Interleukin‐15 reduces mitochondrial activity independent of biogenesis in cardiomyocytes
Authors: Tomac Michael P. , Hennigan Kelly S. , Abbott Marcia J. 
Published: June 2021

Cardiovascular disease (CVD) is one of the leading causes of death in the US. Obesity is a major contributing factor to the development of CVD and its incidence continues to rise. Targeting pathways to reduce obesity may in turn reduce the development and/or progression of CVD. Interluekin‐15 (IL‐15) is a myokine that shows great promise in its ability to reduce obesity by increasing mitochondrial activity in skeletal muscle (SKM). However, the effects of IL‐15 signaling in cardiac muscle metabolism and function remain largely unknown. The objective of our study was to determine the effects of IL‐15 on the mitochondrial phenotype in cardiomyocytes. Based on our previously published data in SKM, we hypothesized that IL‐15 would act to increase mitochondrial associated factors and activity in cardiomyocytes. Differentiated H9C2 cardiomyocytes were treated with 100 ng/ml of IL‐15 for 24 hrs. RNA was extracted and reverse transcribed to cDNA. Subsequently, real‐time qPCR was employed to measure mRNA of mitochondrial associated factors, PPARα, PPARδ, Nrf1, PGC1α, PGC1β, and Tfam. GAPDH was used as a housekeeping gene and data was quantified using the ddCT method. Western blotting was used to measure protein expression levels of Phospho‐Erk1/2 and total Erk1/2, known targets of IL‐15 signaling in other cell types. Additionally, PPARa, PPARδ, PGC1α, PGC1β, and fatty acid transporter CD36, were assessed by western blotting. Genomic DNA was isolated and mitochondrial DNA was normalized to nuclear DNA by qPCR using COXI and 18S as markers, respectively, to determine mitochondrial density. To assess mitochondrial activity in the live cardiomyocytes with IL‐15 stimulation, a Mitotracker assay was employed. Fluorescence levels of the intensity of the Mitotracker dye sequestered in the active mitochondria was quantified using ImageJ. IL‐15 treatment reduced (P<0.05) mRNA expression of PPARα (30%), PPARδ (34%), and Nrf1 (24%) with no effects x on PGC1α and PGC1β expression. IL‐15 reduced (P<0.05) protein expression of PGC1α by 64% and CD36 by 28%, but had no effect on the protein levels of phospho‐Erk1/2, total Erk1/2, PPARa, PPARδ, and PGC1β. Mitochondrial activity was reduced (P<0.05) by 21% with IL‐15 treatment in the live cardiomyocytes. Mitochondrial DNA and Tfam expression levels were unchanged in the presence of IL‐15 in the cardiomyocytes. Our data indicate that IL‐15 acts to reduce mitochondrial activity and its associated factors in cardiomyocytes. These findings are in opposition to ours and others previously published studies in SKM. Conversely, in line with studies in SKM, IL‐15 failed to alter mitochondrial density or biogenesis. Importantly, Erk1/2 can be excluded as a potential route by which IL‐15 signals in cardiomyocytes. Although, IL‐15 may have potential as a therapy for obesity, it is not clear if its effects are detrimental to cardiac muscle metabolism and function. Finally, it is unclear if these in vitro data will translate to in vivo models of obesity and/or cardiovascular dysfunction. Overall, additional studies are warranted to elucidate the effects of IL‐15 signaling in cardiac muscle.Support or Funding InformationAmerican Heart Association. Chapman University.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.