Mechanical Signaling in NF1 Osteoblast Cell Ibraheem Bamaga 1* and Kevin P McHugh 2 1 Department of Dentstry, University of Florida. 1395 Center Dr. Room D10-28 Gainesville, Florida, USA 2 Department of Periodontcs, School of Dentstry, University of Florida, USA * Corresponding author: Ibraheem Bamaga, Department of Dentstry, University of Florida. 1395 Center Dr. Room D10-28 Gainesville, Florida, USA, Tel: 3522153120; E-mail: ibamaga@dental.uf.edu Rec date: September 10, 2017; Acc date: September 14, 2017; Pub date: September 18, 2017 Citaton: Bamaga I, McHugh KP (2017) Mechanical Signaling in NF1 Osteoblast Cell. J Den Craniofac Res Vol.2 No.2:12. Abstract Neurofbromatosis Type I (NF1) syndrome is characterized by neurofbromas and neural tumors but is also associated with skeletal abnormalites. The cellular pathophysiology of skeletal abnormalites in NF1 is not understood. These abnormalites result from consttutve actve RAS and its downstream efectors, RASERK pathway, due to mutaton of NF1 gene which converts actve RAS-GTP into inactve RAS-GDP. In osteoblast cells, RAS-ERK pathway is involved in cell proliferaton and diferentaton and is also involved in mechanical signals transducton. In this study, we propose that Nf1 mutaton in osteoblast cells will afect the response to mechanical stmulaton through the RAS pathway. The Flexcell tension system was used to mechanically stmulate calvarial osteoblast precursor from conditonal knockout mice, Nf1(ob-/-), and wild type calvarial osteoblast precursor cells, (WT. The protocol of cyclic mechanical strain was 2% to 4% elongaton at 0.16 Hz (10 cycles per minute) for 24 h. Mechanically stmulated cells showed lower expression levels of the osteoblast marker gene, RUNX2, measured at 4 h and 8 h post-stretch. Mineralized matrix depositon, assessed by Alizarin red staining, was decreased in Nf1(ob-/-) compared to (WT) cells following mechanical stmulaton. the Nf1(ob-/-) and WT osteoblast precursor cells were then treated with RAS inhibitor (FTI-277), for 4 h and 8 h. RUNX2 expression level was increased in Nf1(ob-/-) cells compared to non-treated cells. However, the opposite result was seen in (WT) cells. The FTI-277 treatment resulted in lower RUNX2 expression level and lower mineralized matrix depositon. This response of (WT) cells was normal. However, the Nf1(ob-/-) response showed that these cells although they have hyper-actve RAS, but when it is exposed to stress, it loses its ability to express osteoblast markers or lay down mineralized matrix. Our results indicate that, the hyper- actve RAS in NF1 mutant osteoblast will result in cells being stuck in proliferatve state and unable to diferentate. Keywords: Neurofbromatosis; Osteoblasts; Bone; Mechanical signaling; Craniofacial Introducton Neurofbromatosis type 1 (NF1) is an autosomal dominant disorder caused by loss of functon mutatons in the NF1 gene with an incidence of approximately 1 in 3000, making it one of the most common genetc disorders [1,2]. NF1 syndrome is primarily characterized by subcutaneous neurofbromas and neural tumors. In additon, NF1 is associated with several skeletal abnormalites including, scoliosis, tbial bowing and sphenoid wing dysplasia [3,4]. Unfortunately, the cellular pathophysiology of the NF1 skeletal dysplasia is stll not fully understood [5]. The main functonal domain of NF1 gene is known to be located between exon 27 and 34, known as RAS- GAP domain which gives the NF1 gene it’s tumor suppressor property [6,7]. The NF1 gene encodes neurofbromin, a RAS GTPase-actvatng protein (GAP) that promotes the conversion of an actve RAS-GTP-bound form to an inactve RAS-GDP form and functons to negatvely regulate the actvity of RAS efectors, including the RAF–MEK–ERK signaling pathway [8,9]. Thus, NF1 mutatons results in actvaton of canonical mitogen- actvated protein kinase (MAPK) signaling [10,11]. Of relevance to skeletal development, NF1 expression has been reported in hypertrophic chondrocytes, which are an important intermediate step during endochondral ossifcaton, and also in adult osteoblast and osteoclasts [12,13] either of which might explain the skeletal involvement in NF1. It is established that skeletal tssue can sense mechanical loading which induces bone remodeling actvity, resultng in structural changes through diferent cellular pathways. Several studies have shown that, RAS-MAPK-ERK pathway is the main contributor in mechanical signaling response in osteoblast cells [14-17]. The role of MAPK signaling components have been shown to favor osteoblastc cell proliferaton and diferentaton. In partcular, ERK1/2 is involved in cell proliferaton, diferentaton and the survival of several cell types, including osteoblasts [18,19]. ERK1/2 signals can promote the proliferaton and anabolism of osteoblasts in order to facilitate bone turnover, thereby contributng to the homeostasis of bone tssue [20,21]. Rapid Communication iMedPub Journals www.imedpub.com DOI: 10.21767/2576-392X.100013 Journal of Dental and Craniofacial Research ISSN 2576-392X Vol.2 No.2:13 2017 © Copyright iMedPub | This article is available from: www.imedpub.com 1