Spatial-Temporal Patterns and Inflammatory Factors of Bone Matrix Remodeling

Figure 1

The rhythmic formation process of collagen. For the formation of collagen, Col1α1 and Col1α2 genes code α1 and α2 polypeptide chains severally. In the RER and Golgi apparatus, polypeptide chains fold into helical procollagen through posttranslational modifications, including hydroxylation and glycosylation. And molecular chaperones in this process like BiP, HSP47, PPIases, and prolyl 3-hydroxylation are responsible for the transport and correct conformation [6, 28]. What is more, the proteins for regulating collagen transport like SEC61, TANGO1, PDE4D, VPS33B, and BiP are under the control of circadian rhythms with different oscillations. When procollagen transports outside osteoblasts to form tropocollagen, its N- and C-termini are hydrolyzed [16, 18]. Tropocollagen deposits side by side and orients parallelly in one fibril but staggers with each other as the -band. Eventually, multiple fibrils constitute collagen fibers with cross-links [19]. RER: rough endoplasmic reticulum; PTMs: posttranslational modifications; PPIases: peptidyl-prolyl cis-trans isomerases; ECM: extracellular matrix.