Osteoimmunology In Rheumatoid and Psoriatic Arthritis: Potential Effects of Tofacitinib on Bone Involvement

Data showing that TOF can inhibit unbalanced osteoclastogenesis in RA suggests that targeting the JAK-STAT pathway can halt bone erosion, as TOF has been shown to reduce articular bone erosion in RA and PsA.The authors in this review summarise current knowledge on the relationship between the immune system and the skeleton before examining the involvement of JAK-STAT signalling in bone homeostasis while discussing the evidence on the benefit of TOF on prevention of bone involvement in RA and PsA.Bone erosion can be expected to affect 80% of RA patients within one year of diagnosis and is correlated with the presence of prolonged, increased inflammation. PsA is characterised by the presence of new abnormal bone deposition at the entheses. The selective JAK 1/3 inhibitor TOF, has shown in preclinical studies that it can inhibit disturbed osteoclastogenesis in RA. Suggesting that targeting the JAK-STAT pathway can help limit bone erosion. Clinical evidence of TOF treatment also indicates a decrease in articular bone erosion even in the presence of persistent inflammation. Further clinical studies are however required to characterise the role of TOF in preventing systemic bone loss in RA and PsA, and in preventing pathologic bone formation at the entheses in PsA.