The ADP receptor P2RY12 regulates osteoclast function and pathologic bone remodeling

in Journal of Clinical Investigation (2012), 122(10), 3579-3592

The adenosine diphosphate (ADP) receptor P2RY12 (purinergic receptor P2Y, G protein coupled, 12) plays a critical role in platelet aggregation, and P2RY12 inhibitors are used clinically to prevent cardiac ... [more ▼]

The adenosine diphosphate (ADP) receptor P2RY12 (purinergic receptor P2Y, G protein coupled, 12) plays a critical role in platelet aggregation, and P2RY12 inhibitors are used clinically to prevent cardiac and cerebral thrombotic events. Extracellular ADP has also been shown to increase osteoclast (OC) activity, but the role of P2RY12 in OC biology is unknown. Here, we examined the role of mouse P2RY12 in OC function. Mice lacking P2ry12 had decreased OC activity and were partially protected from age-associated bone loss. P2ry12-/- OCs exhibited intact differentiation markers, but diminished resorptive function. Extracellular ADP enhanced OC adhesion and resorptive activity of WT, but not P2ry12-/-, OCs. In platelets, ADP stimulation of P2RY12 resulted in GTPase Ras-related protein (RAP1) activation and subsequent αIIbβ3 integrin activation. Likewise, we found that ADP stimulation induced RAP1 activation in WT and integrin β3 gene knockout (Itgb3-/-) OCs, but its effects were substantially blunted in P2ry12-/- OCs. In vivo, P2ry12-/- mice were partially protected from pathologic bone loss associated with serum transfer arthritis, tumor growth in bone, and ovariectomy-induced osteoporosis: all conditions associated with increased extracellular ADP. Finally, mice treated with the clinical inhibitor of P2RY12, clopidogrel, were protected from pathologic osteolysis. These results demonstrate that P2RY12 is the primary ADP receptor in OCs and suggest that P2RY12 inhibition is a potential therapeutic target for pathologic bone loss. [less ▲]

Antibodies to a 64,000 M(r) human islet cell antigen precede the clinical onset of insulin-dependent diabetes

in Journal of Clinical Investigation (1987), 79(3), 926-934

Antibodies in sera from newly diagnosed insulin-dependent diabetes mellitus (IDDM) patients are directed to a human islet cell protein of relative molecular mass (M(r)) 64,000. Since IDDM seems to develop ... [more ▼]

Antibodies in sera from newly diagnosed insulin-dependent diabetes mellitus (IDDM) patients are directed to a human islet cell protein of relative molecular mass (M(r)) 64,000. Since IDDM seems to develop after a prodromal period of β-cell autoimmunity,, this study has examined whether 64,000 M(r) antibodies could be detected in 14 individuals who subsequently developed IDDM and five first degree relatives who have indications of altered β-cell function. Sera were screened by immunoprecipitation on total detergent lysates of human islets and positive sera retested on membrane protein preparations. Antibodies to the 64,000 M(r) membrane protein were consistently detected in 11/14 IDDM patients, and in all 5 first degree relatives. 10 IDDM patients were already positive in the first samples, obtained 4-91 mo before the clinical onset of IDDM, whereas 1 patient progressed to a high 64,000 M(r) immunoreactivity, at a time where a commencement of a decline in β-cell function was detected. 64,000 M(r) antibodies were detected before islet cell cytoplasmic antibodies (ICCA) in two patients. In the control groups of 21 healthy individuals, 36 patients with diseases of the thyroid and 5 SLE patients, the 64,000 M(r) antibodies were detected in only one individual, who was a healthy sibling to an IDDM patient. These results suggest that antibodies against the M(r) 64,000 human islet protein are an early marker of β-cell autoimmunity and may be useful to predict a later development of IDDM. [less ▲]