Objective The 12-15Lipoxygenase (12-15LO) is an enzyme widely distributed in the central nervous system and it has been involved in the neurobiology of Alzheimers disease (AD). levels. Interpretation Our findings demonstrate a novel pathway by which 12-15LO increases the amyloidogenic processing of APP through a Sp1-mediated transcriptional control of BACE1 levels that could have implications for AD pathogenesis and therapy. Introduction The Lipoxygenases (LOs) form a large family of lipid-peroxidizing enzymes, which insert molecular oxygen into free and esterified polyunsaturated fatty acids. Among them, human and rabbit 15LO, as well as leukocyte-type 12LO, are also called 12-15LO because they form both 12-hydroxy-eicosatetraenoic acid Fulvestrant biological activity 12-(HETE) and 15-HETE from arachidonic acid in various ratios1,2. In addition to its presence in the cardiovasculature, 12-15LO is widely distributed in the central nervous system (CNS) where its enzymatic activity as well as protein and mRNA levels have been well documented 3C6. Previously, we showed that 12-15LO protein levels and activity are increased in AD compared with control brains 7, and that cerebrospinal fluid levels of both its metabolic products, 12-HETE and 15-HETE, are elevated in individuals with a clinical diagnosis of AD, suggesting a possible involvement of this pathway in the early stages of the disease 8. In addition, we provided evidence that 12-15LO influences A formation 9 and showed that in vivo 12-15LO-targeted gene disruption significantly reduces A pathology of Tg2576 Des mice 10. However, the precise molecular mechanism underlying the biological effect of 12-15LO on the A Fulvestrant biological activity metabolism and APP proteolytic pathways remains to be fully elucidated. To examine this issue, we undertook a series studies and different experimental approaches. In the first part, by crossing the tg2576 with 12-15LO over-expressing (H12-15LO) mice we show that compared with tg2576 the bigenic animals (i.e., tg2576/H12-15LO) have a significant increase in brain A levels and deposition and a worsening of their memory impairments. Biochemistry analyses demonstrate that this effect is associated with a significant Fulvestrant biological activity up-regulation of the -secretase-1 (BACE1) proteolytic pathway. In vitro and in vivo studies show that 12-15LO directly regulates A production by modulating APP processing via the transcriptional regulation of BACE1 mRNA levels, which involves the activation of the transcription factor Sp1. Taken together these data establish a novel biological pathway by which 12-15LO modulates A and APP processing via a Sp1-mediated transcriptional control of BACE1 levels. This observation has important implications for the development of novel therapeutic approaches in which specific blockers of 12-15LO could be used as disease-modifying drugs to prevent and/or treat AD. METHODS Animals and tissue preparation The animals used in these studies were: H12-15LO and tg2576 mice, which were previously described 10,11. They were backcrossed 10 times on the same genetic background (C57BL6/SJL). The H12-15LO mice were crossbred with tg2576 mice to obtain founder bigenic animals (tg2576/H12-15LO). Bigenic males were crossed with H12-15LO females and only the bigenic females from this cross were always used. We have selected only females because it is known that males carrying the APP transgene are aggressive and need Fulvestrant biological activity to be housed in single cages. By contrast, females do not manifest this aggressive behavior so they can be housed with other mice in the same cage. For this reason it is less expensive to perform a study with only females especially when Fulvestrant biological activity a large number of animals is required. Mice were genotyped by polymerase chain reaction analysis as previously described 10,11. They were kept in a pathogen-free environment and on a 12-hour light/dark cycle and were fed a normal chow and water ad libitum. They were followed until 15 months of age and then sacrificed. Two weeks before sacrifice mice underwent behavioral testing as described.