It has been established that regenerating marrow induces an osteogenic response in distant skeletal sites and that this activity is mediated by factors released into the circulation by the healing tissue. In the present study we have characterized one of these factors, a 14 amino acid peptide named osteogenic growth peptide (OGP). Synthetic OGP, identical in structure to the native molecule, stimulates the proliferation and alkaline phosphatase activity of osteoblastic cells in vitro and increases bone mass in rats when injected in vivo. Immunoreactive OGP in high abundance is present physiologically in the serum, mainly in the form of an OGP‐OGP binding protein complex. A marked increase in serum bound and unbound OGP accompanies the osteogenic phase of post‐ablation marrow regeneration and associated systemic osteogenic response. Authentic OGP is identical to the C‐terminus of histone H4 and shares a five residue motif with a T‐cell receptor beta‐chain V‐region and the Bacillus subtilis outB locus. Since these latter proteins have not been implicated previously in the control of cell proliferation or differentiation, OGP may belong to a novel, heretofore unrecognized family of regulatory peptides. Perhaps more importantly, OGP appears to represent a new class of molecules involved in the systemic control of osteoblast proliferation and differentiation.

The amino acid sequence of osteogenic growth peptide (OGP) consists of 14 residues identical to the C-terminal tail of histone H4. Native and synthetic OGP are mitogenic to osteoblastic and fibroblastic cells and enhance osteogenesis and hematopoiesis in vivo. The C-terminal truncated pentapeptide of OGP, H-Tyr-Gly-Phe-Gly-Gly-OH [OGP(10-14)], is a naturally occurring osteoblastic mitogen, equipotent to OGP. The present study assesses the role of individual amino acid residues and side chains in the OGP(10-14) mitogenic activity which showed a very high correlation between osteoblastic and fibroblastic cell cultures. Truncation of either Tyr10 or its replacement by Ala or D-Ala resulted in substantial, but not complete, loss of activity. Nevertheless, only a small loss of activity was observed following removal of the Tyr10 amino group. No further loss occurred consequent to the monoiodination of desaminoTyr10 on meta-position. However, a marked decrease in proliferative activity followed removal of the Tyr10 phenolic or the Phe12 aromatic group. Loss of activity of a similar magnitude also occurred subsequent to replacing Gly11 with L- or D-Ala. Approximately 50% loss of mitogenic activity occurred subsequent to truncation of Gly14 or blocking the C-terminal group as the methyl ester. All other modifications of the C-terminus and L- or D-Ala substitution of Gly13 resulted in 70-97% decrease in activity. Collectively, these data suggest that the integrity of the pharmacophores presented by Tyr and Phe side chains, as well as the Gly residues at the C-terminus, are important for optimal bioactivity of OGP(10-14).

The osteogenic growth peptide (OGP) is a 14-amino acid stromal cell mitogen that stimulates in vivo osteogenesis and hematopoiesis. In the blood circulation and cell culture conditioned medium immunoreactive OGP (irOGP), identified using antibodies raised against the OGP C-terminal region, presents free and bound forms. The bound form consists entirely of the full length peptide. The present study was designed to investigate the identity of free irOGP under nondenaturing conditions. Fresh human serum and culture medium conditioned with murine osteoblastic MC3T3 E1 cells were fractionated using ultrafiltration (3000 molecular weight cut-off). Hydrophobic chromatography of the ultrafiltrate, immunoscreening of chromatographic fractions with antibodies directed against the OGP C-terminal region and amino acid sequencing of immunoreactive peaks demonstrated the presence of two mitogens, the full length OGP and a C-terminal truncated form, OGP(10-14). The OGP(10-14) derived from both serum and conditioned medium, as well as the synthetic pentapeptide [sOGP(10-14)], shared the in vitro OGP proliferative activity. However, in a competitive binding assay, devised to assess the OGP-OGP binding protein (OGPBP) complex formation, sOGP(10-14) failed to compete out radiolabeled OGP from the complex. It is concluded that OGP(10-14) is a naturally occurring human and murine mitogen. In addition, the data suggests that the OGP(10-14) is generated from OGP by proteolytic cleavage upon dissociation of the OGP-OGPBP complexes.

No abstract

No abstract

Rabbit bone marrow has been separated into core, intermediate, and endosteal cell populations. When plated out in vitro, each of the fractions gave rise to colonies of fibroblastic cells. The colony-forming efficiency increased from the core population by a factor of 4 to a maximum of 3.4 X 10(-6) in the endosteal fraction. The osteogenic potential of each fraction was determined following their implantation in diffusion chambers into host rabbits. Each of the indices of osteogenesis (alkaline phosphatase activity, Ca and P accumulation) were significantly lower in the core population than in the two populations closer to the bone surface. Our results are consistent with the hypothesis that the osteogenic precursor cells of marrow belong to the fibroblast colony-forming cell fraction, and indicate that these cells, although found throughout the marrow, are concentrated close to the bone surface.

No abstract

Severe inflammatory lesions were induced in the periodontal tissues of the rat following the intragingival injection of lipoteichoic acid (LTA) from Streptococcus mutans. There was no difference in the severity and distribution of the lesions between nonimmunized rats and animals immunized against LTA after antigenic challenge. The lesions are characterized by the occurrence of granulation tissue, massive infiltration of PMNs, abscess formation, bone resorption, and new bone formation. Deacylated LTA and saline caused relatively mild inflammation, and no significant bone resorption or new bone formation was evident. The peak response was reached after 3 intragingival infections. The mechanisms by which LTA caused the pathological alterations in the rat periodontium and the possible relations of this experimental model to periodontal disease in the human are discussed.