Stable in vivo expression of glucose-6-phosphate dehydrogenase (G6PD) and rescue of G6PD deficiency in stem cells by gene transfer

Evaluation of Three Mutations in Codon 385 of Glucose-6-Phosphate Dehydrogenase via Biochemical and In Silico Analysis

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an enzymopathy that affects approximately 500 million people worldwide. A great number of mutations in the G6PD gene have been described. However, three class A G6PD variants known as G6PD Tomah (C385R), G6PD Kangnam (C385G), and G6PD Madrid (C385W) have been reported to be clinically important due to their associations with severe clinical manifestations such as hemolytic anemia. Therefore, this work aimed to perform, for the first time, biochemical and functional characterizations of these variants. The G6PD variants were cloned and purified for this purpose, followed by analyses of their kinetic parameters and thermal stability, as well as in silico studies. The results showed that the mutations induced changes in the proteins. Regarding the kinetic parameters, it was observed that the three variants showed lower affinities for G6P and NADP+, as well as lower thermal stability compared to WT-G6PD. Molecular dynamics simulations showed that C385 mutations induced changes around neighboring amino acids. Metadynamics simulations showed that most remarkable changes account for the binding pocket volumes, particularly in the structural NADP+ binding site, with a concomitant loss of affinity for catalytic processes.

Glucose-6-phosphate dehydrogenase deficiency

Glucose 6-phosphate dehydrogenase (G6PD) deficiency is 1 of the commonest human enzymopathies, caused by inherited mutations of the X-linked gene G6PD. G6PD deficiency makes red cells highly vulnerable to oxidative damage, and therefore susceptible to hemolysis. Over 200 G6PD mutations are known: approximately one-half are polymorphic and therefore common in various populations. Some 500 million persons with any of these mutations are mostly asymptomatic throughout their lifetime; however, any of them may develop acute and sometimes very severe hemolytic anemia when triggered by ingestion of fava beans, by any of a number of drugs (for example, primaquine, rasburicase), or, more rarely, by infection. Approximately one-half of the G6PD mutations are instead sporadic: rare patients with these mutations present with chronic nonspherocytic hemolytic anemia. Almost all G6PD mutations are missense mutations, causing amino acid replacements that entail deficiency of G6PD enzyme activity: they compromise the stability of the protein, the catalytic activity is decreased, or a combination of both mechanisms occurs. Thus, genotype-phenotype correlations have been reasonably well clarified in many cases. G6PD deficiency correlates remarkably, in its geographic distribution, with past/present malaria endemicity: indeed, it is a unique example of an X-linked human polymorphism balanced through protection of heterozygotes from malaria mortality. Acute hemolytic anemia can be managed effectively provided it is promptly diagnosed. Reliable diagnostic procedures are available, with point-of-care tests becoming increasingly important where primaquine and its recently introduced analog tafenoquine are required for the elimination of malaria.

Emerging cellular and gene therapies for congenital anemias

Congenital anemias comprise a group of blood disorders characterized by a reduction in the number of peripherally circulating erythrocytes. Various genetic etiologies have been identified that affect diverse aspects of erythroid physiology and broadly fall into two main categories: impaired production or increased destruction of mature erythrocytes. Current therapies are largely focused on symptomatic treatment and are often based on transfusion of donor-derived erythrocytes and management of complications. Hematopoietic stem cell transplantation represents the only curative option currently available for the majority of congenital anemias. Recent advances in gene therapy and genome editing hold promise for the development of additional curative strategies for these blood disorders. The relative ease of access to the hematopoietic stem cell compartment, as well as the possibility of genetic manipulation ex vivo and subsequent transplantation in an autologous manner, make blood disorders among the most amenable to cellular therapies. Here we review cell-based and gene therapy approaches, and discuss the limitations and prospects of emerging avenues, including genome editing tools and the use of pluripotent stem cells, for the treatment of congenital forms of anemia. © 2016 Wiley Periodicals, Inc.

Safe and Efficient Gene Therapy for Pyruvate Kinase Deficiency

Pyruvate kinase deficiency (PKD) is a monogenic metabolic disease caused by mutations in the PKLR gene that leads to hemolytic anemia of variable symptomatology and that can be fatal during the neonatal period. PKD recessive inheritance trait and its curative treatment by allogeneic bone marrow transplantation provide an ideal scenario for developing gene therapy approaches. Here, we provide a preclinical gene therapy for PKD based on a lentiviral vector harboring the hPGK eukaryotic promoter that drives the expression of the PKLR cDNA. This therapeutic vector was used to transduce mouse PKD hematopoietic stem cells (HSCs) that were subsequently transplanted into myeloablated PKD mice. Ectopic RPK expression normalized the erythroid compartment correcting the hematological phenotype and reverting organ pathology. Metabolomic studies demonstrated functional correction of the glycolytic pathway in RBCs derived from genetically corrected PKD HSCs, with no metabolic disturbances in leukocytes. The analysis of the lentiviral insertion sites in the genome of transplanted hematopoietic cells demonstrated no evidence of genotoxicity in any of the transplanted animals. Overall, our results underscore the therapeutic potential of the hPGK-coRPK lentiviral vector and provide high expectations toward the gene therapy of PKD and other erythroid metabolic genetic disorders.

Anemia: progress in molecular mechanisms and therapies

Anemia is a major source of morbidity and mortality worldwide. Here we review recent insights into how red blood cells (RBCs) are produced, the pathogenic mechanisms underlying various forms of anemia, and novel therapies derived from these findings. It is likely that these new insights, mainly arising from basic scientific studies, will contribute immensely to both the understanding of frequently debilitating forms of anemia and the ability to treat affected patients. Major worldwide diseases that are likely to benefit from new advances include the hemoglobinopathies (β-thalassemia and sickle cell disease); rare genetic disorders of RBC production; and anemias associated with chronic kidney disease, inflammation, and cancer. Promising new approaches to treatment include drugs that target recently defined pathways in RBC production, iron metabolism, and fetal globin-family gene expression, as well as gene therapies that use improved viral vectors and newly developed genome editing technologies.

The heme oxygenase system suppresses perirenal visceral adiposity, abates renal inflammation and ameliorates diabetic nephropathy in Zucker diabetic fatty rats

The growing incidence of chronic kidney disease remains a global health problem. Obesity is a major risk factor for type-2 diabetes and renal impairment. Perirenal adiposity, by virtue of its anatomical proximity to the kidneys may cause kidney disease through paracrine mechanisms that include increased production of inflammatory cytokines. Although heme-oxygenase (HO) is cytoprotective, its effects on perirenal adiposity and diabetic nephropathy in Zucker-diabetic fatty rats (ZDFs) remains largely unclear. Upregulating the HO-system with hemin normalised glycemia, reduced perirenal adiposity and suppressed several pro-inflammatory/oxidative mediators in perirenal fat including macrophage-inflammatory-protein-1α (MIP-1α), endothelin (ET-1), 8-isoprostane, TNF-α, IL-6 and IL-1β. Furthermore, hemin reduced ED1, a marker of pro-inflammatory macrophage-M1-phenotype, but interestingly, enhanced markers associated with anti-inflammatory M2-phenotype such as ED2, CD206 and IL-10, suggesting that hemin selectively modulates macrophage polarization towards the anti-inflammatory M2-phenotype. These effects were accompanied by increased adiponectin, HO-1, HO-activity, atrial-natriuretic peptide (ANP), and its surrogate marker, urinary-cGMP. Furthermore, hemin reduced renal histological lesions and abated pro-fibrotic/extracellular-matrix proteins like collagen and fibronectin that deplete nephrin, an important transmembrane protein which forms the scaffolding of the podocyte slit-diaphragm allowing ions to filter but not massive excretion of proteins, hence proteinuria. Correspondingly, hemin increased nephrin expression in ZDFs, reduced markers of renal damage including, albuminuria/proteinuria, but increased creatinine-clearance, suggesting improved renal function. Conversely, the HO-blocker, stannous-mesoporphyrin nullified the hemin effects, aggravating glucose metabolism, and exacerbating renal injury and function. The hemin effects were less-pronounced in Zucker-lean controls with healthy status, suggesting greater selectivity of HO in ZDFs with disease. We conclude that the concomitant reduction of pro-inflammatory/oxidative mediators, macrophage infiltration and profibrotic/extracellular-matrix proteins, coupled to increased nephrin, adiponectin, ANP, cGMP and creatinine clearance may account for improved renal function in hemin-treated ZDFs. These findings suggest that HO-inducers like hemin may be explored against the co-morbidity of perirenal adiposity and diabetic nephropathy.

A new G6PD knockdown tumor-cell line with reduced proliferation and increased susceptibility to oxidative stress

Glucose-6-phosphate dehydrogenase (G6PD) has been implicated in the regulation of cellular antioxidative mechanisms. Tumor cells often lose the balance of oxidation and antioxidation, but the role of G6PD in such an imbalance is still largely unknown. To investigate the related function of G6PD in tumor cells, we established a stable line of A375 human melanoma cells with G6PD gene knockdown by a shRNA lentiviral cloning and expression system. The A375-G6PDDelta cells displayed the stable GFP coexpression after repeated freeze-thaw cycles and multiple passages, accompanied by an 88.83% suppression of the endogenous G6PD expression and a 78.47% decrease in G6PD activity. In comparison with the A375-WT cells, they were characterized by a reduced proliferation with the MTT proliferation assay, a 25% decrease in colony-forming efficiency, and an up to 40% increase of apoptotic rate with flow cytometry analysis. When further challenged by diamide-induced oxidative stress, these cells showed that a median lethal dose (LD(50)) of 1.2 mM decreased from that of the A375-WT cells (1.8 mM), and levels of NADPH and GSH decreased by 2.4-, 8.8-fold, respectively, with a 7.3-fold increase of H(2)O(2), as those of A375-WT cells. These results demonstrated that A375-G6PDDelta is a new, stable G6PD-deficient human tumor cell line, and that silencing G6PD expression decreased tumor-cell proliferation and enhanced apoptosis. In addition, G6PD gene knockdown rendered tumor cells more susceptible to diamide-induced oxidative stress. Together, our data support the important functions of G6PD in the regulation of cell growth and antioxidative capacity of tumor cells.

In vitro and in vivo expression of human erythrocyte pyruvate kinase in erythroid cells: a gene therapy approach

Human pyruvate kinase deficiency (PKD), an autosomal recessive disorder produced by mutations in the PKLR gene, is the most common cause of chronic nonspherocytic hemolytic anemia. Transduction of wild-type erythroid (R-type) pyruvate kinase (RPK) cDNA into deficient hematopoietic stem cells could be of potential use as rescue therapy in severe clinical cases. In this study, gammaretroviral vectors expressing human RPK were designed as possible gene therapy candidates for this disease. Through real-time quantitative reverse transcriptase-polymerase chain reaction, Western blotting, and flow cytometric analysis, we demonstrate stable RPK expression in both undifferentiated and differentiated murine erythroleukemia cells. In this in vitro assay, the proportion of transduced cells and the intensity of expression of the transgene remained unaltered after 6 months of culture. Moreover, transplanting human RPK-transduced Lin(-)Sca-1(+) mouse cells in myeloablated primary and secondary recipients rendered high proportions of erythroid precursors and mature erythrocytes expressing RPK, without inducing hematopoietic effects. These findings suggest that retroviral vectors could be useful for the delivery and expression of RPK in erythroid cells, and provide evidence of the potential use of gene therapy strategies to phenotypically correct erythroid PKD.

Jedi—a novel transmembrane protein expressed in early hematopoietic cells

Self-renewal and differentiation of hematopoietic stem and progenitor cells are defined by the ensembles of genes expressed by these cells. Here we report identification of a novel gene named Jedi, which is expressed predominantly in short- and long-term repopulating stem cells when compared to more mature bone marrow progenitors. Jedi mRNA encodes a transmembrane protein that contains multiple EGF-like repeats. Jedi and two earlier reported proteins, MEGF10 and MEGF11, share a substantial homology and are likely to represent a novel protein family. Studies of the potential role of Jedi in hematopoietic regulation demonstrated that the retrovirally mediated expression of Jedi in bone marrow cells decreased the number of myeloid progenitors in in vitro clonogenic assays. In addition, expression of Jedi in NIH 3T3 fibroblasts resulted in a decreased number of late and early myeloid progenitors in the non-adherent co-cultured bone marrow cells. Jedi shares a number of structural features with the Jagged/Serrate/Delta family of Notch ligands, and our experiments indicate that the extracellular domain of Jedi, similar to the corresponding domain of Jagged1, inhibits Notch signaling. On the basis of obtained results, we suggest that Jedi is involved in the fine regulation of the early stages of hematopoietic differentiation, presumably through the Notch signaling pathway.

Factors that influence VSV-G pseudotyping and transduction efficiency of lentiviral vectors—in vitro andin vivo implications

Pseudotyping viral vectors with vesicular stomatitis virus glycoprotein (VSV-G) enables the transduction of an extensive range of cell types from different species. We have discovered two important parameters of the VSV-G-pseudotyping phenomenon that relate directly to the transduction potential of lentiviral vectors: (1) the glycosylation status of VSV-G, and (2) the quantity of glycoprotein associated with virions. We measured production-cell and virion-associated quantities of two isoform variants of VSV-G, which differ in their glycosylation status, VSV-G1 and VSV-G2, and assessed the impact of this difference on the efficiency of mammalian cell transduction by lentiviral vectors. The glycosylation of VSV-G at N336 allowed greater maximal expression of VSV-G in HEK293T cells, thus facilitating vector pseudotyping. The transduction of primate cell lines was substantially affected (up to 50-fold) by the degree of VSV-G1 or VSV-G2 incorporation, whereas other cell lines, such as D17 (canine), were less sensitive to virion-associated VSV-G1/2 quantities. These data indicate that the minimum required concentration of virion-associated VSV-G differs substantially between cell species/types. The implications of these data with regard to VSV-G-pseudotyped vector production, titration, and use in host-cell restriction studies, are discussed.

G6PD is indispensable for erythropoiesis after the embryonic-adult hemoglobin switch

Glucose 6-phosphate dehydrogenase (G6PD) (EC 1.1.1.42) is an essential enzyme for the rapid production of NADPH, as required on exposure to oxidative stress. Mouse embryonic stem (ES) cells can produce all embryonic and fetal/adult cell types. By studying the in vitro differentiation of embryoid bodies produced from G6pdDelta ES cells that are totally unable to produce G6PD protein, we found that these cells are able to differentiate into mesodermal cells, cardiomyocytes, hepatocytes, and primitive erythroid cells. However, we show here that, after the hemoglobin switch has taken place, definitive erythrocytes die by apoptosis. This apoptotic death is delayed by reducing agents and by a caspase inhibitor, but it is prevented only by the restoration of G6PD activity. Thus, G6PD proves indispensable for definitive erythropoiesis.

Efficient Marking of Murine Long-Term Repopulating Stem Cells Targeting Unseparated Marrow Cells at Low Lentiviral Vector Particle Concentration

HIV-1-derived lentivirus vectors offer unique biological properties for gene delivery to hematopoietic stem cells and, when used at high multiplicities of infection (m.o.i.), permit efficient gene transfer after minimal target cell stimulation. However, such a strategy has been shown to promote multicopy proviral integration, potentially increasing the risk of insertional mutagenesis. To minimize cell manipulation, we targeted unseparated marrow and demonstrated that transduction at an m.o.i. of 1 resulted in up to 12% vector-modified peripheral blood leukocytes and successful repopulation of secondary recipients with vector-marked cells. Real-time PCR showed on average 1.8 proviral integrants per GFP-marked cell. By comparison, a cohort of animals transplanted with cells transduced at m.o.i. of 10 under otherwise unchanged conditions showed up to 45% marking with an average of 7 copies per GFP-expressing cell. Both m.o.i. groups demonstrated sustained proviral expression with stable GFP fluorescence intensity. In summary, we have identified conditions for lentiviral gene transfer involving minimal ex vivo target cell manipulation and have shown that the m.o.i. is a critical determinant of proviral copy number in lentivirus-transduced murine long-term repopulating cells. Thus, gene transfer efficiencies may be limited when single-copy integration is desired and additional strategies such as in vivo selection may be required to improve the frequency of gene-modified cells.

Hematopoietic stem cell gene therapy for inherited bone marrow disorders: past accomplishments and continued challenges

From the time that the genes encoding the defective proteins were cloned for a number of inherited diseases, it became a goal to correct those conditions by restoring the normal gene and thereby, its product. For the inherited disorders affecting the blood and its progenitor cells, the hematopoietic stem cells were the ideal target cells for gene transfer, because the normal gene would then be transferred to all of the progeny cells, theoretically for the lifetime of the recipient. However, the tasks of isolating the hematopoietic stem cells, introducing the new genes in such a manner as to preserve engraftment of the manipulated cells, and achieving long-term gene expression, have not been straightforward in the clinical trial setting, although there has been moderate success for cells in vitro, and in murine studies. With the report of clinical efficacy of gene transfer in children with X-linked severe combined immunodeficiency disease, the dream of clinical gene transfer to hematopoietic cells has become a reality. But there are still significant impediments remaining for a number of diseases. The innovations of introduction of synthetic receptors that confer growth advantage, the use of lentiviral vectors with increased stem cell transduction efficiency, and the addition of modified promoter/enhancer sequences to augment and preserve gene expression may bring wider success to gene therapy clinical trials for bone marrow disorders in the near future.

Development of gene therapy for hematopoietic stem cells using lentiviral vectors

Lentiviral vectors are promising tools for the development of gene therapy since they can transduce both quiescent and dividing target cells. Lentiviral vectors may be particularly promising gene delivery tools for hematopoietic stem cells since these target cells tend to be quiescent and are therefore difficult target cells for vectors that require dividing targets. Human hematopoietic stem cells that can repopulate NOD/SCID mice have been efficiently transduced using HIV-1-based lentiviral vectors and similar vectors can also transduce murine hematopoietic stem cells. HIV-1 vectors that contain strong general promoters can generate high levels of transgene expression and very high expression levels can be generated in erythroid cells in vivo using beta-globin regulatory sequences to control the expression of the transgene. Current lentiviral vectors have a similar level of biosafety as oncoretroviral vectors and can therefore theoretically be used in clinical gene therapy protocols. Future challenges include the generation of lentiviral vectors that can express more than one transgene at high levels and the generation of safe permanent packaging cells for practical use in clinical gene therapy trials.

Globin gene transfer for the treatment of severe hemoglobinopathies: a paradigm for stem cell-based gene therapy

The prospect of treating blood disorders with genetically modified stem cells is highly promising. This therapeutic approach, however, raises a number of fundamental biological questions, spanning several research fields. Further investigation is required to better understand how to isolate and efficiently transduce hematopoietic stem cells (HSCs), while preserving optimal homing and self-renewing properties; how to design safe vectors permitting controlled expression of the transgene products; and how to promote host repopulation by engrafted HSCs. This article addresses basic issues in stem cell-based gene therapy from the perspective of regulating transgene expression, taking globin gene transfer for the treatment of severe hemoglobinopathies as a paradigm.

Frequency of missense mutations in the coding region of a eukaryotic gene transferred by retroviral vectors

A relatively high mutation rate is probably a major factor in the evolutionary success of retroviruses, because it generates the genetic diversity that helps them to cope with changes in the environment. When using recombinant retroviruses as vectors for gene transfer and gene therapy, it is important to consider the implications of this biological characteristic. Until now, the mutation rate has been studied by using noneukaryotic genes as reporters. Here we report point mutations in the human glucose-6-phosphate dehydrogenase (hG6PD) gene transferred by Moloney murine leukemia virus-based vectors into murine bone marrow cells and NIH 3T3 murine fibroblasts. After bone marrow transplantation, we observed an hG6PD with abnormal electrophoretic mobility for 2 out of 34 mice. Next, we studied this phenomenon quantitatively and found 1 electrophoretically abnormal hG6PD variant among 93 independently isolated NIH 3T3 clones, from which we estimate a mutation rate of 1.4 x 10(-5) per base pair per replication cycle. Mutations in the transferred gene can thus contribute to the impairment of the effectiveness of retrovirus-mediated gene transfer.

Glucose 6-phosphate dehydrogenase expression is less prone to variegation when driven by its own promoter

The ability to transfer permanently genes into mammalian cells makes retroviruses suitable vectors for the ultimate purpose of treating inherited genetic disease. However, expression of the retrovirally transferred genes is variable (position effect and expression variegation) because retroviruses are highly susceptible to the influence of the host genome sequences which flank the integration site. We have investigated this phenomenon with respect to the human housekeeping enzyme, glucose 6-phosphate dehydrogenase (hG6PD). We have constructed retroviral vectors in which the hG6PD cDNA is driven by either of two conventional retroviral promoters and enhancers from the Moloney Murine Leukemia Virus (MMLV) and the Myeloproliferative Sarcoma Virus (MPSV) long terminal repeats (LTR) or by the hG6PD own promoter replacing most of enhancer and promoter LTR (GRU5). We have compared the activity of retrovirally transferred hG6PD driven by these promoters after retroviral integration in bulk cultures and in individual clones of murine fibroblasts. The level of hG6PD expressed by the hG6PD promoter of GRU5-G6PD was significantly lower than that expressed by conventional retroviral vectors. However, analysis of the single copy clones showed less variation of expression with GRU5-G6PD (coefficient of variation, CV, 35.5%) than with conventional vectors (CV, 58.9%). Thus we have several vectors competent for reliable transfer and expression of hG6PD. The hG6PD promoter provides reproducible expression of hG6PD and limits the variability of expression. This decreased variability is important in order to help ensuring a consistent level of delivery of the needed gene product in future therapeutic protocols.