Abstract
Excretion of cementum by cementoblasts on the root surface is a process indispensable for the formation of a functional periodontal ligament. This study investigated whether carboxyl group-functionalized multi-walled carbon nanotubes (MWCNT-COOH) could enhance differentiation and mineralization of mammalian cementoblasts (OCCM-30) and the possible signaling pathway involved in this process. Cementoblasts were incubated with various doses of MWCNT-COOH suspension. Cell viability was detected, and a scanning electron microscopy (SEM) observed both the nanomaterials and the growth of cells cultured with the materials. Alizarin red staining was used to investigate the formation of calcium deposits. Real-time PCR and western blot were used to detect cementoblast differentiation and the underlying mechanisms through the expression of the osteogenic genes and the downstream effectors of the TGF-β/Smad signaling. The results showed that 5 µg/mL MWCNT-COOH had the most obvious effects on promoting differentiation without significant toxicity. Alp, Ocn, Bsp, Opn, Col1 and Runx2 gene expression was up-regulated. Smad2 and Smad3 mRNA was up-regulated, while Smad7 was first down-regulated on Day 3 and later up-regulated on Day 7. The elevated levels of phospho-Smad2/3 were also confirmed by western blot. In sum, the MWCNT-COOH promoted cementoblast differentiation and mineralization, at least partially, through interactions with the TGF-β/Smad pathway.
Highlights
Cementum is the bone-like tissue covering the external surface of tooth root in a thin layer [1].Due to its intermediary position, cementum forms the interface between root dentin and periodontal ligament
Data are expressed as the mean ± SD. * p < 0.05, for 15 μg/mL Multi-walled carbon nanotubes (MWCNTs)-COOH cells vs. control cells; a p < 0.001, for 25 μg/mL MWCNT-COOH cells vs. control cells
We examined MWCNT-COOH at three different concentrations (i.e., 5, 15 and 25 μg/mL) in order to determine a toxicological threshold for cementoblasts
Summary
Cementum is the bone-like tissue covering the external surface of tooth root in a thin layer [1]. There are concerns for these therapies, such as high cost, rapid clearance and poor mechanical properties Their effectiveness on new cementum and attachment formation is still unpredictable. CNTs, with a size comparable to extracellular matrix molecules, such as collagens and laminins, have been reported to sustain cell growth and bone formation in osteoblasts [10,13]. Their poor solubility in aqueous solutions remains a major impediment in biological and medical applications. The purpose of this study, was to investigate the effect of in vitro functionalized MWCNTs (MWCNT-COOH, pristine carboxyl group-functionalized MWCNTs), cultured with cementoblasts to form a favorable microenvironment for cementogenesis, on cell proliferation, morphology, mineralization and the underlying molecules and mechanisms
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