|Zhang, Jian -|
|Lazarenko, Oxana -|
|Blackburn, Michael -|
|Ronis, Martin -|
|Chen, Jinran -|
Submitted to: Age
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 17, 2012
Publication Date: June 1, 2013
Citation: Zhang, J., Lazarenko, O.P., Blackburn, M.L., Badger, T.M., Ronis, M.J., Chen, J. 2013. Blueberry consumption prevents loss of collagen in bone matrix and inhibits senescence pathways in osteoblastic cells. Age. 35(3):807-820. Interpretive Summary: It is well known that bone breaks easier in women after menopause when estrogen production declines. Healthy bone requires the balance between born forming cells and bone resorbing cells. Bone loss after menopause or removal of the ovaries is largely due to increase in numbers of bone resorbing cells which digest bone (specifically the matrix collagen of bone). What is less clear, however, is the fate of the resident bone forming cells. In this report, we show that estrogen deficiency-induced bone loss is associated with profound decreases in the expression of two important genes (collagen 1 and SIRT1). Collagen 1 gene codes for protein necessary to make collagen matrix, and the SIRT1 gene is known as an anti-aging gene. Interestingly, when a diet containing blueberries (BB) was fed to pre-pubertal rats [postnatal day 21 (PND21) to PND34], the estrogen deficiency-induced bone loss was prevented. In vitro cell culture studies on the senescence pathway using primary calvarial cells (bone stem cells isolated from the rat skull) and three cell lines (ST2 cells, OB6, MLO-Y4) confirmed our in vivo findings. These results indicate that: 1) Very early feeding of BB can prevent estrogen deficiency-induced bone cell senescence is later life; and 2) the molecular mechanisms underlying these effects involve, at least in part, prevention of collagen degradation.
Technical Abstract: Ovariectomy (OVX)-induced bone loss has been linked to increased bone turnover and higher bone matrix collagen degradation as the result of osteoclast activation. However, the role of degraded collagen matrix in the fate of resident bone-forming cells is unclear. In this report, we show that OVX-induced bone loss is associated with profound decreases in collagen 1 and SIRT1. This was accompanied by increases in collagenase and p16 expression in bone. Feeding a diet supplemented with blueberries (BB) to pre-pubertal rats throughout development or only prior to puberty [postnatal day 21 (PND21) to PND34] prevents OVX-induced effects on expression of these molecules on PND68. We conducted in vitro studies on the senescence pathway using primary calvarial cells and three cell lines (ST2 cells, OB6, MLO-Y4). We found that senescence was inhibited by collagen in a dose-response manner. Treatment of cells with serum from OVX rats accelerated osteoblastic cell senescence pathways, but serum from BB-fed OVX rats had no effect. In the presence of low collagen or treatment with OVX rat serum, ST2 cells exhibited higher potential to differentiate into adipocytes. Finally, we demonstrated that senescence is triggered by decreased SIRT1 expression, leading to acetylation/activation of p53, p16, and p21. These results indicate: 1) a significant prevention of OVX-induced bone cell senescence from adult rats can occur after only 14 days consumption of a BB-containing diet immediately prior to puberty; and 2) the molecular mechanisms underlying this effect involves, at least in part, prevention of collagen degradation.