COL5A1 encodes the α1 chain of type V collagen, a quantitatively minor fibrillar collagen that regulates fibrillogenesis. A variant within the 3'-UTR of COL5A1 is associated with chronic Achilles tendinopathy (AT) and other exercise-related phenotypes but the functional significance of this is unknown. The aim of this study was therefore to identify functional differences between the COL5A1 3'-UTR from patients with AT and asymptomatic controls. To this end we have used a reporter assay in which the COL5A1 3'-UTR from AT patients and controls were cloned downstream of the firefly luciferase gene and luciferase activity measured as an indication of mRNA stability. When the cloned COL5A13'-UTRs were sequenced, two major forms named C- and T-alleles were predominantly identified in the controls and the AT subjects respectively. The luciferase activity of the C-alleles was significantly lower than that of the T-alleles (69.0±22.0% (N=24) vs. 90.6±13.7% (N=30), p<0.001) which suggests an overall increase in mRNA stability for the T-allele. Furthermore, we identified a functional miRNA site for Hsa-miR-608 within the COL5A1 3'-UTR and using deletion constructs we have identified additional elements which regulate COL5A1 mRNA stability. These results have important implications for our understanding of the molecular basis of musculoskeletal soft tissue injuries and other exercise-related phenotypes.
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