Toshiya Atsumi

The proinflammatory mediator macrophage migration inhibitory factor induces glucose catabolism in muscle

Severe infection or tissue invasion can provoke a catabolic response, leading to severe metabolic derangement, cachexia, and even death. Macrophage migration inhibitory factor (MIF) is an important regulator of the host response to infection. Released by various immune cells and by the anterior pituitary gland, MIF plays a critical role in the systemic inflammatory response by counterregulating the inhibitory effect of glucocorticoids on immune-cell activation and proinflammatory cytokine production. We describe herein an unexpected role for MIF in the regulation of glycolysis. The addition of MIF to differentiated L6 rat myotubes increased synthesis of fructose 2,6-bisphosphate (F2,6BP), a positive allosteric regulator of glycolysis. Increased expression of the enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2) enhanced F2,6BP production and, consequently, cellular lactate production. The catabolic effect of TNF-alpha on myotubes was mediated by MIF, which served as an autocrine stimulus for F2, 6BP production. TNF-alpha administered to mice decreased serum glucose levels and increased muscle F2,6BP levels; pretreatment with a neutralizing anti-MIF mAb completely inhibited these effects. Anti-MIF also prevented hypoglycemia and increased muscle F2,6BP levels in TNF-alpha-knockout mice that were administered LPS, supporting the intrinsic contribution of MIF to these inflammation-induced metabolic changes. Taken together with the recent finding that MIF is a positive, autocrine stimulator of insulin release, these data suggest an important role for MIF in the control of host glucose disposal and carbohydrate metabolism.

Phosphorylation of the 6-Phosphofructo-2-Kinase/Fructose 2,6-Bisphosphatase/PFKFB3 Family of Glycolytic Regulators in Human Cancer

Purpose: Fructose 2,6-bisphosphate (F2,6BP) is a potent activator of phosphofructokinase, which is a rate-limiting enzyme of glycolysis. The concentration of F2,6BP depends on the activity of the bifunctional enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase). Four genes encoding PFK-2/FBPase have been identified and termed PFKFB1 to PFKFB4. PFKFB3 protein is expressed in high levels in human tumors in situ. The purpose of this study was to determine the role of functional interactions between the phosphorylation of PFKFB3 and activated glycolysis in human cancer cells. Experimental Design: cDNA from several human tumor cell lines and human colon carcinoma were analyzed by reverse transcription-PCR to identify different splicing variants of PFKFB3. The effect of phosphorylation of Ser461 was studied by recombinantly replacing this residue with glutamate (PFKFB3S461E). The phosphorylation of PFKFB3 protein in human cancer was determined by immunostaining using an anti-phospho-PFK-2(PFKFB3) antibody. Results: Two splicing variants of PFKFB3 are expressed in human cancer cell lines: PFKFB3-ACG and PFKFB3-AG. Quantitative, real-time PCR analysis confirmed the overexpression of PFKFB3 mRNA in colon carcinoma, with the dominant variant being the PFKFB3-ACG isoform that contains a phosphorylation site at Ser461. Forced expression of PFKFB3-ACG in COS-7 cells resulted in enhanced glycolysis. Introduction of PFKFB3-ACGS461E into COS-7 cells led to increased the lactate production and cell proliferation. Highly phosphorylated PFKFB3 protein was found in human tumor cells, vascular endothelial cells, and smooth muscle cells, as determined by immunostaining with an anti-phospho-PFK-2(PFKFB3) antibody. Conclusions: These findings support a potential role for the phosphorylation of PFKFB3 protein in the progression of cancer and angiogenesis.

The Proinflammatory Cytokine Macrophage Migration Inhibitory Factor Regulates Glucose Metabolism during Systemic Inflammation

Inflammation provokes significant abnormalities in host metabolism that result from the systemic release of cytokines. An early response of the host is hyperglycemia and resistance to the action of insulin, which progresses over time to increased glucose uptake in peripheral tissue. Although the cytokine TNF-α has been shown to exert certain catabolic effects, recent studies suggest that the metabolic actions of TNF-α occur by the downstream regulation of additional mediators, such as macrophage migration inhibitory factor (MIF). We investigated the glycemic responses of endotoxemic mice genetically deficient in MIF (MIF−/−). In contrast to wild-type mice, MIF−/− mice exhibit normal blood glucose and lactate responses following the administration of endotoxin, or TNF-α. MIF−/− mice also show markedly increased glucose uptake into white adipose tissue in vivo in the endotoxemic state. Treatment of adipocytes with MIF, or anti-MIF mAb, modulates insulin-mediated glucose transport and insulin receptor signal transduction; these effects include the phosphorylation of insulin receptor substrate-1, its association with the p85 regulatory subunit of PI3K, and the downstream phosphorylation of Akt. Genetic MIF deficiency also promotes adipogenesis, which is in accord with a downstream role for MIF in the action of TNF-α. These studies support an important role for MIF in host glucose metabolism during sepsis.

Immunochemical Detection of Advanced Glycation End Products in Renal Cortex From STZ-Induced Diabetic Rat

To reassess the accumulation of advanced glycation end products in diabetic renal cortex, we used a newly developed enzyme-linked immunosorbent assay to measure AGEs in renal cortex from STZ-induced diabetic and age-matched control rats. Kidneys and aortas were obtained from rats after 5 and 20 wk of STZ injection. At 5 wk of diabetes, the mean AGE content in collagenase-digested materials of renal cortex was > 16-fold higher in diabetic animals compared with controls (1044.4 ± 151.8 vs. 64.3 ± 5.7 arbitrary units, P < 0.01). At 20 wk of diabetes, it was > 45-fold higher in diabetic compared with control animals (3841.0 ± 1077.3 vs. 83.8 ± 12.8 AUs, P < 0.01). These increases were surprisingly large compared with the < 1.5-fold increase in the fluorescence levels both after 5 and 20 wk of diabetes. In control animals, neither the AGE content nor the fluorescence level increased during this period. Moreover, at 20 wk of diabetes, the AGE content was 39-fold higher in renal cortex compared with aorta. This study provided the first immunochemical evidence that collagenase-digested materials of renal cortex, as well as aorta, contained AGE products and that these products were present in much higher levels in diabetic animals than in control animals. With duration of diabetes, the AGE contents increased significantly both in renal cortex and aorta. The excessive accumulation of AGEs was most apparent in the diabetic kidney. These findings suggest that the actual level of AGEs, in particular, in diabetic renal cortex is much higher than previously anticipated, and a newly developed enzyme-linked immunosorbent assay may be a powerful tool for investigating the role of the advanced Maillard reaction in the development of diabetic nephropathy.

Antiphospholipid antibody associated thrombocytopenia and the paradoxical risk of thrombosis

The pathogenesis of thrombocytopenia in patients with antiphospholipid syndrome (APS) is heterogeneous. Patients with antiphospholipid antibodies (aPL) and thrombocytopenia in the absence of clinical manifestations of APS will be diagnosed and treated as idiopathic thrombocytopenic purpura. However, the presence of aPL places those individuals at particular risk for developing both bleeding and thrombotic complications. Therefore, we propose the inclusion of such patients in the subgroup ‘aPL-associated thrombocytopenia’. More attention should be devoted to this subgroup of patients to elucidate the role of aPL in the development of thrombocytopenia and to facilitate the adequate monitoring of its potential thrombotic risk.

A rare case of Gitelman’s syndrome presenting with hypocalcemia and osteopenia

Gitelman’s syndrome (GS), an autosomal recessive disorder caused by a defect of the thiazide-sensitive NaCl cotransporter (TSC) at the distal tubule, is characterized by hyperreninemic hyperaldosteronism with normal or low blood pressure, hypokalemia, metabolic alkalosis, hypomagnesemia and hypocalciuria. An 18-yr-old Japanese man was admitted to our hospital with a history of muscle weakness and transient tetanic episodes. He showed hypocalcemia in addition to hypokalemia, severe hypomagnesemia, hypocalciuria and hyperreninemic hyperaldosteronism with normal blood pressure. Furthermore, bone mineral density at the lumbar spine revealed osteopenia. A diagnosis of GS was made on the basis of clinical features, laboratory data and renal function test. The electrolyte imbalance was corrected and bone mineral density was slightly increased with chronic treatment of magnesium and potassium salts. Genetic analysis revealed that TSC gene of the patient has a heterozygous C to A nucleotide substitution at position 545 in exon 4, which causes a threonine (Thr) to lysine (Lys) substitution at position 180. This is a rare case of GS with hypocalcemia and osteopenia which could be caused by severe hypomagnesemia.

Unilateral adrenalectomy improves insulin resistance and polycystic ovaries in a middle-aged woman with virilizing adrenocortical adenoma complicated with Cushing’s syndrome

A benign virilizing adrenal adenoma is rare among adrenal neoplasms in middle-aged women. A 39-yr-old Japanese woman who presented with hirsutism, obesity, diabetes mellitus and hypertension was admitted. Plasma concentrations of testosterone and DHEAS were high. While the basal level of plasma ACTH was suppressed, serum cortisol level was high and its circadian rhythm was absent. Serum cortisol level was not suppressed with the low- and high-dose overnight dexamethasone suppression test. Abdominal computed tomography showed a left adrenal tumor, and an adrenocortical scintigraphy revealed uptake of the tracer on the left side. Polycystic ovaries were also found and bone mineral density revealed osteoporosis. Histopathological features of resected adrenal tumor were consistent with those of adrenocortical adenoma. Immunoreactivity of all the steroidogenic enzymes was apparent in the tumor cells and particularly dehydroepiandrosterone sulfotransferase (DHEA-ST) immunoreactivity was markedly expressed. Cortical atrophy and reduced expression of DHEA-ST were detected in the cortex of the adjacent non-neoplastic adrenal gland. Plasma testosterone, DHEAS and cortisol levels returned to normal after surgery, concomitantly with the disappearance of polycystic ovaries. This is a very rare case of virilizing adrenocortical adenoma complicated with Cushing’s syndrome (CS).

A case of reversed pituitary dysfunction with intrasellar mass

Hypopituitarism can be caused by tumor, inflammation, granuloma and injuries. Once pituitary function is disturbed, hormone replacement therapy is necessary for the remaining life span in most cases. We have experienced a rare case of a unique intrasellar mass associated with pituitary dysfunction in which both spontaneously reversed. A 61-yr-old woman developed hypoadrenalism and central diabetes insipidus (cDI). Magnetic resonance (MR) imaging revealed a lobular, strong hypointense lesion with spotty signal in the middle of the hypophysis. This spotty lesion showed isointensity on T1- and high-intensity on T2-weighted MR images. The spotty signal as well as the normal pituitary lobe were enhanced by the administration of gadolinium. As replacement therapies for hypoadrenalism and cDI, 10 mg of hydrocortisone and 2.5 μg of desmopressin acetate were prescribed. Three months later, slight shrinkage of intrasellar mass and spontaneous improvement of pituitary functions were found. Hydrocortisone was then discontinued. Furthermore, because polyuria and polydipsia were improved nine months later, desmopressin acetate was stopped. Currently, the intrasellar mass continues to shrink, and the patient shows no symptoms without medication. Based upon the unique features of MR images, we suspect that the origin of the mass is an intrasellar hemangioma.

Antiphospholipid antibodies and cell activation: crucial role of p38 MAPK pathway

Antiphospholipid antibodies (aPL) are a large and heterogeneous family of circulating immunoglobulins found in a wide range of infectious and autoimmune diseases. Since the early 1980s, the interest on these antibodies has increased exponentially due to their associations with thrombotic events and pregnancy morbidity in the antiphospholipid syndrome (APS). Intensive research works, performed in the last decade, have greatly advanced our knowledge of the mechanisms that explain why these antibodies may play a direct role in clot formation. Nowadays, it is recognized worldwide that many of the autoantibodies associated with the APS are directed against phospholipid-binding plasma proteins such as b2glycoprotein I (b2GPI) and prothrombin or phospholipid-protein complexes, expressed on, or bound to, the surface of vascular endothelial cells, platelets or other cells. One of the key events to explain the pathophysiology of thrombosis in patients with APS is the pro-coagulant cell activation mediated by aPL, accompanied with tissue factor (TF) expression and TF pathway upregulation. TF is the major initiator of the extrinsic coagulation system, functioning in coagulation by serving as the protein cofactor for the activated factor VII (FVIIa). Induced TF forms a complex with FVIIa that triggers blood clotting cascade by activating factors IX and X, leading to thrombin generation. In normal conditions, TF is not expressed on intravascular cells but it can be induced under some stimuli such as lipopolysaccharide, tumour necrosis factor a (TNFa), interleukin-1 (IL-1) and shear stress. Experimental data showed that plasma of patients with APS or purified aPL can activate endothelial cells or monocytes leading to the expression of adhesion molecules, TF and other pro-coagulant substances. Furthermore, upregulation of TF in patients with APS has been demonstrated, and we reported that antibodies against b2GPI induce the expression and activity of TF in vitro. In addition, the binding of aPL to platelets, once stimulated, causes activation and aggregation of platelets and thrombosis. – 14 Overall, the effect of aPL in pro-coagulant cell activation has been evident and recent research works have focused on the intracellular events involved in the aPL-mediated cell activation, trying to clarify the signal transduction mechanism implicated in the induction of procoagulants substances by aPL. As a result of these investigations, two groups independently reported that adaptor molecule myeloid differentiation protein (MyD88)-dependent signalling pathway is involved in endothelial cell activation by aPL. Several groups demonstrated the involvement of nuclear factor kappa B (NFkB) in endothelial cell activation. – 19 IgG purified from APS patients induced the nuclear translocation of NFkB leading to the transcription of genes with NFkB-responsive element in their promoter. This nuclear translocation of NFkB, at least in part, mediates the increased expression of TF and adhesion molecules on cell surface. NFkB blocking by statins inhibited endothelial cell activation mediated by anti-b2GPI antibodies and provide an additional use of statins as a therapeutic tool for the treatment of APS. Anti-b2GPI antibodies activate endothelial cell in a b2GPI-dependent manner, and this cell activation might require an interaction between b2GPI and a specific endothelial cell receptor. It has been shown that annexin II, an endothelial cell receptor for tissue plasminogen activator and plasminogen, behaved as a receptor for b2GPI. However it is still unclear whether such a putative receptor is actually involved in cell activation because annexin II does not span the cell membrane and the presence of an unknown ‘adaptor’ was suggested to be necessary to induce activation. Raschi et al. suggested a possible association between b2GPI and members of the Toll-like receptors (TLRs) family. They speculated that antib2GPI antibodies might cross-link b2GPI molecules likely together with TLRs, eventually favouring the receptor polymerization and the signalling cascade activation. Furthermore, Lutters et al. showed that dimeric b2GPI can interact with apolipoprotein E receptor 2 (apoER2), a member of the low density lipoprotein receptor family present in platelets and that dimeric b2GPI induces increased platelet adhesion and thrombus formation, which depend on the activation of apoER2. The p38 mitogen activated protein kinase (MAPK) pathway of cell activation has become an important focus of interest and it has been implicated in the Lupus (2005) 14, 799–801