Dyslipidemia negatively affects several tissues, and is associated with increased BMI. Clinical studies have established a strong correlation between increased BMI and risk of tendinopathy. However, the underlying mechanisms are not well understood. We hypothesised that increased saturated fatty acid levels, which are found in dyslipidemia, would have a negative effect on tenocyte health, and this would be driven by mitochondrial processes.
Rat-tail tenocytes were isolated and treated with stearic and palmitic acid (SA and PA, 10µg/ml). Cell viability was assessed using AlamarBlue™ assay (24hr and 48hr). Cell deposited collagen was assessed using sirius red assay (72hr), and tenocyte gene expression was quantified using RT-PCR. Cell respiration and reactive oxygen species production was measured by oxygraphy and MitoSox staining. To assess whether effects were driven by mitochondrial processes, fatty acid transport into the mitochondria was blocked by pre-treatment with 50µM etomoxir.
Treatment with SA and PA decreased tenocyte viability (p<0.05). PA treatment decreased collagen deposition (p<0.05) and the expression of tendon markers scleraxis (p=0.004) and tenomodulin (p=0.0054), and increased MMP-3 (p=0.036), MMP-13 (p=0.0059) and cox-2 (p=0.0075) gene expression. Cell respiration, as measured by an oxygraphy, increased after PA treatment (p<0.0001), and there was increased ROS production with PA treatment (p<0.0001). Pre-treatment with 50µM etomoxir partially rescued cell death (p=0.02), inhibited PA-induced MMP-3 expression, reduced ROS staining and partially reduced cell respiration, but did not affect PA-induced scleraxis or tenomodullin expression.
Our study indicates that increased saturated fatty acid concentrations in the cellular microenvironment can lead to cell death and altered tenocyte behaviour, which are indicative of tendinopathy. Blocking PA transport into mitochondria partially rescues some of the negative effects of PA, but not all of them, suggesting other pathways are involved. Overall, increased saturated fatty acid levels, which are observed with dyslipidemia, may contribute to poor tendon health.