Imprinting of insulin-like growth factor 2 is modulated during hematopoiesis

HSC and miRNA Regulation with Implication for Foetal Haemoglobin Induction in Beta Haemoglobinopathies

Sickle cell disease (SCD) is one of the most common haemoglobinopathies worldwide, with up to 70 % of global SCD annual births occurring in sub-Saharan Africa. Reports have shown that 50 to 80 % of affected children in these countries die annually. Efforts geared towards understanding and controlling HbF production in SCD patients could lead to strategies for effective control of globin gene expression and therapeutic approaches that could be beneficial to individuals with haemoglobinopathies. Hemopoietic stem cells (HSCs) are characterized by a specific miRNA signature in every state of differentiation. The role of miRNAs has become evident both in the maintenance of the "stemness" and in the early induction of differentiation by modulation of the expression of the master pluripotency genes and during early organogenesis. miRNAs are extra regulatory mechanisms in hematopoietic stem cells (HSCs) via influencing transcription profiles together with transcript stability. miRNAs have been reported to be used to reprogram primary somatic cells toward pluripotency. Their involvement in cell editing holds the potential for therapy for many genetic diseases. This review provides a snapshot of miRNA involvement in cell fate decisions, haemoglobin induction pathway, and their journey as some emerge prime targets for therapy in beta haemoglobinopathies.

Paternal Insulin-like Growth Factor 2 (Igf2) Regulates Stem Cell Activity During Adulthood

Insulin-like Growth Factor 2 (IGF2) belongs to the IGF/Insulin pathway, a highly conserved evolutionarily network that regulates growth, aging and lifespan. Igf2 is highly expressed in the embryo and in cancer cells. During mouse development, Igf2 is expressed in all sites where hematopoietic stem cells (HSC) successively expand, then its expression drops at weaning and becomes undetectable when adult HSC have reached their niches in bones and start to self-renew. In the present study, we aim to discover the role of IGF2 during adulthood. We show that Igf2 is specifically expressed in adult HSC and we analyze HSC from adult mice deficient in Igf2 transcripts. We demonstrate that Igf2 deficiency avoids the age-related attrition of the HSC pool and that Igf2 is necessary for tissue homeostasis and regeneration. Our study reveals that the expression level of Igf2 is critical to maintain the balance between stem cell self-renewal and differentiation, presumably by regulating the interaction between HSC and their niche. Our data have major clinical interest for transplantation: understanding the changes in adult stem cells and their environments will improve the efficacy of regenerative medicine and impact health- and life-span.

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The imprinted gene Igf2 is expressed in adult tissue stem cells.

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Igf2 deficiency increases HSC (hematopoietic stem cells) self-renewal and avoids age-related attrition of the HSC pool.

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Igf2 deficiency decreases HSC differentiation and mobilization.

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Igf2 deficiency modifies the interaction between HSC and their environment.

IGF2 belongs to the IGF/Insulin family that regulates growth, aging and lifespan. This role is evolutionarily conserved from worms to mammals. IGF2 favors cell proliferation during embryonic development but its role in adulthood is unknown. To decipher its function we undertook a lifelong analysis of the consequences of Igf2 deficiency on hematopoiesis, in steady-state conditions and during bone marrow transplantation. We demonstrate that lowering Igf2 levels increases the pool of stem cells, without uncontrolled proliferation and migration of immature cells that would lead to cancer. This is a promising way to enhance the stem cells pool during aging that has major interest for transplantation.

Insulin-like growth factor 2 modulates murine hematopoietic stem cell maintenance through upregulation of p57

Hematopoietic stem cells (HSC) rely on a highly regulated molecular network to balance self-renewal and lineage specification to sustain life-long hematopoiesis. Despite a plethora of studies aimed at identifying molecules governing HSC fate, our current knowledge of the genes responsible is limited. We have found insulin-like growth factor 2 (IGF2) to be expressed predominantly within long-term HSCs. This study examines IGF2 expression patterns and the effects of the gene in HSCs. Through the overexpression and knockdown of IGF2 within purified HSCs, we report that IGF2 expression increases HSC-derived multilineage colonies in vitro and enhances hematopoietic contribution in vivo on competitive bone marrow transplantation. The effects of IGF2 are mediated by direct upregulation of the CDKi p57, exclusively within long-term HSCs, via activation of the PI3K-Akt pathway. Increased expression of p57 resulted in a concomitant increase in HSCs in the G0/G1 stage of the cell cycle. Analysis of genomic DNA methylation revealed that HSCs exhibited a hypomethylated state within the promoter region of the CDKN1C (p57) gene, providing a potential mechanism for the exclusive effects of IGF2 within HSCs. Our studies indicate a novel role for IGF2 in regulating HSC cell cycle and illustrate potential novel therapeutic targets for hematologic diseases.

Imprinted genes in myeloid lineage commitment in normal and malignant hematopoiesis

Genomic imprinting is characterized by the parent-of-origin monoallelic expression of several diploid genes because of epigenetic regulation. Imprinted genes (IGs) are key factors in development, supporting the ability of a genotype to produce phenotypes in response to environmental stimuli. IGs are highly expressed during prenatal stages but are downregulated after birth. They also affect aspects of life other than growth such as cognition, behavior, adaption to novel environments, social dominance and memory consolidation. Deregulated genomic imprinting leads to developmental disorders and is associated with solid and blood cancer as well. Several data have been published highlighting the involvement of IGs in as early as the very small embryonic-like stem cells stage and further during myeloid lineage commitment in normal and malignant hematopoiesis. Therefore, we have assembled the current knowledge on the topic, based mainly on recent findings, trying not to focus on a particular cluster but rather to have a global view of several different IGs in hematopoiesis.

Effects of parental folate deficiency on the folate content, global DNA methylation, and expressions of FRα, IGF-2 and IGF-1R in the postnatal rat liver

We examined the effect of parental folate deficiency on the folate content, global DNA methylation, folate receptor-alpha (FRα), insulin-like-growth factor-2 (IGF-2) and -1 receptor (IGF-1R) in the liver and plasma homocysteine in the postnatal rat. Male and female rats were randomly fed a folic acid-deficient (paternal folate-deficient, PD and maternal folate-deficient, MD), or folic acid-supplemented diet (paternal folate-supplemented, PS and maternal-folate-supplemented, MS) for four weeks. They were mated and grouped accordingly: PSxMS, PSxMD, PDxMS, and PDxMD. Pups were killed on day 21 of lactation. The hepatic folate content was markedly reduced in the PDxMD and PSxMD and PDxMS as compared with the PSxMS group. The hepatic global DNA methylation was decreased in the PDxMS and PSxMD groups as much as in the PDxMD group, and all the three groups were significantly lower as compared to the PSxMS group. There were no significant differences in the hepatic FRα, IGF-2 and IGF-1R expressions among the groups. Positive correlations were found between the hepatic folate content and global DNA methylation and protein expressions of FRα, IGF-2 and IGF-1R, whereas an inverse correlation was found between hepatic folate content and plasma homocysteine level in the 3-week-old rat pup. The results of this study show that both paternal and maternal folate deficiency at mating can influence the folate content and global DNA methylation in the postnatal rat liver.

Methylation of promoters of microRNAs and their host genes in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of hematopoietic malignancies characterized by ineffective hematopoiesis. Recently, we identified MDS-associated microRNAs (miRNAs) that are down-regulated in MDS. This study examines possible explanations for that observed down-regulation of miRNA expression in MDS. Since genomic losses are insufficient to explain the down-regulation of all our MDS-associated miRNAs, we explored other avenues. We demonstrate that these miRNAs are predominantly intragenic, and that, in many cases, they and their host genes are expressed in a similar pattern during myeloid maturation, suggesting their co-regulation. This co-regulation is further supported by the down-regulation of several of the host genes in MDS and increased methylation of the shared promoters of several miRNAs and their respective host genes. These studies identify a role of hypermethylation of miRNA promoters in the down-regulation of MDS-associated miRNAs, unifying research on miRNAs in MDS and epigenetic regulation in MDS into a common pathway.

Impaired mesenchymal stem cell differentiation and osteoclastogenesis in mice deficient for Igf2-P2 transcripts

During embryonic development, Igf2 gene transcription is highly regulated through the use of several promoters whose specific roles are not defined. Here, we show that loss-of-function of one of these promoters, Igf2-P2, results in growth defects that are temporally and quantitatively different from those seen in Igf2-null mutants. In particular, Igf2-P2 mutants exhibit skeletal abnormalities characterized by thin and short bones with reduced mineralization and medullar cavity and with altered bone remodeling. These abnormalities are associated with decreased numbers of embryonic mesenchymal chondroprogenitors, adult mesenchymal stem cells and osteoprogenitors. Differentiation of osteoprogenitors into osteoblasts is impaired in the Igf2-P2 mutant mice in a cell-autonomous manner, and osteopontin is a target of the IGF2 signaling pathway during this differentiation. Igf2-P2 mutant mice also display impaired formation of giant osteoclasts owing to a defective micro-environment. These results support a model wherein transcriptional activity of the Igf2-P2 promoter regulates the fate of mesenchymal progenitors during bone development and remodeling in the adult, and regulates osteogenesis in a cell-autonomous and non-autonomous manner.

The H19 locus: role of an imprinted non-coding RNA in growth and development

The H19 gene produces a non-coding RNA, which is abundantly expressed during embryonic development and down-regulated after birth. Although this gene was discovered over 20 years ago, its function has remained unclear. Only recently a role was identified for the non-coding RNA and/or its microRNA partner, first as a tumour suppressor gene in mice, then as a trans-regulator of a group of co-expressed genes belonging to the imprinted gene network that is likely to control foetal and early postnatal growth in mice. The mechanisms underlying this transcriptional or post-transcriptional regulation remain to be discovered, perhaps by identifying the protein partners of the full-length H19 RNA or the targets of the microRNA. This first in vivo evidence of a functional role for the H19 locus provides new insights into how genomic imprinting helps to control embryonic growth.

Synergistic role of Igf2 and Dlk1 in fetal liver development and hematopoiesis in bi-maternal mice

Mouse bi-maternal embryos (BMEs) that contain two haploid sets of genomes from non-growing (ng) and fully-grown (fg) oocytes develop to embryonic day (E) 13.5. However, the ng/fg BMEs never develop beyond E13.5 because of repression of the paternally expressed imprinted genes, Igf2 and Dlk1. The present study was conducted to address the issue of whether fetal hematopoietic disorder is involved in the restricted development of BMEs. FACS analysis revealed that the livers of ng(wt)/fg BMEs contained increased numbers of immature c-kit(+)/ter119(-) hematopoietic cells, were while the numbers of mature c-kit(-)/ter119(+) hematopoietic cells were decreased. This finding was supported by histological observations. Quantitative gene expression analysis revealed that Igf2 and Dlk1 expression was repressed in the liver. To understand the role of paternally-methylated imprinted genes on chromosomes 7 and 12, particularly Igf2 and Dlk1, in fetal liver hematopoiesis, we constructed ng(Deltach7)/fg, ng(Deltach12)/fg and ng(DeltaDouble)/fg BMEs using ng oocytes harboring deletion of differentially methylated regions at distal chromosomes 7 and/or 12. The ng(Deltach7)/fg, ng(Deltach12)/fg and ng(DeltaDouble)/fg BMEs, respectively, express Igf2, Dlk1 and both, and these embryos developed to term with specific phenotypes; the ng(Deltach7)/fg and ng(Deltach12)/fg BMEs develop to term with severe growth retardation, and the ng(DeltaDouble)/fg BMEs can survive to become normal female adults. By inducing Igf2 and Dlk1 expression, the proportions of mature and immature hematopoietic cells in the livers of the ng(Deltach7)/fg, ng(Deltach12)/fg and ng(DeltaDouble)/fg BMEs were considerably restored, and particularly in the ng(DeltaDouble)/fg BMEs, hematopoiesis occurred normally with appropriate expressions of the related genes. These data suggest that inappropriate expression of Igf2 and Dlk1 is involved in impaired fetal hematopoiesis.

Insulin-like growth factor-II: a novel autocrine growth factor modulating the apoptosis and maturation of umbilical cord blood erythroid progenitors

OBJECTIVE

To search a novel function of erythroid progenitor cells circulating as the major nucleated cell population in umbilical cord blood (CB) cells.

MATERIALS AND METHODS

Human CB-derived CD36(+) erythroid progenitors were subjected to cDNA microarray. Gene expression and biological property of CB-erythroid progenitors and adult peripheral blood (PB)-erythroid progenitors were compared by using real-time polymerase chain reaction (PCR) and serum-free culture system with erythropoietin (EPO).

RESULTS

The microarray revealed 124-fold higher levels of insulin-like growth factor-II (IGF-II) gene expression in CB-CD36(+) erythroid progenitors than in stimulated lymphocytes of adult PB. Real-time PCR verified that IGF-II mRNA levels were highest in CB-CD36(+) erythroid progenitors compared to other CB- or adult PB-fractionated cells. When CB-CD36(+) erythroid progenitors were cultured with EPO in serum-free medium, anti-IGF-II-antibody (Ab) reduced the number of erythroid colonies. When CB- and adult PB-derived erythroid colony-forming cells (ECFCs) were cultured with interleukin-3, stem cell factor, and EPO, mRNA levels per cells of IGF-II peaked on day 12, but those of type 1 and type 2 receptors did not increase with ECFCs maturation. The maturation rate by IGF-II was higher in CB-ECFCs than in adult PB-ECFCs. The majority of CB-ECFCs expressed IGF-II protein. Anti-IGF-II-Ab, but not anti-IGF-I-Ab, reduced the number of CB-ECFCs in liquid culture with EPO. Anti-IGF-II-Ab accelerated apoptosis of ECFCs, assessed by dimethylthiazole tetrazolium bromide, bromodeoxyuridine, and flow cytometric analyses. ECFCs failed to attain full maturity in the presence of anti-IGF-II-Ab.

CONCLUSIONS

These results suggest that IGF-II is produced by erythroid progenitors themselves, and has a crucial role in fetal erythropoiesis by modulating apoptosis and maturation in an autocrine fashion.

Genomic imprinting of insulin-like growth factor 2 (IGF-2) in chronic synovitis

OBJECTIVE

To search for relaxation or loss of IGF-2 imprinting (LOI) in rheumatoid arthritis (RA) synovial tissues.

DESIGN

The genotype of IGF-2 was determined in 25 freshly isolated synovial tissue samples with signs of active inflammation by polymerase chain reaction (PCR) and restriction fragment length polymorphism. Imprinting was determined in synovial tissue mononuclear cells (STMC) of five informative heterozygous patients by reverse transcriptase (RT)-PCR. Mitogen-stimulated peripheral blood mononuclear cells (PBMC) from six informative healthy donors were selected for control.

RESULTS

In vitro proliferation of CD4+ and CD8+ PB T cells, and also of CD19+ PB B cells was detectable upon mitogen stimulation. Furthermore, MHC II molecule expression on synovial B and T cells indicated in vivo cell activation. Monoallelic IGF-2 expression was seen in PBMC cultures from two healthy donors under both, resting and stimulating conditions. In two other PBMC cultures, LOI occurred exclusively after 24 h of stimulation. PBMC from two other healthy donors showed LOI under both, resting and stimulating conditions. Mitogen induced and spontaneous LOI was reversible in each one PBMC culture after 72 h. In contrast, none of the informative STMC cultures showed LOI.

CONCLUSIONS

LOI in lymphocytes may occur spontaneously or inducible. However, longstanding activation of lymphocytes in RA synovitis appears not to be related to this mechanism.

Epigenetic and phenotypic consequences of a truncation disrupting the imprinted domain on distal mouse chromosome 7

The distal end of mouse chromosome 7 (Chr 7) contains a large cluster of imprinted genes. In this region two cis-acting imprinting centers, IC1 (H19 DMR) and IC2 (KvDMR1), define proximal and distal subdomains, respectively. To assess the functional independence of IC1 in the context of Chr 7, we developed a recombinase-mediated chromosome truncation strategy in embryonic stem cells and generated a terminal deletion allele, DelTel7, with a breakpoint in between the two subdomains. We obtained germ line transmission of the truncated Chr 7 and viable paternal heterozygotes, confirming the absence of developmentally required paternally expressed genes distal of Ins2. Conversely, maternal transmission of DelTel7 causes a midgestational lethality, consistent with loss of maternally expressed genes in the IC2 subdomain. Expression and DNA methylation analyses on DelTel7 heterozygotes demonstrate the independent imprinting of IC1 in absence of the entire IC2 subdomain. The evolutionarily conserved linkage between the subdomains is therefore not required for IC1 imprinting on Chr 7. Importantly, the developmental phenotype of maternal heterozygotes is rescued fully by a paternally inherited deletion of IC2. Thus, all the imprinted genes located in the region and required for normal development are silenced by an IC2-dependent mechanism on the paternal allele.

Hematopoietic reconstitution with androgenetic and gynogenetic stem cells

Parthenogenetic embryonic stem (ES) cells with two oocyte-derived genomes (uniparental) have been proposed as a source of autologous tissue for transplantation. The therapeutic applicability of any uniparental cell type is uncertain due to the consequences of genomic imprinting that in mammalian uniparental tissues causes unbalanced expression of imprinted genes. We transplanted uniparental fetal liver cells into lethally irradiated adult mice to test their capacity to replace adult hematopoietic tissue. Both maternal (gynogenetic) and paternal (androgenetic) derived cells conveyed long-term, multilineage reconstitution of hematopoiesis in recipients, with no associated pathologies. We also establish that uniparental ES cells can differentiate into transplantable hematopoietic progenitors in vitro that contribute to long-term hematopoiesis in recipients. Hematopoietic tissue in recipients maintained fidelity of parent-of-origin methylation marks at the Igf2/H19 locus; however, variability occurred in the maintenance of parental-specific methylation marks at other loci. In summary, despite genomic imprinting and its consequences on development that are particularly evident in the androgenetic phenotype, uniparental cells of both parental origins can form adult-transplantable stem cells and can repopulate an adult organ.

Loss of imprinting and promoter usage of the IGF2 in laryngeal squamous cell carcinoma

The gene for insulin-like growth factor two, IGF2 is maternally imprinted. Fifteen heterozygous samples were analyzed for the IGF2 imprinting status and promoter usage. IGF2 LOI was detected in four non-tumorous tissues and in six laryngeal squamous cell carcinoma (LSCC) tumors. There was no clear pattern of specific promoter activity in LSCC tumors and the adjacent normal tissues. P1 promoter usage was active in eight LSCCs, among them four with LOI. As it was activated in four tumors with maintenance of imprinting (MOI) and four non-tumors, we concluded that P1 promoter is not exclusively connected with IGF2 LOI in LSCC.

Resistance to growth hormone releasing hormone and gonadotropins in Albright's hereditary osteodystrophy

Heterozygous inactivating mutations in the Gs alpha gene cause Albright's hereditary osteo-dystrophy (AHO). Consistent with the observation that only maternally inherited mutations lead to resistance to hormone action (pseudohypoparathyroidism type Ia [PHP-Ia), recent studies have provided evidence for a predominant maternal origin of Gs alpha transcripts in endocrine organs, such as thyroid, gonad and pituitary. Accordingly, patients with PHP-Ia display variable degrees of resistance to parathyroid hormone (PTH), thyroid stimulating hormone (TSH), gonadotropins and growth hormone (GH) releasing hormone (GHRH). Although the incidence and the clinical and biochemical characteristics of PTH and TSH resistance have been widely investigated and described, the cause and significance of the reproductive dysfunction in AHO is still poorly understood. The clinical finding of alterations of GH secretion in these patients was described for the first time only 2 years ago. The present report briefly reviews the literature focusing on the actual knowledge about these last two subjects.

Quantification of allele-specific G-protein beta3 subunit mRNA transcripts in different human cells and tissues by Pyrosequencing

The G-protein 825T allele is associated with altered drug responses while the underlying mechanism is not fully understood. Differential expression of transcripts from the C and T alleles could contribute to this process. The C825T polymorphism located in exon 10 is in close linkage disequilibrium with the A(-350)G promoter single nucleotide polymorphism (SNP) and the C1429T SNP and could therefore serve as a marker for allele-specific expression resulting from the promoter SNP. However, alternative splicing of exon 10 in 825T allele carriers may result in under-represented mRNA transcripts. We, therefore, established a novel method based on the Pyrosequencing technology to quantify allele-specific transcript expression and quantified the allelic variance of the C1429T polymorphism located in the 3'-untranslated region of GNB3. Validation of the method was performed using linear regression analysis of measured versus expected ratios of DNA mixed at different known concentrations as well as determining allele-specific mRNA expression of the partially imprinted IGF-2 gene. We genotyped the C1429T polymorphism of 83 samples derived from six different human tissues and cell lines and quantified mRNA transcripts from different alleles using heterozygous samples. No significantly different transcript amounts from the two alleles were found. There were also no significantly different transcript amounts associated with different G(-350)A genotypes (P>0.05). As a result, we could show that Pyrosequencing provides a sensitive tool to quantify allele-specific transcript expression. Our data do not support the hypothesis that differential G-protein activity associated with the C825T SNP results from different transcript amounts associated with specific GNB3 genotypes.

Alterations of DNA methylation in hematologic malignancies

The DNA methylation profile of cancer cells is frequently characterized by global hypomethylation and simultaneous hypermethylation of selected CpG island gene promoters. In recent years, the epigenetic phenomenon of DNA promoter methylation has gained increasing recognition as an important mechanism for transcriptional inactivation of cancer related genes. Studies on both liquid and solid tumors have revealed myriad aberrant methylation events, some of which may provide important clues to the pathogenesis of these tumors. The identification of these methylation alterations and elucidation of the mechanistic events surrounding them are of prime importance, as the methylation status of cancer cells can now be manipulated in vivo with demethylating chemotherapeutics.

Loss of genomic imprinting of insulin-like growth factor 2 is strongly associated with cellular proliferation in normal hematopoietic cells

OBJECTIVE

The human insulin-like growth factor 2 (IGF2) gene was thought to be imprinted and expressed only from the paternal allele in normal tissue.

MATERIALS AND METHODS

Initially, we analyzed the imprinting status of IGF2 in bone marrow cells from 49 patients with myelodysplastic syndromes (MDS) utilizing the Apa I polymorphism of IGF2. Thirteen bone marrow and 14 peripheral blood samples from normal individuals served as controls. We utilized normal peripheral blood T lymphocytes to examine the relationship between genomic imprinting and cell proliferation. Expression of IGF2 was quantified by real-time PCR and proliferation of T cells was measured by 3H-thymidine incorporation. Furthermore, methylation status of the imprinting controlling region (ICR) was analyzed by subcloning and sequencing of genomic DNA after sodium bisulfite modification.

RESULTS

Among 24 patients who were heterozygous for IGF2, loss of imprinting (LOI) occurred in 22 cases (92%). Surprisingly, LOI of IGF2 occurred in the normal bone marrow cells, but the normal peripheral blood cells showed retention of imprinting (ROI). Unstimulated normal T cells showed ROI. After 24 hours of exposure to PHA, these cells changed their IGF2 imprinting status from ROI to LOI. Concomitantly, their IGF2 RNA levels increased up to sixfold and their proliferation increased 10- to 20-fold. In contrast, normal T cells not stimulated with PHA did not develop LOI of IGF2, had negligible levels of IGF2 RNA, and did not increase their proliferation. In unstimulated T cells, the CpG islands of the ICR were completely methylated on one allele and nearly completely unmethylated on the other allele. After PHA stimulation, the CpG islands at the ICR became completely methylated on both alleles.

CONCLUSION

LOI of IGF2 is strongly associated with cell proliferation and is not limited to cancer cells.

The insulin-like growth factor system in hematopoietic cells

The insulin-like growth factor (IGF) system regulates proliferation and differentiation of hematopoietic cells. IGFs exert their effects through specific receptors on growing and differentiating blood cells as they emerge from their small pool of ancestral stem cells. The IGF system is complex as both stimulating and inhibiting effects occur by interaction of IGFs and IGF-binding proteins (IGFBPs). IGFs stimulate erythrocytes and lymphocytes but also promote leukemic hematopoietic cell proliferation. IGF-I appears to be correlated with hemoglobin levels in anemia and could also be of benefit for patients with bone marrow aplasia after transplantation. Hypersensitivity to IGF-I has been implicated as an underlying cause of polycythemia vera. Loss of imprinting of IGF-II is found in acute myeloid leukemia and myelodysplastic syndrome. Apoptosis of hematopoietic cells is significantly reduced by IGF-I involving an intriguing signal transduction pathway. IGFs could therefore, although not classical hematopoietic growth factors, be of benefit for patients with diverse hematopoietic disorders.