Chemotaxis allows polymorphonuclear neutrophils (PMN) to rapidly reach infected and inflamed sites. However excessive influx of PMN damages host tissues. Better knowledge of the mechanisms that control PMN chemotaxis may lead to improved treatments of inflammatory diseases. Based on our recent findings that ATP and adenosine are involved in PMN chemotaxis, we propose to study here how to regulate this purinergic signaling process in order to prevent tissue damage. Purinergic signaling has three essential components: i) sources of the extracellular ATP and adenosine;ii) purinergic receptors that response to ATP and adenosine and, iii) ecto-nucleotidases that modulate cellular responses by hydrolyzing ATP to adenosine. This proposal is based on the following working hypothesis: Chemotactic agents release ATP from PMN. ATP activates nearby P2Y2 receptors, amplifying gradient sensing. A3 adenosine receptors are recruited to the leading edge where adenosine is generated by CD39/E- NTPDase1 and alkaline phosphatase (ALP). Adenosine and positive feedback through A3 receptors drives cell migration, while negative feedback through A2a receptors facilitates membrane retraction at the back of cells. Interfering with these purinergic signaling processes inhibits chemotaxis, which ameliorates PMN-induced tissue damage and organ failure in sepsis and trauma patients. The following specific aims will be addressed: 1. Mechanism of ATP release from PMN: This section will focus on the mechanisms by which PMN release cellular ATP in response to chemotactic stimulation. Specifically, we will focus on the involvement of hTTYH3 tweety maxi-anion channels, connexin hemi-channels, and degranulation. 2. Mechanism of adenosine formation: Experiments are designed to examine the major ecto-nucleotidases that are responsible for the conversion of released ATP to adenosine. Major emphasis will be placed on the contributions of NTPDase1 and ALP. 3. Purinergic signaling complexes: We will explore the co-localization of chemotactic receptors with ATP release sites, purinergic receptors, and ecto-nucleotidases and investigate if purinergic signaling clusters, comprised of these molecules provide """"""""local excitation and global inhibition"""""""" as proposed in theoretical chemotaxis models. 4. Role of purinergic signaling in vivo: We will study the roles of P2Y2, A3, A2a, and NTPDase1 and ALP in mouse models and test the feasibility of targeting these molecules to prevent host tissue damage. The proposed studies are expected to improve our understanding of the mechanisms that control chemotaxis. This could lead to novel therapeutic approaches to ameliorate host tissue damage caused by excessive influx of activated PMN, for example, in trauma and septic shock patients.
Chemotaxis, a key functional response of neutrophils in health and disease is still poorly understood. In this project we propose to determine how release of cellular ATP and purinergic receptors control chemotaxis and whether this control mechanism can be pharmacologically targeted to prevent inflammation and host tissue damage in trauma patients.
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