A Forward Genetic Screen in Caenorhabditis elegans for Genes that Modulate α-synuclein-Induced Neurodegeneration through the Mitochondrial UPR

Overexpression of α-synuclein (α-syn), an inherently disordered protein, triggers chronic activation of the mitochondrial unfolded protein response (UPR ^mt ) pathway in Caenorhabditis elegans with enhanced dopaminergic (DAergic) neurodegeneration. Introduction of a loss-of-function (lf) mutation in atfs-1 , the main transcriptional regulator of the UPR ^mt , into α-syn nematodes results in significant neuroprotection from α-syn-induced DA neuron loss, indicating that compensatory mechanisms provide neuroprotection. We performed a F3 forward genetic screen in C. elegans atfs-1(lf) mutants to identify molecular components associated with the modulation of neurodegeneration via UPR ^mt signaling in α-syn-expressing DA neurons. Homozygous mutant animals were examined for enhanced neurodegeneration; multiple independent alleles were uncovered. Among these, we identified new nonsense alleles encoding the histone lysine demethylases (H3K27me3), jmjd-1.2 and jmjd-3.1 . Another line carried a nonsense allele of twk-14. This gene encodes a conserved protein termed KCNK12 in mammals that facilitates passive background K ⁺ leak currents to set and stabilize resting membrane potential. To further examine the association of these gene products in DA neurodegeneration, mutants and/or RNA interference were employed. DA neurodegeneration was observed in the α-syn + atfs-1(lf) background when jmjd-1.2 , jmjd-3.1, or twk-14 were individually depleted. These results provide evidence that jmjd-1.2 and jmjd-3.1 , which encode previously characterized H3K27me3 demethylases, and the uncharacterized twk-14 gene product, orthologous to human KCNK12, naturally confer protection from α-syn neurotoxicity.