Published online by Cambridge University Press: 15 September 2009
Bacterial protein toxins are powerful biological poisons normally associated with impairment of cellular function and/or cellular death. The wide spectrum of physiological processes and cell types that are affected by bacterial products also includes bone tissue and bone cells. It has been known for many years that bacterial infection or exposure to certain toxins can lead to pathological bone disorders, most commonly, those associated with abnormal or excessive bone loss, such as periodontal disease (reviewed by Henderson and Nair, 2003). However, in most cases the bone-resorbing factors involved in these effects remain part of, or associated with, the bacterial surface. For example, the bone-resorbing effects of endotoxin, a component of lipopolysaccharide, are well established, although for the most part this action appears to be indirect, being dependent on the production of pro-inflammatory cytokines (IL-1, TNFα) from other cell types (Nair et al., 1996; Henderson and Nair 2003). In contrast, the effects of bacterial protein toxins on the cellular constituents of bone remain largely unknown. For simplicity, this review will focus only on bacterial toxins, in particular, those toxins that interfere with key signalling processes that have direct relevance to bone cell differentiation and function. However, a brief overview of the general biology of bone cells is necessary before discussing the mechanisms of toxin action and specific signal transduction pathways in bone.
BONE
Throughout life the vertebrate skeleton is in a constant state of turnover.
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