SLITRK5 is a negative regulator of hedgehog signaling in osteoblasts

Jun Sun,Ren Xu,Dong Yeon Shin,Na Li,Abdul G Khan,Michelle Cung,Ivo C Lorenz,Mark Eiseman,Tommy E White,Shawon Debnath,Sarfaraz Lalani,Jae-Hyuck Shim,Sofia Jenia Marquez,Francis S Lee,Zan Li,Seoyeon Bok,Alisha R Yallowitz,Matthew B Greenblatt

doi:10.1038/s41467-021-24819-w

Abstract

Hedgehog signaling is essential for bone formation, including functioning as a means for the growth plate to drive skeletal mineralization. However, the mechanisms regulating hedgehog signaling specifically in bone-forming osteoblasts are largely unknown. Here, we identified SLIT and NTRK-like protein-5(Slitrk5), a transmembrane protein with few identified functions, as a negative regulator of hedgehog signaling in osteoblasts. Slitrk5 is selectively expressed in osteoblasts and loss of Slitrk5 enhanced osteoblast differentiation in vitro and in vivo. Loss of SLITRK5 in vitro leads to increased hedgehog signaling and overexpression of SLITRK5 in osteoblasts inhibits the induction of targets downstream of hedgehog signaling. Mechanistically, SLITRK5 binds to hedgehog ligands via its extracellular domain and interacts with PTCH1 via its intracellular domain. SLITRK5 is present in the primary cilium, and loss of SLITRK5 enhances SMO ciliary enrichment upon SHH stimulation. Thus, SLITRK5 is a negative regulator of hedgehog signaling in osteoblasts that may be attractive as a therapeutic target to enhance bone formation.

Highlights

Hedgehog signaling is essential for bone formation, including functioning as a means for the growth plate to drive skeletal mineralization
To investigate the role of Slitrk[5] in osteoblast differentiation, calvarial osteoblasts isolated from WT and Slitrk5−/− mice were cultured under osteoblast differentiation conditions
An increase in alkaline phosphatase (ALP) activity was observed in Slitrk5−/− osteoblasts (Fig. 1d)

Summary

Introduction

Hedgehog signaling is essential for bone formation, including functioning as a means for the growth plate to drive skeletal mineralization. Current treatments for osteoporosis all have major limitations, which includes rare but severe toxicities, limits on maximum duration of therapy, efficacy in certain anatomic sites, or inducing a low bone turnover state that is undesirable in some contexts, such as during repair of skeletal injury[1] As many of these effects appear to be inherent to the molecular targets of these agents, addressing this issue will require identification of new therapeutic targets to increase bone formation. Slitrk[5] represses the expression of downstream Hh target genes by its direct interactions with Shh and Ptch[1] Taken together, this identifies Slitrk[5] as a novel Hh co-receptor that represses Hh signaling in osteoblasts to regulate bone formation

Methods

Results

Conclusion