Lithium chloride modulates chondrocyte primary cilia and inhibits Hedgehog signaling

Abstract

Lithium chloride (LiCl) 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 cilium such that maintenance of this compartment is essential for pathway activity. Here we report that LiCl (50 mM) inhibits Hedgehog signaling in bovine articular chondrocytes such that the induction of GLI1 and PTCH1 expression is reduced ​ by 71 and 55%, respectively. Pathway inhibition is associated with a 97% increase in primary cilia length from 2.09 ± 0.7 μm in untreated cells to 4.06 ± 0.9 μm in LiCl-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 lithium to Wistar rats in vivo. Our data provide new insights into the effects of LiCl on chondrocyte primary cilia and Hedgehog signaling and shows for the first time that pharmaceutical targeting of the primary cilium may have therapeutic benefits in the treatment of osteoarthritis.

Identification of Elongated Primary Cilia with Impaired Mechanotransduction in Idiopathic Scoliosis Patients

“…)24. As expected24, LiCl caused a decrease in GSK3B expression. Inhibition of GSK3B is associated with the activation of canonical Wnt signaling, and in both LiCl treated cells and IS cells there was an increase in beta-catenin expression (3.4-fold and 5.8-fold respectively).…”

“…Primary human osteoblast cells from the control group were treated with 10 mM LiCl, for 24 h (Based on work by Thompson et al . )24. As expected24, LiCl caused a decrease in GSK3B expression.…”

“…This is consistent with LiCl induced inactivation of GSK3B, and the fact that GSK3B and Wnt are among RUNX2 regulators45. We assayed Inversin (INVS) as an indicator of non-canonical Wnt activity while PTCH1 and GLI1 were chosen as players in Hedgehog signaling, based on the previous works by Simons46 and Thompson24, respectively. We did not observe significant basal expression differences among IS, LiCl-treated, and controls for INVS or PTCH1.…”

Reduced primary cilia length and altered Arl13b expression are associated with deregulated chondrocyte Hedgehog signaling in alkaptonuria

“…Arl13b is a key regulator of the ciliary trafficking of Hedgehog proteins (Caspary et al, ; Larkins et al, ; Mariani et al, ). Moreover, we have recently demonstrated that alterations in cilia length and Arl13b cilia localization are associated with altered Hedgehog signaling in chondrocytes (Thompson et al, ). Hedgehog signaling was therefore, examined in AKU and +HGA chondrocytes under basal conditions and in response to recombinant Indian Hedgehog (Ihh) using real time PCR.…”

Topography of calcium phosphate ceramics regulates primary cilia length and TGF receptor recruitment associated with osteogenesis

“…In addition to regulation of TGFβ signalling, primary cilia also regulate a number of other osteogenic signalling pathways, such as Wnt [20], [43], runx2 [44], and hedgehog [45], [46]. Indeed, previous studies from Knight’s group have shown that changes in primary cilia length can modulate both hedgehog and Wnt signalling pathways [20], [42], [44], [45].…”