IL‐15 Activates Akt Independent of AMPK Signaling in Cardiomyocytes
Authors: Hennigan Kelly S , Yim Veronica T , Tomac Michael P , Abbott Marcia J 
Published: June 2021

Obesity is a major contributor to the onset and progression of many diseases, such as cardiovascular disease (CVD). Diet and exercise are known to be successful treatments for obesity and ultimately CVD. However, implementation of lifestyle interventions is difficult to maintain. Thus, focus has turned to examine the role of molecular mediators of physical activity to prevent obesity and its related disorders. Following exercise, many factors are secreted into circulation and act to regulate various metabolic processes. Interleukin‐IL‐15 (IL‐15) is a myokine, secreted from skeletal muscle (SKM), and has been shown to increase in circulation as a result of exercise. Further, IL‐15 acts to reduce fat mass while increasing lean mass. On a cellular level, IL‐15 induces mitochondrial activity and glucose metabolism in various cell types. However, it is not known if IL‐15 recapitulates its effects in cardiomyocytes (CM). The objective of the current study was to determine if IL‐15 regulates metabolic processes in CM. Specifically, we aimed to examine the activation of enzymes associated with glucose metabolism following treatment with IL‐15 in CM. AMPK and Akt have been verified to be involved in regulating glucose metabolism and are suggested to be downstream of IL‐15 signaling. H9c2 CM were cultured and differentiated into mature myocytes. Following differentiation, CM were treated for 24 hrs with 100 ng/ml of IL‐15. Total protein lysates were harvested from the CM and a Bradford assay was used to quantify the protein concentrations. Western blotting procedures were carried out to asses both activation and total content of the proteins. Thirty‐five micrograms of total protein was loaded onto 4–20% polyacrylamide gels for electrophoresis. Proteins were then transferred from the gel onto a PVDF membrane. Membranes were blocked with 5% BSA for 1 hour and primary antibodies (phospho‐AMPK, total AMPK, phospho‐Akt and phospho‐Akt substrates) were applied (1:1000). Subsequently, membranes were probed with secondary antibodies (1:2000). The membranes were then imaged using enhanced chemiluminescence. Image J was used to quantify the density of the visualized protein bands. An unpaired t‐test (P<0.05) was used to determine if IL‐15 had significant effects on protein levels. IL‐15 did not alter either phospho‐AMPK or total AMPK levels (P>0.05). Phosphorylation of Akt and its substrates were induced (nearly 10‐fold) with IL‐15 treatment. Our results indicate that IL‐15 acts to increase phosphorylation of Akt and its downstream substrates without activating AMPK. Since Akt is on the insulin signaling pathway, it is feasible that IL‐15 acts to induce glucose metabolism in CM. However, it is not clear if IL‐15 directly mediates glucose uptake in CM. Nevertheless, it appears that IL‐15 may play a role in regulating CM glucose metabolism in a similar manner as in SKM cells. Further studies are needed to determine if our results translate into a whole‐body in vivo situation. If IL‐15 is involved in substrate metabolism in CM, it is necessary to determine if its effects alter heart function, especially in models of obesity.

Support or Funding Information

American Heart Association 16SDG30680003

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.