Neutropenia and neutrophil dysfunction are common in many diseases, although their etiology is often unclear. Previous views held that there was a single ER enzyme, glucose-6-phosphatase-α (G6Pase-α), whose activity -limited to the liver, kidney, and intestine -was solely responsible for the final stages of gluconeogenesis and glycogenolysis, in which glucose-6-phosphate (G6P) is hydrolyzed to glucose for release to the blood. Recently, we characterized a second G6Pase activity, that of G6Pase-β (also known as G6PC), which is also capable of hydrolyzing G6P to glucose but is ubiquitously expressed and not implicated in interprandial blood glucose homeostasis. We now report that the absence of G6Pase-β led to neutropenia; defects in neutrophil respiratory burst, chemotaxis, and calcium flux; and increased susceptibility to bacterial infection. Consistent with this, G6Pase-β-deficient (G6pc3 -/-) mice with experimental peritonitis exhibited increased expression of the glucose-regulated proteins upregulated during ER stress in their neutrophils and bone marrow, and the G6pc3 -/-neutrophils exhibited an enhanced rate of apoptosis. Our results define a molecular pathway to neutropenia and neutrophil dysfunction of previously unknown etiology, providing a potential model for the treatment of these conditions.

G6PC3 deficiency, characterized by neutropenia and neutrophil dysfunction, is caused by deficiencies in the endoplasmic reticulum (ER) enzyme glucose-6-phosphatase-␤ (G6Pase-␤ or G6PC3) that converts glucose-6-phosphate (G6P) into glucose, the primary energy source of neutrophils. Enhanced neutrophil ER stress and apoptosis underlie neutropenia in G6PC3 deficiency, but the exact functional role of G6Pase-␤ in neutrophils remains unknown. We hypothesized that the ER recycles G6Pase-␤-generated glucose to the cytoplasm, thus regulating the amount of available cytoplasmic glucose/ G6P in neutrophils. Accordingly, a G6Pase-␤ deficiency would impair glycolysis and hexose monophosphate shunt activities leading to reductions in lactate production, adenosine-5-triphosphate (ATP) production, and reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Using annexin V-depleted neutrophils, we show that glucose transporter-1 translocation is impaired in neutrophils from G6pc3 ؊/؊ mice and G6PC3-deficient patients along with impaired glucose uptake in G6pc3 ؊/؊ neutrophils. Moreover, levels of G6P, lactate, and ATP are markedly lower in murine and human G6PC3-deficient neutrophils, compared with their respective controls. In parallel, the expression of NADPH oxidase subunits and membrane translocation of p47 phox are down-regulated in murine and human G6PC3-deficient neutrophils. The results establish that in nonapoptotic neutrophils, G6Pase-␤ is essential for normal energy homeostasis. A G6Pase-␤ deficiency prevents recycling of ER glucose to the cytoplasm, leading to neutrophil dysfunction. (Blood. 2010;116(15):2783-2792) IntroductionThere are 2 enzymatically active glucose-6-phosphatases (G6Pases), the liver/kidney/intestine-restricted G6Pase-␣ (or G6PC) 1,2 and the ubiquitously expressed G6Pase-␤ (also known as G6PC3). 3,4 Both enzymes are transmembrane endoplasmic reticulum (ER) proteins, with a similar topology, that places their active site on the luminal side of the ER membrane. 5,6 Both have similar kinetic properties 2,4 and hydrolyze glucose-6-phosphate (G6P) to glucose and phosphate when coupled with the ubiquitously expressed G6P transporter (G6PT) that translocates G6P from the cytoplasm into the lumen of the ER. 7,8 The primary role of the G6Pase/G6PT complex is to provide glucose and phosphate to the ER lumen. The G6Pase-␣/G6PT complex maintains blood glucose homeostasis between meals by hydrolyzing G6P to glucose in the terminal step of gluconeogenesis and glycogenolysis. 1,2 Deficiencies in G6Pase-␣ cause glycogen storage disease type Ia (GSD-Ia) and deficiencies in G6PT result in GSD type Ib (GSD-Ib). 1,2,9 Both GSD-Ia and GSD-Ib patients manifest a phenotype of disturbed blood glucose homeostasis with GSD-Ib patients also suffering neutropenia and neutrophil dysfunction, 1,9 reflecting a role of G6PT in tissues beyond the liver and kidney.The biologic roles of G6Pase-␤ and the G6Pase-␤/G6PT complex are poorly defined. Neutrophils, which express both G6Pase-␤ and G6PT, 10 are capable ...

Fatty acids are integral mediators of energy storage, membrane formation and cell signaling. The pathways that orchestrate uptake of fatty acids remain incompletely understood. Expression of the integrin ligand Mfge8 is increased in human obesity and in mice on a high-fat diet, but its role in obesity is unknown. We show here that Mfge8 promotes the absorption of dietary triglycerides and the cellular uptake of fatty acid and that Mfge8-deficient (Mfge8−/−) mice are protected from diet-induced obesity, steatohepatitis and insulin resistance. Mechanistically, we found that Mfge8 coordinates fatty acid uptake through αvβ3 integrin– and αvβ5 integrin–dependent phosphorylation of Akt by phosphatidylinositide-3 kinase and mTOR complex 2, leading to translocation of Cd36 and Fatp1 from cytoplasmic vesicles to the cell surface. Collectively, our results imply a role for Mfge8 in regulating the absorption and storage of dietary fats, as well as in the development of obesity and its complications.

Evidence supporting an early origin of prostate cancer is growing. We demonstrated previously that brief exposure of neonatal rats to estradiol or bisphenol A elevated their risk of developing precancerous lesions in the prostate upon androgen-supported treatment with estradiol as adults. Epigenetic reprogramming may be a mechanism underlying this inductive event in early life, because we observed overexpression of phosphodiesterase 4D variant 4 (Pde4d4) through induction of hypomethylation of its promoter. This epigenetic mark was invisible in early life (postnatal d 10), becoming apparent only after sexual maturation. Here, we asked whether other estrogen-reprogrammable epigenetic marks have similar or different patterns in gene methylation changes throughout life. We found that hypomethylation of the promoter of nucleosome binding protein-1 (Nsbp1), unlike Pde4d4, is an early and permanent epigenetic mark of neonatal exposure to estradiol/bisphenol A that persists throughout life, unaffected by events during adulthood. In contrast, hippocalcin-like 1 (Hpcal1) is a highly plastic epigenetic mark whose hypermethylation depends on both type of early-life exposure and adult-life events. Four of the eight genes involved in DNA methylation/demethylation showed early and persistent overexpression that was not a function of DNA methylation at their promoters, including genes encoding de novo DNA methyltransferases (Dnmt3a/b) and methyl-CpG binding domain proteins (Mbd2/4) that have demethylating activities. Their lifelong aberrant expression implicates them in early-life reprogramming and prostate carcinogenesis during adulthood. We speculate that the distinctly different fate of early-life epigenetic marks during adulthood reflects the complex nature of lifelong editing of early-life epigenetic reprogramming.