To investigate the effects of dexamethasone on the proliferation and survival of mesenchyme and epithelium at the key stages of palatal development, and the molecular association with Wnt/β-catenin pathway.

Eighty pregnant C57 females (E8.5) were equally divided into two groups. The experimental group was intraperitoneally injected with dexamethasone (8 mg·kg^-1·d^-1) while the control group was with normal saline only untill E12.5. The heads of the embryos at E13.5 - E17.5 were collected and processed to paraffin. Sections were stained with hematoxylin and eosin for the palatal morphological assessment, and BrdU and TUNEL assays for the detection of proliferation and survival of palatal mesenchyme and epithelium, respectively. χ² test was used to analyze the group difference on cell proliferation and t test for cell apoptosis, respectively. The activity of Wnt/β-catenin pathway was analyzed using Western blot.

At E13.5, the cell proliferation rate of anterior palatal mesenchyme in the dexamethasone group was (35.5 ± 8.2) %, comparable to that in the control group[ (40.1 ± 7.4) %, χ²= 3.16, P= 0.075]. At E14.5, the proliferation rate of anterior palatal mesenchyme in the control group was (50.3 ± 10.0) %, and the proliferation rate in the dexamethasone group was significantly decreased [ (32.9 ± 8.8) %, χ²= 5.229, P= 0.011]. At E15.5, the proliferation rate of anterior palatal mesenchyme in the control group was (31.3 ± 6.5) %, and the proliferation rate in the dexamethasone group was also significantly decreased [ (18.5 ± 5.7) %, χ²= 4.433, P= 0.02]. However, no difference was observed for the posterior palatal mesenchyme and the epithelium. The Wnt/β-catenin pathway was significantly depressed in dexamethasone group.

Dexamethasone suppresses palatal mesenchymal cell proliferation by downregulation of Wnt/β-catenin signaling pathway, leading to cleft palate.