Stiffness and axial pain are associated with the progression of calcification in a mouse model of diffuse idiopathic skeletal hyperostosis

Background: Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by progressive calcification of spinal tissues; however, the impact of calcification on pain and function is poorly understood. This study examined the association between progressive ectopic spine calcification in mice lacking equilibrative nucleoside transporter 1 (ENT1 ^−/−), a preclinical model of DISH, and behavioral indicators of pain. Methods: A longitudinal study design was used to assess radiating pain, axial discomfort, and physical function in wild-type and ENT1 ^−/− mice at 2, 4, and 6 months. At endpoint, spinal cords were isolated for immunohistochemical analysis of astrocytes (GFAP), microglia (IBA1), and nociceptive innervation (CGRP). Results: Increased spine calcification in ENT1 ^−/− mice was associated with reductions in flexmaze exploration, vertical activity in an open field, and self-supporting behavior in tail suspension, suggesting flexion-induced discomfort or stiffness. Grip force during the axial stretch was also reduced in ENT1 ^−/− mice at 6 months of age. Increased CGRP immunoreactivity was detected in the spinal cords of female and male ENT1 ^−/− mice compared to wild-type. GFAP- and IBA1-immunoreactivity were increased in female ENT1 ^−/− mice compared to wild-type, suggesting an increase in nociceptive innervation. Conclusion: These data suggest that ENT1 ^−/− mice experience axial discomfort and/or stiffness and importantly that these features are detected during the early stages of spine calcification.