Two novel peptides from ark shell protein stimulate osteoblast differentiation and rescue ovariectomy-induced bone loss.

Osteoporosis is a common bone disease resulting from imbalance between bone formation and bone resorption. Currently, anti-resorptive agents that inhibit bone resorption are the most available drugs on the market. Biosphosphonates, anti-resorptive drugs most commonly used to treat osteoporosis, are limited by their side effects for long-term continuous treatment. It is important to develop appropriate therapeutic stragegies capable of promoting bone formation to counteract osteoporotic bone loss. Thus, anabolic agents that stimulate bone formation are undoubtedly of interest. Here, we purified and identified two novel osteogenic peptides AWLNH and PHDL from ark shell protein hydrolysates. AWLNH and PHDL stimulated osteoblast differentiation via mitogen-activated protein kinase (MAPK) and bone morphogenetic protein-2 (BMP-2) pathways. The activation of BMP-2 pathway stimulated by AWLNH and PHDL was abolished by treating noggin, BMP antagonist, in bone marrow-derived mesenchymal stem cells (BMMSCs), but not the phosphorylation of JNK1/2, ERK1/2, and p38 MAPK. However, treatment with MAPK inhibitors in BMMSCs downregulated the expression of BMP-2 and p-Smad1/5 and inhibited alkaline phosphatase activity. The dominant inhibitory effects by JNK inhibitor and ERK inhibitor are observed. In ovariectomized (OVX) mice, a reduction of femoral bone mineral density (BMD) was significantly observed, however, AWLNH and PHDL (0.2 mg/kg/per day) injection restored BMD as well as the osteoporotic conditions in OVX mice. Moreover, the increased serum osteocalcin and alkaline phosphatase activity in OVX mice were significantly reduced in AWLNH and PHDL injected-OVX mice. These results suggest that two novel osteogenic peptides AWLNH and PHDL could be attractive therapeutic agents for osteoporosis treatment.