ORCID

http://orcid.org/0000-0002-7061-9744

Date of Award

Spring 5-15-2022

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Developmental, Regenerative, & Stem Cell Biology)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Peripheral nerve injury (PNI) is common and has debilitating long term sequelae. Development of new therapies to improve regeneration following PNI is therefore critical. Acellular nerve allografts (ANAs) are increasingly utilized in the clinic for the repair of PNI and an improved mechanistic understanding of nerve regeneration through ANA is important for developing better therapies. Inflammation is an important aspect of regeneration, and the role of macrophage has been increasingly documented. Other aspect of inflammation has not been well-defined. In particular, there is limited understanding on the role of T cells in the regeneration of peripheral nerve. However, evidence in other organ systems, including brain, spinal cord, muscle, and liver support the hypothesis that T cells can play in role in regeneration. Therefore, the overall aim of this work was to identify the impact of T cells on regeneration of peripheral nerve through acellular nerve allograft scaffolds. My thesis is therefore divided into two parts.In the first part, I examined the leukocyte populations in short and long ANAs to identify the changes in leukocyte populations following nerve repair. Two (2) cm ANAs were used as model scaffold that supported robust axon regeneration, while 4 cm ANAs were used as model that did not support axon regeneration. To quantify regeneration, both histology of regenerated ANAs and gene expression from Schwann cells were quantified. Utilizing transgenic rats, I also examined if the altered leukocyte population may contribute to regeneration through ANAs. This study suggested that nerve graft length affected the accumulation of T cells, which in turn contributed to the regeneration of nerve repaired with ANAs. In the second part, I determined how T cells contributed to the regeneration of nerves repaired with ANAs. While T cells have been associated with regulating IL-4 within sites of injury, this has not been demonstrated in nerve repair. Furthermore, what role, if any, IL-4 plays in the regeneration of peripheral nerve is not clear. Finally, how T cells may be regulating IL-4 is also not known. Previous studies have shown that T cells secrete IL-4 or regulate other cells, such as eosinophils, to provide IL-4 indirectly. Thus, identifying the mechanism of IL-4 regulation by T cells is important. In this part of my thesis, a mouse sciatic nerve repair model was used to take advantage of the transgenic animals available. Flow cytometry and gene expression analysis were used to quantify inflammation and its association to T cells. Knockout animals and antibody depletion strategies were used to selectively deplete specific cells or cytokines related to T cells. Regeneration were quantified using histological and immunofluorescence methods. This work demonstrated that T cells recruit eosinophils that express IL-4, which are important for regeneration by promoting myelination. Overall, my thesis work demonstrated the importance of T cells in the regeneration of peripheral nerve and showed that T cells are critical for the regulation of IL-4 within regenerating ANAs by recruiting IL-4 expressing eosinophils.

Language

English (en)

Chair and Committee

Susan E. Mackinnon

Committee Members

Audrey McAlinden

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