Pth1r in Neural Crest Cells Regulates Nasal Cartilage Differentiation

Neural crest cells (NCC) arise from the dorsal margin of the neural plate border and comprise a unique cell population that migrates to and creates the craniofacial region. Although factors including Shh, Fgf8, and bone morphogenetic proteins have been shown to regulate these biological events, the role of parathyroid hormone 1 receptor (Pth1r) has been less studied. We generated an NCC-specific mouse model for Pth1r and researched gene expression, function, and interaction focusing on nasal cartilage framework and midfacial development. Wnt1-Cre;Pth1rfl/fl;Tomatofl/+ mice had perinatal lethality, but we observed short snout and jaws, tongue protrusion, reduced NCC-derived cranial length, increased mineralization in nasal septum and hyoid bones, and less bone mineralization at interfrontal suture in mutants at E18.5. Importantly, the mutant nasal septum and turbinate cartilage histologically revealed gradual, premature accelerated hypertrophic differentiation. We then studied the underlying molecular mechanisms by performing RNA seq analysis and unexpectedly found that expression of Ihh and related signaling molecules was enhanced in mutant nasomaxillary tissues. To see if Pth1r and Ihh signaling are associated, we generated a Wnt1-Cre; Ihhfl/fl;Pth1rfl/fl;Tomatofl/+ (DKO) mouse and compared the phenotypes to those of each single knockout mouse: Wnt1-Cre; Ihhfl/fl;Pth1rfl/+;Tomatofl/+ (Ihh-CKO) and Wnt1-Cre;Ihhfl/+;Pth1rfl/fl;Tomatofl/+ (Pth1r-CKO). Ihh-CKO mice displayed a milder effect. Of note, the excessive hypertrophic conversion of the nasal cartilage framework observed in Pth1r-CKO was somewhat rescued DKO embryos. Further, a half cAMP responsive element and the 4 similar sequences containing 2 mismatches were identified from the promoter to the first intron in Ihh gene. Gli1-CreERT2;Pth1rfl/fl;Tomatofl/+, a Pth1r-deficient model targeted in hedgehog responsive cells, demonstrated the enlarged hypertrophic layer and significantly more Tomato-positive chondrocytes accumulated in the nasal septum and ethmoidal endochondral ossification. Collectively, the data suggest a relevant Pth1r/Ihh interaction. Our findings obtained from novel mouse models for Pth1r signaling illuminate previously unknown aspects in craniofacial biology and development.

Exogenous Indian hedgehog antagonist damages intervertebral discs homeostasis in adult mice

Background

Vismodegib, as an exogenous Indian hedgehog (Ihh) antagonist, has been approved by the Food and Drug Administration (FDA) for the clinical treatment of patients with basal cell carcinoma, and previous observations implicate the potential therapeutic of vismodegib in osteoarthritis treatment. However, there is no direct evidence for the role of Ihh signaling in intervertebral discs (IVDs) homeostasis of adult mice. The aim of the present study is to assess the effect of systemic administration of Smoothened inhibitor (SMOi) - vismodegib on IVDs homeostasis during the adult stage.

Methods

The expression of glioma-associated oncogene homolog 1 (Gli1), the downstream targeting gene of Ihh signaling, in IVDs of adult mice after receiving systemic administration of SMOi was examined by immunohistochemistry. The pathological changes of vertebral bodies after SMOi treatment were evaluated by X-ray and micro-CT. The effects of SMOi on homeostasis of IVDs including cartilaginous endplates (CEP), growth plates (GP) and annulus fibrous (AF) were evaluated by histological analysis. The expressions of Aggrecan, Matrix metalloproteinase 13 (MMP13) and Runt-related transcription factor 2 (Runx2), in IVDs were also investigated by immunohistochemistry. Changes in chondrocyte apoptosis and proliferation in IVDs were evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay and analyzing the expression of the cell proliferation antigen Ki-67.

Results

Systemic administration of SMOi significantly decreased the expression of Gli1 in IVDs that indicating effective inhibition of Ihh signaling. Bone mass of vertebral bodies was diminished after SMOi treatment. Moreover, IVDs degeneration (IDD) like defects including CEP sclerosis, degenerative nucleus pulposus (NP) and fissure within AF, as well as narrowed or fused GP and loss bone mass of vertebral bodies was observed in SMOi-treated mice. The severity of IDD was time-dependent with the administration of SMOi treatment after 2-8 weeks. The expressions of Aggrecan, MMP13 and Runx2 in IVDs of mice receiving SMOi treatment were significantly decreased. In addition, chondrocyte apoptosis was significantly enhanced, while chondrocyte proliferation was significantly inhibited.

Conclusions

Our study propose that systemic administration of vismodegib damages IVDs homeostasis via inhibition of Ihh signaling in adult mice. The clinical application of Ihh signaling antagonists such as vismodegib should be careful considering these side adverse.

The Translational Potential of this Article

Vismodegib as an exogenous antagonist of Ihh signaling has been approved by the FDA for the clinical treatment of patients with basal cell carcinoma. However, it is still unknown whether vismodegib will has adverse effects on the patient or animal model of IVDs cartilage homeostasis. Based on our study, systemic administration of vismodegib damages IVDs homeostasis via inhibition of Ihh signaling in adult mice and special attention should be paid to the clinical application of vismodegib.