Geometry sensing through POR1 regulates Rac1 activity controlling early osteoblast differentiation in response to nanofiber diameter.
Geometry sensing through POR1 regulates Rac1 activity controlling early osteoblast differentiation in response to nanofiber diameter.
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DOI：
10.1039/c4ib00225c
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发表时间：
2015-02
期刊：
影响因子：
--
通讯作者：
Brown JL
中科院分区：
文献类型：
--
作者：
Higgins AM;Banik BL;Brown JL
在美国，骨移植手术严重依赖于自体移植物和同种异体移植物，这是供体依赖性的，导致供体部位疼痛，并可能传播疾病。合成骨移植物可以降低这些风险;然而，合成骨缺乏自体和同种异体移植物的骨分化（骨诱导）能力。目前正在研究通过表面改性来实现合成材料的先天性骨诱导特性。本研究的重点是纳米纤维，重点是纤维直径和潜在的曲率传感器POR 1如何影响信号分子Rac 1和Arf 1的激活，并导致碱性磷酸酶（ALP），骨诱导标志物的表达。将0.1、0.3和1.0 μm直径与平坦对照品进行比较。在最小的纤维（0.1 μm）上实现了最高水平的Rac 1激活，这是POR 1敲低的长期趋势。这支持了这样的假设，即在小的纳米纤维上，POR 1有利地结合到高度弯曲的细胞膜上，这使得Rac 1随后解离并激活。当曲率不足以结合POR 1时，POR 1与失活的Rac 1结合并竞争性抑制其活化。Arf 1活化遵循相反的趋势，最大的纳米纤维表现出最高的活性。这种趋势加强了已知的Rac 1和Arf 1之间的相互作用，通过GIT/PIX复合物，Arf 1 GAP和Rac 1 GEF，分别。大的（1.0μm）纳米纤维表现出最高的ALP活性，表明ALP表达与Rac 1激活呈负相关。敲除POR 1导致整个底物的ALP活性增加，但不考虑先前观察到的曲率感测趋势。因此，POR 1感知弯曲并增加Rac 1活性，从而负调节骨分化。
Bone grafting procedures in the United States rely heavily upon autografts and allografts, which are donor-dependent, cause donor site pain, and can transmit disease. Synthetic bone grafts can reduce these risks; however, synthetics lack the bone differentiating (osteoinductive) abilities of auto- and allografts. Achieving innate osteoinductive properties of synthetics through surface modifications is currently under investigation. This study focuses on nanofibers, with emphasis on how fiber diameter and the potential curvature sensor POR1 affect the activation of the signalingmoleculesRac1 and Arf1, and leading to expression of alkaline phosphatase (ALP), an osteoinductive marker. Diameters of 0.1, 0.3, and 1.0 μm were compared against a flat control. The highest level of Rac1 activation was achieved on the smallest fibers (0.1 μm), a trend that was long in POR1 knockdowns. This supports the hypothesis that on small nanofibers, POR1 favorably binds to highly curved cell membranes, which allows Rac1 to subsequently dissociate and activate. When the curvature is insufficient to bind POR1, POR1 binds to inactive Rac1 and competitively inhibits its activation. Arf1 activation followed an opposite trend, with the largest nanofibers exhibiting the highest activity. This trend reinforces the known interaction between Rac1 and Arf1 through the GIT/PIX complex, an Arf1 GAP and Rac1 GEF, respectively. Large, (1.0μm), nanofibers demonstrated the highest ALP activity, indicating that ALP expression is inversely dependent on Rac1 activation. Knockdown of POR1 resulted in increased ALP activity across the substrates but without regard to the curvature sensing trend seen previously. Thus, POR1 senses curvature and increases Rac1 activity, which negatively regulates bone differentiation.
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