AMPKalpha1 deletion shortens erythrocyte life span in mice: role of oxidative stress

Restoration of energy homeostasis under oxidative stress: Duo synergistic AMPK pathways regulating arginine kinases

Rapid depletion of cellular ATP can occur by oxidative stress induced by reactive oxygen species (ROS). Maintaining energy homeostasis requires the key molecular components AMP-activated protein kinase (AMPK) and arginine kinase (AK), an invertebrate orthologue of the mammalian creatine kinase (CK). Here, we deciphered two independent and synergistic pathways of AMPK acting on AK by using the beetle Tribolium castaneum as a model system. First, AMPK acts on transcriptional factor forkhead box O (FOXO) leading to phosphorylation and nuclear translocation of the FOXO. The phospho-FOXO directly promotes the expression of AK upon oxidative stress. Concomitantly, AMPK directly phosphorylates the AK to switch the direction of enzymatic catalysis for rapid production of ATP from the phosphoarginine-arginine pool. Further in vitro assays revealed that Sf9 cells expressing phospho-deficient AK mutants displayed the lower ATP/ADP ratio and cell viability under paraquat-induced oxidative stress conditions when compared with Sf9 cells expressing wild-type AKs. Additionally, the AMPK-FOXO-CK pathway is also involved in the restoration of ATP homeostasis under oxidative stress in mammalian HEK293 cells. Overall, we provide evidence that two distinct AMPK-AK pathways, transcriptional and post-translational regulations, are coherent responders to acute oxidative stresses and distinguished from classical AMPK-mediated long-term metabolic adaptations to energy challenge.

The pleiotropic AMPK-CncC signaling pathway regulates the trade-off between detoxification and reproduction

The association of decreased fecundity with insecticide resistance and the negative sublethal effects of insecticides on insect reproduction indicates the typical trade-off between two highly energy-demanding processes, detoxification and reproduction. However, the underlying mechanisms are poorly understood. The energy sensor adenosine monophosphate-activated protein kinase (AMPK) and the transcription factor Cap "n" collar isoform C (CncC) are important regulators of energy metabolism and xenobiotic response, respectively. In this study, using the beetle Tribolium castaneum as a model organism, we found that deltamethrin-induced oxidative stress activated AMPK, which promoted the nuclear translocation of CncC through its phosphorylation. The CncC not only acts as a transcription activator of cytochrome P450 genes but also regulates the expression of genes coding for ecdysteroid biosynthesis and juvenile hormone (JH) degradation enzymes, resulting in increased ecdysteroid levels as well as decreased JH titer and vitellogenin (Vg) gene expression. These data show that in response to xenobiotic stress, the pleiotropic AMPK-CncC signaling pathway mediates the trade-off between detoxification and reproduction by up-regulating detoxification genes and disturbing hormonal homeostasis.

Enhanced phosphatidylserine exposure and erythropoiesis in Babesia microti-infected mice

INTRODUCTION

Babesia microti (B. microti) is the dominant species responsible for human babesiosis, which is associated with severe hemolytic anemia and splenomegaly because it infects mammalian erythrocytes. The actual prevalence of B. microti is thought to have been substantially underestimated.

METHODS

In this study, Bagg's albino/c (BALB/c) mice were intraperitoneally injected with B. microti-infected erythrocytes, and parasitemia was subsequently measured by calculating the proportion of infected erythrocytes. The ultrastructure of infected erythrocytes was observed using scanning and transmission electron microscopes. Quantifying phosphatidylserine (PS) exposure, oxidative stress, intracellular Ca2+, and erythropoiesis of erythrocytes were done using flow cytometry. The physiological indicators were analyzed using a Mindray BC-5000 Vet automatic hematology analyzer.

RESULTS

Of note, 40.7 ± 5.9% of erythrocytes changed their structure and shrunk in the B. microti-infected group. The percentage of annexin V-positive erythrocytes and the levels of reactive oxygen species (ROS) in the erythrocytes were higher in the B. microti-infected group than in the control group at 10 dpi. Significant splenomegaly and severe anemia were also observed following B. microti infection. The parasitemia level in the B. microti-infected splenectomized group was higher than that of the B. microti-infected sham group. The population of early erythroblasts increased, and the late erythroblasts decreased in both the bone marrow and spleen tissues of the B. microti-infected group at 10 dpi.

DISCUSSION

PS exposure and elevated ROS activities were hallmarks of eryptosis in the B. microti-infected group. This study revealed for the first time that B. microti could also induce eryptosis. At the higher parasitemia phase, the occurrence of severe anemia and significant changes in the abundance of erythroblasts in B. microti-infected mice group were established. The spleen plays a critical protective role in controlling B. microti infection and preventing anemia. B. microti infection could cause a massive loss of late erythroblasts and induce erythropoiesis.

Liver kinase B1 (LKB1) in murine erythroid progenitors modulates erythropoietin setpoint in association with maturation control

Erythropoiesis is a tightly regulated process. It is stimulated by decreased oxygen in circulation, which leads to the secretion of the hormone erythropoietin (Epo) by the kidneys. An additional layer of control involves the coordinated sensing and use of nutrients. Much cellular machinery contributes to sensing and responding to nutrient status in cells, and one key participant is the kinase LKB1. The current study examines the role of LKB1 in erythropoiesis using a murine in vivo and ex vivo conditional knockout system. In vivo analysis showed erythroid loss of LKB1 to be associated with a robust increase in serum Epo and mild reticulocytosis. Despite these abnormalities, no evidence of anemia or hemolysis was found. Further characterization using an ex vivo progenitor culture assay demonstrated accelerated erythroid maturation in the LKB1-deficient cells. Based on pharmacologic evidence, this phenotype appeared to result from impaired AMP-activated protein kinase (AMPK) signaling downstream of LKB1. These findings reveal a role for LKB1 in fine-tuning Epo-driven erythropoiesis in association with maturational control.

Engineered red blood cells (activating antigen carriers) drive potent T cell responses and tumor regression in mice

Activation of T cell responses is essential for effective tumor clearance; however, inducing targeted, potent antigen presentation to stimulate T cell responses remains challenging. We generated Activating Antigen Carriers (AACs) by engineering red blood cells (RBCs) to encapsulate relevant tumor antigens and the adjuvant polyinosinic-polycytidylic acid (poly I:C), for use as a tumor-specific cancer vaccine. The processing method and conditions used to create the AACs promote phosphatidylserine exposure on RBCs and thus harness the natural process of aged RBC clearance to enable targeting of the AACs to endogenous professional antigen presenting cells (APCs) without the use of chemicals or viral vectors. AAC uptake, antigen processing, and presentation by APCs drive antigen-specific activation of T cells, both in mouse in vivo and human in vitro systems, promoting polyfunctionality of CD8+ T cells and, in a tumor model, driving high levels of antigen-specific CD8+ T cell infiltration and tumor killing. The efficacy of AAC therapy was further enhanced by combination with the chemotherapeutic agent Cisplatin. In summary, these findings support AACs as a potential vector-free immunotherapy strategy to enable potent antigen presentation and T cell stimulation by endogenous APCs with broad therapeutic potential.

Surface Modification of Erythrocytes with Lipid Anchors: Structure-Activity Relationship for Optimal Membrane Incorporation, in vivo Retention, and Immunocompatibility

Red blood cells (RBCs) are natural carriers for sustained drug delivery, imaging, and in vivo sensing. One of the popular approaches to functionalize RBCs is through lipophilic anchors, but the structural requirements for anchor stability and in vivo longevity remain to be investigated. Using fluorescent lipids with the same cyanine 3 (Cy3) headgroup but different lipid chain and linker, the labeling efficiency of RBCs and in vivo stability are investigated. Short-chain derivatives exhibited better insertion efficiency, and mouse RBCs are better labeled than human RBCs. Short-chain derivatives demonstrate low retention in vivo. Derivatives with ester bonds are especially unstable, due to removal and degradation. On the other hand, long-chain, covalently linked derivatives show remarkably long retention and stability (over 80 days half life in the membrane). The clearance organs are liver and spleen with evidence of lipid transfer to the liver sinusoidal endothelium. Notably, RBCs modified with PEGylated lipid show decreased macrophage uptake. Some of the derivatives promote binding of antibodies in human plasma and mouse sera and modest increase in complement deposition and hemolysis, but these do not correlate with in vivo stability of RBCs. Ultra-stable anchors can enable functionalization of RBCs for drug delivery, imaging, and sensing.

What Should Be Responsible for Eryptosis in Chronic Kidney Disease?

BACKGROUND

Renal anemia is an important complication of chronic kidney disease (CKD). In addition to insufficient secretion of erythropoietin (EPO) and erythropoiesis disorders, the impact of eryptosis on renal anemia demands attention. However, a systemic analysis concerning the pathophysiology of eryptosis has not been expounded.

SUMMARY

The complicated conditions in CKD patients, including oxidative stress, osmotic stress, metabolic stress, accumulation of uremic toxins, and iron deficiency, affect the normal skeleton structure of red blood cells (RBCs) and disturbs ionic homeostasis, causing phosphatidylserine to translocate to the outer lobules of the RBC membrane that leads to early elimination and/or shortening of the RBC lifespan. Inadequate synthesis of RBCs cannot compensate for their accelerated destruction, thus exacerbating renal anemia. Meanwhile, EPO treatment alone will not reverse renal anemia. A variety of eryptosis inhibitors have so far been found, but evidence of their effectiveness in the treatment of CKD remains to be established.

KEY MESSAGES

In this review, the pathophysiological processes and factors influencing eryptosis in CKD were elucidated. The aim of this review was to underline the importance of eryptosis in renal anemia and determine some promising research directions or possible therapeutic targets to correct anemia in CKD.

AMPK-mediated glutaminolysis maintains coelomocytes redox homeostasis in Vibrio splendidus-challenged Apostichopus japonicus

Glutaminolysis has been proved to play an irreplaceable role in vertebrate immunity, including effects on cytokine production, bacterial killing, and redox homeostasis maintenance. Our previous metabolomics analysis indicated that glutaminolysis metabolic substrates glutamine (Gln) and metabolites glutamate (Glu) were significantly lower in Skin ulceration syndrome (SUS)-diseased Apostichopus japonicus. To further delineate the role of glutaminolysis, we assayed the levels of Gln and Glu. We found that their contents in coelomocytes were decreased, accompanied by an increase in glutathione (GSH) in pathogen-challenged Apostichopus japonicus. Consistently, the mRNA transcripts of three key genes in glutaminolysis (AjASCT2, AjGOT, and AjGCS) were significantly induced. Moreover, the increased MDA and NADPH/NADP ⁺ levels in response to pathogen infection indicated that oxidative stress occurs during the immune response. The metabolic regulator AMPKβ could regulate glutaminolysis in vertebrates by inducing cells to take up extracellular Gln. To explore the underlying regulatory mechanism behind glutaminolysis that occurred in coelomocytes, the full-length cDNA of AMPKβ was identified from A. japonicus (designated as AjAMPKβ). AjAMPKβ expression was significantly induced in the coelomocytes after pathogen challenge, which was consistent with the expression of key genes of glutaminolysis. A functional assay indicated that AjAMPKβ silencing by siRNA transfection could increase the levels of Gln and Glu and depress the production of GSH. Moreover, the expression of glutaminolysis-related genes was significantly inhibited, and the reduction of redox homeostasis indexes (MDA and NADPH/NADP⁺) was also observed. Contrastingly, AjAMPKβ overexpression promoted redox homeostasis balance. Intracellular ROS is mostly responsible for breaking redox homeostasis and leading to oxidative stress, contributing to cell fate changes in immune cells. Exogenous Gln and GSH treatments could significantly reduce ROS level while the AjAMPKβ silencing induced the level of ROS and accelerated the necrosis rate. All these results collectively revealed that AjAMPKβ could modulate cellular redox homeostasis by affecting the glutaminolysis in A. japonicus.

Enhanced phosphatidylserine exposure and erythropoiesis in Babesia microti-infected mice

Introduction

Babesia microti (B. microti) is the dominant species responsible for human babesiosis, which is associated with severe hemolytic anemia and splenomegaly because it infects mammalian erythrocytes. The actual prevalence of B. microti is thought to have been substantially underestimated.

Methods

In this study, Bagg's albino/c (BALB/c) mice were intraperitoneally injected with B. microti-infected erythrocytes, and parasitemia was subsequently measured by calculating the proportion of infected erythrocytes. The ultrastructure of infected erythrocytes was observed using scanning and transmission electron microscopes. Quantifying phosphatidylserine (PS) exposure, oxidative stress, intracellular Ca²⁺, and erythropoiesis of erythrocytes were done using flow cytometry. The physiological indicators were analyzed using a Mindray BC-5000 Vet automatic hematology analyzer.

Results

Of note, 40.7 ± 5.9% of erythrocytes changed their structure and shrunk in the B. microti-infected group. The percentage of annexin V-positive erythrocytes and the levels of reactive oxygen species (ROS) in the erythrocytes were higher in the B. microti-infected group than in the control group at 10 dpi. Significant splenomegaly and severe anemia were also observed following B. microti infection. The parasitemia level in the B. microti-infected splenectomized group was higher than that of the B. microti-infected sham group. The population of early erythroblasts increased, and the late erythroblasts decreased in both the bone marrow and spleen tissues of the B. microti-infected group at 10 dpi.

Discussion

PS exposure and elevated ROS activities were hallmarks of eryptosis in the B. microti-infected group. This study revealed for the first time that B. microti could also induce eryptosis. At the higher parasitemia phase, the occurrence of severe anemia and significant changes in the abundance of erythroblasts in B. microti-infected mice group were established. The spleen plays a critical protective role in controlling B. microti infection and preventing anemia. B. microti infection could cause a massive loss of late erythroblasts and induce erythropoiesis.

Normal Iron Homeostasis Requires the Transporter SLC48A1 for Efficient Heme-Iron Recycling in Mammals

In mammals over 65% of the total body iron is located within erythrocytes in the heme moieties of hemoglobin. Iron homeostasis requires iron absorbed from the diet by the gut as well as recycling of iron after the destruction of senescent erythrocytes. Senescent erythrocytes are engulfed by reticuloendothelial system macrophages where hemoglobin is broken down in the lysosomes, releasing heme for iron recovery in the cytoplasm. We recently showed that the SLC48A1 protein is responsible for transporting heme from the lysosome to the cytoplasm. CRISPR generated SLC48A1-deficient mice accumulate heme in their reticuloendothelial system macrophages as hemozoin crystals. Here we describe additional features of SLC48A1-deficient mice. We show that visible hemozoin first appears in the reticuloendothelial system macrophages of SLC48A1-deficient mice at 8 days of age, indicating the onset of erythrocyte recycling. Evaluation of normal and SLC48A1-deficient mice on iron-controlled diets show that SLC48A1-mediated iron recycling is equivalent to at least 10 parts per million of dietary iron. We propose that mutations in human SLC48A1 could contribute to idiopathic iron disorders.

Dichlorvos poisoning caused chicken cerebrum tissue damage and related apoptosis-related gene changes

Dichlorvos (DDVP) is an organophosphorus compound with insecticidal effects. Organophosphorus pesticides can easily enter humans or animals through various channels, causing cerebrum nerve cell damage. The purpose of this research was to investigate whether acute dichlorvos poisoning can cause cerebrum neurotoxic injury and change the expression of apoptosis-related genes in broilers, further clarify the neurotoxic mechanism after acute dichlorvos exposure, and provide a research basis for prevention, treatment and gene drug screening in the later stage. In this experiment, healthy yellow-feathered broilers were randomly assigned to the control group, the low-dose group (1.13 mg/kg) and the high-dose group (10.2 mg/kg) for modelling observation, and detection was conducted based on H&E (haematoxylin and eosin) staining, transmission electron microscopy analysis of tissue sections, immunofluorescence techniques and real-time quantitative polymerase chain reaction (qRT-PCR). The results showed that organophosphorus poisoning was accompanied by obvious neurological symptoms such as limb twitching and massive salivation. In addition, we observed that compared with the control group, the number of lysed nuclear neurons, deformed vascular sheaths, and glial cells and the expression of glial fibrillary acidic protein (GFAP) in the poisoned group of broilers increased significantly, and the increase was more obvious in the low-dose group. However, cell apoptosis and mitochondrial structure dissolution were most pronounced in the high-dose group. Moreover, the qRT-PCR results also revealed significant changes in the expression of apoptosis-related genes. The expression levels of ACC, LKB1 and GPAT increased significantly, while the expression of HMGR, PPARα, CPT1 and AMPKα1 decreased significantly. In summary, these results indicated that dichlorvos may cause the lysis of cerebrum nerve cell nuclei, completely destroy the structure of mitochondria, change the expression of related apoptotic genes, enhance cell apoptosis, and cause neurogenic damage to the cerebrum. These research results offer a theoretical foundation for the prevention and treatment of acute organophosphate toxicosis.

Ggct (γ-glutamyl cyclotransferase) plays an important role in erythrocyte antioxidant defense and red blood cell survival

The expression of GGCT (γ-glutamyl cyclotransferase) is upregulated in various human cancers. γ-glutamyl cyclotransferase enzyme activity was originally purified from human red blood cells (RBCs), but the physiological function of GGCT in RBCs is still not clear. Here we reported that Ggct deletion in mice leads to splenomegaly and progressive anaemia phenotypes, due to elevated oxidative damage and the shortened life span of Ggct^-/- RBCs. Ggct^-/- RBCs have increased reactive oxygen species (ROS), and are more sensitive to H₂ O₂ -induced damage compared to control RBCs. Glutathione (GSH) and GSH synthesis precursor l-cysteine are decreased in Ggct^-/- RBCs. Our study suggests a critical function of Ggct in RBC redox balance and life span maintenance through regulating GSH metabolism.

AMPK Metabolism in the B Lineage Modulates Humoral Responses

A large and growing body of evidence supports functions of enzymes that regulate or effect cellular metabolism in governing the development, survival, and effector functions of immune cells—especially T cells, macrophages, and dendritic cells. Among these proteins, adenosine monophosphate-activated protein kinase (AMPK) is a conserved ATP and nutrient sensor that regulates multiple metabolic pathways to promote energy homeostasis. Although AMPK had been shown to regulate aspects of CD4⁺ and CD8⁺ T cell biology, its function in B lymphocytes has been less clear. Here, we review recent advances in our understanding of the role of AMPK in the metabolism, function, and maintenance of the B lineage.

The role of AMP-activated protein kinase α1-mediated endoplasmic reticulum stress in alleviating the toxic effect of uremic toxin indoxyl sulfate on vascular endothelial cells by Klotho

Recently, the Klotho protein (Klotho) has received substantial attention as protective factor against cardiovascular complications of chronic kidney disease (CKD). However, the direct effect and mechanism of Klotho on endothelial cells injury are not well-known. In this study, we incubated human vein umbilical endothelial cells (HUVECs) with uremic toxin indoxyl sulfate (IS) to mimic CKD internal environment and investigated the direct effect of Klotho on the HUVECs injury induced by IS and to explore the mechanism in this process. We found IS inhibited cell viability, increased endoplasmic reticulum stress, and mediated apoptosis of HUVECs. Treatment with Klotho significantly attenuated IS-induced above effects. Furthermore, Klotho alleviated the IS toxic effect on HUVECs via promoting AMP-activated protein kinase (AMPK) α1 phosphorylation instead of directly upregulating AMPKα1, which could be partly blocked by AMPK pathway inhibitor-Compound C. In addition, Klotho also inhibited intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression induced by IS. Altogether, these results indicated that Klotho can protect HUVECs from IS-induced injury by alleviating AMPKα1-mediated endoplasmic reticulum stress.

Differences in the Hemolytic Behavior of Two Isomers in Ophiopogon japonicus In Vitro and In Vivo and Their Risk Warnings

Ophiopogonin D (OPD) and Ophiopogonin D′ (OPD′) are two bioactive ingredients in Ophiopogon japonicus. Previously published studies have often focused on the therapeutic effects related to OPD's antioxidant capacity but underestimated the cytotoxicity-related side effects of OPD′, which may result in unpredictable risks. In this study, we reported another side effect of OPD′, hemolysis, and what was unexpected was that this side effect also appeared with OPD. Although hemolysis effects for saponins are familiar to researchers, the hemolytic behavior of OPD or OPD′ and the interactions between these two isomers are unique. Therefore, we investigated the effects of OPD and OPD′ alone or in combination on the hemolytic behavior in vitro and in vivo and adopted chemical compatibility and proteomics methods to explain the potential mechanism. Meanwhile, to explain the drug-drug interactions (DDIs), molecular modeling was applied to explore the possible common targets. In this study, we reported that OPD′ caused hemolysis both in vitro and in vivo, while OPD only caused hemolysis in vivo. We clarified the differences and DDIs in the hemolytic behavior of the two isomers. An analysis of the underlying mechanism governing this phenomenon showed that hemolysis caused by OPD or OPD′ was related to the destruction of the redox balance of erythrocytes. In vivo, in addition to the redox imbalance, the proteomics data demonstrated that lipid metabolic disorders and mitochondrial energy metabolism are extensively involved by hemolysis. We provided a comprehensive description of the hemolysis of two isomers in Ophiopogon japonicus, and risk warnings related to hemolysis were presented. Our research also provided a positive reference for the development and further research of such bioactive components.

AMPKα1 in B Cells Dampens Primary Antibody Responses yet Promotes Mitochondrial Homeostasis and Persistence of B Cell Memory

Emerging evidence indicates that metabolic programs regulate B cell activation and Ab responses. However, the metabolic mediators that support the durability of the memory B cell and long-lived plasma cell populations are not fully elucidated. Adenosine monophosphate-activated protein kinase (AMPK) is an evolutionary conserved serine/threonine kinase that integrates cellular energy status and nutrient availability to intracellular signaling and metabolic pathways. In this study, we use genetic mouse models to show that loss of ΑMPKα1 in B cells led to a weakened recall Ab response associated with a decline in the population of memory-phenotype B cells. AMPKα1-deficient memory B lymphocytes exhibited aberrant mitochondrial activity, decreased mitophagy, and increased lipid peroxidation. Moreover, loss of AMPKα1 in B lymphoblasts was associated with decreased mitochondrial spare respiratory capacity. Of note, AMPKα1 in B cells was dispensable for stability of the bone marrow-resident, long-lived plasma cell population, yet absence of this kinase led to increased rates of Ig production and elevated serum Ab concentrations elicited by primary immunization. Collectively, our findings fit a model in which AMPKα1 in B cells supports recall function of the memory B cell compartment by promoting mitochondrial homeostasis and longevity but restrains rates of Ig production.

Changes in energy metabolism induced by fluoride: Insights from inside the mitochondria

The mechanisms involved in changes in energy metabolism caused by excessive exposure to fluoride (F) are not completely understood. The present study employed proteomic tools to investigate the molecular mechanisms underlying the dose- and time-dependency of the effects of F in the rat liver mitochondria. Thirty-six male Wistar rats received water containing 0, 15 or 50 mgF/L (as NaF) for 20 or 60 days. Rat liver mitochondria were isolated and the proteome profiles were examined using label-free quantitative nLC-MS/MS. PLGS software was used to detect changes in protein expression among the different groups. The bioinformatics analysis was done using the software CYTOSCAPE^® 3.0.7 (Java^®) with the aid of ClueGo plugin. The dose of 15 mgF/L, when administered for 20 days, reduced glycolysis, which was counterbalanced by an increase in other energetic pathways. At 60 days, however, an increase in all energy pathways was observed. On the other hand, the dose of 50 mgF/L, when administered for 20 days, reduced the enzymes involved in all energetic pathways, indicating a lower rate of energy production, with less generation of ROS and consequent reduction of antioxidant enzymes. However, when the 50 mgF/L dose was administered for 60 days, an increase in energy metabolism was seen but in general no changes were observed in the antioxidant enzymes. Except for the group treated with 50 mgF/L for 20 days, all the other groups had alterations in proteins in attempt to maintain calcium homeostasis and avoid apoptosis. The results suggest that the organism seems to adapt to the effects of F over time, activating pathways to reduce the toxicity of this ion. Ultimately, our findings corroborate the safety of the use of fluoride for caries control.

Myeloid-Specific Deletion of the AMPKα2 Subunit Alters Monocyte Protein Expression and Atherogenesis

The AMP-activated protein kinase (AMPK) is an energy sensing kinase that is activated by a drop in cellular ATP levels. Although several studies have addressed the role of the AMPKα1 subunit in monocytes and macrophages, little is known about the α2 subunit. The aim of this study was to assess the consequences of AMPKα2 deletion on protein expression in monocytes/macrophages, as well as on atherogenesis. A proteomics approach was applied to bone marrow derived monocytes from wild-type mice versus mice specifically lacking AMPKα2 in myeloid cells (AMPKα2^∆MC mice). This revealed differentially expressed proteins, including methyltransferases. Indeed, AMPKα2 deletion in macrophages increased the ratio of S-adenosyl methionine to S-adenosyl homocysteine and increased global DNA cytosine methylation. Also, methylation of the vascular endothelial growth factor and matrix metalloproteinase-9 (MMP9) genes was increased in macrophages from AMPKα2^∆MC mice, and correlated with their decreased expression. To link these findings with an in vivo phenotype, AMPKα2^∆MC mice were crossed onto the ApoE^-/- background and fed a western diet. ApoExAMPKα2^∆MC mice developed smaller atherosclerotic plaques than their ApoExα2^fl/fl littermates, that contained fewer macrophages and less MMP9 than plaques from ApoExα2^fl/fl littermates. These results indicate that the AMPKα2 subunit in myeloid cells influences DNA methylation and thus protein expression and contributes to the development of atherosclerotic plaques.

FBXO7 sensitivity of phenotypic traits elucidated by a hypomorphic allele

FBXO7 encodes an F box containing protein that interacts with multiple partners to facilitate numerous cellular processes and has a canonical role as part of an SCF E3 ubiquitin ligase complex. Mutation of FBXO7 is responsible for an early onset Parkinsonian pyramidal syndrome and genome-wide association studies have linked variants in FBXO7 to erythroid traits. A putative orthologue in Drosophila, nutcracker, has been shown to regulate the proteasome, and deficiency of nutcracker results in male infertility. Therefore, we reasoned that modulating Fbxo7 levels in a murine model could provide insights into the role of this protein in mammals. We used a targeted gene trap model which retained 4-16% residual gene expression and assessed the sensitivity of phenotypic traits to gene dosage. Fbxo7 hypomorphs showed regenerative anaemia associated with a shorter erythrocyte half-life, and male mice were infertile. Alterations to T cell phenotypes were also observed, which intriguingly were both T cell intrinsic and extrinsic. Hypomorphic mice were also sensitive to infection with Salmonella, succumbing to a normally sublethal challenge. Despite these phenotypes, Fbxo7 hypomorphs were produced at a normal Mendelian ratio with a normal lifespan and no evidence of neurological symptoms. These data suggest that erythrocyte survival, T cell development and spermatogenesis are particularly sensitive to Fbxo7 gene dosage.

Manipulating Eryptosis of Human Red Blood Cells: A Novel Antimalarial Strategy?

Malaria is a major global health burden, affecting over 200 million people worldwide. Resistance against all currently available antimalarial drugs is a growing threat, and represents a major and long-standing obstacle to malaria eradication. Like many intracellular pathogens, Plasmodium parasites manipulate host cell signaling pathways, in particular programmed cell death pathways. Interference with apoptotic pathways by malaria parasites is documented in the mosquito and human liver stages of infection, but little is known about this phenomenon in the erythrocytic stages. Although mature erythrocytes have lost all organelles, they display a form of programmed cell death termed eryptosis. Numerous features of eryptosis resemble those of nucleated cell apoptosis, including surface exposure of phosphatidylserine, cell shrinkage and membrane ruffling. Upon invasion, Plasmodium parasites induce significant stress to the host erythrocyte, while delaying the onset of eryptosis. Many eryptotic inducers appear to have a beneficial effect on the course of malaria infection in murine models, but major gaps remain in our understanding of the underlying molecular mechanisms. All currently available antimalarial drugs have parasite-encoded targets, which facilitates the emergence of resistance through selection of mutations that prevent drug-target binding. Identifying host cell factors that play a key role in parasite survival will provide new perspectives for host-directed anti-malarial chemotherapy. This review focuses on the interrelationship between Plasmodium falciparum and the eryptosis of its host erythrocyte. We summarize the current knowledge in this area, highlight the different schools of thoughts and existing gaps in knowledge, and discuss future perspectives for host-directed therapies in the context of antimalarial drug discovery.

Finely-tuned regulation of AMP-activated protein kinase is crucial for human adult erythropoiesis

AMP-activated protein kinase (AMPK) is a heterotrimeric complex containing α, β, and γ subunits involved in maintaining integrity and survival of murine red blood cells. Indeed, Ampk α1^-/- , Ampk β1^-/- and Ampk γ1^-/- mice develop hemolytic anemia and the plasma membrane of their red blood cells shows elasticity defects. The membrane composition evolves continuously along erythropoiesis and during red blood cell maturation; defects due to the absence of Ampk could be initiated during erythropoiesis. We, therefore, studied the role of AMPK during human erythropoiesis. Our data show that AMPK activation had two distinct phases in primary erythroblasts. The phosphorylation of AMPK (Thr172) and its target acetyl CoA carboxylase (Ser79) was elevated in immature erythroblasts (glycophorin A^low), then decreased conjointly with erythroid differentiation. In erythroblasts, knockdown of the α1 catalytic subunit by short hairpin RNA led to a decrease in cell proliferation and alterations in the expression of membrane proteins (band 3 and glycophorin A) associated with an increase in phosphorylation of adducin (Ser726). AMPK activation in mature erythroblasts (glycophorin A^high), achieved through the use of direct activators (GSK621 and compound 991), induced cell cycle arrest in the S phase, the induction of autophagy and caspase-dependent apoptosis, whereas no such effects were observed in similarly treated immature erythroblasts. Thus, our work suggests that AMPK activation during the final stages of erythropoiesis is deleterious. As the use of direct AMPK activators is being considered as a treatment in several pathologies (diabetes, acute myeloid leukemia), this observation is pivotal. Our data highlighted the importance of the finely-tuned regulation of AMPK during human erythropoiesis.

Type 2 Diabetes Leads to Axon Initial Segment Shortening in db/db Mice

Cognitive and mood impairments are common central nervous system complications of type 2 diabetes, although the neuronal mechanism(s) remains elusive. Previous studies focused mainly on neuronal inputs such as altered synaptic plasticity. Axon initial segment (AIS) is a specialized functional domain within neurons that regulates neuronal outputs. Structural changes of AIS have been implicated as a key pathophysiological event in various psychiatric and neurological disorders. Here we evaluated the structural integrity of the AIS in brains of db/db mice, an established animal model of type 2 diabetes associated with cognitive and mood impairments. We assessed the AIS before (5 weeks of age) and after (10 weeks) the development of type 2 diabetes, and after daily exercise treatment of diabetic condition. We found that the development of type 2 diabetes is associated with significant AIS shortening in both medial prefrontal cortex and hippocampus, as evident by immunostaining of the AIS structural protein βIV spectrin. AIS shortening occurs in the absence of altered neuronal and AIS protein levels. We found no change in nodes of Ranvier, another neuronal functional domain sharing a molecular organization similar to the AIS. This is the first study to identify AIS alteration in type 2 diabetes condition. Since AIS shortening is known to lower neuronal excitability, our results may provide a new avenue for understanding and treating cognitive and mood impairments in type 2 diabetes.

Squeezing for Life - Properties of Red Blood Cell Deformability

Deformability is an essential feature of blood cells (RBCs) that enables them to travel through even the smallest capillaries of the human body. Deformability is a function of (i) structural elements of cytoskeletal proteins, (ii) processes controlling intracellular ion and water handling and (iii) membrane surface-to-volume ratio. All these factors may be altered in various forms of hereditary hemolytic anemia, such as sickle cell disease, thalassemia, hereditary spherocytosis and hereditary xerocytosis. Although mutations are known as the primary causes of these congenital anemias, little is known about the resulting secondary processes that affect RBC deformability (such as secondary changes in RBC hydration, membrane protein phosphorylation, and RBC vesiculation). These secondary processes could, however, play an important role in the premature removal of the aberrant RBCs by the spleen. Altered RBC deformability could contribute to disease pathophysiology in various disorders of the RBC. Here we review the current knowledge on RBC deformability in different forms of hereditary hemolytic anemia and describe secondary mechanisms involved in RBC deformability.

Erythrocytic ferroportin reduces intracellular iron accumulation, hemolysis, and malaria risk

Malaria parasites invade red blood cells (RBCs), consume copious amounts of hemoglobin, and severely disrupt iron regulation in humans. Anemia often accompanies malaria disease; however, iron supplementation therapy inexplicably exacerbates malarial infections. Here we found that the iron exporter ferroportin (FPN) was highly abundant in RBCs, and iron supplementation suppressed its activity. Conditional deletion of the Fpn gene in erythroid cells resulted in accumulation of excess intracellular iron, cellular damage, hemolysis, and increased fatality in malaria-infected mice. In humans, a prevalent FPN mutation, Q248H (glutamine to histidine at position 248), prevented hepcidin-induced degradation of FPN and protected against severe malaria disease. FPN Q248H appears to have been positively selected in African populations in response to the impact of malaria disease. Thus, FPN protects RBCs against oxidative stress and malaria infection.

AMPKα1 deletion in fibroblasts promotes tumorigenesis in athymic nude mice by p52-mediated elevation of erythropoietin and CDK2

Angiogenesis is essential for tumor development. Accumulating evidence suggests that adenosine monophosphate-activated protein kinase (AMPK), an energy sensor and redox modulator, is associated with cancer development. However, the effect of AMPK on tumor development is controversial, and whether AMPK affects tumor angiogenesis has not been resolved. We show that deletion of AMPKα1, but not AMPKα2, upregulates non-canonical nuclear factor kappa B2 (NF-κB2)/p52-mediated cyclin-dependent kinase 2 (CDK2), which is responsible for the anchorage-independent cell growth of immortalized mouse embryo fibroblasts (MEFs). Co-culture with AMPKα1 knockout MEFs (or their conditioned medium) enhances the migration and network formation of human microvascular endothelial cells, which is dependent on p52-upregulated erythropoietin (Epo). AMPKα1 deletion stimulates cellular proliferation of allograft MEFs, angiogenesis, and tumor development in athymic nu/nu mice, which is partly ameliorated by antibody-mediated Epo neutralization. Therefore, the AMPKα1-p52-Epo pathway may be involved in stromal fibroblast-mediated angiogenesis and tumorigenesis.

Off-tumor targets compromise antiangiogenic drug sensitivity by inducing kidney erythropoietin production

Anti-VEGF drugs are commonly used for treatment of a variety of cancers in human patients, and they often develop resistance. The mechanisms underlying anti-VEGF resistance in human cancer patients are largely unknown. Here, we show that in mouse tumor models and in human cancer patients, the anti-VEGF drug-induced kidney hypoxia augments circulating levels of erythropoietin (EPO). Gain-of-function studies show that EPO protects tumor vessels from anti-VEGF treatment and compromises its antitumor effects. Loss of function by blocking EPO function using a pharmacological approach markedly increases antitumor activity of anti-VEGF drugs through inhibition of tumor angiogenesis. Similarly, genetic loss-of-function data shows that deletion of EpoR in nonerythroid cells significantly increases antiangiogenic and antitumor effects of anti-VEGF therapy. Finally, in a relatively large cohort study, we show that treatment of human colorectal cancer patients with bevacizumab augments circulating EPO levels. These findings uncover a mechanism of desensitizing antiangiogenic and anticancer effects by kidney-produced EPO. Our work presents conceptual advances of our understanding of mechanisms underlying antiangiogenic drug resistance.

Metabolic Regulation of the Immune Humoral Response

Productive humoral responses require that naive B cells and their differentiated progeny move among distinct micro-environments. In this review, we discuss how studies are beginning to address the nature of these niches as well as the interplay between cellular signaling, metabolic programming, and adaptation to the locale. Recent work adds evidence to the expectation that B cells at distinct stages of development or functional subsets are influenced by the altered profiles of nutrients and metabolic by-products that distinguish these sites. Moreover, emerging findings reveal a cross-talk among the external milieu, signal transduction pathways, and transcription factors that direct B cell fate in the periphery.

Leptin inhibits AMPKα2 down-regulation induced decrease in the osteocytic MLO-Y4 cell proliferation and the expression of osteogenic markers

AMP-activated protein kinase (AMPK) is of biological and clinical importance for regulating cellular and systemic energy homeostasis. Although AMPKα1, one of the two AMPK's catalytic subunit α, expresses in the bone and stimulates bone nodule formation, the role of AMPKα2 in osteogenesis remains incompletely understood. The aim of this study was to determine the role of AMPKα2 in osteocytic MLO-Y4 cellproliferation and the expression of osteogenic markers. The current study silenced AMPKα2 in MLO-Y4 cells by transfection with pLKO.1-AMPKα2-shRNA vector and analyzed cell proliferation and the expression of osteogenic markers in MLO-Y4 cells with or without 100 μg/ml leptin treatment through CCK-8, Real-time PCR, Western blot and RNA-seq assay. We found that knockdown of AMPKα2 significantly decreased the mRNA level of AMPKα2 and the cell proliferation of MLO-Y4 cellsas well as the mRNA and protein levels of OPG, OCN, OPN, ALP and BMP6 and the protein expression of p-Smad5/Smad5. However, leptin treatment increased the MLO-Y4 cell proliferation and the expression of these osteogenic markers in MLO-Y4 cells with or without AMPKα2 silencing. Furthermore, RNA-seq assay showed 1019 transcriptors decreased in AMPKα2-silencing group and 995 transcriptors increased in leptin group compared with control group, respectively. 737 transcriptors decreased in AMPKα2-silencing group and 1282 transcriptors increased inleptin group compared with AMPKα2-silencing+leptin group, respectively. These findings suggest that AMPKα2 knockdown inhibited MLO-Y4 cell proliferation and osteogenic marker expressions, which implicates an important role of AMPKα2 in osteogenesis in vitro.

The CD47-SIRPα signaling axis as an innate immune checkpoint in cancer

Immune checkpoint inhibitors, including those targeting CTLA-4/B7 and the PD-1/PD-L1 inhibitory pathways, are now available for clinical use in cancer patients, with other interesting checkpoint inhibitors being currently in development. Most of these have the purpose to promote adaptive T cell-mediated immunity against cancer. Here, we review another checkpoint acting to potentiate the activity of innate immune cells towards cancer. This innate immune checkpoint is composed of what has become known as the 'don't-eat me' signal CD47, which is a protein broadly expressed on normal cells and often overexpressed on cancer cells, and its counter-receptor, the myeloid inhibitory immunoreceptor SIRPα. Blocking CD47-SIRPα interactions has been shown to promote the destruction of cancer cells by phagocytes, including macrophages and neutrophils. Furthermore, there is growing evidence that targeting of the CD47-SIRPα axis may also promote antigen-presenting cell function and thereby stimulate adaptive T cell-mediated anti-cancer immunity. The development of CD47-SIRPα checkpoint inhibitors and the potential side effects that these may have are discussed. Collectively, this identifies the CD47-SIRPα axis as a promising innate immune checkpoint in cancer, and with data of the first clinical studies with CD47-SIRPα checkpoint inhibitors expected within the coming years, this is an exciting and rapidly developing field.

Loss of the clock protein PER2 shortens the erythrocyte life span in mice

Cell proliferation and release from the bone marrow have been demonstrated to be controlled by circadian rhythms in both humans and mice. However, it is unclear whether local circadian clocks in the bone marrow influence physiological functions and life span of erythrocytes. Here, we report that loss of the clock gene Per2 significantly decreased erythrocyte life span. Mice deficient in Per2 were more susceptible to acute stresses in the erythrocytes, becoming severely anemic upon phenylhydrazine, osmotic, and H₂O₂ challenges. ¹H NMR-based metabolomics analysis revealed that the Per2 depletion causes significant changes in metabolic profiles of erythrocytes, including increased lactate and decreased ATP levels compared with wild-type mice. The lower ATP levels were associated with hyperfunction of Na⁺/K⁺-ATPase activity in Per2-null erythrocytes, and inhibition of Na⁺/K⁺-ATPase activity by ouabain efficiently rescued ATP levels. Per2-null mice displayed increased levels of Na⁺/K⁺-ATPase α1 (ATP1A1) in the erythrocyte membrane, and transfection of Per2 cDNA into the erythroleukemic cell line TF-1 inhibited Atp1a1 expression. Furthermore, we observed that PER2 regulates Atp1a1 transcription through interacting with trans-acting transcription factor 1 (SP1). Our findings reveal that Per2 function in the bone marrow is required for the regulation of life span in circulating erythrocytes.

Modeling the dynamics of mouse iron body distribution: hepcidin is necessary but not sufficient

BACKGROUND

Iron is an essential element of most living organisms but is a dangerous substance when poorly liganded in solution. The hormone hepcidin regulates the export of iron from tissues to the plasma contributing to iron homeostasis and also restricting its availability to infectious agents. Disruption of iron regulation in mammals leads to disorders such as anemia and hemochromatosis, and contributes to the etiology of several other diseases such as cancer and neurodegenerative diseases. Here we test the hypothesis that hepcidin alone is able to regulate iron distribution in different dietary regimes in the mouse using a computational model of iron distribution calibrated with radioiron tracer data.

RESULTS

A model was developed and calibrated to the data from adequate iron diet, which was able to simulate the iron distribution under a low iron diet. However simulation of high iron diet shows considerable deviations from the experimental data. Namely the model predicts more iron in red blood cells and less iron in the liver than what was observed in experiments.

CONCLUSIONS

These results suggest that hepcidin alone is not sufficient to regulate iron homeostasis in high iron conditions and that other factors are important. The model was able to simulate anemia when hepcidin was increased but was unable to simulate hemochromatosis when hepcidin was suppressed, suggesting that in high iron conditions additional regulatory interactions are important.

Purinergic control of red blood cell metabolism: novel strategies to improve red cell storage quality

Transfusion of stored blood is regarded as one of the great advances in modern medicine. However, during storage in the blood bank, red blood cells (RBCs) undergo a series of biochemical and biomechanical changes that affect cell morphology and physiology and potentially impair transfusion safety and efficacy. Despite reassuring evidence from clinical trials, it is universally accepted that the storage lesion(s) results in the altered physiology of long-stored RBCs and helps explain the rapid clearance of up to one-fourth of long-stored RBCs from the recipient's bloodstream at 24 hours after administration. These considerations explain the importance of understanding and mitigating the storage lesion. With the emergence of new technologies that have enabled large-scale and in-depth screening of the RBC metabolome and proteome, recent studies have provided novel insights into the molecule-level metabolic changes underpinning the accumulation of storage lesions to RBCs in the blood bank and alternative storage strategies to mitigate such lesion(s). These approaches borrow from recent insights on the biochemistry of RBC adaptation to high altitude hypoxia. We recently conducted investigations in genetically modified mice and revealed novel insights into the role of adenosine signalling in response to hypoxia as a previously unrecognised cascade regulating RBC glucose metabolism and increasing O₂ release, while decreasing inflammation and tissue injuries in animal models. Here, we will discuss the molecular mechanisms underlying the role of purinergic molecules, including adenosine and adenosine triphosphate in manipulating RBCs and blood vessels in response to hypoxia. We will also speculate about new therapeutic possibilities to improve the quality of stored RBCs and the prognosis after transfusion.

In vitro inhibition of human erythrocyte hexokinase by various hyperglycemic drugs

Hemolysis is the red blood cell abnormality most often associated with adverse effect of drug therapy. Drug-induced or drug-associated hyperglycemia could decrease the activity of hexokinase. The aim of this study was to investigate the inhibitory effects of some commonly used drugs that have hyperglycemic side effect on the human erythrocyte hexokinase enzyme in vitro. Hexokinase was purified from human erythrocytes using sequential chromatography, with a specific activity of 0.96 ± 0.18 U/g hemoglobin, and assayed in the presence of selected drugs that have hyperglycemic side effect. The IC₅₀ were determined from the regression analysis graph. Correlation analysis showed that there was positive correlation between the hyperglycemic side effect of some of the tested drugs and decrease of hexokinase activity. This suggests that, at least in part, these drugs exert their hyperglycemic effect by inhibiting glucose phosphorylation by the hexokinase, which consequently causes the glucose accumulation.

AMPK deficiency in chondrocytes accelerated the progression of instability-induced and ageing-associated osteoarthritis in adult mice

Osteoarthritis (OA) is a progressive degenerative disease of the joints that is associated with both joint injury and ageing. Here, we investigated the role of the energy sensor AMP-activated protein kinase (AMPK) in maintaining a healthy state of articular cartilage and in OA development. Using cartilage-specific, tamoxifen-inducible AMPKα1 conditional knockout (AMPKα1 cKO), AMPKα2 conditional knockout (AMPKα2 cKO) and AMPKα1α2 conditional double knockout (AMPKα cDKO) mice, we found that compared with wild-type (WT) littermates, mutant mice displayed accelerated severity of surgically induced OA, especially AMPKα cDKO mice. Furthermore, male but not female AMPKα cDKO mice exhibited severely spontaneous ageing-associated OA lesions at 12 months of age. The chondrocytes isolated from AMPKα cDKO mice resulted in an enhanced interleukin-1β (IL-1β)-stimulated catabolic response. In addition, upregulated expression of matrix metalloproteinase-3 (MMP-3), MMP-13 and phospho-nuclear factor-κB (phospho-NF-κB) p65 and increased levels of apoptotic markers were detected in the cartilage of AMPKα cDKO mice compared with their WT littermates in vivo. Thus, our findings suggest that AMPK activity in chondrocytes is important in maintaining joint homeostasis and OA development.

Beneficial Role of Erythrocyte Adenosine A2B Receptor-Mediated AMP-Activated Protein Kinase Activation in High-Altitude Hypoxia

BACKGROUND

High altitude is a challenging condition caused by insufficient oxygen supply. Inability to adjust to hypoxia may lead to pulmonary edema, stroke, cardiovascular dysfunction, and even death. Thus, understanding the molecular basis of adaptation to high altitude may reveal novel therapeutics to counteract the detrimental consequences of hypoxia.

METHODS

Using high-throughput, unbiased metabolomic profiling, we report that the metabolic pathway responsible for production of erythrocyte 2,3-bisphosphoglycerate (2,3-BPG), a negative allosteric regulator of hemoglobin-O2 binding affinity, was significantly induced in 21 healthy humans within 2 hours of arrival at 5260 m and further increased after 16 days at 5260 m.

RESULTS

This finding led us to discover that plasma adenosine concentrations and soluble CD73 activity rapidly increased at high altitude and were associated with elevated erythrocyte 2,3-BPG levels and O2 releasing capacity. Mouse genetic studies demonstrated that elevated CD73 contributed to hypoxia-induced adenosine accumulation and that elevated adenosine-mediated erythrocyte A2B adenosine receptor activation was beneficial by inducing 2,3-BPG production and triggering O2 release to prevent multiple tissue hypoxia, inflammation, and pulmonary vascular leakage. Mechanistically, we demonstrated that erythrocyte AMP-activated protein kinase was activated in humans at high altitude and that AMP-activated protein kinase is a key protein functioning downstream of the A2B adenosine receptor, phosphorylating and activating BPG mutase and thus inducing 2,3-BPG production and O2 release from erythrocytes. Significantly, preclinical studies demonstrated that activation of AMP-activated protein kinase enhanced BPG mutase activation, 2,3-BPG production, and O2 release capacity in CD73-deficient mice, in erythrocyte-specific A2B adenosine receptor knockouts, and in wild-type mice and in turn reduced tissue hypoxia and inflammation.

CONCLUSIONS

Together, human and mouse studies reveal novel mechanisms of hypoxia adaptation and potential therapeutic approaches for counteracting hypoxia-induced tissue damage.

Erythrocyte survival is controlled by microRNA-142

Hematopoietic–specific microRNA-142 is a critical regulator of various blood cell lineages, but its role in erythrocytes is unexplored. Herein, we characterize the impact of microRNA-142 on erythrocyte physiology and molecular cell biology, using a mouse loss-of-function allele. We report that microRNA-142 is required for maintaining the typical erythrocyte biconcave shape and structural resilience, for the normal metabolism of reactive oxygen species, and for overall lifespan. microRNA-142 further controls ACTIN filament homeostasis and membrane skeleton organization. The analyses presented reveal previously unappreciated functions of microRNA-142 and contribute to an emerging view of small RNAs as key players in erythropoiesis. Finally, the work herein demonstrates how a housekeeping network of cytoskeletal regulators can be reshaped by a single micro-RNA denominator in a cell type specific manner.

Kidney-specific genetic deletion of both AMPK α-subunits causes salt and water wasting

AMP-activated kinase (AMPK) controls cell energy homeostasis by modulating ATP synthesis and expenditure. In vitro studies have suggested AMPK may also control key elements of renal epithelial electrolyte transport but in vivo physiological confirmation is still insufficient. We studied sodium renal handling and extracellular volume regulation in mice with genetic deletion of AMPK catalytic subunits. AMPKα1 knockout (KO) mice exhibit normal renal sodium handling and a moderate antidiuretic state. This is accompanied by higher urinary aldosterone excretion rates and reduced blood pressure. Plasma volume, however, was found to be increased compared with wild-type mice. Thus blood volume is preserved despite a significantly lower hematocrit. The lack of a defect in renal function in AMPKα1 KO mice could be explained by a compensatory upregulation in AMPK α2-subunit. Therefore, we used the Cre-loxP system to knock down AMPKα2 expression in renal epithelial cells. Combining this approach with the systemic deletion of AMPKα1 we achieved reduced renal AMPK activity, accompanied by a shift to a moderate water- and salt-wasting phenotype. Thus we confirm the physiologically relevant role of AMPK in the kidney. Furthermore, our results indicate that in vivo AMPK activity stimulates renal sodium and water reabsorption.

The AMP-activated protein kinase beta 1 subunit modulates erythrocyte integrity

Failure to maintain a normal in vivo erythrocyte half-life results in the development of hemolytic anemia. Half-life is affected by numerous factors, including energy balance, electrolyte gradients, reactive oxygen species, and membrane plasticity. The heterotrimeric AMP-activated protein kinase (AMPK) is an evolutionarily conserved serine/threonine kinase that acts as a critical regulator of cellular energy balance. Previous roles for the alpha 1 and gamma 1 subunits in the control of erythrocyte survival have been reported. In the work described here, we studied the role of the beta 1 subunit in erythrocytes and observed microcytic anemia with compensatory extramedullary hematopoiesis together with splenomegaly and increased osmotic resistance.

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Prkab1^tm1b/tm1b mice were generated and phenotyped.

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Prkab1^tm1b/tm1b mice presented with microcytic anemia.

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Erythrocytes lacking Prkab1 have a variable morphologic appearance.

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Prkab1-deficient erythrocytes have increased osmotic resistance.

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The importance of the beta 1 isoform in erythrocyte integrity is discussed.

Erythropoietin-regulated oxidative stress negatively affects enucleation during terminal erythropoiesis

Differentiating erythroblasts are exposed to an oxidative environment. The dynamics of oxidative status during terminal erythropoiesis and how they affect cell differentiation in response to erythropoietin (Epo) are unclear. Here, we show that Epo induces reactive oxygen species (ROS) production in the early stages of terminal erythropoiesis. The levels of ROS correlate with CD71 surface expression and the uptake of iron and transferrin. ROS decreases in the late stages of terminal erythropoiesis, when the cells are preparing for enucleation. Consistently, treatment of erythroblasts with a low dose (5 mM) of N-acetyl-cysteine (NAC), a ROS scavenger, promotes enucleation. However, a high dose (20 mM) of NAC leads to significant cell death. Our study reveals an important function of Epo in regulating the dynamics of oxidative status and enucleation.

Toxicogenomics of Phenylhydrazine Induced Hematotoxicity and its Attenuation by Plumbagin from Plumbago zeylanica

BACKGROUND

High regenerative and proliferative capacity of blood and its components renders it to be at higher risk of adverse drug reactions (ADRs) which are manifested in several treatment regimens against various ailments such as cancers, viral diseases, and several metabolic disorders.

OBJECTIVE

It is prudent to come up with some therapeutic entity that can prevent this damage and protects the blood from these ADRs.

MATERIALS AND METHODS

We examined protective effects of Plumbago zeylanica (PZ) and its active constituent plumbagin (PL) on Sprague Dawley (SD) rats using a phenylhydrazine (Phz) induced hematotoxicity model. Hemoglobin (Hgb), red blood cells (RBCs), mean corpuscular volume, mean corpuscular Hgb (MCH), MCH concentration (MCHC), leukocytes and platelets were studied. Anti-oxidant enzymes superoxide dismutases 2 and 3 (SODs) and nuclear erythroid 2 p45-related factor 1 and 2 (Nfer-1 and 2) were also studied using quantitative real-time polymerase chain reaction (PCR).

RESULTS

In Phz treated rats, the positive hematotoxic response was obtained in terms of deviated endpoints of blood indices. In PLtreated groups protective response was obtained in terms of normal endpoints of blood indices. In PCR studies, we observed the similar trend. Thus, it can be postulated that PL exerts its protective effects via modulation of anti-oxidant enzymes.

CONCLUSION

The study proves that PL can be employed against combatting the ADRs associated with several therapeutic treatment regimens. Similar studies employing such pharmacological entities and their combinations may further prove to be effective against ADRs, especially in the context of blood cells.

SUMMARY

Hematotoxicity is generally encountered in various therapeutic regimens as ADRs (Adverse Drug Reactions). Plumbagin, an active constituent of plant Plumbago zeylanica is tested for its anti-hematotoxic potential in Phenylhydrazine induced hematotoxicity model in Sprague dawley rats. In vivo, in-vitro and molecular studies confirmed the peremptory actions of PL. It was revealed in our studies that the anti-hematotoxic actions of Plumbagin are due to its capacity to modulate anti-oxidant enzyme system.

The mechanical properties of stored red blood cells measured by a convenient microfluidic approach combining with mathematic model

The mechanical properties of red blood cells (RBCs) are critical to the rheological and hemodynamic behavior of blood. Although measurements of the mechanical properties of RBCs have been studied for many years, the existing methods, such as ektacytometry, micropipette aspiration, and microfluidic approaches, still have limitations. Mechanical changes to RBCs during storage play an important role in transfusions, and so need to be evaluated pre-transfusion, which demands a convenient and rapid detection method. We present a microfluidic approach that focuses on the mechanical properties of single cell under physiological shear flow and does not require any high-end equipment, like a high-speed camera. Using this method, the images of stretched RBCs under physical shear can be obtained. The subsequent analysis, combined with mathematic models, gives the deformability distribution, the morphology distribution, the normalized curvature, and the Young's modulus (E) of the stored RBCs. The deformability index and the morphology distribution show that the deformability of RBCs decreases significantly with storage time. The normalized curvature, which is defined as the curvature of the cell tail during stretching in flow, suggests that the surface charge of the stored RBCs decreases significantly. According to the mathematic model, which derives from the relation between shear stress and the adherent cells' extension ratio, the Young's moduli of the stored RBCs are also calculated and show significant increase with storage. Therefore, the present method is capable of representing the mechanical properties and can distinguish the mechanical changes of the RBCs during storage. The advantages of this method are the small sample needed, high-throughput, and easy-use, which make it promising for the quality monitoring of RBCs.

Chondrocyte-Specific Ablation of AMPKα1 Does Not Affect Bone Development or Pathogenesis of Osteoarthritis in Mice

AMP-activated protein kinase (AMPK) acts as an intracellular sensor that modulates the energy balance within the cell. AMPKα1 is the dominant catalytic isoform expressed in the bone, but the significance of AMPKα1 in articular cartilage has not been well studied. In this study, we aimed to assess the in vivo function of AMPKα1 in chondrocytes. We created chondrocyte-specific AMPKα1 conditional knockout (KO) mice using Col2α1-Cre and analyzed and compared growth characteristics, HE staining, and AMPKα gene expression between wild-type (WT) mice and AMPKα1 conditional KO mice under normal physiological conditions or following activation of AMPK by metformin intake or treadmill exercise. Microcomputed tomography and safranin O-fast green staining were compared between WT and KO mice after induction of experimental osteoarthritis (OA). Our data showed that there was no somatic difference between WT mice and KO mice of the same age. Metformin intake and treadmill exercise did not alter the phenotype of KO mice, and no difference in cartilage degradation was observed in WT mice or in KO mice after induction of traumatic arthritis. We thought that chondrocyte-specific ablation of AMPKα1 had no effect on bone growth or on pathogenesis of OA in mice, probably because the feedback overexpression of AMPKα2 compensated for loss of AMPKα1 and maintained the combination of AMPKα subunits.

Animal Models to Study AMPK

AMPK is an evolutionary conserved energy sensor involved in the regulation of energy metabolism. Based on biochemical studies, AMPK has brought much of interest in recent years due to its potential impact on metabolic disorders. Suitable animal models are therefore essential to promote our understanding of the molecular and functional roles of AMPK but also to bring novel information for the development of novel therapeutic strategies. The organism systems include pig (Sus scrofa), mouse (Mus musculus), fly (Drosophila melanogaster), worm (Caenorhabditis elegans), and fish (Danio rerio) models. These animal models have provided reliable experimental evidence demonstrating the crucial role of AMPK in the regulation of metabolism but also of cell polarity, autophagy, and oxidative stress. In this chapter, we update the new development in the generation and application of animal models for the study of AMPK biology. We also discuss recent breakthroughs from studies in mice, flies, and worms showing how AMPK has a primary role in initiating or promoting pathological or beneficial impact on health.

Auditory Pathology in a Transgenic mtTFB1 Mouse Model of Mitochondrial Deafness

The A1555G mutation in the 12S rRNA gene of human mitochondrial DNA causes maternally inherited, nonsyndromic deafness, an extreme case of tissue-specific mitochondrial pathology. A transgenic mouse strain that robustly overexpresses the mitochondrial 12S ribosomal RNA methyltransferase TFB1M (Tg-mtTFB1 mice) exhibits progressive hearing loss that we proposed models aspects of A1555G-related pathology in humans. Although our previous studies of Tg-mtTFB1 mice implicated apoptosis in the spiral ganglion and stria vascularis because of mitochondrial reactive oxygen species-mediated activation of AMP kinase (AMPK) and the nuclear transcription factor E2F1, detailed auditory pathology was not delineated. Herein, we show that Tg-mtTFB1 mice have reduced endocochlear potential, indicative of significant stria vascularis dysfunction, but without obvious signs of strial atrophy. We also observed decreased auditory brainstem response peak 1 amplitude and prolonged wave I latency, consistent with apoptosis of spiral ganglion neurons. Although no major loss of hair cells was observed, there was a mild impairment of voltage-dependent electromotility of outer hair cells. On the basis of these results, we propose that these events conspire to produce the progressive hearing loss phenotype in Tg-mtTFB1 mice. Finally, genetically reducing AMPK α1 rescues hearing loss in Tg-mtTFB1 mice, confirming that aberrant up-regulation of AMPK signaling promotes the observed auditory pathology. The relevance of these findings to human A1555G patients and the potential therapeutic value of reducing AMPK activity are discussed.

AMPK Protects Leukemia-Initiating Cells in Myeloid Leukemias from Metabolic Stress in the Bone Marrow

How cancer cells adapt to metabolically adverse conditions in patients and strive to proliferate is a fundamental question in cancer biology. Here we show that AMP-activated protein kinase (AMPK), a metabolic checkpoint kinase, confers metabolic stress resistance to leukemia-initiating cells (LICs) and promotes leukemogenesis. Upon dietary restriction, MLL-AF9-induced murine acute myeloid leukemia (AML) activated AMPK and maintained leukemogenic potential. AMPK deletion significantly delayed leukemogenesis and depleted LICs by reducing the expression of glucose transporter 1 (Glut1), compromising glucose flux, and increasing oxidative stress and DNA damage. LICs were particularly dependent on AMPK to suppress oxidative stress in the hypoglycemic bone marrow environment. Strikingly, AMPK inhibition synergized with physiological metabolic stress caused by dietary restriction and profoundly suppressed leukemogenesis. Our results indicate that AMPK protects LICs from metabolic stress and that combining AMPK inhibition with physiological metabolic stress potently suppresses AML by inducing oxidative stress and DNA damage.

Overexpression of Aldose Reductase Render Mouse Hepatocytes More Sensitive to Acetaminophen Induced Oxidative Stress and Cell Death

Acetaminophen (APAP) a commonly used drug for decrease the fever and pain but is capable to induced hepatotoxicity at over dose. This study was carried out to investigate the effect of APAP on the expression of anti-apoptotic and antioxidative defense genes, and whether aldose reductase over-expressing plasmid capable to protect against APAP-induced oxidative stress and cell death. APAP treatment induced oxidative stress and hepatotoxicity, and significantly increased aldose reductase mRNA and protein expression in mouse hepatocyte (AML-12). Unexpectedly, AML-12 cells over-expressing aldose reductase augmented APAP-induced reduction in cell viability, reactive oxygen species (ROS) production, glutathione (GSH) depletion and glutathione S-transferase A2 expression. Moreover, over-expression of aldose reductase potentiated APAP induced reduction on proliferating cell nuclear antigen, B cell lymphoma-extra large (bcl-xL), catalase, glutathione peroxidase-1 (GPx-1) and abolished APAP-induced B-cell lymphoma 2 (bcl-2) inductions. Further, over-expression of aldose reductase significantly abolished AMP activated protein kinase (AMPK) activity in APAP-treated cells and induced p53 expression. This results demonstrate that APAP induced toxicity in AML-12, increased aldose reductase expression, and over-expression of aldose reductase render this cell more susceptible to APAP induced oxidative stress and cell death, this probably due to inhibition AMPK or bcl-2 activity, or may due to competition between aldose reductase and glutathione reductase for NADPH.

Role of glutathione, glutathione transferase, and glutaredoxin in regulation of redox-dependent processes

Over the last decade fundamentally new features have been revealed for the participation of glutathione and glutathione-dependent enzymes (glutathione transferase and glutaredoxin) in cell proliferation, apoptosis, protein folding, and cell signaling. Reduced glutathione (GSH) plays an important role in maintaining cellular redox status by participating in thiol-disulfide exchange, which regulates a number of cell functions including gene expression and the activity of individual enzymes and enzyme systems. Maintaining optimum GSH/GSSG ratio is essential to cell viability. Decrease in the ratio can serve as an indicator of damage to the cell redox status and of changes in redox-dependent gene regulation. Disturbance of intracellular GSH balance is observed in a number of pathologies including cancer. Consequences of inappropriate GSH/GSSG ratio include significant changes in the mechanism of cellular redox-dependent signaling controlled both nonenzymatically and enzymatically with the participation of isoforms of glutathione transferase and glutaredoxin. This review summarizes recent data on the role of glutathione, glutathione transferase, and glutaredoxin in the regulation of cellular redox-dependent processes.