Saturday, September 7, 2024
9/7/2024
PROJECT SUMMARY NK cells are required for antiviral immunity against viral infection in mice and humans. Patients with NK cell deficiencies display increased susceptibility to infection from human cytomegalovirus (HCMV), varicella zoster virus, and other herpesviruses. During the response to viral infection, activated NK cells expand, produce inflammatory cytokines such as interferon-γ (IFN-γ), and directly kill virally infected host cells. Potent induction of these effector functions is tightly linked to metabolic reprogramming, as NK cells undergo drastic metabolic changes to optimize energy production. Recent studies have identified the mammalian target of rapamycin complex 1 (mTORc1) and the sterol regulatory element-binding protein (SREBP) family of transcription factors as being key regulators of activated NK cell metabolism. Despite the importance of these metabolic adaptations, however, the precise molecular regulators linking extracellular activating signals to these intracellular metabolic mediators remain poorly understood. Our results indicate that the transcription factor myocyte enhancing factor 2C (MEF2C) is a central regulator of mature human NK cell proliferation, IFN-γ production, and cytotoxicity. CRISPR-Cas9 ribonucleoprotein (RNP)-mediated knockout of MEF2C resulted in impaired human NK cell effector function in vitro. Likewise, MEF2C loss resulted in impaired expansion of mouse NK cells during mouse cytomegalovirus (MCMV) infection in vivo. Metabolic analyses revealed that MEF2C promotes glycolysis, oxidative phosphorylation, and lipid uptake and accumulation in cytokine-activated human NK cells. MEF2C expression was induced by IL-2 and IL-15 stimulation in a phosphoinositol-3-kinase (PI3K)-dependent manner, while Cleavage Under Targets & Tagmentation (CUT&Tag) analysis indicated that MEF2C binds at the SREBF1 locus encoding SREBP1 to increase transcript expression. These results suggest that MEF2C is required for cytokine-activated NK cell proliferation, effector function, and metabolism through regulation of SREBP1. Thus, we propose studies to test the hypothesis that MEF2C activates SREBP1 to increase lipid synthesis and import after IL-2/15 activation to fuel NK cell effector function and proliferation to mediate protective antiviral responses during CMV infection. Aim 1 will i) test whether MEF2C is required for mouse NK cell antiviral activity during in vivo MCMV infection and ii) determine if MEF2C augments human NK cell clearance of HCMV-infected targets. Aim 2 will i) determine the MEF2C-dependent metabolic pathways in human NK cells and ii) test whether neutral lipid supplementation can restore effector function and metabolism in MEF2C-deficient human NK cells. Our proposal will delineate a novel transcriptional regulator of human NK cell metabolism that enhances our understanding of basic NK cell biology as well as clinically relevant mechanisms of antiviral immunity.
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