Metabolic reprogramming and metabolic dependency in T cells

Abstract

Upon activation, quiescent naive T cells undergo a growth phase followed by massive clonal expansion and differentiation that are essential for appropriate immune defense and regulation. Accumulation of cell biomass during the initial growth and rapid proliferation during the expansion phase is associated with dramatically increased bioenergetic and biosynthetic demands. This not only requires a metabolic rewiring during the transition between resting and activation but also 'addicts' active T cells to certain metabolic pathways in ways that naive and memory T cells are not. We consider such addiction in terms of the biological effects of deprivation of metabolic substrates or inhibition of specific pathways in T cells. In this review, we illustrate the relevant metabolic pathways revealed by recent metabolic flux analysis and discuss the consequences of metabolic intervention on specific metabolic pathways in T lymphocytes.

Fig. 1. Growth and proliferation of T cells following activation

T-cell proliferation (A) and cell size (B) at the indicated time points following activation with anti-CD3 plus anti-CD28 were determined by CFSE dilution and FSC, respectively.

Fig. 2. Increased biosynthesis and energy production upon T-cell activation

Protein and lipid biosynthesis were determined by the incorporation of [¹⁴C]-acetate into the chloroform soluble lipid fraction and [³H]-amino acid mixture into the 10%TCA insoluble protein fraction, respectively (A). The cellular ATP content was determined using a luciferase-based bioluminescence assay (B). Methods are described elsewhere (4). The value in resting T cells was set to 1 in all cases.

Fig. 3. Metabolic reprogramming in activated T cells

The indicated metabolic activities in resting T cells and activated T cells (collected at 24 h after activation) were determined by previously described metabolic flux assays (4).

Fig. 4. The role of c-Myc in activation-induced T-cell metabolic reprogramming

The indicated metabolic activities in WT (black bar) and Myc-KO (white bar) active T cells were determined by tracer-based (red) metabolic assays. See (4) for methods. The value in WT samples was set to 1 in all cases.

Fig. 5. Metabolic targets during T-cell activation

Relevant pharmacological compounds are shown that target the indicated metabolic steps in the metabolic pathways that are either elevated (illustrated in black) or inhibited (illustrated in gray) following T-cell activation.

Fig. 6. Metabolic ‘addiction’ in activated T cells

T-cell proliferation of nutrient starved cells (A) or inhibitor-treated cells (B) was determined by CFSE dilution 48hr after activation. Proliferation is indicated as the percentage of cells with CFSE diluted more than one peak.

Fig. 7. Glutamine is required for sustained expression of c-Myc

Myc expression was determined by Western blot in cells collected at the indicated time following T-cell activation. T cells were activated with anti-CD3 plus anti-CD28 in either complete or glutamine-free medium as described (4).