Demyelination and Impaired Oligodendrogenesis in the Corpus Callosum Following Lead Exposure.

Abstract

The corpus callosum is an oligodendrocyte-enriched brain region, replenished by newborn oligodendrocytes from oligodendrocyte progenitor cells (OPCs) in subventricular zone (SVZ). Lead (Pb) exposure has been associated with multiple sclerosis, a disease characterized by the loss of oligodendrocytes. This study aimed to investigate effects of Pb exposure on oligodendrogenesis in SVZ and myelination in corpus callosum. Adult female mice were used for a disproportionately higher prevalence of multiple sclerosis in females. Acute Pb exposure (one ip-injection of 27 mg Pb/kg as PbAc2 24 hrs before sampling) caused mild Pb accumulation in corpus callosum. Ex vivo assay using isolated SVZ tissues collected from acute Pb-exposed brains showed a diminished oligodendrogenesis in SVZ-derived neurospheres compared to controls. In vivo subchronic Pb exposure (13.5 mg Pb/kg by daily oral gavage 4 wks) revealed significantly decreased newborn BrdU+/MBP+ oligodendrocytes in corpus callosum, suggesting demyelination. Mechanistic investigations indicated decreased Rictor in SVZ OPCs, defective self-defense pathways, and reactive gliosis in corpus callosum. Given the interwined pathologies between multiple sclerosis and Alzheimers's disease, effect of Pb on myelination was evalued in AD-modeled APP/PS1 mice. Myelin MRI on mice following chronic exposure (1000 ppm Pb in drinking water as PbAc2 for 20 wks) revealed a profound demyelination in corpus callosum compared to controls. Immunostaining of choroid plexus showed diminished signalling molecule (Klotho, OTX2) expressions in Pb-treated animals. These observations suggest that Pb caused demyelination in corpus callosum, likely by disrupting oligodendrogenesis from SVZ OPCs. Pb-induced demyelination represents a crucial pathogenic pathway in Pb neurotoxicity, including multiple sclerosis.