Lithium chloride modulates chondrocyte primary cilia and inhibits Hedgehog signaling

Abstract

Lithium chloride (LiCI) exhibits significant therapeutic potential as a treatment for osteoarthritis. Hedgehog signaling is activated in osteoarthritis, where it promotes chondrocyte hypertrophy and cartilage matrix catabolism. Hedgehog signaling requires the primary ciliumsuch thatmaintenance of this compartment is essential for pathway activity. Here we report that LiCl (50 μm) inhibits Hedgehog signaling in bovine articular chondrocytes such that the induction of GLII and PTCHI expression is reduced by 71 and 55%, respectively. Pathway inhibition is associated with a 97% increase in primary cilia lengthfrom2.09±0.7 μminuntreated cells to 4.06±0.9 μm in LiCI-treated cells. We show that cilia elongation disrupts trafficking within the axoneme with a 38%reduction in Arl13b ciliary localization at the distal region of the cilium, consistent with the role of Arl13b in modulating Hedgehog signaling. In addition, we demonstrate similar increases in cilia length in human chondrocytes in vitro and after administration of dietary lithiumto Wistar rats in vivo. Our data provide new insights into the effects of LiCI on chondrocyte primary cilia and Hedgehog signaling and shows for thefirst timethat pharmaceutical targeting of the primary cilium may have therapeutic benefits in the treatment of osteoarthritis.