Nucleotide structure of equine platelet-derived growth factor-A and -B and expression in horses with induced acute tendinitis

Objective-To characterize the nucleoticle sequence of equine platelet-derived growth factor (PDGF)-A and -13 and analyze temporal expression of these genes in equine tendon after induced tendinitis injury. Animals-18 mature horses. Procedures-Genes for equine PDGFA and -13 were reverse transcribed and sequenced from synovial tissue mRNA obtained from a 3-year-old horse. Collagenase-induced lesions were created in the tensile region of the superficial digital flexor tendon in 14 horses; 3 horses served as uninjured control animals. Tendons were harvested and total RNA was isolated from experimental horses 1, 2, 4, 8, and 24 weeks after collagenase injection. Temporal gene expression for PDGFA and -13 was determined by use of quantitative PCB analysis. Results-Equine PDGFLA shared 83.8% sequence and 875% pepticle homology with human PDGFA, with a discrepancy of 70 bp from the human sequence. Equine PDGF-B was similar in length to the human gene, sharing 90.3% and 91.7% nucleoticle and peptice identity, respectively. Expression of PDGFLA mRNA in collagenase-induced tenclinitis lesions was unchanged, compared with expression for normal control tendon, and remained steady throughout the 24-week study. Expression of PDGF-B mRNA decreased over time, and the expression at 24 weeks was significantly reduced, compared with expression in normal and acutely injured tendon. Conclusions and Clinical Relevance-Injured tendon mounts a minimal constitutive PDGFA or -13 mRNA response. Serial exogenous treatment with either PDGF isoform within the first 2 to 4 weeks after tendon injury may bolster the meager PDGF paracrine-autocrine intrinsic response to injury.