PRG4 and rheumatoid arthritis: Lubricin’s glycosylation varies in disease, with altered sialylation of Core 1 O-glycans and reduced levels of Core 2 O-glycans in equine joints with OA lesions and osteochondral fragmentation as compared to normal joints46 and increased sialylation of Core 1 O-glycans in human rheumatoid arthritis as compared to OA47.