Blood flow restriction training does not negatively alter the mechanical strength or histomorphology of uninjured equine superficial digital flexor tendons.

BACKGROUND: Low load exercise training with blood flow restriction (BFR) has become increasingly used by human physical therapists to prescribe controlled exercise following orthopaedic injury; its effects on the equine superficial digital flexor tendon (SDFT), however, are unknown. OBJECTIVE: To investigate outcomes of pressure specific BFR walking exercise on uninjured equine SDFT biomechanics and histomorphology. STUDY DESIGN: Controlled in vivo experiment. METHODS: Four forelimbs of four horses were exposed to 40 BFR-walk sessions (10-min interval walking) on a treadmill over a 56-day study period with their contralateral forelimbs serving as untreated controls. Similarly, four forelimbs of four control horses were exposed to 40 sham cuff walk sessions. On study Day 56, all horses (n = 8) were humanely euthanised and forelimb SDFTs underwent non-destructive biomechanical testing and corresponding histomorphological analysis. Significance in biomechanical parameters between treatment groups was analysed using a mixed-effects ANOVA with Tukey's post-hoc tests. RESULTS: Statistically significant differences in SDFT stiffness for both first (p = 0.02) and last cycles (p = 0.03) were appreciated within the BFR treated group only, with BFR exposed forelimbs being significantly stiffer than the contralateral unexposed forelimbs. When normalised to cross-sectional area, no significant differences were appreciated among treatment groups in elastic modulus for the first (p = 0.5) or last cycles (p = 0.4). No histological differences were appreciated among treatment groups according to Bonar, Movin, or musculotendinous junction evaluation criteria. MAIN LIMITATIONS: Short-term comparisons were performed in a small sample population without correlation to performance outcome measures. Optimal occlusion percentages and walk protocols remain unknown. CONCLUSIONS: This study demonstrated no negative impact of BFR on mechanical strength of the equine SDFT; however, evidence suggests that BFR results in increased tendon stiffness based on biomechanical testing and subsequent calculations. No consistent detrimental histomorphological changes were seen.

CONTEXTO: Exercício de baixa carga com restrição do fluxo sanguíneo (RFS) tem sido cada vez mais utilizado por fisioterapeutas humanos para tratar lesões ortopédicas. Porém, seus efeitos no tendão flexor digital superficial (TFDS) de equinos não é conhecida. OBJETIVOS: O objetivo deste estudo foi investigar o efeito de específicas pressões com RFS durante o passo em cavalos sem lesão no TFDS, por meio de histologia e análise biomecânica. DELINEAMENTO DO ESTUDO: Estudo controlado. MÉTODOS: Quatro membros torácicos de quatro cavalos foram expostos a 40 sessões de RFS durante o passo (10 minutos de caminhada intervalada), ao longo de 56 dias. O membro contralateral foi utilizado como controle. Da mesma forma, quatro membros de quatro cavalos controle foram expostos a 40 sessões simuladas de caminhada com torniquete. No dia 56, todos os cavalos (n = 8) foram eutanasiados, e os TFDS foram submetidos a testes biomecânicos não destrutivos e análise histológica. A significância dos parâmetros biomecânicos entre tratamentos foi analisada utilizando ANOVA de efeitos mistos, seguida pelo teste de Tukey. RESULTADOS: A rigidez do TFDS foi estatisticamente diferente nos primeiros (p = 0.02) e últimos (p = 0.03) ciclos no grupo submetido à RFS, sendo os membros tratados significativamente mais rígidos do que os membros contralaterais não expostos ao tratamento. Quando normalizado para a área transversal, não foi observada diferença significativa entre os grupos de tratamento no módulo de elasticidade para os primeiros (p = 0.5) e últimos (p = 0.4) ciclos. Não foram identificadas diferenças histológicas nos diferentes tipos de tratamento, de acordo com os critérios de avaliação Bonar, Movin e de junção musculo­tendínea. PRINCIPAIS LIMITAÇÕES: Comparações de curto prazo foram realizadas em uma amostra pequena da população, sem correlação com medidas de resultados de desempenho. As porcentagens ideais de oclusão e os protocolos de caminhada permanecem desconhecidos. CONCLUSÕES: Este estudo não demonstrou impacto negativo do RFS na resistência mecânica do TFDS equino; no entanto, as evidências sugerem que a RFS resulta em aumento da rigidez do tendão com base em testes biomecânicos e cálculos subsequentes. Nenhuma alteração histológica prejudicial consistente foi observada.

A Stage-Specific OTX2 Regulatory Network and Maturation-Associated Gene Programs Are Inherent Barriers to RPE Neural Competency.

The retinal pigment epithelium (RPE) exhibits a diverse range of plasticity across vertebrates and is a potential source of cells for the regeneration of retinal neurons. Embryonic amniotes possess a transitory ability to regenerate neural retina through the reprogramming of RPE cells in an FGF-dependent manner. Chicken RPE can regenerate neural retina at embryonic day 4 (E4), but RPE neural competence is lost by embryonic day 5 (E5). To identify mechanisms that underlie loss of regenerative competence, we performed RNA and ATAC sequencing using E4 and E5 chicken RPE, as well as at both stages following retinectomy and FGF2 treatment. We find that genes associated with neural retina fate remain FGF2-inducible in the non-regenerative E5 RPE. Coinciding with fate restriction, RPE cells stably exit the cell cycle and dampen the expression of cell cycle progression genes normally expressed during regeneration, including E2F1. E5 RPE exhibits progressive activation of gene pathways associated with mature function independently of retinectomy or FGF2 treatment, including retinal metabolism, pigmentation synthesis, and ion transport. Moreover, the E5 RPE fails to efficiently repress OTX2 expression in response to FGF2. Predicted OTX2 binding motifs undergo robust accessibility increases in E5 RPE, many of which coincide with putative regulatory elements for genes known to facilitate RPE differentiation and maturation. Together, these results uncover widespread alterations in gene regulation that culminate in the loss of RPE neural competence and implicate OTX2 as a key determinant in solidifying the RPE fate. These results yield valuable insight to the basis of RPE lineage restriction during early development and will be of importance in understanding the varying capacities for RPE-derived retinal regeneration observed among vertebrates.