title: Are skeletal muscle FNDC5 gene expression and irisin release regulated by exercise and related to health?
abstract: Recently, contradictory findings have been reported concerning the function of irisin and its precursor gene, skeletal muscle FNDC5, in energy homeostasis, and the associated regulatory role of exercise and PGC-1α. We therefore evaluated whether muscle FNDC5 mRNA and serum irisin are exercise responsive and whether PGC-1α expression is associated with FNDC5 expression. The male subjects in the study performed single exercises: (1) 1 h low-intensity aerobic exercise (AE) (middle-aged, n = 17), (2) a heavy-intensity resistance exercise (RE) bout (young n = 10, older n = 11) (27 vs. 62 years), (3) long-term 21 weeks endurance exercise (EE) training alone (twice a week, middle-aged, n = 9), or (4) combined EE and RE training (both twice a week, middle-aged, n = 9). Skeletal muscle mRNA expression was analysed by quantitative PCR and serum irisin by ELISA. No significant changes were observed in skeletal muscle PGC-1α, FNDC5 and serum irisin after AE, EE training or combined EE + RE training. However, a single RE bout increased PGC-1α by 4-fold in young and by 2-fold in older men, while FNDC5 mRNA only increased in young men post-RE, by 1.4-fold. Changes in PGC-1α or serum irisin were not consistently accompanied by changes in FNDC5. In conclusion, for the most part, neither longer-term nor single exercise markedly increases skeletal muscle FNDC5 expression or serum irisin. Therefore their changes in response to exercise are probably random and not consistent excluding the confirmation of any definitive link between exercise and FNDC5 expression and irisin release in humans. Moreover, irisin and FNDC5 were not associated with glucose tolerance and being overweight, or with metabolic disturbances, respectively. Finally, factor(s) other than PGC-1α and transcription may regulate FNDC5 expression.
authors.affiliation: S. Pekkala: Department of Health Sciences, University of Jyväskylä, PO Box 35, FI-40014 University of Jyväskylä, Finland. satu.p.pekkala@jyu.fi.
authors.forename: Satu
authors.initials: S
authors.lastname: Pekkala
authors.forename: Petri K
authors.initials: PK
authors.lastname: Wiklund
authors.forename: Juha J
authors.initials: JJ
authors.lastname: Hulmi
authors.forename: Juha P
authors.initials: JP
authors.lastname: Ahtiainen
authors.forename: Mia
authors.initials: M
authors.lastname: Horttanainen
authors.forename: Eija
authors.initials: E
authors.lastname: Pöllänen
authors.forename: Kari A
authors.initials: KA
authors.lastname: Mäkelä
authors.forename: Heikki
authors.initials: H
authors.lastname: Kainulainen
authors.forename: Keijo
authors.initials: K
authors.lastname: Häkkinen
authors.forename: Kai
authors.initials: K
authors.lastname: Nyman
authors.forename: Markku
authors.initials: M
authors.lastname: Alén
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Herzig
authors.forename: Sulin
authors.initials: S
authors.lastname: Cheng
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D016022:Case-Control Studies; D005353:Fibronectins / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010807:Physical Endurance; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D055070:Resistance Training; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: C577593:FNDC5 protein, human; D005353:Fibronectins; C486497:PPARGC1A protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D012333:RNA, Messenger; D014157:Transcription Factors