RNaseZ Linked Cardiomyopathy in D. melanogaster
Cardiomyopathy (CM) is a group of diseases characterized by morphological changes of cardiac muscle that lead to reduction in heart contractility. CMs are heterogeneous in their etiology and symptoms. A very severe form of infantile CM has been linked to ELAC2 gene mutations. ELAC2 is a human gene with homologs in all eukaryotes. It encodes RNaseZL endoribonuclease that plays an essential role in the production of mature tRNAs. To establish a causal connection between ELAC2 variants and CM, here we use a model organism Drosophila melanogaster, which carries an ELAC2 homolog - RNaseZ. Even though RNaseZ and ELAC2 have diverged in some of their biological functions, our study demonstrates the utility of the fly model to study the mechanism of ELAC2 related pathology. We established transgenic lines harboring RNaseZ with CM-linked mutations in the background of endogenous RNaseZ knockout. Importantly, we found that the phenotype of these flies is consistent with pathological features in human patients. Specifically, expression of CM-linked variants in flies causes heart hypertrophy and leads to reduction in cardiac contractility associated with a rare form of CM. This study provides first experimental evidence for the pathogenicity of CM-causing mutations in the ELAC2 protein. To further understand the origin of the processes underlying ELAC2/RNaseZ linked CM, we investigate if the pathological effect of RNaseZ variants is cell autonomous. Using CRISPR-TRiM technology we studied the role of cardiac RNaseZ by knocking out this gene in a heart specific manner. We found this protein to be essential for normal heart morphology and function, as well as vital for the organism. To explore the cell autonomous role of this gene in CM we expressed pathological RNaseZ variants only in the heart, with wild type RNaseZ everywhere else in the body. We found out that heart specific mutations of RNaseZ are associated with heart hypertrophy and systolic dysfunction. ELAC2/RNaseZ variants have pleiotropic effect; in addition to heart disorder, human patients experience a variety of symptoms, including lactic acidosis and mitochondrial respiratory chain deficiency. The pleiotropy associated with these mutations is partially due to the multiple roles of this enzyme in nucleus, cytoplasm and mitochondria. To understand better the mode of action of RNaseZ variants, we studied their effect in mitochondria and found that they cause accumulation of bicistronic mt-transcript intermediates as well as mt-complex I deficiency. To learn the role of the mitochondria dysfunction in heart disease, we limited the expression of mutant RNaseZ form to mitochondria. We discovered that having RNaseZ variants only in mitochondria is sufficient to cause heart hypertrophy. We then investigated the heart specific effect of mitochondrial RNaseZ variants and found out that their effect on heart morphology and function is cell autonomous. Altogether, in this study, using multiple Drosophila models, we simplified and analyzed different aspects of the complex effect of RNaseZ variants on the organism and particularly heart. These findings lay the foundation to improve our understanding, diagnosis, and treatment of this rare infantile disease.
Migunova, Ekaterina, "RNaseZ Linked Cardiomyopathy in D. melanogaster" (2022). ETD Collection for Fordham University. AAI29394632.