har-1/CHCHD10 mutations induce neurodegeneration and mitochondrial fragmentation in Caenorhabditis elegans

Abstract

CHCHD10 encodes a mitochondrial protein that plays a role in cristae morphology and oxidative phosphorylation, with mutations associated with neurodegenerative diseases, including the spectrum of amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD). The Caenorhabditis elegans ortholog of CHCHD10 is har-1 , which can be used to model CHCHD10-related neurodegenerative diseases. We focused on two har-1 mutant strains: one featuring a 260 bp deletion ( gk3124 ) and the other with a G73E point mutation ( ad2155 ). Both har-1 mutants displayed progressive paralysis, degeneration of GABAergic motor neurons, and mitochondrial fragmentation. These strains may be valuable tools for investigating pathogenic mechanisms and therapeutic strategies for neurodegenerative diseases.

Figure 1. Phenotypic characterization of har-1 disruption

( A ) har-1 ( gk3124 ) does not affect lifespan, while the har-1 ( ad2155 ) mutation shortens lifespan compared to N2 (Log-rank (Mantel-Cox) test). ( B ) har-1 ( gk3124 ) and har-1 ( ad2155 ) mutants exhibited motility defects leading to age-dependent paralysis when compared to N2 worms (Log-rank (Mantel-Cox) test). ( C ) A representative image shows GABAergic neurodegeneration observed in har-1 ( ad2155 ) mutants, with the white arrow indicating a neuronal gap indicative of neurodegeneration. har-1 ( gk3124 ) and har-1 ( ad2155 ) worms display GABAergic motor neuron degeneration at ( D ) day 1 and ( E ) day 9 (One-way ANOVA followed by Dunnett's multiple comparisons test). ( F ) har-1 ( gk3124 ) and har-1 ( ad2155 ) worms are more sensitive to aldicarb-induced paralysis than N2 worms, although not to the same extent as unc-47 ( e307 ) animals (Log-rank (Mantel-Cox) test). ( G ) Representative images of transgenic animals expressing TOM20::mRFP in body-wall muscle cells show mitochondrial organization quantified as either “Linear,” “Intermediate,” or “Fragmented.” har-1 mutants exhibited higher levels of mitochondrial impairment compared to N2 animals at ( H ) day 1, Linear: N2 vs. har-1 ( gk3124 ) **** P <0.0001, N2 vs. har-1 ( ad2155 ) **** P <0.0001; Intermediate: N2 vs. har-1 ( gk3124 ) *** P <0.001, N2 vs. har-1 ( ad2155 ) *** P <0.001, Fragmented: N2 vs. har-1 ( gk3124 ) n.s., N2 vs. har-1 ( ad2155 ) ** P <0.01) and day 9 (Linear: N2 vs. har-1 ( gk3124 ) **** P <0.0001, N2 vs. har-1 ( ad2155 ) **** P <0.0001; Intermediate: N2 vs. har-1 ( gk3124 ) n.s., N2 vs. har-1 ( ad2155 ) n.s., Fragmented: N2 vs. har-1 ( gk3124 ) **** P <0.0001, N2 vs. har-1 ( ad2155 ) **** P <0.0001) (Two-way ANOVA followed by Dunnett's multiple comparisons test) ( I ) har-1 ( gk3124 ) worms were hypersensitive to oxidative stress, while har-1 ( ad2155 ) mutants displayed resistance to acute juglone exposure (Log-rank (Mantel-Cox) test). ( J ) N2 animals were slightly paralyzed when fed RNAi against har-1 starting at day 1 of adulthood but did not exhibit GABAergic neurodegeneration (Log-rank (Mantel-Cox) test and One-way ANOVA followed by Dunnett's multiple comparisons test). ( K ) Neuronal har-1 RNAi knockdown in worms beginning at day 1 of adulthood did not result in motility issues or neurodegeneration (Log-rank (Mantel-Cox) test and One-way ANOVA followed by Dunnett's multiple comparisons test). ( L ) N2 worms and ( M ) unc-119 p:: sid-1 transgenics displayed age-dependent paralysis and GABAergic neurodegeneration when given RNAi against har-1 starting at the L1 stage. n.s. : non-significant, *: P < 0.05, **: P < 0.01, ***: P < 0.001, ****: P < 0.0001 (Log-rank (Mantel-Cox) test and One-way ANOVA followed by Dunnett's multiple comparisons test).