Repetitive jumping and sprinting until exhaustion alters hamstring reflex responses and tibial translation in males and females

The incidence of anterior cruciate ligament injuries is considerably higher in females than in males and the underlying mechanisms are still under debate. Research indicates that the neuromuscular system of females and males might respond differently to the same fatigue protocol due to differences in muscle activation during movement tasks. This study analyzed sex differences in hamstring reflex responses and posterior‐anterior tibial translation (TT) before and after fatiguing exercise. We measured the isolated movement of the tibia relative to the femur as a consequence of mechanically induced TT in standing subjects as well as muscle activity of the hamstrings before and after repetitive jumping and sprinting until exhaustion. Muscle fatigue delayed reflex onset latencies in females and males. A reduction in reflex responses associated with an increased TT was observed after fatiguing exercise for both sexes. Data indicate that the used fatigue protocol altered the latency and magnitude of reflex responses as well as TT in females and males. Based on the results of previous research and the outcome of this study, it might be that sex‐specific effects of fatigue on reflex activity and mechanical stability of the knee depend on the kind of fatiguing exercise. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1687–1692, 2015.     

SDF‐1/CXCR4/CXCR7 is pivotal for vascular smooth muscle cell proliferation and chronic allograft vasculopathy

Chronic rejection remains a major obstacle in transplant medicine. Recent studies suggest a crucial role of the chemokine SDF‐1 on neointima formation after injury. Here, we investigate the potential therapeutic effect of inhibiting the SDF‐1/CXCR4/CXCR7 axis with an anti‐SDF‐1 Spiegelmer (NOX‐A12) on the development of chronic allograft vasculopathy. Heterotopic heart transplants from H‐2bm12 to B6 mice and aortic transplants from Balb/c to B6 were performed. Mice were treated with NOX‐A12. Control animals received a nonfunctional Spiegelmer (revNOX‐A12). Samples were retrieved at different time points and analysed by histology, RT‐PCR and proliferation assay. Blockade of SDF‐1 caused a significant decrease in neointima formation as measured by intima/media ratio (1.0 ± 0.1 vs. 1.8 ± 0.1, P < 0.001 AoTx; 0.35 ± 0.05 vs. 1.13 ± 0.27, P < 0.05 HTx). In vitro treatment of primary vascular smooth muscle cells with NOX‐A12 showed a significant reduction in proliferation (0.42 ± 0.04 vs. 0.24 ± 0.03, P < 0.05). TGF‐β, TNF‐α and IL‐6 levels were significantly reduced under SDF‐1 inhibition (3.42 ± 0.37 vs. 1.67 ± 0.33, P < 0.05; 2.18 ± 0.37 vs. 1.0 ± 0.39, P < 0.05; 2.18 ± 0.26 vs. 1.6 ± 0.1, P < 0.05). SDF‐1/CXCR4/CXCR7 plays a critical role in the development of chronic allograft vasculopathy (CAV). Therefore, pharmacological inhibition of SDF‐1 with NOX‐A12 may represent a therapeutic option to ameliorate chronic rejection changes.     

Factor IX variants improve gene therapy efficacy for hemophilia B

Intramuscular injection of adeno-associated viral (AAV) vector to skeletal muscle of humans with hemophilia B is safe, but higher doses are required to achieve therapeutic factor IX (F.IX) levels. The efficacy of this approach is hampered by the retention of F.IX in muscle extracellular spaces and by the limiting capacity of muscle to synthesize fully active F.IX at high expression rates. To overcome these limitations, we constructed AAV vectors encoding F.IX variants for muscle- or liver-directed expression in hemophilia B mice. Circulating F.IX levels following intramuscular injection of AAV-F.IX-K5A/V10K, a variant with low-affinity to extracellular matrix, were 2-5 fold higher compared with wild-type (WT) F.IX, while the protein-specific activities remained similar. Expression of F.IX-R338A generated a protein with 2- or 6-fold higher specific activity than F.IX-WT following vector delivery to skeletal muscle or liver, respectively. F.IX-WT and variant forms provide effective hemostasis in vivo upon challenge by tail-clipping assay. Importantly, intramuscular injection of AAV-F.IX variants did not trigger antibody formation to F.IX in mice tolerant to F.IX-WT. These studies demonstrate that F.IX variants provide a promising strategy to improve the efficacy for a variety of gene-based therapies for hemophilia B.     

Mutation of POC1B in a Severe Syndromic Retinal Ciliopathy

We describe a consanguineous Iraqi family with Leber congenital amaurosis (LCA), Joubert syndrome (JBTS), and polycystic kidney disease (PKD). Targeted next‐generation sequencing for excluding mutations in known LCA and JBTS genes, homozygosity mapping, and whole‐exome sequencing identified a homozygous missense variant, c.317G>C (p.Arg106Pro), in POC1B, a gene essential for ciliogenesis, basal body, and centrosome integrity. In silico modeling suggested a requirement of p.Arg106 for the formation of the third WD40 repeat and a protein interaction interface. In human and mouse retina, POC1B localized to the basal body and centriole adjacent to the connecting cilium of photoreceptors and in synapses of the outer plexiform layer. Knockdown of Poc1b in zebrafish caused cystic kidneys and retinal degeneration with shortened and reduced photoreceptor connecting cilia, compatible with the human syndromic ciliopathy. A recent study describes homozygosity for p.Arg106Pro_POC1B in a family with nonsyndromic cone‐rod dystrophy. The phenotype associated with homozygous p.Arg106Pro_POC1B may thus be highly variable, analogous to homozygous p.Leu710Ser in WDR19 causing either isolated retinitis pigmentosa or Jeune syndrome. Our study indicates that POC1B is required for retinal integrity, and we propose POC1B mutations as a probable cause for JBTS with severe PKD.