Date of Award

Summer 8-15-2021

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Computational & Systems Biology)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

The ability to discern gene expression at single cell level is revolutionizing our understanding of both basic biology and human health. Peripheral nerves are essential communicators between the outside world and the CNS, as evidenced by the devastating effects of diseases that disrupt them, such as ALS, Charcot-Marie-Tooth Syndrome and diabetic neuropathy. Understanding peripheral nerve dysfunction at a mechanistic level is of considerable interest due to the increasing prevalence and associated patient care costs of these disorders. Although most research of the peripheral nerve has focused on glial-axonal interactions, the important contributions of other cell types besides Schwann cells, such as fibroblasts and immune cells, are increasingly appreciated. This more comprehensive focus on the cellular components of peripheral nerve stimulated a number of studies using single cell sequencing approaches for cell characterization. While interesting information has been gleaned from these efforts, they all largely failed to identify myelinating Schwann cells in their samples due to extreme capture bias secondary to their complex morphology and the close apposition of these glial cells to the axon. For my dissertation, I set out to generate a comprehensive single nuclei atlas of peripheral nerves with the hope to unbiasedly characterize the glial population and to understand how glia contributes to the homeostasis of peripheral nerves. My work began with the development of a fluorescent-activated cell sorting (FACS)-based nuclei isolation approach to avoid issues with capture bias, and to allow an examination of the potential diversity of peripheral glia and other cell types across multiple types of peripheral nerves. Our atlases highlight over 20 cell types in mouse sciatic, peroneal, sural and vagus nerves and show that Schwann cell, as the principal glia, are consistently the predominant cell type across all nerves. In-depth analysis of the immune populations at single cell level has revealed two PNS macrophage populations with unique microglia signatures. I next performed extensive transcriptional characterization of PNS macrophages and showed that, through comparative analytics with CNS diseased microglia data, PNS macrophages constitutively expressed gene previously identified to be upregulated by activated microglia during aging, neurodegeneration, or loss of Sall1. Interestingly, myelinating Schwann cell is the source of IL-34 which is required for the maintenance of PNS macrophages in peripheral nerves. Finally, through the peripheral nerve atlases, I identified multiple Schwann cell sub-populations, including two non-myelinating and four myelinating subtypes. Specifically, a distinct myelinating Schwann cell subtype that expresses Cldn14, Adamtsl1 and Pmp2 exhibits unique transcriptional signature with high NAD and pyruvate metabolisms, and preferentially ensheath large motor axons that innervate fast twitch muscle fiber. The number of these motor-associated, Pmp2+ SCs is significantly reduced in motor neuropathy models and human ALS nerve samples. Collectively, these findings reveal the diversity of SCs and other cell types in peripheral nerve and serve as a reference for future studies of nerve biology and disease.

Language

English (en)

Chair and Committee

Jeffrey Milbrandt

Committee Members

Aaron DiAntonio, David Gutmann, Benjamin Humphreys, Rob Mitra,

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