A Genetic Model Therapy Proposes a Critical Role for Liver Dysfunction in Mitochondrial Biology and Disease

Abstract

14The clinical and largely unpredictable heterogeneity of phenotypes in patients with 15 mitochondrial disorders demonstrates the ongoing challenges in the understanding of this semi-16 autonomous organelle in biology and disease. Here we present a new animal model that 17 recapitulates key components of Leigh Syndrome, French Canadian Type (LSFC), a 18 mitochondrial disorder that includes diagnostic liver dysfunction. LSFC is caused by allelic 19 variations in the Leucine Rich Pentatricopeptide repeat-containing motif (LRPPRC) gene. 20 LRPPRC has native functions related to mitochondrial mRNA polyadenylation and translation as 21 well as a role in gluconeogenesis. We used the Gene-Breaking Transposon (GBT) cassette to 22 create a revertible, insertional mutant zebrafish line in the LRPPRC gene. lrpprc zebrafish 23 homozygous mutants displayed impaired muscle development, liver function and lowered levels 24 of mtDNA transcripts and are lethal by 12dpf, all outcomes similar to clinical phenotypes 25 observed in patients. Investigations using an in vivo lipidomics approach demonstrated 26 accumulation of non-polar lipids in these animals. Transcript profiling of the mutants revealed 27 dysregulation of clinically important nuclearly encoded and mitochondrial transcripts. Using 28 engineered liver-specific rescue as a genetic model therapy, we demonstrate survival past the 29 initial larval lethality, as well as restored normal gut development, mitochondrial morphology 30 2 and triglyceride levels functionally demonstrating a critical role for the liver in the 31 pathophysiology of this model of mitochondrial disease. Understanding the molecular 32mechanism of the liver-mediated genetic rescue underscores the potential to improve the clinical 33 diagnostic and therapeutic developments for patients suffering from these devastating disorders. 35

A Primer Genetic Toolkit for Exploring Mitochondrial Biology and Disease Using Zebrafish

“…coq2 zebrafish mutants exhibited an altered expression of key mitochondrial genes such as cytochrome c oxidase subunit 5B2 ( cox5b2) and cytochrome c oxidase subunit 7C (cox7c) . The overlapping transcriptomic signatures observed across all these mitochondrial mutants was due to an alteration of pathways related to oxidative phosphorylation and translation, which were consistent with one of the characterized models from the MMC collection that harbors a disruptive insertion in the lrpprc genetic locus [ 94 ]. Zebrafish lrpprc mutants recapitulated the clinical phenotypes of Leigh Syndrome French-Canadian type such as altered mitochondrial gene expression, larval lethality, and defects in lipid homeostasis.…”

Loss of mitochondrial Chchd10 or Chchd2 in zebrafish leads to an ALS‐like phenotype and Complex I deficiency independent of the mitochondrial integrated stress response

“…The zebrafish model system offers the opportunity to manipulate both genes in isolation or in combination, and both Chchd2 and Chchd10 are well conserved, with 65% and 67% amino acid identity to their human orthologs, respectively. As zebrafish have already been successfully used to model mitochondrial pathology (Anichtchik et al, 2008;Byrnes et al, 2018;Flinn et al, 2009;Sabharwal et al, 2022;Steele et al, 2014), we generated zebrafish Chchd10 and Chchd2 single and double KO models and explored the biological ramifications during development, enabling us to gain insight into their roles during vertebrate development. We report that loss of either or both protein leads to several defects, including impaired motor function, neuromuscular junction (NMJ) defects, and reduced survival supporting the notion that zebrafish models might complement mouse models when studying CHCHD10 and CHCHD2.…”

Loss of mitochondrial Chchd10 or Chchd2 in zebrafish leads to an ALS-like phenotype and Complex I deficiency independent of the mt-ISR

“…The zebrafish model system offers the opportunity to manipulate both genes in isolation or in combination, as both chchd2 and chchd10 are well-conserved, with 65% and 67% identity to human, and 60% and 72% identity at the amino acid level, respectively. As zebrafish have already been successfully used to model mitochondrial pathology (34)(35)(36)(37)(38), we generated zebrafish CHCHD10 and CHCHD2 single and double KO models and explored the biological ramifications during development, enabling us to gain insight into their roles during vertebrate development.…”