Understanding the metabolic basis for T cell-mediated inflammation in the Central Nervous System

Relapsing remitting multiple sclerosis (RRMS) is a disease that affects hundreds of thousands of people in the US and millions worldwide. RRMS is most commonly diagnosed in the third decade of life, and as a disease with no cure and limited treatment options, is a lifetime sentence to progressively worsening debilitation. There is a critical need for novel therapeutic strategies to manage RRMS.

Current disease modifying therapies (DMT) for RRMS achieve therapeutic efficacy by suppressing the immune system, but suffer from the side effects of blanket immunosuppression. Indeed, while depleting the immune system provides important short-term benefits for RRMS patients, this approach is inherently limited due to the side effects of long-term immunosuppression. Efforts to develop more targeted ways of singling out specific lineages of cells that contribute significantly to pathology are under intense investigation. A very promising lineage of cells to target are pathologic subsets of CD4+ T cells, agents of the adaptive immune system that play critical if not orchestrating roles in the RRMS disease process. A major focus of this thesis is identifying ways to defuse pathology driven by CD4+ T cells with the capacity to produce the pro- inflammatory cytokine IL-17A, called Th17 cells.
In experimental autoimmune encephalomyelitis (EAE), a mouse model in which all currently approved DMT for RRMS have been validated, Th17 cells play myriad pathologic roles. Th17 contribute to central nervous system (CNS) demyelination by (i) inducing of glial cell death, (ii) organizing ectopic foci of inflammation in meningeal tissues, (iii) disrupting the blood brain barrier, and (iv) recruiting peripheral immune cells such as neutrophils and monocyte-derived cells into the CNS. Genetic and pharmacologic strategies to destabilize the Th17 lineage ameliorate disease outcomes in EAE, and in many cases, prevent disease altogether. As a result, there is tremendous enthusiasm and value into discovering new ways to subvert Th17 development and functions. Inflammatory T cells require changes to their quiescent state metabolism to support the biosynthetic and bioenergetic requirements of their effector functions such as cytokine production. These metabolic adaptations often hinge on the potent induction of specific isoforms of metabolic machinery. Thus, revealing the metabolic basis for pathologic T cell functions in the context of EAE has the potential to identify novel targets through which this significant source of pathology may be defused. The overarching goal of this thesis is to identify and exploit metabolic peculiarities and vulnerabilities of T cells that drive disease in the EAE model, and especially the Th17 cell.

The major focus of the first half of the work presented herein is to gain a better understanding of how metabolism interfaces with inflammatory functions of T cells in the EAE model. Toward this end, I identify that T cells at the site of disease (spinal cord) in the EAE model are metabolically distinct compared to those in the periphery. In particular, spinal cord T cells exhibit a heightened glycolytic flux that correlates with elevated expression levels of specific isoforms of glycolytic machinery, including the M2 isoform of pyruvate kinase (PKM2). Interestingly, I find that glycolytic inhibition is relatively ineffective at regulating IL-17A production in ex vivo cultures of EAE spinal cords, suggesting that sources of IL-17A may be refractory to this type of metabolic intervention. In the second half of my thesis work, I build upon these observations by using pharmacologic and genetic approaches to interrogate the metabolic and non-metabolic ways in which PKM2 can be manipulated to alter a Th17 response seemingly resilient to glycolytic inhibition.

The work presented in this thesis provide insight into the means by which T cell use metabolic machinery to facilitate their inflammatory responses in the demyelinating CNS. It is my hope that these studies have made even a small contribution to the development of improved therapeutic treatment strategies for RRMS and beyond.