Autophagy driven by a master regulator of hematopoiesis

Urolithin A prevents age-related hearing loss in C57BL/6J mice likely by inducing mitophagy

Mitochondrial dysfunction with aging is associated with the development of age-related hearing loss. Mitophagy is a cardinal mechanism to maintain a healthy mitochondrial population through the turnover of damaged mitochondria. Declining mitophagy with age causes a buildup of damaged mitochondria, leading to sensory organ dysfunction. The effect of Urolithin A (UA), a mitophagy inducer, was investigated on age-related hearing loss in a mouse model. C57BL/6J mice were treated with UA from 6 to 10 months of age. UA attenuated an auditory brainstem responses (ABR) threshold shift at 8, 16, and 32 kHz frequencies, and improved mitochondrial DNA integrity and ATP production in the cochlea and auditory cortex. The mRNA levels of mitophagy-related genes and protein levels of PINK1, Parkin, BNIP3, and LC3B increased in the cochlea and auditory cortex. The expression of mitophagosomes and mitophagolysosomes in the cochlea, spiral ganglion, auditory cortex, and inferior colliculus increased, together with the expression of Parkin and BNIP3 in the cochlea, spiral ganglion, auditory cortex, and inferior colliculus. These results indicate that UA counteracted mitophagy decline in the auditory system and prevented age-related hearing loss. UA can be used as a potential agent to prevent age-related hearing loss.

Biallelic loss-of-function variants of ZFTRAF1 cause neurodevelopmental disorder with microcephaly and hypotonia

PURPOSE

Neurodevelopmental disorders exhibit clinical and genetic heterogeneity, ergo manifest dysfunction in components of diverse cellular pathways; the precise pathomechanism for the majority remains elusive.

METHODS

We studied 5 affected individuals from 3 unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We used exome sequencing and prioritized variants that were subsequently characterized using immunofluorescence, immunoblotting, pulldown assays, and RNA sequencing.

RESULTS

We identified biallelic variants in ZFTRAF1, encoding a protein of yet unknown function. Four affected individuals from 2 unrelated families segregated 2 homozygous frameshift variants in ZFTRAF1, whereas, in the third family, an intronic splice site variant was detected. We investigated ZFTRAF1 at the cellular level and signified it as a nucleocytoplasmic protein in different human cell lines. ZFTRAF1 was completely absent in the fibroblasts of 2 affected individuals. We also identified 110 interacting proteins enriched in mRNA processing and autophagy-related pathways. Based on profiling of autophagy markers, patient-derived fibroblasts show irregularities in the protein degradation process.

CONCLUSION

Thus, our findings suggest that biallelic variants of ZFTRAF1 cause a severe neurodevelopmental disorder.

Therapeutic Relevance of Inducing Autophagy in β-Thalassemia

The β-thalassemias are inherited genetic disorders affecting the hematopoietic system. In β-thalassemias, more than 350 mutations of the adult β-globin gene cause the low or absent production of adult hemoglobin (HbA). A clinical parameter affecting the physiology of erythroid cells is the excess of free α-globin. Possible experimental strategies for a reduction in excess free α-globin chains in β-thalassemia are CRISPR-Cas9-based genome editing of the β-globin gene, forcing "de novo" HbA production and fetal hemoglobin (HbF) induction. In addition, a reduction in excess free α-globin chains in β-thalassemia can be achieved by induction of the autophagic process. This process is regulated by the Unc-51-like kinase 1 (Ulk1) gene. The interplay with the PI3K/Akt/TOR pathway, with the activity of the α-globin stabilizing protein (AHSP) and the involvement of microRNAs in autophagy and Ulk1 gene expression, is presented and discussed in the context of identifying novel biomarkers and potential therapeutic targets for β-thalassemia.

Saracatinib prompts hemin-induced K562 erythroid differentiation but suppresses erythropoiesis of hematopoietic stem cells

Human myeloid leukemia cells (such as K562) could be used for the study of erythropoiesis, and mature erythroid markers and globins could be induced during leukemia cell differentiation; however, the pathways involved are different compared with those of hematopoietic stem cells (HSCs).We identified the differentially expressed genes (DEGs) of K562 cells and HSCs associated with stem cells and erythroid differentiation. Furthermore, we showed that hemin-induced differentiation of K562 cells could be induced by serum starvation or treatment with the tyrosine kinase inhibitor saracatinib. However, erythroid differentiation of HSCs was inhibited by the deprivation of the important serum component erythropoietin (EPO) or treatment with saracatinib. Finally, we found that the mRNA expression of K562 cells and HSCs was different during saracatinib-treated erythroid differentiation, and the DEGs of K562 cells and HSCs associated with tyrosine-protein kinase were identified.These findings elucidated the cellular phenomenon of saracatinib induction during erythroid differentiation of K562 cells and HSCs, and the potential mechanism is the different mRNA expression profile of tyrosine-protein kinase in K562 cells and HSCs.

A review of the role of zinc finger proteins on hematopoiesis

The bone marrow is responsible for producing an incredible number of cells daily in order to maintain blood homeostasis through a process called hematopoiesis. Hematopoiesis is a greatly demanding process and one entirely dependent on complex interactions between the hematopoietic stem cell (HSC) and its surrounding microenvironment. Zinc (Zn2+) is considered an important trace element, playing diverse roles in different tissues and cell types, and zinc finger proteins (ZNF) are proteins that use Zn2+ as a structural cofactor. In this way, the ZNF structure is supported by a Zn2+ that coordinates many possible combinations of cysteine and histidine, with the most common ZNF being of the Cys2His2 (C2H2) type, which forms a family of transcriptional activators that play an important role in different cellular processes such as development, differentiation, and suppression, all of these being essential processes for an adequate hematopoiesis. This review aims to shed light on the relationship between ZNF and the regulation of the hematopoietic tissue. We include works with different designs, including both in vitro and in vivo studies, detailing how ZNF might regulate hematopoiesis.

A transcriptional network governing ceramide homeostasis establishes a cytokine-dependent developmental process

Transcriptional mechanisms controlling developmental processes establish and maintain proteomic networks, which can govern the levels of intracellular small molecules. Although dynamic changes in bioactive small molecules can link transcription factor and genome activity with cell state transitions, many mechanistic questions are unresolved. Using quantitative lipidomics and multiomics, we discover that the hematopoietic transcription factor GATA1 establishes ceramide homeostasis during erythroid differentiation by regulating genes encoding sphingolipid metabolic enzymes. Inhibiting a GATA1-induced sphingolipid biosynthetic enzyme, delta(4)-desaturase, or disrupting ceramide homeostasis with cell-permeable dihydroceramide or ceramide is detrimental to erythroid, but not myeloid, progenitor activity. Coupled with genetic editing-based rewiring of the regulatory circuitry, we demonstrate that ceramide homeostasis commissions vital stem cell factor and erythropoietin signaling by opposing an inhibitory protein phosphatase 2A-dependent, dual-component mechanism. Integrating bioactive lipids as essential components of GATA factor mechanisms to control cell state transitions has implications for diverse cell and tissue types.

Integrated analysis of a miRNA-mRNA network related to immunity and autophagy in Macrobrachium rosenbergii infected with Aeromonas hydrophila

MicroRNAs (miRNAs) are a group of RNAs that regulate gene expression in the post-transcriptionally. miRNAs can regulate numerous processes, such as the immune response, due to their dynamic expression patterns. The giant freshwater prawn Macrobrachium rosenbergii is a major freshwater aquaculture prawn that is attacked by various bacteria, including Aeromonas hydrophila. For this study, we performed an analysis of the miRNA and mRNA transcriptome analysis of M. rosenbergii which was infected with A. hydrophila. We identified 56 differentially expressed miRNAs (DEMs) and 1542 differentially expressed mRNAs. Furthermore, an integrated analysis of miRNA-mRNA expression led to the identification of 729 differentially predicted target genes (DETGs) of the DEMs. Multiple functional categories related to immunity, apoptosis, and autophagy were found to be enriched in the DETGs. During the infection of M. rosenbergii by A. hydrophila, an elaborate regulatory network involving Toll and immune deficiency (IMD) signaling, mitogen-activated protein kinase (MAPK) signaling, lysosome, and cell apoptosis was formed by a complex interplay of 40 crucial DEMs and 22 DETGs, all associated with the immune and autophagy pathway. The findings suggest that infection with A. hydrophila triggers intricate responses in both miRNA and mRNA, significantly impacting immune and autophagy processes in M. rosenbergii.

Interferon regulatory factor-8-dependent innate immune alarm senses GATA2 deficiency to alter hematopoietic differentiation and function

PURPOSE OF REVIEW

Recent discoveries have provided evidence for mechanistic links between the master regulator of hematopoiesis GATA2 and the key component of interferon and innate immunity signaling pathways, interferon-regulatory factor-8 (IRF8). These links have important implications for the control of myeloid differentiation in physiological and pathological states.

RECENT FINDINGS

GATA2 deficiency resulting from loss of the Gata2 -77 enhancer in progenitors triggers an alarm that instigates the transcriptional induction of innate immune signaling and distorts a myeloid differentiation program. This pathological alteration renders progenitors hyperresponsive to interferon γ, toll-like receptor and interleukin-6 signaling and impaired in granulocyte-macrophage colony-stimulating factor signaling. IRF8 upregulation in -77-/- progenitors promotes monocyte and dendritic cell differentiation while suppressing granulocytic differentiation. As PU.1 promotes transcription of Irf8 and other myeloid and B-lineage genes, GATA2-mediated repression of these genes opposes the PU.1-dependent activating mechanism.

SUMMARY

As GATA2 deficiency syndrome is an immunodeficiency disorder often involving myelodysplastic syndromes and acute myeloid leukemia, elucidating how GATA2 commissions and decommissions genome activity and developmental regulatory programs will unveil mechanisms that go awry when GATA2 levels and/or activities are disrupted.

Advances in Understanding the Links between Metabolism and Autophagy in Acute Myeloid Leukemia: From Biology to Therapeutic Targeting

Autophagy is a highly conserved cellular degradation process that regulates cellular metabolism and homeostasis under normal and pathophysiological conditions. Autophagy and metabolism are linked in the hematopoietic system, playing a fundamental role in the self-renewal, survival, and differentiation of hematopoietic stem and progenitor cells, and in cell death, particularly affecting the cellular fate of the hematopoietic stem cell pool. In leukemia, autophagy sustains leukemic cell growth, contributes to survival of leukemic stem cells and chemotherapy resistance. The high frequency of disease relapse caused by relapse-initiating leukemic cells resistant to therapy occurs in acute myeloid leukemia (AML), and depends on the AML subtypes and treatments used. Targeting autophagy may represent a promising strategy to overcome therapeutic resistance in AML, for which prognosis remains poor. In this review, we illustrate the role of autophagy and the impact of its deregulation on the metabolism of normal and leukemic hematopoietic cells. We report updates on the contribution of autophagy to AML development and relapse, and the latest evidence indicating autophagy-related genes as potential prognostic predictors and drivers of AML. We review the recent advances in autophagy manipulation, combined with various anti-leukemia therapies, for an effective autophagy-targeted therapy for AML.

Transcriptional regulation of autophagy and its implications in human disease

Macroautophagy/autophagy is a conserved catabolic pathway that is vital for maintaining cell homeostasis and promoting cell survival under stressful conditions. Dysregulation of autophagy is associated with a variety of human diseases, such as cancer, neurodegenerative diseases, and metabolic disorders. Therefore, this pathway must be precisely regulated at multiple levels, involving epigenetic, transcriptional, post-transcriptional, translational, and post-translational mechanisms, to prevent inappropriate autophagy activity. In this review, we focus on autophagy regulation at the transcriptional level, summarizing the transcription factors that control autophagy gene expression in both yeast and mammalian cells. Because the expression and/or subcellular localization of some autophagy transcription factors are altered in certain diseases, we also discuss how changes in transcriptional regulation of autophagy are associated with human pathophysiologies.

Crosstalk between miR-144/451 and Nrf2 during Recovery from Acute Hemolytic Anemia

miR-144/451 and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) regulate two antioxidative systems that have been identified to maintain redox homeostasis in erythroid cells by removing excess reactive oxygen species (ROS). Whether these two genes coordinate to affect ROS scavenging and the anemic phenotype, or which gene is more important for recovery from acute anemia, has not been explored. To address these questions, we crossed miR-144/451 knockout (KO) and Nrf2 KO mice and examined the phenotype change in the animals as well as the ROS levels in erythroid cells either at baseline or under stress condition. Several discoveries were made in this study. First, Nrf2/miR-144/451 double-KO mice unexpectedly exhibit similar anemic phenotypes as miR-144/451 single-KO mice during stable erythropoiesis, although compound mutations of miR-144/451 and Nrf2 lead to higher ROS levels in erythrocytes than single gene mutations. Second, Nrf2/miR-144/451 double-mutant mice exhibit more dramatic reticulocytosis than miR-144/451 or Nrf2 single-KO mice during days 3 to 7 after inducing acute hemolytic anemia using phenylhydrazine (PHZ), indicating a synergistic effect of miR-144/451 and Nrf2 on PHZ-induced stress erythropoiesis. However, the coordination does not persist during the whole recovery stage of PHZ-induced anemia; instead, Nrf2/miR-144/451 double-KO mice follow a recovery pattern similar to miR-144/451 single-KO mice during the remaining period of erythropoiesis. Third, the complete recovery from PHZ-induced acute anemia in miR-144/451 KO mice takes longer than in Nrf2 KO mice. Our findings demonstrate that complicated crosstalk between miR-144/451 and Nrf2 does exist and the crosstalk of these two antioxidant systems is development-stage-dependent. Our findings also demonstrate that miRNA deficiency could result in a more profound defect of erythropoiesis than dysfunctional transcription factors.

Pathogenic human variant that dislocates GATA2 zinc fingers disrupts hematopoietic gene expression and signaling networks

Although certain human genetic variants are conspicuously loss of function, decoding the impact of many variants is challenging. Previously, we described a patient with leukemia predisposition syndrome (GATA2 deficiency) with a germline GATA2 variant that inserts 9 amino acids between the 2 zinc fingers (9aa-Ins). Here, we conducted mechanistic analyses using genomic technologies and a genetic rescue system with Gata2 enhancer-mutant hematopoietic progenitor cells to compare how GATA2 and 9aa-Ins function genome-wide. Despite nuclear localization, 9aa-Ins was severely defective in occupying and remodeling chromatin and regulating transcription. Variation of the inter-zinc finger spacer length revealed that insertions were more deleterious to activation than repression. GATA2 deficiency generated a lineage-diverting gene expression program and a hematopoiesis-disrupting signaling network in progenitors with reduced granulocyte-macrophage colony-stimulating factor (GM-CSF) and elevated IL-6 signaling. As insufficient GM-CSF signaling caused pulmonary alveolar proteinosis and excessive IL-6 signaling promoted bone marrow failure and GATA2 deficiency patient phenotypes, these results provide insight into mechanisms underlying GATA2-linked pathologies.

Heterochromatin rewiring and domain disruption-mediated chromatin compaction during erythropoiesis

Mammalian erythropoiesis involves progressive chromatin compaction and subsequent enucleation in terminal differentiation, but the mechanisms underlying the three-dimensional chromatin reorganization remain obscure. Here, we systematically analyze the higher-order chromatin in purified populations of primary human erythroblasts. Our results reveal that heterochromatin regions undergo substantial compression, with H3K9me3 markers relocalizing to the nuclear periphery and forming a significant number of long-range interactions, and that ~58% of the topologically associating domain (TAD) boundaries are disrupted, while certain TADs enriched for markers of the active transcription state and erythroid master regulators, GATA1 and KLF1, are selectively maintained during terminal erythropoiesis. Finally, we demonstrate that GATA1 is involved in safeguarding selected essential chromatin domains during terminal erythropoiesis. Our study therefore delineates the molecular characteristics of a development-driven chromatin compaction process, which reveals transcription competence as a key indicator of the selected domain maintenance to ensure appropriate gene expression during the extreme compaction of chromatin.

Heme-dependent induction of mitophagy program during differentiation of murine erythroid cells

Although establishment and maintenance of mitochondria are essential for the production of massive amounts of heme in erythroblasts, mitochondria must be degraded upon terminal differentiation to red blood cells (RBCs), thus creating a biphasic regulatory process. Previously, we reported that iron deficiency in mice promotes mitochondrial retention in RBCs, suggesting that a proper amount of iron and/or heme is necessary for the degradation of mitochondria during erythroblast maturation. Because the transcription factor GATA1 regulates autophagy in erythroid cells, which involves mitochondrial clearance (mitophagy), we investigated the relationship between iron or heme and mitophagy by analyzing the expression of genes related to GATA1 and autophagy and the impact of iron or heme restriction on the amount of mitochondria. We found that heme promotes the expression of GATA1-regulated mitophagy-related genes and the induction of mitophagy. GATA1 might induce the expression of the autophagy-related genes Atg4d and Stk11 for mitophagy through a heme-dependent mechanism in murine erythroleukemia (MEL) cells and a genetic rescue system with G1E-ER-GATA1 erythroblast cells derived from Gata1-null murine embryonic stem cells. These results provide evidence for a biphasic mechanism in which mitochondria are essential for heme generation, and the heme generated during differentiation promotes mitophagy and mitochondrial disposal. This mechanism provides a molecular framework for understanding this fundamentally important cell biological process.

Strain-Specific Behavior of Mycobacterium tuberculosis in Interruption of Autophagy Pathway in Human Alveolar Type II Epithelial A549 Cells

BACKGROUND

Autophagy induction has been shown to differ in magnitude depending on the mycobacterial species. However, few studies have investigated the specific autophagic capacity of different Mycobacterium tuberculosis (Mtb) strains in alveolar epithelial cells (ATs). This study aimed to elucidate the host autophagic response to different Mtb strains in ATs responsible for TB in the capital of Iran, Tehran.

METHODS

A549 cells were infected with three different Mtb clinical isolates (Beijing, NEW1, and CAS1/Delhi) and the reference strain H37Rv. Following RNA extraction, the expression of eight ATG genes, four mycobacterial genes, and three miRNAs was evaluated using quantitative RT-PCR.

RESULTS

The results revealed that all four strains influenced the autophagy pathway in various ways at different magnitudes. The Beijing and H37Rv strains could inhibit autophagosome formation, whereas the CAS and NEW1 strains induced autophagosome formation. The expression of genes involved in the fusion of autophagosomes to lysosomes (LAMP1) indicated that all the studied strains impaired the autophagolysosomal fusion; this result is not unexpected as Mtb can block the autophagolysomal fusion. In addition, the Beijing and H37RV strains prevented the formation of autophagic vacuoles, besides mycobacterial targeting of lysosomes and protease activity.

CONCLUSION

This preliminary study improved our understanding of how Mtb manages to overcome the host immune system, such as autophagy, and evaluated the genes used by specific strains during this process. Further studies with a large number of Mtb strains, encompassing the other main Mtb lineages, are inevitable.

Effect of Glucocorticosteroids in Diamond-Blackfan Anaemia: Maybe Not as Elusive as It Seems

Diamond-Blackfan anaemia (DBA) is a red blood cell aplasia that in the majority of cases is associated with ribosomal protein (RP) aberrations. However, the mechanism by which this disorder leads to such a specific phenotype remains unclear. Even more elusive is the reason why non-specific agents such as glucocorticosteroids (GCs), also known as glucocorticoids, are an effective therapy for DBA. In this review, we (1) explore why GCs are successful in DBA treatment, (2) discuss the effect of GCs on erythropoiesis, and (3) summarise the GC impact on crucial pathways deregulated in DBA. Furthermore, we show that GCs do not regulate DBA erythropoiesis via a single mechanism but more likely via several interdependent pathways.

Ferroptosis: regulation by competition between NRF2 and BACH1 and propagation of the death signal

Ferroptosis is triggered by a chain of intracellular labile iron-dependent peroxidation of cell membrane phospholipids. Ferroptosis is important not only as a cause of ischaemic and neurodegenerative diseases but also as a mechanism of cancer suppression, and a better understanding of its regulatory mechanism is required. It has become clear that ferroptosis is finely controlled by two oxidative stress-responsive transcription factors, NRF2 (NF-E2-related factor 2) and BACH1 (BTB and CNC homology 1). NRF2 and BACH1 inhibit and promote ferroptosis, respectively, by activating or suppressing the expression of genes in the major regulatory pathways of ferroptosis: intracellular labile iron metabolism, the GSH (glutathione) -GPX4 (glutathione peroxidase 4) pathway and the FSP1 (ferroptosis suppressor protein 1)-CoQ (coenzyme Q) pathway. In addition to this, NRF2 and BACH1 control ferroptosis through the regulation of lipid metabolism and cell differentiation. This multifaceted regulation of ferroptosis by NRF2 and BACH1 is considered to have been acquired during the evolution of multicellular organisms, allowing the utilization of ferroptosis for maintaining homeostasis, including cancer suppression. In terms of cell-cell interaction, it has been revealed that ferroptosis has the property of propagating to surrounding cells along with lipid peroxidation. The regulation of ferroptosis by NRF2 and BACH1 and the propagation phenomenon could be used to realize anticancer cell therapy in the future. In this review, these points will be summarized and discussed.

Resveratrol induces proliferation in preosteoblast cell MC3T3-E1 via GATA-1 activating autophagy

Resveratrol (RSV) could promote osteogenic activity, but its clinical application has been hampered in view of its poor bioavailability. Therefore, it is desirable to identify with certainty the molecular target of its bone mass boosting function, which is crucial to the design of an effective therapeutic strategy for the optimal treatment of osteoporosis. Emerging evidence has indicated that GATA-1, an important transcription factor in megakaryocyte and erythrocyte differentiation, can directly activate autophagy in erythrocytes, alluding to its impact on bone metabolism. In light of this, we sought to determine whether GATA-1 would be a putative target by which RSV would act on osteoblast proliferation and, if so, to explore the underlying mechanism involved in the process. We examined the cell viability, colony formation, cell cyclin expression, autophagy level, and the expression levels of GATA-1 and adenosine 5'-monophosphate (AMP)-activated protein kinase α (AMPKα) in osteoblastic cell strain MC3T3-E1. The results showed that RSV promoted the proliferation process in MC3T3-E1 coupled with increased expression of GATA-1 and phosphorylated AMPKα and activated autophagy. When GATA-1 was interfered with siRNA, both autophagy and proliferation were decreased. Administration of the agonist of phosphorylated AMPKα1 (Thr172) promoted the translocation of GATA-1 into the nucleus. Based on the above results, we concluded that RSV induces the proliferation of MC3T3-E1 by increasing GATA-1 expression, which thence activates autophagy; and of note, AMPKα is one of the upstream regulators of GATA-1.

zmiz1a zebrafish mutants have defective erythropoiesis, altered expression of autophagy genes, and a deficient response to vitamin D

ZMIZ1 is a transcriptional coactivator that is related to members of the protein inhibitor of activated STAT (PIAS) family. ZMIZ1 regulates the activity of various transcription factors including the androgen receptor, p53, and Smad3. ZMIZ1 also interacts with Notch1 and selectively regulates Notch1 target genes relevant for T cell development and leukemogenesis in mammals. Human ZMIZ1 is additionally characterized as a latitude-dependent autoimmune disease (LDAD) risk gene, as it is responsive to vitamin D and has been associated with at least eleven blood cell traits. To address the function of ZMIZ1 in fish, we introduced CRISPR/Cas9 mutations in the zmiz1a gene in zebrafish. We observed that inactivation of zmiz1a in developing zebrafish larvae results in lethality at 15 days post fertilization (dpf) and delayed erythroid maturation. Differential gene expression analysis indicated that 15 dpf zmiz1a-null larvae had altered expression of autophagy genes, and erythrocytes that lacked Zmiz1a function exhibited an accumulation of mitochondrial DNA. Furthermore, we observed that autophagy gene expression was dysregulated at earlier stages of development, which suggests the involvement of Zmiz1a in the regulation of autophagy genes beyond the process of red blood cell differentiation. Finally, we showed that the loss of Zmiz1a decreased the capacity of the embryos to respond to vitamin D, indicating additional participation of Zmiz1a as a mediator of vitamin D activity.

Using the Zebrafish as a Genetic Model to Study Erythropoiesis

Vertebrates generate mature red blood cells (RBCs) via a highly regulated, multistep process called erythropoiesis. Erythropoiesis involves synthesis of heme and hemoglobin, clearance of the nuclei and other organelles, and remodeling of the plasma membrane, and these processes are exquisitely coordinated by specific regulatory factors including transcriptional factors and signaling molecules. Defects in erythropoiesis can lead to blood disorders such as congenital dyserythropoietic anemias, Diamond–Blackfan anemias, sideroblastic anemias, myelodysplastic syndrome, and porphyria. The molecular mechanisms of erythropoiesis are highly conserved between fish and mammals, and the zebrafish (Danio rerio) has provided a powerful genetic model for studying erythropoiesis. Studies in zebrafish have yielded important insights into RBC development and established a number of models for human blood diseases. Here, we focus on latest discoveries of the molecular processes and mechanisms regulating zebrafish erythropoiesis and summarize newly established zebrafish models of human anemias.

Autophagy and Metabolism in Normal and Malignant Hematopoiesis

The hematopoietic system relies on regulation of both metabolism and autophagy to maintain its homeostasis, ensuring the self-renewal and multipotent differentiation potential of hematopoietic stem cells (HSCs). HSCs display a distinct metabolic profile from that of their differentiated progeny, while metabolic rewiring from glycolysis to oxidative phosphorylation (OXPHOS) has been shown to be crucial for effective hematopoietic differentiation. Autophagy-mediated regulation of metabolism modulates the distinct characteristics of quiescent and differentiating hematopoietic cells. In particular, mitophagy determines the cellular mitochondrial content, thus modifying the level of OXPHOS at the different differentiation stages of hematopoietic cells, while, at the same time, it ensures the building blocks and energy for differentiation. Aberrations in both the metabolic status and regulation of the autophagic machinery are implicated in the development of hematologic malignancies, especially in leukemogenesis. In this review, we aim to investigate the role of metabolism and autophagy, as well as their interconnections, in normal and malignant hematopoiesis.

RNA-regulatory exosome complex confers cellular survival to promote erythropoiesis

Cellular differentiation requires vast remodeling of transcriptomes, and therefore machinery mediating remodeling controls differentiation. Relative to transcriptional mechanisms governing differentiation, post-transcriptional processes are less well understood. As an important post-transcriptional determinant of transcriptomes, the RNA exosome complex (EC) mediates processing and/or degradation of select RNAs. During erythropoiesis, the erythroid transcription factor GATA1 represses EC subunit genes. Depleting EC structural subunits prior to GATA1-mediated repression is deleterious to erythroid progenitor cells. To assess the importance of the EC catalytic subunits Dis3 and Exosc10 in this dynamic process, we asked if these subunits function non-redundantly to control erythropoiesis. Dis3 or Exosc10 depletion in primary murine hematopoietic progenitor cells reduced erythroid progenitors and their progeny, while sparing myeloid cells. Dis3 loss severely compromised erythroid progenitor and erythroblast survival, rendered erythroblasts hypersensitive to apoptosis-inducing stimuli and induced γ-H2AX, indicative of DNA double-stranded breaks. Dis3 loss-of-function phenotypes were more severe than those caused by Exosc10 depletion. We innovated a genetic rescue system to compare human Dis3 with multiple myeloma-associated Dis3 mutants S447R and R750K, and only wild type Dis3 was competent to rescue progenitors. Thus, Dis3 establishes a disease mutation-sensitive, cell type-specific survival mechanism to enable a differentiation program.

Discovering How Heme Controls Genome Function Through Heme-omics

Protein ensembles control genome function by establishing, maintaining, and deconstructing cell-type-specific chromosomal landscapes. A plethora of small molecules orchestrate cellular functions and therefore may link physiological processes with genome biology. The metabolic enzyme and hemoglobin cofactor heme induces proteolysis of a transcriptional repressor, Bach1, and regulates gene expression post-transcriptionally. However, whether heme controls genome function broadly or through prescriptive actions is unclear. Using assay for transposase-accessible chromatin sequencing (ATAC-seq), we establish a heme-dependent chromatin atlas in wild-type and mutant erythroblasts lacking enhancers that confer normal heme synthesis. Amalgamating chromatin landscapes and transcriptomes in cells with sub-physiological heme and post-heme rescue reveals parallel Bach1-dependent and Bach1-independent mechanisms that target heme-sensing chromosomal hotspots. The hotspots harbor a DNA motif demarcating heme-regulated chromatin and genes encoding proteins not known to be heme regulated, including metabolic enzymes. The heme-omics analysis establishes how an essential biochemical cofactor controls genome function and cellular physiology.

Three Signatures of Adaptive Polymorphism Exemplified by Malaria-Associated Genes

Malaria has been one of the strongest selective pressures on our species. Many of the best-characterized cases of adaptive evolution in humans are in genes tied to malaria resistance. However, the complex evolutionary patterns at these genes are poorly captured by standard scans for nonneutral evolution. Here, we present three new statistical tests for selection based on population genetic patterns that are observed more than once among key malaria resistance loci. We assess these tests using forward-time evolutionary simulations and apply them to global whole-genome sequencing data from humans, and thus we show that they are effective at distinguishing selection from neutrality. Each test captures a distinct evolutionary pattern, here called Divergent Haplotypes, Repeated Shifts, and Arrested Sweeps, associated with a particular period of human prehistory. We clarify the selective signatures at known malaria-relevant genes and identify additional genes showing similar adaptive evolutionary patterns. Among our top outliers, we see a particular enrichment for genes involved in erythropoiesis and for genes previously associated with malaria resistance, consistent with a major role for malaria in shaping these patterns of genetic diversity. Polymorphisms at these genes are likely to impact resistance to malaria infection and contribute to ongoing host-parasite coevolutionary dynamics.

Autophagy Paradox of Cancer: Role, Regulation, and Duality

Autophagy, a catabolic process, degrades damaged and defective cellular materials through lysosomes, thus working as a recycling mechanism of the cell. It is an evolutionarily conserved and highly regulated process that plays an important role in maintaining cellular homeostasis. Autophagy is constitutively active at the basal level; however, it gets enhanced to meet cellular needs in various stress conditions. The process involves various autophagy-related genes that ultimately lead to the degradation of targeted cytosolic substrates. Many factors modulate both upstream and downstream autophagy pathways like nutritional status, energy level, growth factors, hypoxic conditions, and localization of p53. Any problem in executing autophagy can lead to various pathological conditions including neurodegeneration, aging, and cancer. In cancer, autophagy plays a contradictory role; it inhibits the formation of tumors, whereas, during advanced stages, autophagy promotes tumor progression. Besides, autophagy protects the tumor from various therapies by providing recycled nutrition and energy to the tumor cells. Autophagy is stimulated by tumor suppressor proteins, whereas it gets inhibited by oncogenes. Due to its dynamic and dual role in the pathogenesis of cancer, autophagy provides promising opportunities in developing novel and effective cancer therapies along with managing chemoresistant cancers. In this article, we summarize different strategies that can modulate autophagy in cancer to overcome the major obstacle, i.e., resistance developed in cancer to anticancer therapies.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

GATA factor-regulated solute carrier ensemble reveals a nucleoside transporter-dependent differentiation mechanism

Developmental-regulatory networks often include large gene families encoding mechanistically-related proteins like G-protein-coupled receptors, zinc finger transcription factors and solute carrier (SLC) transporters. In principle, a common mechanism may confer expression of multiple members integral to a developmental process, or diverse mechanisms may be deployed. Using genetic complementation and enhancer-mutant systems, we analyzed the 456 member SLC family that establishes the small molecule constitution of cells. This analysis identified SLC gene cohorts regulated by GATA1 and/or GATA2 during erythroid differentiation. As >50 SLC genes shared GATA factor regulation, a common mechanism established multiple members of this family. These genes included Slc29a1 encoding an equilibrative nucleoside transporter (Slc29a1/ENT1) that utilizes adenosine as a preferred substrate. Slc29a1 promoted erythroblast survival and differentiation ex vivo. Targeted ablation of murine Slc29a1 in erythroblasts attenuated erythropoiesis and erythrocyte regeneration in response to acute anemia. Our results reveal a GATA factor-regulated SLC ensemble, with a nucleoside transporter component that promotes erythropoiesis and prevents anemia, and establish a mechanistic link between GATA factor and adenosine mechanisms. We propose that integration of the GATA factor-adenosine circuit with other components of the GATA factor-regulated SLC ensemble establishes the small molecule repertoire required for progenitor cells to efficiently generate erythrocytes.

GATA transcription factors endow blood stem and progenitor cells with activities to produce progeny that transport oxygen to protect cells and tissues, evade pathogens and control physiological processes. GATA factors regulate hundreds of genes, and the actions of these genes mediate important biological functions. While the genes have been documented, many questions remain regarding how the “network” components mediate biological functions. The networks include members of large gene families, and the relationships between the regulation and function of individual family members is not well understood. Analyzing datasets from genetic complementation and enhancer mutant systems revealed that GATA factors regulate an ensemble of membrane transporters termed solute carrier proteins (SLCs), which dictate the small molecule composition of cells. Genetic analyses with Slc29a1, which transports adenosine, revealed its function to promote erythrocyte development, and Slc29a1 attenuated anemia in a mouse model. This study revealed the importance of SLC transporters in GATA factor networks. We propose that the GATA factor-adenosine circuit integrates with other SLCs to establish/maintain the small molecule constitution of progenitor cells as a new mechanism to control blood cell development.

Master regulator genes and their impact on major diseases

Master regulator genes (MRGs) have become a hot topic in recent decades. They not only affect the development of tissue and organ systems but also play a role in other signal pathways by regulating additional MRGs. Because a MRG can regulate the concurrent expression of several genes, its mutation often leads to major diseases. Moreover, the occurrence of many tumors and cardiovascular and nervous system diseases are closely related to MRG changes. With the development in omics technology, an increasing amount of investigations will be directed toward MRGs because their regulation involves all aspects of an organism’s development. This review focuses on the definition and classification of MRGs as well as their influence on disease regulation.

Autophagy is involved in the protective effect of p21 on LPS-induced cardiac dysfunction

p21 has emerged as an important protein involved in cardiovascular diseases, but its role remains controversial. Recently, p21 has been reported to mediate inflammatory responses. As inflammatory responses are a feature of sepsis, our study investigated whether p21 has a role in cardiac dysfunction induced by sepsis and analyzed the mechanisms involved. To establish a mouse sepsis model, p21 global knockout (p21KO) and C57BL/6J wild-type (WT) male mice were treated with 5 mg/kg LPS intraperitoneally for 6, 24, or 48 h. After LPS stimulation, the level of p21 had significantly increased in the WT mice and in cardiomyocytes. Cardiac dysfunction induced by LPS was markedly aggravated in p21KO mice relative to that of WT mice. Downregulation of p21 expression exacerbated the LPS-mediated inflammatory response, and it increased oxidative stress as well as mitochondrial damage in the heart and in cardiomyocytes. In contrast, overexpressing p21 attenuated the increase of TNFα and promoted the increase of SOD2. Moreover, p21 regulated the LPS-induced autophagy activation; that is, the increase in autophagy was impaired when p21 expression was decreased, whereas the increase was significant when p21 was overexpressed. The autophagy inducer rapamycin partially rescued the cardiac deterioration caused by p21 downregulation in the LPS-stimulated groups. In addition, p21 regulated the autophagy level by interacting with LC3B. These results revealed that p21 controls LPS-induced cardiac dysfunction by modulating inflammatory and oxidative stress, and it is partially dependent on regulating the autophagy level. This study is the first to show that p21 could interact with LC3B to promote autophagy for the improvement of cardiac function during sepsis.

Oxidation and erythropoiesis

PURPOSE OF REVIEW

Erythropoiesis is a complex multistep process going from committed erythroid progenitors to mature red cells. Although recent advances allow the characterization of some components of erythropoiesis, much still remains to be investigated particularly on stress erythropoiesis. This review summarizes recent progresses made to understand the impact of oxidative stress on normal and pathologic erythropoiesis.

RECENT FINDINGS

During erythroid maturation, reactive oxygen species might function as second messenger through either transient oxidation of cysteine residues on signaling targets or modulation of intracellular signaling pathways. Thus, in erythropoiesis, efficient cytoprotective systems are required to limit possible reactive oxygen species-related toxic effects especially in stress erythropoiesis characterized by severe oxidation such as β-thalassemia. In addition, prolonged or severe oxidative stress impairs autophagy, which might contribute to the block of erythroid maturation in stress erythropoiesis. Understanding the functional role of cytoprotective systems such as peroxiredoxin-2 or classical molecular chaperones such as the heat shock proteins will contribute to develop innovative therapeutic strategies for ineffective erythropoiesis.

SUMMARY

We provide an update on cytoprotective mechanisms against oxidation in normal and stress erythropoiesis. We discuss the role of oxidative sensors involved in modulation of intracellular signaling during erythroid maturation process in normal and stress erythropoiesis.

Motifs enable communication efficiency and fault-tolerance in transcriptional networks

Analysis of the topology of transcriptional regulatory networks (TRNs) is an effective way to study the regulatory interactions between the transcription factors (TFs) and the target genes. TRNs are characterized by the abundance of motifs such as feed forward loops (FFLs), which contribute to their structural and functional properties. In this paper, we focus on the role of motifs (specifically, FFLs) in signal propagation in TRNs and the organization of the TRN topology with FFLs as building blocks. To this end, we classify nodes participating in FFLs (termed motif central nodes) into three distinct roles (namely, roles A, B and C), and contrast them with TRN nodes having high connectivity on the basis of their potential for information dissemination, using metrics such as network efficiency, path enumeration, epidemic models and standard graph centrality measures. We also present the notion of a three tier architecture and how it can help study the structural properties of TRN based on connectivity and clustering tendency of motif central nodes. Finally, we motivate the potential implication of the structural properties of motif centrality in design of efficient protocols of information routing in communication networks as well as their functional properties in global regulation and stress response to study specific disease conditions and identification of drug targets.

Autophagy in aging and longevity

Our understanding of the process of autophagy and its role in health and diseases has grown remarkably in the last two decades. Early work established autophagy as a general bulk recycling process which involves the sequestration and transport of intracellular material to the lysosome for degradation. Currently, autophagy is viewed as a nexus of metabolic and proteostatic signalling that can determine key physiological decisions from cell fate to organismal lifespan. Here, we review the latest literature on the role of autophagy and lysosomes in stress response and longevity. We highlight the connections between autophagy and metabolic processes, the network associated with its regulation, and the links between autophagic dysfunction, neurodegenerative diseases, and aging.

Regulation of GATA1 levels in erythropoiesis

GATA1 is considered as the "master" transcription factor in erythropoiesis. It regulates at the transcriptional level all aspects of erythroid maturation and function, as revealed by gene knockout studies in mice and by genome-wide occupancies in erythroid cells. The GATA1 protein contains two zinc finger domains and an N-terminal transactivation domain. GATA1 translation results in the production of the full-length protein and of a shorter variant (GATA1s) lacking the N-terminal transactivation domain, which is functionally deficient in supporting erythropoiesis. GATA1 protein abundance is highly regulated in erythroid cells at different levels, including transcription, mRNA translation, posttranslational modifications, and protein degradation, in a differentiation-stage-specific manner. Maintaining high GATA1 protein levels is essential in the early stages of erythroid maturation, whereas downregulating GATA1 protein levels is a necessary step in terminal erythroid differentiation. The importance of maintaining proper GATA1 protein homeostasis in erythropoiesis is demonstrated by the fact that both GATA1 loss and its overexpression result in lethal anemia. Importantly, alterations in any of those GATA1 regulatory checkpoints have been recognized as an important cause of hematological disorders such as dyserythropoiesis (with or without thrombocytopenia), β-thalassemia, Diamond-Blackfan anemia, myelodysplasia, or leukemia. In this review, we provide an overview of the multilevel regulation of GATA1 protein homeostasis in erythropoiesis and of its deregulation in hematological disease.

Autophagy regulation and its role in normal and malignant hematopoiesis

Autophagy, the molecular machinery of self-eating, plays a dual role of a tumor promoter and tumor suppressor. This mechanism affects different clinical responses in cancer cells. Autophagy is targeted for treating patients resistant to chemotherapy or radiation. Limited reports investigate the significance of autophagy in cancer therapy, the regulation of hematopoietic and leukemic stem cells and leukemia formation. In the current review, the role of autophagy is discussed in various stages of hematopoiesis including quiescence, self-renewal, and differentiation.

Targeting GATA transcription factors - a novel strategy for anti-aging interventions?

GATA transcription factors (TFs) are a conserved family of zinc-finger TFs that fulfill diverse functions across eukaryotes. Accumulating evidence suggests that GATA TFs also play a role in lifespan regulation. In a recent study, we have identified a natural compound, 4,4' dimethoxychalcone (DMC) that extends lifespan depending on reduced activity of distinct GATA TFs. Prolonged lifespan by DMC treatment depends on autophagy, a protective cellular self-cleaning mechanism. In yeast, DMC reduces the activity of the GATA TF Gln3 and, at the same time, deletion of GLN3 increases autophagy levels during cellular aging per se. Here, we examine current data on the involvement of GATA TFs in the regulation of both autophagy and lifespan in different organisms and explore, if GATA TFs are suitable targets for anti-aging interventions.

Identification of transcription factors that regulate ATG8 expression and autophagy in Arabidopsis

Autophagy is a conserved catabolic process in eukaryotes that contributes to cell survival in response to multiple stresses and is important for organism fitness. In Arabidopsis thaliana, the core machinery of autophagy is well defined, but its transcriptional regulation is largely unknown. The ATG8 (autophagy-related 8) protein plays central roles in decorating autophagosomes and binding to specific cargo receptors to recruit cargo to autophagosomes. We propose that the transcriptional control of ATG8 genes is important during the formation of autophagosomes and therefore contributes to survival during stress. Here, we describe a yeast one-hybrid (Y1H) screen for transcription factors (TFs) that regulate ATG8 gene expression in Arabidopsis, using the promoters of 4 ATG8 genes. We identified a total of 225 TFs from 35 families that bind these promoters. The TF-ATG8 promoter interactions revealed a wide array of diverse TF families for different promoters, as well as enrichment for families of TFs that bound to specific fragments. These TFs are not only involved in plant developmental processes but also in the response to environmental stresses. TGA9 (TGACG (TGA) motif-binding protein 9)/AT1G08320 was confirmed as a positive regulator of autophagy. TGA9 overexpression activated autophagy under both control and stress conditions and transcriptionally up-regulated expression of ATG8B, ATG8E and additional ATG genes via binding to their promoters. Our results provide a comprehensive resource of TFs that regulate ATG8 gene expression and lay a foundation for understanding the transcriptional regulation of plant autophagy.Abbreviations: ABRC: Arabidopsis biological resource center; AP2-EREBP: APETALA2/Ethylene-responsive element binding protein; ARF: auxin response factor; ATF4: activating transcription factor 4; ATG: autophagy-related; ChIP: chromatin immunoprecipitation; DAP-seq: DNA affinity purification sequencing; FOXO: forkhead box O; GFP: green fluorescent protein; GO: gene ontologies; HB: homeobox; LD: long-day; LUC: firefly luciferase; MAP1LC3: microtubule associated protein 1 light chain 3; MDC: monodansylcadaverine; 3-MA: 3-methyladenine; OE: overexpressing; PCD: programmed cell death; qPCR: quantitative polymerase chain reaction; REN: renilla luciferase; RT: room temperature; SD: standard deviation; TF: transcription factor; TFEB: transcription factor EB; TGA: TGACG motif; TOR: target of rapamycin; TSS: transcription start site; WT: wild-type; Y1H: yeast one-hybrid.

Transcription factors FOXO in the regulation of homeostatic hematopoiesis

PURPOSE OF REVIEW

Work in the past decade has revealed key functions of the evolutionary conserved transcription factors Forkhead box O (FOXO) in the maintenance of homeostatic hematopoiesis. Here the diverse array of FOXO functions in normal and diseased hematopoietic stem and progenitor cells is reviewed and the main findings in the past decade are highlighted. Future work should reveal FOXO-regulated networks whose alterations contribute to hematological disorders.

RECENT FINDINGS

Recent studies have identified unanticipated FOXO functions in hematopoiesis including in hematopoietic stem and progenitor cells (HSPC), erythroid cells, and immune cells. These findings suggest FOXO3 is critical for the regulation of mitochondrial and metabolic processes in hematopoietic stem cells, the balanced lineage determination, the T and B homeostasis, and terminal erythroblast maturation and red blood cell production. In aggregate these findings highlight the context-dependent function of FOXO in hematopoietic cells. Recent findings also question the nature of FOXO's contribution to heme malignancies as well as the mechanisms underlying FOXO's regulation in HSPC.

SUMMARY

FOXO are safeguards of homeostatic hematopoiesis. FOXO networks and their regulators and coactivators in HSPC are greatly complex and less well described. Identifications and characterizations of these FOXO networks in disease are likely to uncover disease-promoting mechanisms.

Activation of the vitamin D receptor transcription factor stimulates the growth of definitive erythroid progenitors

The pathways that regulate the growth of erythroid progenitors are incompletely understood. In a computational analysis of gene expression changes during erythroid ontogeny, the vitamin D receptor (Vdr) nuclear hormone receptor transcription factor gene was identified in fetal and adult stages, but not at the embryonic stage of development. Vdr was expressed in definitive erythroid (EryD) progenitors and was downregulated during their maturation. Activation of Vdr signaling by the vitamin D3 agonist calcitriol increased the outgrowth of EryD colonies from fetal liver and adult bone marrow, maintained progenitor potential, and delayed erythroid maturation, as revealed by clonogenic assays, suspension culture, cell surface phenotype, and gene expression analyses. The early (cKit⁺CD71^lo/neg), but not the late (cKit⁺CD71^hi), EryD progenitor subset of Lin^negcKit⁺ cells was responsive to calcitriol. Culture of cKit⁺CD71^lo/neg progenitors in the presence of both vitamin D3 and glucocorticoid receptor ligands resulted in an increase in proliferation that was at least additive compared with either ligand alone. Lentivirus shRNA-mediated knockdown of Vdr expression abrogated the stimulation of early erythroid progenitor growth by calcitriol. These findings suggest that Vdr has a cell-intrinsic function in early erythroid progenitors. Targeting of downstream components of the Vdr signaling pathway may lead to new approaches for the expansion of erythroid progenitors ex vivo.

The flavonoid 4,4'-dimethoxychalcone promotes autophagy-dependent longevity across species

Ageing constitutes the most important risk factor for all major chronic ailments, including malignant, cardiovascular and neurodegenerative diseases. However, behavioural and pharmacological interventions with feasible potential to promote health upon ageing remain rare. Here we report the identification of the flavonoid 4,4'-dimethoxychalcone (DMC) as a natural compound with anti-ageing properties. External DMC administration extends the lifespan of yeast, worms and flies, decelerates senescence of human cell cultures, and protects mice from prolonged myocardial ischaemia. Concomitantly, DMC induces autophagy, which is essential for its cytoprotective effects from yeast to mice. This pro-autophagic response induces a conserved systemic change in metabolism, operates independently of TORC1 signalling and depends on specific GATA transcription factors. Notably, we identify DMC in the plant Angelica keiskei koidzumi, to which longevity- and health-promoting effects are ascribed in Asian traditional medicine. In summary, we have identified and mechanistically characterised the conserved longevity-promoting effects of a natural anti-ageing drug.

Therapeutic Modulation of Autophagy in Leukaemia and Lymphoma

Haematopoiesis is a tightly orchestrated process where a pool of hematopoietic stem and progenitor cells (HSPCs) with high self-renewal potential can give rise to both lymphoid and myeloid lineages. The HSPCs pool is reduced with ageing resulting in few HSPC clones maintaining haematopoiesis thereby reducing blood cell diversity, a phenomenon called clonal haematopoiesis. Clonal expansion of HSPCs carrying specific genetic mutations leads to increased risk for haematological malignancies. Therefore, it comes as no surprise that hematopoietic tumours develop in higher frequency in elderly people. Unfortunately, elderly patients with leukaemia or lymphoma still have an unsatisfactory prognosis compared to younger ones highlighting the need to develop more efficient therapies for this group of patients. Growing evidence indicates that macroautophagy (hereafter referred to as autophagy) is essential for health and longevity. This review is focusing on the role of autophagy in normal haematopoiesis as well as in leukaemia and lymphoma development. Attenuated autophagy may support early hematopoietic neoplasia whereas activation of autophagy in later stages of tumour development and in response to a variety of therapies rather triggers a pro-tumoral response. Novel insights into the role of autophagy in haematopoiesis will be discussed in light of designing new autophagy modulating therapies in hematopoietic cancers.

Fyn kinase is a novel modulator of erythropoietin signaling and stress erythropoiesis

The signaling cascade induced by the interaction of erythropoietin (EPO) with its receptor (EPO-R) is a key event of erythropoiesis. We present here data indicating that Fyn, a Src-family-kinase, participates in the EPO signaling-pathway, since Fyn^-/- mice exhibit reduced Tyr-phosphorylation of EPO-R and decreased STAT5-activity. The importance of Fyn in erythropoiesis is also supported by the blunted responsiveness of Fyn^-/- mice to stress erythropoiesis. Fyn^-/- mouse erythroblasts adapt to reactive oxygen species (ROS) by activating the redox-related-transcription-factor Nrf2. However, since Fyn is a physiologic repressor of Nrf2, absence of Fyn resulted in persistent-activation of Nrf2 and accumulation of nonfunctional proteins. ROS-induced over-activation of Jak2-Akt-mTOR-pathway and repression of autophagy with perturbation of lysosomal-clearance were also noted. Treatment with Rapamycin, a mTOR-inhibitor and autophagy activator, ameliorates Fyn^-/- mouse baseline erythropoiesis and erythropoietic response to oxidative-stress. These findings identify a novel multimodal action of Fyn in the regulation of normal and stress erythropoiesis.

Sphingolipid-mediated inflammatory signaling leading to autophagy inhibition converts erythropoiesis to myelopoiesis in human hematopoietic stem/progenitor cells

Elevated levels of the pro-inflammatory cytokine tumor necrosis factor-α (TNFα) inhibit erythropoiesis and cause anemia in patients with cancer and chronic inflammatory diseases. TNFα is also a potent activator of the sphingomyelinase (SMase)/ceramide pathway leading to ceramide synthesis and regulating cell differentiation, proliferation, apoptosis, senescence, and autophagy. Here we evaluated the implication of the TNFα/SMase/ceramide pathway on inhibition of erythropoiesis in human CD34⁺ hematopoietic stem/progenitor cells (CD34/HSPCs) from healthy donors. Exogenous synthetic C2- and C6-ceramide as well as bacterial SMase inhibited erythroid differentiation in erythropoietin-induced (Epo)CD34/HSPCs shown by the analysis of various erythroid markers. The neutral SMase inhibitor GW4869 as well as the genetic inhibition of nSMase with small interfering RNA (siRNA) against sphingomyelin phosphodiesterase 3 (SMPD3) prevented the inhibition by TNFα, but not the acid SMase inhibitor desipramine. Moreover, sphingosine-1-phosphate (S1P), a ceramide metabolite, restored erythroid differentiation, whereas TNFα inhibited sphingosine kinase-1, required for S1P synthesis. Analysis of cell morphology and colony formation demonstrated that erythropoiesis impairment was concomitant with a granulomonocytic differentiation in TNFα- and ceramide-treated EpoCD34/HSPCs. Inhibition of erythropoiesis and induction of granulomonocytic differentiation were correlated to modulation of hematopoietic transcription factors (TFs) GATA-1, GATA-2, and PU.1. Moreover, the expression of microRNAs (miR)-144/451, miR-146a, miR-155, and miR-223 was also modulated by TNFα and ceramide treatments, in line with cellular observations. Autophagy plays an essential role during erythropoiesis and our results demonstrate that the TNFα/neutral SMase/ceramide pathway inhibits autophagy in EpoCD34/HSPCs. TNFα- and ceramide-induced phosphorylation of mTOR^S2448 and ULK1^S758, inhibited Atg13^S355 phosphorylation, and blocked autophagosome formation as shown by transmission electron microscopy and GFP-LC3 punctae formation. Moreover, rapamycin prevented the inhibitory effect of TNFα and ceramides on erythropoiesis while inhibiting induction of myelopoiesis. In contrast, bafilomycin A1, but not siRNA against Atg5, induced myeloid differentiation, while both impaired erythropoiesis. We demonstrate here that the TNFα/neutral SMase/ceramide pathway inhibits erythropoiesis to induce myelopoiesis via modulation of a hematopoietic TF/miR network and inhibition of late steps of autophagy. Altogether, our results reveal an essential role of autophagy in erythroid vs. myeloid differentiation.

Distinct role of autophagy on angiogenesis: highlights on the effect of autophagy in endothelial lineage and progenitor cells

Autophagy plays a critical role in the dynamic growth of each cell through different conditions. It seems that this intracellular mechanism acts as a two-edged sword against the numerous cell insults. Previously, autophagy was described in the context of cell activity and behavior, but little knowledge exists related to the role of autophagy in endothelial cells, progenitors, and stem cells biology from different tissues. Angiogenic behavior of endothelial lineage and various stem cells are touted as an inevitable feature in the restoration of different damaged tissues and organs. This capacity was found to be dictated by autophagy signaling pathway. This review article highlights the fundamental role of cell autophagic response in endothelial cells function, stem cells dynamic, and differentiation rate. It seems that elucidation of the mechanisms related to pro- and/or anti-angiogenic potential of autophagy inside endothelial cells and stem cells could help us to modulate stem cell therapeutic feature post-transplantation.

Long non-coding RNA-dependent mechanism to regulate heme biosynthesis and erythrocyte development

In addition to serving as a prosthetic group for enzymes and a hemoglobin structural component, heme is a crucial homeostatic regulator of erythroid cell development and function. While lncRNAs modulate diverse physiological and pathological cellular processes, their involvement in heme-dependent mechanisms is largely unexplored. In this study, we elucidated a lncRNA (UCA1)-mediated mechanism that regulates heme metabolism in human erythroid cells. We discovered that UCA1 expression is dynamically regulated during human erythroid maturation, with a maximal expression in proerythroblasts. UCA1 depletion predominantly impairs heme biosynthesis and arrests erythroid differentiation at the proerythroblast stage. Mechanistic analysis revealed that UCA1 physically interacts with the RNA-binding protein PTBP1, and UCA1 functions as an RNA scaffold to recruit PTBP1 to ALAS2 mRNA, which stabilizes ALAS2 mRNA. These results define a lncRNA-mediated posttranscriptional mechanism that provides a new dimension into how the fundamental heme biosynthetic process is regulated as a determinant of erythrocyte development.

LncRNAs modulate diverse physiological cellular processes, however, their involvement in heme-dependent processes are not yet clear. Here the authors reveal the role of lncRNA UCA1 in erythroid cell development.

Crosstalk Between Mammalian Autophagy and the Ubiquitin-Proteasome System

Autophagy and the ubiquitin-proteasome system (UPS) are the two major intracellular quality control and recycling mechanisms that are responsible for cellular homeostasis in eukaryotes. Ubiquitylation is utilized as a degradation signal by both systems, yet, different mechanisms are in play. The UPS is responsible for the degradation of short-lived proteins and soluble misfolded proteins whereas autophagy eliminates long-lived proteins, insoluble protein aggregates and even whole organelles (e.g., mitochondria, peroxisomes) and intracellular parasites (e.g., bacteria). Both the UPS and selective autophagy recognize their targets through their ubiquitin tags. In addition to an indirect connection between the two systems through ubiquitylated proteins, recent data indicate the presence of connections and reciprocal regulation mechanisms between these degradation pathways. In this review, we summarize these direct and indirect interactions and crosstalks between autophagy and the UPS, and their implications for cellular stress responses and homeostasis.

TFAP2 transcription factors are regulators of lipid droplet biogenesis

How trafficking pathways and organelle abundance adapt in response to metabolic and physiological changes is still mysterious, although a few transcriptional regulators of organellar biogenesis have been identified in recent years. We previously found that the Wnt signaling directly controls lipid droplet formation, linking the cell storage capacity to the established functions of Wnt in development and differentiation. In the present paper, we report that Wnt-induced lipid droplet biogenesis does not depend on the canonical TCF/LEF transcription factors. Instead, we find that TFAP2 family members mediate the pro-lipid droplet signal induced by Wnt3a, leading to the notion that the TFAP2 transcription factor may function as a 'master' regulator of lipid droplet biogenesis.