PRRX1+MSCs Enhance Mandibular Regeneration during Distraction Osteogenesis.

Bone defect (BD) caused by trauma, infection, congenital defects, or neoplasia is a major cause of physical limitation. Distraction osteogenesis (DO) is a highly effective procedure for bone regeneration, while the concrete mechanism remains unknown. In this study, canine DO and BD models of the mandible were established. The results of micro-computed tomography and histological staining revealed that DO led to an increased mineralized volume fraction and robust new bone formation; in contrast, BD demonstrated incomplete bone union. Mesenchymal stem cells (MSCs) from DO and BD calluses were isolated and identified. Compared with BD-MSCs, DO-MSCs were found to have a stronger osteogenic capability. Single-cell RNA sequencing analysis was further performed to comprehensively define cell differences between mandibular DO and BD calluses. Twenty-six clusters of cells representing 6 major cell populations were identified, including paired related homeobox 1-expressing MSCs (PRRX1+MSCs), endothelial cells (ECs), T cells, B cells, neutrophils, and macrophages. Interestingly, 2 subpopulations in PRRX1+MSCs in the DO group were found to express the marker of neural crest cells (NCCs) and were associated with the process of epithelial-mesenchymal transition. The immunofluorescence assay was performed to further corroborate these results in vivo and in vitro, experimentally validating that continuous distraction maintained the PRRX1+MSCs in an embryonic-like state. Finally, we used CRISPR/Cas9 to knock out (KO) PRRX1 in the context of DO, which significantly blunted the capability of jawbone regeneration, resulting in a diminished NCC-like program and reduction of new bone volume. In addition, the ability of osteogenesis, cell migration, and proliferation in cultured PRRX1KO MSCs was inhibited. Taken together, this study provides a novel, comprehensive atlas of the cell fates in the context of DO regeneration, and PRRX1+MSCs act essential roles.

Treatment of large bone defects with a novel biological transport disc in non-vascular transport distraction osteogenesis.

The aim of this study was to investigate a potential novel biological transport disc that avoids secondary injury to the body and facilitates bone healing. Twenty-seven dogs were divided randomly into three groups: group A were treated with human bone morphogenetic protein 2 (BMP-2) modified bone mesenchymal stem cell (BMSC) sheets combined with freeze-dried bone allograft as biological transport disc; group B were treated with BMSC sheets combined with freeze-dried bone allograft as transport disc (control); and group C were treated with direct extension only (blank). There were nine dogs in each group. Non-vascular transport distraction osteogenesis was performed in groups A and B to repair the mandibular bone defects, and in group C only mandibular truncation surgery was performed. The regeneration of bone was evaluated through X-ray, haematoxylin and eosin assay, and immunohistochemistry. After 2, 4, and 8 weeks of distraction, new bone density values in group A were 49.00±1.16, 66.63±2.62, and 72.78±2.67, respectively, and these were significantly different to values in groups B (P=0.0005, P=0.0004, P=0.0012) and C (P<0.0005, P=0.0001, P=0.0003). The average grey value for BMP-2 expression in group A after 4 weeks of distraction was 195.63±4.45, which was significantly different when compared to groups B (P=0.0022) and C (P=0.0006). This novel biological transport disc represents an effective non-secondary injury method to enhance new bone formation in non-vascular transport distraction osteogenesis.

Sister chromatid exchange induced by chromium compounds in human lymphocytes.

The objective of this study was to study was to compare chromium (Cr), nickel-chromium (Ni-Cr), and control groups for sister chromatid exchange (SCE) in lymphocytes to obtain an understanding of the mutagenic effect of Cr(VI) in humans. Subjects totaled 91 persons from the 3 groups, including 14 Cr and 34 Ni-Cr electroplating workers and 43 control group members. Results showed that blood and urine Cr concentrations were highest among Cr workers (11.39 microg/l, 14.7 microg/g creatinine), next highest among Ni-Cr workers (5.28 microg/l, 6.2 microg/g creatinine), and lowest among the control group (2.36 microg/l, NA). After adjustment for smoking habits, SCE/cell values were 10.6, 9.4, and 8.3 for Cr workers, Ni-Cr workers, and controls, respectively. A synergetic effect was shown on HFC (high-frequency cells) percentages for Cr workers who also smoked. Odds ratios were 31.78 and 3.66 that Cr and Ni-Cr workers would have higher HFC percentages than the control group, respectively. The authors conclude that SCE in lymphocytes is useful for evaluation of the biological effects of environmental mutagens.