Yasuaki Sakata

Functional role of acetylcholine and the expression of cholinergic receptors and components in osteoblasts

Recent studies have indicated that acetylcholine (ACh) plays a vital role in various tissues, while the role of ACh in bone metabolism remains unclear. Here we demonstrated that ACh induced cell proliferation and reduced alkaline phosphatase (ALP) activity via nicotinic (nAChRs) and muscarinic acetylcholine receptors (mAChRs) in osteoblasts. We detected mRNA expression of several nAChRs and mAChRs. Furthermore, we showed that cholinergic components were up‐regulated and subunits/subtypes of acetylcholine receptors altered during osteoblast differentiation. To our knowledge, this is the first report demonstrating that osteoblasts express specific acetylcholine receptors and cholinergic components and that ACh plays a possible role in regulating the proliferation and differentiation of osteoblasts.

Nicotine induces cell proliferation in association with cyclin D1 up-regulation and inhibits cell differentiation in association with p53 regulation in a murine pre-osteoblastic cell line.

Recent studies have suggested that nicotine critically affects bone metabolism. Many studies have examined the effects of nicotine on proliferation and differentiation, but the underlying molecular mechanisms remain unclear. We examined cell cycle regulators involved in the proliferation and differentiation of MC3T3-E1 cells. Nicotine induced cell proliferation in association with p53 down-regulation and cyclin D1 up-regulation. In differentiated cells, nicotine reduced alkaline phosphatase activity and mineralized nodule formation in dose-dependent manners. Furthermore, p53 expression was sustained in nicotine-treated cells during differentiation. These findings indicate that nicotine promotes the cell cycle and inhibits differentiation in association with p53 regulation in pre-osteoblastic cells.

Immunoglobulin G4–related sclerosing sialadenitis: report of two cases and review of the literature

A new concept of IgG4-related disease characterized by a high serum IgG4 level and tissue infiltration of IgG4-positive plasmacytes that can involve salivary glands has been proposed. In this article, 2 patients with IgG4-related sclerosing sialadenitis involving the submandibular glands are reported. One patient presented with bilateral and painless swelling of the submandibular glands. He had already been treated with systemic prednisolone owing to the occurrence of retrobulbar neuritis. Laboratory examinations showed high serum IgG4 concentrations, and a biopsy of the submandibular gland revealed the infiltration of IgG4-positive plasmacytes. Abdominal computerized tomography demonstrated tumefaction in the tail of the pancreas, thus suggesting localized autoimmune pancreatitis. The other patient also showed bilateral and painless swelling of the submandibular glands, but there was no involvement of any other organs. These patients were effectively treated with corticosteroids, which resulted in a reduction of the swelling of the submandibular gland and increased saliva. When a patient is suspected of having sclerosing sialadenitis, it is important to consider that the patient may have a systemic IgG4-related plasmacytic disease.

Expression of TLE3 by bone marrow stromal cells is regulated by canonical Wnt signaling

Transducing‐like enhancer of split 3 (TLE3), one of the Groucho/TLE family members, targets Runx2 transcription and suppresses osteoblast differentiation in bone marrow stromal cells (BMSCs). Here, we identify Wnt responsive elements of the TLE3 promoter region through comparative genomic and functional analyses and show that expression of TLE3 is increased by Wnt signaling, which is important for osteoblast differentiation. We also demonstrated that TLE3 is able to suppress canonical Wnt signaling in BMSCs. Taken together, our data suggest that induction of TLE3 by Wnt signaling is part of a negative feedback loop active during osteoblast differentiation.

Preliminary results of a study comparing conventional radiography with phase-contrast radiography for assessing root morphology of mandibular third molars

OBJECTIVES The aim of this study was to evaluate the usefulness of phase-contrast radiography for assessing root morphology of mandibular third molars in comparison with conventional radiography. METHODS We studied 37 extracted mandibular third molars. One oral surgeon compared the number of roots and root curvature of the extracted teeth on conventional radiographs with those on phase-contrast images. RESULTS The number of roots and root curvature on conventional images differed significantly from those on phase-contrast images. CONCLUSIONS Our results suggest the possibility that phase-contrast radiography is more useful than conventional radiography for assessing the root morphology of mandibular third molars.