An in vitro study of senescent events of human embryonic lung (WI-38) cells

Senescence-associated beta-galactosidase is lysosomal beta-galactosidase

Replicative senescence limits the proliferation of somatic cells passaged in culture and may reflect cellular aging in vivo. The most widely used biomarker for senescent and aging cells is senescence-associated beta-galactosidase (SA-beta-gal), which is defined as beta-galactosidase activity detectable at pH 6.0 in senescent cells, but the origin of SA-beta-gal and its cellular roles in senescence are not known. We demonstrate here that SA-beta-gal activity is expressed from GLB1, the gene encoding lysosomal beta-D-galactosidase, the activity of which is typically measured at acidic pH 4.5. Fibroblasts from patients with autosomal recessive G(M1)-gangliosidosis, which have defective lysosomal beta-galactosidase, did not express SA-beta-gal at late passages even though they underwent replicative senescence. In addition, late passage normal fibroblasts expressing small-hairpin interfering RNA that depleted GLB1 mRNA underwent senescence but failed to express SA-beta-gal. GLB1 mRNA depletion also prevented expression of SA-beta-gal activity in HeLa cervical carcinoma cells induced to enter a senescent state by repression of their endogenous human papillomavirus E7 oncogene. SA-beta-gal induction during senescence was due at least in part to increased expression of the lysosomal beta-galactosidase protein. These results also indicate that SA-beta-gal is not required for senescence.

Senescence-associated (beta)-galactosidase reflects an increase in lysosomal mass during replicative ageing of human endothelial cells

Senescence-associated (beta)-galactosidase is widely used as a biomarker of replicative senescence. However, it remains unknown whether this is a distinct enzyme active at pH 6, and differentially expressed in senescence, or a manifestation of an increase in the classic acid lysosomal (beta)-galactosidase. Here we have investigated the origin of senescence-associated-(beta)-galactosidase activity by modifying the intracellular and lysosomal pH of young and senescent human umbilical vein endothelial cells and examining the effect of these manipulations on the levels of activity, using a flow cytometric assay. Lysosomal alkalinisation with chloroquine or bafilomycin A(1), as well as equilibration of the intracellular milieu to pH 6 with nigericin, caused a profound (92-99%) inhibition of the total intracellular (beta)-galactosidase activity. However, independent of pH alterations, senescent cells showed levels of (beta)-galactosidase activity three- to sixfold higher than young cells. This increase in activity occurred in parallel to an increase in (beta)-galactosidase protein levels. Acridine Orange staining revealed an increase in lysosomal content with replicative age, which correlated with the increase in (beta)-galactosidase. These findings demonstrate that senescence-associated (beta)-galactosidase is a manifestation of residual lysosomal activity at a suboptimal pH, which becomes detectable due to the increased lysosomal content in senescent cells.

Isozyme polymorphisms in human diploid cell strains for research on cellular aging

Six human lung diploid cell strains established for the study of in vitro cellular aging (TIG-1, TIG-7, WI-38, IMR-90, MRC-5, MRC-9, and HeLa cells as a control) were studied by cellulose acetate membrane electrophoresis for allozymic differences at 18 enzyme loci. Eight enzyme loci (G6PD, PGM1, PGM3, PepA, PGD, ADA, GLO1, and ME), proved to be informative in establishing unique allozyme genetic signatures for all of the cell strains established from the same species and from the same organ. Changes in the allozyme genetic signatures were not observed throughout the life span of TIG-1 and MRC-9 cells. The allozyme genetic signatures can be used as a quick monitor of cell identification and intraspecific cell contamination.

Chromatin structure, DNA synthesis and transcription through the lifespan of human embryonic lung fibroblasts

The presence in terminal embryonic fibroblasts of small molecular weight (MW) DNA independent of bulk DNA could be ascertained by three different techniques performed in parallel. This alteration was not artifactually induced, either by high pH and the detergent used or by the release of cellular enzymes. An increased thermolability of old chromatin was also observed. Cells with altered chromatin synthesized DNA and RNA according to a pattern similar to young type nuclei. Long-term treatment with hydrocortisone significantly increased the cell yield but did not prevent, in the late passages, the occurrence of old-type chromatin; the nucleolar filamentous masses, however, maintained a 'young' pattern. Short-term treatment induced only a moderate reversion in the appearance of chromatin lesions. Direct evidence was obtained of increased gene expression in the presence of hydrocortisone.

Multiparametric evaluation of the toxic responses of normal human cells treated in vitro with different classes of environmental toxicants

Eight compounds representing three classes of chemicals were evaluated for their toxic effects on normal neonatal human foreskin fibroblasts in vitro. A battery of toxicity assays was employed to measure the effects of the chemicals on cell viability, DNA synthesis, protein synthesis, DNA repair synthesis, cell ultrastructure, membrane-bound and soluble cytoplasmic proteins, and the activities of six enzymes: beta-glucuronidase, acid phosphatase, gamma-glutamyl transpeptidase, alkaline phosphatase, 5'mononucleotidase, and calcium-magnesium activated (Na+,K+)-dependent ATPase. The compounds evaluated included two antibiotics, each with a metabolic derivative-sulfamethazine (SMZ) and acetylsulfamethazine (ASZ), and carbadox (CBX) and desoxycarbadox (DCX); two anthelmintics-haloxon (HAL) and sansalid (SAN); and a steroid with a metabolic derivative, 17 alpha-estradiol (17-AE) and 17 alpha-estradiol-17-beta-D-glucoside (AE-G). Compounds with similar biological functions often elicited different patterns of response in the normal fibroblasts. For example, the two anthelmintics, HAL and SAN, were similar to each other in that they induced 50% relative cloning efficiencies (EC50) at approximately the same concentrations (HAL = 52 microgram/ml, SAN = 58 microgram/ml), and neither inhibited protein synthesis. They differed, however, in their effects of DNA synthesis. SAN did not inhibit DAN synthesis, while HAL was a profound inhibitor of DNA synthesis (98% inhibition after 4 h at 100 microgram/ml). Because the various toxicants elicited such a variety of response patterns as measured by a multiplicity of parameters, we conclude that similarities in survival responses of cells to closely related toxicants may arise frequently through toxic action at different sites within the cells.

Characterization of human cells transformed by chemical and physical carcinogens in vitro

Several different classes of chemical carcinogens induced the transformation of human fibroblasts grown in vitro. Characteristics of the events that occur from time of treatment through the expression of neoplastic transformation are presented. The S-phase appeared to be the portion of the cell cycle most vulnerable to insult. Staging of the cells by blocking them in G1 before releasing them to proceed through scheduled DNA synthesis (S) was required to induce reproducible transformation. Compounds such as insulin were added to the cells upon release from the block to sensitize the cells to the carcinogen that was added during S. Growth of the transformed cells as distinct from nontransformed cells was promoted by growth in medium supplemented with 8X nonessential amino acids. Carcinogen-treated cells in the early stage of transformation exhibited abnormal colony morphology and were able to grow at 41 degrees C, in air atmosphere, and in medium supplemented with only 1% serum. In addition, the transformed cells were insensitive to KB cell lysate and exhibited density independent, as well as anchorage independent, growth (i.e., growth in 0.33% agar). Cells that grew in soft agar also produced undifferentiated mesenchymal tumors in preirradiated nude mice.

Ageing and the fusion sensitivity potential of human cells in culture: relation to tissue origin, donor age, and in vitro culture level and condition

Cell fusion was induced by inactivated Sendai virus in different human diploid cell lines. These were derived from the kidney, lung or skin originating from embryos or adult donors and representing predominantly epithelioid cells (kidney) and fibroblastic cells (lung and skin). The fusion sensitivity (FS) potentials of these cell lines were determined and related to various aspects of cell ageing. In case of the fibroblastic lines, an inverse relation was demonstrated both to the culture age in vitro and to the donor age. The FS potential of embryonal fibroblasts decreased some 40-50% during the in vitro cultivation. In comparison to exponentially growing fibroblasts, the FS potentials were higher in cells in the stationary phase of growth. This was shown to correlate well with the fact that the life-span in calendar time also increased in cultures predominantly grown in the stationary phase. In the case of the kidney cells, the FS potentials were some 50% higher than those of fibroblasts. Since the cellular manifestation of the FS potential most likely primarily resides in the cell membrane-cytoskeleton structure, the results emphasize the importance of this system in relation to ageing.

Presensitization of human cells with extrinsic signals to induced chemical carcinogenesis

Foreskin-derived low-passage human cell populations were reproducibly transformed with chemical carcinogens when the cells were blocked in G1, released from the block, and treated with either the carcinogen N-methyl-N-nitro-N-nitrosoguanidine (MNNG) or with Aflatoxin B1 in the S period of the cell cycle. Arginine- and glutamine-deficient medium was required to effectively block the cells in the G1 period. Estradiol, insulin, anthralin or phorbol myristate acetate sensitized the cell population to carcinogen treatment when added 10 h before the carcinogen in early S period. Presensitized cells kept blocked in G1 period for 48 h or longer, released and treated in S period with MNNG or Aflatoxin B1 were not transformed; nor did transformation occur in presensitized cell populations treated in G2 (4.5 h), M (1.5 h) or G1 (8.2 h). Cells derived from carcinogen-treated presensitized cells grew as colonies in soft agar at 16-20 PDL. When cells derived from colonies isolated from the soft agar were injected subcutaneously into nude mice, tumors developed.

Inhibition of S37 ascites cell amino acid transport systems by alpha-chloromethylketone analogs

Alanine chloromethylketone and leucine chloromethylketone were synthesized and their effects on amino acid transport in sarcoma 37 mirone ascites tumor (S37) cells were studied. Alanine chloromethylketone preincubation weakly inhibited system A. Leucine chloromethylketone preincubation strongly inhibited both amino acid transport systems L and A. Leucine chloromethylketone was also a competitive inhibitor of leucine transport. Labeled leucine chloromethylketone was concentrated by S37 cells. Leucine chloromethylketone preincubation inhibition was concentration dependent and partial protection of transport was afforded by leucine. Steady-state retention of amino acids was decreased more than the initial velocity of transport by leucine chloromethylketone preincubation. Glutathione was also depleted. Labeled leucine chloromethylketone was incorporated in a plasma membrane protein fraction comigrating on a DEAE-cellulose column (DE52) with gamma-glutamyltranspeptidase activity. There was a modest increase in vital staining after treatment of S37 cells with leucine chloromethylketone, and glucose uptake was also inhibited. Whilst several effects occur during treatment of S37 cells with leucine chloromethylketone, it is suggested than one prominent effect is alkylation of amino acid transport system components.

Effect of cell density and senescence of WI-38 cells on cytochemically demonstrable phosphatases

Exponentially growing and stationary phase young and old cultures of the human cell line WI-38 were studied using cytochemistry at the ultrastructural level. 5'-Nucleotidase activity was present in the plasma membrane of all cells examined; in exponentially growing cultures the reaction was more intense in mitotic cells than in interphase cells. An increase in the amount of the reaction product was observed at confluencey, especially in older cells. The reaction of Mg2+-activated adenosine 5'-triphosphatase was absent or very weak in exponentially growing cells and increased at confluency, especially in older cells. Alkaline phosphatase was detectable only in the cell membranes and in intercellular spaces of young cells at confluency. Acid phosphatase activity was increased in old cells, especially at confluency. In these old cells, positive reactions appeared in numerous small lysosomes, autophagic vacuoles and in some flattened sacs of the Golgi apparatus. The obtained results confirm and extend previous biochemical observations and indicate that changes in phosphatase activity are associated with proliferative activity and senescence of cells growing in vitro.

Effects of steroid hormones in fetal bovine serum on plating ang cloning of human cells in vitro

Fetal bovine sera from each of three different commercial sources were tested for their ability to support cloning of human fibroblastoid cells in vitro. Cloning efficiencies varied according to serum source. Serum (10 samples) from company A did not support growth, while sera (10 samples) from companies B and C provided adequate to excellent conditions for cloning and growth. Cells from neonatal foreskin or embryonic lung responded to each serum similarly. Bovine serum albumin type H7 from company C supported cell growth in media without serum. Sera containing 1.0 ng per ml or more of progesterone inhibited growth, whereas sera containing less than 1.0 ng per ml supported cloning and growth. In the low progesterone sera, the concentration of 17-beta-estradiol exceeded 100 pg per ml. Growth supporting sera could be made non-supportive by adding 0.1 mug per ml of progesterone. The addition to non-supporative sera of 0.1 mug per ml of 17-beta-estradiol or hydrocortisone made these sera supportive of cell growth. Addition of estrogen or hydrocortisone to a culture medium that inhibits growth, with subsequent reversal of the inhibitory effect, implies that these hormones competitively regulate growth of responsive cells in vitro.