Effects of PYY on IL‐6 Signaling in Primary Human Myotubes

Rationale Life expectancy is increasing and as a result, the older adult population in the United States is growing. Diminishing skeletal muscle function can impact the lives of older adults by limiting mobility and independence. Inflammation is thought to contribute to the development skeletal muscle metabolic dysfunction. Thus, identifying and understanding biological molecules that affect inflammatory signaling will inform interventions designed to support preservation of healthy skeletal muscle metabolism. Peptide Tyrosine Tyrosine (PYY), a novel skeletal muscle factor identified by our laboratory, is a potential mediator of inflammation in skeletal muscle. The effects of PYY in skeletal muscle need to be elucidated. Skeletal muscle gene expression of PYY is down‐regulated with aging and in individuals whose skeletal muscles do not hypertrophy in response to resistance exercise training. Exogenous administration of PYY decreases inflammatory signaling in various cell‐lines. Hypothesis Based on observations from microarray analysis conducted on RNA from skeletal muscle biopsies as well as preliminary data from our laboratory, we hypothesized that PYY down‐regulates inflammatory signaling in human primary skeletal muscle cells. Methods Biopsies were taken from the vastus lateralis muscle of two healthy, young females. Primary human skeletal muscle progenitor cells were isolated. Cells were pooled and cultured in Ham's F12 supplemented with 20% HI FBS and bFGF (GM). Once cells reached 75% confluence (t=0 h) all cultures were switched to differentiation medium [(DM), Ham's F12 + 2% HI Equine Serum] without (CONT) or with 500 pM PYY 3‐36 (pPYY). At t=72 h, the medium on CONT and pPYY plates was replaced with DM + 0.5% Fatty Acid Free BSA (FAF‐BSA) without or with 100 ng/ml IL‐6 (CONT inflame and pPYY inflame ) for 24 h. A subset of the cells from all treatment groups were exposed to a 20 min 200nM insulin challenge (CONT +I , pPYY +I , CONT inflame+I , and pPYY inflame+I ) prior to harvesting the cells for RNA. Gene expression was measured using quantitative PCR. Results Differentiating primary human myoblasts that were pretreated with PYY 3‐36 then incubated in IL‐6 and insulin challenged had a −1.87 and −1.79 fold change in AMPK and STAT3 mRNA expression, respectively (pPYY inflame+I vs. CONT inflame+I , p<0.05). This difference however, was not observed in cells pretreated with PYY 3‐36 and incubated in IL‐6 without an insulin challenge (CONT inflame vs. pPYY inflame , p>0.05) or in cells incubated without IL‐6 (CONT vs. pPYY, p>0.05 and CONT +I vs. pPYY +I , p>0.05). Conclusions PYY pretreatment appears to have a protective effect against IL‐6 inflammatory signaling when an anabolic stimulus is given; PYY down‐regulates IL‐6 signaling through both AMPK and STAT3 pathways in the presence of insulin. Ongoing research in our laboratory is clarifying the role of the insulin stimulus in facilitating this effect of PYY. Support or Funding Information Cornell Start‐up