The metabolism of bone collagen has received little attention in relation to age-related loss of bone mass and strength. The aim of the present study was to analyze bone collagen content and metabolism in human bone with respect to age. The material consisted of iliac crest bone biopsies from 94 individuals: 46 women (ages 18-96, mean age 60.8 years) and 48 men (ages 23-92, mean age 59.5 years). Excluded from the study were all individuals with known osteoporotic lumbar vertebral fractures and renal, hepatic, or malignant diseases. Prior to collagen analysis the biopsies were scanned in a pQCT scanner for density assessment and then tested biomechanically. The results showed a decline in apparent bone density with age (P < 0.0001), a decline in maximum stress, Young's modulus, and energy absorption with age (P < 0.001). Concomittantly, there was an age-related decline in the intrinsic collagen content with age (P < 0.001). However, there were no biochemical modifications of the bone collagen during aging. There were no significant differences between women and men in the slopes of the regressions-curves. When multiple regression analyses were performed, only apparent bone density came out as a significant contributor in the correlation to biomechanical properties. Nevertheless, the decrease in bone collagen content with age might indicate an increase in the mineralization degree (probably due to decreased bone turnover) and thereby a change in material properties of bone. In conclusion, the present study has shown that loss of bone mass plays the major role in loss of bone strength. However, there is also a change in bone composition during normal aging, leading to a decrease in collagen content and an increase in the degree of mineralization. At this skeletal site, in a normal population there was no change in the biochemical properties of bone collagen.

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Research into the aetiology of osteoarthritis has for several decades been concentrated on the destruction of the articular cartilage, the initiating events being believed to be changes in the proteoglycans and subsequently in the supporting collagenous framework, whereafter the disease is irreversible. Recent evidence has supported an old contention that the underlying bone may be involved, namely, increased technetium scintigraphy correlated with increased severity of the osteoarthritis as demonstrated by joint narrowing, and a demonstration of increased metabolism of cancellous bone collagen compared to age-matched controls. These studies have not been able to answer the question of the primary initiating event: does increased bone metabolism initiate cartilage destruction or vice versa? However, recent detailed studies on animal models, particularly the macaque, have demonstrated that in this case thickening of the subchondral bone precedes fibrillation of the cartilage, which is possibly due to increased resistance of the bone to compression. Further, MRI studies on the guinea pig suggest that the initial site of activity is at the ligament bone insertion site, prior to endochondral bone sclerosis. We propose that the biomechanics of the joint are perturbed by the loss of tension from the ligament following trauma, leading to remodelling of the subchondral bone. Certainly in humans damage to the cruciate ligament often results in osteoarthritis. It may be that subclinical damage also ultimately results in osteoarthritis. Although the results from animal models will need to be treated with caution, the concept that bone ligament changes precede articular cartilage destruction should lead to a redirection of research, and perhaps therapy, for this important and cruelly disabling disease.

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SummaryMicrobial interactions with host molecules, and programmed responses to host environmental stimuli, are critical for colonization and initiation of pathogenesis. Bacteria of the genus Streptococcus are primary colonizers of the human mouth. They express multiple cell-surface adhesins that bind salivary components and other oral bacteria and enable the development of polymicrobial biofilms associated with tooth decay and periodontal disease. However, the mechanisms by which streptococci invade dentine to infect the tooth pulp and periapical tissues are poorly understood. Here we show that production of the antigen I/ II (AgI/II) family polypeptide adhesin and invasin SspA in Streptococcus gordonii is specifically upregulated in response to a collagen type I signal, minimally the tri-peptide Gly-Pro-Xaa (where Xaa is hydroxyproline or alanine). Increased AgI/II polypeptide expression promotes bacterial adhesion and extended growth of streptococcal cell chains along collagen type I fibrils that are characteristically found within dentinal tubules. These observations define a new model of host matrix signal-induced tissue penetration by bacteria and open the way for novel therapy opportunities for oral invasive diseases.