Mechanical strain-mediated reduction in RANKL expression is associated with RUNX2 and BRD2.

Mechanical loading-related strains trigger bone formation by osteoblasts while suppressing resorption by osteoclasts, uncoupling the processes of formation and resorption. Osteocytes may orchestrate this process in part by secreting sclerostin (SOST), which inhibits osteoblasts, and expressing receptor activator of nuclear factor-κB ligand (RANKL/TNFSF11) which recruits osteoclasts. Both SOST and RANKL are targets of the master osteoblastic transcription factor RUNX2. Subjecting human osteoblastic Saos-2 cells to strain by four point bending down-regulates their expression of SOST and RANKL without altering RUNX2 expression. RUNX2 knockdown increases basal SOST expression, but does not alter SOST down-regulation following strain. Conversely, RUNX2 knockdown does not alter basal RANKL expression, but prevents its down-regulation by strain. Chromatin immunoprecipitation revealed RUNX2 occupies a region of the RANKL promoter containing a consensus RUNX2 binding site and its occupancy of this site decreases following strain. The expression of epigenetic acetyl and methyl writers and readers was quantified by RT-qPCR to investigate potential epigenetic bases for this change. Strain and RUNX2 knockdown both down-regulate expression of the bromodomain acetyl reader BRD2. BRD2 and RUNX2 co-immunoprecipitate, suggesting interaction within regulatory complexes, and BRD2 was confirmed to interact with the RUNX2 promoter. BRD2 also occupies the RANKL promoter and its occupancy was reduced following exposure to strain. Thus, RUNX2 may contribute to bone remodeling by suppressing basal SOST expression, while facilitating the acute strain-induced down-regulation of RANKL through a mechanosensitive epigenetic loop involving BRD2.

Association analysis of the ACTN3 R577X polymorphism with passive muscle stiffness and muscle strain injury.

Passive muscle stiffness is considered to be a major factor affecting joint flexibility and is thought to relate to the occurrence of muscle strain injury. In skinned muscle fiber experiments, the R577X polymorphism of the α-actinin-3 gene (ACTN3) has been associated with passive muscle stiffness. Our primary purpose was to clarify whether the ACTN3 R577X polymorphism influences passive stiffness of human muscle in vivo. We also examined whether the ACTN3 R577X polymorphism is associated with the occurrence of hamstring strain injury. Seventy-six healthy young male subjects were genotyped for the ACTN3 R577X (rs1815739) polymorphism. Shear modulus (an index of stiffness) of each hamstring muscle (biceps femoris, semitendinosus, and semimembranosus) was assessed using ultrasound shear wave elastography, and history of hamstring strain injury was collected via a questionnaire. The muscle shear moduli of the semitendinosus and semimembranosus were significantly higher in R-allele (RR + RX genotype) carriers than in XX genotype carriers, whereas the shear modulus of the biceps femoris did not differ among the ACTN3 R577X genotypes. Frequency of past hamstring strain injury also did not differ between the 3 genotypes nor between the R-allele and XX genotype carriers. This study indicates that RR and RX genotypes of the ACTN3 R577X polymorphism (corresponding to the presence of α-actinin-3 in type II muscle fibers) are associated with increased passive muscle stiffness of the human hamstring in vivo. However, this altered mechanical property might not affect the risk of hamstring muscle strain injury.

Two genetic loci associated with ankle injury.

Ankle injuries, including sprains, strains and other joint derangements and instability, are common, especially for athletes involved in indoor court or jumping sports. Identifying genetic loci associated with these ankle injuries could shed light on their etiologies. A genome-wide association screen was performed using publicly available data from the Research Program in Genes, Environment and Health (RPGEH) including 1,694 cases of ankle injury and 97,646 controls. An indel (chr21:47156779:D) that lies close to a collagen gene, COL18A1, showed an association with ankle injury at genome-wide significance (p = 3.8x10-8; OR = 1.99; 95% CI = 1.75-2.23). A second DNA variant (rs13286037 on chromosome 9) that lies within an intron of the transcription factor gene NFIB showed an association that was nearly genome-wide significant (p = 5.1x10-8; OR = 1.63; 95% CI = 1.46-1.80). The ACTN3 R577X mutation was previously reported to show an association with acute ankle sprains, but did not show an association in this cohort. This study is the first genome-wide screen for ankle injury that yields insights regarding the genetic etiology of ankle injuries and provides DNA markers with the potential to inform athletes about their genetic risk for ankle injury.

The association between the ACTN3 R577X polymorphism and noncontact acute ankle sprains.

Ankle sprains are one of the most severe musculoskeletal soft tissue injuries during physical activity. Although many risk factors have been offered, it is unclear why some individuals develop noncontact ankle sprains when participating in comparable levels of physical exertion under identical environmental conditions and others do not. The ACTN3 gene that encodes the α-actinin-3 protein, which is, only expressed in the Z line of fast glycolytic muscle fibres was found to associate with power/strength performance. The aim of this study was therefore to investigate whether the ACTN3 gene polymorphism is associated with noncontact acute ankle sprains. One hundred and forty-two participants with clinically diagnosed noncontact acute ankle sprains as well as 280 physically active controls participants without any history of ankle sprains were included in this case-control genetic association study. The RR genotype (odds ratio (OR) = 0.56; 95% confidence interval (CI), 0.32-0.65, P = 0.011) and R allele (OR = 0.64; 95% CI, 0.37-0.68, P = 0.002) of the ACTN3 were significantly low-represented in the acute ankle sprains group compared with the control group. The ACTN3 R577X is associated with acute ankle sprains in Chinese participants in this study. This is the first study to suggest that an individual with a RR genotype is at a decreased risk of acute ankle sprains.

The impact of single nucleotide polymorphisms on patterns of non-contact musculoskeletal soft tissue injuries in a football player population according to ethnicity / Impacto de los polimorfismos de nucleótido único en los patrones de lesiones de tejido muscular esqueletico, sin mecanismo de contacto, en una población de jugadores de fútbol según la etnia

Background and objective: The prevention, diagnosis, and management of non-contact musculoskeletal soft tissue injuries (NCMSTIs) related to participation in sports are key components of sport and exercise medicine. Epidemiological data have demonstrated the existence of interindividual differences in the severity of NCMSTIs, indicating that these injuries occur as a consequence of both extrinsic and intrinsic factors, including genetic variations. Subjects and methods: We have collected data on NCMSTIs suffered by 73 elite players of White, black African and Hispanic ethnicity of European football over the course of three consecutive seasons. We have also examined eight single nucleotide polymorphisms (SNPs) in genes related to tissue recovery and tissue repair in blood drawn from the players and correlated our findings with type and severity of injuries in each ethnic group. Results: The frequency of the SNPs varied among the three ethnic sub-groups (p < 0.0001). Among Whites, a significant relationship was observed between ligament injuries and ELN (p = 0.001) and between tendinous injuries and ELN (p = 0.05) and IGF2 (p = 0.05). Among Hispanics, there was a significant relation between muscle injuries and ELN (p = 0.032) and IGF2 (p = 0.016). Conclusions: Interracial genotypic differences may be important in the study of NCMSTIs. A genetic profile based on SNPs may be useful tool to describe each individual's injuribility risk and provide specific treatment and preventive care for football players (AU)

Fundamento y objetivo: La prevención, el diagnóstico y el tratamiento de las non-contact musculoskeletal soft tissue injuries(NCMSTI, «lesiones musculoesqueléticas producidas por el mecanismo de no contacto») son factores clave en el deporte y en la medicina deportiva. La interacción entre factores extrínsecos e intrínsecos, incluyendo en estos últimos los factores genéticos, es determinante en la causalidad de las NCMSTI. Sujetos y métodos: Se han recogido las lesiones sufridas por 73 jugadores de fútbol profesional de diferentes razas (caucásicos, africanos subsaharianos e hispánicos), ocurridas durante 3 temporadas consecutivas. Se analizó la presencia de single nucleotide polymorphisms (SNP, «polimorfismos genéticos de un solo nucleótido») en un conjunto de genes relacionados con la reparación y la regeneración del tejido a partir de sangre obtenida de los jugadores, y se correlacionó con el tipo y grado de lesión en cada grupo racial. Resultados: La frecuencia de aparición de los SNP varía en las 3 poblaciones estudiadas (p < 0,0001). En cuanto a la población caucásica, se observa una relación estadísticamente significativa entre lesiones ligamentosas y ELN (p = 0,001) y entre lesión tendinosa y ELN (p = 0,05) e IGF2 (p = 0,05). En cuanto a la población hispánica, existe una relación estadísticamente significativa entre la lesión muscular y ELN (p = 0,032) e IGF2 (p = 0,016). Conclusiones: Las diferencias genotípicas interraciales pueden ser importantes en el estudio de las NCMSTI. Un perfil genético basado en los SNP podría ser una herramienta útil para describir el riesgo individual de un individuo a lesionarse y poder aplicar de esta manera los tratamientos preventivos adecuados (AU)

[[Screening of differentially expressed miRNAs related to muscle strain and their target genes].

Muscle strain is one of the most common muscle injuries seen in the office of a practicing physician. To get a better understanding of this injury, we identified the differentially expressed miRNAs in muscle stem cells collected from injured muscle tissues of mouse. In this study, we downloaded the gene expression microarray (GSE26780) from Gene Expression Omnibus database. The dataset contained a total of 12 samples (murine muscle stem cells), including normal controls and samples collected from tissues at different time points after the injury. Differentially expreesed miRNAs were identified by LIMMA package and target genes of mmu-miR-143 were found by TargetScan. Then, a protein-protein in- teraction (PPI) network was constructed for the products of these target genes by using KUPS. Finally, Cytoscape and its plugins were used to identify and analyze the modules in this network. According to the results, 121, 136 and 148 differentially expressed miRNAs were identified in injured samples at each time point, and among them, 60 miRNAs were overlapping between all three groups. The expression values of mmu-miR-143 were most significantly altered over time at 36-72 h after the injury. Therefore, 510 target genes of mmu-miR-143 were found and a PPI network for the products of these target genes was constructed. Moreover, two modules were identified in the PPI network. Together with the previous studies, we suppose that proteins in module B, most of which are collagens or integrins, most likely participate in healing of strain injuries through cell adhesion processes.

Genomic loci and candidate genes underlying inflammatory nociception.

Heritable genetic factors contribute significantly to inflammatory nociception. To determine candidate genes underlying inflammatory nociception, the current study used a mouse model of abdominal inflammatory pain. BXD recombinant inbred (RI) mouse strains were administered the intraperitoneal acetic acid test, and genome-wide quantitative trait locus (QTL) mapping was performed on the mean number of abdominal contraction and extension movements in 3 distinct groups of BXD RI mouse strains in 2 separate experiments. Combined mapping results detected 2 QTLs on chromosomes (Chr) 3 and 10 across experiments and groups of mice; an additional sex-specific QTL was detected on Chr 16. The results replicate previous findings of a significant QTL, Nociq2, on distal Chr 10 for formalin-induced inflammatory nociception and will aid in identification of the underlying candidate genes. Comparisons of sensitivity to intraperitoneal acetic acid in BXD RI mouse strains with microarray mRNA transcript expression profiles in specific brain areas detected covarying expression of candidate genes that are also found in the detected QTL confidence intervals. The results indicate that common and distinct genetic mechanisms underlie heritable sensitivity to diverse inflammatory insults, and provide a discrete set of high-priority candidate genes to investigate further in rodents and human association studies. Novel genomic regions linked to inflammatory nociception were detected, a previously reported locus was confirmed, and high-priority candidate genes for inflammatory nociception and pain were identified.

Molecular and cellular adaptations to chronic myotendinous strain injury in mdx mice expressing a truncated dystrophin.

Myotendinous strain injury is the most common injury of human skeletal muscles because the majority of muscle forces are transmitted through this region. Although the immediate response to strain injury is well characterized, the chronic response to myotendinous strain injury is less clear. Here we examined the molecular and cellular adaptations to chronic myotendinous strain injury in mdx mice expressing a microdystrophin transgene (microdystrophin(DeltaR4-R23)). We found that muscles with myotendinous strain injury had an increased expression of utrophin and alpha7-integrin together with the dramatic restructuring of peripheral myofibrils into concentric rings. The sarcolemma of the microdystrophin(DeltaR4-R23)/mdx gastrocnemius muscles was highly protected from experimental lengthening contractions, better than wild-type muscles. We also found a positive correlation between myotendinous strain injury and ringed fibers in the HSA(LR) (human skeletal actin, long repeat) mouse model of myotonic dystrophy. We suggest that changes in protein expression and the formation of rings are adaptations to myotendinous strain injury that help to prevent muscle necrosis and retain the function of necessary muscles during injury, ageing and disease.