P2Y2 Antagonists Increase Bone Mass and Enhances the Anabolic Response to Exercise in Adult Mice

Document Type

Conference Proceeding

Publication Date

9-27-2024

Publication Title

J Bone Miner Res

Abstract

Osteocytes' induction of bone formation in response to loading is extremely age dependent, such that exercise is known to be less and less effective with age. Modifying osteocytes' mechanosensitivity may enable adults to better capitalize on the anabolic nature of exercise or daily activities to increase bone mass and reduce fracture risk. Based on previous work, we hypothesize inhibiting P2Y2 activity can enhance the anabolic response to loading of adult mice. To test this hypothesis, 9-month old male C57/Bl6J mice were treated with P2Y2 inhibitor AR-C11892XX (ARC) and exposed to sedentary of treadmill exercise for 5-weeks. Treating sedentary mice with ARC alone significantly increased cortical area by 10% in the tibia and 6.5% in the femur (Fig 1A). The gains in bone mass following ARC treatment in sedentary mice coincided with significant gains in endocortical bone formation rate and a 43% increase in strength based on mechanical testing (Fig 1B). Subjecting mice to treadmill exercise alongside ARC treatment significantly increased cortical area by 40% compared to vehicle mice subjected to same exercise regimen. The gains bone mass were associated with a significant increase in both periosteal and endocortical bone formation rates compared to vehicle treated controls. At the cellular level, ARC treatment in sedentary mice significantly decreased the expression of Sost and Rankl in osteocyte-enriched tibia samples when compared to vehicle treated controls. Exercise further decreased the expression of Sost and Rankl in ARC treated mice when compared to ARC treated sedentary mice or vehicle treated mice subjected to the same exercise regimen. To further understand the effects of ARC, osteoblast and osteoclast function were examined by differentiating bone marrow stromal cells and hemopoietic stem cells in the absence or presence of ARC alongside the respective inducers of ascorbic acid and β-glycerophosphate or Rankl and MCSF. Osteoblast differentiation and function based on alizarin red and gene expression was unaffected by the presence of ARC. Similarly, ARC had no effect on osteoclast differentiation based on the number of multi-nucleated cells stained for tartrate resistant acid phosphatase. These findings demonstrate that ARC has no direct effect on osteoblast or osteoclast function. However, we found osteoclast differentiation was significantly reduced when supplementing the induction media with conditioned media from MLO-Y4 cells treated with ARC when compared to supplementing with condition media from non-treated MLO-Y4 cells (Fig 1C). These findings suggest that ARC indirectly reduces osteoclast activity by decreasing osteocytes' support of osteoclast activity. Overall, these findings demonstrate that antagonizing P2Y2 function in adults increases bone mass and the sensitivity to loading, namely treadmill exercise.

Volume

39

First Page

26

Last Page

27

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