Effect of elevated glucose on primary human tenocytes and implications for diabetic tendinopathy

Diabetes mellitus (DM) is associated with a variety of musculoskeletal manifestations, including tendinopathy. The incidence of tendon disease in DM patients is increased compared to the general population, suggesting that tendon is a tissue sensitive to elevated blood glucose. Furthermore, it has been shown that chronic high blood glucose levels cause damage to cells in several ways, including increased oxidative stress. Therefore cellular responses of in vitro primary human tenocytes to a range of chronic glucose conditions (5, 17 and 30 mM) were investigated. Additionally, cells were also exposed to H2O2. Streptozotocin-induced type I diabetic (T1D) rats were used to evaluate in vivo changes. First, tenocyte physiology exhibited changes in multiple aspects in response to ele- vated glucose concentration. Gene expression of collagen, asporin, biglycan and aggrecan was upregulated in 17 mM glucose condition. Data further indicated that SOD-2 was markedly increased in response to elevated glucose (12-fold increase in 17 mM glucose and 5-fold increase in 30 mM glucose, both compared to 5 mM glucose control). Immuno- histochemistry on T1D rats indicated that skeletal muscle tissue was 3NT-positive to a high degree in diabetic condition compared to control. Second, oxidative stress was induced in primary human tenocyes by H2O2 treatment. Extracellular glucose affected cellular response to H2O2: 1 mM H2O2-treated tenocytes in high glucose media had cell metabolic activity significantly decreased compared to iden- tical H2O2 treatment in low glucose media. Furthermore, acute treatment with glucose identified that even short (72 h) bursts of elevated glucose can aggravate the response of cells to H2O2. A panel of protective agents was tested; N-acetylcysteine was the sole treat- ment that proved to be effective to a certain degree. Overall, negative effects of H2O2 were more pronounced under elevated glucose condition in primary human tenocytes. Findings of this thesis provide a necessary fundamental insight into diabetic tendon problems and may inform the development of new clinical treatments.