Neurodegenenerative diseases like AD include brain inflammation as a major component of the disease process. The brain's own macrophage, the microglia, participate in the chronic inflammatory response, releasing cytoactive factors such as reactive oxygen species. Our goal is to understand the brain's immune response during disease in the context of oxidative stress. To accomplish this goal we have focused on the control of microglial production of ROS in models of human neurodegenerative disease. Our new data show that release of NO from microglia depends upon APOE genotype. Since APOE genotype is the major risk factor for the development of AD and since AD is associated with an increased presence of oxidative stress, then NO as an oxyradical species probably plays a direct role. Additional new data demonstrate that apoE treatment alters specific Cationic Amino acid Transporters (CATs) in an isoform specific manner. Since CAT transporters regulate arginine entry into cells, which is then converted by the action of NOS to NO, then this may be one important mechanism regulating NO release. We hypothesize that regulation of microglial nitric oxide production is mediated by specific """"""""restriction"""""""" points in the arginine utilization pathway. Our preliminary data demonstrate that regulating the level of substrate for iNOS by altering the cellular uptake of arginine via CAT transporters is one such point. A reciprocal path regulated by arginase competes for arginine and may also serve as a restriction point for NO production. Immune activation of the microglia by extrinsic factors alters the restriction points, thereby modulating NO. Intrinsic genes and their products relevant to AD (APOE) also affects the restriction point regulation and thus predispose the microglia to overproduction of NO and promote tissue redox imbalance. We propose to examine arginine utilization pathways in microglia and the regulation of these pathways by extrinsic immune factors (viral mediators, bacterial components and cytokines) and by APOE. Since our preliminary data demonstrate that microglial immune activation promotes a gene switching process, whereby mENA for CAT1 appears repressed and CAT2b mRNA appears enhanced, we will investigate the gene induction process and the regulation of the gene switching by extrinsic vs intrinsic factors.
| Czapiga, M; Colton, C A (2003) Microglial function in human APOE3 and APOE4 transgenic mice: altered arginine transport. J Neuroimmunol 134:44-51 |
