BMC Seminar - Cholesterol-Binding Pocket Mutations in Osteoarthritis

BMC Seminar Thursday 18th of September at 12:30 - 13:10 in Árnagarður, room 306

Speaker: Abbi Elise Smith, PhD student, Faculty of Medicine, School of Health Sciences, University of Iceland

Title: The Impact of Smoothened Cholesterol-Binding Pocket Mutations on Hedgehog Signaling and Osteoarthritis

Abstract: The hedgehog signaling pathway plays a vital role in development, and is particularly important for limb patterning, somitogenesis, craniofacial development, and bone growth. When aberrantly activated later in life, elevated hedgehog signaling contributes to the development of osteoarthritis and is associated with worsened cartilage phenotype. A deCODE genetics GWAS study identified a variant in the hedgehog pathway gene Smoothened (SMO) that is associated with increased risk of hip osteoarthritis. Surprisingly, structural analysis of this variant (p.Arg173Cys; SMOR173C) predicted that the mutation would decrease the binding of cholesterol to SMO, a critical step for downstream hedgehog signaling. The anticipated result would be a decrease in hedgehog signaling activity, which contradicts the well-described relationship between elevated hedgehog signaling activity and osteoarthritis.

We used monolayer and 3D hydrogel culture of mouse prechondrogenic ATDC5 cells harboring the SmoR173C mutation to determine it did not abolish or significantly reduce downstream hedgehog signaling activity. This finding was confirmed in vivo when we found that smo-/- zebrafish embryos microinjected with SMOR173C mRNA showed significantly improved hedgehog signaling-driven morphological recovery.

To further investigate the role of the SmoR173C variant in osteoarthritis development, we promoted chondrogenic differentiation in ATDC5 cells using 3D culture and then treated them with a cytokine cocktail to induce an osteoarthritis-like phenotype. We found elevated Mmp13 mRNA expression in SmoR173C ATDC5 cells at baseline and after cytokine treatment. MMP13 is a collagenase commonly elevated in osteoarthritic cartilage and causes cartilage damage by degrading the extracellular collagen network. This study lays the groundwork to identify a direct link between the hedgehog signaling pathway and MMP13 expression.

Bio: Abbi Elise Smith is currently a PhD student in Sara Sigurbjörnsdóttir laboratory and will be defending her dissertation in October. Sara’s group primarily studies the role of the hedgehog signaling pathway in osteoarthritis, a degenerative joint disease. The group is completing a thorough functional investigation of a pathological variant (p.Arg173Cys) of the Smoothened gene (SMO) associated with hip osteoarthritis. In addition to studying hedgehog signaling in osteoarthritis, Sara’s lab is investigating the role of noncanonical hedgehog signaling in cartilage and bone cancers such as chondrosarcoma and Ewing’s sarcoma. Abbi received her Master’s degree in Biology from the University of Maryland in 2011. Prior to moving to Iceland to pursue her PhD, Abbi was a research analyst in a preclinical therapeutic laboratory at Indiana University School of Medicine using mouse models of two tumor predisposition syndromes, Neurofibromatosis Types 1 and 2, to find effective therapies. Their work contributed to the first FDA-approved treatment for Neurofibromatosis Type 1, and clinical trials for other treatments for both syndromes are ongoing.