BACKGROUND:The effectiveness of bone repair is determined by the balance of proliferative and destructive factors in the fracture union site. It can be enhanced by using various nanostructured materials possessing osteoinductive properties, in particular titanium implants with biodegradable calciumphosphate coatings. The effects of these coatings on the state of stem cells, their differentiation and distribution in the repair zone is unknown. OBJECTIVE: To study the dynamics of proliferation, differentiation, and apoptosis of stem cells after experimental fracture followed by implantation of titanium implants with calcium phosphate coatings. METHODS:The localization of proliferation (PCNA) and differentiation (CD44 and osteocalcin) factors and apoptotic molecules (MDM2, p53, caspase-3) was studied in a rat femoral fracture model with implant placement. Titanium implant screws with bioactive calcium phosphate and hydroxyapatite coatings formed by plasma electrolytic oxidation were used in the study. Experimental rats were arranged into three groups (15 animals per group): control group; rats implanted with uncoated implants; and rats implanted with coated implants. Control rats were subject to a similar fracture as experimental ones and were allowed to heal conservatively. Rats from all groups were sampled on days 7, 14, and 30 after injury. RESULTS:Low-differentiated PCNA-, osteocalcin-, and CD44-immunopositive cells were localized around the implant in the inner layer of the periosteum, layer of outer circumferential lamellae, and connective tissue lining of haversian canals. The spatial density of cells expressing the above proliferation and differentiation factors, as well as that of MDM2-immunoreactive cells, increased on day 7 and decreased by day 30 after injury. The spatial density of apoptotic cells reached the maximum on day 14 after injury. They were mainly found in the inner layer of the periosteum and outer circumferential lamellae. p53- and caspase-3-positive cells occurred on the surface of the concentric lamellae surrounding haversian canals and under the periosteum. Their spatial density decreased by day 30 after injury. CONCLUSIONS:Calcium phosphate coatings stimulate cell proliferation at early stages of fracture restoration and apoptotic cell death at later stages. Coating components may provide positional information guiding the differentiation of mesenchymal stromal cells. A change in the activity of apoptotic factors, osteocalcin, and CD44 is caused by gene induction in response to the diffusion of calcium phosphate compounds from coating to surrounding tissue.

中文翻译：

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钛种植体磷酸钙生物降解涂层对实验性骨折大鼠骨组织细胞分化和凋亡的影响

背景：骨修复的有效性取决于骨折愈合部位增殖和破坏因素的平衡。它可以通过使用具有骨诱导特性的各种纳米结构材料来增强，特别是具有可生物降解磷酸钙涂层的钛植入物。这些涂层对干细胞状态、它们在修复区的分化和分布的影响尚不清楚。目的：研究实验性骨折继以磷酸钙涂层钛种植体植入后干细胞增殖、分化和凋亡的动态变化。方法：增殖 (PCNA) 和分化（CD44 和骨钙素）因子和凋亡分子（MDM2、p53、caspase-3) 在带有植入物的大鼠股骨骨折模型中进行了研究。研究中使用了具有生物活性磷酸钙和通过等离子体电解氧化形成的羟基磷灰石涂层的钛种植体螺钉。实验大鼠分为三组（每组15只）：对照组；植入无涂层植入物的大鼠；和植入涂层植入物的大鼠。对照大鼠遭受与实验大鼠相似的骨折，并允许保守愈合。在受伤后第 7、14 和 30 天对所有组的大鼠进行采样。结果：低分化的 PCNA、骨钙素和 CD44 免疫阳性细胞位于植入物周围的骨膜内层、外周板层和哈弗氏管结缔组织衬里。表达上述增殖和分化因子的细胞以及 MDM2 免疫反应性细胞的空间密度在损伤后第 7 天增加并在第 30 天下降。凋亡细胞的空间密度在损伤后第 14 天达到最大值。它们主要存在于骨膜内层和外周薄层中。p53 和 caspase-3 阳性细胞出现在哈弗氏管周围的同心薄片表面和骨膜下。它们的空间密度在受伤后第 30 天下降。结论：磷酸钙涂层在骨折修复的早期阶段刺激细胞增殖，在后期细胞凋亡。涂层成分可以提供指导间充质基质细胞分化的位置信息。