BMP-2 Long-Term Stimulation of Human Pre-Osteoblasts Induces Osteogenic Differentiation and Promotes Transdifferentiation and Bone Remodeling Processes.

Lena-Christin Ingwersen,Marcus Frank,Hendrik Naujokat,Klaas Loger,Anika Jonitz-Heincke,Rainer Bader

doi:10.3390/ijms23063077

Abstract

Bone morphogenic protein (BMP-) 2 plays an important role in the regeneration of bone defects by promoting osteogenic differentiation. However, several animal studies have reported adverse side effects of BMP-2, including osteoclast activation, induction of peroxisome proliferator- activated receptor gamma (PPARG)expression, and inflammation. High BMP-2 concentrations are thought to be responsible for these side effects. For this reason, primary pre-osteoblasts were exposed to lower BMP-2 concentrations (1 and 2 µg/mL). Long-term exposure (up to 28 days) was performed to investigate whether this stimulation protocol may promote osteogenic differentiation without causing the side effects mentioned above. The results showed that BMP-2 treatment for 14 or 28 days resulted in increased osteogenesis, through an increase in runt-related transcription factor 2, osterix, alkaline phosphatase, and integrin-binding sialoprotein expression. However, an increase in tumor necrosis factor alpha and receptor activator of nuclear factor kappa-Β ligand protein levels was observed after BMP-2 exposure, indicating also an increased potential for osteoclast activation by osteoblasts. Additionally, morphological changes like intracellular, filled vacuoles could be detected. Enhanced PPARG and perilipin 1 mRNA transcripts and lipid droplets indicated an induced adipogenic differentiation. Overall, the data demonstrate that long-term BMP-2 exposure promotes not only osteogenic differentiation but also adipogenesis and regulates mediators involved in osteoclast activation in vitro.

Highlights

In the reconstruction of mandibular defects caused by trauma, infection, tumors, or congenital malformation, the aim is to rehabilitate the defect in an aesthetically and functionally satisfactory manner
Preosteoblasts are characterized by active proliferation and expression of collagen, fibronectin, and transforming growth factor—β (TGF-β) receptor 1 [6–8]
Matrix maturation gets completed via the expression of various osteoblastic markers, like osteopontin (OPN), osteocalcin (OC), integrin-binding sialoprotein (IBSP), ALPL, and COL1A1 [6,9]

Summary

Introduction

In the reconstruction of mandibular defects caused by trauma, infection, tumors, or congenital malformation, the aim is to rehabilitate the defect in an aesthetically and functionally satisfactory manner. A disadvantage of this form of therapy is the partially insufficient fit and the high morbidity caused by bone harvesting. Osteogenic differentiation, in general, is organized in three developmental stages: (i) cell proliferation, (ii) extracellular matrix deposition and matrix maturation, and (iii) matrix mineralization [5]. During these stages, different proteins are expressed. Proliferation is downregulated and expression rates of collagen type 1 alpha chain (COL1A1) and alkaline phosphatase (ALPL) increase [6–8]. Matrix maturation gets completed via the expression of various osteoblastic markers, like osteopontin (OPN), osteocalcin (OC), integrin-binding sialoprotein (IBSP), ALPL, and COL1A1 [6,9]. OPN thereby promotes bone formation and mineralization, whereas IBSP regulates the hydroxyapatite crystal formation [10,11]. The transcription factors runt-related transcription factor 2 (RUNX2) and osterix (OSX) function as master regulators [12–16]

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