J David Symons, University of Utah
Autophagy plays a central role in cellular quality control by destroying damaged or excess proteins, lipids, membranes, and organelles that accumulate in response to deviations from homeostasis. The existence and role of autophagy in endothelial cells (ECs) and blood vessels has not been established. Autophagy can be quantified by assessing the ratio of the membrane bound conjugate of microtubule-associated protein light chain 3 (LC3-II) to the cytosolic non-lipidated conjugate LC3-1 (LC3-II:LC3-I) or GAPDH (LC3-II:GAPDH) via immunoblotting. We sought to determine the extent to which a variety of cellular stressors induces autophagy in ECs and intact blood vessels. LC3-II:LC3-I or LC3-II:GAPDH was elevated (p<0.05) (i) 450±6% (n=4) in ECs incubated for 2 h in amino acid (AA)-deplete vs. AA-replete media; (ii) 47±3% (n=3) in arteries from fasted (14 h) vs. fasted / refed (1 h) mice; (iii) 40±2% (n=3) in arteries from mice that completed acute exercise vs. sedentary controls; (iv) 38±1% in arteries from exercise-trained vs. sedentary mice under basal conditions (n=2 per group); and was decreased (p<0.05) (v) 57±8% (n=4) in arteries from ~30 month-old (i.e., old) vs. ~6 month-old (i.e., young) mice. Further, indices of autophagy were elevated (p<0.05) 101±6% in ECs exposed to 3 h x 500 uM palmitate vs. vehicle (n=4), and 50±6% in arteries from obese vs. lean mice (n=4 per group). Thus, autophagy is altered in ECs and blood vessels in response to physiological (e.g., fasting, acute exercise, exercise training, aging) and pathophysiological (acute lipotoxicity, diet-induced obesity) stimuli. Ongoing research will determine the functional role of vascular autophagy in health and disease.