Acrylamide-induced noradrenergic axon degeneration is promoted via a non-cell autonomous mechanism, involving microglial Tnfaip2/TNF-α and oxidative stress pathways

Environmental toxicants such as acrylamide or 1-bromopropane induce cognitive dysfunction in humans. We previously reported specific noradrenergic neuronal degeneration induced by acrylamide or 1-bromopropane in rodents. In this study, we applied in vivo and in vitro models as well as bulk and single-cell transcriptomic analyses to uncover the underlying mechanisms. RNA-seq of brains of acrylamide-exposed mice revealed a transcriptomic profile involving genes related to multiple neurodegenerative diseases and oxidative stress pathways. Single-cell RNA-seq for microglia identified upregulation of immunoregulation-, inflammation-, and oxidative stress- related pathways, and identified the upregulation of Tnfaip2 (a TNF-α effector), in multiple microglial sub-clusters. Further results of our in vitro interaction model showed that compared to direct acrylamide exposure, exposure to conditioned medium (CM) of acrylamide-exposed BV2 microglia significantly decreased 1C11^NE axon density, and RNA-seq for 1C11^NE identified similar transcriptomic profiles to those of brains of acrylamide-exposed mice. RNA-seq for BV2 microglia showed upregulation of various oxidative stress related genes. Further inhibition experiments demonstrated that TNF-α inhibition or anti-oxidation alleviated acrylamide-induced axonal degeneration in 1C11^NE neurons. Finally, in vivo TNF-α knockout alleviated acrylamide-induced neurotoxicity. Our study demonstrated that acrylamide-induced noradrenergic axon degeneration is promoted via a non-cell autonomous mechanism, involving microglial Tnfaip2/TNF-α and oxidative stress pathways.