Development of early-stage alpha-synucleinopathy is not governed by myelin status in mice of either sex

Lewy body disorders are characterized by alpha-synucleinopathic inclusions that tend to develop in neurons extending long, thin, and unmyelinated fibers. It is unknown if this selective vulnerability reflects poor myelination per se. We have observed that preformed fibrils (PFFs) of alpha-synuclein tend to induce pathology in gray matter, even when infused into regions penetrated by white matter bundles. In addition, we found that levels of insoluble, hyperphosphorylated alpha-synuclein correlate inversely with myelin markers in the postmortem amygdala of men—but not women—with Lewy body disease. Thus, we tested if myelin disruption with pharmacologic or genetic tools exacerbates alpha-synucleinopathic lesions in a model of early-stage, limbic Lewy body disease. In genetically outbred CD-1 mice infused with PFFs in the caudal olfactory bulb, the myelin-disruptor cuprizone caused subtle exacerbation of α-synucleinopathy, but without impacting PFF-induced neuron loss or behavior deficits. Furthermore, in C57BL/6J mice heterozygous for myelin basic protein (Mbp+/shi), PFF-induced increases in the insolubility and hyperphosphorylation of alpha-synuclein were not amplified and histological outcomes were not markedly exacerbated. Given our observations of inverse correlations between α-synucleinopathy and myelin markers in the human male amygdala, Lewy body disease may disrupt myelination, rather than poor myelination status regulating the emergence of limbic α-synucleinopathy. This new perspective is reinforced by suppressed expression of select oligodendrocytic markers in the amygdalae of men with Lewy body disease compared to women. Thus, resilient neurons may defy the initial development of Lewy-related pathologies due to properties unrelated to myelination per se.