Summary How cells adapt metabolism to meet demands is an active area of interest across biology. Among a broad range of functions, the polyamine spermidine is needed to hypusinate the translation factor eukaryotic initiation factor 5A (eIF5A). We show here that hypusinated eIF5A (eIF5A H ) promotes the efficient expression of a subset of mitochondrial proteins involved in the TCA cycle and oxidative phosphorylation (OXPHOS). Several of these proteins have mitochondrial targeting sequences (MTSs) that in part confer an increased dependency on eIF5AH. In macrophages, metabolic switching between OXPHOS and glycolysis supports divergent functional fates stimulated by activation signals. In these cells, hypusination of eIF5A appears to be dynamically regulated after activation. Using in vivo and in vitro models, we show that acute inhibition of this pathway blunts OXPHOS-dependent alternative activation, while leaving aerobic glycolysis-dependent classical activation intact. These results might have implications for therapeutically controlling macrophage activation by targeting the polyamine-eIF5A-hypusine axis.

Highlights d FABP5 inhibition in Tregs alters mitochondria and enhances suppression d Disrupting FABP5 in Tregs results in mtDNA release and type I IFN signaling d cGAS/-STING-dependent type I IFN signals promote Treg IL-10 production d Tumor Tregs exhibit mitochondrial alterations and a type I IFN gene signature

The H2.0-like homeobox transcription factor (HLX) regulates hematopoietic differentiation and is overexpressed in Acute Myeloid Leukemia (AML), but the mechanisms underlying these functions remain unclear. We demonstrate here that HLX overexpression leads to a myeloid differentiation block both in zebrafish and human hematopoietic stem and progenitor cells (HSPCs). We show that HLX overexpression leads to downregulation of genes encoding electron transport chain (ETC) components and upregulation of PPARδ gene expression in zebrafish and human HSPCs. HLX overexpression also results in AMPK activation. Pharmacological modulation of PPARδ signaling relieves the HLX-induced myeloid differentiation block and rescues HSPC loss upon HLX knockdown but it has no effect on AML cell lines. In contrast, AMPK inhibition results in reduced viability of AML cell lines, but minimally affects myeloid progenitors. This newly described role of HLX in regulating the metabolic state of hematopoietic cells may have important therapeutic implications.

Polyamine synthesis represents one of the most profound metabolic changes during T cell activation, but the biological implications of this are scarcely known. Here, we show that polyamine metabolism is a fundamental process governing the ability of CD4 + helper T cells (T H ) to polarize into different functional fates. Deficiency in ornithine decarboxylase, a crucial enzyme for polyamine synthesis, results in a severe failure of CD4 + T cells to adopt correct subset specification, underscored by ectopic expression of multiple cytokines and lineage-defining transcription factors across T H cell subsets. Polyamines control T H differentiation by providing substrates for deoxyhypusine synthase, which synthesizes the amino acid hypusine, and mice in which T cells are deficient for hypusine develop severe intestinal inflammatory disease. Polyamine-hypusine deficiency caused widespread epigenetic remodeling driven by alterations in histone acetylation and a re-wired tricarboxylic acid (TCA) cycle. Thus, polyamine metabolism is critical for maintaining the epigenome to focus T H cell subset fidelity. ll

Purpose: The prognosis for patients with glioblastoma multiforme (GBM) remains extremely poor despite recent treatment advances. There is an urgent need to develop novel therapies for this disease.Experimental Design: We used the implantable GL261 murine glioma model to investigate the therapeutic potential of a vaccine consisting of intravenous injection of irradiated whole tumor cells pulsed with the immuno-adjuvant a-galactosylceramide (a-GalCer).Results: Vaccine treatment alone was highly effective in a prophylactic setting. In a more stringent therapeutic setting, administration of one dose of vaccine combined with depletion of regulatory T cells (Treg) resulted in 43% long-term survival and the disappearance of mass lesions detected by MRI. Mechanistically, the a-GalCer component was shown to act by stimulating "invariant" natural killer-like T cells (iNKT cells) in a CD1d-restricted manner, which in turn supported the development of a CD4 þ T-cell-mediated adaptive immune response. Pulsing a-GalCer onto tumor cells avoided the profound iNKT cell anergy induced by free a-GalCer. To investigate the potential for clinical application of this vaccine, the number and function of iNKT cells was assessed in patients with GBM and shown to be similar to agematched healthy volunteers. Furthermore, irradiated GBM tumor cells pulsed with a-GalCer were able to stimulate iNKT cells and augment a T-cell response in vitro.Conclusions: Injection of irradiated tumor cells loaded with a-GalCer is a simple procedure that could provide effective immunotherapy for patients with high-grade glioma.