Death receptor 3 (TNFRSF25) increases mineral apposition by osteoblasts and region specific new bone formation in the axial skeleton of male DBA/1 mice

Objectives. Genome wide association studies identified TNFSF member TNF-like protein 1A (TL1A, TNFSF15) as a potential modulator of ankylosing spondylitis (AS). TL1A is the only confirmed TNFSF ligand of death receptor 3 (DR3, TNFRSF25); however, its role in disease pathology is not characterised. We evaluated DR3's role in controlling osteoblast-(OB-) dependent bone formation in vitro and in vivo. Methods. Osteoprogenitor cells and OB were cultured from male DR3-deficient (DR 3 ko) and wild-type (DR 3 wt) DBA/1 mice. DR3 and RANKL expression were tested by flow cytometry. Alkaline phosphatase and mineralization were quantified. Osteopontin, osteoprotegerin, and pro MMP-9 were measured by ELISA. A fluorescent probe (BoneTag) was used to measure in vivo mineralization in 10-month-old mice. Results. DR3 was expressed on osteoprogenitors and OB from DR 3 wt mice. Alkaline phosphatase, osteopontin, and mineral apposition were significantly elevated in DR 3 wt cultures. Levels of RANKL were comparable whilst osteoprotegerin was significantly increased in DR 3 wt cultures. In vivo incorporation of BoneTag was significantly lower in the thoracic vertebrae of 10-month-old DR 3 ko mice. Conclusions. These data identify new roles for DR3 in regulating OB-dependent bone mineral apposition. They potentially begin to explain the atypical pattern of new bone formation observed in the axial skeleton of grouped, aging DBA/1 mice.