Zhang Shuang, Chen Xiaoting, Hu Yan, Wu Jin, Cao Qing, Chen Shuyan, Gao Yanhong
Department of Geriatrics, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
Shanghai Institute for Pediatric Research, Shanghai Jiaotong University School of Medicine, Shanghai, China.
Mol Cell Endocrinol. 2016 Feb 15;422:243-253. doi: 10.1016/j.mce.2015.12.018. Epub 2015 Dec 31.
Osteogenic differentiation of mesenchymal stem cells (MSCs) is a vital process for the maintenance of healthy bone tissue and is mediated by numerous factors. Canonical Wnt signalling is essential for MSC osteogenic differentiation, and it interacts with several nuclear receptors, including the retinoic acid receptor, vitamin D receptor, and glucocorticoid receptor. Here, we explored whether Wnt3A and all-trans-retinoic acid (ATRA) play synergistic roles in MSC osteogenic differentiation. We found that ATRA potentiated the Wnt3A-induced expression of early and late osteogenic markers as well as matrix mineralization and further confirmed the phenomena using foetal limb explant culture and MSC implantation experiments. Mechanistically, ATRA cooperated with Wnt3A to induce β-catenin translocation from cell-cell contacts into the cytosol and nucleus, thereby activating Wnt/β-catenin signalling. Additionally, Wnt3A attenuated ATRA-induced Cyp26a1 expression, inhibiting the degradation of ATRA into its oxidative forms. β-catenin silencing abolished the stimulatory effect of ATRA on Wnt3A-induced alkaline phosphatase (ALP) activity and reversed its inhibitory effect on Cyp26a1 expression. Furthermore, ATRA and Wnt3A synergistically promoted AKT phosphorylation, enhancing β-catenin-dependent transcription through GSK3β inhibition or direct β-catenin phosphorylation at Ser552. This event was largely abolished by LY294002 pre-treatment, suggesting that ATRA and Wnt3A at least partially promote osteogenic differentiation via activating the PI3K/AKT/GSK3β signalling pathway. Thus, crosstalk between the Wnt/β-catenin and retinoic acid signalling pathways may be an effective therapeutic target for bone diseases, such as osteoporosis.
间充质干细胞（MSCs）的成骨分化是维持健康骨组织的关键过程，且受多种因素介导。经典Wnt信号通路对MSCs的成骨分化至关重要，它与多种核受体相互作用，包括视黄酸受体、维生素D受体和糖皮质激素受体。在此，我们探究了Wnt3A和全反式维甲酸（ATRA）在MSCs成骨分化中是否发挥协同作用。我们发现，ATRA增强了Wnt3A诱导的早期和晚期成骨标志物的表达以及基质矿化，并通过胎儿肢体外植体培养和MSCs植入实验进一步证实了这些现象。从机制上讲，ATRA与Wnt3A协同作用，诱导β-连环蛋白从细胞间连接转位至细胞质和细胞核，从而激活Wnt/β-连环蛋白信号通路。此外，Wnt3A减弱了ATRA诱导的Cyp26a1表达，抑制了ATRA向其氧化形式的降解。β-连环蛋白沉默消除了ATRA对Wnt3A诱导的碱性磷酸酶（ALP）活性的刺激作用，并逆转了其对Cyp26a1表达的抑制作用。此外，ATRA和Wnt3A协同促进AKT磷酸化，通过抑制GSK3β或直接在Ser552位点磷酸化β-连环蛋白来增强β-连环蛋白依赖性转录。LY294002预处理在很大程度上消除了这一现象，表明ATRA和Wnt3A至少部分通过激活PI3K/AKT/GSK3β信号通路促进成骨分化。因此，Wnt/β-连环蛋白和视黄酸信号通路之间的相互作用可能是骨质疏松等骨疾病的有效治疗靶点。
