Background/Purpose: Milk consumption during childhood stimulates bone growth but the claimed beneficial effect of milk on bone at adulthood is a matter of debate. Recently extracellular vesicles (EVs) that contain proteins and RNA were discovered in milk but their effect on bone formation has not yet been determined. Our aim was to evaluate the effect of bovine milk-derived EVs (BMEVs) on the differentiation of human mesenchymal stem cells (hMSCs) into osteoblasts, and on bone formation in mice.

Methods: hMSCs in osteogenic medium were treated with BMEVs (200µg/ml protein) and healthy female DBA1/J mice received orally two different particle concentrations of BMEVs 4.7×10⁶/ml (low) or 14.3×10⁶/ml (high) in their drink water during 7 weeks.

Results: Proteomic analysis in BMEVs showed the presence of proteins with a known effect on bone formation. The exposure of hMSCs to BMEVs during 21 days resulted in less mineralization but higher cell proliferation. Interestingly, BMEVs reduced the collagen production per cell, but enhanced the expression of osteoblast genes (Runx2, ALP, osteopontin, RANKL, FGF-2)  that are characteristic of immature osteoblasts. A kinetic study up to day 28 showed that BMEVs upregulated many osteogenic genes within the first 4 days of culture. However, the production of type I collagen and its genes (COL1A1 and COL1A2) were markedly reduced at days 21 and 28. At day 28, BMEVs again lead to higher proliferation, but mineralization that was lower at day 21 was significantly increased at day 28. Nonetheless the formation of bone nodules was impaired at day 28 and this was corroborated by a reduction in osteonectin expression. Moreover, BMEVs increased the expression of sclerostin, a marker gene of osteocytes at the same time point. Oral delivery of BMEVs to mice did not alter the tibia trabecular bone area, however the osteocytes numbers increased  independent of the dose. In addition, the highest dose of BMEVs reduced the adipose area in bone marrow of the femoral tibia bone and markedly increased the woven bone tissue and the number of osteoclasts by TRAP staining.

Conclusion: Our study showed that BMEVs on hMSCs increased osteoblast differentiation, proliferation and mineralization, probably by the induction of FGF-2 and WISP1. However, the lower type I collagen synthesis, and osteonectin expression could be explained by the presence of miR-29 in BMEVs. The net result of BMEVs exposure is impaired bone nodule formation in vitro and more woven bone formation in mice and this suggest that BMEVs could lead to more brittle bones. Our study add BMEVs to the list of milk components that can affect bone formation and may shed new light on the contradictory claims of milk on bone formation.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/extracellular-vesicles-from-cow-milk-accelerate-osteoblast-differentiation-into-osteocytes-however-type-i-collagen-synthesis-is-reduced-and-bone-matrix-organization-is-impaired/