Lack of Effect of Murine Norovirus Infection on a Mouse Model of Bacteria-Induced Colon Cancer

Murine norovirus (MNV) is endemic in mouse research facilities in the United States and Europe, with a prevalence as high as 58% to 64%. Because of MNV's orofecal route of infection, clinically silent persistent infections in some mouse strains, and proclivity for macrophage and dendritic cells, its presence in mouse colonies has potential to alter phenotypes in experimental mouse models, particularly those involving inflammation and immunologic responses. Although MNV is subclinical, not causing overt disease in immunocompetent mice, we found that MNV infection can accelerate bacteria-induced inflammatory bowel disease (IBD) progression in Mdr1a^(-/-) mice. The studies presented here examined whether MNV infection also affects the phenotype of a bacterially driven mouse model of inflammation-associated colon cancer in genetically susceptible Smad3^(-/-) mice. In vitro culture of bone-marrow—derived macrophages (BMDM) was used to determine whether MNV4 influenced macrophage cytokine production. For in vivo studies, Smad3-/- mice were infected with MNV4 one week prior to infection with Helicobacter. Mice were monitored for 17 to 32 wk for development of IBD and colon cancer, and tissues were analyzed histopathologically. Although in vitro infection of BMDM with MNV4 led to increased inflammatory cytokine production, infection with MNV4 in vivo did not result in any statistically significant differences in survival, IBD scores, tumor incidence, or tumor phenotype in Smad3^(-/-) mice. In addition, MNV infection alone did not result in IBD or colon cancer. Therefore MNV infection alone or in conjunction with Helicobacter does not alter the development or progression of IBD or colon cancer in Smad3^(-/-) mice

Endogenous Inhibitor of Bone Cell Proliferation

Abstract A substance recovered from the medium of embryonic chick bones growing in organ culture inhibits the proliferation of chick calvarial bone cells in vitro. This inhibition of proliferation occurs within 3 hr after exposure of the cells to the inhibitory substance (IS) in a manner which does not appear to affect the protein synthesis or the gross morphology of the cells. The medium from which IS is obtained can be diluted 500-fold and still retain significant inhibitory activity. Cells in culture spontaneously escape the inhibition of a single dose of IS within 24 hr of exposure, however, upon further addition of IS to these cells inhibition of proliferation is again observed. Cells derived from chick bone as well as rat and human bone are more sensitive to the inhibition than are chick dermal fibroblasts and chick liver and muscle cells. IS is not destroyed after treatment of the conditioned medium with trypsin, phospholipase A2, RNase, neuraminidase, or heat. IS is also not a commonly produced prostaglandin. Estimates of the molecular weight of IS range from 6000 to 14,000 daltons. While these features do not disclose the exact nature of this substance, they are consistent with this substance being a small polypeptide without the exposed amino acids, lysine or arginine. We conclude that the presence of such a substance supports the concept of local regulation of bone metabolism

Regulation of DNA Synthesis in Chick Calvaria Cells by Factors from Bone Organ Culture

Abstract Embryonic chick bones growing in organ culture release a substance into the culture medium which stimulates bone formation in previously untreated bones. This “conditioned” medium also enhances proliferation of monolayer cultures of chick calvaria cells in serum-free medium. The active principle is nondialyzable, indicating a molecular weight greater than 12,000 daltons. Dialysis also separates the mitogenic activity from a low-molecular-weight inhibitor. The amount of the mitogen found in conditioned medium increases as the rate of bone resorption increases in response to treatment with parathyroid hormone or 1,25-dihydroxyvitamin D3. Maximal stimulation of DNA synthesis in calvaria cells is evident with conditioned medium obtained 3 to 5 days after treatment of bone cultures with parathyroid hormone. The cells must be treated with the conditioned medium continuously for 20 hr in order to obtain peak enhancement of DNA synthesis; there is no detectable effect in the first 8 hr. In contrast, the inhibitor acts within 4 hr. The data suggest that the stimulatory factor acts to increase cell proliferation by promoting entry of cells into the S phase of mitosis. We conclude that this stimulator is a locally produced regulator of bone formation, probably acting via an increased proliferation in osteoblast precursor cells

Coupling Factor

Several years ago we intiated studies to clarify the problem of osteoporosis. On the basis of historical prospective, we reasoned that a disease of an organ is always attributable to inadequate regulation. That regulatory dysfunction may, in turn, be due to an overwhelmed regulatory mechanism, or to a faulty regulatory mechanism. Thus, inasmuch as osteoporosis is a disease of too little bone, we sought to characterize the regulation of bone volume