Phospholipid membranes drive abdominal aortic aneurysm development through stimulating coagulation factor activity

Abdominal aortic aneurysm (AAA) is an inflammatory vascular disease with high mortality and limited treatment options. How blood lipids regulate AAA development is unknown. Here lipidomics and genetic models demonstrate a central role for procoagulant enzymatically oxidized phospholipids (eoxPL) in regulating AAA. Specifically, through activating coagulation, eoxPL either promoted or inhibited AAA depending on tissue localization. Ang II administration to ApoE−/− mice increased intravascular coagulation during AAA development. Lipidomics revealed large numbers of eoxPL formed within mouse and human AAA lesions. Deletion of eoxPL-generating enzymes (Alox12 or Alox15) or administration of the factor Xa inhibitor rivaroxaban significantly reduced AAA. Alox-deficient mice displayed constitutively dysregulated hemostasis, including a consumptive coagulopathy, characterized by compensatory increase in prothrombotic aminophospholipids (aPL) in circulating cell membranes. Intravenously administered procoagulant PL caused clotting factor activation and depletion, induced a bleeding defect, and significantly reduced AAA development. These data suggest that Alox deletion reduces AAA through diverting coagulation away from the vessel wall due to eoxPL deficiency, instead activating clotting factor consumption and depletion in the circulation. In mouse whole blood, ∼44 eoxPL molecular species formed within minutes of clot initiation. These were significantly elevated with ApoE−/− deletion, and many were absent in Alox−/− mice, identifying specific eoxPL that modulate AAA. Correlation networks demonstrated eoxPL belonged to subfamilies defined by oxylipin composition. Thus, procoagulant PL regulate AAA development through complex interactions with clotting factors. Modulation of the delicate balance between bleeding and thrombosis within either the vessel wall or circulation was revealed that can either drive or prevent disease development

Genetic deletion of Alox15 is associated with spatial and anxiety phenotypes related to normal ageing.

Lipoxygenases are a family of enzymes that generate bioactive inflammatory lipid mediators. Among them, the Alox15 gene product (15-LOX, 12/15-LOX) has been detected in neurons and glial cells in mice. There is an emerging interest in its potential role in neurodegenerative disease; however, the biological role of this enzyme in the healthy brain has not yet been characterised. This thesis investigates the impact of 12/15-LOX deletion on mouse cognitive function and lipid profiling. Two independent groups of young to middle-aged and old wild type (WT) or Alox15-/- mice were studied. A range of behavioural tests, including a novel object recognition task, object location task and elevated plus maze, were used to assess the effects of deletion on cognition and emotional reactivity compared with similarly aged control WT mice. At 10 months of age, both male and female Alox15-/- mice displayed spatial memory deficits that may be linked to hippocampal impairments. In contrast, knock-out mice showed normal novel object recognition memory. Also, Alox15-/- mice manifested increased anxiety-like behaviour compared to controls. Their increased anxiety phenotype was connected to alterations in the expression levels of various protein markers, including parvalbumin, GABAergic, corticotrophin-releasing factor, and serotonergic receptors. Separately, liquid chromatography with tandem mass spectrometry was used to quantify oxylipins and enzymatically oxidised phospholipids (oxPL) generated via the 12/15- LOX during healthy brain ageing across various brain regions in both groups of mice. Lipidomic analysis of brain regions extracted and revealed elevated levels of selected oxylipins (5-HETE, prostaglandins) but reduced levels of the Alox15 product, 12-HETE. In eoxPL analysis, the deficiency of Alox15 did not change the levels of PE 18:0a_12-HETE between genotypes. Taken together, these results suggest a role for 12/15-LOX in regulating normal brain function, and further work is required to determine the biological basis of the anxiety phenotype in mice lacking this enzyme