Keratinocyte Growth Factor Promotes Preadipocyte Proliferation via an Autocrine Mechanism Ting Zhang, Haiyan Guan, and Kaiping Yang * Children’s Health Research Institute & Lawson Health Research Institute, Departments of Obstetrics & Gynaecology and Physiology & Pharmacology, University of Western Ontario, 800 Commissioners Rd. E., London, Ontario, Canada N6A 4G5 ABSTRACT Keratinocyte growth factor (KGF; also known as FGF-7) is a well-characterized paracrine growth factor for tissue growth and regeneration. However, its role in adipose tissue, which is known to undergo tremendous expansion in obesity, is virtually unknown. Given that we previously identified KGF as one of the up-regulated growth factors in adipose tissue of an early-life programmed rat model of visceral obesity, the present study was undertaken to examine the hypothesis that KGF promotes adipogenesis. Using 3T3-L1 and rat primary preadipocytes as in vitro model systems, we demonstrated that (1) KGF stimulated preadipocyte proliferation in a concentration-dependent manner with a maximal effect at 2.5 ng/ml (2-fold increase); (2) KGF mRNA was highly expressed in rat adipocytes and preadipocytes as well as 3T3-L1 cells; (3) treatment of preadipocytes with a neutralizing antibody against KGF and siRNA-mediated knockdown of KGF led to a 50% reduction in their proliferative capacity; (4) KGF activated the protein kinase Akt, and the PI3 kinase inhibitor LY294002 blocked KGF stimulation of preadipocyte proliferation; and (5) KGF did not promote differentiation of preadipocytes to mature adipocytes. Together, these results reveal adipocytes and their precursor cells as novel sites of KGF production. Importantly, they also demonstrate that KGF promotes preadipocyte proliferation by an autocrine mechanism that involves activation of the PI3K/Akt signaling pathway. Aberrant KGF expression may have consequences not only for normal adipose tissue growth but also for the pathogenesis of obesity. J. Cell. Biochem. 109: 737–746, 2010. ß 2010 Wiley-Liss, Inc. KEY WORDS: ADIPOGENESIS; KGF; FGF-7; PI3 KINASE; SIGNAL TRANSDUCTION O besity is becoming a leading health problem not only because of its high prevalence but also because of its substantially impairs quality of life and increases the risk of cardiovascular and metabolic diseases as well as certain cancers [Mokdad et al., 2003; Brown et al., 2009]. Obesity is characterized by excess adipose tissue expansion in all or certain fat depots in the body. Visceral obesity (excess adipose tissue accumulation within the abdomen) is the best predictor of obesity-associated morbidity and mortality [Montague and O’Rahilly, 2000]. Although the etiology of visceral obesity remains largely unknown, accumulating epidemiological evidence indicates that low-birth weight is associated with increased visceral adiposity in adult life, suggesting an early-life origin for this disorder [Hales and Barker, 1992; Ong and Dunger, 2002]. Recently, we have demonstrated that poor early nutrition, evoked by maternal protein restriction (MPR) during pregnancy and lactation, leads to low-birth weight and subsequent development of increased visceral adiposity in adult male rat offspring [Guan et al., 2005]. Moreover, we have obtained evidence suggesting that increased visceral adiposity in our rat model is characterized by adipocyte hyperplasia. Indeed, adipocyte precursor cells derived from MPR offspring exhibit accelerated rate of proliferation, even a few days after removal from their in vivo environment [Zhang et al., 2007]. This suggests that MPR permanently alters adipocyte development, but the factors and molecular mechanisms that are responsible for programming this aberrant phenotype remain largely unknown. As a first step in identifying the causal factors involved, we utilized a candidate gene approach by capitalizing on our previously published visceral adipose tissue gene expression profiling database generated with our rat model of increased visceral adiposity. Journal of Cellular Biochemistry ARTICLE Journal of Cellular Biochemistry 109:737–746 (2010) 737 Ting Zhang and Haiyan Guan contributed equally to this work. Grant sponsor: Heart & Stroke Foundation of Ontario; Grant number: NA-6049; Grant sponsor: Canadian Institutes of Health Research (Operating Grant); Grant number: MOP-79484. *Correspondence to: Dr. Kaiping Yang, Children’s Health Research Institute, Room A5-132, Victoria Research Laboratories, Westminster Campus, 800 Commissioners Road East, London, Ontario, Canada N6A 4G5. E-mail: kyang@uwo.ca Received 26 June 2009; Accepted 12 November 2009  DOI 10.1002/jcb.22452  ß 2010 Wiley-Liss, Inc. Published online 12 January 2010 in Wiley InterScience (www.interscience.wiley.com).