Although Anatomically Micrometers Apart: Human Periodontal Ligament Cells Are Slightly More Active in Bone Remodeling Than Alveolar Bone Derived Cells

Abstract

The periodontal ligament (PDL) and the alveolar bone are part of the periodontium, a complex structure that supports the teeth. The alveolar bone is continuously remodeled and is greatly affected by several complex oral events, like tooth extraction, orthodontic movement, and periodontitis. Until now, the role of PDL cells in terms of osteogenesis and osteoclastogenesis has been widely studied, whereas surprisingly little is known about the bone remodeling capacity of alveolar bone. Therefore, the purpose of this study was to compare the biological character of human alveolar bone cells and PDL cells in terms of osteogenesis and osteoclastogenesis in vitro. Paired samples of PDL cells and alveolar bone cells from seven patients with compromised general and oral health were collected and cultured. Bone A (early outgrowth) and bone B (late outgrowth) were included. PDL, bone A, bone B cell cultures all had a fibroblast appearance with similar expression pattern of six mesenchymal markers. These cultures were subjected to osteogenesis and osteoclastogenesis assays. For osteoclastogenesis assays, the cells were co-cultured with peripheral blood mononuclear cells, a source for osteoclast precursor cells. The total duration of the experiments was 21 days. Osteogenesis was slightly favored for PDL compared to bone A and B as shown by stronger Alizarin red staining and higher expression of RUNX2 and Collagen I at day 7 and for ALP at day 21. PDL induced approximately two times more osteoclasts than alveolar bone cells. In line with these findings was the higher expression of cell fusion marker DC-STAMP in PDL-PBMC co-cultures compared to bone B at day 21. In conclusion, alveolar bone contains remodeling activity, but to a different extent compared to PDL cells. We showed that human alveolar bone cells can be used as an in vitro model to study bone remodeling.

Diabetes Medication Metformin Inhibits Osteoclast Formation and Activity in In Vitro Models for Periodontitis

“…Figure 1A ). As in previous studies from our group ( Karlis et al, 2020 ; Loo-Kirana et al, 2021 ), the observed Alizarin Red staining was due to so-called nodules or hot-spots of mineralization that formed on top of the fibroblasts ( Figure 1D ). Interestingly, mineralization medium only induced osteopontin expression when compared to normal medium, whereas RUNX-2, Collagen-I expression and the activity of Alkaline phosphatase was not influenced, not by mineralization medium nor by metformin.…”

“…These promising results with metformin in animal studies as well as in clinical studies urge mechanistic insight using a relevant cell system. Periodontal ligament fibroblasts anchor teeth in bone and also play a crucial role in both osteogenesis and osteoclastogenesis, processes that can be elegantly mimicked in vitro (De Vries et al, 2017;Ruppeka-Rupeika et al, 2018;De Vries et al, 2019;Karlis et al, 2020;Loo-Kirana R.;Gilijamse M.;Hogervorst J., 2021). Support for the relevance of periodontal ligament fibroblasts comes from an animal study where periodontal ligament fibroblasts were shown to play a key role in alveolar bone regeneration (Ren et al, 2015).…”

Plap-1/Aspn lineage tracing and single-cell transcriptomics reveals cellular dynamics in the periodontal ligament

“…Notably, the stromal compartment was collectively divided into Plap-1 + fibroblastic cells or Ibsp + osteo-/cementoblastic cells in a mutually exclusive manner. Plap-1 is also highly expressed in the human PDL and used as a cultured PDLC marker (Yamada et al 2001; Loo-Kirana et al 2021; Mun et al 2022). RNA velocity analysis indicated that cluster 9, Plap-1 high , with a positive velocity of Plap-1 mRNA, constituted a potential cellular source of other PDL clusters.…”

“…Plap-1 is also highly expressed in the human PDL and used as a cultured PDLC marker (Yamada et al 2001;Loo-Kirana et al 2021;Mun et al 2022). RNA velocity analysis indicated that cluster 9, Plap-1 high , with a positive velocity of Plap-1 mRNA, constituted a potential cellular source of other PDL clusters.…”

Tooth transplantation and replantation: Biological insights towards therapeutic improvements

“…Osteoclasts differentiate from monocyte–macrophage‐lineage progenitor cells by two critical cytokines, macrophage colony‐stimulating factor and receptor activator of nuclear factor‐κB (RANK) ligand (RANKL). PDLFs, osteoprogenitors, and osteoblasts express RANKL, which binds to the RANK receptor on osteoclast progenitor cells (Loo‐Kirana et al, 2021). RANKL‐RANK binding is followed by signal transduction via the NF‐κB/NFATc1 pathway, leading to osteoclast‐specific gene expression.…”