Background COL5A1 encodes the à1 chain of type V collagen, a minor fibrillar collagen that regulates fibrillogenesis within non-cartilaginous connective tissues. A variant within the COL5A1 3'-untranslated region (UTR) is associated with Achilles tendinopathy (AT), Anterior cruciate ligament ruptures in females, flexibility and endurance running performance.

Objective To provide functional evidence for these genetic associations, the aim of this study was to identify common variants of the COL5A1 3′-UTR from patients with chronic AT and asymptomatic controls. Functional differences between the different variants were tested using reporter gene constructs.

Methods The entire COL5A1 3′-UTR from four AT patients and three controls were cloned, from genomic DNA using nested PCR, within the pGL3-Promoter vector, substituting the poly (A) signal of the firefly-luciferase reporter gene. The constructs were transiently co-transfected with an internal control HT1080 cells. The normalised results were expressed as relative luciferase activity.

Results Inter-individual variation was demonstrated with a 2.6-fold difference (p<0.001) in the highest activity for an AT patient (110.5±11.6%) and the lowest activity for an asymptomatic subject (42.8±8.6%). In addition, an overall significantly higher activity (87.5±14.3% vs 67.6±20.0%, p<0.001) was observed for the clones from the AT patients. Two major forms of the COL5A1 3′-UTR were identified when all the cloned 3′-UTRs were sequenced. One form (WT-allele) was predominantly identified in the controls, while the second form (TEN-allele) was predominately identified in AT subjects. The luciferase activity of the WT-allele was also significantly lower than the TEN-allele (68.3±24.9% vs 86.0±18.5%, p=0.007).

Conclusion Two major COL5A1 3′-UTR alleles were identified; one from the AT patients and the other from the asymptomatic controls. There was an overall increase in mRNA stability for the TEN-allele. These results demonstrate that the COL5A1 3′-UTR may play an important regulatory role which could results is susceptibility to musculoskeletal soft tissue injures and other phenotypes.