title: Distinct Gene Expression Patterns Defining Human Osteoblasts' Response to BMP2 Treatment: Is the Therapeutic Success All a Matter of Timing?
abstract: BACKGROUND
  Bone morphogenetic proteins (BMPs) play a key role in bone formation. Local application of BMP2 (Dibotermin alfa) supports bone formation when applied to complex fractures. However, up to 33% of patients do not respond to this therapy.
  
  
  OBJECTIVE
  Aiming to investigate whether inter-individual responses to BMP2 treatment can be predicted by gene expression patterns, we investigated the effect of BMP2 on primary human osteoblasts and THP-1 cell-derived osteoclasts from 110 donors.
  
  
  METHODS
  Osteoblasts were obtained by collagenase digestion of spongy bone tissues. Osteoclasts were differentiated from THP-1 cells using the conditioned media of the osteoblasts. Viability was determined by resazurin conversion. As functional characteristics AP and Trap5B activity were measured. Gene expression levels were determined by RT-PCR in 21 of the 110 evaluated donors and visualized by electrophoresis.
  
  
  RESULTS
  Based on our data, we could classify three response groups: (i) In 51.8% of all donors, BMP2 treatment induced osteoblast function. These donors strongly expressed the BMP2 inhibitor Noggin (NOG), the alternative BMP2 receptors repulsive guidance molecule B (RGMb) and activin receptor-like kinase 6 (Alk6), as well as the Wnt inhibitor sclerostin (SOST). (ii) In 17.3% of all donors, BMP2 treatment induced viability. In these donors, the initial high SOST expression significantly dropped with BMP2 treatment. (iii) 30.9% of all donors were not directly affected by BMP2 treatment. These donors expressed high levels of the pseudoreceptor BMP and activin membrane-bound inhibitor (BAMBI) and lacked SOST expression. In all donors, SOST expression correlated directly with receptor activator of NF-κB ligand (RANKL) expression, defining the cells' potential to stimulate osteoclastogenesis.
  
  
  CONCLUSIONS
  Our data identified three donor groups profiting from BMP2 treatment either directly via stimulation of osteoblast function or viability and/or indirectly via inhibition of osteoclastogenesis, depending on their expression of BAMBI, SOST, NOG, and RANKL. On the basis of patients' respective expression profiles, the clinical application of BMP2 as well as its timing might be modified in order to better fit the patients' needs to promote bone formation or to inhibit bone resorption.
authors.affiliation: BG Trauma Center, Eberhard Karls University Tübingen, Tübingen, Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Ehnert
authors.forename: Romina Haydée
authors.initials: RH
authors.lastname: Aspera-Werz
authors.forename: Thomas
authors.initials: T
authors.lastname: Freude
authors.forename: Marie Karolina
authors.initials: MK
authors.lastname: Reumann
authors.forename: Björn Gunnar
authors.initials: BG
authors.lastname: Ochs
authors.forename: Christian
authors.initials: C
authors.lastname: Bahrs
authors.forename: Steffen
authors.initials: S
authors.lastname: Schröter
authors.forename: Elke
authors.initials: E
authors.lastname: Wintermeyer
authors.forename: Andreas Klaus
authors.initials: AK
authors.lastname: Nussler
authors.forename: Stefan
authors.initials: S
authors.lastname: Pscherer
mesh_terms: D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology* / Q000627:therapeutic use; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics; D010006:Osteoblasts / Q000187:drug effects* / Q000502:physiology; D053244:Osteoprotegerin / Q000235:genetics; D053245:RANK Ligand / Q000235:genetics; D011994:Recombinant Proteins / Q000494:pharmacology / Q000627:therapeutic use; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000494:pharmacology* / Q000627:therapeutic use; D060449:Wnt Signaling Pathway
chemical_list: C485671:BAMBI protein, human; D055396:Bone Morphogenetic Protein 2; D008565:Membrane Proteins; D053244:Osteoprotegerin; D053245:RANK Ligand; D011994:Recombinant Proteins; C505688:TNFSF11 protein, human; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2