In vivo migration of transplanted myoblasts requires matrix metalloproteinase activity

Tumour-cell invasion and migration: diversity and escape mechanisms

Cancer cells possess a broad spectrum of migration and invasion mechanisms. These include both individual and collective cell-migration strategies. Cancer therapeutics that are designed to target adhesion receptors or proteases have not proven to be effective in slowing tumour progression in clinical trials--this might be due to the fact that cancer cells can modify their migration mechanisms in response to different conditions. Learning more about the cellular and molecular basis of these different migration/invasion programmes will help us to understand how cancer cells disseminate and lead to new treatment strategies.

Migration of adult myogenic precursor cells as revealed by GFP/nLacZ labelling of mouse transplantation chimeras

We studied the migratory behaviour of adult muscle precursor cells in the mouse into and from skeletal muscle grafts using green fluorescent protein (GFP) and nuclear LacZ transgenes as complementary and double markers of the cell's origin. Owing to the small molecular mass and extreme solubility of GFP, this label provided a drastically increased sensitivity for detection compared with the markers that had been used previously. During the first six weeks after the operation, the graft/host border was well defined, with only occasional local intermingling and co-fusion of host and donor myogenic cells. Seven to eleven weeks after the operation we found that the host myogenic cells had migrated into the graft, and graft myogenic cells had migrated into the adjacent host muscle, with integration of donor nuclei into pre-existing myotubes or muscle fibres. There was no indication of an origin of, or target for, these myogenic cells besides neighbouring muscles. Our observations indicate migration of these cells through solid muscle tissue, over a distance of several millimetres. The migratory activity of adult myogenic precursor cells can be stimulated by traumatic events in either the target muscle or the muscle of origin.

Growth factor stimulation of matrix metalloproteinase expression and myoblast migration and invasion in vitro

We investigated the role of growth factors and fibronectin on matrix metalloproteinase (MMP) expression and on migration and invasion of mouse skeletal myoblasts in vitro. None of the growth factors tested significantly affected MMP-1 or MMP-2 activity as revealed by gelatin zymography, but both basic FGF (bFGF) and tumor necrosis factor (TNF)-alpha significantly increased MMP-9 activity (10- and 30-fold, respectively). The increase in secreted MMP-9 activity with TNF-alpha stimulation was due at least in part to an increase in MMP-9 gene transcription, because an MMP-9 promoter construct was approximately fivefold more active in TNF-alpha-treated myoblasts than in control myoblasts, as well as an increase in MMP-9 proteolytic activation. However, whereas fibronectin, bFGF, hepatocyte growth factor, and TGF-beta1 significantly augmented migration of mouse myoblasts, TNF-alpha did not, nor did PDGF-BB or IGF-I. Fibronectin and bFGF also significantly augmented invasion of myoblasts across a Matrigel barrier, and plasmin cotreatment potentiated whereas N-acetyl cysteine suppressed the effects of bFGF and fibronectin on myoblast migration and invasion. Finally, transient transfection with an MMP-9 overexpression construct had only minimal effects on myoblast migration/invasion, whereas overexpression of either MMP-2 or MMP-1 significantly augmented myoblast migration and invasion. These observations support the hypothesis that MMP activity is a necessary component of growth factor-mediated myoblast migration but suggest that other consequences of growth factor signaling are also necessary for migration to occur.

Soluble glucocorticoid-induced tumor necrosis factor receptor (sGITR) increased MMP-9 activity in murine macrophage

Glucocorticoid induced tumor necrosis factor receptor (GITR), a new TNFR family, increased production of matrix matalloproteinase (MMP-9) in murine macrophages. Murine macrophages produced a band of gelatinolytic activity at 100 kDa when stimulated for 18 h with soluble GITR. MMP-9 was identified by gelatin zymography and Western blot. Previous results demonstrated that murine macrophages express GITR and GITR ligand constitutively. Induction of MMP-9 was synergistic with co-treatment of INF-gamma. MMPs could play a critical role in progression and promotion of tissue injury after inflammation stimulated by GITR/ligand system.

Mitotic activity of rat muscle satellite cells in response to serum stimulation: relation with cellular metabolism

Cellular and molecular adaptations of satellite cells isolated from rat hindlimb muscles (n = 10) were investigated in response to serum stimulation. Flow cytometry analysis of the amounts of DNA and RNA indicated that 97.7 +/- 0.7% of satellite cells were in G0 at the end of the isolation procedure, whereas 93.2 +/- 2.0% of cells were cycling after serum exposure. The length of cell division was 34.0 +/- 2.8 h. Myoblast proliferation was asynchronous, suggesting the existence of heterogeneous cell populations in skeletal muscle. Myoblast proliferation was also accompanied by a significant increase in c-met expression, and major adaptations of energetic and proteolytic metabolisms, including an increase in the relative contribution of glycolytic metabolism for energy production, an increase in proteasome and matrix metalloproteinases 2 and 9 activities, and a decrease in plasminogen activator activities. Our data suggest that, along with molecular adaptations leading to cell cycle activation itself, adaptations in energetic and proteolytic metabolisms are crucial events involved in satellite cell activation and myoblast proliferation.

Endothelin-1 is a potent stimulator of alpha1beta1 integrin-mediated collagen matrix remodeling by rat mesangial cells

Endothelin-1 (ET) is known to stimulate mesangial cell (MC) proliferation, extracellular matrix (ECM) synthesis, and thereby contribute to the progression of glomerulonephritis (GN). To clarify the molecular and cellular mechanisms of how ET is involved in the development of glomerular sclerosis, we investigated the influence of ET on the MC-alpha1beta1 integrin-mediated collagen matrix reorganization using a collagen gel contraction assay. ET enhanced MC-alpha1beta1 integrin-mediated gel contraction in a dose-dependent manner. Addition of the endothelin A (ETA) receptor antagonist, BQ123, into collagen gels abolished ET-induced gel contraction by MC. Cell behavior involved in ET-induced gel contraction was investigated in combination with function-blocking anti-alpha1-integrin antibody. Migration and adhesion assays revealed that ET stimulated alpha1beta1 integrin-mediated MC migration but did not influence cell adhesion to type I collagen (collagen I). Integrin-function blocking studies using anti-alpha1 integrin antibody indicated that MC-alpha1beta1 integrin is required not only for collagen-dependent migration, but also for gel contraction. Zymography showed that ET increased MC matrix metalloproteinase-2 (MMP-2) activity in a dose-dependent manner during MC-induced gel contraction process. Finally, flow cytometry analysis indicated that ET did not affect the cell surface expression of the MC-alpha1beta1 integrin within the collagen gel. These data suggested that ET promotes collagen matrix reorganization through the enhancement of MC-alpha1beta1 integrin-dependent migration and MMP-2 activity. We therefore conclude that ET is a potential molecule inducing pathological collagen matrix remodeling observed in progressive GN.

In vitro migration of melanoblasts requires matrix metalloproteinase-2: implications to vitiligo therapy by photochemotherapy

It is known that the migration of melanocyte precursors (melanoblasts) from the outer root sheath of hair follicles into clinically depigmented epidermis is crucial to the repigmentation of vitiliginous skin treated with photochemotherapy (PUVA), but such migratory cells must penetrate extracellular matrix tissue barriers in vivo. To test the hypothesis that matrix metalloproteinases (MMPs) are required for this process, we determined whether cultured melb-a cells, an immortal line of melanoblasts isolated from neonatal mouse epidermis, express and secrete MMPs and whether a synthetic metalloproteinase inhibitor, GM6001 (Galardin), inhibits their migratory behavior in vitro. Reverse transcriptase-polymerase chain reaction and Western blotting were used to determine the patterns of MMP expression by melanoblasts at the mRNA and protein levels, respectively. The proteolytic activities of MMPs secreted into the culture medium were assessed by gelatin zymography. The capacity of melanoblasts to migrate on fibronectin, laminin or laminin-5 substrates was estimated using Transwell migration assays. The results show that MMP2, MMP9 and MT1-MMP transcripts are expressed by these melanoblasts, but only MMP2 is secreted and activated in the extracellular environment. Although the therapeutic efficacy of PUVA in stimulating repigmentation of vitiliginous skin might derive from direct effects of UVA and/or 8-methoxypsoralen (8MOP), recent studies have shown that keratinocyte-derived factors induced by ultraviolet radiation, especially alpha-melanocyte stimulating hormone (alpha MSH), play a major role in regulating melanocyte function. Therefore, we also examined whether 8MOP and/or alphaMSH are involved in the up-regulation of MMP2 expression in melanoblasts. Western blotting and zymographic analyses revealed that MMP2 synthesis and secretion were induced by 8MOP and/or by alpha MSH. This induction of MMP2 resulted in significant increases of migration by melanoblasts on laminin or on laminin-5 substrates, while concomitant treatment with GM6001 blocked that induced migration. Taken together, these results suggest the importance of MMP2 in melanoblast migration and in the response to PUVA therapy.

Myogenic cell proliferation and generation of a reversible tumorigenic phenotype are triggered by preirradiation of the recipient site

Environmental influences have profound yet reversible effects on the behavior of resident cells. Earlier data have indicated that the amount of muscle formed from implanted myogenic cells is greatly augmented by prior irradiation (18 Gy) of the host mouse muscle. Here we confirm this phenomenon, showing that it varies between host mouse strains. However, it is unclear whether it is due to secretion of proliferative factors or reduction of antiproliferative agents. To investigate this further, we have exploited the observation that the immortal myogenic C2 C12 cell line forms tumors far more rapidly in irradiated than in nonirradiated host muscle. We show that the effect of preirradiation on tumor formation is persistent and dose dependent. However, C2 C12 cells are not irreversibly compelled to form undifferentiated tumor cells by the irradiated muscle environment and are still capable of forming large amounts of muscle when reimplanted into a nonirradiated muscle. In a clonal analysis of this effect, we discovered that C2 C12 cells have a bimodal propensity to form tumors; some clones form no tumors even after extensive periods in irradiated graft sites, whereas others rapidly form extensive tumors. This illustrates the subtle interplay between the phenotype of implanted cells and the factors in the muscle environment.

Efficacy of myoblast transplantation in nonhuman primates following simple intramuscular cell injections: toward defining strategies applicable to humans

Nonhuman primates were used to define myoblast transplantation strategies applicable to humans. Nevertheless, previous experiments were based on the use of myotoxins concomitant with the myoblast injections. Since myotoxins must be avoided for clinical applications, we analyzed the efficacy of simple myoblast injections (i.e., myoblasts resuspended only in saline) into monkey muscles. We also evaluated different FK506 dosages (in combination or not with mycophenolate mofetil) for immunosuppression. Allogeneic myoblasts transduced with the beta-galactosidase (beta-Gal) gene were implanted in the muscles of 19 monkeys by injections placed 1 to 2 mm from each other. A biopsy was performed at the implanted sites 1 month later, and histologically studied for demonstration of beta-Gal+ myofibers, lymphocyte infiltration, and CD8+ cells. The presence of antibodies against the donor myoblasts and the blood levels of FK506 were analyzed. Our results show that: (1) If myoblast injections are sufficiently close to each other, high percentages of hybrid myofibers can be obtained following myoblast transplantation in primates (25 to 67% with an interinjection distance of 1 mm). (2) Efficient immunosuppression can be reached by increasing FK506 dosages, but also by combining this drug with mycophenolate mofetil, a combination that reduces toxic effects. The present results represent a step towards a better designing of myoblast transplantation strategies in humans.

The extracellular matrix of muscle--implications for manipulation of the craniofacial musculature

Successful adaptation of craniofacial skeletal muscle is dependent upon the connective tissue component of the muscle. This is exemplified by procedures such as distraction histo/osteogenesis. The mechanisms underlying remodelling of intramuscular connective tissue are complex and multifactorial and involve extracellular matrix (ECM) molecules, receptors for the ECM (integrins) and enzymes that remodel the ECM (MMPs). This review discusses the current state of knowledge and clinical implications of connective tissue biology as applied to craniofacial skeletal muscle.

Absence of MyoD increases donor myoblast migration into host muscle

Donor myoblast migration is a major limiting factor in the success of myoblast transfer therapy, a potential treatment for Duchenne muscular dystrophy. A possible strategy to promote the migration of donor myoblasts into host muscle is to enhance their proliferation and delay their fusion, two properties that are major characteristics of myoblasts in regenerating skeletal muscle in MyoD null (-/-) mice. Here we investigate whether the migration of MyoD (-/-) donor myoblasts into host muscle is enhanced in vivo. Sliced muscle grafts from male MyoD (-/-) or normal control (Balb/c) mice were transplanted into the muscles of female normal (Balb/c) host mice. Muscles were sampled at 1, 3, and 12 weeks after grafting, and the fate of male donor myoblasts within female host muscles determined by in situ hybridization with the mouse Y-chromosome-specific Y-1 probe. MyoD (-/-) donor myoblasts migrated into host muscle continuously over 1, 3, and 12 weeks after grafting, in contrast with Balb/c donor myoblasts, whose overall numbers and migratory distances did not increase significantly after 1 week. These results strongly support a role for elevated donor myoblast proliferation and/or their delayed fusion in enhancing migration into host muscle in vivo, and endorse the use of either genetically engineered donor myoblasts, or the administration of exogenous myoblast mitogens to improve donor myoblast migration in myoblast transfer therapy.

Unusual laminin alpha2 processing in myoblasts from a patient with a novel variant of congenital muscular dystrophy

We recently described a novel congenital muscular dystrophy (CMD) syndrome characterized by mental retardation, microcephaly, and partial merosin deficiency on muscle biopsy. Linkage analysis excluded involvement of the known CMD loci. We now report on a study performed on the differentiation of cultured myoblasts from one patient affected by this condition to evaluate the potential to form myotubes and merosin processing in these cells. The differentiation rate was comparable to controls and myotubes were stable in culture. Biochemical analysis showed the expected 80-kDa merosin subunit in myoblasts. However, a shifted 60-kDa protein was detected in myotubes. Matrix-metalloproteinases (MMPs) zymography showed increased gelatinolytic activity, and immunoblotting identified an increased amount of membrane-type 1 matrix-metalloproteinase in pathological myotube preparations. Our results show that these CMD-derived myotubes contain a low molecular weight merosin. They further suggest that an altered regulation of MMPs can be involved in basal lamina damage.