Metabolic Control of T cell responses by HDAC3

Abstract After activation, CD4+ T cells undergo metabolic modifications in order to orchestrate successful immune responses. In particular, naïve T cells shift to a more glycolysis-heavy metabolic program that produces the necessary metabolites for growth, division, and exertion of effector function. Histone Deacetylase 3 (HDAC3) has been shown to epigenetically regulate many T cell fate decisions and is also capable of post-translationally modifying non-histone proteins. Deletion of HDAC3 in mature CD4+ T cells using a distal Lck-Cre HDAC3 cKO mouse revealed a reduction in differentiated T-helper cell populations in vivo. In contrast, in vitro differentiation of HDAC3-deficient CD4+ T cells occurred normally, however, the numbers of T cells present within each culture was greatly diminished. CD3/CD28-stimulated HDAC3-deficient cells exhibited poor proliferation with decreased blastogenesis, decreased CD25 expression, and decreased IL-2 production. Signaling downstream of TCR is disrupted in the HDAC3-deficient T cells. HDAC3-deficient CD4+ T cells have an overabundance of Foxo1 protein, and diminished signaling downstream of mTOR, including reduced phosphorylation of Ribosomal Protein S6, and decreased expression of Egr2. Key transporters involved in cholesterol efflux, ABCA1 and ABCG1, were upregulated in HDAC3-deficient CD4+ T cells. Strikingly, the proliferation and blasting defects of HDAC3-deficient CD4+ T cells are restored with the addition of exogenous cholesterol, but the signaling defects remain. Thus, the failure of HDAC3-deficient CD4+ T cells to proliferate is due to alterations in cholesterol homeostasis.