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. Purpose: 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.

A Synthetic Peptide, CK2.3, Inhibits RANKL-Induced Osteoclastogenesis through BMPRIa and ERK Signaling Pathway

“…Clinical evidence shows that rhBMP2 is less successful in the clinic due to a variety of side effects and complications [ 94 , 95 ]. Furthermore, several researchers have reported unresponsiveness to the BMP2 stimulation of bone marrow stromal cells (BMSCs) isolated from osteoporotic patients [ 96 , 97 , 98 ]. These reports may be related to reports on the aberrance of BMP2 signaling in osteoporotic patients [ 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 ].…”

“…Furthermore, several researchers have reported unresponsiveness to the BMP2 stimulation of bone marrow stromal cells (BMSCs) isolated from osteoporotic patients [ 96 , 97 , 98 ]. These reports may be related to reports on the aberrance of BMP2 signaling in osteoporotic patients [ 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 ]. We have also reported the unresponsiveness of BMSCs isolated from osteoporotic patients to BMP2, but they respond to CK2.3 [ 104 ].…”

Dose-Dependent Effects of a Novel Selective EP4 Prostaglandin Receptor Agonist on Treatment of Critical Size Femoral Bone Defects in a Rat Model

“…However, bone mineral density was below the contralateral control and lowest among all other groups, which is expected, based on other preclinical and clinical studies [ 26 ]. Additionally, in contrast to its high osteoinductive success in rodents, BMP-2 fails in up to 33% of human patients because of patient-specific gene expression profiles modulating the response to BMP-2 [ 27 ]. These results, coupled with its high cost and stringent storage conditions, limit its widespread use in dental and orthopedic applications.…”

From the Clinical Problem to the Basic Research—Co-Culture Models of Osteoblasts and Osteoclasts

“…This permeable barrier can either be a removable permeable divider [49] or a transwell system [50]. When the effect of one special cell type on another cell type is investigated without the physiological feedback, transfer of conditioned medium from one cell type to another is a feasible option [51,52]. In the same line, one type of cells can be seeded onto an extracellular matrix (ECM) that has been produced by another type of cells [53].…”

“…Thus, in a co-culture approach, no additional cytokines should be needed. Simply by using the conditioned medium of differentiating primary osteoblasts, mononuclear cells can be differentiated into osteoclastic cells [51,52]. On the other hand, to avoid diverse supplements from interfering with the differentiation process of the other cell type in co-culture, Schulze presented a direct co-culture model of human B-MSCs and PBMCs without exogenous cytokines, which is suitable to mimic bone-remodeling [110].…”