ORIGINAL ARTICLE Basic fibroblast growth factor is pro-adipogenic in rat skeletal muscle progenitor clone, 2G11 cells Shin-ichi NAKANO, Katsuyuki NAKAMURA, Naomi TERAMOTO, Keitaro YAMANOUCHI and Masugi NISHIHARA Department of Veterinary Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan ABSTRACT Intramuscular adipose tissue (IMAT) formation is a hallmark of marbling in cattle. IMAT is considered to originate from skeletal muscle progenitor cells with adipogenic potential. However, the mechanism involved in IMAT formation from these progenitor cells in vivo remains unclear. In the present study, among the growth factors tested, which were known to be expressed in skeletal muscle, we found only basic fibroblast growth factor (bFGF) has a pro-adipogenic effect on skeletal muscle derived adipogenic progenitor clone, 2G11 cells. Pre-exposure of 2G11 cells to bFGF did not affect initial gene expressions of CCAAT/enhancer-binding protein (C/EBP)β and C/EBPδ, while resulting in an enhancement of subsequent expressions of C/EBPα and proliferator-activated receptor gamma (PPARγ) during adipogenesis, indicating that bFGF is acting on the transcriptional regulation of C/EBPα and PPARγ. In addition, the effect of bFGF is mediated via two types of FGF receptor (FGFR) isoforms: FGFR1 and FGFR2 IIIc, and both receptors are prerequisite for bFGF to express its pro-adipogenic effect. These results suggest that bFGF plays an important role as a key trigger of IMAT formation in vivo. Key words: adipogenesis, basic fibroblast growth factor, fibroblast growth factor receptor, skeletal muscle. INTRODUCTION Intramuscular adipose tissue (IMAT) formation is a hallmark of marbling in cattle (Japan Meat Grading Association 1989) as well as some skeletal muscle pathologies such as Duchenne muscular dystrophy and Sarcopenia (Mora 1989; Song et al. 2004; Marden et al. 2005; Marcus et al. 2012). IMAT is considered to originate from skeletal muscle progenitor cells with adipogenic potential. Joe et al. (2010) and Uezumi et al. (2010, 2014) showed that platelet-derived growth factor receptor (PDGFR)α-positive mesen- chymal progenitor cells are the origin of IMAT in mice and human skeletal muscle. We also reported previ- ously the establishment of a rat skeletal muscle pro- genitor cell clone, namely 2G11 cells, that are highly adipogenic both in vitro and in vivo (Murakami et al. 2011). However, the mechanism involved in IMAT formation from these adipogenic cells in vivo is largely unknown. Adipogenesis is composed of a multistep process that requires the sequential activation of numerous tran- scription factors, including the CCAAT/enhancer- binding protein (C/EBP) gene family and peroxisome proliferator activated receptor (PPAR) gene family (Spiegelman & Flier 1996; Mandrup & Lane 1997). First, two members of C/EBP family genes, C/EBPβ and C/EBPδ, are rapidly expressed upon induction of adipogenic differentiation. C/EBPβ and C/EBPδ then activate the expressions of C/EBPα and PPARγ (Tang & Lane 1999). Once expressed, C/EBPα and PPARγ acti- vate mutually through their C/EBP regulatory ele- ments (Elberg et al. 2000) and trans-activate a large group of genes that produce the mature adipocyte phenotype (Yeh & McKnight 1995; Tang & Lane 2012). Basic fibroblast growth factor (bFGF), a member of the FGF family, is a pleiotropic cytokine that modu- lates cellular functions such as proliferation, differen- tiation, apoptosis, migration, adhesion and motility (Chlebova et al. 2009), and are a family of ligands that bind to four different types of cell surface receptors, Correspondence: Keitaro Yamanouchi, Department of Veteri- nary Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. (Email: akeita@mail.ecc.u-tokyo .ac.jp) Received 25 December 2014; accepted for publication 14 January 2015. Animal Science Journal (2016) 87, 99–108 doi: 10.1111/asj.12397 © 2015 Japanese Society of Animal Science