by high cell density, or that this component(s) may be lost from these membranes during purification.

Physiological quiescence in plasma-derived serum: influence of platelet-derived growth factor on cell growth in culture

A platelet-derived growth factor can be shown to be the principal stimulant of DNA synthesis in whole blood serum for those cells that require serum for maintenance and growth in culture. Cell free plasma-derived serum lacks such platelet-derived material. 3T3 cells and primate arterial smooth muscle cells can be maintained in a quiescent state in culture for as long as six weeks in plasma-derived serum. Such cells can grow logarithmically after exposure to 5% whole blood serum or as little as 100 ng/ml of partially purified platelet factor. The cell cycle of smooth muscle cells has been studied in the quiescent (5% plasma-derived serum) and growing state (5% whole blood serum or 5% plasma-derived serum plus platelet factor). The generation time of smooth muscle cells is 16 to 18 hours as shown by autoradiographic frequency of labelled mitoses. The generation time is the same for cells in the growth fraction in either 5% whole blood serum or 5% plasma-derived serum. Thus, platelet factor acts by recruiting cells into the growth fraction rather than effecting a change in the duration of the cell cycle. Flow microfluorimetry studies on cells growing logarithmically in 5% whole blood serum give the following phase durations: G1 = 5.6 hours; S = 7.6 hours; and G2 + M = 3.8 hours. Based on these studies the argument is presented that cells cultured in 5% plasma-derived serum provide a more physiological base for the study of quiescence than do cells in low concentrations of whole blood serum or confluent, density inhibited cells at high (5% or greater) concentrations of whole blood serum. Furthermore, 5% plasma-derived serum represents an appropriate state to examine the perturbation of quiescent cells.

Platelet derived growth factor(s) for a hormone-responsive rat mammary tumor cell line

Mammary tumor cell growth factor(s) has been identified in extracts of platelets from both male and female rats, as well as in extracts prepared from pooled outdated human platelets. When assayed by the growth promotion of MTW9/PL rat mammary tumor cells in culture, platelet extracts alone were able to support growth 50--75% as well as whole serum. The mitogenic activity from crude human platelet lysates was shown to be trypsin sensitive, relatively stable to extremes of pH, labile to heat treatment at 70 degrees, non-dialysable, ammonium sulfate precipitable, not removed by 56 degrees charcoal treatment, and of apparent molecular weight of 30,000 to 50,000 daltons as estimated by G-100 Sephadex chromatography. The platelet derived mammary growth factor activity was not replaced or potentiated by thrombin or known hormones and growth factors such as prolactin, insulin, 17-beta-estradiol, progesterone, hydrocortisone, L-thyroxine, and mouse epidermal growth factor. The experimental report demonstrates that platelets are a rich source growth factor activity for rat epithelial mammary tumor cells, and that the activity appears to be a polypeptide(s) different from other mitogenic activities known to influence growth of mammary tissue.

Age-related and carcinogen-induced alterations of the extracellular growth factor requirements for cell proliferation in vitro

Cells from thigh muscles of fetal rats proliferate readily in vitro in medium containing homologous adult rat "plasma". As the donor animals mature, these cells become unable to make DNA and proliferate in "plasma" medium, but retain an ability to proliferate in medium containing fetal bovine serum (FBS). This age-related loss of the ability to proliferate in "plasma"-medium is due to an increasing need by the cells for an exogenous prereplicative promoter which is found in FBS and a crude preparation of bovine luteinizing hormone. Adult cells (and possibly fetal cells) also require a "cycle-completion" factor which is found in FBS and adult rat "plasma". The requirements for such external proliferative promoters is completely eliminated by neoplastic transformation in vivo, and neoplastic adult cells isolated from a nickel sulfide-induced mixed rhabdomyo-fibro-sarcoma can make DNA and proliferate in vitro in the complete absence of exogenous growth factors.

The sodium-potassium pump in volume expanded hypertension

Decreased arterial Na+-K+ pump and cardiac Na+, K-+ATPase activities have now been demonstrated in several types of experimental volume expanded hypertension. The changes are not secondary to elevated pressure since they also occur in veins and right ventricle where the pressure is not elevated. Decreased arterial Na+-K+ pump activity can be reproduced by acute volume expansion of the normal rat and plasma extracts from this rat suppress pump activity when applied to arteries from another rat. Suppression of Na+-K+ pump activity in arteries, veins and heart, with ouabain for example, leads to increased contractile activity. Thus the volume expansion, reduced pump activity, and hypertension appear to be causally related through an ouabain-like humoral agent. Certain other evidence suggests that the pump defect extends to the sympathetic nerve endings, thereby reducing the efficiency of neural compensatory mechanisms.

Clonal growth of bovine vascular endothelial cells: fibroblast growth factor as a survival agent

Bovine vascular endothelial cells do not grow when cultured at low density unless fibroblast growth factor is included in the culture medium. When endothelial cells obtained from the intimal surface of fetal and adult aortas were seeded at low density (8 cells per cm2), they formed small colonies of large, irregular, vacuolated cells. At very low density (0.3 cells per cm2) they did not survive. The addition of fibroblast growth factor to endothelial cells maintained at such low densities resulted in the formation of vigorously growing colonies of small, uniform cells. Electron microscopy showed that the cultured endothelial cells had the fine structure characteristics of endothelial cells. Immunofluorescence microscopy revealed antihemophilic factor (Factor VIII) antigen in the cells. Our results demonstrated that fibroblast growth factor permits the survival of endothelial cells plated at extremely low cell density. With the use of fibroblast growth factor, endothelial cell clones are easily produced.

Regulation of cell cycles

Of the major achievements in cell biology during the last 25 years, none is more important than the understanding of regulation of cell cycles. In 1953 two fundamental observations concerning DNA were made. Watson and Crick suggested that the three-dimensional structure of DNA exists as a double helix with specific base pairings, and Howard and Pelc observed that DNA is replicated during a specific phase in the mitotic cycle. Thus developed the theory of cell cycles. Next, investigators explored which events occur during each phase of the cycle and what controls the readout of the genes of proliferation or differentiation. In 1961, Jacob and Monod proposed that for prokaryotic cells the operon is the mechanism which controls the readout of the genes; and by the end of the 1960s, several investigators had defined the role of cyclic AMP and its mechanism of action at the gene level. The control mechanisms of eukaryotic cells are less well defined. Basically there are two types of regulatory molecules: those that arrive at the cell surface and send messages inside the cell; and those that enter the cell, bind to receptors, and then enter the nucleus to interact with the genes. During the past five to ten years, the cell surface and its receptors have received considerable attention as the recognition and control areas for cell proliferation and differentiation, and currently the role of the cyclic nucleotides and prostaglandins is being investigated. Various model systems are now available for detailed studies of these control mechanisms.