A CHEMICAL BIOLOGY APPROACH TO UNDERSTANDING CELLULAR MANGANESE HOMEOSTASIS IN THE BRAIN

Abstract

Manganese (Mn) is a biologically essential metal, critical as a cofactor for numerous enzymes such a glutamine synthetase and kinases such as ataxia-telangiectasia mutated (ATM). Similar to other essential metals, such as iron and zinc, proper levels of Mn need to be achieved while simultaneously being careful to avoid excess levels of Mn that can be neurotoxic. A chronic occupational exposure to Mn can lead to a Parkinsonian-condition, known as “manganism”, characterized by impaired gait, muscle spasms, and tremors. In addition, environmental exposures of Mn have been linked to neurodevelopmental delay and cognitive deficits in children. Despite the importance of its regulation, the mechanisms underlying the transport and homeostasis of Mn are poorly understood. Recent clinical research has identified three genes whose proteins transport Mn, but in rare cases are mutated which impair systemic Mn regulation. Rather than taking a protein/gene-targeted approach, our lab recently took a high-throughput-screening (HTS) approach to identify 41 small molecules that could significantly increase or decrease intracellular Mn in a neuronal cell model. Here, we report the characterization of these 41 small molecules, which we refer to as the “Mn toolbox”. Without knowing the targets of these small molecules, we functionally classified their effects in cellular models of Mn homeostasis, and explored how these molecules can be exploited as tools and inform potential pharmacological intervention of Mn regulation on a cellular level. We report small molecules of interest that modulate the Mn-handling deficit in Huntington’s disease (HD), other small molecules that modulate the function of the Mn-specific transporter SLC30A10, and set the stage for other Mn-related related targets to be screened. In the process, we identified a previously unknown Mn-selective ionophore (MESM), and used it to develop the first non-lethal assay (MESMER) to determine Mn content in cell cultures, including immortalized neuronal cell models and human iPSC-derived cultures. Lastly, the new MESMER assay is used to demonstrate that neuronal cultures can adapt to repeated Mn exposures, establishing that Mn homeostasis does occur at a cellular level.