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R C Strohman

Publications and source records attributed to R C Strohman.

At least 19 recordsLinked to original sources
PubMed1998

Muscle satellite cells from dystrophic (mdx) mice have elevated levels of heparan sulphate proteoglycan receptors for fibroblast growth factor.

Skeletal muscle has the remarkable capacity to regenerate new muscle fibres in the event of injury or disease. This capacity lies in the satellite cells, which are myogenic stem cells residing in adult muscle. While the signals that activate satellite cells to divide in vivo are not fully understood, satellite cells grown in culture respond to the mitogenic action of fibroblast growth factor (FGF). Satellite cells from the dystrophic mdx mouse are more sensitive to FGF in culture than satellite cells from normal mice. In this study we investigated the basis for this heightened sensitivity of mdx satellite cells to FGF by measuring the number and affinity of protein and heparan sulphate proteoglycan (HSPG) receptors for FGF. We found that HSPG receptors were elevated over four-fold in the mdx cells compared with cells from normal animals. We supported this observation by measuring the synthesis of heparan sulphate (HS) and chondroitin sulphate (CS) by satellite cells in culture. Mdx satellite cells synthesized approximately ten times more of these sulphated glycosaminoglycans (GAGs) than did normal cells. For muscle fibroblasts, however, we found no significant difference in the number or affinity of protein or HSPG receptors, or in the amount of sulphated GAGs synthesized, between normal and mdx cells. We propose that the increase in FGF HSPG receptors is the basis for the heightened response of mdx satellite cells to FGF in culture and may reflect exposure of the cells to growth factors in the degenerating mdx muscle.

Animals↗
PubMed1992

Gene therapy.

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Genetic Therapy↗
PubMed1991

Fiber regeneration is not persistent in dystrophic (MDX) mouse skeletal muscle.

Fiber replacement has been measured in adult mdx mouse limb skeletal muscles. During the first 10 days after birth all fibers appear normal; between Week 3 and 4 there is massive fiber degeneration followed by regeneration in which close to 100% of the fibers are repaired or replaced. New fibers arising in adult mice are characterized by expression of fetal myosin mRNAs in whole muscle extracts, and by staining of individual fibers with an embryonic myosin heavy chain-specific antibody. By 10 weeks of age new fiber replacement rate, indicated by frequency of fibers reacting with antibody, is reduced to about 10%, and by 1 year of age less than 1% of the fibers are being replaced at rates above control. Total fiber number also remains fairly constant. We conclude that the fibers regenerating up to 10 weeks of age become stabilized and do not undergo further rounds of degeneration and regeneration. This is consistent with the observed benign phenotype of adult mdx animals and with the idea that once-regenerated fibers escape the catastrophic dystrophic phenotype by acquiring a function that compensates for their mdx mutation. The mechanism by which regenerated mdx fibers restore adequate function in the absence of dystrophin may, when understood, provide clues to effective nongenetic interventions for muscular dystrophy in humans where regenerated fibers continue to degenerate and where the disease is often fatal.

Animals↗
PubMed1990

Myogenesis and histogenesis of skeletal muscle on flexible membranes in vitro.

Primary muscle cell cultures consisting of single myocytes and fibroblasts are grown on flexible, optically clear biomembranes. Muscle cell growth, fusion and terminal differentiation are normal. A most effective membrane for these cultures is commercially available Saran Wrap. Muscle cultures on Saran will, once differentiated, contract vigorously and will deform the Saran which is pinned to a Sylgard base. At first, the muscle forms a two-dimensional network which ultimately detaches from the Saran membrane allowing an undergrowth of fibroblasts so that these connective tissue cells completely surround groups of muscle fibers. A three-dimensional network is thus formed, held in place through durable adhesions to stainless steel pins. This three-dimensional, highly contractile network is seen to consist of all three connective tissue compartments seen in vivo, the endomysium, perimysium and epimysium. Finally, this muscle shows advanced levels of maturation in that neonatal and adult isoforms of myosin heavy chain are detected together with high levels of myosin fast light chain 3.

Animals↗
PubMed1989

Fibroblast growth factor in the extracellular matrix of dystrophic (mdx) mouse muscle.

Polyclonal antibody F547 reacts with a bovine basic fibroblast growth factor (bFGF) and a human recombinant bFGF, but not with bovine acidic fibroblast growth factor. This antibody localized bFGF in the extracellular matrix of mouse skeletal muscle, primarily in the fiber endomysium, which includes the heparin-containing basal lamina. In mdx mouse muscle, which displays persistent regeneration, FGF levels in the extracellular matrix are higher than those in controls. Overabundance of matrix FGF in mdx muscles may be related to an increase in both satellite cell and regenerative activity in the dystrophic muscle and may help explain the benign phenotype of mdx animals compared with the genetically identical human Duchenne muscular dystrophy.

Animals↗
PubMed1989

Fibroblast growth factor is stored in fiber extracellular matrix and plays a role in regulating muscle hypertrophy.

A polyclonal antibody specific to bovine basic fibroblast growth factor (bFGF) localizes bFGF in the extracellular matrix of rat skeletal muscle fibers, where it is bound by the heparin-rich basal lamina. FGF accumulation appears to be augmented in hypertrophied compared to control fibers. In addition, FGF-like growth activity can be isolated from hypertrophied muscle. This growth activity binds to heparin and can be purified by heparin-affinity chromatography. When assayed in a chick myogenic cell culture system, the purified rat growth activity stimulates myobenic cell replication and stimulates myosin accumulation and synthesis. The function, in vivo, of basal lamina-localized FGF in rat muscle is not known, but it is most probably related to increased satellite cell replication seen during normal fiber maturation, during work-induced hypertrophy, and during regeneration. During hypertrophy, we observe the appearance of new fibers in addition to growth of preexisting fibers. It is hypothesized that muscle hypertrophy involves activation of satellite cells which may then fuse with existing fibers and, in addition, also form new fibers.

Animals↗
PubMed1988

Heparin inhibits skeletal muscle growth in vitro.

Heparin or heparan sulfate proteoglycan (HeSPG), but not chondroitin sulfate or hyaluronic acid, exerts a pronounced inhibitory effect on muscle growth in vitro, as determined by total protein, myosin accumulation or synthesis, and [3H]thymidine incorporation studies. Primary muscle fibroblast culture growth is also inhibited by heparin but to a substantially lesser degree compared to muscle (30% and over 90% inhibition of growth, respectively). Heparin-induced inhibition of skeletal muscle growth is a consequence of its interaction with a growth factor(s) present in the media used to support myogenesis; heparin-Sepharose column absorbed horse serum can support muscle growth only in the presence of added heparin-binding growth factors like fibroblast growth factor (FGF) or chicken muscle growth factor (CMGF). Furthermore, heparin prevents the binding of iodinated FGF to the myoblast surface. We also show that the extent of muscle growth is a function of the relative amounts of heparin and FGF in culture. Finally, we provide evidence indicating that FGF can combine with endogenously occurring heparin-like components: immobilized FGF binds sodium-[35S]sulfate labeled components secreted in muscle culture conditioned medium, an interaction inhibited by anti-HeSPG antibodies or heparin, but not by other sulfated glycosaminoglycans. Since heparin binding growth factors not only stimulate myoblast proliferation but also actively inhibit the onset of muscle differentiation (G. Spitzz, D. Roman, and A. Strauss (1986). J. Biol. Chem. 261, 9483-9488), their interaction with naturally occurring heparin-like components may be an important physiological mechanism for modulating muscle growth and differentiation in development and regeneration.

Animals↗
PubMed1988

Satellite cells from dystrophic (mdx) mouse muscle are stimulated by fibroblast growth factor in vitro.

Satellite cells cultured from dystrophic (mdx) and from control mouse hindlimb muscles grow and fuse to form muscle fibers within 4-5 days. Total cell number and muscle-fiber formation are stimulated by bovine fibroblast growth factor (FGF). At low FGF levels (0.02-0.20 ng/ml) control satellite cells as well as fibroblasts are unresponsive, while mdx satellite cells show three- to four-fold increases in growth. Control cells do not begin to respond until FGF levels reach 1-5 ng/ml. Heparin, a major constituent of muscle fiber basal lamina, inhibits myogenesis in these mouse muscle cultures. The heightened sensitivity of mdx satellite cells to FGF may permit high rates of new fiber formation in vivo without a parallel hyperplasia in the muscle fibroblast population. This finding may be important in explaining successful regeneration in mdx muscle in vivo and the fact that mdx animals escape the catastrophic symptoms seen in the related human Duchenne muscular dystrophy.

Animals↗