Endothelial Cells Promote Migration of Mesenchymal Stem Cells via PDGF-BB/PDGFRß-Src-Akt in the Context of Inflammatory Microenvironment upon Bone Defect.

Homing of mesenchymal stem cells (MSCs) to the defect site is indispensable for bone repair. Local endothelial cells (ECs) can recruit MSCs; however, the mechanism remains unclear, especially in the context of the inflammatory microenvironment. This study was aimed to investigate the role of ECs in MSCs migration during the inflammatory phase of bone repair. The inflammatory microenvironment was mimicked in vitro via adding a cytokine set (IL-1ß, IL-6, and TNF-α) to the culture medium of ECs. The production of PDGF-BB from ECs was measured by ELISA. Transwell and wound healing assays were employed to assess MSCs migration toward ECs and evaluate the implication of PDGF-BB/PDGFRß. A series of shRNA and pathway inhibitors were used to screen signal molecules downstream of PDGF-BB/PDGFRß. Then, mouse models of femoral defects were fabricated and DBM scaffolds were implanted. GFP+ MSCs were injected via tail vein, and the relevance of PDGF-BB/PDGFRß, as well as screened signal molecules, in cell homing was further verified during the early phase of bone repair. In the mimicked inflammatory microenvironment, MSCs migration toward ECs was significantly promoted, which could be abrogated by pdgfrb knockout in MSCs. Inhibition of Src or Akt led to negative effects analogous to pdgfrb knockout. Blockade of JNK, MEK, and p38 MAPK had no impact. Meanwhile, the secretion of PDGF-BB from ECs was evidently motivated by the inflammatory microenvironment. Adding recombinant PDGF-BB protein to the culture medium of ECs phenocopied the inflammatory microenvironment with regard to attracting MSCs, which was abolished by pdgfb, src, or akt in MSCs. Moreover, pdgfb knockout suppressed the expression and phosphorylation of Src and Akt in migrating MSCs. Src knockout impaired Akt expression but not vice versa. In vivo, reduced infiltration of CD31+ ECs was correlated with diminished PDGF-BB in local defect sites, and silencing pdgfb, src, or akt in MSCs markedly hampered cell homing. Together, these findings suggest that in the inflammatory microenvironment, MSCs migrate toward ECs via PDGF-BB/PDGFRß and the downstream Src-Akt signal pathway.

Wnt/ß-catenin signalling promotes more effective fracture healing in aged mice than in adult mice by inducing angiogenesis and cell differentiation.

To investigate whether activating the Wnt/ß-catenin signalling pathway differentially promotes fracture healing in aged and adult individuals. CatnbTM2Kem, Catnblox(ex3) and wild-type adult and aged mice were used in this study. The femur was electroporated through a hole with a diameter of 0.6 mm. On the 7th, 14th and 21st days after fracture establishment, repair of the femoral diaphyseal bone was examined using X-ray and CT, the levels of mRNAs related to Wnt/ß-catenin signalling were detected using real-time polymerase chain reaction (RT-PCR), and angiogenesis and cell differentiation were observed using immunohistochemistry. The numbers of osteoclasts were determined by TRAP staining. Wnt/ß-catenin activation accelerated fracture healing in adult mice, with more pronounced effects on aged mice. Compared with wild-type mice at the corresponding ages, Wnt/ß-catenin signalling activation induced higher levels of angiogenesis and cell differentiation in aged mice than in adult mice and promoted fracture healing. The administration of medications targeting Wnt/ß-catenin signalling to aged patients may accelerate fracture healing to a greater extent.

Different effects of Wnt/ß-catenin activation and PTH activation in adult and aged male mice metaphyseal fracture healing.

BACKGROUND: Fractures in older men are not uncommon and need to be healed as soon as possible to avoid related complications. Anti-osteoporotic drugs targeting Wnt/ß-catenin and PTH (parathyroid hormone) to promote fracture healing have become an important direction in recent years. The study is to observe whether there is a difference in adult and aged situations by activating two signal paths. METHODS: A single cortical hole with a diameter of 0.6 mm was made in the femoral metaphysis of Catnblox(ex3) mice and wild-type mice. The fracture healing effects of CA (Wnt/ß-catenin activation) and PTH (activated by PTH (1-34) injections) were assessed by X-ray and CT imaging on days 7, 14, and 21 after fracture. The mRNA levels of ß-catenin, PTH1R(Parathyroid hormone 1 receptor), and RUNX2(Runt-related transcription factor 2) in the fracture defect area were detected using RT-PCR. Angiogenesis and osteoblasts were observed by immunohistochemistry and osteoclasts were observed by TRAP (Tartrate-resistant Acid Phosphatase). RESULT: Adult CA mice and adult PTH mice showed slightly better fracture healing than adult wild-type (WT) mice, but there was no statistical difference. Aged CA mice showed better promotion of angiogenesis and osteoblasts and better fracture healing than aged PTH mice. CONCLUSION: The application of Wnt/ß-catenin signaling pathway drugs for fracture healing in elderly patients may bring better early effects than PTH signaling pathway drugs, but the long-term effects need to be observed.

Preactivation of ß-catenin in osteoblasts improves the osteoanabolic effect of PTH in type 1 diabetic mice.

Type 1 diabetes (T1D) is correlated with osteopenia primarily due to low bone formation. Parathyroid hormone (PTH) is a known anabolic agent for bone, the anabolic effects of which are partially mediated through the Wnt/ß-catenin signaling pathway. In the present study, we first determined the utility of intermittent PTH treatment in a streptozotocin-induced T1D mouse model. It was shown that the PTH-induced anabolic effects on bone mass and bone formation were attenuated in T1D mice compared with nondiabetic mice. Further, PTH treatment failed to activate ß-catenin signaling in osteoblasts of T1D mice and was unable to improve osteoblast proliferation and differentiation. Next, the Col1-3.2 kb-CreERTM; ß-cateninfx(ex3) mice were used to conditionally activate ß-catenin in osteoblasts by injecting tamoxifen, and we addressed whether or not preactivation of ß-catenin boosted the anabolic action of PTH on T1D-related bone loss. The results demonstrated that pretreatment with activation of osteoblastic ß-catenin followed by PTH treatment outperformed PTH or ß-catenin activation monotherapy and led to greatly improved bone structure, bone mass, and bone strength in this preclinical model of T1DM. Further analysis demonstrated that osteoblast proliferation and differentiation, as well as osteoprogenitors in the marrow, were all improved in the combination treatment group. These findings indicated a clear advantage of developing ß-catenin as a target to improve the efficacy of PTH in the treatment of T1D-related osteopenia.

Different effects of Wnt/ß-catenin activation and parathyroid hormone on diaphyseal and metaphyseal in the early phase of femur bone healing of mice.

Parathyroid hormone (PTH) and agents related to the manipulation of Wnt/ß-catenin signalling are two promising anabolic anti-osteoporotic therapies that have been shown to promote the healing of bone fractures. Now, it is widely accepted that cortical bone and trabecular bone are two different compartments, and should be treated as separate compartments in pathological processes, such as fracture healing. It is currently unknown whether PTH and the activation of ß-catenin signalling would demonstrate different effects on cortical bone and trabecular bone healing. In the current study, single 0.6-mm cortex holes were made in the femur metaphysis and diaphysis of mice, and then, PTH application and ß-catenin activation were used to observe the promoting effect on bone healing. The effects of ß-catenin and PTH signalling on fracture healing were observed by X-ray and CT at 3, 6, and 14 days after fracture, and the levels of ß-catenin were detected by RT-PCR assay, and the number of specific antigen-positive cells of BRDU, OCN, RUNX2 was counted by immunohistochemical staining. While ß-catenin activation and PTH were found to demonstrate similar effects on accelerating metaphyseal bone healing, activation of ß-catenin showed a more striking effect than PTH on promoting diaphyseal bone healing. These findings might be helpful for selecting proper medication to accelerate fracture healing of different bone compartments.

Differential effects of type 1 diabetes mellitus and subsequent osteoblastic ß-catenin activation on trabecular and cortical bone in a mouse model.

Type 1 diabetes mellitus (T1DM) is a pathological condition associated with osteopenia. WNT/ß-catenin signaling is implicated in this process. Trabecular and cortical bone respond differently to WNT/ß-catenin signaling in healthy mice. We investigated whether this signaling has different effects on trabecular and cortical bone in T1DM. We first established a streptozotocin-induced T1DM mouse model and then constitutively activated ß-catenin in osteoblasts in the setting of T1DM (T1-CA). The extent of bone loss was greater in trabecular bone than that in cortical bone in T1DM mice, and this difference was consistent with the reduction in the expression of ß-catenin signaling in the two bone compartments. Further experiments demonstrated that in T1DM mice, trabecular bone showed lower levels of insulin-like growth factor-1 receptor (IGF-1R) than the levels in cortical bone, leading to lower WNT/ß-catenin signaling activity through the inhibition of the IGF-1R/Akt/glycogen synthase kinase 3ß (GSK3ß) pathway. After ß-catenin was activated in T1-CA mice, the bone mass and bone strength increased to substantially greater extents in trabecular bone than those in cortical bone. In addition, the cortical bone of the T1-CA mice displayed an unexpected increase in bone porosity, with increased bone resorption. The downregulated expression of WNT16 might be responsible for these cortical bone changes. In conclusion, we found that although the activation of WNT/ß-catenin signaling increased the trabecular bone mass and bone strength in T1DM mice, it also increased the cortical bone porosity, impairing the bone strength. These findings should be considered in the future treatment of T1DM-related osteopenia.

Expert consensus on the evaluation and diagnosis of combat injuries of the Chinese People's Liberation Army.

The accurate assessment and diagnosis of combat injuries are the basis for triage and treatment of combat casualties. A consensus on the assessment and diagnosis of combat injuries was made and discussed at the second annual meeting of the Professional Committee on Disaster Medicine of the Chinese People's Liberation Army (PLA). In this consensus agreement, the massive hemorrhage, airway, respiration, circulation and hypothermia (MARCH) algorithm, which is a simple triage and rapid treatment and field triage score, was recommended to assess combat casualties during the first-aid stage, whereas the abbreviated scoring method for combat casualty and the MARCH algorithm were recommended to assess combat casualties in level II facilities. In level III facilities, combined measures, including a history inquiry, thorough physical examination, laboratory examination, X-ray, and ultrasound examination, were recommended for the diagnosis of combat casualties. In addition, corresponding methods were recommended for the recognition of casualties needing massive transfusions, assessment of firearm wounds, evaluation of mangled extremities, and assessment of injury severity in this consensus.