Multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE) arebelieved to be initiated by T cell-mediated immune responses to myelin antigens. In recent years, however, asignificant body of evidence has been compiled indicating the contribution of various cell populations within thecentral nervous system (CNS), such as microglia and astrocytes, to the development and progression of thedisease. Nevertheless, the role of these cell types is far from being clearly understood. Chronicneuroinflammation and demyelination may also contribute to disease progression and chronic neurologicaldeficits. In all these processes, in MS as well as in many other neurodegenerative diseases, astrocytes havebeen demonstrated to play an active role. Astrocytes respond to injury by becoming 'reactive' or 'gliotic', a complex cellular response whosefunctional significance is still poorly understood. For instance, reactive astrocytes release neurotrophinsessential for neuronal survival and repair, and are also responsible for the production of pro-inflammatorymolecules (cytokines, chemokines, growth factors, NO etc) growth-inhibitory molecules detrimental tofunctional recovery. Many of the processes occurring in reactive astrocytes are regulated by NF-kB, a keymodulator of inflammation and secondary injury. The studies outlined in this proposal are designed to investigate the role of astroglial NF-kB in thepathophysiology of experimental autoimmune encephalomyelitis (EAE), taking advantage of a transgenicmouse model generated in our laboratory (GFAP-IkBa-dn mice) where NF-kB is functionally inactivated in cellsexpressing GFAP, such as astrocytes and non-myelinating Schwann cells. Preliminary data indicate thatblocking astroglial NF-kB significantly reduces disease severity, improves functional recovery following EAEand reduces neuroinflammation and demyelination. This leads us to hypothesize that reactive astrocytessignificantly contribute to disease progression and development of chronic neurological deficits in EAE andMS. This hypothesis will be tested in the four specific aims outlined below. While the results generated in ourtransgenic mice are very promising, the studies in Aim 1 will compare our GFAP-IkBa-dn mice to twoadditional mouse lines (described below) to confirm that the results obtained so far in our experimental modelare uniquely associated with the astrocyte-specific inhibition of the NF-kB pathway. The first mouse line(73.12xffIKKb) is obtained by breeding a GFAP-Cre line developed in Dr. Sofroniew's laboratory to a floxed (f/f)IKKb line generated in the laboratory of Dr. Michael Karin. The second mouse line (GFAPCreERT2xffIKKb) isobtained by breeding a tamoxifen inducible GFAP-Cre line (CreERT2) developed in Dr. McCarthy's lab to thesame floxed (f/f) IKKb line.
In Aims 2 and 3 we will use the line(s) that provides the most robust clinicalimprovement over the corresponding control mice to further investigate the mechanisms at the basis of theprotection provided by blocking astroglial NF-kB. Specifically, studies in Aim 2 will determine if there aredifferences in blood brain permeability and infiltration of leukocytes in the CNS of diseased WT and mutantmice. Studies in Aim 3 will determine the mechanisms through which inhibiting astroglial NF-kB promotes ananti-inflammatory response. Studies in this aim will focus on how inhibiting astroglial NF-kB alters T and B cellresponses in the spinal cord. Finally, since demyelination is a hallmark of this disease and could be modulatedby neuroinflammation, studies in Aim 4 will investigate the effect of the inhibition of astroglial-NF-kB onoligodendrocyte survival and demyelination. Our experiments will not only give insights into NF-kB signaling mechanisms, but also elucidateastrocyte responses under pathological conditions. Ultimately, our goal is to determine if interfering with theseresponses could be beneficial as a therapeutic strategy for MS and other neurological disorders.
The objective of this application is to better understand the role astrocytes; a non-neuronal cell found in the brain and spinal cord; play in the pathogenesis of multiplesclerosis and its animal model EAE. Understanding the pathology of this and otherdiseases will help in the development of more effective therapies.
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