The Effect of Loading Frequency on Tenocyte Metabolism

Abstract

Achilles tendinopathy is a prevalent, highly debilitating condition. It is believed to result from repetitive overuse, which creates micro-damage tendon, and initiates a catabolic cell response. The aetiology of tendinopathy remains poorly understood, therefore appropriate treatment remains unclear. Current data support the use of shock wave therapy and eccentric exercise as some of the more effective treatment options for tendinopathy. Studies have shown that these treatments generate perturbations within tendon at a frequency of approximately 8-12Hz. Consequently, it is hypothesised that 10Hz loading initiates increased anabolic tenocyte behaviour promoting tendon repair. The primary aim of this thesis is to investigate the effects of 10Hz perturbations on tenocyte metabolism, comparing tenocyte gene expression in response to a 10Hz and 1Hz loading profile. A variety of in vitro models for mechanically stimulating cells were explored, comparing tissue explants with isolated cells on a 2D or within a 3D collagen gel. The mechanical environment of each model was investigated, in addition to cell viability and gene stabilisation following strain, as needed for future cell studies. 3D collagen gels arose as the most suitable model. Human tenocytes from healthy semitendinosus and tendinopathic Achilles tendons were seeded into 3D collagen gels and subjected to cyclic strain at 10Hz and 1Hz to establish cell response. Tenocyte gene expression was characterised using qRT-PCR. Healthy tenocytes showed increased expression of all analysed genes in response to loading. Furthermore, the increase was significantly larger in the 10Hz loading group. Tendinopathic tenocytes showed a more varied response, possibly indicative of an early healing response. Nevertheless, the response to 10Hz loading was consistently greater than seen with 1Hz loading. Analysis of the signalling pathways involved suggested that the IL1 signalling pathway may be involved in the strain response reported. This study has demonstrated for the first time that loading at a frequency of 10Hz may enhance metabolic response in healthy tenocytes.