Tissue and Cell 44 (2012) 182–194 Contents lists available at SciVerse ScienceDirect Tissue and Cell j our na l ho me p age: www.elsevier.com/locate/tice Expression patterns of Notch receptors and their ligands in human osteoarthritic and healthy articular cartilage  M. Mahjoub a,1 , N. Sassi a,1 , M. Driss b , L. Laadhar a , M. Allouche c , M. Hamdoun c , K. Ben Romdhane b , S. Sellami a,∗ , S. Makni a a Immuno-Rheumatology Research Laboratory, Rheumatology Department, La Rabta Hospital, University of Tunis-El Manar, 1007 Tunis, Tunisia b Anatomo-Pathology Department, Salah Azaiez Health Institute, 1007 Tunis, Tunisia c Forensics Department, Charles Nicolle Hospital, 1007 Tunis, Tunisia a r t i c l e i n f o Article history: Received 30 July 2011 Received in revised form 2 March 2012 Accepted 2 March 2012 Available online 26 March 2012 Keywords: Notch signaling Osteoarthritis Human articular cartilage Immunohistochemistry a b s t r a c t Notch pathway plays a pivotal role in cell fate determination. There is much interest surrounding its therapeutic potential, in osteoarthritis, but the expression profile of Notch-related molecules, as well as their relation with cartilage pathological parameters, remains unclear. The purpose of our study is to analyze the expression pattern of Notch family members, type II and type I collagen, in normal (healthy) and osteoarthritic human knee cartilage. Osteoarthritic cartilages were obtained from 3 patients under- going a total knee replacement. Macroscopically normal cartilage was dissected from 3 human knees at the time of autopsy or surgery. Immunohistochemical staining was performed using Notch1,2,3 and 4, Delta, Jagged, type II collagen and type I collagen antibodies. In healthy cartilage, type II collagen was abundantly expressed while type I was absent. This latter increased proportionally to the osteoarthritic grade. Type II collagen expression remained intense in osteoarthritic cartilage. In healthy cartilage as well as in cartilage with minor lesions, Notch family member’s proteins were not or just weakly expressed at the surface and in the cells. However, Notch molecules were over-expressed in osteoarthritic cartilage compared to healthy one. This expression pattern was different according to the cartilage zone and the severity of OA. Our data suggest that Notch signaling is activated in osteoarthritic cartilage, compared to healthy cartilage, with a much more abundant expression in the most damaged areas. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The Notch pathway is known to be a highly conserved mech- anism beyond species that plays a pivotal role in cell fate determination, during intervertebrate and vertebrate development as well as in the adulthood, while controlling differentiation, prolif- eration and apoptosis (Dumortier et al., 2005). Four Notch receptors (Notch1–4) and five ligands (Delta1,3,4; Jagged1,2) belonging to the DSL family (Delta, Serrate for Drosophila and Lag-2 for Caenorhabdi- tis elegans) have been identified in mammals (Artavanis-Tsakonas et al., 1995, 1999; Kopan and Weintraub, 1993; Lardelli et al., 1994; Weinmaster et al., 1991, 1992). Abbreviations: Col I, type I collagen; Col II, type II collagen; NL, normal; OA, osteoarthritis/OA; ECM, extracellular matrix.  This work was financially supported by the Tunisian Ministry of Higher Educa- tion and Scientific Research. ∗ Corresponding author. Tel.: +216 71 560 432; fax: +216 71 560 432. E-mail address: slaheddine.sellami@rns.tn (S. Sellami). 1 These authors contributed equally to this work. The functional involvement of Notch signaling in chondro- genesis has been previously reported (Hardingham et al., 2006; Oldershaw et al., 2005). Recent studies revealed that Notch is expressed in murine chondrocytes during cartilage development and in chondrocytes from adult normal articular cartilage (Hayes et al., 2001; Hiraoka et al., 2006). Besides, Dowthwaite et al. (2004) identified at the surface of a 7-day-old-bovine articular cartilage, a chondroprogenitor cell population that highly expresses the Notch1 receptor. Moreover, our team and others (Blaise et al., 2009; Haughton et al., 2006; Karlsson et al., 2007, 2008; Khan et al., 2010; Sassi et al., 2009; Watanabe et al., 2003), have reported a possible role of the Notch cascade during some pathological processes that occur during osteoarthritis (OA). OA is the most common articular disease and is becoming a major health problem with the aging of the population. It is char- acterized by a loss of the structural and functional properties of cartilage. During OA, chondrocytes undergo phenotypical changes leading to dedifferentiation, which promote matrix degradation and unsuccessful cartilage repair (Poole et al., 2002). Understanding the underlying mechanisms of Notch signaling during chondro- cytes dedifferentiation may eventually allow scientists to modulate 0040-8166/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.tice.2012.03.001