title: JNK inhibitors increase osteogenesis in Nf1-deficient cells.
abstract: Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder that is associated with a variety of manifestations, including orthopedic complications such as scoliosis and tibial pseudarthrosis. Orthopedic management of these skeletal complications is rendered more challenging due to a lack of standardized adjunctive pharmacotherapies. NF1 leads to disruption of the canonical Ras/Raf-1/MEK/ERK axis, and this has been associated with defects in bone anabolism. The roles of other non-canonical Ras effector pathways, such as the c-Jun N-terminal Kinase (JNK) pathway, are less well understood. In this study we examine the effects of an anthrapyrazolone inhibitor of JNK (SP600125) on inducible osteoprogenitors as well as Nf1-deficient and Nf1-null primary osteoblasts. C2C12 cells, which are highly responsive to rhBMP-2, were examined with exogenous rhBMP-2 and a range of SP600125 doses. Based on the expression of early and late bone markers and matrix mineralization, 10 μM SP600125 was found to be pro-osteogenic whether delivered concurrent with or following 2 days of rhBMP-2 treatment. Aberrant JNK activity was identified in Nf1-deficient osteoprogenitors (increased rhBMP-2 induced phospho-c-Jun) and in Nf1-null mature osteoblasts (increased total c-Jun). Next, SP600125 was used to treat these cells and was found to facilitate osteogenesis in Nf1-deficient osteoprogenitors, and in Nf1-null osteoblasts when given in conjunction with rhBMP-2. Outcome measures included alkaline phosphatase activity, matrix mineralization, and osteogenic gene expression. In summary, JNK inhibitors represent a class of potentially useful adjunctive agents for orthopedic medicine, particularly in the context of NF1.
authors.affiliation: Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Sydney, Australia. kate.sullivan@sydney.edu.au
authors.forename: Kate
authors.initials: K
authors.lastname: Sullivan
authors.forename: Jad
authors.initials: J
authors.lastname: El-Hoss
authors.forename: David G
authors.initials: DG
authors.lastname: Little
authors.forename: Aaron
authors.initials: A
authors.lastname: Schindeler
mesh_terms: D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D015415:Biomarkers / Q000378:metabolism; D001854:Bone Marrow Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology; D002113:Calcification, Physiologic / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D032446:Myoblasts / Q000187:drug effects / Q000201:enzymology; D025542:Neurofibromin 1 / Q000172:deficiency* / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000494:pharmacology; D012886:Skull / Q000166:cytology; D017154:Stromal Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D018631:ras Proteins / Q000378:metabolism
chemical_list: D000873:Anthracenes; D015415:Biomarkers; D055396:Bone Morphogenetic Protein 2; D025542:Neurofibromin 1; D047428:Protein Kinase Inhibitors; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; C432165:pyrazolanthrone; D048031:JNK Mitogen-Activated Protein Kinases; D018631:ras Proteins