Mapping lubricin in canine musculoskeletal tissues

Lubricin, also known as superficial zone protein or PRG4, has many distinct biological functions, including lubrication, antiadhesion, and as a regulator of cell growth. This study investigated lubricin in canine musculoskeletal tissues using RT-PCR and immunohistochemistry. One or more variants were noted in canine flexor digitorum profundus (FDP) tendon, Achilles tendon, patellar tendon, A2 pulley, anterior cruciate ligament (ACL), knee lateral collateral ligament (LCL), articular cartilage, meniscus, muscle, and skin. We found 6 N-terminal lubricin splicing variants. The variants with larger sizes were identified in FDP tendon, ACL, LCL, A2 pulley, and cartilage. Lubricin was distributed both on the tissue surfaces and at the interface of fiber bundles within tissues, but this distribution varied by tissue type. We conclude that lubricin is present in many tissues; variations in splicing and physical distribution suggest that the variants of lubricin may play different roles in different locations.