Sonic hedgehog (Shh) and its main receptor Patched (Ptc) are implicated in both neural development and tumorigenesis1, 2. Beside the classic morphogen activity of Shh, Shh is also a survival factor3, 4. Along this line, Ptc has been shown to function as a dependence receptor, inducing apoptosis in the absence of Shh, while its pro-apoptotic activity is blocked in Shh presence5. Here we show that, in the absence of its ligand, Ptc interacts with the adaptor protein DRAL/FHL2. DRAL/FHL2 is required for the pro-apoptotic activity of Ptc both in immortalized cells and during neural tube development in chick embryo. We demonstrate that, in the absence of Shh, Ptc recruits a protein complex that includes DRAL, the CARD containing domain proteins TUCAN or NALP1 and the apical caspase-9. Ptc triggers caspase-9 activation and enhances cell death via a caspase-9-dependent mechanism. Thus, we propose that, upon absence of its ligand Shh, the dependence receptor Ptc serves as the anchor for a caspase-activating complex that includes DRAL, a CARD domain containing protein and caspase-9.

Numerous studies have demonstrated oxidative damage in the central nervous system in subjects with Alzheimer disease and in animal models of this dementing disorder. In the current study, we show that transgenic mice modeling Alzheimer disease-PDAPP mice with Swedish and Indiana mutations in human amyloid precursor protein (APP)-develop oxidative damage in brain, including elevated levels of protein oxidation (indexed by protein carbonyls and 3-nitrotyrosine) and lipid peroxidation (indexed by protein-bound 4-hydroxy-2-nonenal). This oxidative damage requires the presence of a single methionine residue at position 35 of the amyloid β-peptide (Aβ), since all indices of oxidative damage in brain were completely prevented in genetically and age-matched PDAPP mice with a M631L mutation in APP. No significant differences in levels of APP, Aβ(1-42), Aβ (1-40), or the ratio Aβ(1-42)/Aβ(1-40) were found, suggesting that the loss of oxidative stress in vivo in brain of PDAPP(M631L) mice results solely from the mutation of the Met35 residue to Leu in the Aβ peptide. However, a marked reduction in Aβ-immunoreactive plaques was observed in the M631L mice, which instead displayed small punctate areas of non-plaque immunoreactivity and a microglial response. In contrast to the requirement for Met at residue 35 of the Aβ sequence (M631 of APP) for oxidative damage, indices of spatial learning and memory were not significantly improved by the M631L substitution. Furthermore, a genetically matched line with a different mutation-PDAPP(D664A)-showed the reverse: no reduction in oxidative damage but marked improvement in memory. This is the first in vivo study to demonstrate the requirement for Aβ residue Met35 for oxidative stress in brain of a mammalian model of Alzheimer disease. However, in this specific transgenic mouse model of AD, oxidative stress is neither required nor sufficient for memory abnormalities.