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

Abstract

Overexpression of -synuclein (-syn), an inherently disordered protein, triggers chronic activation of the mitochondrial unfolded protein response (UPRmt) 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 UPRmt, into -syn nematodes results in significant neuroprotection from -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 UPRmt signaling in -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 -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 -syn neurotoxicity.