Cysteine-Rich Repeat Domains 2 and 4 are Amyloid-β Binding Domains of Neurotrophin Receptor p75NTR and Potential Targets to Block Amyloid-β Neurotoxicity.

The p75 neurotrophin receptor (p75NTR) is an amyloid-beta (A beta) receptor that both mediates A beta neurotoxicity and regulates A beta production and deposition, thus playing an important role in the pathogenesis of Alzheimer's disease (AD). The extracellular domain of p75NTR (p75ECD), consisting of four cysteine-rich repeat domains (CRDs), was recently reported to be an endogenous anti-A beta scavenger to block p75NTR-mediated neuronal death and neurite degeneration signaling of A beta and pro-neurotrophins. Identification of the specific A beta binding domains of p75NTR is crucial for illuminating their interactions and the etiology of AD. CRDs of p75ECD were obtained by expression of recombinant plasmids or direct synthesis. A beta aggregation inhibiting test and immunoprecipitation assay were applied to locate the specific binding domains of A beta to p75ECD. The A beta neurotoxicity antagonistic effects of different CRDs were examined by cytotoxicity experiments including neurite outgrowth assay, propidium iodide (PI) staining, and MTT assay. In the A beta aggregation inhibiting test, the fluorescence intensity in the CRD2 and CRD4 treatment groups was significantly lower than that in the CRD1 and CRD3 treatment groups. Immunoprecipitation assay and western blot confirmed that A beta could bind to CRD2 and CRD4. Besides, CRD2 and CRD4 antagonized A beta neurotoxicity suggested by longer neurite length, less PI labelled cells, and higher cell viability than the control group. Our results indicate that CRD2 and CRD4 are A beta binding domains of p75NTR and capable of antagonizing A beta neurotoxicity, and therefore are potential therapeutic targets to block the interaction of A beta and p75NTR in the pathogenesis of AD.