De Novo Fatty Acid Synthesis During Mycobacterial Infection Is a Prerequisite for the Function of Highly Proliferative T Cells, But Not for Dendritic Cells or Macrophages.

Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis, is able to efficiently manipulate the host immune system establishing chronic infection, yet the underlying mechanisms of immune evasion are not fully understood. Evidence suggests that this pathogen interferes with host cell lipid metabolism to ensure its persistence. Fatty acid metabolism is regulated by acetyl-CoA carboxylase (ACC) 1 and 2; both isoforms catalyze the conversion of acetyl-CoA into malonyl-CoA, but have distinct roles. ACC1 is located in the cytosol, where it regulates de novo fatty acid synthesis (FAS), while ACC2 is associated with the outer mitochondrial membrane, regulating fatty acid oxidation (FAO). In macrophages, mycobacteria induce metabolic changes that lead to the cytosolic accumulation of lipids. This reprogramming impairs macrophage activation and contributes to chronic infection. In dendritic cells (DCs), FAS has been suggested to underlie optimal cytokine production and antigen presentation, but little is known about the metabolic changes occurring in DCs upon mycobacterial infection and how they affect the outcome of the immune response. We therefore determined the role of fatty acid metabolism in myeloid cells and T cells during Mycobacterium bovis BCG or Mtb infection, using novel genetic mouse models that allow cell-specific deletion of ACC1 and ACC2 in DCs, macrophages, or T cells. Our results demonstrate that de novo FAS is induced in DCs and macrophages upon M. bovis BCG infection. However, ACC1 expression in DCs and macrophages is not required to control mycobacteria. Similarly, absence of ACC2 did not influence the ability of DCs and macrophages to cope with infection. Furthermore, deletion of ACC1 in DCs or macrophages had no effect on systemic pro-inflammatory cytokine production or T cell priming, suggesting that FAS is dispensable for an intact innate response against mycobacteria. In contrast, mice with a deletion of ACC1 specifically in T cells fail to generate efficient T helper 1 responses and succumb early to Mtb infection. In summary, our results reveal ACC1-dependent FAS as a crucial mechanism in T cells, but not DCs or macrophages, to fight against mycobacterial infection.

5-Aminoimidazole-4-carboxamide ribonucleoside-mediated adenosine monophosphate-activated protein kinase activation induces protective innate responses in bacterial endophthalmitis.

The retina is considered to be the most metabolically active tissue in the body. However, the link between energy metabolism and retinal inflammation, as incited by microbial infection such as endophthalmitis, remains unexplored. In this study, using a mouse model of Staphylococcus aureus (SA) endophthalmitis, we demonstrate that the activity (phosphorylation) of 5' adenosine monophosphate-activated protein kinase alpha (AMPKα), a cellular energy sensor and its endogenous substrate; acetyl-CoA carboxylase is down-regulated in the SA-infected retina. Intravitreal administration of an AMPK activator, 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), restored AMPKα and acetyl-CoA carboxylase phosphorylation. AICAR treatment reduced both the bacterial burden and intraocular inflammation in SA-infected eyes by inhibiting NF-kB and MAP kinases (p38 and JNK) signalling. The anti-inflammatory effects of AICAR were diminished in eyes pretreated with AMPK inhibitor, Compound C. The bioenergetics (Seahorse) analysis of SA-infected microglia and bone marrow-derived macrophages revealed an increase in glycolysis, which was reinstated by AICAR treatment. AICAR also reduced the expression of SA-induced glycolytic genes, including hexokinase 2 and glucose transporter 1 in microglia, bone marrow-derived macrophages and the mouse retina. Interestingly, AICAR treatment enhanced the bacterial phagocytic and intracellular killing activities of cultured microglia, macrophages and neutrophils. Furthermore, AMPKα1 global knockout mice exhibited increased susceptibility towards SA endophthalmitis, as evidenced by increased inflammatory mediators and bacterial burden and reduced retinal function. Together, these findings provide the first evidence that AMPK activation promotes retinal innate defence in endophthalmitis by modulating energy metabolism and that it can be targeted therapeutically to treat ocular infections.

Regulator of fatty acid metabolism, acetyl coenzyme a carboxylase 1, controls T cell immunity.

Fatty acids (FAs) are essential constituents of cell membranes, signaling molecules, and bioenergetic substrates. Because CD8(+) T cells undergo both functional and metabolic changes during activation and differentiation, dynamic changes in FA metabolism also occur. However, the contributions of de novo lipogenesis to acquisition and maintenance of CD8(+) T cell function are unclear. In this article, we demonstrate the role of FA synthesis in CD8(+) T cell immunity. T cell-specific deletion of acetyl coenzyme A carboxylase 1 (ACC1), an enzyme that catalyzes conversion of acetyl coenzyme A to malonyl coenzyme A, a carbon donor for long-chain FA synthesis, resulted in impaired peripheral persistence and homeostatic proliferation of CD8(+) T cells in naive mice. Loss of ACC1 did not compromise effector CD8(+) T cell differentiation upon listeria infection but did result in a severe defect in Ag-specific CD8(+) T cell accumulation because of increased death of proliferating cells. Furthermore, in vitro mitogenic stimulation demonstrated that defective blasting and survival of ACC1-deficient CD8(+) T cells could be rescued by provision of exogenous FA. These results suggest an essential role for ACC1-mediated de novo lipogenesis as a regulator of CD8(+) T cell expansion, and may provide insights for therapeutic targets for interventions in autoimmune diseases, cancer, and chronic infections.

Cell cycle regulation of the BRCA1/acetyl-CoA-carboxylase complex.

Germ-line alterations in BRCA1 are associated with an increased susceptibility to breast and ovarian cancer. The BRCA1 protein has been implicated in multiple cellular functions. We have recently demonstrated that BRCA1 reduces acetyl-CoA-carboxylase alpha (ACCA) activity through its phospho-dependent binding to ACCA, and further established that the phosphorylation of the Ser1263 of ACCA is required for this interaction. Here, to gain more insight into the cellular conditions that trigger the BRCA1/ACCA interaction, we designed an anti-pSer1263 antibody and demonstrated that the Ser1263 of ACCA is phosphorylated in vivo, in a cell cycle-dependent manner. We further showed that the interaction between BRCA1 and ACCA is regulated during cell cycle progression. Taken together, our findings reveal a novel mechanism of regulation of ACCA distinct from the previously described phosphorylation of Ser79, and provide new insights into the control of lipogenesis through the cell cycle.

The pea chloroplast membrane-associated protein, IEP96, is a subunit of acetyl-CoA carboxylase.

Two forms of acetyl-CoA carboxylase (ACCase) have been characterized in pea (Pisum sativum L.) leaves; a heteromeric chloroplast enzyme and a homomeric, presumably cytosolic enzyme. The biotin carboxylase (BC), biotin carboxyl carrier protein (BCCP), and beta-carboxyltransferase (CT) subunits of the plastidial-ACCase have recently been characterized and cloned. To further characterize the carboxyltransferase, an improved assay for CT was developed and used to follow its partial purification. CT activity co-purifies with ACCase activity during gel permeation chromatography. However, upon anion-exchange chromatography or native PAGE, CT separates from the BC and BCCP subunits of plastidial-ACCase and ACCase activity is lost. In addition, it is demonstrated that a previously sequenced pea chloroplast cDNA of unknown function (IEP96) with a predicted molecular weight of 91 kDa encodes the alpha-CT subunit of the MS-ACCase. Antibodies raised against the first 404 amino acids of IEP96 protein detected a polypeptide with molecular weight of 91 kDa that co-eluted during gel permeation chromatography with plastidial CT and ACCase activities. These antibodies also immunoprecipitated the activities of both ACCase and CT with the concomitant precipitation of the beta-CT subunit. Furthermore, antibodies against beta-CT immunoprecipitated the IEP96 protein. Two-dimensional PAGE and DEAE purification of ACCase protein demonstrated that the beta-CT forms a tight association with the IEP96 protein. Pea leaf was fractionated into soluble and membrane fractions and the alpha-CT subunit was primarily associated with the membrane fraction. Together, these data demonstrate that IEP96 is the alpha-CT subunit of pea chloroplast ACCase.

Acetyl-coenzyme-A carboxylase from rat liver. Subunit structure and proteolytic modification.

The subunit structure of rat liver acetyl-coenzyme-A carboxylase has been studied by polyacrylamide gel electrophoresis in the presence of dodecylsulfate. A number of individual preparations of the enzyme purified by the same procedures exhibited three different types of electrophoretic patterns as follows: first, a single slow-moving protein bands (Mr 230000); secondly, two adjacent fast-moving protein band (M4 124000 and 118 000); finally, all three protein bands. With the use of the [14C]biotin-labelled enzyme, the biotinyl prosthetic group was shown to be associated with the polypeptide of 230000 Mr as well as with that of 124000 Mr, but not with the polypeptide of 118000 Mr. Studies were next made with the labelled enzyme to examine the possibility that the two light polypeptides might have been formed by proteolytic modification of the heavy polypeptide during the procedures used for the purification of the enzyme. Treatment of the enzyme with trypsin or chymotrypsin resulted in cleavage of the heavy polypeptide into two nonidentical polypeptides with molecular weights of approximately 120000. Incubation of the enzyme with proteases derived from rat liver converted the heavy polypeptide into lighter polypeptides of 80000-130000 Mr. Acetyl-CoA carboxylase isolated from crude rat liver extracts by means of immunoprecipitation with specific antibody invariably showed only the heavy polypeptide. The biotin content of the enzyme was found to be 1 mol per 237000 g protein. These results indicate that rat liver acetyl-CoA carboxylase, unlike bacterial and plant biotin enzymes, has only one kind of subunit, which has a molecular weight of 230000 and contains one molecular of biotin. Thus, the mammalian enzyme exhibits a highly integrated subunit structure.