Platelet activation is characterized by shape change, induction of fibrinogen receptor expression and release of granular contents, leading to aggregation and plug formation. While this response is essential for hemostasis, it is also important in the pathogenesis of a broad spectrum of diseases, including myocardial infarction, stroke and unstable angina. Adenosine 5'-diphosphate (ADP) induces platelet aggregation, but the mechanism for this has not been established, and the relative contribution of ADP in hemostasis and the development of arterial thrombosis is poorly understood. We show here that the purinoceptor P2Y1 is required for platelet shape change in response to ADP and is also a principal receptor mediating ADP-induced platelet aggregation. Activation of P2Y1 resulted in increased intracellular calcium but no alteration in cyclic adenosine monophosphate (cAMP) levels. P2Y1-deficient platelets partially aggregated at higher ADP concentrations, and the lack of P2Y1 did not alter the ability of ADP to inhibit cAMP, indicating that platelets express at least one additional ADP receptor. In vivo, the lack of P2Y1 expression increased bleeding time and protected from collagen- and ADP-induced thromboembolism. These findings support the hypothesis that the ATP receptor P2Y1 is a principal receptor mediating both physiologic and pathological ADP-induced processes in platelets.

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Genetic evidence supports a critical role for the epithelial sodium channel (ENaC) in both clearance of fetal lung liquid at birth and total body electrolyte homeostasis. Evidence from heterologous expression systems suggests that expression of the ␣ ENaC subunit is essential for channel function, whereas residual channel function can be measured in the absence of ␤ or ␥ subunits. We generated mice without ␥ ENaC (

Acute inflammation in response to both exogenous and endogenous danger signals can lead to the assembly of cytoplasmic inflammasomes that stimulate the activation of caspase-1. Subsequently, caspase-1 facilitates the maturation and release of cytokines and also, under some circumstances, the induction of cell death by pyroptosis. Using a mouse line lacking expression of NLRP1, we show that assembly of this inflammasome in cells is triggered by a toxin from Anthrax and that it initiates caspase-1 activation and release of IL-1β. Furthermore, NLRP1 inflammasome activation also leads to cell death, which escalates over three days following exposure to the toxin and culminates in acute lung injury and death of the mice. We show that these events are not dependent on production of IL-1β by the inflammasome but are dependent on caspase-1 expression. In contrast, MDP mediated inflammasome formation is not dependent on NLRP1, but NLRP3. Taken together, our findings show that assembly of the NLRP1 inflammasome is sufficient to initiate pyroptosis, which subsequently leads to a self-amplifying cascade of cell injury within the lung from which the lung cannot recover, eventually resulting in catastrophic consequences for the organism.

Antigen-mediated cross-linking of IgE bound to mast cells via the high affinity receptor for IgE triggers a signaling cascade that results in the release of intracellular calcium stores, followed by an influx of extracellular calcium. The collective increase in intracellular calcium is critical to the release of the granular contents of the mast cell, which include the mediators of acute anaphylaxis. We show that the sensitivity of the mast cell to antigen-mediated degranulation through this pathway can be dramatically influenced by the A2b adenosine receptor. Loss of this Gs-coupled receptor on mouse bone marrow–derived mast cells results in decreased basal levels of cyclic AMP and an excessive influx of extracellular calcium through store-operated calcium channels following antigen activation. Mice lacking the A2b receptor display increased sensitivity to IgE-mediated anaphylaxis. Collectively, these findings show that the A2b adenosine receptor functions as a critical regulator of signaling pathways within the mast cell, which act in concert to limit the magnitude of mast cell responsiveness when antigen is encountered.