| Description |
Macroautophagy is operational during basal conditions to maintain intracellular organelle and protein quality control, but is upregulated during cellular stress (e.g., dynamic exercise) to adapt to changing nutritional and energy demands. We tested the hypothesis that intact endothelial cell (EC) autophagy is required to observe traininginduced vascular adaptations. 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., Beclin-1+/- mice, were refractory to training-induced improvements concerning glucose homeostasis. In preliminary studies, we demonstrated that : (i) workload achieved during a maximal treadmill test; (ii) soleus muscle citrate synthase activity; (iii) mRNA and protein expression of vascular autophagy; and (iv) intraluminal flow-mediated vasodilation (FMD) of femoral arteries examined ex vivo, was greater (all p<0.05) in ~ 7-month old male C57Bl/6 mice that completed 12-weeks of treadmilltraining vs. age-matched sedentary animals (n=10 mice per group). These findings indicate that our efficacious training protocol improves vascular autophagy and arterial function in adult mice. Next, ~ 4-month old male C75Bl/6 mice with inducible Cre/LoxPbased impairment of autophagy-related gene 3 (Atg3) specifically in ECs (iecAtg3KO mice) and their Cre negative littermates (WT) were treated with tamoxifen. Two weeks later, one cohort of iecAtg3KO mice initiated a treadmill training program; 15.6-18.6 m/min x 5-20% grade x 10-60 min per day x 6 days per week x 12 weeks (ETR). Another cohort of iecAtg3KO mice maintained familiarity with treadmill by running 5-10 m/min x 5% grade x 10 min per day x 1 day per week x 12 weeks (SED). Two cohorts of WT iii littermates were treated identically. After 12-weeks efficacy of the training protocol was established as described earlier and verification of our mutant was confirmed. With regard to the latter, primary arterial ECs indicated Atg3 mRNA and protein expression was minimal (p<0.05) in iecAtg3KO vs. WT mice, whereas vascular smooth muscle cell Atg3 was similar between groups. As expected, intraluminal FMD responses were greater (p<0.05) in WT-ETR vs. WT-SED mice, while vascular smooth muscle responses to sodium nitroprusside were not different between groups. In addition, intraluminal FMD was blunted (p<0.05) in iecAtg3KO-SED vs. WT-SED mice, substantiating our previous findings and underscoring the importance of intact EC autophagy to vasodilation. Contrary to our hypothesis, training-induced vascular adaptations indeed were observed (p<0.05) in iecAtg3KO-ETR vs. iecAtg3KO-SED mice, while vascular smooth muscle responses were not different between groups. These findings indicate that intact Atg3 mRNA and protein expression are not required for training-induced vascular adaptations to occur. |
