Glycosaminoglycan and surface glycoprotein syntheses by rat muscle fibroblast monolayers: response to solubilized bone matrix and effect of serum

Newly synthesized proteoglycans secreted by sequentially derived populations of cells from new-born rat calvaria: effects of transforming growth factor-beta and matrigenin activity

Three populations (1, 3 and 6) of bone cells, derived from rat calvaria by sequential enzymatic digestion, were cultured with [3H]glucosamine and [35S]sulfate, in the presence or absence of transforming growth factor-beta (TGF-beta) or bone-derived matrigenin activity. Population 6 synthesized a chondroitin sulfate proteoglycan (PG) and responded to the addition of the factors by increased rates of synthesis of hyaluronic acid (HA) and PG and an increase in the size of the HA. Comparisons of populations 1, 3 and 6 showed an ordered, spontaneous increase in HA and PG synthesis. However, the addition of matrigenin activity resulted in a much greater stimulation of PG, but not HA, synthesis in population 1 compared to population 6, suggesting a cellular organization in the calvarium whose net effect would be to direct PG synthesis towards the periphery of the tissue.

Comparison of the stimulation of glycosaminoglycan synthesis in cultures of mononuclear cells from blood and of fibroblastic cells

A small molecular weight factor, derived from bovine bone ('matrigenin'), stimulated glycosaminoglycan and proteoglycan synthesis of cultured human fibroblastic cells but not of mononuclear cells from human blood. However, proteoglycan synthesis and secretion by the mononuclear cells was stimulated by the addition of concanavalin A. The proteoglycan from the concanavalin-A-stimulated mononuclear cells was of smaller molecular weight than the proteoglycan from the 'matrigenin'-stimulated fibroblastic cells. The major increase in proteoglycan synthesis and secretion occurred much later during the culture period for concanavalin-A-stimulated mononuclear cells than for 'matrigenin'-stimulated fibroblastic cells.

"Matrigenin" activity from bovine bone--I. Partial purification of activity

1. Bovine bone contains an extractable activity which stimulated the synthesis of glycosaminoglycans by bovine synovial, human synovial and mouse 3T3 fibroblastic cells in culture. Human cells were used to develop an assay for purification of the stimulatory activity ("matrigenin" activity) from bovine bone. 2. Partial purification of "matrigenin" activity was achieved by precipitation of the EDTA extract at pH 3.5 and Sepharose CL-6B chromatography in 4 M guanidinium HCl. Dissociative conditions were necessary to prevent aggregation. 3. On SDS-polyacrylamide gel electrophoresis the activity ran with a mobility equivalent to a Mr = 27,500 and could be recovered from the SDS gels.

Control of repair in articular tissues and the development of osteoarthritis

Bones from different mammalian species, including man, contain a low molecular weight extractable activity which stimulates proteoglycan synthesis by connective tissue cells in culture ("matrigenin" activity). Partial purification of matrigenin activity has been achieved from bovine bone. The activity shows a strong tendency for reversible physical associations in low ionic strength solutions and binds tightly to collagenous and other bone matrix proteins. It is speculated that the pathophysiological role of matrigenins may be to initiate repair during injury to bone. Chronic repair reactions are more likely to occur at sites of repeated anatomical stress at the ligamentous, tendon and synovial attachments at the ends of bones, in the subchondral bone and in the articular cartilage regions abbuting to subchondral bone. At these sites, repair reactions may be broadly viewed as the development of osteophytes and fibrocartilage and the progression of subchondral bone sclerosis. Repeated anatomical stress leads to the activation of extracellular, small molecular weight factors, which in turn, stimulate the biosynthesis of matrix macromolecules that are an important feature of these repair reactions of osteoarthritis.

An electron microscopic demonstration of induction of chondrogenesis in neonatal rat muscle outgrowth cells in monolayer cultures

Second passage fibroblast-like cells grown from explants of neonatal rat muscle continue to demonstrate fibroblast-like properties for many days when cultured on plastic surfaces. Such cells can be induced to change to a chondrocyte-like mode of expression by the addition of effector materials prepared from bovine cortical bone decalcified with 0.6 N HCl. Other studies show that similar demineralized bone particles and extracts from them have, in vivo, osteoinductive properties. Optimum conditions for this differentiation in monolayer culture were found in the use of 2% fetal calf serum with Dulbecco's modified Eagles medium. At 10% fetal calf serum the chondrogenic changes could not be detected. Light microscopy showed a sequence of morphological changes, after 36 h in culture, which resembled those seen at the beginning of osteogenesis in vivo. Induced cultures showed abundant extracellular proteoglycan production. Isotope incorporation studies showed stimulation of glycosaminoglycan synthesis in response to effector materials in soluble form. Type II collagen could be detected after three days. Electron microscopic analysis of induced and control cultures showed unequivocal evidence for marked production of an extensive extracellular matrix in the region of effector particles. The cells themselves change shape and develop an abundant system of lysosome-like vesicles and a very active, highly engorged endoplasmic reticulum and Golgi apparatus. After nine days in culture, evidence for the formation of a ruthenium red stained structure on the surface of the cells in contact with inductive particles, was observed. The simple monolayer culture system described provides a direct means by which the presence of active chondrogenic fractions may be assessed, and in which the mechanism of action of the effectors can be studied.

Glycosaminoglycan synthesis by rat fibroblast monolayers: effects of serum and solubilized bone matrix fractions

Glycosaminoglycan synthesis by fibroblasts, from skeletal muscle of the neonatal rat, is stimulated by a bone matrix preparation, soluble in isotonic medium, obtained by extracting decalcified rat bone with 4 M guanidine HCl. The stimulation in glycosaminoglycan synthesis is dependent on the presence of serum in the culture, but the stimulatory effect can be clearly distinguished from that of serum. The stimulatory activity in the bone matrix has been fractionated by ion-exchange chromatography and coelutes largely with anionic, non-collagenous matrix glycoproteins.

The effect of solubilized bone matrix fractions from different mammalian species on glycosaminoglycan synthesis by cultured fibroblasts

Human and bovine bone matrices were extracted with salt solutions of different composition and the extracts tested for stimulation of incorporation of radioactivity from [3H]glucosamine and [35S]SO4 into the hyaluronic acid and chondroitin sulfate of the cell pellet, the cell surface and the medium fractions of human synovial cells in culture. Stimulatory activity was extracted with a solution of 0.3 M EDTA in 2.5 M NaCl from bovine but not human bone. Subsequent extraction of the residues with 4 M guanidinium hydrochloride yielded activity from both matrices. A major stimulation of incorporation of radioactivity was observed in the cell surface fractions. Human synovial cells constitute a more sensitive assay system for the stimulatory activity than rabbit synovial cells.

Incorporation of radioactive precursors into glycosaminoglycans by rat muscle fibroblasts exposed to a solubilized rat bone matrix fraction

Confluent cultures of rat muscle fibroblastic cells respond by increased glycosaminoglycan (GAG) synthesis when cultured in medium containing a solubilized bone matrix fraction (SBM) at a concentration of 100 micrograms/ml. The metabolism of the GAG associated with the cell pellet, the cell surface and the tissue culture medium fractions was studied, in the presence and absence of SBM, by measuring the incorporation of radioactivity from [3H]glucosamine and [35S]SO4 into the isolated GAG. Net synthesis of hyaluronic acid and of chondroitin sulfate in the medium fraction increased more rapidly in cultures containing SBM compared to controls, and the accumulation of labelled GAG in the medium of the treated cultures was approximately linear with respect to the length of incubation. The addition of SBM also resulted in increased incorporation of 3H and of 35S into the GAG of the cell surface and cell pellet fractions. In these fractions, stimulation of incorporation of radioactivity occurred in two waves: an early, relatively minor increase and a later relatively major increase. The relatively major stimulation of radioactivity into the GAG of the cell surface fraction occurred between 24 and 48 h and was independent of any apparent effect of serum.