Effects of Inflammation on Arginine Transport and Metabolism in Human Primary Myotubes
Authors: Gupta Diwakar , Riddle Emily S , Blum Jamie E , Roman Heather , Thalacker‐Mercer Anna 
Published: November 2023

RationaleSkeletal muscle atrophy among older adults increases the risk for falls and fractures, loss of mobility and independence, physical disabilities, and even mortality. Development of efficacious therapies to attenuate skeletal muscle loss in the older population is necessary. Metabolomics research from our laboratory indicates that skeletal muscle mass (measured as appendicular lean mass divided by height squared) in older adults is associated with arginine metabolism. Arginine supplementation, as part of a multi‐nutrient supplement, has been given to individuals to attenuate skeletal muscle wasting induced by diseases with heightened inflammation (e.g., HIV and cancer cachexia). Older adults in general have chronic increased circulating and intramuscular levels of the proinflammatory cytokine tumor necrosis factor alpha (TNFα) that is associated with skeletal muscle atrophy. The effect of TNFα on skeletal muscle arginine metabolism is largely unknown.ObjectiveTo investigate the effects of age and TNFα on skeletal muscle arginine metabolism.MethodsSkeletal muscle biopsies were collected from 11 younger (21–39 years old) and 5 older (68–80 years old) males and females (YM, YF, OM, OF) after an overnight fast. To assess inflammatory signaling and arginine metabolism, the gene expression of TNFα, signal transducer and activator of transcription 3 (STAT3), interleukin‐6 (IL‐6), the IL‐6 receptors (IL‐6R and IL‐6ST), and cationic amino acid transporter 1 and 2 (CAT‐1 and CAT‐2) in whole tissue lysate was measured using quantitative PCR. To investigate the effects of TNFα specifically, primary skeletal muscle progenitor cells from 6 YM were cultured in growth media for 7 days, switched to differentiation media (DM) for 3 days, then incubated in DM containing 10 ng/mL TNFα for 2 days. Gene expression of the arginine transporters and metabolic enzymes in the TNFα treated primary human myotubes was measured using quantitative PCR.ResultsThere was no difference between young and old adults for CAT‐1 or CAT‐2 gene expression in whole skeletal muscle tissue lysate. There was also no difference in the gene expression of TNFα, STAT3, IL‐6, or the IL‐6 receptors. Incubation with TNFα decreased CAT‐1 gene expression slightly (−1.1 fold change, p=0.045) and increased CAT‐2 gene expression (11.2‐fold change, p=0.002) in primary human myotubes.ConclusionsThe proinflammatory cytokine TNFα increased gene expression of the arginine transporter CAT‐2 in primary human myotubes, indicating that older adults with elevated TNFα may have altered arginine transport, and potentially altered metabolism, in skeletal muscle. Ongoing research in our laboratory is assessing the effects of increased arginine availability in the skeletal myotubes in a proinflammatory culture. Future research is needed to determine if altering dietary arginine consumption in older adults can attenuate the atrophic effects of TNFα and thus, be a possible therapy to reduce skeletal muscle atrophy.Support or Funding InformationCornell Start‐up