ARTHRITIS & RHEUMATISM Vol. 60, No. 6, June 2009, pp 1704–1709 DOI 10.1002/art.24522 © 2009, American College of Rheumatology Expression and Modulation of Ghrelin O-Acyltransferase in Cultured Chondrocytes Rodolfo Go ´mez, 1 Francisca Lago, 1 Juan J. Go ´mez-Reino, 1 Carlos Dieguez, 2 and Oreste Gualillo 1 Objective. To use reverse transcription–polymerase chain reaction to detect ghrelin O-acyltransferase (GOAT) transcripts in both murine and human chon- drocytes, to evaluate the effect of pharmacologic in vitro treatments with lipopolysaccharide (LPS), growth hor- mone, ghrelin, and dexamethasone on GOAT messenger RNA (mRNA) expression, and to study the GOAT mRNA profile during chondrocyte differentiation. Methods. Murine and human GOAT and ghrelin mRNA levels were determined by the SYBR Green– based quantitative real-time polymerase chain reaction method. Results. GOAT mRNA was expressed in murine cartilage explants as well as in the cultured murine chondrogenic ATDC-5 cell line. GOAT was also ex- pressed in human immortalized chondrocyte cell lines and in human cultured primary chondrocytes. In addi- tion, GOAT mRNA expression in differentiating ATDC-5 cells was lower at the early stage of differenti- ation (days 3–7), whereas GOAT mRNA levels increased progressively at the late stages. Finally, among the drugs and hormones tested, only LPS was able to strongly decrease GOAT mRNA expression. Conclusion. These data indicate that chondro- cytes are equipped with biochemical machinery for the synthesis of acylated ghrelin and suggest a novel role of the ghrelin axis in prehypertrophic and hypertrophic chondrocyte differentiation during endochondral ossifica- tion. Ghrelin is a peptide hormone that is secreted prevalently from the stomach in response to hunger and starvation and serves as a peripheral orexigenic signal informing the brain, leading to increased food consump- tion (1). Ghrelin has been identified in almost all vertebrates examined so far. In its biologically active form, ghrelin has 28 amino acids and a specific acyl modification of the third serine. This chemical modifi- cation is necessary for ghrelin to bind to the ghrelin receptor and to exert biologic activity. The carboxylic chain that normally esterifies the hydroxyl of serine is primarily n-octanoic acid, but other residues (6 to 10 carbon chain) may modify the structure of ghrelin (2). Acylated ghrelin represents 20–30% of circu- lating ghrelin molecules, whereas the remaining mole- cules circulate as unacylated ghrelin (3). Recent findings have demonstrated that ghrelin, apart from the multi- plicity of its physiologic functions affecting growth hor- mone release, food intake, energy and glucose ho- meostasis, and gastrointestinal, cardiovascular, pulmonary, and immune functions (4), also has relevant physiologic actions on bone (5) and cartilage (6). Inter- est in ghrelin has been fostered by characterization of the long-sought enzyme responsible for its acylation. Recently, Yang et al (7) and Gutierrez et al (8) inde- pendently described an enzyme named ghrelin O-acyltransferase (GOAT) that catalyzed the n-octanoyl modification of ghrelin in cultured cells. GOAT- knockout mice lack octanoylated ghrelin, which is con- Mr. Go ´mez is recipient of a Pre-Doctoral Fellowship from the Instituto de Salud Carlos III (FIS-PI05/0525). Drs. Lago and Gualillo’s work was supported by the Instituto de Salud Carlos III and the Xunta de Galicia (SERGAS) through a research-staff stabilization contract and individual grants (PI050419, PI060919, PI08/0044, and PGIDIT06PXIB918307PR to Dr. Lago and PI05/0525, PI08/0040, and PGIDIT07PXIB918090PR to Dr. Gualillo). 1 Rodolfo Go ´mez, BS, Francisca Lago, PhD, Juan J. Go ´mez- Reino, MD, PhD, Oreste Gualillo, PharmD, PhD: Santiago University Clinical Hospital, Santiago de Compostela, Spain; 2 Carlos Dieguez, MD, PhD: Santiago University School of Medicine, Santiago de Compostela, Spain. Address correspondence and reprint requests to Oreste Gua- lillo, PharmD, PhD, Santiago University Clinical Hospital, Research Laboratory 9: Laboratory of Neuro Endocrine Interactions in Rheu- matology and Inflammatory Diseases, Building C, Level-2, Calle Choupana s/n, 15706 Santiago de Compostela, Spain. E-mail: oreste.gualillo@sergas.es. Submitted for publication December 19, 2008; accepted in revised form February 17, 2009. 1704