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Cytokines and Inflammation in the CNS in Transgenic Mice

I.L. Campbell, V. Asensio, M. Benedict, C. Kincaid, A.K. Stalder, S. Lassmann, M. Carson,* E. Masliah,** H.C. Powell**

* Department of Molecular Biology, TSRI
** University of California, San Diego, CA

Cytokines are pivotal modulators of inflammatory responses. Inappropriate expression of cytokines and inflammation in the CNS occur in a variety of neurologic disorders, including multiple sclerosis, stroke, Alzheimer's disease, infectious diseases, and trauma. Understanding the consequences of cytokine expression in the CNS is therefore an important research objective, with implications for the understanding of the pathogenesis and possible treatment of these neurologic disorders. Key issues include the following: (1) Is the presence of cytokines in CNS pathophysiologic states a primary or a secondary pathogenetic phenomenon? (2) Does a cause-and-effect relationship exist between the expression of a particular cytokine (or cytokines) and the development of a specific neuropathologic feature? (3) What are the mechanisms that underlie cytokine-elicited responses in the CNS? (4) Can manipulation of the cytokines or of the responses they evoke be used as focal points for therapeutic intervention? To address these issues, we use a transgenic approach to direct the expression of cytokines to astrocytes in the CNS in mice.

Using glial fibrillary acidic protein (GFAP) fusion gene constructs, we generated transgenic mice that express the murine cytokines IL-6, IL-3, IFN-, TNF-, or IL-12 in astrocytes. Transgenic expression of each cytokine in the intact CNS produced divergent inflammatory responses associated with the development of wide-ranging and progressive molecular, cellular, and functional CNS impairments. These transgenic mice provide a powerful tool for defining novel mechanisms that might underlie the individual cytokine-driven neuroinflammatory responses. This point is exemplified in Figure 1, which summarizes the key pathogenetic findings evolving from our studies in GFAP-TNF mice.

One focus of these investigations is the elucidation of the pathways involved in the recruitment and trafficking of leukocytes to the CNS. Despite evidence for intrinsic resistance of the CNS to the induction of acute inflammatory responses, we observed pronounced recruitment and infiltration of the CNS parenchyma with different classes of leukocytes in the different GFAP-cytokine transgenic mice (Fig. 2). Tissue leukocyte migration is a complex process that involves multiple factors, including cellular adhesion molecules, chemokines, and matrix metalloproteinases. Our results clearly show distinct patterns of cerebral expression of these key molecules in the inflammatory response. The differential expression of these regulatory molecules may therefore play a key role in controlling the phenotypic and functional properties of the neuroinflammatory process in each type of GFAP-cytokine transgenic mouse.

In addition, these studies led us to identify some novel components of the inflammatory response evoked in the GFAP-cytokine transgenic mice. For example, we found that the chemokine C10 is a dominant chemokine expressed in the brain during inflammatory demyelinating disease. Subsequent studies revealed that this chemokine is produced by macrophages and functions as an autocrine chemoattractant signal for these cells. The apparent central role of C10 in macrophage chemotaxis to the CNS makes this molecule an attractive target for potential therapeutic intervention. In ongoing studies, we are using GFAP-cytokine transgenic mice to advance our understanding of the mechanisms of inflammation in the CNS, define the individual role of specific molecular components in inflammation, and determine potentially novel targets in the inflammatory response for therapeutic intervention.

Finally, with colleagues in the Department of Neuropharmacology, we are using these transgenic models in multilevel analyses to link molecular and cellular alterations to specific electrophysiologic, neuroendocrine, and behavioral outcomes. Integrative studies such as those in GFAP-cytokine transgenic mice are providing a more thorough understanding of the actions of cytokines in the CNS and bridge the gap between structural and functional neuropathology.

PUBLICATIONS

Campbell, I.L. Structural and functional impact of transgenic expression of cytokines in the CNS. Ann. N.Y. Acad. Sci. 840:82, 1998.

Campbell, I.L. Transgenic mice and cytokine actions in the brain: Bridging the gap between structural and functional neuropathology. Brain Res. Rev. 26:327, 1998.

Campbell, I.L., Stalder, A.K., Akwa, Y., Pagenstecher, A., Asensio, V.C. Transgenic models to study the actions of cytokines in the central nervous system. Neuroimmunomodulation, in press.

Carr, D.J., Noisakran, S., Halford, W.P., Lukacs, N., Asensio, V., Campbell, I.L. Cytokine and chemokine production in HSV-1 latently infected trigeminal ganglion cell cultures: Effects of hyperthermic stress. J. Neuroimmunol. 85:111, 1998.

Carrasco, J., Hernandez, J., Campbell, I.L., Hidalgo, J. Localization of metallothionein-I and -III expression in the CNS of transgenic mice with astrocyte-targeted expression of interleukin-6. Exp. Neurol., in press.

Castelnau, P., Campbell, I.L., Powell, H.C. Prion protein (PrP) is not involved in the pathogenesis of spongiform encephalopathy in transgenic mice expressing interleukin-6 in the brain. Neurosci. Lett. 234:15, 1997.

Castelnau, P.A., Garrett, R.S., Palinski, W., Witzum, J.L., Campbell, I.L., Powell, H.C. Abnormal iron deposition associated with lipid peroxidation in transgenic mice expressing interleukin-6 in the brain. J. Neuropathol. Exp. Neurol. 57:268, 1998.

Lane, T.E., Asensio, V.C., Naichen, Y., Paoletti, A.D., Campbell, I.L.. Buchmeier, M.J. Dynamic regulation of and ß chemokine expression in the central nervous system during mouse hepatitis virus-induced demyelinating disease. J. Immunol. 160:970, 1998.

Nelson, T.E., Campbell, I.L., Gruol, D.L. Altered physiology of Purkinje neurons in cerebellar slices from transgenic mice with chronic central nervous system expression of interleukin-6. Neuroscience, in press.

Pagenstecher, A., Masliah, E., Stalder, A.K., Campbell, I.L. Transgenic mice expressing cytokines in the CNS as model systems for the study of inflammatory neurodegenerative and demyelinating disorders. In: Neuroimmunodegeneration. Wong, P., Lynn, W.S. (Eds.). Landes, Austin, TX, in press.

Pagenstecher, A., Stalder, A.K., Kincaid, C.L., Shapiro, S.D., Campbell, I.L. Differential expression of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinase genes in the mouse CNS in normal and inflammatory states. Am. J. Pathol. 152:729, 1998.

Paradisis, P.M., Campbell, I.L., Barnum, S.R. Elevated complement C5a receptor expression on glial cells and neurons induced by the central nervous system production of interleukin-3 in transgenic mice. Glia, in press.

Raber, J., O'Shea, R., Bloom, F.E., Campbell, I.L. Modulation of hypothalamic-pituitary-adrenal function by transgenic expression of interleukin-6 in the central nervous system of mice. J. Neurosci. 17:9473, 1997.

Raber, J., Sorg, O., Horn, T., Yu, N., Koob, G.F., Campbell, I.L., Bloom, F.E. Inflammatory cytokines: Putative regulators of neuronal and neuro-endocrine function. Brain Res. Rev 26:320, 1998.

Rodriguez, F., An, L.L., Harkins, S., Zhang, J., Yokoyama, M., Widera, G., Fuller, T., Kincaid, C., Campbell, I.L., Whitton, L.J. DNA immunization with minigenes: Low frequency of memory CTL and inefficient antiviral protection are rectified by ubiquitination. J. Virol. 72:5174, 1998.

Stalder, A., Pagenstecher, A., Kincaid, C., Campbell, I.L. Analysis of gene expression by multi-probe RNase protection assay. In: Methods in Molecular Medicine. Harry, J. (Ed.). Academic Press, San Diego, in press.