Stanley Ching-Cheng Huang

Network Integration of Parallel Metabolic and Transcriptional Data Reveals Metabolic Modules that Regulate Macrophage Polarization

Macrophage polarization involves a coordinated metabolic and transcriptional rewiring that is only partially understood. By using an integrated high-throughput transcriptional-metabolic profiling and analysis pipeline, we characterized systemic changes during murine macrophage M1 and M2 polarization. M2 polarization was found to activate glutamine catabolism and UDP-GlcNAc-associated modules. Correspondingly, glutamine deprivation or inhibition of N-glycosylation decreased M2 polarization and production of chemokine CCL22. In M1 macrophages, we identified a metabolic break at Idh, the enzyme that converts isocitrate to alpha-ketoglutarate, providing mechanistic explanation for TCA cycle fragmentation. (13)C-tracer studies suggested the presence of an active variant of the aspartate-arginosuccinate shunt that compensated for this break. Consistently, inhibition of aspartate-aminotransferase, a key enzyme of the shunt, inhibited nitric oxide and interleukin-6 production in M1 macrophages, while promoting mitochondrial respiration. This systems approach provides a highly integrated picture of the physiological modules supporting macrophage polarization, identifying potential pharmacologic control points for both macrophage phenotypes.

Cell-intrinsic lysosomal lipolysis is essential for alternative activation of macrophages

Alternative (M2) activation of macrophages driven via the α-chain of the receptor for interleukin 4 (IL-4Rα) is important for immunity to parasites, wound healing, the prevention of atherosclerosis and metabolic homeostasis. M2 polarization is dependent on fatty acid oxidation (FAO), but the source of the fatty acids that support this metabolic program has not been clear. We found that the uptake of triacylglycerol substrates via the scavenger receptor CD36 and their subsequent lipolysis by lysosomal acid lipase (LAL) was important for the engagement of elevated oxidative phosphorylation, enhanced spare respiratory capacity (SRC), prolonged survival and expression of genes that together define M2 activation. Inhibition of lipolysis suppressed M2 activation during infection with a parasitic helminth and blocked protective responses to this pathogen. Our findings delineate a critical role for cell-intrinsic lysosomal lipolysis in M2 activation.

TLR-driven early glycolytic reprogramming via the kinases TBK1-IKKɛ supports the anabolic demands of dendritic cell activation

The ligation of Toll-like receptors (TLRs) leads to rapid activation of dendritic cells (DCs). However, the metabolic requirements that support this process remain poorly defined. We found that DC glycolytic flux increased within minutes of exposure to TLR agonists and that this served an essential role in supporting the de novo synthesis of fatty acids for the expansion of the endoplasmic reticulum and Golgi required for the production and secretion of proteins that are integral to DC activation. Signaling via the kinases TBK1, IKKɛ and Akt was essential for the TLR-induced increase in glycolysis by promoting the association of the glycolytic enzyme HK-II with mitochondria. In summary, we identified the rapid induction of glycolysis as an integral component of TLR signaling that is essential for the anabolic demands of the activation and function of DCs.

Memory CD8+ T Cells Use Cell-Intrinsic Lipolysis to Support the Metabolic Programming Necessary for Development

Generation of CD8(+) memory T cells requires metabolic reprogramming that is characterized by enhanced mitochondrial fatty-acid oxidation (FAO). However, where the fatty acids (FA) that fuel this process come from remains unclear. While CD8(+) memory T cells engage FAO to a greater extent, we found that they acquired substantially fewer long-chain FA from their external environment than CD8(+) effector T (Teff) cells. Rather than using extracellular FA directly, memory T cells used extracellular glucose to support FAO and oxidative phosphorylation (OXPHOS), suggesting that lipids must be synthesized to generate the substrates needed for FAO. We have demonstrated that memory T cells rely on cell intrinsic expression of the lysosomal hydrolase LAL (lysosomal acid lipase) to mobilize FA for FAO and memory T cell development. Our observations link LAL to metabolic reprogramming in lymphocytes and show that cell intrinsic lipolysis is deterministic for memory T cell fate.

CD8 memory T cells have a bioenergetic advantage that underlies their rapid recall ability

A characteristic of memory T (TM) cells is their ability to mount faster and stronger responses to reinfection than naïve T (TN) cells do in response to an initial infection. However, the mechanisms that allow this rapid recall are not completely understood. We found that CD8 TM cells have more mitochondrial mass than CD8 TN cells and, that upon activation, the resulting secondary effector T (TE) cells proliferate more quickly, produce more cytokines, and maintain greater ATP levels than primary effector T cells. We also found that after activation, TM cells increase oxidative phosphorylation and aerobic glycolysis and sustain this increase to a greater extent than TN cells, suggesting that greater mitochondrial mass in TM cells not only promotes oxidative capacity, but also glycolytic capacity. We show that mitochondrial ATP is essential for the rapid induction of glycolysis in response to activation and the initiation of proliferation of both TN and TM cells. We also found that fatty acid oxidation is needed for TM cells to rapidly respond upon restimulation. Finally, we show that dissociation of the glycolysis enzyme hexokinase from mitochondria impairs proliferation and blocks the rapid induction of glycolysis upon T-cell receptor stimulation in TM cells. Our results demonstrate that greater mitochondrial mass endows TM cells with a bioenergetic advantage that underlies their ability to rapidly recall in response to reinfection.

Helminth infection reactivates latent γ-herpesvirus via cytokine competition at a viral promoter

Parasites make it hard to fight viruses Microbial co-infections challenge the immune system—different pathogens often require different flavors of immune responses for their elimination or containment (see the Perspective by Maizels and Gause). Two teams studied what happens when parasitic worms and viruses infect mice at the same time. Reese et al. found that parasite co-infection woke up a dormant virus. Osborne et al. found that mice already infected with parasitic worms were worse at fighting off viruses. In both cases, worms skewed the immune response so that the immune cells and the molecules they secreted created an environment favorable for the worm at the expense of antiviral immunity. Science, this issue p. 573 and p. 578; see also p. 517 Coinfection with intestinal parasites leads to altered antiviral immunity in mice. Mammals are coinfected by multiple pathogens that interact through unknown mechanisms. We found that helminth infection, characterized by the induction of the cytokine interleukin-4 (IL-4) and the activation of the transcription factor Stat6, reactivated murine γ-herpesvirus infection in vivo. IL-4 promoted viral replication and blocked the antiviral effects of interferon-γ (IFNγ) by inducing Stat6 binding to the promoter for an important viral transcriptional transactivator. IL-4 also reactivated human Kaposi’s sarcoma–associated herpesvirus from latency in cultured cells. Exogenous IL-4 plus blockade of IFNγ reactivated latent murine γ-herpesvirus infection in vivo, suggesting a “two-signal” model for viral reactivation. Thus, chronic herpesvirus infection, a component of the mammalian virome, is regulated by the counterpoised actions of multiple cytokines on viral promoters that have evolved to sense host immune status.

Gata6 regulates aspartoacylase expression in resident peritoneal macrophages and controls their survival

Gata6 regulates differentiation, metabolism and survival of peritoneal macrophages.

Metabolic Reprogramming Mediated by the mTORC2-IRF4 Signaling Axis Is Essential for Macrophage Alternative Activation

Macrophage activation status is intrinsically linked to metabolic remodeling. Macrophages stimulated by interleukin 4 (IL-4) to become alternatively (or, M2) activated increase fatty acid oxidation and oxidative phosphorylation; these metabolic changes are critical for M2 activation. Enhanced glucose utilization is also characteristic of the M2 metabolic signature. Here, we found that increased glucose utilization is essential for M2 activation. Increased glucose metabolism in IL-4-stimulated macrophages required the activation of the mTORC2 pathway, and loss of mTORC2 in macrophages suppressed tumor growth and decreased immunity to a parasitic nematode. Macrophage colony stimulating factor (M-CSF) was implicated as a contributing upstream activator of mTORC2 in a pathway that involved PI3K and AKT. mTORC2 operated in parallel with the IL-4Rα-Stat6 pathway to facilitate increased glycolysis during M2 activation via the induction of the transcription factor IRF4. IRF4 expression required both mTORC2 and Stat6 pathways, providing an underlying mechanism to explain how glucose utilization is increased to support M2 activation.

Th2 responses in schistosomiasis

Schistosomiasis is caused by infection with parasitic flatworms of the genus Schistosoma. It is characterized by the development of strong CD4+ T cell and B cell responses that, during primary infection, fail to eliminate the parasites, but in collaboration with cells of the innate immune system allow survival in the face of ongoing tissue damage caused by the lodging of parasite eggs in the liver and the passage of eggs across the intestinal epithelium. Mounting a tightly controlled Th2 response is key to this outcome, and while this type of response is a risk factor for the development of fibrosis, it also underpins the development of resistance to further infection; as such, understanding how Th2 responses are induced and regulated in schistosomiasis remains a critical area of research.

Migratory CD103+ dendritic cells suppress helminth-driven type 2 immunity through constitutive expression of IL-12

Everts et al. use Batf3−/− mice to examine the role of Batf3-dependent CD8α+ and CD103+ DCs in Th2 immunity in response to helminth infection. Loss of Batf3-dependent DCs resulted in rapid control of normally chronic infection with Heligmosomoides polygyrus, whereas liver fibrosis was exacerbated with Schistosoma mansoni infection. Mechanistically, steady-state IL-12 production by migratory CD103+ DCs was found to antagonize Th2 responses.