Abstract
The tendons in the turkey leg have specific well-defined areas which become mineralized as the animal ages and they are a thoroughly characterized model system for studying the mineralization process of bone. In this study, nondestructive Raman spectroscopic analysis was used to explore the hypothesis that regions of the turkey tendon that are associated with mineralization exhibit distinct and observable chemical modifications of the collagen prior to the onset of mineralization. The Raman spectroscopy features associated with mineralization were identified by probing (on the micrometer scale) the transition zone between mineralized and nonmineralized regions of turkey leg tendons. These features were then measured in whole tendons and identified in regions of tendon which are destined to become rapidly mineralized around 14 weeks of age. The data show there is a site-specific difference in collagen prior to the deposition of mineral, specifically the amide III band at 1270 cm(-1) increases as the collagen becomes more ordered (increased amide III:amide I ratio) in regions that become mineralized compared to collagen destined to remain nonmineralized. If this mechanism were present in materials of different mineral fraction (and thus material properties), it could provide a target for controlling mineralization in metabolic bone disease.
Highlights
A number of bird species have tendons that ossify in specific regions to maximize the stiffness of the organ and improve its energy efficiency.[1,2] An example is the extensor tendon of the turkey leg which begins to mineralize proximal and distal to the tarsometatarsal joints when the bird is 10−14 weeks old.[3,4] This mineralization pattern creates two zones of “transition” (1−2 mm wide) between mineralized and nonmineralized tendon; one is one-third of the length of the organ from the proximal end, and the second is one-third of the length of the organ from the distal end (Figure 1)
Biochemical analyses of the collagen from turkey tendons have shown that different post-translational modifications occur in regions of the turkey leg tendon (TLT) associated with future mineralization status, that collagen cross-linking in the mineralizing and nonmineralizing regions differ, and that the differences are present in young animals prior to mineralization.[6]
Low levels of hydroxylysylpyridinoline and lysylpyridinoline are associated with a mineralized collagen matrix
Summary
A number of bird species have tendons that ossify in specific regions to maximize the stiffness of the organ and improve its energy efficiency.[1,2] An example is the extensor tendon of the turkey leg which begins to mineralize proximal and distal to the tarsometatarsal joints when the bird is 10−14 weeks old.[3,4] This mineralization pattern creates two zones of “transition” (1−2 mm wide) between mineralized and nonmineralized tendon; one is one-third of the length of the organ from the proximal end, and the second is one-third of the length of the organ from the distal end (Figure 1). Biochemical analyses of the collagen from turkey tendons have shown that different post-translational modifications occur in regions of the TLT associated with future mineralization status, that collagen cross-linking in the mineralizing and nonmineralizing regions differ, and that the differences are present in young animals prior to mineralization (the transition zones were not analyzed in that study).[6] Lysyl hydroxylation. Other infrared (IR) studies of mineralization in related connective tissues have been reported; these include in vitro bone nodules,[9] microdamaged sections of bone,[10] cartilage,[11] and dental lesions.[12] FTIR studies of the turkey leg tendon itself have shown that the mineralization commenced in the middle of the tendon and progressed proximally, with the mineral subsequently maturing; that is, the more distal part of the tendon region is initially more mature than the proximal end (until mineralization is complete).[13]
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