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  • Eggs have been recognized as an important

    2019-11-29

    Eggs have been recognized as an important contributor of functional ingredients for humans [3]. Egg yolk is composed of various biologically active proteins. The water-soluble proteins of egg yolk have been examined for their functional effects on longitudinal bone growth during the growth period in adolescent rats [4]. Scholars reported that yolk water-soluble protein (YSP) stimulated bone formation in osteoblastic MC3T3-E1 cell line and inhibited bone resorption in osteoclast precursor 82 7 receptor [5]. Their further studies with the peptides prepared with a water-soluble fraction of egg yolk indicated that the peptides also had significant effects on bone metabolism in vitro as well as in vivo [6, 7]. Phosvitin (PV), which has the highest known level of phosphorylation among egg yolk proteins [8, 9], has been reported to possess a strong Ca-binding capacity and regulate the properties of biological mineralization [[10], [11], [12], [13]] or increase calcium incorporation into bones [14, 15]. Liu et al. [16] reported that PV showed bioactivities in connective tissues and bone organogenesis. Although PV has been reported to be a bone growth factor both in vitro and in vivo, current evidences about the regulation mechanisms of PV on bone calcification are not sufficient. Our previous work indicated that PV was involved in the bone formation of chicken embryo through the dephosphorylation [17]. Thus, we are interested in exploring whether PV with different degree of phosphorylation has a direct effect to the osteoblasts. Bone-forming osteoblasts involve the proliferation and differentiation of osteoblastic cells in response to some factors in vivo. During differentiation, pre-osteoblastic cells express proteins of extra-cellular 82 7 receptor matrix such as collagen, alkaline phosphatase (ALP), osteocalcin and other bone matrix proteins [18, 19], and then osteoblastic cells form mineralized bone. MC3T3-E1 cell line, a kind of pre-osteoblastic cell, is widely used in bone remodeling studies because it has the capacity to differentiate into osteoblasts [20]. The process of osteogenesis can be modulated through several signaling pathways (i.e. RANK/RANKL/OPG, Smads and MAPK pathway). Bone remodeling is mediated by osteoblast/osteoclast coordination, which converges at the RANK/RANKL/OPG [20, 21]. Molecular factors involved in the RANK/RANKL/OPG include the receptor activator of nuclear fact r-kappa B (RANK), the RANK ligand (RANKL) and osteoprotegerin (OPG) - a natural inhibitor of RANKL [22]. OPG is an important mediator in RANKL and RANK association, which could regulate osteoclast activity. OPG inhibits osteoclastic bone resorption by blocking RANKL, which reduces RANKL-RANK binding [23]. Therefore, the RANKL/OPG ratio is a key factor in bone remodeling. So, the objective of this study was to investigate whether PV with different degree of phosphorylation had any impacts to the RANKL/OPG ratio.
    Materials and methods
    Results
    Conclusion
    Conflict of interest
    Acknowledgements This work was supported by the National Key Research and Development Program of China (2018YFD0400302) and General Program of National Natural Science Foundation of China (31471602).
    Introduction Giardia intestinalis is a pathogenic microorganism inhabiting the upper small intestine of humans and many other vertebrates, and is one of the most frequent diarrhoea-causing parasites worldwide (Adam, 2001). G. intestinalis is a binucleated, flagellated protozoan which is considered one of the earliest branching eukaryotes (Svard et al., 2003). The complete G. intestinalis genome has been reported, showing that this parasite have less complex molecular machineries than other eukaryotes (Morrison et al., 2007). Additionally G. intestinalis lacks some of the typical organelles of higher eukaryotic cells, such as mitochondria, peroxisomes and a classical Golgi apparatus (Adam, 2001). Giardia possesses an interesting life cycle that may be a primitive adaptation to different environmental conditions, permitting Giardia to survive both within and outside hosts, alternating between its two stages: trophozoites and cysts (Lujan et al., 1998). The trophozoite is the motile and vegetative stage, which lives and colonizes the upper small intestine by attaching to the epithelial cells. The quadrinucleated cyst is the transmissible stage and is extremely resistant to harsh environmental conditions due to the presence of a protective cell wall. The life cycle begins when cysts are ingested by the host from contaminated water, food, or interpersonal contact. The cysts sense the low pH in the stomach and start a process called excystation, which is finally completed in the upper small intestine where the trophozoites rapidly emerge and proliferate. Some trophozoites are forced down with the intestinal flow and are induced to encyst when confronting low cholesterol concentration in the lower parts of the small intestine. Cysts mature in the large intestine and are then released with the feces (Lujan et al., 1998, Adam, 2001). Giardia\'s encystations involves important molecular and cellular processes (DNA replication, nuclear division), turnover of proteins, and a special regulation of synthesis, sorting and transport of cyst wall components (Carranza and Lujan, 2010).