Apolipoprotein E and peptide mimetics modulate inflammation by binding the SET protein and activating protein phosphatase 2A.

The molecular mechanism by which apolipoprotein E (apoE) suppresses inflammatory cytokine and NO production is unknown. Using an affinity purification approach, we found that peptide mimetics of apoE, derived from its receptor binding domain residues 130-150, bound to the SET protein, which is a potent physiological inhibitor of protein phosphatase 2A (PP2A). Both holo-apoE protein and apoE-mimetic peptides bound to the C-terminal region of SET, which is then associated with an increase in PP2A-mediated phosphatase activity. As physiological substrates for PP2A, the LPS-induced phosphorylation status of signaling MAPK and Akt kinase is reduced following treatment with apoE-mimetic peptides. On the basis of our previous report, in which apoE-mimetic peptides reduced I-κB kinase and NF-κB activation, we also demonstrate a mechanism for reduced production of inducible NO synthase protein and its NO product. These data provide evidence for a novel molecular mechanism by which apoE and apoE-mimetic peptides antagonize SET, thereby enhancing endogenous PP2A phosphatase activity, which reduces levels of phosphorylated kinases, signaling, and inflammatory response.

Lack of zinc finger protein 521 upregulates dopamine ß-hydroxylase expression in the mouse brain, leading to abnormal behavior.

AIM: Previously, we reported that mice deficient in most of the Zfp521 coding region (Zfp521Δ/Δ mice) displayed abnormal behaviors, including hyperlocomotion and lower anxiety. In this study, we aimed to elucidate the involvement and mechanisms of monoamine variation. MAIN METHODS: First, we compared the levels of dopamine (DA), noradrenaline (NA), and serotonin in the brains of Zfp521Δ/Δ and Zfp521+/+ mice using enzyme-linked immunosorbent assay. Next, we elucidated the mechanisms using quantitative PCR and Western Blotting. Additionally, we administered inhibitory drug to the mice and performed behavioral tests. KEY FINDINGS: Our results showed that the DA level decreased and the NA level increased in Zfp521Δ/Δ mice. We found that ZFP521 suppresses the expression of dopamine ß-hydroxylase (DBH), which converts DA into NA. We also demonstrated that paired homeodomain transcription factor 2 and early growth response protein-1, which are the transcription factors for Dbh, were involved in the upregulation of Dbh by ZFP521. The administration of nepicastat, a specific inhibitor of DBH, attenuated the abnormal behaviors of Zfp521Δ/Δ mice. SIGNIFICANCE: These results suggest that the lack of ZFP521 upregulates the expression of DBH, which leads to a decrease in the DA level and an increase in the NA level in the brain, resulting in abnormal behaviors.

Transferrin receptor 1 is required for enucleation of mouse erythroblasts during terminal differentiation.

Enucleation is the process whereby the nucleus is extruded from the erythroblast during late stage mammalian erythropoiesis. However, the specific signaling pathways involved in this process remain unclear. To better understand the mechanisms underlying erythroblast enucleation, we investigated erythroblast enucleation using both the spleens of adult mice with phenylhydrazine-induced anemia and mouse fetal livers. Our results indicated that both iron-bound transferrin (holo-Tf) and the small-molecule iron transporter hinokitiol with iron ions (hinokitiol plus iron) promote hemoglobin synthesis and the enucleation of mouse spleen-derived erythroblasts. Although an antitransferrin receptor 1 (TfR1) monoclonal antibody inhibited both enucleation and hemoglobin synthesis promoted by holo-Tf, it inhibited only enucleation, but not hemoglobin synthesis, promoted by hinokitiol plus iron. Furthermore, siRNA against mouse TfR1 were found to suppress the enucleation of mouse fetal liver-derived erythroblasts, and the endocytosis inhibitor MitMAB inhibited enucleation, hemoglobin synthesis, and the internalization of TfR1 promoted by both types of stimuli. Collectively, our results suggest that TfR1, iron ions, and endocytosis play important roles in mouse erythroblast enucleation.

Protective effect of ginsenosides Rg(2) and Rh(1) on oxidation-induced impairment of erythrocyte membrane properties.

The extract from Panax ginseng has been reported to improve the microcirculation in various organs. However, the mechanisms underlying this phenomenon are still poorly understood. In the present study, using the rheological properties of erythrocytes as an index, we have screened the components of Panax ginseng extract and identified Rg(2) and Rh(1) as the active ingredients. These two ginsenosides prevented the oxidative stress-induced elevation of erythrocyte suspension viscosity and the impairment of erythrocyte elongation in response to shear stress. Rg(2) and Rh(1) ginsenosides did not have antioxidant activity in an aqueous phase and did not inhibit the peroxidation of membrane lipids, either. However, they inhibited the oxidation-induced decrease of SH-groups in band 3 (anion exchanger-1), one of the important structural proteins of the erythrocyte membrane, but not in other structural proteins: bands 1 and 2 (spectrins), band 4.2 or band 5 (actin). These results suggest that ginsenosides Rg(2) and Rh(1) protect the rheological functions of erythrocytes against oxidative stress by preventing the oxidation of SH-groups in band 3 protein.

Participation of caspase-3-like protease in oxidation-induced impairment of erythrocyte membrane properties.

Erythrocytes are very susceptible to oxidative stress, having a high content of intracellular oxygen and hemoglobin. In the present study, exposure to oxidative stress resulted in a significant impairment of erythrocyte membrane functions, such as deformability and anion exchange. Band 3 protein, also known as anion exchanger-1, plays an important role in these two functions. We show that oxidative stress activated caspase-3 inside the erythrocytes, which resulted in band 3 protein cleavage. Interestingly, inhibition of the caspase-3 with its specific inhibitor not only suppressed the digestion of band 3 protein, but also blunted the functional damage to erythrocytes, such as deformability and anion exchange, without changing the level of peroxidation of membrane lipids. These results provide experimental evidence that activation of caspase-3 plays an important role in the oxidative stress-induced impairment of membrane functions of erythrocytes.

Apolipoprotein E and Reelin ligands modulate tau phosphorylation through an apolipoprotein E receptor/disabled-1/glycogen synthase kinase-3beta cascade.

Neurofibrillary tangles comprised of highly phosphorylated tau proteins are a key component of Alzheimer's disease pathology. Mice lacking Reelin (Reln), double-knockouts lacking the VLDL receptor (VLDLR) and ApoE receptor2 (ApoER2), and mice lacking disabled-1 (Dab1) display increased levels of phosphorylated tau. Because Reln binds to recombinant ApoE receptors, assembly of a Reln/ApoE-receptor/Dab1 (RAD) complex may initiate a signal transduction cascade that controls tau phosphorylation. Conversely, disruption of this RAD complex may increase tau phosphorylation and lead to neurodegeneration. To substantiate this concept, we mated Reln-deficient mice to ApoE-deficient mice and found that in the absence of Reln, tau phosphorylation increased as the amount of ApoE decreased. Paralleling the change in tau phosphorylation levels, we found that GSK-3beta activity increased in Reln-deficient mice and further increased in mice lacking both Reln and ApoE. CDK-5 activity was similar in mice lacking Reln, ApoE, or both. GSK-3beta and CDK-5 activity increased in Dab1-deficient mice, independent of ApoE levels. Further supporting the idea that increased tau phosphorylation results primarily from increased kinase activity, the activity of two phosphatases was similar in all conditions tested. These data support a novel, ligand-mediated signal transduction cascade--initiated by the assembly of a RAD complex that suppresses kinase activity and controls tau phosphorylation.

N141I mutant presenilin-2 gene enhances neuronal cell death and decreases bcl-2 expression.

A missense mutation (N1411) in Presenilin-2 (PS-2) gene is associated with early-onset familial Alzheimer's disease. In this study, SK-N-SH human neuroblastoma cells were transfected with wild-type and mutant PS-2 gene to examine presenilin-2 effects on apoptosis. Serum deprivation resulted in enhanced apoptosis in mutant PS-2 comparing with wild-type PS-2. Similarly, mutant PS-2 induced lactate dehydrogenase release to greater extent than wild-type PS-2. Time course experiment demonstrated that the increase in caspase-3-like activity was more pronounced and accelerated in mutant PS-2, compared to wild-type PS-2. While a significant decrease in bcl-2, an anti-apoptotic molecule, occurred in the cells overexpressing mutant PS-2, no significant change was observed in bax, a pro-apoptotic molecule, as compared with the cells overexpressing wild-type PS-2. Our study demonstrated that mutant PS-2 induces apoptosis accompanied by increased caspase-3-like activity and decreased bcl-2 expression in neuronal cells after serum-deprivation.

Abnormal behaviors and developmental disorder of hippocampus in zinc finger protein 521 (ZFP521) mutant mice.

Zinc finger protein 521 (ZFP521) regulates a number of cellular processes in a wide range of tissues, such as osteoblast formation and adipose commitment and differentiation. In the field of neurobiology, it is reported to be an essential factor for transition of epiblast stem cells into neural progenitors in vitro. However, the role of ZFP521 in the brain in vivo still remains elusive. To elucidate the role of ZFP521 in the mouse brain, we generated mice lacking exon 4 of the ZFP521 gene. The birth ratio of our ZFP521Δ/Δ mice was consistent with Mendel's laws. Although ZFP521Δ/Δ pups had no apparent defect in the body and were indistinguishable from ZFP521+/+ and ZFP521+/Δ littermates at the time of birth, ZFP521Δ/Δ mice displayed significant weight reduction as they grew, and most of them died before 10 weeks of age. They displayed abnormal behavior, such as hyper-locomotion, lower anxiety and impaired learning, which correspond to the symptoms of schizophrenia. The border of the granular cell layer of the dentate gyrus in the hippocampus of the mice was indistinct and granular neurons were reduced in number. Furthermore, Sox1-positive neural progenitor cells in the dentate gyrus and cerebellum were significantly reduced in number. Taken together, these findings indicate that ZFP521 directly or indirectly affects the formation of the neuronal cell layers of the dentate gyrus in the hippocampus, and thus ZFP521Δ/Δ mice displayed schizophrenia-relevant symptoms. ZFP521Δ/Δ mice may be a useful research tool as an animal model of schizophrenia.

Accelerated destruction of erythrocytes in Tie2 promoter-driven STAT3 conditional knockout mice.

AIMS: STAT3 is a key modulator of activation and differentiation of macrophages. But it is still unknown if deficiency of STAT3 activates macrophages to destroy erythrocytes by phagocytosis. We generated STAT3 conditional knockout mice by crossing floxed STAT3 mice with Tie2 promoter-driven Cre-recombinase transgenic mice and clarified that Stat3 plays a critical role in the formation and activation of macrophages. MAIN METHODS: Blood cell count, reticulocyte count, serum lactate dehydrogenase, erythropoietin, iron and ferritin concentration, and life span of the erythrocytes in Tie2 promoter-driven STAT3 conditional knockout mice were analyzed. To explore the erythropoietic function of the mice, we subjected them to brief hemolytic anemia by injecting them intraperitoneally with phenylhydrazine. The fragility of erythrocytes was examined by scanning electron microscopy and osmotic tolerance test. KEY FINDINGS: The conditional knockout mice had mild normocytic anemia. They also displayed higher lactate dehydrogenase, ferritin and erythropoietin concentration, higher reticulocyte count, and a shorter lifespan of erythrocytes compared with wild-type controls. These data suggest that destruction of erythrocytes and secondary blood formation were accelerated in the STAT3 conditional knockout mice. It didn't appear due to the fragility of erythrocytes. A few of the conditional knockout mice suddenly developed acute severe anemia, high body temperature and massive splenomegaly, and died within 2weeks after the onset of anemia. SIGNIFICANCE: This study provided evidence that STAT3 have a critical role in the destruction of erythrocytes by resident macrophages in the spleen.

Essential role of p38 MAPK in caspase-independent, iPLA(2)-dependent cell death under hypoxia/low glucose conditions.

The mechanisms of cell death induced by hypoxia or ischemia are not yet fully understood. We have previously demonstrated that cell death induced by hypoxia occurs independently of caspases, and is mediated by phospholipase A(2) (PLA(2)). Here, we show that p38 mitogen-activated protein kinase is activated under hypoxia. A selective inhibitor of p38 or decrease in the p38alpha protein level prevents hypoxia-induced cell death. The p38 inhibitor abolishes PLA(2) activation by hypoxia, indicating that p38 acts upstream of PLA(2). The antioxidant N-acetyl-cysteine inhibits activation of p38 and cell death induced by hypoxia, indicating that reactive oxygen species (ROS) are responsible for p38 activation. These results demonstrate that the ROS/p38/PLA(2) signaling axis has a crucial role in caspase-independent cell death induced by hypoxia.

Reelin signals survival through Src-family kinases that inactivate BAD activity.

Reelin plays an important role in the migration of embryonic neurons, but its continuing presence suggests additional functions in the brain. We now report a novel function where reelin protects P19 embryonal cells from apoptosis during retinoic acid-induced neuronal differentiation. This increased survival is associated with reelin activation of the phosphatidyl-inositol-3-kinase (PI3 K)/Akt pathway. When PI3 K was inhibited with LY294002, reelin failed to protect against this retinoic acid-induced apoptosis. The protective effect of reelin includes activating the Src-family kinases/PI3 K/Akt pathway which then led to selective phosphorylation of Bcl-2/Bcl-XL associated death promoter (BAD) at serine-136, while the phosphorylation-incompetent mutation of BAD (S136A) suppressed this protection. These and additional studies define a novel pathway where reelin binds apoE receptors, significantly activates the PI3 K/Akt pathway causing phosphorylation of BAD which helps to protect cells from apoptosing, thus serving an important role in promoting the survival of maturing neurons in the brain.

NFkappaB regulates plasma apolipoprotein A-I and high density lipoprotein cholesterol through inhibition of peroxisome proliferator-activated receptor alpha.

The levels of plasma HDL cholesterol and apoA-I in NFkappaB p50 subunit-deficient mice were significantly higher than those in wild-type mice under regular and high fat diets, without any significant difference in the level of total cholesterol. To examine the role of NFkappaBin lipid metabolism, we studied its effect on the regulation of apoA-I secretion from human hepatoma HepG2 cells. Lipopolysaccharide-induced activation of NFkappaB reduced the expression of apoA-I mRNA and protein, whereas adenovirus-mediated expression of IkappaBalpha super-repressor ameliorated the reduction. This IkappaBalpha-induced apoA-I increase was blocked by preincubation with MK886, a selective inhibitor of peroxisome proliferator-activated receptor alpha (PPARalpha), suggesting that NFkappaB inactivation induces apoA-I through activation of PPARalpha. To further support this idea, the expression of IkappaBalpha increased apoA-I promoter activity, and this increase was blocked by preincubation with MK886. Mutations in the putative PPARalpha-binding site in the apoA-I promoter or lack of the site abrogated these changes. Taking these results together, inhibition of NFkappaB increases apoA-I and HDL cholesterol through activation of PPARalpha in vivo and in vitro. Our data suggest a new aspect of lipid metabolism and may lead to a new paradigm for prevention and treatment of atherosclerotic disease.