Abstract
In the initiation phase of autophagy, the ULK1 complex translocates to endoplasmic reticulum membranes which eventually give rise to autophagosomes via an omegasome intermediate. We studied ULK1 complex accumulation in both starvation-induced non-selective autophagy and ivermectin-induced selective autophagy of mitochondria (mitophagy) using fluorescence imaging and mathematical modelling. In non-selective autophagy, a single accumulation event occurred, whose intensity and duration were reduced upon wortmannin-dependent inhibition of the Class III PI-3 kinase VPS34 and a block in omegasome formation. In contrast, oscillatory dynamics were observed in mitophagy, with increasing time between peaks. We hypothesise that these oscillations reveal successive ULK1 complex translocations, each similar to the event observed in non-selective autophagy. These translocations would only happen on portions of the mitochondrial surface not already covered by LC3-containing autophagosomal membrane. Our mathematical model reproduced ULK1 repeated aggregations (oscillations) and predicted a positive correlation between the number of events and the mitochondrial diameter.
- Abbreviations
- AIC
- Akaike Information Criterion
- ATG13
- Autophagy-related protein 13
- CI
- Confidence interval
- CL
- Confidence level
- EC50
- Half maximal effective concentration
- IVM
- Ivermectin drug
- LC3
- Microtubule-associated proteins 1A/1B light chain 3B
- ODE
- Ordinary Differential Equation
- PI3P
- Phosphatidylinositol 3-phosphate
- ULK1
- Unc-51 like autophagy activating kinase 1
- VPS34
- Phosphatidylinositol 3-kinase VPS34