Symons, John David; Cho, Jae Min; Ly, Kellsey; Thompson, Lauren; Lee, Sebastian; Hansen, Michele; Carter, Kandis (University of Utah)
Faculty Advisor: Symons, John David (University of Utah; Nutrition and Integrative Physiology)
The process of macroautophagy is operational during basal conditions to maintain organelle and protein quality control, but is upregulated during cellular stress to adapt to changing nutritional and energy demands. We tested the hypothesis that intact endothelial cell (EC) autophagy is required to observe exercise training-induced vascular improvements. Rationale for this hypothesis was provided by an earlier report that obese mice with germline, whole body mutation of a protein requisite for autophagy i.e., Bcl2-AAA mice were refractory to training-induced improvements concerning glucose homeostasis. First we demonstrated that : (i) workload achieved during a maximal treadmill test; (ii) soleus muscle citrate synthase activity; (iii) vascular indices of autophagy; and (iv) endothelium-dependent function were greater (p<0.05) in male C57Bl/6 mice that completed 10-weeks of treadmill-training vs. age-matched sedentary animals. These findings indicate that an efficacious training protocol improves vascular autophagy and arterial function. Next, age-matched male mice on a C75Bl/6 background with tamoxifen-inducible Cre/LoxP-based impairment of autophagy-related gene 3 (Atg3) specifically in ECs (iecAtg3KO mice) or wild-type (WT) littermates were trained (ETR) identically or remained sedentary (SED). Atg3 mRNA was minimal (p<0.05) in ECs obtained from iecAtg3KO vs. WT mice, but vascular smooth muscle cell Atg3 was similar between groups. These data verify that specific knockdown of Atg3 existed in ECs but not vascular smooth muscle of iecAtg3KO mice. As expected, intraluminal flow-mediated vasodilation (FMD) improved (p<0.05) in WT-ETR vs. WT-SED mice, while vascular smooth muscle responses to sodium nitroprusside were similar between groups. Further, as anticipated, intraluminal FMD was blunted (p<0.05) in iecAtg3KO-SED vs. WT-SED mice, indicating the importance of EC autophagy to FMD induced vasodilation. Contrary to our hypothesis, however, training-induced vascular adaptations were observed (p<0.05) in iecAtg3KO-ETR vs. iecAtg3KO-SED mice, while vascular smooth muscle responses were similar between groups. Indeed, training-induced vascular improvements concerning intraluminal FMD were not different between WT-ETR and iecAtg3KO-ETR mice. These findings are not congruent with our original hypothesis, and indicate that intact EC Atg3 is not required for training-induced vascular adaptations to occur.