ULK2 Regulates p62‐ and NBR1‐Dependent Selective Autophagy In Skeletal Muscle

Abstract

Autophagy is an anciently conserved pathway responsible for the degradation of long‐lived proteins, protein aggregates, and organelles, thereby contributing to efficient protein homeostasis. Autophagy is stimulated by nutrient deprivation and is required for certain beneficial adaptations of exercise. Conversely, insufficient autophagy is a common feature of muscle diseases, obesity, type 2 diabetes, and aging; yet the regulation of autophagy is incompletely understood at the molecular level. Here, our goal was to define the role of muscle unc‐51 like autophagy activating kinase 2 (ULK2), and contrast with that of its close homolog ULK1, in regulation of autophagy. To do so, we performed 2 complementary studies. First, DNA plasmids encoding either Ulk1 or Ulk2 pre‐micro RNAs (miR) were electroporated into the tibialis anterior (TA) muscle of one leg, and a control miR plasmid into the contralateral leg of wild type mice. Muscles were harvested 7–8 days afterwards, either at basal conditions or after 24h of starvation. Second, ULK2fl/fl differentiated primary mouse myotubes were transduced with Ad‐Cre‐GFP or Ad‐GFP (control) viruses, and harvested up to 96h afterwards. Our results revealed that ULK2 is highly expressed in skeletal muscle, and that deficiency of ULK2, but not of its close homolog ULK1, leads to accumulation of ubiquitinated proteins. In addition, the autophagy receptors p62 and NBR1, which are degraded by autophagy and serve as receptors for ubiquitinated cargos, accumulate in muscles and primary myotubes deficient only in ULK2, independent of lysosomal fusion and function. Of note, the levels of the autophagy receptor optineurin were unaffected under the same conditions. These results indicate a novel and fundamental role for ULK2 in regulating p62‐ and NBR1‐dependent selective autophagy in skeletal muscle revealing ULK2 as a potential therapeutic target for skeletal muscle contractile and metabolic dysfunction.Support or Funding InformationSupported by AHA (16SDG30360001) and Dept. of Health & Human Physiology, University of Iowa.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.