5-Lipoxygenase gene disruption reduces amyloid-beta pathology in a mouse model of Alzheimer's disease.

5-Lipoxygenase (5LO), by producing leukotrienes, is a proinflammatory enzyme, and there is evidence suggesting that it is up-regulated with aging and may be involved in Alzheimer's disease (AD). In this paper, we studied the effect of 5LO-targeted gene disruption on the amyloid phenotype of a transgenic mouse model of AD, the Tg2576. Amyloid-beta (Abeta) deposition in the brains of Tg2576 mice lacking 5LO was reduced by 64-80% compared with Tg2576 controls. This reduction was associated with a similar significant decrease in Abeta levels measured by sandwich ELISA. Absence of 5LO did not induce any significant change in amyloid-beta precursor protein (APP) levels and processing, or Abeta catabolic pathways. Furthermore, in vitro studies showed that 5LO activation or 5LO metabolites increase, whereas 5LO inhibition decreases, Abeta formation, secondary to correspondent changes in gamma-secretase activity. These data establish for the first time a novel functional role for 5LO in the pathogenesis of AD-like amyloidosis, thereby modulating gamma-secretase activity. Our work suggests that pharmacological inhibition of 5LO could provide a novel therapeutic tool for AD.

The 5-lipoxygenase enzymatic pathway in the mouse brain: young versus old.

The 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism is an important source of inflammatory mediators, and is also present in the central nervous system. In this study, we assayed the expression levels and activity of 5-LO in different brain regions of young versus old C57Bl/6 mice. 5-LO mRNA was expressed in all the brain regions considered, i.e. cortex, hippocampus, and cerebellum. The highest expression level was observed in cerebellum compared with cortex and hippocampus, although it was not affected by aging. By contrast, 5-LO mRNA and protein levels were significantly increased in the hippocampus of old (25 months) versus young (3 months) mice. Finally, levels of the leukotriene B4, a metabolic product of 5-LO, were significantly increased in the hippocampus of old mice, but no difference was observed in cortex and cerebellum. These results demonstrate that the 5-LO enzymatic pathway is widely expressed in the mouse CNS, where significant changes are region-specific and age-dependent. This observation supports the hypothesis that 5-LO may be involved in diseases of the brain associated with aging.

Absence of 12/15 lipoxygenase reduces brain oxidative stress in apolipoprotein E-deficient mice.

The enzyme 12/15 lipoxygenase (12/15LO) has been implicated in the oxidative modification of lipoproteins and phospholipids in vivo. In addition, mice deficient in apolipoprotein E (ApoE-/-) are characterized by spontaneous hypercholesterolemia and a systemic increase in oxidative stress. Whereas the absence of 12/15LO reduces lipid peroxidation in the plasma and urine of ApoE-/- mice, the relative contribution of this enzyme to oxidative stress in the central nervous system remains unknown. Here, we provide the first in vivo evidence that 12/15LO modulates brain oxidative stress reactions using ApoE-/- mice crossbred with 12/15LO-deficient (12/15LO-/-) mice (12/15LO-/-/ApoE-/-). In chow-fed 12-month-old 12/15LO-/-/ApoE-/- mice, the amount of brain isoprostane iPF2alpha-VI, a marker of lipid peroxidation, and carbonyls, markers of protein oxidation, were significantly reduced when compared with 12/15LO-expressing controls (12/15LO+/+/ApoE-/-). These results were observed despite the fact that cholesterol, triglyceride, and lipoprotein levels were similar to those of ApoE-/- mice. These data indicate a functional role for 12/15LO in the modulation of oxidative reactions in the central nervous system, supporting the hypothesis that inhibition of this enzymatic pathway may be a novel therapeutic target in clinical settings involving increased brain oxidative stress.

CiC3-1a-mediated chemotaxis in the deuterostome invertebrate Ciona intestinalis (Urochordata).

Deuterostome invertebrates possess complement genes, and in limited instances complement-mediated functions have been reported in these organisms. However, the organization of the complement pathway(s), as well as the functions exerted by the cloned gene products, are largely unknown. To address the issue of the presence of an inflammatory pathway in ascidians, we expressed in Escherichia coli the fragment of Ciona intestinalis C3-1 corresponding to mammalian complement C3a (rCiC3-1a) and assessed its chemotactic activity on C. intestinalis hemocytes. We found that the migration of C. intestinalis hemocytes toward rCiC3-1a was dose dependent, peaking at 500 nM, and was specific for CiC3-1a, being inhibited by an anti-rCiC3-1a-specific Ab. As is true for mammalian C3a, the chemotactic activity of C. intestinalis C3-1a was localized to the C terminus, because a peptide representing the 18 C-terminal amino acids (CiC3-1a(59-76)) also promoted hemocyte chemotaxis. Furthermore, the CiC3-1a terminal Arg was not crucial for chemotactic activity, because the desArg peptide (CiC3-1a(59-75)) retained most of the directional hemocyte migration activity. The CiC3-1a-mediated chemotaxis was inhibited by pretreatment of cells with pertussis toxin, suggesting that the receptor molecule mediating the chemotactic effect is G(i) protein coupled. Immunohistochemical analysis with anti-rCiC3-1a-specific Ab and in situ hybridization experiments with a riboprobe corresponding to the 3'-terminal sequence of CiC3-1, performed on tunic sections of LPS-injected animals, showed that a majority of the infiltrating labeled hemocytes were granular amebocytes and compartment cells. Our findings indicate that CiC3-1a mediates chemotaxis of C. intestinalis hemocytes, thus suggesting an important role for this molecule in inflammatory processes.