Mandy Chan

Program: Immunology

Current advisor: Joel Schilling, MD, PhD

Undergraduate university: Emory University, 2018

Enrollment year: 2018

Research summary
Kupffer cell lipid metabolism and cell death in metabolic dysfunction-associated steatotic liver diseases

During the development of metabolic dysfunction-associated steatotic liver disease (MASLD), liver resident macrophages/Kupffer cells (KCs) decrease in number, and monocyte-derived macrophages (MdMs) infiltrate the liver. However, the mechanism(s) and consequences of KC loss remains unclear. Using a mouse model of MASLD, we discovered that as liver disease progresses KCs develop perturbed phagolysosomal function and fail to store fatty acids in neutral lipid droplets.

To devise a strategy for KCs to counter these cellular abnormalities, we generated an in vivo model in which TFEB, a master transcriptional regulator of lysosomal biogenesis and lipid metabolism, is overexpressed selectively in KCs (KCTfeb). Both KCTfeb and their Cre-only littermates (KCCre) had similar weight gain when fed a MASLD-inducing diet. However, KC number was preserved and inflammatory MdM recruitment was reduced in KCTfeb mice. In terms of liver pathology, overexpression of TFEB in KCs reduced liver steatosis and injury. Electron microscopy of macrophages revealed that TFEBTg KCs contained large lipid droplets in vacuoles. RNA sequencing of KCs from KCTfeb and KCCre animals confirmed the induction of several lysosomal lipid metabolic genes in the transgenic KCs after diet feeding. To track lipids in vivo and in vitro, we utilized labeled fatty acids to show that TFEB-overexpressing macrophages have enhanced uptake of exogenous free fatty acid and lipoproteins compared to WT macrophages, potentially serve as a lipid sink for the steatotic hepatocytes.

To investigate the mechanism of KC preservation, we first confirm that overexpressing TFEB itself does not induce rapid upregulation of KC markers in vivo nor stimulate the proliferation of remaining KCs. Instead, TFEB-overexpression in KCs promotes the survival of bona fide KCs during MASLD. We discovered that TFEB induction in macrophages led to upregulation of pro-survival BCL family members, and confer protection from necroptosis and ferroptosis. KCs isolated from diet-fed KCTfeb mice also had reduced levels of oxidized lipids, which promote ferroptosis. In conclusion, TFEB induction contributes to KC survival in MASLD and reduces hepatic lipid load by re-programming lysosomal handling of lipids in KCs.

Graduate publications
Han J, Gallerand A, Erlich EC, Helmink BA, Mair I, Li X, Eckhouse SR, Dimou FM, Shakhsheer BA, Phelps HM, Chan MM, Mintz RL, Lee DD, Schilling JD, Finlay CM, Allen JE, Jakubzick CV, Else KJ, Onufer EJ, Zhang N, Randolph GJ. 2024 Human serous cavity macrophages and dendritic cells possess counterparts in the mouse with a distinct distribution between species. Nat Immunol, 25(1):155-65. PMCID: PMC10990619

Chan MM, He L, Finck BN, Schilling JD, Daemen S. 2024 Cutting Edge: Hepatic Stellate Cells Drive the Phenotype of Monocyte-derived Macrophages to Regulate Liver Fibrosis in Metabolic Dysfunction-associated Steatohepatitis. J Immunol, 13(3):251-56. PMCID: PMC11254326

Chan MM, Daemen S, Beals JW, Terekhova M, Yang BQ, Fu CF, He L, Park AC, Smith GI, Razani B, Byrnes K, Beatty WL, Eckhouse SR, Eagon JC, Ferguson D, Finck BN, Klein S, Artyomov MN, Schilling JD. 2023 Steatosis drives monocyte-derived macrophage accumulation in human metabolic dysfunction-associated fatty liver disease. JHEP Rep, 5(11):100877. PMCID: PMC10585307

Borcherding N, Jia W, Giwa R, Field RL, Moley JR, Kopecky BJ, Chan MM, Yang BQ, Sabio JM, Walker EC, Osorio O, Bredemeyer AL, Pietka T, Alexander-Brett J, Morley SC, Artyomov MN, Abumrad NA, Schilling J, Lavine K, Crewe C, Brestoff JR. 2022 Dietary lipids inhibit mitochondria transfer to macrophages to divert adipocyte-derived mitochondria into the blood. Cell Metab, 34(10):1499-1513. PMCID: PMC9547954

Daemen S, Gainullina A, Kalugotla G, He L, Chan MM, Beals JW, Liss KH, Klein S, Feldstein AE, Finck BN, Artyomov MN, Schilling JD. 2021 Dynamic Shifts in the Composition of Resident and Recruited Macrophages Influence Tissue Remodeling in NASH. Cell Rep, 34(2):108626. PMCID: PMC7877246

Daemen S, Chan MM, Schilling JD.. 2021 Comprehensive analysis of liver macrophage composition by flow cytometry and immunofluorescence in murine NASH. STAR Protocols, 2(2):100511. PMCID: PMC8102804