Osteoclast Differentiation is Downregulated by Select Polyphenolic Fractions from Dried Plum via Suppression of MAPKs and Nfatc1 in Mouse C57BL/6 Primary Bone Marrow Cells

Background. Clinical and pre-clinical studies have shown that dietary supplementation with dried plum improves bone health. These osteoprotective effects are a result, in part, of the anti-resorptive properties of the fruit, which appear to be mediated by its polyphenolic compounds. Objective. This study was designed to determine if certain fractions of the polyphenolic compounds in dried plums are responsible for the anti-resorptive effects and whether they alter key MAPK and calcium signaling pathways (i.e., MAPK and calcium signaling), which are essential to osteoclast differentiation and activity, under normal and inflammatory conditions. Methods. Six polyphenolic fractions were derived from the total polyphenolic extract of dried plum based on solubility. Initial screening, using the Raw 264.7 a monocyte/macrophage cell line, revealed three fractions had the most marked capacity to downregulate osteoclast differentiation. This response was confirmed in two of the fractions using primary bone marrow-derived cultures and all subsequent experiments to determine how osteoclast differentiation function were altered focused on these two fractions in primary cultures. Data were analyzed using ANOVA followed by post-hoc analyses. Results. Both of The two dried plum the polyphenol fractions also decreased osteoclast differentiation and activity coincident with down-regulating Nfatc1, which is required for osteoclast differentiation as indicated by the resorption pit assay. Calcium signaling,, which is essential for to the auto-amplification of Nfatc1 required for osteoclast differentiation, was suppressed by the polyphenolic fractions under both normal as indicated by suppressed mRNA expression of co-stimulatory receptors Oscar, Sirpb1, and Trem2, but not and inflammatory conditions. In contrast, in the present of TNF-α, Intracellular calcium concentrations, as well as mRNA expression of the co-stimulatory receptors Oscar, Sirpb1, and Trem2, were suppressed under normal conditions, while only Sirpb1 was downregulated under inflammatory conditions. In addition to calcium signaling, phosphorylation of Erk and p38 MAPK, involved in the expression and activation of Nfatc1, was also suppressed by the polyphenolic fractions. Conclusions. These results show that certain types of polyphenolic compounds from dried plum downregulate calcium and MAPK signaling, resulting in suppression of Nfatc1 expression which ultimately decreases osteoclast formation and activity.