Affiliations: 1) University of Osnabrueck, Department of Zoology and Developmental Genetics (Germany); 2) Erich and Hanna Klessmann Institute, Heart and Diabetes Center NRW, University Hospital of the Ruhr-University Bochum, Bad Oeynhausen (Germany); 3) Roskilde University, Department of Science and Environment (Denmark)
Keywords: j. cardiovascular disease; j. cardiovascular disease
Human TMEM43 encodes a membrane protein with four transmembrane domains, which localizes to the ER- outer membrane compartment. A point mutation in TMEM43 results in arrhythmogenic right ventricular cardiomyopathy (ARVC) type 51,2,3. Characteristics of ARVC-5 are ventricular tachycardia, heart attacks, and sudden cardiac death4. Mostly, men between the ages of 20-40 years are affected. The identified point mutation is a missense mutation in the human TMEM43 gene that results in incorporation of the amino acid leucine rather than serine at position 358 of the protein, S358L.
TMEM43 is a highly conserved protein throughout different species. Homologous proteins exist in chimpanzees, rhesus monkeys, dogs, cows, mice, frogs and fruit flies. The corresponding homolog in Drosophila melanogaster is CG8111. Interestingly, the serine, which is involved in the familial mutation in humans, as well as the surrounding region, are highly conserved in fruit flies (S333) and other species5.
To investigate the effect of the point mutation in flies, we overexpressed CG8111S333L ubiquitously or in a tissue specific manner. Our studies showed that ubiquitous overexpression of the mutant, but not the wild type form of CG8111, leads to lethality at pupal stages, less food uptake and increased lipid droplets in adipocytes of 3rd larvae. Furthermore, we applied mass spectrometry (MS)-based proteomics and are able to show that CG8111S333L animals up-regulate proteins, which are involved in fatty acid metabolism pathways. Subsequent metabolomic analysis by nuclear magnetic resonance (NMR) spectroscopy revealed that short fatty acids accumulate in animals overexpressing CG8111S333L compared to controls.
Moreover, we examined the effect of heart specific overexpression of CG8111S333L. Therefore, we used the Semi-automatic Optical Heartbeat Analysis (SOHA) software to analyse heart beat parameters like heart rate, systolic and diastolic interval, fractional shortening and arrhythmicity index. We found that heart specific overexpression of CG8111S333L leads to arrhythmia in five week old male flies.
In the end, we compare our findings with models for TMEM43S358L in mouse and rat.
1 Baskin et al., Human Genetics, 2013 2 Christensen et al., Clinical Genetics, 2011 3 Milting et al., European Heart Journal, 2015 4 Fontaine et al., Circulation, 1998 5 Merner et al., The American Journal of Human Genetics, 2008