Loss of dopamine-containing neurons (red) is accelerated in the brains of Fas-deficient mice (bottom).

A deadly receptor reveals a benevolent side in a study on page 575. Landau and colleagues show that the cell death–inducing receptor Fas is required for protection against neurodegeneration in a mouse model of Parkinson's disease (PD).

The Fas receptor (Fas), best known for its apoptotic role in the immune system, is widely expressed in nonimmune tissues, including the central nervous system. In the brains of patients with PD, the expression of both Fas and Fas ligand (FasL) is reduced, whereas the expression of soluble Fas is elevated. Soluble Fas is a decoy receptor that impairs Fas signaling by competing for free ligand. Apoptosis has been implicated in PD neurodegeneration, but this occurs independently of caspase-8, an upstream activator in Fas-mediated apoptosis, suggesting that Fas may not be the predominant...

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