All-trans retinoic acid (atRA), the oxidative metabolite of
retinoic acid (RA), is essential for palatogenesis. Overdose RA is capable of inducing
cleft palate in mice and humans. Normal embryonic palatal mesenchymal (EPM) cell growth is crucial for shelf growth. Smad signaling is involved in many biological processes. However, it is not much clear if atRA could affect Smad signaling during EPM cells growth. In this study, the timed pregnant mice with maternal administration of 100 mg/kg
body weight of RA by gastric intubation were cervical dislocation executed to evaluate growth changes of palatal shelves by
hematoxylin and
eosin (H&E) staining. At the same time, a primary mouse EPM (MEPM) cell culture model was also established. MEPM cells were treated with atRA (0.1, 0.5, 1, 5 and 10 μM) for 24, 48 and 72 h. The results indicated that the sizes of the shelves were smaller than those in control. AtRA inhibited MEPM cell growth with both increasing concentration and increasing incubation time, especially at 72 h in vitro. Moreover, atRA significantly increased the
mRNA and
protein expression levels of Smad7 (P < .05), but the
mRNA and
protein expression levels of
PCNA were reduced (P < .05). We also found atRA inhibited phosphorylation of Smad2 compared with untreated group (P < .05). However, the
protein and
mRNA levels of Smad2 did not change both in atRA-treated and untreated group (P > .05). We demonstrated that RA induced inhibition of MEPM cell growth that could cause
cleft palate partly by down-regulation of Smad pathway.