Non-cell autonomous inhibition of the Shh pathway due to impaired cholesterol biosynthesis requires Ptch1/2

Abstract

Congenital birth defects due to mutations of enzymes involved cholesterol synthesis, like Smith-Lemli-Opitz syndrome (SLOS) and Lathosterolosis are characterized by an accumulation of cholesterol precursors. The phenotype of both SLOS and Lathosterolosis have similarities to syndromes associated with abnormal Sonic hedgehog (Shh) signaling, consistent with the observation that cholesterol precursors and their derivative can inhibit Shh signaling. Two types of multipass membrane proteins play central roles in Shh signal transduction, the putative Resistance, Nodulation and Division (RND) antiporters Patched (Ptch)1 and -2, and the G-protein coupled receptor Smoothened (Smo). Sterols have been suggested as cargo for Ptch1/2, while Smo activity can affected both positively and negatively by steroidal molecules. We demonstrate that embryonic stem cells with mutations in the 7-dehydroxycholesterol reductase (7Dhcr) or sterol-C5-desaturase (Sc5d) gene reduce the Hh response in adjacent wildtype cells when grown in mosaic organoids. This non-cell autonomous inhibitory activity of the mutant cells requires the presence of both Ptch1 and Ptch2. These observations support a model in which late cholesterol precursors that accumulate in cells lacking 7Dhcr are the cargo for Ptch1 and Ptch2 efflux activity and mediate the non-cell autonomous inhibition of Smo.