Fig. 5 ∣. Changes in accessible cholesterol influence Hh signaling in target cells.

a, Accessible cholesterol can be reduced (left) in the plasma membrane by trapping it in the outer leaflet with ALOD4 (Fig. 4b) or by removing it with methyl-β-cyclodextrin (MβCD). Conversely, accessible cholesterol can be increased (right) by depleting sphingomyelin (SM) or by delivering cholesterol to the outer leaflet using MβCD–cholesterol complexes. Due to rapid flip-flop of cholesterol between the leaflets, changes in the outer leaflet are also transmitted to the inner leaflet. b, Changes in total cholesterol, the accessible pool of cholesterol and Hedgehog signaling strength after each of the manipulations shown immediately above in a. c, Conceptual cholesterol activity vs. concentration curves (see Fig. 4a for description) depicting how the manipulations shown in a change total and accessible cholesterol in the plasma membrane. The starting set-point in both panels is point A. ALOD4 (left panel) traps cholesterol (and shifts the curve to the right) without changing total cholesterol abundance (A→B), while cholesterol removal by MβCD reduces total and accessible cholesterol (A→C). Right panel shows two manipulations that increase cholesterol accessibility either by shifting the curve to the left (SM depletion, A→B) or by increasing total cholesterol (A→C).