Date of Award

Summer 8-11-2017

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

Advisor

Ling Cao

Second Committee Member

Lucy Liaw

Third Committee Member

Ah Kau Ng

Additional Committee Members

Stephen C Pelsue

James M Vaughn

Abstract

CGRP is a neuropeptide released primarily by sensory neurons upon injury and infection. It modulates the response of glial cells via CGRP receptors by regulating the production of several immune mediators. CGRP can contribute to spinal cord or peripheral nerve injury-induced sensory hypersensitivity in rodents. Mice infected with a murine retrovirus, LP-BM5, an established murine model of HIV infection, expressed elevated levels of CGRP in the spinal cord along with the development of sensory hypersensitivity, a sign of infection-induced peripheral neuropathy. In this study we investigated the role of CGRP on glial cells infected with LP-BM5 using in vitro systems. Unexpectedly, we observed an antiretroviral effect of CGRP in primary spinal cord mixed glia, which was microglial content-dependent, but not associated with changes of the production of several proinflammatory cytokines (IL-6, TNF-a, IL-12 and CCL2) induced by LP-BM5. The observed reduction of viral load in mixed glia following CGRP treatment was not due to CGRP decreased LP-BM5 infectivity or promoted glial cell death. Further investigation using astrocyte and microglial cell lines revealed differential cellular pathways that were utilized by CGRP to promote its antiviral effects in astrocytes verses microglia. In astrocytes, CGRP mediates its antiviral effect through upregulating interferon-b (IFN-b), a well-known antiviral cytokine, and the subsequent upregulation of CCL4 and CCL5. IFN-b knockdown diminished CGRP antiviral effect in astrocytes. In microglia, CD40 expression was found to be critical as primary mixed glia, prepared from CD40 knockout mice, did not display CGRP’s antiviral effect. CD40 has been reported to be involved in LP-BM5-induced immunodeficiency and peripheral neuropathy. CGRP also reduced LP-BM5-induced increase of the percentage of CD40+ microglia. CGRP’s effects on the changes of several chemokines that could be downstream to CD40 signaling were also evaluated.

Taken together, our study showed a novel antiviral function of CGRP in retroviral infection and investigated potential underlying mechanisms associated with CGRP’s antiviral effects. Future in vivo studies are necessary to validate CGRP’s antiviral function and explore novel CGRP-related approaches for treating HIV and other retroviral infections.

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