Characterizations and the Mechanism Underlying Osteogenic Activity of Peptides from Enzymatic Hydrolysates of <i>Stichopus japonicus</i>

Sea cucumber (Stichopus japonicus) is a kind of fishery product with high nutritional value. It exhibits a wide range of biological activity and has potential application in the food, pharmaceutical, and biomedical industries. However, there are no reports available on the effects of S. japonicus peptides (SJP) on bone mineral density regulations. The purpose of this work was to analyze the composition and osteogenic activity of SJP and explore its underlying mechanism. The results showed that SJP stimulated cell proliferation, differentiation, and mineralization in a dose-dependent manner. In addition, SJP could promote the proliferation of MC3T3-E1 cells by altering the cell cycle progression and regulating the expression of Cyclins. Besides, SJP activated the WNT/β-catenin pathway and increased the nuclear level of the active form β-catenin. Furthermore, SJP also induced the expression of bone morphogenetic protein (BMP-2) and increase the phosphorylation levels of p38, JNK, and ERK, suggesting that the osteogenic activity of SJP may be achieved through the activation of WNT/β-catenin and BMP/MAPK signal pathways. In vivo, SJP significantly inhibited the serum levels of RANKL, ALP, and TRAP, whereas it increased the levels of osteocalcin and osteoprotegerin in OVX-mice. These results indicate that SJP may have the potential to stimulate bone formation and regeneration, and may be used as a functional food or nutritional supplement to prevent osteoporosis

Novel Peptide Derived from Gadus morhua Stimulates Osteoblastic Differentiation and Mineralization through Wnt/β-Catenin and BMP Signaling Pathways

Marine biodiversity offers a wide array of active ingredient resources. Gadus morhua peptides (GMPs) showed excellent osteoprotective effects in ovariectomized mice. However, the potential osteogenesis mechanisms of key osteogenic peptides in GMP were seldom reported. In this study, a novel osteogenic peptide (GETNPADSKPGSIR, P-GM-2) was screened from GMP. P-GM-2 has a high stability coefficient and a strong interaction with epidermal growth factor receptor. Cell culture experiments showed that P-GM-2 stimulated the expression of osteogenic differentiation markers to promote osteoblast proliferation, differentiation, and mineralization. Additionally, P-GM-2 phosphorylates GSK-3β, leading to the stabilization of β-catenin and its translocation to the nucleus, thus initiating the activation of the Wnt/β-catenin signaling pathway. Meanwhile, P-GM-2 could also regulate the osteogenic differentiation of preosteoblasts by triggering the BMP/Smad and mitogen-activated protein kinase signaling pathways. Further validation with specific inhibitors (ICG001 and Noggin) demonstrated that the osteogenic activity of P-GM-2 was revealed by the activation of the BMP and Wnt/β-catenin pathways. In summary, these results provide theoretical and practical insights into P-GM-2 as an effective antiosteoporosis active ingredient