Cerebellar Dysfunction in a Mouse Model of Childhood-Onset Manganese-Induced Dystonia Parkinsonism

Humans with pathogenic variants in the manganese (Mn) transporter gene SLC39A14 exhibit highly elevated brain Mn concentrations and childhood-onset dystonia-parkinsonism. Here we show that Slc39a14-knockout (KO) mice, a preclinical model of the disease, express deficits in physiological tremor implicating cerebellar (CB) dysfunction in the presence of elevated CB Mn levels. Imaging of intracellular Mn levels using synchrotron-based X-ray fluorescence microscopy revealed highly increased Mn concentrations in Purkinje cells (PCs). We performed RNAseq studies to determine biological pathways altered in the CB of Slc39a14-KO mice relative to wildtype (WT), which revealed an upregulation of pathways and genes responsible for immune response and cell death. To confirm these findings, we performed quantitative autoradiography of the neuroinflammation biomarker Translocator Protein 18kDa (TSPO) which was significantly increased in the CB of Slc39a14-KO mice relative to WT and was further confirmed with Iba-1 positive microglia activation and clustering in the CB cortex. Immunostaining for cleaved caspase-3 (cCASP3), a marker of apoptosis, revealed a widespread increase in cCASP3 immunoreactivity in PCs, which was supported by Hematoxylin and Eosin (H&E) staining demonstrating pyknotic PCs. Lastly, functional electrophysiological assessment of CB neurocircuitry revealed marked decrease in firing rates of cerebellar nuclei (CN) neurons and an increase in variability of PCs simple spikes firing. These findings show, for the first time, Mn-induced PCs degeneration in the CB of Slc39a14-KO mice and provide a pathological substrate for the dystonia-like movement, balance, and gait abnormalities in SLC39A14 mutation carriers.