Li Meng C M, Chow Simon K-H, Wong Ronald M Y, Chen Bailing, Cheng Jack C Y, Qin Ling, Cheung Wing-Hoi
Musculoskeletal Research Laboratory, Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Hong Kong, China.
Department of Spine Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China.
Bone Joint Res. 2022 Jul;11(7):465-476. doi: 10.1302/2046-3758.117.BJR-2021-0476.R2.
There is an increasing concern of osteoporotic fractures in the ageing population. Low-magnitude high-frequency vibration (LMHFV) was shown to significantly enhance osteoporotic fracture healing through alteration of osteocyte lacuno-canalicular network (LCN). Dentin matrix protein 1 (DMP1) in osteocytes is known to be responsible for maintaining the LCN and mineralization. This study aimed to investigate the role of osteocyte-specific DMP1 during osteoporotic fracture healing augmented by LMHFV.
A metaphyseal fracture was created in the distal femur of ovariectomy-induced osteoporotic Sprague Dawley rats. Rats were randomized to five different groups: 1) DMP1 knockdown (KD), 2) DMP1 KD + vibration (VT), 3) Scramble + VT, 4) VT, and 5) control (CT), where KD was performed by injection of short hairpin RNA (shRNA) into marrow cavity; vibration treatment was conducted at 35 Hz, 0.3 g; 20 minutes/day, five days/week). Assessments included radiography, micro-CT, dynamic histomorphometry and immunohistochemistry on DMP1, sclerostin, E11, and fibroblast growth factor 23 (FGF23). In vitro, murine long bone osteocyte-Y4 (MLO-Y4) osteocyte-like cells were randomized as in vivo groupings. DMP1 KD was performed by transfecting cells with shRNA plasmid. Assessments included immunocytochemistry on osteocyte-specific markers as above, and mineralized nodule staining.
Healing capacities in DMP1 KD groups were impaired. Results showed that DMP1 KD significantly abolished vibration-enhanced fracture healing at week 6. DMP1 KD significantly altered the expression of osteocyte-specific markers. The lower mineralization rate in DMP1 KD groups indicated that DMP1 knockdown was associated with poor fracture healing process.
The blockage of DMP1 would impair healing outcomes and negate LMHFV-induced enhancement on fracture healing. These findings reveal the importance of DMP1 in response to the mechanical signal during osteoporotic fracture healing. Cite this article: 2022;11(7):465-476.
老年人群中骨质疏松性骨折问题日益受到关注。低强度高频振动（LMHFV）已被证明可通过改变骨细胞陷窝 - 小管网络（LCN）显著促进骨质疏松性骨折愈合。已知骨细胞中的牙本质基质蛋白1（DMP1）负责维持LCN和矿化。本研究旨在探讨骨细胞特异性DMP1在LMHFV增强的骨质疏松性骨折愈合过程中的作用。
在卵巢切除诱导的骨质疏松性Sprague Dawley大鼠的股骨远端制造干骺端骨折。将大鼠随机分为五组：1）DMP1基因敲低（KD）组，2）DMP1 KD + 振动（VT）组，3）乱序序列 + VT组，4）VT组，5）对照组（CT），其中KD组通过向骨髓腔内注射短发夹RNA（shRNA）来实现；振动治疗频率为35 Hz，0.3 g；每天20分钟，每周五天）。评估包括X线摄影、显微CT、动态组织形态计量学以及对DMP1、硬化蛋白、E11和成纤维细胞生长因子23（FGF23）的免疫组织化学检测。在体外，将小鼠长骨骨细胞样细胞MLO - Y4按照体内分组方式进行随机分组。通过用shRNA质粒转染细胞来实现DMP1 KD。评估包括上述对骨细胞特异性标志物的免疫细胞化学检测以及矿化结节染色。
DMP1 KD组的愈合能力受损。结果显示，DMP1 KD在第6周时显著消除了振动增强的骨折愈合效果。DMP1 KD显著改变了骨细胞特异性标志物的表达。DMP1 KD组较低的矿化率表明DMP1基因敲低与骨折愈合过程不佳有关。
DMP1的阻断会损害愈合结果，并消除LMHFV诱导的骨折愈合增强作用。这些发现揭示了DMP1在骨质疏松性骨折愈合过程中对机械信号响应的重要性。引用本文：2022；11（7）：465 - 476。
