Growth of adult human cells in culture at clonal densities

A Low-Serum Culture System for Prolonged in Vitro Toxicology Experiments on a Macrophage System

Immunotoxicology sensu lato comprises not only toxicity toward immune cells, but also biological reactions from immune cells exposed to toxicants, reactions that may have deleterious effects at the organismal level. Within this wide frame, a specific case of interest is represented by the response of macrophages to particulate materials, with the epitome examples of asbestos and crystalline silica. For such toxicants that are both persistent and often encountered in an occupational setting, i.e. at low but repeated doses, there is a need for in vitro systems that can take into account these two parameters. Currently, most in vitro systems are used in an acute exposure mode, i.e., with a single dose and a readout made shortly if not immediately after exposure. We describe here how adequate changes of the culture methods applied to the murine macrophage cell line J774A.1 enable longer periods of culture (several days), which represents a first opportunity to address the persistence and dose-rate issues. To respond to this, the protocol uses a reduction in the concentration of the animal serum used for cell culture, as well as a switch from fetal to adult serum, which is less rich in proliferation factors. By doing so, we have considerably reduced cell proliferation, which is a problem with cell lines when they are supposed to represent slowly-dividing cells such as resident macrophages. We also succeeded in maintaining the differentiated functions of macrophages, such as phagocytosis or inflammatory responses, over the whole culture period. Furthermore, the presence of serum, even at low concentrations, provides excellent cell viability and keeps the presence of a protein corona on particulate materials, a feature that is known to strongly modulate their effects on cells and is lost in serum-free culture. Besides data showing the impact of these conditions on macrophages cell line cultures, illustrative examples are shown on silica- and cobalt-based pigments.

Chicken embryo extract mitigates growth and morphological changes in a spontaneously immortalized chicken embryo fibroblast cell line

The SC-1 spontaneously immortalized chicken embryo fibroblast (CEF) cell line has been established recently. Although this cell line had been in culture for over 3 yr, its growth rate has remained lower than that of primary CEF cells, and the morphology has not been as uniform as observed in primary cells. In the present study, the SC-1 cell line was treated with chicken embryo extract (CEE) to determine whether growth rates could be increased and cell morphology enhanced. The CEE also was tested on primary CEF cells, another spontaneously immortalized CEF cell line (DF-1), and on 2 other nonvirally and nonchemically immortalized CEF cell lines (BCEFi and HCEFi). Results indicated that concentrations of CEE > or = 100 microg/mL inhibited growth of all cells tested. However, addition of 50 microg of CEE/mL enhanced the growth rate and improved the morphology of the SC-1 cells. Addition of CEE to the other immortal or primary CEF cells did not increase the growth rate or change their morphology. Analysis of mRNA expression revealed that SC-1 cells treated with 50 microg of CEE/mL had lower levels of the p16(INK4a) alternate reading frame sequence (ARF) and E2F-1 than untreated SC-1 cells. The increased growth rate and improved morphology of the SC-1 cells achieved with CEE treatment were retained following removal of CEE, and these improvements should aid in increasing the utility of the SC-1 cell line as a cellular/molecular reagent.

Increased density of satellite cells in the absence of fibre degeneration in muscle of myotonic mice

A mutant mouse with a hereditary myotonia, 'arrested development of righting response', ADR, was investigated with respect to mononucleated cell populations in skeletal muscle. Upon enzymatic dissociation of different muscles from mice aged between 15 and 120 days, a 3- to 5-fold higher yield of mononucleated cells per muscle fresh weight was obtained from mice with the ADR syndrome than from control mice. Clonal cell culture showed that the absolute number of cells with myogenic potential was increased and that mutant clones had shorter generation times than wild-type controls. Morphological differentiation of ADR myotubes was indistinguishable from that of the controls. Light microscopy confirmed the presence of increased numbers of mononucleated cells per muscle volume. At the ultrastructural level, there were 3.3 times as many satellite cells (the myogenic stem cells of mature muscle) per myofibre nucleus in ADR than in controls. Because no fibre degeneration was observed in the ADR mutant, we conclude that the enlarged mutant satellite cell pool is not a result of compensatory proliferation but is a consequence of fibre-type transformation and/or delayed maturation of the myotonic muscle.

Decreased creatine kinase activity in cultured Duchenne dystrophic muscle cells

Muscle cells were cultured from six patients with Duchenne muscular dystrophy and nine normal subjects. Protein and myosin content and pyruvate kinase (PK) activity were similar in normal and Duchenne muscular dystrophy cultures. Creatine kinase (CK) activity was lower in Duchenne muscular dystrophy cultures and the isoenzyme distribution indicated MB-CK was significantly lower, while BB-CK was significantly higher in later Duchenne muscular dystrophy cultures. This abnormal isoenzyme pattern suggested aberrant or impaired maturation of Duchenne muscular dystrophy myotubes in vitro.

Tissue culture studies of muscle disorders: Part 1. Techniques, cell growth, morphology, cell surface

Tissue culture has been used extensively in studies of human inherited disorders, and its application in the field of the neuromuscular disorders has increased rapidly in recent years. This review, covering the period 1977 to 1984, deals with tissue culture studies of both human and animal muscle disorders, although Duchenne muscular dystrophy (DMD) figures prominently because of the overwhelming interest in that disorder. The review is in two parts. In the first part, I discuss technical innovations in the field, the morphology and growth of cells, and a variety of studies related to the cell surface. Important findings in relation to DMD include reports of abnormal growth rates and reduced lifespan of DMD cells, hypersensitivity to DNA-damaging agents, abnormal cell-to-cell and cell-to-substratum adhesion, and a more "fluid" cell membrane. However, these findings are controversial or have so far been reported only by single laboratories.

Oxidative metabolism of cultured human skeletal muscle cells in comparison with biopsy material

Human muscle cell cultures were examined for capacities to oxidize several substrates, and for activities of some enzymes related to intermediate metabolism. The results indicate that mitochondrial activities attained appreciable degrees of maturity. The specific activity of creatine kinase increased during myoblast fusion. In contrast, parameters of oxidative metabolism (palmitate and pyruvate oxidation, and cytochrome c oxidase and citrate synthase) did not significantly change throughout myogenesis and thereafter. In differentiated cells (myotubes) the oxidation capacities were pyruvate greater than 2-oxoglutarate greater than malate (+ acetylcarnitine) greater than malate (+ pyruvate), as in muscle biopsies. With regard to protein the cultured human muscle cells showed higher activities than the original biopsies (= 100%) with respect to citrate synthase (179%), but lower values for cytochrome c oxidase (50%) and creatine kinase (7%). Palmitate oxidation capacities were the same in both systems. The presence of antimycin and rotenon inhibited to a comparable extent the palmitate oxidation in cultured muscle and biopsies.

Transformation of human skeletal muscle cells by simian virus 40

Molecular studies of the biochemical alterations involved in human myopathies have been restricted because of the finite life-span and slow growth rate of cultures derived from primary tissue. Because the tumor virus simian virus 40 (SV40) can alter both the growth properties and longevity of human cells, we have infected skeletal muscle cultures derived from four biopsies with a small-plaque variant of SV40 and analyzed the biological and biochemical properties of cloned myoblast derivatives. At early times after infection, myoblasts fused normally into multinucleated myotubes, and both unfused and fused cells contained SV40 tumor antigen (T antigen). After six to eight subcultures after infection, the ability of myoblasts to fuse diminished, and clonal cell lines were generated with increased growth rates and saturation densities. Transformed cultures also lost contact inhibition of growth and became anchorage independent. Unlike untransformed myoblasts, SV40-transformed clones did not undergo an increase in creatine kinase activity or a transition of creatine kinase isoenzymes from the BB form to the muscle-specific MM form. Analysis of the pattern of SV40 DNA integration by Southern blotting hybridization analysis in two cloned SV40-transformed myoblast cell lines (KJ-SV40 and PK-SV40) indicated that KJ-SV40 contained at least one site of SV40 DNA integration into chromosomal DNA and PK-SV40 contained at least three sites of SV40 DNA covalently linked to cellular DNA. Cell lysates and growth medium from PK-SV40 transformants contained infectious small-plaque variant SV40, whereas KJ-SV40 did not contain or produce detectable virus. These studies demonstrate that human myoblasts can be immortalized by SV40. This procedure may prove useful for generating large quantities of genetically deficient human cells for biochemical and molecular analysis.

New approaches to the study of human dystrophic muscle cells in culture

Tissue culture provides a system for studying the growth and differentiation of muscle cells in a controlled environment. Several studies have been carried out on diseased muscle cells in culture in attempts to elucidate the aetiology of Duchenne muscular dystrophy (DMD) but the results were equivocal. Work in our laboratory in recent years has yielded an improved method for preparing primary muscle cell cultures from dissociated biopsies which permits the morphological and biochemical evaluation of these cultures at all stages of growth and development. Our results have shown abnormalities in cell behaviour, ultrastructure and creatine kinase synthesis. The background to these studies is reviewed. Recently we have developed a cell cloning procedure that allows the accumulation of a large number of cells from a single selected cell. We can with this technique monitor quantitative and qualitative cellular and cytochemical differences between individual cell types without the ambiguities inherent in the use of mixed cell populations. The results obtained with 4 different clonal preparations derived from dystrophic muscle have shown that a number of specific features were expressed by each of the 4 clones with respect to their growth pattern, ultrastructure, synthesis of muscle specific protein and cell surface antigen. These findings clearly illustrate the potential of these cloning procedures for studying the genetic expression of homogeneous cell populations derived from normal adult human muscle and patients with X-linked muscle disease.