PTGS1 (cyclooxygenase 1, COX-1) is an enzyme that metabolizes arachidonic acid to prostaglandin G2 and H2, a necessary step in prostanoid synthesis. In endothelial cells, PTGS1 regulates angiogenesis and functions in maintaining tissue homeostasis. In gastric epithelial cells, PTGS1 is involved in the generation of prostaglandins and is important for cyto-protection. In platelets, it is involved in the generation of thromboxane A2 (TXA2), which promotes platelet activation and aggregation, vasoconstriction, and the proliferation of vascular smooth muscle cells. NSAIDs like aspirin inhibit PTGS1 and consequently the platelet aggregation normally induced by TXA2, which in turn can help reduce cardiac events. Finally, in the brain, PTGS1 has high expression in astrocytes (with fifteen-fold expression over neurons). It is involved in cerebrovascular regulatory processes such as maintaining resting vascular tone and increasing cerebral blood flow during hypercapnia. In immunohistochemistry, antibodies to PTGS1 show cytoplasmic positivity in the brain, squamous epithelia, the fallopian tube, the endometrium, hematopoietic cells, megakaryocytes and tissue stroma. References: Prostaglandins & other lipid mediators. 68–69: 115–28. doi:10.1016/s0090-6980(02)00025-4. PMID 12432913; Harrison's Principles of Internal Medicine (17th ed.). New York: McGraw-Hill Medical. ISBN: 978-0-07-146633-2; Journal of Neuroscience 1 March 2017, 37 (9) 2403-2414; DOI: 10.1523/JNEUROSCI.0005-16.2016; Circ Res. 2001 Mar 30;88(6):600-8, PMID: 11282894