LXR alters CD4⁺ T cell function through direct regulation of glycosphingolipid synthesis

Abstract

Liver X Receptors (LXRs) are important transcriptional regulators of intracellular cholesterol, fatty acid, and phospholipid levels. LXRs can dampen inflammation in macrophages by promoting cholesterol efflux and altering plasma membrane lipid rafts; microdomains enriched for cholesterol and glycosphingolipids that regulate immune-cell signalling. However, little is known about the impact of LXR activators on T cell plasma membrane lipid rafts, which are critical for T-cell antigen receptor (TCR) signalling. Here we show that the LXR synthetic agonist GW3965 significantly increases glycosphingolipid levels and reduces cholesterol and lipid order (stability) in the plasma membrane of human CD4 + T cells. Moreover, the GSL biosynthesis enzyme UGCG was identified as a novel direct target of LXR activation. Importantly, LXR-mediated changes in T cell lipid composition were associated with altered spatiotemporal distribution of lipids and signalling molecules at the immune synapse. Crucially, LXR activation altered the kinetics of proximal TCR-signalling events in activated T cells, reduced T cell proliferation and enhanced the production of IL-2 and IL-4. Thus, LXR activation influences T cell function via alteration of the plasma membrane lipid profile. Finally, the expression of UGCG and other LXR-regulated genes and lipids was significantly dysregulated in T-cells isolated from people with multiple sclerosis. Overall, a novel action of LXR has been characterised that involves modulation of lipid raft-associated cholesterol and glycosphingolipids in CD4 + T-cells, which could be of therapeutic relevance in multiple sclerosis. Keywords liver X receptor -CD4 + T cell -lipid metabolismcholesterolglycosphingolipid-multiple sclerosis 3

Sex differences in autoimmunity could be associated with altered regulatory T cell phenotype and lipoprotein metabolism

“…In support of this, we show that Tregs had no difference in cholesterol expression. However Treg GSL expression and GSL:cholesterol ratio was increased in male compared to female Tregs suggesting the plasma membrane was less ordered and more fluidic in males; this could have functional implications on cell signalling [24,25]. Furthermore, GLUT-1, CD69 and GATA3 expression correlated positively with GSL levels in males but not in females.…”

“…Our previous work shows that T-cell activation and polarisation is influenced by changes in the plasma membrane lipid profile ( Figure 2D [24,25]). The increase in GSL expression in male Tregs was matched by elevated UDP-Glucose Ceramide Glucosyltransferase (UGCG) gene expression, the rate limiting enzyme in the GSL synthesis pathway [26] (Figure 2E).…”

“…Differences in T-cell plasma membrane glycosphingolipids and cholesterol (lipid raft components) are known to influence cell function by altering lipid raft structure and membrane fluidity [24,25,39,40]. Cholesterol enrichment in CD4 T-cells results in increased proliferation and Th1 differentiation [41].…”

Disrupted Lipid Metabolism in Multiple Sclerosis: A Role for Liver X Receptors?

“…Our recent work shows that LXR activation accelerates the conversion of ceramide to hexosylceramide (a key event in glycosphingolipid biosynthesis) in human CD4 + T-cells. LXR stimulation regulated CD4 + T-cell function in part by upregulating plasma membrane glycosphingolipids and reducing cholesterol thereby altering T-cell receptor-mediated signalling (96).…”

The Role of Protein and Lipid Clustering in Lymphocyte Activation

“…Additionally, LXR activation of CD4+ T cells from healthy donors can also upregulate expression of glycosphingolipids leading to reduced membrane order at the TCR immunological synapse. Altered spatiotemporal distribution of lipids promoted Lck recruitment to the immunological synapse and increased phosphorylation of CD3 and LAT, dysregulating effector functions via disruption of ordered lipids (52). Additionally, kinase phosphorylation in SLE patient-derived T cells is restored by statin inhibition of cholesterol synthesis (53).…”