Ganglioside-Mediated Assembly of Amyloid ß-Protein: Roles in Alzheimer's Disease

Assembly and deposition of amyloid ss-protein (A ss) is an early and invariable pathological event of Alzheimer's disease (AD), a chronic neurodegenerative disease affecting the neurons in the brain of aging population. Thus, clarification of the molecular mechanism underlying A ss assembly is crucial not only for understanding the pathogenesis of AD, but also for developing disease-modifying remedies. In 1995, ganglioside-bound A ss (GA ss), with unique molecular characteristics, including its altered immunoreactivity and its conspicuous ability to accelerate A ss assembly, was discovered in an autopsied brain showing early pathological changes of AD. Based on these findings, it was hypothesized that GA ss is an endogenous seed for amyloid fibril formation in the AD brain. A body of evidence that supports the GA ss hypothesis has been growing for over 20 years as follows. First, the conformational changes of A ss from a random coil to an a-helix, and then to a ss-sheet in the presence of ganglioside were validated by several techniques. Second, the seed activity of GA ss to accelerate the assembly of soluble A ss into amyloid fibrils was confirmed by various in vitro and in vivo experiments. Third, it was found that the A ss binding to ganglioside to form GA ss occurs under limited conditions, which were provided by the lipid environment surrounding ganglioside. Fourth, the region-specific A ss deposition in the brain appeared to be dependent on the presence of the lipid environment that was in favor of GA ss generation. In this chapter, further progress of the study of ganglioside-mediated A ss assembly, especially from the aspects of physicochemistry, structural biology, and neuropathology, is reviewed.