Transcriptional Regulation of human natural killer cell function

Natural killer (NK) cells have the innate capacity to identify and eliminate virally infected cells. Human cytomegalovirus (HCMV) infection increases the risk of severe health issues in newborns and patients with immune deficiencies (such as AIDS patients or solid organ transplant recipients). Previous work in mice and humans has demonstrated that NK cells are essential for host protection against herpesviruses such as HCMV, and that mouse cytomegalovirus (MCMV) infection can be utilized to model and study HCMV infection in vivo. While the transcriptional and epigenetic regulators associated with mouse NK cell activation and persistence during viral infection have been well studied, they are still not well understood in human NK cells. Our long-term goals seek to identify the relevant transcriptional regulators of human NK cell function following viral infection. To address this, we performed a targeted CRISPR screen in primary PBMC-derived human NK cells concentrated on transcription factors differentially expressed during human NK cell development. Of these candidates, MEF2C was the sole transcription factor broadly required for human NK cell cytotoxicity, proliferation, and antiviral cytokine production ex vivo. Analysis of PBMCs from patients with MEF2C haploinsufficiency syndrome (MCHS) further demonstrated defects in NK cell proliferation and effector function ex vivo, and Mef2c haploinsufficient mice displayed increased mortality during viral infection associated with defective NK cell function. MEF2C was required to promote SREBP-dependent lipid import in response to cytokine activation, and oleate supplementation restored intracellular lipid levels and the cytotoxicity of MCHS patient NK cells. CRISPR-mediated knockout of individual SREBP isoforms in human NK cells revealed that SREBP2, but not SREBP1, is required for NK cell effector functions. These results suggest that MCHS patients with increased susceptibility to viral infections may be caused by an NK cell-intrinsic functional defect, and oleate supplementation may represent an effective strategy to enhance immunity in these patients. While these preliminary results implicate MEF2C as a critical regulator of human NK cells through regulation of the SREBP2 pathway, the precise mechanisms by which MEF2C is induced, and controls human NK cell functionality are unknown. In Aim 1, we will determine the transcriptional and post-translational mechanisms of MEF2C regulation in human NK cells. In Aim 2, we will determine the mechanism of action and in vivo therapeutic efficacy of oleate supplementation on NK cell cytotoxicity. In Aim 3, we will investigate how the SREBP2 pathway promotes antiviral cytokine production in human NK cells. In summary, the studies included in this proposal will contribute to the fundamental understanding of how human NK cell effector functions are regulated by cell-intrinsic metabolism, while also contributing to novel strategies to enhance the clinical use of NK cells during viral infection and in immunocompromised patients. Project Number: 1R01AI186079-01A1 | Fiscal Year: 2025 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Timothy O'Sullivan | Institution: UNIVERSITY OF CALIFORNIA LOS ANGELES, LOS ANGELES, CA | Award Amount: $666,567 | Activity Code: R01 | Study Section: Innate Immunity B Study Section[IIB] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R01AI18607901A1