All-trans-retinoic acid inhibits chondrogenesis of rat embryo hindlimb bud mesenchymal cells by downregulating p53 expression.

Despite the well-established role of all-trans-retinoic acid (ATRA) in congenital clubfoot (CCF)-like deformities in in vivo models, the essential cellular and molecular targets and the signaling mechanisms for ATRA-induced CCF-like deformities remain to be elucidated. Recent studies have demonstrated that p53 and p21, expressed in the hindlimb bud mesenchyme, regulate cellular proliferation and differentiation, contributing to a significant proportion of embryonic CCF-like abnormalities. The objective of the present study was to investigate the mechanisms for ATRA-induced CCF, by assessing ATRA-regulated chondrogenesis in rat embryo hindlimb bud mesenchymal cells (rEHBMCs) in vitro. The experimental study was based on varying concentrations of ATRA exposure on embryonic day 12.5 rEHBMCs in vitro. The present study demonstrated that ATRA inhibited the proliferation of cells by stimulating apoptotic cell death of rEHBMCs. It was also observed that ATRA induced a dose-dependent reduction of cartilage nodules compared with the control group. Reverse transcription-polymerase chain reaction and western blotting assays revealed that the mRNA and protein expression of cartilage-specific molecules, including aggrecan, Sox9 and collagen, type II, α 1 (Col2a1), were downregulated by ATRA in a dose-dependent manner; the mRNA levels of p53 and p21 were dose-dependently upregulated from 16 to 20 h of incubation with ATRA, but dose-dependently downregulated from 24 to 48 h. Of note, p53 and p21 were regulated at the translational level in parallel with the transcription with rEHBMCs treated with ATRA. Furthermore, the immunofluorescent microscopy assays indicated that proteins of p53 and p21 were predominantly expressed in the cartilage nodules. The present study demonstrated that ATRA decreases the chondrogenesis of rEHBMCs by inhibiting cartilage-specific molecules, including aggrecan, Sox9 and Col2al, via regulating the expression of p53 and p21.

All-trans-retinoid acid (ATRA) suppresses chondrogenesis of rat primary hind limb bud mesenchymal cells by downregulating p63 and cartilage-specific molecules.

P63 null mice have no or truncated limbs and mutations in human p63 cause several skeletal syndromes that also show limb and digit abnormalities, suggesting its essential role in bone development. In the current study, we investigated the effect of ATRA on chondrogenesis using mesenchymal cells from rat hind limb bud and further examined the mRNA and protein expression of Sox9 and Col2a1 and p63 in rat hind limb bud cells. Limb buds were isolated from embryos from euthanized female rats. Growth of hind limb bud mesenchymal cells was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assays. Formation of cartilage nodules was examined by Alcian blue-nuclear fast red staining. The expression of Sox9, Col2al and p63 was determined by Real-time RT-PCR and immunoblotting assays, respectively. Our MTT assays revealed that ATRA at 1 and 10µM significantly suppressed the growth of mesenchymal cells from rat hind limb bud at 24 and 48h (P<0.01 vs. controls). Alcian blue staining further showed that ATRA caused a significant dose-dependent reduction in the area of cartilage nodules (P<0.05 in all vs. controls). At 1µM ATRA, the area of cartilage nodules from hind limb bud cells was reduced to 0.05±0.03mm from 0.15±0.01mm in controls. Real-time RT-PCR assays further indicated that 1 and 10µM ATRA markedly reduced the mRNA expression of Sox9, Col2al and p63 in hind limb bud cells (P<0.05 in all vs. controls). In addition, ATRA time-dependently inhibits the mRNA expression of p63, Sox9 and Col2al. Western blotting assays additionally showed that ATRA dose-dependently reduced the expression of Sox9, Col2al and p63 (P<0.05 in all vs. controls). Together, our results suggest that ATRA suppresses chondrogenesis by modulating the expression of Sox9, Col2al and p63 in primary hind limb bud mesenchymal cells.

All-trans-retinoid acid (ATRA) may have inhibited chondrogenesis of primary hind limb bud mesenchymal cells by downregulating Pitx1 expression.

Despite frequently well-established role of all-trans-retinoid acid (ATRA) in congenital limb deformities, its mechanism of action, thus far, is still ambiguous. Pitx1, which is expressed in the hindlimb bud mesenchyme, or its pathways may be etiologically responsible for the increased incidence of clubfoot. Here, we sought to investigate the mechanisms whereby Pitx1 regulated chondrogenesis of hindlimb bud mesenchymal cells in vitro. E12.5 embryonic rat hind limb bud mesenchymal cells were treated with ATRA at appropriate concentrations. Cell Counting Kit-8 (CCK-8) assay was performed to evaluate cell proliferation. Hematoxylin-safranin-O-fast-green staining assays were used to observe cartilage nodules, and Pitx1 expression was examined by immunofluorescent microscopy. Real-time quantitative PCR and immunoblotting assays were applied to determine the mRNA expressions of Pitx1, Sox9 and type II collagen (Col2al), respectively. The results showed that ATRA inhibited the proliferation of hind limb bud cells dose-dependently. ATRA also induced a dose-dependent reduction in the number of cartilage nodules and the area of cartilage nodules compared with controls. Our real-time quantitative RT-PCR assays revealed that the mRNA expression of Pitx1, Sox9 and Col2al were significantly downregulated by ATRA. Furthermore, our immunofluorescent microscopy and Western blotting assays indicated that Pitx1 was mainly expressed in the cartilage nodules and the levels of Pitx1, Sox9 and Col2al were also downregulated by ATRA dose-dependently. The results indicated that ATRA may decrease chondrogenesis of hind limb bud mesenchymal cells by inhibiting cartilage-specific molecules, such as Sox9 and Col2al, via downregulating Pitx1 expression.