Chronic up-regulation of sonic hedgehog has little effect on postnatal craniofacial morphology of euploid and trisomic mice

Background: In Ts65Dn, a mouse model of Down syndrome (DS), brain and craniofacial abnormalities that parallel those in people with DS are linked to an attenuated cellular response to sonic hedgehog (SHH) signaling. If a similarly reduced response to SHH occurs in all trisomic cells, then chronic up-regulation of the pathway might have a positive effect on development in trisomic mice, resulting in amelioration of the craniofacial anomalies. Results: We crossed Ts65Dn with Ptch1^tm1Mps/+ mice and quantified the craniofacial morphology of Ts65Dn;Ptch^+/- offspring to assess whether a chronic up-regulation of the SHH pathway rescued DS-related anomalies. Ts65Dn;Ptch1^+/- mice experience a chronic increase in SHH in SHH-receptive cells due to haploinsufficiency of the pathway suppressor, Ptch1. Chronic up-regulation had minimal effect on craniofacial shape and did not correct facial abnormalities in Ts65Dn;Ptch^+/- mice. We further compared effects of this chronic up-regulation of SHH with acute pathway stimulation in mice treated on the day of birth with a SHH pathway agonist, SAG. We found that SHH affects facial morphology differently based on chronic vs. acute postnatal pathway up-regulation. Conclusions: Our findings have implications for understanding the function of SHH in craniofacial development and for the potential use of SHH-based agonists to treat DS-related abnormalities.