Xinshou Ouyang, PhD

Identify molecular pathways and the key metabolic regulators integrating stress and inflammatory responses with liver steatosis and fibrosis.

The development of sterile inflammation after cell death is a ubiquitous response that occurs in all organs. The amplitude of this response, however, varies widely, and the liver is notable for developing exceptionally strong sterile inflammation. This is seen in alcoholic steatohepatitis (ASH), and metabolic syndrome-associated development of non-alcoholic steatohepatitis (NASH). Such a high amplitude of sterile inflammation in the liver has major clinical consequences as NASH is by far the most common liver disease in industrialized countries.

We have demonstrated that HIF-1α pathway activation potentiates and sustains the amplitude of acute inflammatory responses, and is vital for the transition from acute self-limiting to sustained chronic inflammation. These mechanistic insights into the role of the HIF-1α pathway in sterile inflammation may have great clinical relevance due to the ability of cardiac glycosides (CGs) to inhibit HIF-1α activation. Digoxin improves oxidative stress during liver injury through maintaining cellular redox homeostasis, and the suppression of HIF-1α pathway activation and downstream signature genes in the liver. We have further identified pyruvate kinase isoform 2 (PKM2) as a digoxin-binding protein. The active nuclear PKM2 directly interacts with multiple modified chromatin proteins, and digoxin reduces the binding of histones to PKM2.

Delineate the RNA modification, specifically m6A-dependent cellular pathways by metabolic signal (s) that control liver steatosis, inflammation, and fibrosis.

The 'epitranscriptome', a collective term for chemical modifications that influence the structure, metabolism, and functions of RNA, has recently emerged as vitally important for the regulation of gene expression. To date, more than 170 types of RNA modifications have been identified, including 5' cap modification, poly(A) tail, pseudouridine (Ψ), N¹-methyladenosine (m¹A) and N⁶,2'-O-dimethyladenosine (m⁶A_m), and N⁶-methyladenosine (m⁶A). Among these modifications, m⁶A is the most abundant internal RNA modification in eukaryotic cells that widely occurs in mRNA and non-coding RNAs (ncRNAs). Myeloid lineage-driven metabolic inflammation is associated with significant changes in post-transcriptional mRNA modification and mRNA pool resulting in marked changes in myeloid cell functional status. We have demonstrated that myeloid lineage-restricted deletion of the m⁶A "writer" protein Methyltransferase Like 3 (METTL3) prevents age-related and diet-induced development of NAFLD and obesity in mice with improved inflammatory and metabolic phenotypes. Our study indicates that m⁶A methylation is critical in the control of myeloid cell-directed metabolic programming through the regulation of immune transcripts in NAFLD and obesity.

Identify the enzymatic and spatiotemporal steps in inflammasome activation and provide novel insights and a potential target for therapeutic intervention in chronic inflammation.

Inflammasomes are multiprotein cytosolic complexes that serve as a platform for caspase-1-dependent production of several proinflammatory cytokines, such as interleukin-1β (IL-1β) and IL-18, and constitute a crucial step in the initiation of innate immune responses. Excessive inflammasome activity has been involved in diverse chronic inflammatory diseases, notably including metabolic disorders such as NASH. The NLRP3 inflammasome can be activated by a variety of structurally unrelated molecules ranging from insoluble particulates, endogenous danger signals, and pathogen molecules. A common theme from recent studies supports that reorganization of the intracellular organelle network is necessary for NLRP3 inflammasome activation, including lipid directed NLRP3 localization to mitochondria, microtubule-mediated NLRP3 inflammasome assembly, and NLRP3 interaction with Golgi-localized phosphatidylinositol-4-phosphate in response to diverse stimuli. We investigated the organelle dynamics and molecular requirement for NLRP3 recruitment in live cells. We have demonstrated a comprehensive model of GSK3β signaling mediated NLRP3 activation resulting in distinct NLRP3 trafficking, organelle reorganization, and inflammasome assembly.

The current model of inflammasome activation in macrophages explains the initial steps in acute inflammation but is inadequate to explain how the activity is sustained in chronic inflammation, repair, and fibrosis. We have demonstrated that cAMP/PKA/CREB/HIF-1α pathway is required for sustained inflammasome activation.