Neutrophil stress and apoptosis underlie myeloid dysfunction in glycogen storage disease type Ib

Abstract

Glycogen storage disease type Ib (GSDIb) is caused by a deficiency in the glucose-6-phosphate (G6P) transporter (G6PT) that works with a liver/kidney/ intestine-restricted glucose-6-phosphatase-␣ (G6Pase-␣) to maintain glucose homeostasis between meals. Clinically, GSD-Ib patients manifest disturbed glucose homeostasis and neutrophil dysfunctions but the cause of the latter is unclear. Neutrophils express the ubiquitously expressed G6PT and G6Pase-␤ that together transport G6P into the endoplasmic reticulum (ER) lumen and hydrolyze it to glucose. Because we expected G6PT-deficient neutrophils to be unable to produce endogenous glucose, we hypothesized this would lead to ER stress and increased apoptosis. Using GSD-Ib mice, we showed that GSD-Ib neutrophils exhibited increased production of ER chaperones and oxidative stress, consistent with ER stress, and increased annexin V binding and caspase-3 activation, consistent with an increased rate of apoptosis. Bax activation, mitochondrial release of proapoptotic effectors, and caspase-9 activation demonstrated the involvement of the intrinsic mitochondrial pathway in these processes. The results demonstrate that G6P translocation and hydrolysis are required for normal neutrophil functions and support the hypothesis that neutrophil dysfunction in GSD-Ib is due, at least in part, to ER stress and increased apoptosis. (Blood. 2008;111: 5704-5711) IntroductionGlycogen storage disease type I (GSD-I) is a group of autosomal recessive disorders caused by a deficiency in the glucose-6-phosphatase-␣ (G6Pase-␣) complex that consists of a glucose-6-phosphate transporter (G6PT, also known as SLC37A4) and the hydrolytic enzyme G6Pase-␣ (also known as G6PC). 1,2 Between meals, blood glucose homeostasis is maintained by glucose produced in the terminal steps of gluconeogenesis and glycogenolysis, 1,2 via G6Pase-␣-mediated hydrolysis of glucose-6-phosphate (G6P). Both G6Pase-␣ 3 and G6PT 4 are anchored in the endoplasmic reticulum (ER) by multiple transmembrane domains with G6PT transporting cytoplasmic G6P across the ER membrane to the G6Pase-␣ active site situated inside the ER lumen. 5 A deficiency of G6PT causes GSD type Ib (GSD-Ib, MIM232220 6 ) and a deficiency in G6Pase-␣ causes GSD type Ia (GSD-Ia, MIM232200 6 ). Because G6PT and G6Pase-␣ must be functionally coupled to transport and hydrolyze G6P to glucose, 7,8 a detrimental mutation in either protein prevents the other from functioning efficiently and leads to a common metabolic phenotype of disturbed glucose homeostasis manifested initially by changes in the glucose and lipid profiles of blood, and in the longer term with liver and kidney disease. 1,2 This profile is consistent with the expression pattern of G6Pase-␣, which is restricted primarily to the liver, and kidney, with a low level of expression in the small intestine 9 and G6PT, which is expressed ubiquitously. 10 Although G6Pase-␣ is not expressed in myeloid cells, GSD-Ib patients do manifest symptoms of neutropenia and neutrophil dysfunctions. 1,2,11,12 Their...

G6PT Inhibition Model Using HL-60 Cells and Induction of ROS Production through PKC/NOX2 Activation: Clinical Condition for Elucidation of Glycogen Storage Disease Type Ib

“…8,9) To prepare a model of GSDIb neutrophils, we induced differentiation of HL-60 cells to neutrophils using the culture conditions described above and added the G6PT inhibitor, DIDS, on Day 2 of differentiation. ROS production was significantly higher in cells exposed to DIDS compared with control cells, and increased in a timeand concentration-dependent manner (Figs.…”

“…Previous reports by Kuijpers et al 8) and Kim et al 9) show that oxidative stress and apoptosis are significantly increased in neutrophils of patients with GSD-Ib and G6PT (−/−) mice compared with healthy subjects and G6PT…”

Diagnosis and management of glycogen storage disease type I: a practice guideline of the American College of Medical Genetics and Genomics

“…The mechanism for tumorigenesis remains to be elucidated in GSD Ia, although it could include chronic inflammation. Intriguingly, a subclinical abnormality of neutrophil metabolism was reported in G6Pase (−/−) mice 181 ; furthermore, neutrophil infiltrates were demonstrated in human GSD Ia livers accompanied by elevated interleukin 8, consistent with ongoing inflammation. 182 Progressive nephropathy is associated with proteinuria in adult patients.…”

Molecular mechanisms of neutrophil dysfunction in glycogen storage disease type Ib

“…1,2 Neutropenia arises from disruption of the activity of an analogous G6PT/G6Pase-b complex [5][6][7][8] that also hydrolyzes G6P to glucose. 5 Therefore, in nongluconeogenic cells, such as neutrophils [8][9][10] and macrophages, 11 which lack the G6PT/G6Pase-a complex, the G6PT/G6Pase-b complex plays a critical role in meeting increased demands for glucose. 1,2 This explains why both GSD-Ib 9,12 and G6Pase-b-deficient 6,8,10 patients manifest neutropenia caused by enhanced neutrophil ER stress, oxidative stress, and apoptosis, arising from loss of G6PT/G6Pase-b activity.…”

“…Several observations already supported this hypothesis. G6PT-deficient neutrophils exhibit enhanced oxidative stress and have elevated levels of reactive oxygen species (ROS), 9,12 which can stabilize and induce the HIF-1a protein. 29 Neutrophils constitutively express PPAR-g, 30 and ligand-activation of PPAR-g inhibits their chemotactic responses.…”