Metformin accelerates bone fracture healing by promoting type H vessel formation through inhibition of YAP1/TAZ expression.

Due to increasing morbidity worldwide, fractures are becoming an emerging public health concern. This study aimed to investigate the effect of metformin on the healing of osteoporotic as well as normal fractures. Type H vessels have recently been identified as a bone-specific vascular subtype that supports osteogenesis. Here, we show that metformin accelerated fracture healing in both osteoporotic and normal mice. Moreover, metformin promoted angiogenesis in vitro under hypoxia as well as type H vessel formation throughout fracture healing. Mechanistically, metformin increased the expression of HIF-1α, an important positive regulator of type H vessel formation, by inhibiting the expression of YAP1/TAZ in calluses and hypoxia-cultured human microvascular endothelial cells (HMECs). The results of HIF-1α or YAP1/TAZ interference in hypoxia-cultured HMECs using siRNA further suggested that the enhancement of HIF-1α and its target genes by metformin is primarily through YAP1/TAZ inhibition. Finally, overexpression of YAP1/TAZ partially counteracted the effect of metformin in promoting type H vessel-induced angiogenesis-osteogenesis coupling during fracture repair. In summary, our findings suggest that metformin has the potential to be a therapeutic agent for fractures by promoting type H vessel formation through YAP1/TAZ inhibition.

MiR-19b-3p regulates osteogenic differentiation of PDGFRα+ muscle cells by specifically targeting PTEN.

Heterotopic ossification (HO) is a common disturbing complication of intra-articular fractures. Its prevention and treatment are still difficult as its pathogenesis is unclear. It was reported that PDGFRα+ muscle cells in skeletal muscle may participate in the formation of HO; however, the specific mechanism is still unknown. This study investigated the function of miR-19b-3p in osteogenic differentiation of PDGFRα+ muscle cells. MiR-19b-3p was upregulated during PDGFRα+ muscle cell osteogenic differentiation. The exogenous expression of miR-19b-3p led to an increase in osteogenic marker gene transcription and translation during the osteogenic differentiation of PDGFRα+ muscle cells. Furthermore, both alkaline phosphatase and alizarin red staining increased in miR-19b-3p mimic transfected cells. Over-expression of miR-19b-3p led to the down-regulation of gene of phosphate and tension homology deleted on chromosome ten (PTEN). Additionally, the dual luciferase reporter assay demonstrated that PTEN was a direct target of miR-19b-3p. The increase of osteocalcin, osteopontin, and Runt-related transcription factor 2 protein levels induced by ectopic miR-19b-3p expression could be partially reversed by PTEN over-expression. In conclusion, our results suggested that miR-19b-3p may be a promising target in inhibiting PDGFRα+ muscle cell osteogenic differentiation and treatment of HO.

Network Meta-Analysis of Pharmacological Agents for Osteoporosis Treatment and Fracture Prevention.

BACKGROUND AND OBJECTIVE: Osteoporosis afflicts a large number of populations in the world and is featured by systemic impairment of bone mass and strength which may further trigger an increase in the risk of fragile fractures. This network meta-analysis (NMA) is designed to distinguish therapies more preferable than others with respect to efficacy and safety. METHODS: We searched the medical literature for relevant studies systematically. Both direct and indirect evidence were synthesized to compare the efficacy, described by odds ratios (OR) and 95% credible intervals (CrI). Moreover, the surface under cumulative ranking curve was calculated to rank probabilities with respect to clinical outcomes. The new non-vertebral fractures, hip and wrist fractures, and adverse events were evaluated in this NMA. RESULTS: Patients treated by alendronate, denosumab, teriparatide were associated with a reduced risk of new non-vertebral fractures compared to those treated by placebo. Alendronate, denosumab and zoledronic acid had better efficacy in preventing hip fractures. With respect to wrist fractures prevention, no significant difference was observed. Zoledronic acid exhibited significantly increased risk of adverse events than placebo, alendronate, denosumab, and raloxifene. According to SUCRA, teriparatide ranked highest in new non-vertebral fractures prevention, etidronate and denosumab balanced safety and efficacy well. CONCLUSION: In summary, teriparatide appeared to be the most efficacious drug for preventing new non-vertebral fractures, while etidronate and denosumab were preferable for balancing safety and efficacy well.

Effect of partial and complete posterior cruciate ligament transection on medial meniscus: A biomechanical evaluation in a cadaveric model.

BACKGROUND: The relationship between medial meniscus tear and posterior cruciate ligament (PCL) injury has not been exactly explained. We studied to investigate the biomechanical effect of partial and complete PCL transection on different parts of medial meniscus at different flexion angles under static loading conditions. MATERIALS AND METHODS: TWELVE FRESH HUMAN CADAVERIC KNEE SPECIMENS WERE DIVIDED INTO FOUR GROUPS: PCL intact (PCL-I), anterolateral bundle transection (ALB-T), posteromedial bundle transection (PMB-T) and PCL complete transection (PCL-T) group. Strain on the anterior horn, body part and posterior horn of medial meniscus were measured under different axial compressive tibial loads (200-800 N) at 0°, 30°, 60° and 90° knee flexion in each groups respectively. RESULTS: Compared with the PCL-I group, the PCL-T group had a higher strain on whole medial meniscus at 30°, 60° and 90° flexion in all loading conditions and at 0° flexion with 400, 600 and 800 N loads. In ALB-T group, strain on whole meniscus increased at 30°, 60° and 90° flexion under all loading conditions and at 0° flexion with 800 N only. PMB-T exihibited higher strain at 0° flexion with 400 N, 600 N and 800 N, while at 30° and 60° flexion with 800 N and at 90° flexion under all loading conditions. CONCLUSIONS: Partial PCL transection triggers strain concentration on medial meniscus and the effect is more pronounced with higher loading conditions at higher flexion angles.

Granulocyte colony-stimulating factor enhances bone marrow mononuclear cell homing to the liver in a mouse model of acute hepatic injury.

BACKGROUND: Experiments have reported that granulocyte colony stimulating factor (G-CSF) can mobilize stem cells. However, few studies have examined the effect of G-CSF on bone marrow mononuclear cell (BMMC) mobilization, in particular regarding their capability to home to acutely injured liver. AIMS: The aim of this study was to evaluate the effort of G-CSF on BMMC homing to the liver following chemically-induced hepatic failure. METHODS: BMMC were isolated from mice, pre-labeled with PKH26 and infused into the mice in which hepatic injury had been induced followed by administration of G-CSF or vehicle. Livers were studied by fluorescent microscopy after transplantation of pre-labeled BMMC. RESULTS: PKH26 labeled cells were found in liver tissue at 102 ± 10 cells/high power field in the BMMC+G-CSF group and 30 ± 5 cells/high power field in the BMMC group, but none in the G-CSF group and the control group (P < 0.05). In the former two groups the majority of PKH26 labeled cells colocalized with proliferative cell nuclear antigen (PCNA). The number of PCNA positive cells in the BMMC+G-CSF group was 20 ± 4 cells/high power field, while in the BMMC group it was 14 ± 2 cells/high power field, in the G-CSF group 12 ± 2 cells/high power field, and 8 ± 1 cells/high power field in the control group. Moreover, albumin expression was increased in the BMMC+G-CSF treated group (149 ± 7/high power field) relative to the BMMC group (48 ± 6/high power field), the G-CSF group (44 ± 5/high power field) and the vehicle group (30 ± 6/high power field), with the former three groups showing elevated levels as compared to vehicle control (30 ± 6) (P < 0.05). CONCLUSION: Transplanted BMMC may home to injured liver, which appears to be enhanced by G-CSF administration.

Alterations of bone marrow sinusoidal endothelium in rat and patients with liver cirrhosis.

Whether bone marrow changes occur and potentially contribute to the hematological abnormalities in liver cirrhosis remain unclear. In this study, we established a rat model of liver cirrhosis induced by carbon tetrachloride. Electron microscopy examination showed focal lesions in bone marrow sinusoidal endothelium and hematopoietic cells in animals with cirrhosis. With the persistence of liver cirrhosis, injuries of bone marrow sinusoidal endothelium progressed from mild mitochondrial changes to nuclear pycnosis and cell disruption, and the trilineage hematopoietic cells showed apoptosis and necrosis. Immunohistochemistry revealed increased expression of E-selectin, P-selectin and vWF in bone marrow sinusoidal endothelium of the cirrhotic rats, which was consistent with the data from semiquantitative reverse transcriptase-polymerase chain reaction analysis. Autopsy specimens from patients with liver cirrhosis (in the absence of other disease) showed the same findings as detected by immunohistochemistry in animal models. The results provide evidence of the association between liver cirrhosis and bone marrow alterations by demonstrating the bone marrow sinusoidal endothelium lesions in both a rat model and patients. It also indicates that activation or injury of bone marrow sinusoidal endothelium mediated by E-selectin, P-selectin, and vWF might have a role in pathogenesis of bone marrow changes during liver cirrhosis. The lesions of bone marrow sinusoidal endothelium might contribute to the hematological abnormalities in the end stage of liver disease.

Electrophysiological and neuroanatomical evidence of sexual dimorphism in aortic baroreceptor and vagal afferents in rat.

Evidence for sexual dimorphism in autonomic control of cardiovascular function is both compelling and confounding. Across healthy and disease populations sex-associated differences in neurocirculatory hemodynamics are far too complex to be entirely related to sex hormones. As an initial step toward identifying additional physiological mechanisms, we investigated whether there is a sex bias in the relative expression of low-threshold-myelinated and high-threshold-unmyelinated aortic baroreceptor afferents in rats. These two types of afferent fibers have markedly different reflexogenic effects upon heart rate and blood pressure and thus the potential impact upon baroreflex dynamics could be substantial. Our results, using a combination of a patch-clamp study of fluorescently identified aortic baroreceptor neurons (ABN) and morphometric analysis of aortic baroreceptor nerve fibers, demonstrate that females exhibit a greater percentage of myelinated baroreceptor fibers (24.8% vs. 18.7% of total baroreceptor fiber population, P < 0.01) and express a functional subtype of myelinated ABN rarely found in age-matched males (11% vs. 2.3%, n = 107, P < 0.01). Interestingly, this neuronal phenotype is more prevalent in the general population of female vagal afferent neurons (17.7% vs. 3.8%, n = 169, P < 0.01), and ovariectomy does not alter its expression but does lessen neuronal excitability. These data suggest there are fundamental neuroanatomical and electrophysiological differences between aortic baroreceptor afferents of female and male rats. Possible explanations are presented as to how such a greater prevalence of low-threshold myelinated afferents could be a contributing factor to the altered baroreflex sensitivity and vagal tone of females compared with males.