ABSTRACT
Axon degeneration is a programed process that takes place during development, in response to neuronal injury, and as a component of neurodegenerative disease pathology, yet the molecular mechanisms that drive this process remain poorly defined. In this study, we have developed a semi-automated, 384-well format axon degeneration assay in rat dorsal root ganglion (DRG) neurons using a trophic factor withdrawal paradigm. Using this setup, we have screened a library of known drugs and bioactives to identify several previously unappreciated regulators of axon degeneration, including lipoxygenases. Multiple structurally distinct lipoxygenase inhibitors as well as mouse DRG neurons lacking expression of 12/15-lipoxygenase display protection of axons in this context. Retinal ganglion cell axons from 12/15-lipoxygenase-null mice were similarly protected from degeneration following nerve crush injury. Through additional mechanistic studies, we demonstrate that lipoxygenases act cell autonomously within neurons to regulate degeneration, and are required for mitochondrial permeabilization and caspase activation in the axon. These findings suggest that these enzymes may represent an attractive target for treatment of neuropathies and provide a potential mechanism for the neuroprotection observed in various settings following lipoxygenase inhibitor treatment.
Subject(s)
Arachidonate 12-Lipoxygenase/metabolism , Arachidonate 15-Lipoxygenase/metabolism , Axons/pathology , Nerve Degeneration/enzymology , Algorithms , Animals , Arachidonate 12-Lipoxygenase/genetics , Arachidonate 15-Lipoxygenase/genetics , Axons/metabolism , Cells, Cultured , Coculture Techniques , Disease Models, Animal , Dose-Response Relationship, Drug , Embryo, Mammalian , Enzyme Inhibitors/pharmacology , Female , Ganglia, Spinal/cytology , Gene Library , Male , Mice , Mice, Transgenic , Mitochondria/drug effects , Mitochondria/metabolism , Nerve Degeneration/diagnosis , Nerve Degeneration/drug therapy , Nerve Degeneration/etiology , Neuroglia/cytology , Neuroglia/drug effects , Neuroglia/metabolism , Neurons/cytology , Neurons/drug effects , Neurons/metabolism , Optic Nerve Diseases/complications , Rats , Rats, Wistar , Signal Transduction/drug effects , Signal Transduction/geneticsABSTRACT
Atherosclerosis involves a macrophage-rich inflammation in the aortic intima. It is increasingly recognized that this intimal inflammation is paralleled over time by a distinct inflammatory reaction in adjacent adventitia. Though cross talk between the coordinated inflammatory foci in the intima and the adventitia seems implicit, the mechanism(s) underlying their communication is unclear. Here, using detailed imaging analysis, microarray analyses, laser-capture microdissection, adoptive lymphocyte transfers, and functional blocking studies, we undertook to identify this mechanism. We show that in aged apoE(-/-) mice, medial smooth muscle cells (SMCs) beneath intimal plaques in abdominal aortae become activated through lymphotoxin beta receptor (LTbetaR) to express the lymphorganogenic chemokines CXCL13 and CCL21. These signals in turn trigger the development of elaborate bona fide adventitial aortic tertiary lymphoid organs (ATLOs) containing functional conduit meshworks, germinal centers within B cell follicles, clusters of plasma cells, high endothelial venules (HEVs) in T cell areas, and a high proportion of T regulatory cells. Treatment of apoE(-/-) mice with LTbetaR-Ig to interrupt LTbetaR signaling in SMCs strongly reduced HEV abundance, CXCL13, and CCL21 expression, and disrupted the structure and maintenance of ATLOs. Thus, the LTbetaR pathway has a major role in shaping the immunological characteristics and overall integrity of the arterial wall.
