PGI2 regulation of CD4+ Th2 metabolism in allergic airway inflammation

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Asthma is one of the most common chronic diseases in the United States. There is mounting evidence that medications that inhibit the cyclooxygenase (COX) pathway of arachidonic acid metabolism are linked to new onset asthma, strongly suggesting that COX metabolic products inhibit the development of asthma. These data are supported by numerous mechanistic animal studies published by the Principal Investigator (PI) which revealed that COX inhibition increased lung expression of the CD4 T helper 2 (Th2) cytokines IL-5 and IL-13 that are important in airway eosinophilia, mucus expression, and airway responsiveness (AR), all hallmarks of allergic asthma. Several studies by the PI and other groups revealed that the COX product prostaglandin (PG)I2 restrains the development of allergic inflammation by inhibiting proinflammatory cytokine secretion by CD4 Th2 cells; however, the mechanisms by which PGI2 exerts these anti-inflammatory effects are not completely defined. Our novel, unpublished preliminary data reveals that PGI2 signaling inhibited glycolysis, glycolytic capacity, and glycolytic reserve in CD4 Th2 cells, suggesting that PGI2 has a critical role in CD4 T cell immunometabolism. We provide evidence in our preliminary data that PGI2 decreases CD4 Th2 expression of Glut1, the glucose transporter that is essential for the uptake of glucose and amino acids into the cell and which is required for glycolysis. Additional preliminary data of targeted metabolomics identified the glutamine metabolism pathway as being substantially regulated when CD4 Th2 cells were polarized in the presence or absence of the PGI2 analog cicaprost. However, the mechanisms by which PGI2 signaling inhibits glycolysis and the glutamine metabolic pathway are not known. In this application, we will test the overall hypothesis that PGI2 restrains allergen-induced airway inflammation by inhibiting glucose and glutamine metabolism in Th2 effector cells, thus defining the immunometabolic mechanisms by which PGI2 restrains allergic inflammation in the lung. In this application, we will use complementary genetic and pharmacologic approaches, both in vivo and in in vitro experiments using primary CD4 T lymphocytes. We will create novel model organisms to definitively determine how regulates glycolysis and glutamine metabolism using conditional mice floxed for the PGI2 receptor IP, that were specifically created through funding of the last cycle of this Merit Award. This current Merit proposal is clinically relevant in defining the immunometabolic mechanisms by which PGI2 inhibits CD4 differentiation and function in allergic airway inflammation, thus providing support for the use of PGI2 in the treatment of allergic diseases such as asthma. The proposed experiments will be paradigm shifting by being the first to define how a prostaglandin regulates immunometabolism and will advance the field and the health of our nation's Veterans by discovering new therapeutic pathways for diseases that are exacerbated by increases in the glycolytic and glutaminolysis pathways. Further, these studies may define new mechanisms by which PGI2 is beneficial in other diseases states, such as pulmonary hypertension, for which CD4 T lymphocytes are becoming increasingly recognized as having a pathogenic role. Thus, this application provides an opportunity for basic science discovery, as well as having important treatment implications for hypersensitivity diseases, including asthma. PGI2