Improved media for normal human muscle satellite cells: serum-free clonal growth and enhanced growth with low serum

Angiotensin and bradykinin metabolism by peptidases identified in cultured human skeletal muscle myocytes and fibroblasts

Angiotensin (ANG) and kinin metabolizing enzymes, angiotensin-converting enzyme (ACE; EC 3.4.15.1), neutral endopeptidase-24.11 (NEP-24.11; EC 3.4.24.11), and aminopeptidase M (AmM; EC 3.4.11.2), have recently been identified in a purified skeletal muscle glycoprotein fraction. We have analyzed the cellular localization of these enzymes. In cultured human skeletal muscle adult myoblasts, myotubes, and fibroblasts, kinins and angiotensins were metabolized by NEP-24.11 and AmM but not by ACE. NEP-24.11 degraded ANG II, ANG III. and bradykinin (BK) and converted ANG I to the active metabolite ANG(1-7). ANG III was converted to the novel ANG IV metabolite [des-Arg1]ANG III by AmM. These data suggest that, due to their abundance in the body, skeletal muscle myocytes and fibroblasts may play a major role in modulation of the systemic and local effects of angiotensins and kinins. This role could be particularly important in individuals receiving treatment with ACE inhibitors.

Lymphocyte infiltration following allo- and xenomyoblast transplantation in mdx mice

Human and mouse (C57BL/10SnJ+/+) myoblasts were injected separately in the muscles of C57BL/10ScSn mdx/mdx mice. Mouse myoblasts (C57BL/10SnJ+/+) were also injected in normal mice (C57BL/10SnJ+/+ and BALB/c+/+). Some muscles that received a xenotransplantation (i.e., human myoblasts) were previously injected with a myotoxin, i.e., notexin. This treatment was not used for the allografts (i.e., mouse myoblasts). Human myoblast injections did not increase the number of dystrophin-positive cells above the background level due to backmutation. Moreover, the human myoblasts detected with an anti-HLA antibody decreased rapidly during the 6-week follow-up. The injection of normal mouse myoblasts in mdx mice did, however, increase the number of dystrophin-positive fibers. Moreover, numerous cells expressing mouse MHC class II, macrophages, granulocytes, neutrophils, natural killer cells, and a subset of T lymphocytes were detected by immunohistochemistry in cryostat sections of myoblast-injected muscles. These cells were present within 1 week of the myoblast injection in the muscle regions containing injected human or mouse myoblasts, and progressively decreased during the 6-week follow-up in the human myoblast transplantation. Lymphocyte infiltration reached a significant level following xeno- and alloincompatible transplantations. Antibodies against the human myoblasts and against alloincompatible myoblasts were also detected in the serum of the recipients. These results suggest that humoral and cellular immune reactions are responsible for the poor outcome of myoblast transplantation in mice and could be involved in failure of transplantation in Duchenne muscular dystrophy patients. These results indicate that adequate immunosuppression must be used in these patients.

The regulation of alpha 5 beta 1 integrin expression in human muscle cells

The expression of alpha 5 beta 1 integrin was examined in either cloned or fluorescence-activated cell-sorted satellite cells derived from human biceps muscle. Removal of serum and factors required for muscle cell growth and proliferation both induced terminal differentiation and resulted in a coordinate downregulation of mRNA transcripts encoding alpha 5 and beta 1 integrin subunits. A corresponding downregulation of the alpha 5 subunit occurred at the protein level. Treatment of cultures with 5-bromo-2'-deoxyuridine (BUdR), a thymidine analog which inhibits muscle cell differentiation, resulted in increased expression of alpha 5 integrin subunit at both the mRNA and protein levels. However, levels of alpha 5 subunit message and protein were still markedly downregulated on removal of serum and growth factors from BUdR-treated cultures, indicating that downregulation of alpha 5 beta 1 integrin during myogenesis does not require and is not a consequence of muscle cell terminal differentiation. Downregulation of alpha 5 integrin subunit expression could be prevented by maintenance of cells in medium supplemented with serum and growth factors, although no single defined component of this medium could on its own prevent the downregulation of alpha 5 integrin subunit expression. Collectively, these results suggest that downregulation of alpha 5 beta 1 integrin expression is not a consequence of muscle cell terminal differentiation, but is dependent on a combination of exogenous growth factors which are also required for muscle cell growth and proliferation.

High efficiency of muscle regeneration after human myoblast clone transplantation in SCID mice

SCID mouse tibialis anterior muscles were first irradiated to prevent regeneration by host myoblasts and injected with notexin to damage the muscle fibers and trigger regeneration. The muscles were then injected with roughly 5 million human myoblasts. 1 mo later, 16-33% of the normal number of muscle fibers were present in the injected muscle, because of incomplete regeneration. However, > 90% of these muscle fibers contained human dystrophin. Some newly formed muscle fibers had an accumulation of human dystrophin and desmin on a part of their membrane. Such accumulations have been demonstrated at neuromuscular junctions before suggesting that the new muscle fibers are innervated and functional. The same pool of clones of human myoblasts produced only < or = 4% of muscle fibers containing human dystrophin when injected in nude mice muscles. Several of the human myoblasts did not fuse and remained in interstitial space or tightly associated with muscle fibers suggesting that some of them have formed satellite cells. Moreover, cultures of 98% pure human myoblasts were obtained from transplanted SCID muscles. In some mice where the muscle regeneration was not complete, the muscle fibers containing human dystrophin also expressed uniformly HLA class 1, confirming that the fibers are of human origin. The presence of hybrid muscle fibers containing human dystrophin and mouse MHC was also demonstrated following transplantation. These results establish that in absence of an immune reaction, transplanted human myoblasts participate to the muscle regeneration with a high degree of efficacy even if the animals were killed only 1 mo after the transplantation.

Human myoblast transplantation in immunodeficient and immunosuppressed mice: evidence of rejection

Normal human myoblasts were cloned and transplanted in the tibialis anterior of immunodeficient nude and SCID mice and in mdx mice under different immunosuppressive treatments (cyclosporine A, CsA; antilymphocyte serum, ALS) or not immunosuppressed. This permitted us to show the interaction of the immune system in the myoblast transplantation. The graft success was assessed by verifying signs of humoral and cellular immune reactions and the presence of dystrophin produced by the fusion of the donor myoblasts. This study showed that clones of human myoblasts were able to fuse and produce dystrophin in injected muscles of immunodeficient mice and mdx mice receiving an effective immunosuppressive treatment (i.e., ALS+CsA). However, the same pool of human myoblasts injected in mdx mice inadequately immunosuppressed (i.e., CsA alone or ALS alone) triggered an immune reaction and was rejected. Cells expressing CD4 and CD8 antigens were observed in the injected muscles of mice treated with CsA alone. Therefore, evidence of humoral and cellular rejection was observed following human myoblasts transplantation.

Utilization of an antibody specific for human dystrophin to follow myoblast transplantation in nude mice

Human myoblasts were transplanted in nude mice. The efficacy of these transplantations was analyzed using a monoclonal antibody (NCLDys3) specific for human dystrophin. This antibody did not reveal any dystrophin in nude mice that did not receive a human myoblast transplantation. However, about 30 days after a human myoblast transplantation, dystrophin-positive muscle fibers were observed. They were not abundant, and were present either in small clusters or isolated. This technique follows the fate of myoblast transplantation in animals that already have dystrophin, and distinguishes between new dystrophin-positive fibers due to the transplantation and the revertant fibers in mdx mice. Moreover, this technique does not require any labelling of the myoblasts before transplantation. It can also be used to detect dystrophin produced following the fusion of myoblasts transfected with the human dystrophin gene.

Results of a triple blind clinical study of myoblast transplantations without immunosuppressive treatment in young boys with Duchenne muscular dystrophy

The effects of myoblast transplantations without an immunosuppressive treatment on muscle strength, and the formation of dystrophin-positive fibers was studied in five young boys with Duchenne muscular dystrophy (DMD) using a triple blind design. Injections of myoblasts were made into one biceps brachii (BB), and the opposite BB, used as a control, was sham-injected; the experimenters and the patient were blind to the myoblast-injected side. At the same time, myoblasts were also injected in the left tibialis anterior (TA) of these patients. The strength developed during maximal static contractions of the elbow flexor and extensor muscles was measured with a Kin-Com dynamometer. No increase in static elbow flexion torque was measured at any time from 2 mo up to 18 mo after the transplantation. One month after the transplantation, the percentage of dystrophin-positive fibers in the myoblast-injected TA ranged from 0 to 36%, while it ranged from 0 to 4% on the control side. The expression of dystrophin in these fibers, however, was generally low, and most likely less than 10% of the normal level. In the biceps brachii of both sides 6 mo after the transplantation, less than 1.5% of dystrophin-positive fibers were detected. The injections also triggered a humoral immune response of the host. Antibodies were capable of fixing the complement, and of lysing the newly formed myotubes. One of the antigens recognized by this immune response is possibly dystrophin. These results strongly suggest that myoblast transplantations, as well as gene therapy for DMD, cannot be done without immunosuppression.

Growth of normal human ovarian surface epithelial cells in reduced-serum and serum-free media

The human ovarian surface epithelium (OSE) is believed responsible for over 85% of ovarian cancers, yet little is known about the normal biology of these cells. To date, culture of OSE has only been reported in media with high serum supplements. We have developed two media, one with less than 1% of serum (OSEM-1) and the other comprised of highly purified and defined materials (OSEM-2), which allow us to study OSE under relatively defined conditions. By substituting 0.05% of Pedersen's fetuin for 15% fetal bovine serum (FBS) with Medium 199/MCDB105 basal medium, the cell numbers reached 50 to 60% of those in the presence of 15% FBS over 7 days. However, over several weeks, the total number of population doublings achieved were comparable to those in 15% FBS. Addition of insulin, transferrin, ethanolamine, lipoic acid, and phosphatidylcholine to the medium with Pedersen's fetuin (OSEM-1) enhanced growth up to 20% more than in their absence. Supplementation of M199/105 with highly purified (> 99%) fetuin, alpha 2-macroglobulin, and hydrocortisone resulted in a defined medium (OSEM-2) that permitted 1 to 2 doublings/7 days. In addition, cells maintained a more normal, epithelial-like morphology in culture for a longer period in the presence of Pedersen's or purified fetuin than in M199/105/15% FBS, thus increasing the number of morphologically normal cells available for experimentation. Addition of 0.05% Pedersen's fetuin to M199/105 in the presence of 6 to 8% FBS resulted in levels of growth equivalent to those in M199/105/15% FBS alone. We are now able to study the effects of various compounds on the growth and differentiation of OSE under defined conditions, and have reduced the requirement for FBS to produce large numbers of OSE cells.

Notechis scutatus venom increases the yield of proliferating muscle cells from biopsies of normal and dystrophic canine muscle--a possible source for myoblast transfer studies

The injection of 1 micrograms Notechis scutatus (Australian tiger snake) venom (notexin) induces localized necrosis in the muscles of normal and dystrophic dogs. Biopsies taken from the muscles on the second day of postnecrotic regeneration provide about 8-16 x 10(6) cells capable of proliferation per g tissue, about 100 fold more than the untreated adult dog muscles. Muscle specific markers, such as the capacity of the cells to fuse, surface labelling with N-CAM antibodies (Leu-19 and 5.1.H11), and immunostaining with desmin, indicated that over 90% of the cultivated cells are indeed myogenic. The method is a safe and cost effective way to generate large amounts of proliferating muscle cells from biopsies of adult animals, which could provide a useful step in the therapeutic efforts in inherited muscle diseases by the implantation of normal myoblasts or genetically corrected myoblasts.

Fetuin: its enigmatic property of growth promotion

A variety of cell types in culture respond to fetuin, a glycoprotein from fetal bovine serum, which is often an important supplement to many serum-free media. Bovine fetuin preparation has been shown to inhibit trypsin activity and promote cellular attachment, growth, and differentiation in many different culture systems. In addition, fetuin associates with various growth factors or growth-promoting substances. However, whether the growth-promoting activity of fetuin preparation is due to fetuin per se or to its minor contaminant(s) has been a long-standing puzzle. The present review surveys the literature concerning this enigmatic property of fetuin and summarizes three possibilities: 1) fetuin itself is active, although the majority of studies do not support this; 2) various contaminants of fetuin preparations, including potentially unidentified ones, are responsible for the activity, a possibility supported by numerous reports; and 3) one of the fetuin subspecies, one of its contaminants, or a combination of both of these is responsible for growth of a specific cell type. In addition, the basic physicochemical properties and other biological functions of fetuin have also been presented.

Improved medium with EGF and BSA for differentiated human skeletal muscle cells

Epidermal growth factor (EGF) and bovine serum albumin (BSA) are both required for serum-free clonal growth of human muscle satellite cells (HMSC). However, neither inhibits differentiation of HMSC, and when both are added to a minimal serum-free differentiation medium, they enhance survival and maintenance of human myotubes. A combination of 10 ng/mL EGF and 0.5 mg/mL BSA, added to MCDB 120 plus 10 micrograms/mL insulin, increases both total protein per dish and total creatine kinase activity, and keeps the myotubes in good condition for a longer period of time. The myotubes become cross-striated and exhibit frequent spontaneous twitching. Substantial amounts of neonatal myosin heavy chain and the MM isozyme of creatine kinase are expressed, together with detectable amounts of adult fast myosin heavy chain. With regular feeding, these cultures can be maintained for at least 3 weeks with no overgrowth by mononucleate cells, and with far less degeneration than with insulin as the only supplement.

Human myoblast transplantation: preliminary results of 4 cases

Myoblasts from immunocompatible donors have been transplanted into the muscles (tibialis anterior, biceps brachii, and/or extensor carpi radialis longus) of 4 Duchenne patients in the advanced stages of the disease. Although no immunosuppressive treatment was used, none of the patients showed any clinical signs of rejection such as fever, redness, and inflammation. One patient transiently produced antibodies against the donor myoblasts as determined by cytofluorometric analysis. This patient and 2 others were shown to form antibodies against their donor's myotubes. Muscle biopsies of the injected tibialis anterior of 4 patients revealed that 80%, 75%, 25%, and 0% of the muscle fibers, respectively, showed some degree of dystrophin immunostaining. The contralateral noninjected muscles of the latter 3 patients did not contain any dystrophin positive fibers, while that of the first patient showed dystrophin expression in 16% of the fibers examined. Myoblasts were also injected into the extensor carpi radialis longus or the biceps brachii of these patients. A few months subsequent to injection, one patient was shown to have a 143% increase of strength during static wrist extension. This result must be interpreted with caution because a double-blind strength-measuring protocol was not used. Furthermore, we have noted that this change slowly decayed over time. The strength of 2 other patients was increased less remarkably (41% and 51%), while the strength of the fourth patient was unchanged.

Primary cultures of normal rat kidney proximal tubule epithelial cells for studies of renal cell injury

Normal rat kidney proximal tubule epithelial cell cultures were obtained by collagenase digestion of cortex and studied for 10 days. To assess the purity of the seeding suspension, we histochemically demonstrated gamma-glutamyltranspeptidase in greater than 95% of the starting material. To identify cell types in cultures, we investigated several markers. Cells stained positively for lectin Arachis hypogaea (rat proximal tubule) and negatively for Lotus tetragonolobus (rat distal tubule). Intermediate filament expression of cytokeratin confirmed the epithelial differentiation of the cultured cells. Using indirect immunofluorescence, we found that cultures were negative for vimentin and Factor VIII. Cells exhibited activities of two brush border enzymes, gamma-glutamyltranspeptidase and leucine aminopeptidase, and Na(+)-dependent glucose transport activity. Multicellular domes were evident in the Week 2 of culture. Proliferation was studied by comparing growth factor-supplemented serum-free medium to cells grown in serum; growth enhancers included insulin, hydrocortisone, transferrin, glucose, bovine albumin, and epidermal growth factor. Cells proliferate best in medium with 5 or 10% serum and in serum-free medium supplemented with insulin, hydrocortisone, transferrin, glucose, and bovine albumin. Proliferation was assessed by determining cell number (population doublings). By light microscopy, the cells were squamous with numerous mitochondria, a central nucleus, and a rather well-defined homogeneous ectoplasm. By electron microscopy, the cells were polarized with microvilli and cell junctions at the upper surface and a thin basal lamina toward the culture dish. These data show that the proximal tubule epithelial cells retain a number of functional characteristics and that they represent an excellent model for studies of normal and abnormal biology of the renal proximal tubule epithelium.

Separation of growth-promoting activity for human muscle cells from fetuin

Whether the growth-promoting activity of Pedersen fetuin is due to fetuin itself or to a contaminant(s) has been a long-standing puzzle. The possibility that the growth-promoting activity of Pedersen fetuin for human muscle satellite cells (HMSC) could be caused by some other component of fetal bovine serum (FBS) that remained in the fetuin as a contaminant has been investigated. One liter of FBS was first precipitated with 50% saturated ammonium sulfate, which leaves the serum albumin in solution, and then with 25% polyethylene glycol, which leaves the fetuin in solution, to generate a fraction 50 PEG 2x that was enriched 11-fold in growth-promoting activity for HMSC, with 68% recovery of total activity. Further purification with FPLC anion exchange chromatography achieved 99-fold enrichment of the activity with 30% overall recovery. The activity is heat labile and pH sensitive, suggesting that it is of protein nature, and the size of the activity is above 70 kDa. SDS-PAGE of the most active fractions shows that they are virtually free of fetuin. Thus, although the active fractions are not homogeneous, these studies demonstrate that the growth-promoting activity for HMSC can be fully separated from fetuin.

In vitro development of precursor cells in the myogenic lineage

Expression of the muscle-specific integral membrane protein H36 and the intermediate filament protein desmin, detected by immunofluorescence, was used to identify cells at distinct stages in the skeletal myogenic lineage. These proteins were coordinately expressed in cultures of rat hindlimb myoblasts from 17- and 19-day fetuses and newborn pups, and in satellite cells from juveniles. Both H36+ and desmin+ cells were present in cultures from 13.5- and 15-day embryonic hindlimbs, but desmin expression was more prevalent: H36-/desmin+ myoblasts predominate during this early stage of development. H36 was not detected in Day 12 embryo hindlimb bud cells in vivo nor in cultures soon after plating. Initially, only 1% of the Day 12 limb bud cells expressed desmin. When these cells were serially passaged every 3-4 days, cells with all three possible myogenic phenotypes developed: that is, H36+/desmin-, H36+/desmin+, and H36-/desmin+ cells. There was a progressive increase in the frequency of H36+ cells, with 75% of cells positive by passage 6 (Day 27 in vitro). The maximum frequency of cells that expressed desmin occurred in passage 5 (Day 23 in vitro). These results demonstrate that precursors to the cells that express H36 and desmin are present in the 12-day embryo hindlimb bud and that the transition from H36-/desmin- precursors to cells with a myogenic phenotype can occur in vitro. MyoD1 and myogenin were not detected in these cells, suggesting that the initial expression of H36 and desmin in the myogenic lineage may precede and/or is independent of these regulatory proteins. The conversion of precursor cells in the 12-day limb bud to a more advanced stage of development serves to define additional cells in the myogenic lineage. The ability to monitor in vitro these stages of development affords the opportunity to study how they are regulated.

Selective growth and serial passage of mouse melanocytes from neonatal epidermis in a medium supplemented with bovine pituitary extract

Suspensions of disaggregated epidermal cells from skins of newborn C57BL/10JHir mice were plated in a growth medium that consisted of Ham's F-10 plus bovine pituitary extract (BPE), insulin, and transferrin. Fetal bovine serum (FBS) was added to the culture medium at a concentration of 4% at the time of plating. On the second day of culture, a small number of melanocytes was randomly distributed among large sheets of keratinocytes. From the third day onward, FBS was excluded from the culture medium to prevent the proliferation of keratinocytes and fibroblasts. The melanocytes began to grow preferentially, and after 12 days pure and enriched populations of melanocytes could be harvested. In the absence of the proliferation of keratinocytes and fibroblasts, melanocytes could be serially passaged in the growth medium supplemented with a conditioned medium (CM) prepared from keratinocyte-enriched cultures, namely, those at the early stages of the primary culture. FBS was added at a concentration of 1% for the first day. These results suggest that both BPE and keratinocyte CM contain growth factors required for proliferation of melanocytes.

Human myoblast transplantation: a simple assay for tumorigenicity

A simple assay for tumorigenicity of myoblasts to be transplanted to Duchenne patients has been developed. The assay is based on culture in a soft agar medium for 2-3 weeks. The tumor cell line forms large cell clusters while the normal myoblasts do not proliferate and remain isolated.

Methylprednisolone increases dystrophin levels by inhibiting myotube death during myogenesis of normal human muscle in vitro

The glucocorticoid methylprednisolone (Mepd) increased dystrophin and myosin heavy chain levels in differentiated cultures of cloned human myoblasts. Mepd increased the number of myotubes per area by preventing myotube death and detachment during myogenesis in vitro. Myotube death was the result of an endogenous process initiated early during myoblast fusion. It occurred between days 4 and 5 of differentiation (3 days after its initiation) and was inhibited by cycloheximide, indicating that a programmed death mechanism may be involved. Inhibition of myotube death accounted for the increased levels of muscle-specific proteins; the amount of dystrophin per myonucleus was the same with or without Mepd treatment. These effects of glucocorticoids on primary muscle cultures may bear on the recent observation that prednisone transiently enhances muscle function in Duchenne muscular dystrophy.

Expression of muscle-specific isozymes of phosphorylase and creatine kinase in human muscle fibers cultured aneurally in serum-free, hormonally/chemically enriched medium

Primary cultures of muscle cells derived from a biopsied adult human skeletal muscle were grown up to 6 weeks in a hormonally/chemically enriched serum-free medium. The expression of muscle-specific isozymes of creatine kinase, glycogen phosphorylase, and phosphoglycerate mutase, indicative of muscle cell maturation, was studied after 1, 4 and 6 weeks of growth. The maturation of muscle fibers cultured in serum-free medium was comparable to that achieved by muscle fibers cultured in medium containing 10% serum and supplemented with growth factors (insulin, epidermal growth factor, and fibroblastic growth factor) and was greater than that achieved in medium containing 10% serum only. Our study demonstrates that adult human muscle can be cultured aneurally for a long period of time in a serum-free medium, and that it can achieve a high degree of maturation. This study provides an important basis for investigations related to: (1) assessment of the influence of individual components of the medium on human muscle maturation in culture; (2) studies of regulation of abnormal gene expression in diseased human muscle cultured in serum-fre medium.

Effects of medium and substratum on ovine satellite cell attachment, proliferation and differentiation in vitro

The ability of ovine-derived satellite cells to attach, proliferate and differentiate in response to seven horse serum-supplemented media and eleven substrata was evaluated in vitro. Satellite cells attached equally well when exposed to CRCM-30, Medium-199 and high glucose Dulbecco's modified Eagles medium (DMEM, P less than 0.05). Proliferation of satellite cells was greatest using McCoy's 5A, supplemented with 15% horse serum (P less than 0.05), and differentiation was most efficient with low glucose DMEM, supplemented with 1% horse serum (P less than 0.05). Pig-skin gelatin facilitated the greatest ovine satellite cell proliferative and differentiative responses when compared to the performance of ten other substrata (P less than 0.05). Further, 0.5 mg/16 mm2-well pig-skin gelatin appeared to be the optimum concentration of substratum for expression of satellite cell growth characteristics. Thus, consideration must be given to the processes of attachment and proliferation in experiments attempting to maximize satellite cell differentiation in vitro.