Aging‐Associated Differences in Skeletal Muscle Expression of the Trimeric IL‐15R.

The purpose of this study was to examine whether skeletal muscle expressed mRNA for the trimeric IL‐15R (IL‐15Rα, IL‐2Rβ, γ c) and if expression is altered as a result of aging. The medial gastrocnemius (MG) muscles of young adult (5–7 mo, n=8) and aged (33 mo, n=8) Fischer Brown Norway (FBN) rats were excised, and flash frozen in isopentane cooled in liquid nitrogen. Seventy‐five milligram samples of MG were processed for RT‐PCR by isolating total RNA and synthesizing cDNA. RNA was isolated from rat spleens as a positive control for the individual receptor chains. Computer predicted PCR product sizes were as follows: IL‐15Rα – 325bp, IL‐2Rβ – 534bp, γ c – 535bp, and IL‐2Rα – 526bp. PCR reactions were performed using 18S as an internal standard. Aged muscle expressed greater levels of IL‐15Rα mRNA (35%, p=0.005) and IL‐2Rβ (80%, p<0.001) while no differences were observed in γ c mRNA expression. Skeletal muscle also expressed very little if any IL‐2Rα mRNA. Gel electrophoresis of IL‐15Rα PCR products revealed a band size of approximately 420bp, 100bp greater than the predicted 325bp product. These PCR products were gel purified and sequenced. Acquired data revealed a sequence of 103bp that was unique and not included in the GenBank sequenceXM_577598. In conclusion, aged skeletal muscle showed greater mRNA levels of the IL‐15Rα and IL‐2Rβ chains. In addition, a unique mRNA sequence in rat skeletal muscle was identified for the IL‐15Rα chain and submitted to GenBank (accession no. DQ157696). Funded by NIH:NIA R01AG021530.