title: Analysis of cartilage differentiation from skeletal muscle grown on bone matrix. III. Environmental regulation of glycosaminoglycan and proteoglycan synthesis.
abstract: The ability of numerous nutritional and topographic factors to influence differentiation of embryonic mesenchyme has given rise to several theories which attempt to explain the development of muscle and cartilage from these similar-appearing cells. Some theories are challenged by the observation that a substratum of demineralized bone is capable of supporting the transformation of skeletal muscle into cartilage in vitro and that the potential to form cartilage still resides within cloned myoblasts and fibroblasts of skeletal muscle. In the present study, culture media CMRL-1066, minimal essential medium (MEM), and F-12 provide varied nutritional environments and are tested for their ability to support the morphological and biochemical transformation of skeletal muscle into cartilage. Morphologically, CMRL-1066 reproducibly supports hyaline cartilage formation, whereas MEM does so in only one out of three explants onto demineralized bone, and F-12 is incapable of supporting formation of a hyaline matrix. Biochemically, each medium is sufficient to elicit synthesis of cartilage-like patterns of sulfated glycosaminoglycans and proteoglycan monomer. Synthesis of hyaluronic acid (HA) initially increases in explants grown in CMRL-1066, but decreases prior to chondrogenesis. MEM elicits a similar increase in HA synthesis, but the subsequent decrease is not as rapid. In F-12, synthesis remains depressed throughout the experiment. The data show that increases in HA synthesis occur concurrent with the appearance of fibroblast-like cells, which normally precede chondroblasts. Decreases in HA synthesis correlate well with the onset of chondrogenesis. Explants grown in CMRL-1066 reproducibly from cartilage and synthesize the greatest amounts of proteoglycan aggregate. Those grown in MEM form cartilage infrequently, synthesize reduced amounts of proteoglycan aggregate-like material, and contain greater amounts of HA, of low molecular weight. The data demonstrate that chondrogenesis can be subtly regulated by environmental factors, and such factors regulate both the morphological and biochemical expression of the phenotype through HA synthesis.
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000502:physiology*; D002356:Cartilage / Q000502:physiology*; D002454:Cell Differentiation; D004622:Embryo, Mammalian; D005260:Female; D006025:Glycosaminoglycans / Q000302:isolation & purification; D009132:Muscles / Q000166:cytology / Q000502:physiology*; D009924:Organ Culture Techniques; D011247:Pregnancy; D011509:Proteoglycans / Q000302:isolation & purification; D051381:Rats
chemical_list: D006025:Glycosaminoglycans; D011509:Proteoglycans