Vitamin D Receptor–Dependent 1α,25(OH)2 Vitamin D3–Induced Anti‐Apoptotic PI3K/AKT Signaling in Osteoblasts
Vitamin D Receptor–Dependent 1α,25(OH)2 Vitamin D3–Induced Anti‐Apoptotic PI3K/AKT Signaling in Osteoblasts
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DOI：
10.1359/jbmr.080326
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发表时间：
2008-08
影响因子：
6.2
通讯作者：
Xiaoyu Zhang;L. Zanello
中科院分区：
文献类型：
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作者：
Xiaoyu Zhang;L. Zanello
成骨细胞凋亡在骨重塑中起着至关重要的作用。生理剂量的1α，25(OH)2 -维生素D3 （1,25 d）保护成骨细胞免受凋亡，其机制仅部分了解。我们研究了成骨细胞中1,25 d非基因组刺激磷脂酰肌苷激酶（PI3K）下游Akt存活级联的激活。我们在培养的成骨细胞中测量了剂量和时间依赖性的1,25 d诱导Akt磷酸化（p - Akt）。给药10 nM， 1,25D， 5 min后达到最大反应。我们发现STSP诱导的细胞凋亡在1,25d预处理的成骨细胞中显著减少。当细胞与PI3K激活抑制剂预孵育时，1,25 d的促生存作用被消除。通过siRNA沉默，我们证明了1,25D诱导p - Akt需要成骨细胞中经典的维生素D受体（VDR）。此外，转染增强绿色荧光蛋白(EGFP) - VDR构建物的非成骨细胞CV - 1细胞对1,25 d处理有快速的p - Akt反应，与细胞存活增加相关，这在原生未转染的细胞中未检测到。我们测量了1,25 d处理后，p - Akt底物p - Bad和p - FKHR水平升高，caspases 8和3/7活性显著降低。此外，1,25 d诱导的细胞凋亡保护作用在百日咳毒素预孵育成骨细胞时被消除。我们得出结论，1,25 d在成骨细胞中的抗凋亡作用是通过非基因组激活VDR/PI3K/Akt存活途径发生的，包括多种p - Akt底物的磷酸化和caspase活性的降低。
Osteoblast apoptosis plays a crucial role in bone remodeling. Physiological doses of 1α,25(OH)2‐vitamin D3 (1,25D) protect osteoblasts against apoptosis by means of mechanisms only partially understood. We studied activation of an Akt survival cascade downstream of 1,25D nongenomic stimulation of phosphatidylinositide‐3′‐kinase (PI3K) in osteoblastic cells. We measured a dose‐ and time‐dependent 1,25D induction of Akt phosphorylation (p‐Akt) in cultured osteoblastic cells. Maximal response was achieved with 10 nM 1,25D after 5 min. We found that staurosporine (STSP)‐induced apoptosis was significantly reduced in 1,25D‐pretreated osteoblasts. 1,25D prosurvival effects were abolished when cells were preincubated with inhibitors of PI3K activation. By means of siRNA silencing, we proved that 1,25D induction of p‐Akt requires a classic vitamin D receptor (VDR) in osteoblasts. Furthermore, non‐osteoblastic CV‐1 cells transfected with an enhanced green fluorescent protein (EGFP)‐VDR construct responded to 1,25D treatment with a rapid p‐Akt response associated with increased cell survival not detected in native, nontransfected cells. We measured increased levels of p‐Akt substrates p‐Bad and p‐FKHR and significantly reduced activity of caspases 8 and 3/7 after 1,25D treatment. In addition, 1,25D‐induced protection against apoptosis was abolished when osteoblasts were preincubated with pertussis toxin. We conclude that anti‐apoptotic effects of 1,25D in osteoblasts occur through nongenomic activation of a VDR/PI3K/Akt survival pathway that includes phosphorylation of multiple p‐Akt substrates and reduction of caspase activities.