Silencing P2Y12 and P2Y13 receptors rehabilitates the ADP-induced P2Y1-mediated osteogenic commitment of post-menopausal mesenchymal stromal cells.

Background: Participation of ADP-sensitive metabotropic P2Y₁, P2Y₁₂ and P2Y₁₃ receptors in human osteogenesis is controversial. Here, we investigated the variations in the expression and bone-forming properties of the P2Y₁R in osteogenic-differentiating bone marrow-derived mesenchymal stromal cells (BM-MSCs) isolated from post-menopausal (Pm) women. We also tested whether observed P2Y₁-related functional deficits result from the crosstalk with co-localized P2Y₁₂ and P2Y₁₃ receptors.

Methods: Pm BM-MSCs were cultured in an osteogenic-inducing medium in either the absence or presence of the selective P2Y₁ receptor agonist, MR2365; this compound was applied alone or after cells' incubation with selective P2Y₁₂ and P2Y₁₃ receptor antagonists or short hairpin RNAs designed to silence P2Y₁₂ or P2Y₁₃ receptors gene expression.

Results: BM-MSCs present immunoreactivity against all ADP-sensitive P2Y receptor subtypes, but their relative density varied among different Pm women and with the time of the cells in the culture. The P2Y₁receptor agonist increased the alkaline phosphatase activity and bone nodule formation in BM-MSCs originating from a younger female, but it failed to promote the osteogenic differentiation of BM-MSCs from Pm women unless P2Y₁₂ or P2Y₁₃ receptors are blocked with AR-C66096 and MRS211, respectively. Silencing the P2Y₁₃, but not the P2Y₁₂, receptor gene expression restored the P2Y₁-mediated osteogenic commitment of Pm BM-MSCs. The P2Y₁ receptor agonist failed to elicit [Ca²⁺]_i transients inside Pm BM-MSCs except after acute cholesterol depletion and lipid rafts disruption with methyl-β-cyclodextrin to prevent the P2Y₁/P2Y₁₃ receptors interplay.

Conclusions: Thus, personalized offsetting the activity and/or expression of P2Y₁₃ receptor (and P2Y₁₂) may be a good strategy to rehabilitate the P2Y₁-mediated osteogenic potential of BM-MSCs and to reduce the fracture risk in Pm women.