Item Details

title

MORE THAN A POWERHOUSE: MITOCHONDRIA, CENTRAL REGULATORS OF MACROPHAGE ACUTE INFLAMMATION

author

Meyers, Allison Kenna

abstract

Sepsis is an infection that leads to systemic damage, but at its core, it is an immunometabolic pathological condition. Herein we discuss the intersection of these pathologies, the metabolic defects and the immunological failures that occur during sepsis. The majority of the studies in this dissertation focus on inflammation driven by the NLRP3 inflammasome during sepsis and, ultimately, how this inflammation is regulated by the mitochondrial metabolic regulator pyruvate dehydrogenase kinase (PDHK). The NLRP3 inflammasome is a multimeric cytosolic protein complex that senses both intrinsic and extrinsic signals that alert cells to danger. Recognition of danger leads to inflammasome complex assembly and initiates an inflammatory response via the production of the pro-inflammatory cytokine IL-1β. NLRP3 inflammasome activation also results in GSDMD-mediated pyroptotic cell death (pyroptosis), directly removing macrophages from the fight against secondary infections. To study this, we utilized murine bone marrow-derived macrophages (BMDM), thioglycollate-elicited peritoneal macrophages, human peripheral blood mononuclear cell (PBMC)-derived macrophages, and a cecal ligation and puncture (CLP) model of sepsis. We found that pharmacological inhibition of PDHK by using dichloroacetate (DCA, a pyruvate analog and pan-PDHK inhibitor), JX06 (a synthetic small-molecule selective PDHK1 inhibitor), or PDHK- targeted siRNAs can significantly attenuate the activity of the NLRP3 inflammasome activation in macrophages or septic mice. Inhibition of PDHK in macrophages also induced broad rewiring of metabolism, notably in pyruvate metabolism and in the citric acid cycle, reversing metabolic paralysis in NLRP3 inflammasome-activated macrophages. Additionally, inhibition of PDHK can enhance autophagic and mitophagic activation. Interestingly, despite broad ameliorative metabolic changes in PDHK-inhibited macrophages, these changes were not found to be responsible for reducing inflammasome activation in those macrophages. Instead, we found that PDHK inhibition protects mitochondrial integrity and reprograms mitochondria from ROS production to ATP generation in line with the central role of mitochondria in the activation of the NLRP3 inflammasome. Our data suggest that the mitochondrial protective role of PDHK is a novel function completely separate from its canonical role as a regulator of the pyruvate dehydrogenase complex (PDC). Furthermore, we briefly investigated other means of mitochondrial regulation during sepsis. In a THP1 model of sepsis tolerance, we found that free cholesterol loading inhibited the metabolic function of LPS-stimulated monocytes, particularly that of their respiratory capacity. Although these studies were preliminary, our data suggest that cholesterol trafficking may be one of many pathways that induce damage to mitochondria during sepsis. Taken together, these data identify the mitochondria as a central regulator of both inflammation and metabolic function and highlight the feasibility of targeting the mitochondria for future sepsis therapeutics.

subject

Cholesterol Metabolism

Macrophage Inflammation

Mitochondria

NLRP3 Inflammasome

Pyruvate Metabolism

Sepsis

contributor

Zhu, Xuewei (committee chair)

Parks, John S (committee member)

Alenander-Miller, Martha A (committee member)

Yoza, Barbara K (committee member)

Ornelles, David A (committee member)

date

2022-05-24T08:36:20Z (accessioned)

2023-05-23T08:30:13Z (available)

2022 (issued)

degree

Microbiology & Immunology (discipline)

embargo

2023-05-23 (terms)

identifier

http://hdl.handle.net/10339/100787 (uri)

language

en (iso)

publisher

Wake Forest University

type

Dissertation