BMP-2 Expression Induced by LL37 in Human Pulp Cells

Objectives: Bone morphogenetic protein 2 (BMP-2) is known to be capable of inducing the differentiation of human pulp (HP) cells into odontoblasts, which are the key cells responsible for the formation of reparative dentin. Recently, the human cathelicidin antimicrobial peptide LL37 has been reported to promote bone regeneration in a rat calvarial bone defect. Still, whether this peptide can also induce reparative dentin formation in the context of pulp tissue is unknown. To address this issue, the effect of LL37 on the expression of BMP-2 in HP cells and its underlying mechanism were investigated.

Methods: Primary HP cells were obtained from healthy premolars extracted for orthodontic reasons from three patients with their informed consent according to a protocol (D47-2) approved by the Ethical Authorities at Hiroshima University. The cells at passage 6 were treated with 10 μg/ml of synthesized LL37, and an inhibition assay was performed with MAPK or NF-κB inhibitors to identify the possible signaling pathway. BMP-2 mRNA expression and p38 phosphorylated levels were determined by real-time PCR and immunoblotting, respectively.
Results: LL37 significantly increased BMP-2 mRNA levels, with a peak being observed at 6 h, in a dose-dependent fashion. However, this elevation was suppressed by a p38 inhibitor, while p38 phosphorylation was induced by LL37.

Conclusions: LL37 boosts BMP-2 expression in HP cells via p38 signaling. The increased levels of BMP-2 by LL37 may enhance the odontoblastic differentiation of pulp cells, which in turn facilitates the formation of reparative dentin.