The formation and organization of skeletal tissue is strongly influenced by mechanical stimulation. There is increasing evidence that gravitational stress has an impact on the expression of early response genes in mammalian cells and may play a role in the formation of extracellular matrix. In particular, osteoblasts may be unique in their response to gravitational stimuli since in these cells microgravity has been reported to reduce collagen synthesis, while in fibroblasts the opposite effect was observed. Here, we have investigated the influence of hypergravity induced by centrifugation on the collagen synthesis of human osteoblast-like cells (hOB) and studied the possible involvement of the mitogen-activated protein (MAP) kinase signaling cascade. Collagen synthesis was significantly increased by 42+/-16% under hypergravity at 13 x g, an effect paralleled by the enhanced expression of the collagen I alpha 2 (COL1A2) mRNA. No difference was seen in the proportion of collagen types I, III, and V synthesized by hOB. Hypergravity induced a markedly elevated phosphorylation of the p44/42 MAP kinases (ERK 1/2). The inhibition of this pathway suppressed the hypergravity-induced stimulation of both collagen synthesis as well as COL1A2 mRNA expression by about 50%. Our results show that the collagen synthesis of non-transformed hOB is stimulated under hypergravitational conditions. This response appears to be partially mediated by the MAP kinase pathway.

High concentrations of fulvic acid and selenium deficiency are the main causative factors of Kashin-Beck disease, an endemic, chronic and degenerative osteoarticular disorder found in China. In the search for an animal model of this disease, mice were exposed to these pathogenetic conditions for two generations and the collagen types from skin, bone and cartilage were analysed. The growth of the treated mice was slightly retarded, and the rate of reproduction was lower in animals maintained on a fulvic acid-supplemented and/or selenium-deficient diet. Irregular bone formation was seen by radiography and morphometry. Biochemical analysis indicated that lysine residues in collagen I from bone and in collagen II from cartilage were overmodified. The values of Hyl/(Hyl+Lys) in bone collagen alpha 1(I) chains from treated mice were about 0.434-0.484, i.e. substantially higher than that of the control (0.277). The values of this parameter for collagen II were 0.482 for control and 0.546-0.566 for treated mice. The melting temperature of collagen I from bones of treated mice was 1 degrees C lower than that of control collagen, indicating decreased thermal stability. The breakage point of the tibiae of treated mice occurred at a lower preload force than for controls, suggesting that the overmodified and thermally less stable collagen molecules are causally related to a lower mechanical strength of bones.

We describe a male patient with osteogenesis imperfecta (OI) who was born with contractures of the knee, elbow and ankle joints. During the first 4 years he suffered from recurrent fractures. He has white sclerae, mild dentinogenesis imperfecta, multiple wormian bones, severe scoliosis and short stature. Morphological analysis of cortical bone revealed typical characteristics of OI including varying width of the osteoid, swollen mitochondria and a dilated endoplasmic reticulum of the osteoblasts. Collagen fibrils of the osteoid had a varying diameter, a feature not found in typical OI patients. Analysis of compact bone showed that the size of apatite crystals and the extractability of collagen with pepsin were markedly elevated compared to controls and other OI type III and IV patients. Lysyl hydroxylation of collagen from the organic bone matrix and the electrophoretic mobility of collagen alpha 1(I)- and alpha 2(I)-chains were normal. Our results provide evidence that this patient belongs to a subtype of OI. The biochemical studies indicate that the underlying defect involves defective fibril-formation of collagen type I leading to an altered mineralization of bone.

No abstract

Immunoglobulin (Ig) concentrations were investigated in white matter samples of two adrenoleukodystrophy (ALD), three multiple sclerosis (MS), two systemic lupus erythematosus (SLE), one rheumatoid arthritis, and three control brains obtained at autopsy. "Free" Igs were extracted at pH 7.4; subsequently, bound Igs were extracted at pH 2.5 and 10.8, respectively. Igs were quantified by radial immunodiffusion. In ALD material there was an increase of free IgG and IgA, in one sample also of IgM, as compared to controls. No significant amounts of Igs were detected in the pH 2.5 and 10.8 extracts of ALD brain. Similarly to ALD, an increase of free IgG and IgA was a characteristic finding in MS brain; in contrast to ALD and control material, significant amounts of bound Igs (IgG) extractable at acid or alkaline pH, respectively, were present in MS tissue. In both SLE brains increase of free IgM was conspicuous. Preliminary studies on binding of Igs extracted at pH 7.4 from brain to frozen sections of normal human and bovine brain tissue revealed different binding properties of Igs from ALD, MS, SLE, and control brains. Immunochemical findings in ALD indicating pathologic accumulation of Igs in brain tissue were paralleled by immunocytochemical observations demonstrating accumulation of lymphoid cells staining for IgG, IgA, and IgM, respectively, mainly in areas of recent demyelination. Participation of Igs in the pathogenesis of ALD lesions may be considered but needs further confirmation.