Gut and Liver, Vol. 5, No. 3, September 2011, pp. 367-376 ORiginal Article Proliferation of Hepatic Oval Cells via Cyclooxygenase-2 and Extracellular Matrix Protein Signaling during Liver Regeneration Following 2-AAF/Partial Hepatectomy in Rats Si Hyun Bae*, Seh Hoon Oh†, Seung Kew Yoon*, Joung Ah Park‡, Gi Dae Kim§, Wonhee Hur‡, Jong Young Choi*, Il Hoan Oh‡, and Kun Ho Yoon* *Department of Internal Medicine, The Catholic University of Korea, College of Medicine, Seoul, Korea, Wake Forest Institute for Regenerative Medicine, Wake Forest University School of Medicine, Winston-Salem, NC, USA, High Performance Cell Therapy Center, The Catholic University of Korea College of Medicine, Seoul, Korea, and §The Seoul National University, College of Pharmacy, Seoul, Korea Background/Aims: In the 2-acetylaminofluorene (2-AAF)/ 70% partial hepatectomy (PHx) model, the mechanism underlying the differentiation of activated hepatic oval cells (HOCs) into hepatocytes and bile ductile cells is unclear. We investigated the role of cyclooxygenase-2 (COX-2) in HOCs and the relationship between COX-2 and extracellular matrix proteins in cellular proliferation. Methods: Reverse transcrip- tion-polymerase chain reaction, immunohistochemical stain- ing, and Western blotting were used to assess COX-2 expres- sion. The co-localization of COX-2 with Thy1, c-Met, epithelial cell adhesion molecule, and α-smooth muscle actin was also examined. Additionally, we investigated whether connective tissue growth factor (CTGF), fibronectin (FN), extracellular signal-regulated kinase 1/2 (P-ERK1/2), and AKT were expressed in HOCs. Results: The expression of COX-2, pros- taglandin E2 receptors, and c-Met was upregulated in HOCs. However, HOCs treated with the COX-2 inhibitor NS398 showed decreased COX-2, CTGF, FN, and AKT expression, whereas P-ERK1/2 was unaffected. Additionally, NS398 inhibited HOC proliferation, but not the proliferation of HOCs cultured on FN-coated dishes. Furthermore, the prolifera- tive response of HOCs treated with NS398 was reversed by hepatic growth factor treatment. Conclusions: These results suggest that HOC proliferation is mediated through COX-2, extracellular FN expression, and AKT activation. Thus, COX- 2 plays an important role in HOC proliferation following acute injury. (Gut Liver 2011;5:367-376) Key Words: Hepatic oval cells; Cyclooxygenase-2; Liver gen- eration INTRODUCTION The proliferative liver responds to traumatic, chemical, meta- bolic, infectious, and other injuries by activating a complex mixture of cytokines and chemokines from remnant tissue.1 In hepatic injury animal models, the administration of 2-acety- laminofluorene (2-AAF) before and during hepatic injury is associated with increased numbers of hepatic oval cells (HOCs) and increased differentiation to hepatocytes and bile ductu- lar cells during liver regeneration, as the impaired hepatocyte response-to-growth signal suppresses hepatocyte proliferation.2-5 HOCs display distinct phenotypic markers, including CD34, c- kit, c-Met, alpha-fetoprotein (AFP), and Thy1 surface antigen.6-8 Among them, Thy1, which is expressed on bone marrow cells and stem cells in the fetal liver, plays an important role in he- matopoiesis and hepatic development.9-11 In an animal model of HOC activation, Thy1+ HOCs express high levels of connective tissue growth factor (CTGF), which is critical for HOC activa- tion during liver regeneration.12 HOCs that possess epithelial cell adhesion molecule (EpCAM) (EpCAM+ HOCs) are potential adult hepatic epithelial progenitors, but they do not express the previ- ously reported hematopoietic stem cell markers CD34, c-kit, or Thy1.13 The conversion of arachidonic acid to prostaglandins (PGs), which is the irreversible step in prostanoid biosynthesis, is mediated by two cyclooxygenases (COXs), COX-1 and COX-2, which are encoded by unique genes located on different chro- mosomes.14,15 Between them, COX-2, which was initially identi- fied as an immediate early growth-response gene, is induced by a wide variety of stimuli such as cytokines, hormones, mito- Correspondence to: Seung Kew Yoon Department of Internal Medicine, Seoul St. Mary’s Hospital, The Catholic University of Korea College of Medicine, 505 Banpo-dong, Seocho-gu, Seoul 137-040, Korea Tel: +82-2-2258-7533, Fax: +82-2-536-9559, E-mail: yoonsk@catholic.ac.kr Received on December 10, 2010. Accepted on April 27, 2011. pISSN 1976-2283 eISSN 2005-1212 http://dx.doi.org/10.5009/gnl.2011.5.3.367 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.