Constitutive Activation of Smoothened Leads to Impaired Developments of Postnatal Bone in Mice

Abstract

Sonic hedgehog (Shh) signaling regulates patterning, proliferation, and stem cell self-renewal in many organs. Smoothened (Smo) plays a key role in transducing Shh signaling into the nucleus by activating a glioma family of transcription factors; however, the cellular and molecular mechanisms underlying the role of sustained Smo activation in postnatal development are still unclear. In this study, we explored the effects of Shh signaling on bone development using a conditional knock-in mouse model that expresses a constitutively activated form of Smo (SmoM2) upon osteocalcin (OCN)-Cre-mediated recombination (SmoM2; OCN-Cre mice). We also evaluated the expression pattern of bone formation-related factors in primary calvarial cultures of mutant and control mice. The SmoM2;OCN-Cre mutant showed growth retardation and reduction of bone mineral density compared to control mice. Constitutively activated SmoM2 also repressed mRNA expression of Runx2, osterix, type I collagen, and osteocalcin. Further, sustained SmoM2 induction suppressed mineralization in calvarial primary osteoblasts cultures, whereas such induction did not affect cell proliferation in the mutant cultures as compared with SmoM2 only control cultures. These results suggest that sustained Smo activation inhibits postnatal development of bone by suppressing gene expression of bone formation regulatory factors in mice.

The role of GPCRs in bone diseases and dysfunctions

“…Frizzled-9 knockout induced mouse osteopenia by reducing osteoblast-mediated bone formation 288 and reduced new bone formation after fractures by disturbing osteoblast function. 289 Smoh knockout reduced BMD, body length, and bone callus formation by reducing osteogenic differentiation in mice 38,290 (Table 7).…”

“…289 Smoh knockout reduced BMD, body length, and bone callus formation by reducing osteogenic differentiation in mice 38,290 (Table 7).…”

Overexpressed miR‐196a accelerates osteogenic differentiation in osteoporotic mice via GNAS‐dependent Hedgehog signaling pathway

“…Another essential finding in the investigation was the overexpression of Smo, Runx2, ALP, Gli1, and OPN, accompanied by reduced GNAS and PTCH, once miR‐196a was overexpressed or GNAS was silenced. As a receptor of the Hedgehog pathway, Smo was an important factor in transducing the Hedgehog signaling pathway into the nucleus . Runx2 represents a transcription factor during the process of osteoblast differentiation and chondrocyte maturation .…”

Constitutive Activation of Smoothened in the Renal Collecting Ducts Leads to Renal Hypoplasia, Hydronephrosis, and Hydroureter

“…Inappropriate activation of the Gli/ Shh signaling pathway occurs in several human cancers, including hematological neoplams [Ok et al, 2012]. Constitutive activation of Smo leads to increased proliferation, altered differentiation, and ductal dysplasia in mammary glands [Moraes et al, 2007] as well as impaired postnatal development and suppression of gene expression in bone formation [Cho et al, 2012]. However, although studies on the role of sustained Smo have progressed extensively, little is known about the detailed function and mechanism of sustained Smo on postnatal kidney development.…”

“…SmoM2 mice [Jeong et al, 2004;Cho et al, 2012], Homeobox ( Hox ) b7-Cre mice [Kress et al, 1990], and R26R f/f [Soriano, 1999] mice have been described previously and were purchased from the Jackson Laboratory. SmoM2; Hoxb7-Cre mice were maintained by crossing SmoM2 mice with Hoxb7-Cre mice ( Fig.…”