Background and Aims

Homozygosity for loss-of-function mutations in the ANGPTL3 gene leads to a rare phenotype called familial combined hypolipidemia (FHBL2), characterized by a comprehensive reduction of circulating lipoproteins (VLDL, LDL and HDL) and reduced risk of atherosclerosis. Regulatory T-cells (Treg) play a role as inflammation modulators in the atherosclerotic plaque environment and are highly sensitive to metabolic changes. Indeed, recent evidence has highlighted the central role of cholesterol and the mevalonate pathway in Treg functionality.

The aim of this study was to investigate the possible effect of hypolipidemia due to ANGPTL3 deficiency in modulating Treg distribution and characteristics.

Methods

Peripheral blood mononuclear cells (PBMCs) isolated from 5 FHBL2 subjects and 5 healthy sex and age -matched control subjects were analyzed by flow cytometry (FC). Tregs were gated as CD4⁺/CD127^low/FOXP3⁺ cells. HELIOS staining was used as a stability marker, whereas CD45RA^- was used as a marker of Treg cell activation. Cellular lipid content was analyzed through Bodipy staining.

Results

FHBL2 subjects showed an increased Treg fraction (7.80±1.61% vs 4.52±1.05 %, P<0.01), with a stable effector phenotype. Percentages of circulating Tregs were inversely related to plasma levels of total (r=-0.7212; P=0.023) and LDL cholesterol (r= -0.7818; p=0.0105). Bodipy staining highlighted a significantly lower lipid content in activated Tregs of FHBL2 subjects when compared to healthy controls (2613 average gMFI vs. 2033 average gMFI, P<0.05).

Conclusions

The expansion of Treg population characterized by with reduced lipid content in FHBL2 subjects might potentially contribute to the atheroprotective role of ANGPTL3 deficiency throughout the induction of a regulatory immune profile.