A mouse model for osseous heteroplasia.

GNAS/Gnas encodes G(s)α that is mainly biallelically expressed but shows imprinted expression in some tissues. In Albright Hereditary Osteodystrophy (AHO) heterozygous loss of function mutations of GNAS can result in ectopic ossification that tends to be superficial and attributable to haploinsufficiency of biallelically expressed G(s)α. Oed-Sml is a point missense mutation in exon 6 of the orthologous mouse locus Gnas. We report here both the late onset ossification and occurrence of benign cutaneous fibroepithelial polyps in Oed-Sml. These phenotypes are seen on both maternal and paternal inheritance of the mutant allele and are therefore due to an effect on biallelically expressed G(s)α. The ossification is confined to subcutaneous tissues and so resembles the ossification observed with AHO. Our mouse model is the first with both subcutaneous ossification and fibroepithelial polyps related to G(s)α deficiency. It is also the first mouse model described with a clinically relevant phenotype associated with a point mutation in G(s)α and may be useful in investigations of the mechanisms of heterotopic bone formation. Together with earlier results, our findings indicate that G(s)α signalling pathways play a vital role in repressing ectopic bone formation.

HIF-VEGF pathways are critical for chronic otitis media in Junbo and Jeff mouse mutants.

Otitis media with effusion (OME) is the commonest cause of hearing loss in children, yet the underlying genetic pathways and mechanisms involved are incompletely understood. Ventilation of the middle ear with tympanostomy tubes is the commonest surgical procedure in children and the best treatment for chronic OME, but the mechanism by which they work remains uncertain. As hypoxia is a common feature of inflamed microenvironments, moderation of hypoxia may be a significant contributory mechanism. We have investigated the occurrence of hypoxia and hypoxia-inducible factor (HIF) mediated responses in Junbo and Jeff mouse mutant models, which develop spontaneous chronic otitis media. We found that Jeff and Junbo mice labeled in vivo with pimonidazole showed cellular hypoxia in inflammatory cells in the bulla lumen, and in Junbo the middle ear mucosa was also hypoxic. The bulla fluid inflammatory cell numbers were greater and the upregulation of inflammatory gene networks were more pronounced in Junbo than Jeff. Hif-1α gene expression was elevated in bulla fluid inflammatory cells, and there was upregulation of its target genes including Vegfa in Junbo and Jeff. We therefore investigated the effects in Junbo of small-molecule inhibitors of VEGFR signaling (PTK787, SU-11248, and BAY 43-9006) and destabilizing HIF by inhibiting its chaperone HSP90 with 17-DMAG. We found that both classes of inhibitor significantly reduced hearing loss and the occurrence of bulla fluid and that VEGFR inhibitors moderated angiogenesis and lymphangiogenesis in the inflamed middle ear mucosa. The effectiveness of HSP90 and VEGFR signaling inhibitors in suppressing OM in the Junbo model implicates HIF-mediated VEGF as playing a pivotal role in OM pathogenesis. Our analysis of the Junbo and Jeff mutants highlights the role of hypoxia and HIF-mediated pathways, and we conclude that targeting molecules in HIF-VEGF signaling pathways has therapeutic potential in the treatment of chronic OM.