Interference with cellular differentiation by D-serine through antagonism at N-methyl-D-aspartate receptors composed of NR1 and NR3A subunits in chondrocytes
✍ Scribed by Takeshi Takarada; Yoshifumi Takahata; Mika Iemata; Eiichi Hinoi; Kyosuke Uno; Takao Hirai; Tomomi Yamamoto; Yukio Yoneda
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 349 KB
- Volume
- 220
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Abstract
Serine racemase (SR) is responsible for the biosynthesis of D‐serine (D‐Ser), an endogenous co‐agonist for the glycine (Gly)‐binding site on N‐methyl‐D‐aspartate (NMDA) receptors, from L‐Ser in the brain. We have previously demonstrated high expression of SR by chondrocytes in cartilage. In this study, we attempted to elucidate the possible functional role of D‐Ser in chondrogenesis. Expression of mRNA and corresponding protein was seen for SR in cultured rat costal chondrocytes, while the addition of L‐Ser significantly increased intracellular and extracellular levels of D‐Ser. In organotypic cultured mouse embryonic metatarsals isolated before vascularization, SR mRNA was highly localized in hypertrophic and calcified chondrocytes. Exposure to D‐Ser not only suppressed several chondrocytic maturation markers, including alkaline phosphatase (ALP) activity, Ca^2+^ accumulation, nodule formation, and osteopontin expression, in rat chondrocytes, but also delayed chondral mineralization in mouse metatarsals. Either NMDA or Gly alone significantly increased Ca^2+^ accumulation in cultured chondrocytes, whereas D‐Ser significantly prevented Ca^2+^ accumulation by Gly, but not by NMDA. Gly alone also significantly increased gene transactivation by the introduction of runt‐related transcription factor‐2 (Runx2) in COS7 cells transfected with NR1 and NR3A subunits, while D‐Ser significantly prevented the increase by Gly without affecting the promoter activity of Runx2. In both cultured chondrocytes and metatarsals from NR1‐null mice, significant decreases were seen in ALP activity and chondral mineralization, respectively. These results suggest that D‐Ser may negatively regulate cellular differentiation through inhibiting NMDA receptors composed of NR1 and NR3A subunits in a manner related to Runx2 transcriptional activity in chondrocytes. J. Cell. Physiol. 220: 756–764, 2009. © 2009 Wiley‐Liss, Inc.