An emerging feature of neurodegenerative disease is synaptic dysfunction and loss, leading to the suggestion that mechanisms required for synaptic maturation may be linked to disease. Synaptic maturation requires the transmission of signals between nascent synaptic sites and the nucleus, but how these signals are generated is not well understood. We posit that proteolytic cleavage of receptors, which enables their translocation to the nucleus, may be a shared molecular mechanism between the events that promote synaptic maturation and those linked to later-onset disorders of the nervous system, including neurodegenerative disease. Here we show during synaptic development, that cleavage of synaptic maturation molecules requires γ-secretase, a protein complex linked to Alzheimer’s Disease, a devastating neurodegenerative condition, is required for postsynaptic maturation. In the absence of γ-secretase, Drosophila neuromuscular synapses fail to appropriately recruit postsynaptic scaffolding and cytoskeletal proteins, and mutant larvae display behavioral deficits. At the NMJ, γ-secretase promotes synaptic maturation through the cleavage of the Wnt receptor Fz2, and the subsequent entry of its C-terminus into the nucleus. A developmental synaptic role for γ-secretase is also conserved in both the Drosophila central nervous system and mammalian cortical neuron dendrites. Finally, we found that similar maturation defects are evident in fly models for ALS, Alzheimer’s, Huntington’s, and Parkinson’s Diseases. The previously unknown, but conserved, role for γ-secretase coupled with its well-known role in neurodegenerative disease suggest that neurodevelopmental defects may be common to diverse neurodegenerative disease models.
The good, the bad, and the opportunities of the complement system in neurodegenerative disease
