Abstract 1491 FYCO1 facilitates autophagy and protects heart function against adverse cardiac remodeling in response to myocardial ischemia

Background

Imbalances in autophagy are known to have either protective or detrimental effects on cardiac function. Although there are significant insights into the early steps of the autophagy pathway, the mechanisms of autophagosome-lysosome transport and fusion in cardiomyocytes are less understood. Fyco1 is highly expressed in the heart and facilitates transport of autophagosomes in cardiomyocytes, enhancing global autophagic flux. The purpose of our study was to investigate the effects of FYCO1 post myocardial infarction. Our hypothesis is that by overexpressing FYCO1 in vivo we will facilitate activation of autophagy with a beneficial impact on remodeling and heart function.

Methods

FYCO1-Tg mice were crossbred with RFP-EGFP-LC3-Tg reporter mice and myocardial ischemia was induced by permanent ligation of left anterior descending artery (LAD). Mice were analyzed 3 days and 30 days post LAD ligation. Cardiac function (ejection fraction, EF) and left ventricular (LV) mass were measured by echocardiography and myocardial fibrosis, Midline Infarct size (%) and LV circumference were assessed in Masson’s Trichrome stainings. Transport of autophagosomes and lysosomes as well as their fusion were analyzed using confocal microscopy. Furthermore, autophagy activity was analyzed by Western blot for LC3 II and LC3 II/LC3 I.

Results

In FYCO1-TGxRGFP mice 3 days post LAD we observed a completely increased autophagic flux demonstrated by significantly increased LC3 II protein levels (WT sham: 1±0,3; WT LAD: 1,3±0,2; TG sham: 10,8±1,2; TG LAD:8,8±0,9) and LC3 II/LC3 I ratios (WT sham:1±0,3; WT LAD:0,99±0,1; TG sham:10,5±1,2; TG LAD:5,6±1) post LAD. Using confocal microscopy, we were able to observe a shift in transport of autophagosomes towards plus-end-directed transport, shown by peripheral accumulation of autophagosomes (WT:1,4±0,8; TG:46,6±5,8) and increased levels of autolysosomes (WT:79,2±19,2; TG:181,1±36,7). Fibrosis in LV (WT:21,7±2,6%; TG:8,5±1,1%) and infarct size (WT:40,2 ±5,4%; TG:4,9±1,5%) were found significantly decreased in FYCO1-TGxRGFP-mice. FYCO1-TGxRGFP mice presented with increased LV mass (WT:106,2±25,5 mg; TG:114,2±38,3mg) but comparable LV circumference/tibia length (WT:11,1±0,9; TG:11,4±1,5). Remarkably, global heart function of FYCO1-TGxRGFP-mice was significantly improved post LAD compared to WT (EF WT:36,7±6,3%; TG:46,3±18,3%).

Conclusion

Our study proves our hypothesis, that the activation of autophagy via FYCO1 overexpression protects against adverse cardiac remodeling and improves cardiac function post myocardial ischemia. These findings may thus offer translational potential in the treatment of myocardial infarction.

Clin Res Cardiol (2023). https://doi.org/10.1007/s00392-023-02180-w
FYCO1 facilitates autophagy and protects heart function against adverse cardiac remodeling in response to myocardial ischemia
F. Senger¹, A. Remes², C. Tannert², O. J. Müller², N. Schmiedel², C. Kuhn², N. Frey¹
¹Klinik für Innere Med. III, Kardiologie, Angiologie u. Pneumologie, Universitätsklinikum Heidelberg, Heidelberg; ²Molekulare Kardiologie, Universitätsklinikum Schleswig-Holstein, Kiel;
Background Imbalances in autophagy are known to have either protective or detrimental effects on cardiac function. Although there are significant insights into the early steps of the autophagy pathway, the mechanisms of autophagosome-lysosome transport and fusion in cardiomyocytes are less understood. Fyco1 is highly expressed in the heart and facilitates transport of autophagosomes in cardiomyocytes, enhancing global autophagic flux. The purpose of our study was to investigate the effects of FYCO1 post myocardial infarction. Our hypothesis is that by overexpressing FYCO1 in vivo we will facilitate activation of autophagy with a beneficial impact on remodeling and heart function. Methods FYCO1-Tg mice were crossbred with RFP-EGFP-LC3-Tg reporter mice and myocardial ischemia was induced by permanent ligation of left anterior descending artery (LAD). Mice were analyzed 3 days and 30 days post LAD ligation. Cardiac function (ejection fraction, EF) and left ventricular (LV) mass were measured by echocardiography and myocardial fibrosis, Midline Infarct size (%) and LV circumference were assessed in Masson’s Trichrome stainings. Transport of autophagosomes and lysosomes as well as their fusion were analyzed using confocal microscopy. Furthermore, autophagy activity was analyzed by Western blot for LC3 II and LC3 II/LC3 I. Results In FYCO1-TGxRGFP mice 3 days post LAD we observed a completely increased autophagic flux demonstrated by significantly increased LC3 II protein levels (WT sham: 1±0,3; WT LAD: 1,3±0,2; TG sham: 10,8±1,2; TG LAD:8,8±0,9) and LC3 II/LC3 I ratios (WT sham:1±0,3; WT LAD:0,99±0,1; TG sham:10,5±1,2; TG LAD:5,6±1) post LAD. Using confocal microscopy, we were able to observe a shift in transport of autophagosomes towards plus-end-directed transport, shown by peripheral accumulation of autophagosomes (WT:1,4±0,8; TG:46,6±5,8) and increased levels of autolysosomes (WT:79,2±19,2; TG:181,1±36,7). Fibrosis in LV (WT:21,7±2,6%; TG:8,5±1,1%) and infarct size (WT:40,2 ±5,4%; TG:4,9±1,5%) were found significantly decreased in FYCO1-TGxRGFP-mice. FYCO1-TGxRGFP mice presented with increased LV mass (WT:106,2±25,5 mg; TG:114,2±38,3mg) but comparable LV circumference/tibia length (WT:11,1±0,9; TG:11,4±1,5). Remarkably, global heart function of FYCO1-TGxRGFP-mice was significantly improved post LAD compared to WT (EF WT:36,7±6,3%; TG:46,3±18,3%). Conclusion Our study proves our hypothesis, that the activation of autophagy via FYCO1 overexpression protects against adverse cardiac remodeling and improves cardiac function post myocardial ischemia. These findings may thus offer translational potential in the treatment of myocardial infarction.
https://dgk.org/kongress_programme/jt2023/aP2246.html