FYCO1 ameliorates adverse cardiac remodeling in response to myocardial ischemia by enhancing autophagic flux
Authors: Senger F , Remes A , Schmiedel N , Tannert C , Mueller O J , Kuhn C , Frey N 
Published: October 2022

Abstract

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.

Purpose
The aim of our study was to investigate the effects of FYCO1 overexpression post myocardial infarction. Our hypothesis is that FYCO1 overexpression leads to enhanced autophagic flux and hence blunted cardiac remodeling and improved heart function.

Methods
FYCO1-Tg mice were crossbred with RFP-EGFP-LC3-Tg reporter mice (FYCO1-TGxRGF) to enable the analysis of autophagic flux using confocal microscopy. 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. Myocardial fibrosis, Midline Infarct size (%) and LV circumference were assessed in Masson's Trichrome stainings. Autophagy activaty was analyzed by Western blot for LC3 II and LC3 II/LC3 I. Furthermore, Evans blue/TTC staining was performed to assess the area at risk and to define perfused, ischemic and necrotic area post LAD.

Results
In FYCO1-TGxRGFP mice 3 days post LAD we observed an overall 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. Moreover, using confocal microscopy revealed a shift in autophagosomal transport 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). In Evans blue/TTC staining, FYCO1-TGxRGFP mice demonstrated comparable ischemic but markedly decreased necrotic area (ischemic: 1,9±1,8%; necrotic: 37,1±11,5%) within the LV as compared to WT (ischemic: 2,1±1,9%; necrotic: 53,4±31,4%). Fibrosis in LV (WT: 19,6±1,8%; TG: 10,6±1,6%) and infarct size (WT: 34,5±3,9%; TG: 5,5±2%) 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). Importantly, 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 demonstrates 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.

Funding Acknowledgement
Type of funding sources: None.