Myokine/Cardiokine Follistatin-like Protein 1 Promotes Oxidative MyHC Expression and Mitochondrial Function in Myogenic Cells

Abstract

Follistatin-like Protein 1 (FSTL1) is a glycoprotein secreted by cardiac and skeletal muscle tissues under stressful conditions. An elevated level of plasma FSTL1 has been observed after a single bout of exercise suggesting its potential myokine-like role involved in the crosstalk between muscle and other organs. PURPOSE: To investigate autocrine effects of FSTL1 on myotube differentiation, myosin heavy chain expression and mitochondrial respiration in various myogenic cells. METHODS: Primary myoblasts were isolated from canine gastrocnemius muscle. Myotube differentiation was induced by a low serum condition for 4 days. Immunostainings were performed using MF20 antibody (rod-like tail region of myosin) and DAPI (nuclei); and fusion index was determined by calculating the ratio between total number of nuclei and number of nuclei within myotubes formed. RT-PCR assays were performed using primer sets precisely designed to amplify each fiber type-associated myosin heavy chain isoforms. Oxygen consumption of intact cells were measured using a Clark-type oxygen sensor; and mitochondrial respiration was measured using Seahorse XF96 analyzer. RESULTS: During canine myotube formation, FSTL1 treatment (300 ng/ml, 4 days) significantly enhanced myogenic potential determined by fusion index (~2-fold increase). There was a significant increase in MyHC7 expression (~1.5 fold) in myotubes treated with FSTL1 during differentiation compared to non-treated myotubes. Acute FSTL1 treatment (up to 500 ng/ml) had no significant effect on mitochondrial respiration in canine myoblasts. Acute FSTL1 treatments (250 ng/ml) significantly increased mitochondrial respiration in L6 myotubes (~1.5 fold) and human rhabdomyosarcoma cells. Chronic FSTL1 treatments (250 ng/ml, 64 hours) significantly increased oxygen consumption in intact canine myoblasts and myotubes. CONCLUSION: Our preliminary data suggest that FSTL1 enhances differentiation potential and increases oxidative metabolism in myogenic cells suggesting that FSTL1 may be an important cellular mediator of the beneficial effects of exercise in the context of skeletal muscle adaptation. Supported by NIH Grant RO1 HL133248.