Glycosaminoglycans accelerate biomimetic collagen mineralization in a tissue-based in vitro model

Abstract

Mammalian teeth are attached to the jawbone through an exquisitely controlled mineralization process: unmineralized collagen fibers of the periodontal ligament anchor directly into the outer layer of adjoining mineralized tissues (cementum and bone). The sharp interface between mineralized and nonmineralized collagenous tissues makes this an excellent model to study the mechanisms by which extracellular matrix macromolecules control collagen mineralization. While acidic phosphoproteins, localized in the mineralized tissues, play key roles in control of mineralization, the role of glycosaminoglycans (GAGs) is less clear. As several proteoglycans are found only in the periodontal ligament, it has been hypothesized that these inhibit mineralization of collagen in this tissue. Here we used an in vitro model based on remineralization of mouse dental tissues to determine the role of matrix GAGs in control of mineralization. GAGs were selectively removed from demineralized mouse periodontal sections via enzymatic digestion. Proteomic analysis confirmed that enzymatic GAG removal does not significantly alter protein content. Analysis of remineralized tissue sections by transmission electron microscopy (TEM) shows that GAG removal reduced the rate of remineralization in mineralized tissues compared to the untreated control, while the ligament remained unmineralized. Protein removal with trypsin also reduced the rate of mineralization, but to a lesser extent than GAG removal, despite a much larger effect on protein content. These results indicate that GAGs promote mineralization in mineralized dental tissues rather than inhibiting mineral formation in the ligament, which may have broader implications for understanding control of collagen mineralization in connective tissues.

Bioinspired Silk Fibroin Mineralization for Advanced In Vitro Bone Remodeling Models

“…Although the origin of these GAGs is unclear, they have been shown to inhibit collagen degradation by osteoclastic cathepsin K, promote osteogenic differentiation and bone‐like matrix formation, and promote mineralization. [ 57–60 ]…”

Cementum is key to periodontal tissue regeneration: A review on apatite microstructures for creation of novel cementum‐based dental implants

“…As the growth rate controls crystal morphology, dentin, and cementum crystal size and morphology may differ, although a similar macro‐organizational structure is formed by HAP on the collagen fibers. In addition, the proteins involved in cementum crystallization differ from those required for dentin crystallization (Correa et al, 2019; Wojtas, Lausch, & Sone, 2020), which may significantly impact the crystal morphology. Thus, comprehensively describing the crystals constituting cementum at the nanoscale is essential for tissue regeneration, as crystal morphology reflects the mechanism and environment of crystal growth.…”

Periodontal regeneration: Lessons from the periodontal ligament-cementum junction in diverse animal models

“…In this context, we have developed an in vitro model of mineralization based on remineralization of demineralized sections of mouse periodontium, in which we demonstrated that the extracellular matrix contains sufficient information to control the rate of mineralization into mineralized tissues (bone, cementum, dentin) as compared to the non-mineralized PDL (31). We further used selective enzymatic digestions to explore the respective roles in mineralization of phosphoproteins (32) and glycosaminoglycans (GAGs) (33), the linear polysaccharides often attached to a protein core in proteoglycans. This latter research demonstrated that GAGs play an important role in promoting mineralization in dental tissues rather than inhibiting mineralization in the ligament.…”