Loss of autophagy leads to failure in megakaryopoiesis, megakaryocyte differentiation, and thrombopoiesis in mice

Comprehensive analysis and prediction model of mitophagy and ferroptosis in primary immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is linked to specific pathogenic mechanisms, yet its relationship with mitophagy and ferroptosis is poorly understood. This study aimed to identify new biomarkers and explore the role of mitophagy and ferroptosis in ITP pathogenesis. Techniques such as differential analysis, Mfuzz expression pattern clustering, machine learning, gene set enrichment analysis, single-cell RNA sequencing (scRNA-seq) and immune infiltration analysis were employed to investigate the molecular pathways of pivotal genes. Two-sample Mendelian randomization (TSMR) assessed the causal effects in ITP. Key genes identified in the training set included GABARAPL1, S100A8, LIN28A, and GDF9, which demonstrated diagnostic potential in validation sets. Functional analysis indicated these genes' involvement in ubiquitin phosphorylation, PPAR signalling pathway and T-cell differentiation. Immune infiltration analysis revealed increased macrophage presence in ITP, related to the critical genes. scRNA-seq indicated reduced GABARAPL1 expression in ITP bone marrow macrophages. TSMR linked S100A8 with ITP diagnosis, presenting an OR of 0.856 (95% CI = 0.736-0.997, p = 0.045). The study pinpointed four central genes, GABARAPL1, S100A8, LIN28A, and GDF9, tied to mitophagy and ferroptosis in ITP. It posits that diminished GABARAPL1 expression may disrupts ubiquitin phosphorylation and PPAR signalling, impairing mitophagy and inhibiting ferroptosis, leading to immune imbalance.

Insights on E1-like enzyme ATG7: functional regulation and relationships with aging-related diseases

Autophagy is a dynamic self-renovation biological process that maintains cell homeostasis and is responsible for the quality control of proteins, organelles, and energy metabolism. The E1-like ubiquitin-activating enzyme autophagy-related gene 7 (ATG7) is a critical factor that initiates classic autophagy reactions by promoting the formation and extension of autophagosome membranes. Recent studies have identified the key functions of ATG7 in regulating the cell cycle, apoptosis, and metabolism associated with the occurrence and development of multiple diseases. This review summarizes how ATG7 is precisely programmed by genetic, transcriptional, and epigenetic modifications in cells and the relationship between ATG7 and aging-related diseases.

AC-73 and Syrosingopine Inhibit SARS-CoV-2 Entry into Megakaryocytes by Targeting CD147 and MCT4

Coagulation disorders are described in COVID-19 and long COVID patients. In particular, SARS-CoV-2 infection in megakaryocytes, which are precursors of platelets involved in thrombotic events in COVID-19, long COVID and, in rare cases, in vaccinated individuals, requires further investigation, particularly with the emergence of new SARS-CoV-2 variants. CD147, involved in the regulation of inflammation and required to fight virus infection, can facilitate SARS-CoV-2 entry into megakaryocytes. MCT4, a co-binding protein of CD147 and a key player in the glycolytic metabolism, could also play a role in SARS-CoV-2 infection. Here, we investigated the susceptibility of megakaryocytes to SARS-CoV-2 infection via CD147 and MCT4. We performed infection of Dami cells and human CD34+ hematopoietic progenitor cells induced to megakaryocytic differentiation with SARS-CoV-2 pseudovirus in the presence of AC-73 and syrosingopine, respective inhibitors of CD147 and MCT4 and inducers of autophagy, a process essential in megakaryocyte differentiation. Both AC-73 and syrosingopine enhance autophagy during differentiation but only AC-73 enhances megakaryocytic maturation. Importantly, we found that AC-73 or syrosingopine significantly inhibits SARS-CoV-2 infection of megakaryocytes. Altogether, our data indicate AC-73 and syrosingopine as inhibitors of SARS-CoV-2 infection via CD147 and MCT4 that can be used to prevent SARS-CoV-2 binding and entry into megakaryocytes, which are precursors of platelets involved in COVID-19-associated coagulopathy.

Autophagy and its consequences for platelet biology

Autophagy, the continuous recycling of intracellular building blocks, molecules, and organelles is necessary to preserve cellular function and homeostasis. In this context, it was demonstrated that autophagy plays an important role in megakaryopoiesis, the development and differentiation of hematopoietic progenitor cells into megakaryocytes. Furthermore, in recent years, autophagic proteins were detected in platelets, anucleate cells generated by megakaryocytes, responsible for hemostasis, thrombosis, and a key cell in inflammation and host immune responses. In the last decade studies have indicated the occurrence of autophagy in platelets. Moreover, autophagy in platelets was subsequently demonstrated to be involved in platelet aggregation, adhesion, and thrombus formation. Here, we review the current knowledge about autophagy in platelets, its function, and clinical implications. However, at the advent of platelet autophagy research, additional discoveries derived from evolving work will be required to precisely define the contributions of autophagy in platelets, and to expand the ever increasing physiologic and pathologic roles these remarkable and versatile blood cells play.

High Autophagy Patterns in Swelling Platelets During Apheresis Platelet Storage

Platelets undergo remarkable morphological changes during storage. Platelets change into different sizes and densities and differ in their biochemistry and functions. However, the correlation between structural heterogeneity and platelet autophagy is largely unknown. The aim of this study was to investigate the autophagy process in vitro, such as routine storage of platelets, and explore the role of reactive oxygen species (ROS) involved in the regulation of platelet autophagy. The ROS and autophagy levels of platelet concentrates from apheresis platelets were evaluated through flow cytometry. The expression levels of autophagy-associated proteins (LC3I, LC3II, Beclin1, Parkin, and PINK1) were measured via Western blot. All biomarkers were dynamically monitored for seven days. Moreover, the morphological characteristics of platelet morphology during storage were analyzed through transmission electron microscopy (TEM). Flow cytometry showed that the levels of total cell ROS and mitochondria ROS increased in the stored platelets. Together with the increase in mitochondrial ROS, the autophagy signal LC3 in the platelets was strongly amplified. The number of swollen platelets (large platelets) considerably increased, and that of autophagy signal LC3 was remarkably higher than that of the normal platelets. Western blot revealed that the expression levels of Beclin1 and LC3 II/LC3 I ratio were enhanced, whereas those of Parkin and PINK1 almost did not change during the seven days of storage. The existence of autophagosomes or autophagolysosomes in the platelets at the middle stage of platelet storage was observed via TEM. Our data demonstrated that the subpopulation of large (swollen) platelets exhibited different autophagy patterns. Furthermore, increased platelet autophagy was associated with mitochondrial ROS. These preliminary results suggest that swelling platelets have a higher autophagy pattern than normal platelets during storage.

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.

Histone deacetylation-regulated cell surface Siglec-7 expression promoted megakaryocytic maturation and enhanced platelet-like particle release

BACKGROUND

Functioning as important hematologic cells for hemostasis, wound healing and immune defense platelets are produced before being released into the blood by cytoplasmic fragmentation at the end of the megakaryocyte (MK) differentiation, during which the involvement of both apoptosis and autophagy has been reported. Inhibitory sialic acid-binding immunoglobulin-like lectin-7 gene (Siglec-7) can be expressed on platelets and induce apoptosis on activation for uncharacterized function.

OBJECTIVE

We aimed to investigate the regulatory mechanism for Siglec-7 activation along MK differentiation and its physiologic role during the MK maturation and platelet formation.

METHODS

By using 2 well-established MK differentiation models (HEL and K562) and human primary CD34⁺ cell, we examined the upregulations of transcript and protein levels of Siglec-7 during MK differentiation, and the effect of Siglec-7 surface presence on MK differentiation and platelet-like particles (PLPs) release.

RESULTS

We show that both transcripts and surface Siglec-7 were elevated during MK differentiation, and the histone deacetylase 1 (HDAC1) acted as a negative regulator for Siglec-7 activation. By increasing Siglec-7 surface expression, we found that increased presence of Siglec-7 not only enhanced MK maturation but also the release of PLPs by activating caspase 3-dependent signaling, as evidenced in the observation of more CD41, polyploidy, and platelet factor 4 transcript formations.

CONCLUSION

In this study, we demonstrated that Siglec-7 activation was subjected to epigenetic regulation, and the resulting induced expression of surface Siglec-7 played an important regulatory role in promoting MK differentiation, maturation, and PLP formation.

Apoptosis in megakaryocytes: Safeguard and threat for thrombopoiesis

Platelets, generated from precursor megakaryocytes (MKs), are central mediators of hemostasis and thrombosis. The process of thrombopoiesis is extremely complex, regulated by multiple factors, and related to many cellular events including apoptosis. However, the role of apoptosis in thrombopoiesis has been controversial for many years. Some researchers believe that apoptosis is an ally of thrombopoiesis and platelets production is apoptosis-dependent, while others have suggested that apoptosis is dispensable for thrombopoiesis, and is even inhibited during this process. In this review, we will focus on this conflict, discuss the relationship between megakaryocytopoiesis, thrombopoiesis and apoptosis. In addition, we also consider why such a vast number of studies draw opposite conclusions of the role of apoptosis in thrombopoiesis, and try to figure out the truth behind the mystery. This review provides more comprehensive insights into the relationship between megakaryocytopoiesis, thrombopoiesis, and apoptosis and finds some clues for the possible pathological mechanisms of platelet disorders caused by abnormal apoptosis.

Autophagy and Its Lineage-Specific Roles in the Hematopoietic System

Autophagy is a dynamic process that regulates the selective and nonselective degradation of cytoplasmic components, such as damaged organelles and protein aggregates inside lysosomes to maintain tissue homeostasis. Different types of autophagy including macroautophagy, microautophagy, and chaperon-mediated autophagy (CMA) have been implicated in a variety of pathological conditions, such as cancer, aging, neurodegeneration, and developmental disorders. Furthermore, the molecular mechanism and biological functions of autophagy have been extensively studied in vertebrate hematopoiesis and human blood malignancies. In recent years, the hematopoietic lineage-specific roles of different autophagy-related (ATG) genes have gained more attention. The evolution of gene-editing technology and the easy access nature of hematopoietic stem cells (HSCs), hematopoietic progenitors, and precursor cells have facilitated the autophagy research to better understand how ATG genes function in the hematopoietic system. Taking advantage of the gene-editing platform, this review has summarized the roles of different ATGs at the hematopoietic cell level, their dysregulation, and pathological consequences throughout hematopoiesis.

An Insight into Platelets at Older Age: Cellular and Clinical Perspectives

Higher access to medical care, advanced diagnostic tools, and overall public health improvements have favored increased humans lifespan. With a growing proportion of older adults, the associated costs to care for ageing-associated conditions will continue to grow. This chapter highlights recent cellular and clinical evidence of platelets at an older age, from the hyperreactive phenotype associated with thrombosis to the well-known hallmarks of ageing identifiable in platelets and their potential functional implications on platelets at an older age. Therefore, it is imperative to understand platelets' molecular and cellular mechanisms during ageing in health and disease. New knowledge will favor the development of new ways to prevent some of the age-associated complications where platelets are key players.

Current therapeutic strategies and perspectives in refractory ITP: What have we learned recently?

Immune thrombocytopenia (ITP) is an acquired autoimmune bleeding disorder featured by increased platelet destruction and deficient megakaryocyte maturation. First-line treatments include corticosteroids, intravenous immunoglobulin and intravenous anti-D immunoglobulin. Second-line treatments consist of rituximab, thrombopoietin receptor agonists and splenectomy. Although most patients benefit from these treatments, an individualized treatment approach is warranted due to the large heterogeneity among ITP patients. In addition, ITP patients may relapse and there remains a subset of patients who become refractory to treatments. The management of these refractory patients is still a challenge. This review aims to summarize emerging therapeutic approaches for refractory ITP in several categories according to their different targets, including macrophages, platelets/megakaryocytes, T cells, B cells, and endothelial cells. Moreover, current management strategies and combination regimens of refractory ITP are also discussed.

Upregulation of autophagy in M2 macrophage by vitamin D alleviates crystalline silica-induced pulmonary inflammatory damage

Crystalline silica (CS) is a universal environmental pollutant, which causes a typical inflammatory lung injury. Vitamin D shows huge potential against particles-induced lung injury, while little known about the molecular mechanism involved in macrophage autophagy. In this study, we aim to identify the protective effects of vitamin D on CS caused lung inflammatory injury and clarify the detail mechanism. After exposure to CS (3 mg/mice in 50 μl PBS), wildtype and Atg7^flox/flox Lyz2-cre mice were treated with or without vitamin D₃ (40,000 IU/kg). The results indicated that exposure to CS caused an obvious lung injury, manifesting as pathological structural changes, macrophage-dominated inflammatory cell infiltration and increased pro-inflammatory cytokines. Remarkably, these damages were more serious in Atg7^flox/flox Lyz2-cre mice. Vitamin D was found to inverse CS-induced inflammatory cell infiltration and restored anti-inflammatory M2 macrophages by inducing autophagy, which attenuated lung injury, as determined by decreased levels of apoptosis and inflammatory response. While, this effects of vitamin D were slashed in Atg7^flox/flox Lyz2-cre mice. This study reveals the adverse effect of CS on lung tissue and the protective mechanism of vitamin D involved in M2 macrophages autophagy, which attenuates CS-caused lung injury.

Human platelets display dysregulated sepsis-associated autophagy, induced by altered LC3 protein-protein interaction of the Vici-protein EPG5

Platelets mediate central aspects of host responses during sepsis, an acute profoundly systemic inflammatory response due to infection. Macroautophagy/autophagy, which mediates critical aspects of cellular responses during inflammatory conditions, is known to be a functional cellular process in anucleate platelets, and is essential for normal platelet functions. Nevertheless, how sepsis may alter autophagy in platelets has never been established. Using platelets isolated from septic patients and matched healthy controls, we show that during clinical sepsis, the number of autophagosomes is increased in platelets, most likely due to an accumulation of autophagosomes, some containing mitochondria and indicative of mitophagy. Therefore, autophagy induction or early-stage autophagosome formation (as compared to decreased later-stage autophagosome maturation or autophagosome-late endosome/lysosome fusion) is normal or increased. This was consistent with decreased fusion of autophagosomes with lysosomes in platelets. EPG5 (ectopic P-granules autophagy protein 5 homolog), a protein essential for normal autophagy, expression did increase, while protein-protein interactions between EPG5 and MAP1LC3/LC3 (which orchestrate the fusion of autophagosomes and lysosomes) were significantly reduced in platelets during sepsis. Furthermore, data from a megakaryocyte model demonstrate the importance of TLR4 (toll like receptor 4), LPS-dependent signaling for regulating this mechanism. Similar phenotypes were also observed in platelets isolated from a patient with Vici syndrome: an inherited condition caused by a naturally occurring, loss-of-function mutation in EPG5. Together, we provide evidence that autophagic functions are aberrant in platelets during sepsis, due in part to reduced EPG5-LC3 interactions, regulated by TLR4 engagement, and the resultant accumulation of autophagosomes.Abbreviations: ACTB: beta actin; CLP: cecal ligation and puncture; Co-IP: co-immunoprecipitation; DAP: death associated protein; DMSO: dimethyl sulfoxide; EPG5: ectopic P-granules autophagy protein 5 homolog; ECL: enhanced chemiluminescence; HBSS: Hanks' balanced salt solution; HRP: horseradish peroxidase; ICU: intensive care unit; LPS: lipopolysaccharide; LAMP1: lysosomal associated membrane protein 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; MKs: megakaryocytes; PFA: paraformaldehyde; PBS: phosphate-buffered saline; PLA: proximity ligation assay; pRT-PCR: quantitative real-time polymerase chain reaction; RT: room temperature; SQSTM1/p62: sequestosome 1; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TLR4: toll like receptor 4; TEM: transmission electron microscopy; WGA: wheat germ agglutinin.

Disruption of autophagy by increased 5-HT alters gut microbiota and enhances susceptibility to experimental colitis and Crohn's disease

Autophagy, an essential intracellular recycling process, is linked to the pathogenesis of various diseases including Crohn’s disease (CD). Factors that lead to the development of impaired autophagy during intestinal inflammation remain largely unexplored. Here, we report the impact of the interaction between serotonin [5-hydroxytryptamine;(5-HT)] and autophagy in colitis in mouse and human studies. In mice, increased gut 5-HT inhibited autophagy and led to enhanced colitis susceptibility. Reciprocally, mice with reduced 5-HT exhibited up-regulated autophagy via the mammalian target of rapamycin pathway, which resulted in significantly decreased colitis. Deletion of autophagy gene, Atg7, in an epithelial-specific manner, in concert with reduced 5-HT, promoted the development of a colitogenic microbiota and abolished the protective effects conferred by reduced 5-HT. Notably, in control and patient peripheral blood mononuclear cells, we uncovered that 5-HT treatment inhibited autophagy. Our findings suggest 5-HT as a previously unidentified therapeutic target in intestinal inflammatory disorders such as CD that exhibits dysregulated autophagy.

Quantitative LC-MS/MS uncovers the regulatory role of autophagy in immune thrombocytopenia

BACKGROUND

Immune thrombocytopenia (ITP) is an autoimmune haemorrhagic disease whose pathogenesis is associated with bone marrow megakaryocyte maturation disorder and destruction of the haematopoietic stem cell microenvironment.

METHODS

In this study, we report the qualitative and quantitative profiles of the ITP proteome. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was conducted to elucidate the protein profiles of clinical bone marrow mononuclear cell (BMMC) samples from ITP patients and healthy donors (controls). Gene Ontology (GO) and Kyoto Encyclopaedia Genes and Genome (KEGG) pathway analyses were performed to annotate the differentially expressed proteins. A protein-protein interaction (PPI) network was constructed with the BLAST online database. Target proteins associated with autophagy were quantitatively identified by parallel reaction monitoring (PRM) analysis.

RESULTS

Our approaches showed that the differentially expressed autophagy-related proteins, namely, HSPA8, PARK7, YWHAH, ITGB3 and CSF1R, were changed the most. The protein expression of CSF1R in ITP patients was higher than that in controls, while other autophagy-related proteins were expressed at lower levels in ITP patients than in controls.

CONCLUSION

Bioinformatics analysis indicated that disruption of the autophagy pathway is a potential pathological mechanism of ITP. These results can provide a new direction for exploring the molecular mechanism of ITP.

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.

Autophagy is dispensable for the maintenance of hematopoietic stem cells in neonates

Hematopoietic stem cells (HSCs) undergo self-renewal or differentiation to sustain lifelong hematopoiesis. HSCs are preserved in quiescence with low mitochondrial activity. Recent studies indicate that autophagy contributes to HSC quiescence through suppressing mitochondrial metabolism. However, it remains unclear whether autophagy is involved in the regulation of neonatal HSCs, which proliferate actively. In this study, we clarified the role of autophagy in neonatal HSCs using 2 types of autophagy-related gene 7 (Atg7)-conditional knockout mice: Mx1-Cre inducible system and Vav-Cre system. Atg7-deficient HSCs exhibited excess cell divisions with enhanced mitochondrial metabolism, leading to bone marrow failure at adult stage. However, Atg7 deficiency minimally affected hematopoiesis and metabolic state in HSCs at neonatal stage. In addition, Atg7-deficient neonatal HSCs exhibited long-term reconstructing activity, equivalent to wild-type neonatal HSCs. Taken together, autophagy is dispensable for stem cell function and hematopoietic homeostasis in neonates and provide a novel aspect into the role of autophagy in the HSC regulation.

Reduced IL-35 in patients with immune thrombocytopenia

: The occurrence and development of primary immune thrombocytopenia is closely related to autoimmune imbalanced. Thus, we conducted the current study to investigate the modulation of IL-35, a newly identified immunological self-tolerance factor on immune thrombocytopenic purpura (ITP). We were enrolled peripheral blood in 21 adult healthy volunteers, 21 active primary ITP patients and 16 ITP patients in remission. In the same period, bone marrow plasma was drawn from active primary ITP patients and 16 bone marrow donors. Enzyme-linked immunoassay was used to measure IL-35 levels in bone marrow mononuclear cells and peripheral blood mononuclear cells. Real-time quantitative PCR was used to study the mRNA expression levels of p35, Epstein-Barr virus-induced gene 3 in bone marrow mononuclear cells and peripheral blood mononuclear cells. Compared with the normal group, IL-35 levels of in ITP patients were decreased significantly. IL-35 level in bone marrow plasma was decreased more significantly than that in peripheral blood plasma at the same stage. The results showed that plasma IL-35 levels were significantly decreased in patients with active ITP compared with those of control individuals, and IL-35 levels in bone marrow plasma were decreased more significantly compared with those at the same stage. The pathogenesis of ITP is associated with decreased IL-35 levels. Further studies are needed to expand sample content and explore more in-depth investigate a possible role of IL-35 in the pathogenesis and course of ITP.

Functional role and molecular mechanisms underlying prohibitin 2 in platelet mitophagy and activation

Platelet mitophagy is a major pathway involved in the clearance of injured mitochondria during hemostasis and thrombosis. Prohibitin 2 (PHB2) has recently emerged as an inner mitochondrial membrane receptor involved in mitophagy. However, the mechanisms underlying PHB2-mediated platelet mitophagy and activation are not completely understood. PHB2 is a highly conserved inner mitochondrial membrane protein that regulates mitochondrial assembly and function due to its unique localization on the mitochondrial membrane. The present study aimed to investigate the role and mechanism underlying PHB2 in platelet mitophagy and activation. Phorbol-12-myristate-13-acetate (PMA) was used to induce MEG-01 cells maturation and differentiate into platelets following PHB2 knockdown. Cell Counting Kit-8 assays were performed to examine platelet viability. Flow cytometry was performed to assess platelet mitochondrial membrane potential. RT-qPCR and western blotting were conducted to measure mRNA and protein expression levels, respectively. Subsequently, platelets were exposed to CCCP and the role of PHB2 was assessed. The results of the present study identified a crucial role for PHB2 in platelet mitophagy and activation, suggesting that PHB2-mediated regulation of mitophagy may serve as a novel strategy for downregulating the expression of platelet activation genes. Although further research into mitophagy is required, the present study suggested that PHB2 may serve as a novel therapeutic target for thrombosis-related diseases due to its unique localization on the mitochondrial membrane.

Insights on chronic immune thrombocytopenia pathogenesis: A bench to bedside update

Immune thrombocytopenia (ITP) is a heterogeneous disease with an unpredictable course. Chronicity can develop in up to two-thirds of adults and 20-25% of children, representing a significant burden on patients' quality of life. Despite acceptable responses to treatment, precise etiology and pathophysiology phenomena driving evolution to chronicity remain undefined. We analyzed reported risk factors for chronic ITP and associated them with proposed underlying mechanisms in its pathogenesis, including bone marrow (BM) microenvironment disturbances, clinical features, and immunological markers. Their understanding has diagnostic implications, such as screening for the presence of specific antibodies or BM examination employing molecular tools, which could help predict prognosis and recognize main pathogenic pathways in each patient. Identifying these underlying mechanisms could guide the use of personalized therapies such as all-trans retinoic acid, mTor inhibitors, FcRn inhibitors, oseltamivir, and others. Further research should lead to tailored treatments and chronic course prevention, improving patients' quality of life.

Deciphering the Role of the Coagulation Cascade and Autophagy in Cancer-Related Thrombosis and Metastasis

Thrombotic complications are the second leading cause of death among oncology patients worldwide. Enhanced thrombogenesis has multiple origins and may result from a deregulation of megakaryocyte platelet production in the bone marrow, the synthesis of coagulation factors in the liver, and coagulation factor signaling upon cancer and the tumor microenvironment (TME). While a hypercoagulable state has been attributed to factors such as thrombocytosis, enhanced platelet aggregation and Tissue Factor (TF) expression on cancer cells, further reports have suggested that coagulation factors can enhance metastasis through increased endothelial-cancer cell adhesion and enhanced endothelial cell activation. Autophagy is highly associated with cancer survival as a double-edged sword, as can both inhibit and promote cancer progression. In this review, we shall dissect the crosstalk between the coagulation cascade and autophagic pathway and its possible role in metastasis and cancer-associated thrombosis formation. The signaling of the coagulation cascade through the autophagic pathway within the hematopoietic stem cells, the endothelial cell and the cancer cell are discussed. Relevant to the coagulation cascade, we also examine the role of autophagy-related pathways in cancer treatment. In this review, we aim to bring to light possible new areas of cancer investigation and elucidate strategies for future therapeutic intervention.

Expansion of senescent megakaryocyte-lineage cells maintains CML cell leukemogenesis

BCR-ABL, an oncogenic fusion gene, plays a central role in the pathogenesis of chronic myeloid leukemia (CML). Oncogenic signaling induces oncogene-induced senescence and senescence-associated secretory phenotype (SASP), which is characterized by enhanced production of various cytokines. BCR-ABL gene transduction confers senescent phenotype in vitro; however, the in vivo relevance of senescence has not been explored in this context. Transplantation of BCR-ABL-expressing hematopoietic stem/progenitor cells caused CML in mice with an increase in bone marrow BCR-ABL+CD41+CD150+ leukemic megakaryocyte-lineage (MgkL) cells, which exhibited enhanced senescence-associated β-galactosidase staining and increased expression of p16 and p21, key molecules that are crucially involved in senescence. Moreover, knockout of p16 and p21 genes reduced both BCR-ABL-induced abnormal megakaryopoiesis and the maintenance of CML cell leukemogenic capacity, as evidenced by attenuated leukemogenic capacity at secondary transplantation. The expression of transforming growth factor-β1 (TGF-β1), a representative SASP molecule, was enhanced in the leukemic MgkL cells, and TGF-β1 inhibition attenuated CML cell leukemogenic capacity both in vitro and in vivo. Furthermore, BCR-ABL-expressing MgkL cells displayed enhanced autophagic activity, and autophagy inhibition reduced bone marrow MgkL cell number and prolonged the survival of CML mice, which had transiently received the tyrosine kinase inhibitor, imatinib, earlier. Thus, BCR-ABL induced the expansion of senescent leukemic MgkL cells, which supported CML leukemogenesis by providing TGF-β1.

Loss of Atg7 causes chaotic nucleosome assembly of mouse bone marrow CD11b+Ly6G- myeloid cells

Atg7, a critical component of autophagy machinery, is essential for counteracting hematopoietic aging. However, the non-autophagic role of Atg7 on hematopoietic cells remains fundamentally unclear. In this study, we found that loss of Atg7, but not Atg5, another autophagy-essential gene, in the hematopoietic system reduces CD11b myeloid cellularity including CD11b⁺Ly6G⁺ and CD11b⁺Ly6G^- populations in mouse bone marrow. Surprisingly, Atg7 deletion causes abnormally accumulated histone H3.1 to be overwhelmingly trapped in the cytoplasm in the CD11b⁺Ly6G^-, but not the CD11b⁺Ly6G⁺ compartment. RNA profiling revealed extensively chaotic expression of the genes required in nucleosome assembly. Functional assays further indicated upregulated aging markers in the CD11b⁺Ly6G^- population. Therefore, our study suggests that Atg7 is essential for maintaining proper nucleosome assembly and limiting aging in the bone marrow CD11b⁺Ly6G^- population.

Germline genetic factors in the pathogenesis of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPN) are clonal hematological malignancies that lead to overproduction of mature myeloid cells. They are due to acquired mutations in genes encoding for AK2, MPL and CALR that result in the activation of the cytokine receptor/JAK2 signaling pathway. In addition, it exists germline variants that can favor the initiation of the disease or may affect its phenotype. First, they can be common risk alleles, which correspond to frequent single nucleotide variants present in control population and that contribute to the development of either sporadic or familial MPN. Second, some variants predispose to the onset of MPN with a higher penetrance and lead to familial clustering of MPN. Finally, some extremely rare genetic variants can induce MPN-like hereditary disease. We will review these different subtypes of germline genetic variants and discuss how they impact the initiation and/or development of the MPN disease.

Rapamycin induces megakaryocytic differentiation through increasing autophagy in Dami cells

: Autophagy is a conserved cellular process that involves the degradation of cytoplasmic components in eukaryotic cells. However, the correlation between autophagy and megakaryocyte development is unclear. This study aims to explore the role of autophagy in megakaryocyte differentiation. To test our hypothesis, we used the Dami cell line in-vitro experiments. Rapamycin and Bafilomycin A1 were used to stimulate Dami cells. CD41 expression and apoptosis were analysed by flow cytometry. Autophagy-related proteins were detected by Western blotting. 12-O-Tetradecanoylphorbol 13-acetate-treated Dami cells can simulate endomitosis of megakaryocytes in vitro. Rapamycin-induced autophagic cell death was verified by LC3-II conversion upregulation. Meanwhile, Bafilomycin A1 blocked endomitosis and autophagy of Dami cells. Our results provide evidence that autophagy is involved in megakaryocyte endomitosis and platelet development. Rapamycin inhibited cell viability and induced multiple cellular events, including apoptosis, autophagic cell death, and megakaryocytic differentiation, in human Dami cells. Upregulated autophagy triggered by rapamycin can promote the differentiation of Dami cells, while endomitosis is accompanied by enhanced autophagy.

Assessing Autophagy in Archived Tissue or How to Capture Autophagic Flux from a Tissue Snapshot

Autophagy is a highly conserved degradation mechanism that is essential for maintaining cellular homeostasis. In human disease, autophagy pathways are frequently deregulated and there is immense interest in targeting autophagy for therapeutic approaches. Accordingly, there is a need to determine autophagic activity in human tissues, an endeavor that is hampered by the fact that autophagy is characterized by the flux of substrates whereas histology informs only about amounts and localization of substrates and regulators at a single timepoint. Despite this challenging task, considerable progress in establishing markers of autophagy has been made in recent years. The importance of establishing clear-cut autophagy markers that can be used for tissue analysis cannot be underestimated. In this review, we attempt to summarize known techniques to quantify autophagy in human tissue and their drawbacks. Furthermore, we provide some recommendations that should be taken into consideration to improve the reliability and the interpretation of autophagy biomarkers in human tissue samples.

Metabolic pathways mediate pathogenesis and offer targets for treatment in rheumatic diseases

PURPOSE OF REVIEW

The cause of autoimmune diseases remains incompletely understood. Here, we highlight recent advances in the role of proinflammatory metabolic pathways in autoimmune disease, including treatment with antioxidants and mechanistic target of rapamycin (mTOR) inhibitors.

RECENT FINDINGS

Recent studies show that mTOR pathway activation, glucose utilization, mitochondrial oxidative phosphorylation, and antioxidant defenses play critical roles in the pathogenesis of autoimmune diseases, including rheumatoid arthritis, immune thrombocytopenia, Sjögren's syndrome, large vessel vasculitis, and systemic lupus erythematosus. mTOR activity leads to Th1 and Th17 cell proliferation, Treg depletion, plasma cell differentiation, macrophage dysfunction, and increased antibody and immune complex production, ultimately resulting in tissue inflammation. mTOR also affects the function of connective tissue cells, including fibroblast-like synoviocytes, endothelial cells, and podocytes. mTOR inhibition via rapamycin and N-acetylcysteine, and blockade of glucose utilization show clinical efficacy in both mouse models and clinical trials, such as systemic lupus erythematosus.

SUMMARY

The mTOR pathway is a central regulator of growth and survival signals, integrating environmental cues to control cell proliferation and differentiation. Activation of mTOR underlies inflammatory lineage specification, and mTOR blockade-based therapies show promising efficacy in several autoimmune diseases.

The Effect of Autophagic Activity on the Function of Apheresis Platelets and on the Efficacy of Clinical Platelet Transfusion

Platelet activation and survival jointly determine the efficacy of clinical platelet transfusion. This study aimed to discuss the effect of autophagic activity on activation and aggregation of apheresis platelets and on the efficacy of clinical platelet transfusion. In this study, we investigated the effects of autophagic activity of apheresis platelets for different blood types and after different storage durations on platelet activation and aggregation functions. By Western blot, immunofluorescence, and RT-qPCR detection, we found that with the prolongation of the storage duration, the expressions of both autophagy-related proteins and genes were upregulated in apheresis platelets and their expressions were insignificantly higher in the apheresis platelets of type A and O blood than in those of type B and type AB blood. After RAPA/IGF-1 pretreatment, there was a significant increase/reduction in autophagic activity. After RAPA and IGF-1 pretreatment, an opposite variation trend was observed with platelet activation and aggregation. Autophagic activity of platelets correlated negatively with the efficacy of clinical platelet transfusion. These research findings provide a theoretical basis for effective clinical platelet transfusion.

Role of Platelet Mitochondria: Life in a Nucleus-Free Zone

Platelets are abundant, small, anucleate circulating cells, serving many emerging pathophysiological roles beyond hemostasis; including active critical roles in thrombosis, injury response, and immunoregulation. In the absence of genomic DNA transcriptional regulation (no nucleus), platelets require strategic prepackaging of all the needed RNA and organelles from megakaryocytes, to sense stress (e.g., hyperglycemia), to protect themselves from stress (e.g., mitophagy), and to communicate a stress response to other cells (e.g., granule and microparticle release). Distinct from avian thrombocytes that have a nucleus, the absence of a nucleus allows the mammalian platelet to maintain its small size, permits morphological flexibility, and may improve speed and efficiency of protein expression in response to stress. In the absence of a nucleus, platelet lifespan of 7–10 days, is largely determined by the mitochondria. The packaging of 5–8 mitochondria is critical in aerobic respiration and yielding metabolic substrates needed for function and survival. Mitochondria damage or dysfunction, as observed with several disease processes, results in greatly attenuated platelet survival and increased risk for thrombovascular events. Here we provide insights into the emerging roles of platelets despite the lack of a nucleus, and the key role played by mitochondria in platelet function and survival both in health and disease.

Autophagic regulation of platelet biology

Platelets, developed from megakaryocytes, are characterized by anucleate and short-life span hemocyte in mammal vessel. Platelets are very important in the cardiovascular system. Studies indicate the occurrence of autophagy platelets and megakaryocytes. Moreover, abnormal autophagy decreases the number of platelets and suppresses platelet aggregation. In addition, mitophagy, as a kind of selective autophagy, could inhibit platelet aggregation under oxidative stress or hypoxic, whereas promote platelet aggregation after reperfusion. Finally, autophagy regulates hemorrhagic and thrombosis diseases by influencing the number and function of platelets. In this paper, the role of autophagy in platelets and megakaryocytes, as well as coupled with the promotive or inhibitory role of hemorrhagic and thrombosis diseases are elucidated. Therefore, autophagy may be a potentially therapeutic target in modulating the platelet-related diseases.

Autophagy-deficient mice are more susceptible to engrafted leukemogenesis

Autophagy is primarily considered as an important survival mechanism for both normal cells and cancer cells in response to metabolic stress or chemotherapy; but the role of autophagy in leukemogenesis is not fully understood. The aim of this study is to explore the role of intrinsic autophagy in the leukemogenesis of B-cell acute lymphoblastic leukemia (B-ALL). In this study, conditional knockout mice Atg7^f/f;Ubc-Cre, in which an autophagy-essential gene Atg7 is universally deleted, were used as recipients, B-ALL cell line 697 was used as donor cells to generate leukemia mouse model. Compared to wild-type mice, Atg7 knockout mice were more susceptible to engrafted leukemogenesis, shown by increase in white blood cells, lymphocytes, and platelets, decrease in HSPC number and its colony-forming unit (CFU). The liver and spleen displayed hepatosplenomegaly and inflammatory cell infiltration. Furthermore, second competitive transplantation revealed dysfunction of the HSPC in Atg7-knockout leukemia mice represented by destructive self-renew ability (CFU) and reconstitution ability including decreased B220, Ter 119 cells, and increased Gr-1 cell percentage. In summary, Mice with universal deletion of Atg7 are more inclined to the occurrence of engrafted human leukemia, which is largely attributed to the deterioration of the function of HSPC in autophagy deficient mice.

Megakaryocytic dysfunction in immune thrombocytopenia is linked to autophagy

Immune thrombocytopenic purpura (ITP) is a multifactorial autoimmune disease characterized by both increased platelet destruction and/or reduced platelet production. Even though they are detected in ≤ 50% of ITP patients, auto-antibodies play a pivotal role in the pathogenesis of ITP. Recent experimental and clinical observations have revealed abnormal autophagy in ITP patients. Autophagy is a catabolic process responsible for the elimination and recycling of cytoplasmic constituents, such as organelles and macromolecules, in eukaryotic cells. Additionally, it triggers cell death or promotes cell survival following various forms of stress, and maintains the microenvironment and stemness of haematopoietic stem cells. The role of autophagy in megakaryopoiesis, thrombopoiesis, and platelet function is slowly being uncovered. The abnormal autophagy in ITP patients may be caused by deletion of autophagy-related genes such as ATG7 and abnormal signalling due to overexpression of mTOR. These changes are thought to affect markers of haematopoietic stem cells, such as CD41 and CD61, and differentiation of megakaryocytes, ultimately decreasing the function and quantity of platelets and leading to the onset of ITP. This review highlights recent evidence on the essential role played by autophagy in megakaryopoiesis, megakaryocyte differentiation, thrombopoiesis, and platelet production. It also discusses the potential of targeting the autophagy pathway as a novel therapeutic approach against ITP.

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.

Autophagy promotes hepatic differentiation of hepatic progenitor cells by regulating the Wnt/β-catenin signaling pathway

Hepatic progenitor cells (HPCs) can be activated when the liver suffers persistent and severe damage and can differentiate into hepatocytes to maintain liver regeneration and homeostasis. However, the molecular mechanism underlying the hepatic differentiation of HPCs is unclear. Therefore, in this study, we aimed to investigate the roles of autophagy and the Wnt/β-catenin signaling pathway during hepatic differentiation of HPCs in vivo and in vitro. First, immunohistochemistry, immunofluorescence and electron microscopy showed that Atg5 and β-catenin were highly expressed in human fibrotic liver and mouse liver injury induced by feeding a 50% choline-deficient diet plus 0.15% ethionine solution in drinking water (CDE diet) for 21 days; in addition, these factors were expressed in CK19-positive HPCs. Second, Western blotting and immunofluorescence confirmed that CK19-positive HPCs incubated in differentiation medium for 7 days can differentiate into hepatocytes and that differentiated HPCs were able to take up ICG and secrete albumin and urea. Further investigation via Western blotting, immunofluorescence and electron microscopy revealed autophagy and the Wnt/β-catenin pathway to be activated during hepatic differentiation of HPCs. Next, we found that inhibiting autophagy by downregulating Atg5 gene expression impaired hepatic differentiation of HPCs and inhibited activation of the Wnt/β-catenin pathway, which was rescued by overexpression of the β-catenin gene. Moreover, downregulating β-catenin gene expression without inhibiting autophagy still impeded the differentiation of HPCs. Finally, coimmunoprecipitation demonstrated that P62 forms a complex with phosphorylated glycogen synthase kinase 3 beta (pGSK3β). Third, in mouse CDE-induced liver injury, immunohistochemistry and immunofluorescence confirmed that downregulating Atg5 gene expression inhibited autophagy, thus impeding hepatic differentiation of HPCs and inhibiting activation of the Wnt/β-catenin pathway. As observed in vitro, overexpression of β-catenin rescued this phenomenon caused by autophagy inhibition, though decreasing β-catenin levels without autophagy inhibition still impeded HPC differentiation. We also found that HPCs differentiated into hepatocytes in human fibrotic liver tissue. Collectively, these results demonstrate that autophagy promotes HPC differentiation by regulating Wnt/β-catenin signaling. Our results are the first to identify a role for autophagy in promoting the hepatic differentiation of HPCs.

Amentoflavone Induces Autophagy and Modulates p53

Objective

Amentoflavone is the main component of Selaginella tamariscina widely known as an oriental traditional medicinal stuff that has been known to have a variety of medicinal effects such as the induction of apoptosis, anti- metastasis, and anti-inflammation. However, the effect of amentoflavone on autophagy has not been reported until now. The aim of this study was to investigate whether amentoflavone has a positive effect on the induction of autophagy related to cell aging.

Materials and Methods

In this experimental study, the aging of young cells was induced by the treatment with insulin- like growth factor-1 (IGF-1) at 50 ng/mL three times every two days. The effect of amentoflavone on the cell viability was evaluated in A549 and WI-38 cells using 3-(4,5-dimethyl-2-yl)-2,5- diphenyl tetrazolium bromide (MTT) assay. The induction of autophagy was detected using autophagy detection kit. The expression of proteins related to autophagy and IGF-1 signaling pathway was examined by western blot analysis and immunofluorescence assay.

Results

First of all, it was found that amentoflavone induces the formation of autophagosome. In addition, it enhanced the expression level of Atg7 and increased the expression levels of Beclin1, Atg3, and LC3 associated with the induction of autophagy in immunofluorescence staining and western blot analyses. Moreover, amentoflavone inhibited the cell aging induced by IGF-1 and hydrogen peroxide. In particular, the levels of p53 and p-p21 proteins were increased in the presence of amentoflavone. Furthermore, amentoflavone increased the level of SIRT1 deacetylating p53.

Conclusion

Our results suggest that amentoflavone could play a positive role in the inhibition of various diseases associated with autophagy and the modulation of p53.

Aggregation is impaired in starved platelets due to enhanced autophagy and cellular energy depletion

Platelet hyperactivity is the hallmark of thrombosis and hemostasis disorders including atherosclerosis, diabetes, stroke, arthritis, and cancer causing significant mortality and morbidity. Therefore, regulating platelet hyperactivity is an ever growing interest. Very recently, basal autophagic process has been demonstrated to be essential for normal functioning of platelets. However, autophagy can be elevated above basal level under conditions like starvation, and how platelets respond in these settings remains to be elucidative. Therefore, in this study we demonstrate a substantial autophagy induction (above basal level) by starvation, which decreases platelet aggregation responses to various agonists. The decreased aggregation in starved platelets was restored in combination with autophagy inhibitors (3-methyladenine and NH₄Cl) and acetate supplementation. Starved platelets also showed decreased calcium mobilization, granule release, and adhesive properties. Furthermore, ex vivo platelets obtained from starved rats showed increased autophagy markers and decreased aggregation responses to various agonists. Our results distinctly explain that enhanced autophagy and cellular energy depletion are the cause for decreased platelet activation and aggregation. The study emphasizes the cardinal role of starvation and autophagy in the management of diseases and disorders associated with platelet hyperactivity.

Autophagy as a pharmacological target in hematopoiesis and hematological disorders

Autophagy is involved in many cellular processes, including cell homeostasis, cell death/survival balance and differentiation. Autophagy is essential for hematopoietic stem cell survival, quiescence, activation and differentiation. The deregulation of this process is associated with numerous hematological disorders and pathologies, including cancers. Thus, the use of autophagy modulators to induce or inhibit autophagy emerges as a potential therapeutic approach for treating these diseases and could be particularly interesting for differentiation therapy of leukemia cells. This review presents therapeutic strategies and pharmacological agents in the context of hematological disorders. The pros and cons of autophagy modulators in therapy will also be discussed.

Low Autophagy (ATG) Gene Expression Is Associated with an Immature AML Blast Cell Phenotype and Can Be Restored during AML Differentiation Therapy

Autophagy is an intracellular degradation system that ensures a dynamic recycling of a variety of building blocks required for self-renewal, homeostasis, and cell survival under stress. We used primary acute myeloid leukemia (AML) samples and human AML cell lines to investigate the regulatory mechanisms of autophagy and its role in AML differentiation. We found a significantly lower expression of key autophagy- (ATG-) related genes in primary AML as compared to healthy granulocytes, an increased autophagic activity during all-trans retinoic acid- (ATRA-) induced neutrophil differentiation, and an impaired AML differentiation upon inhibition of ATG3, ATG4D, and ATG5. Supporting the notion of noncanonical autophagy, we found that ATRA-induced autophagy was Beclin1-independent compared to starvation- or arsenic trioxide- (ATO-) induced autophagy. Furthermore, we identified PU.1 as positive transcriptional regulator of ATG3, ATG4D, and ATG5. Low PU.1 expression in AML may account for low ATG gene expression in this disease. Low expression of the autophagy initiator ULK1 in AML can partially be attributed to high expression of the ULK1-targeting microRNA-106a. Our data clearly suggest that granulocytic AML differentiation relies on noncanonical autophagy pathways and that restoring autophagic activity might be beneficial in differentiation therapies.

Mitophagy in Cardiomyocytes and in Platelets: A Major Mechanism of Cardioprotection Against Ischemia/Reperfusion Injury

Mitophagy, a process that selectively removes damaged organelles by autolysosomal degradation, is an early cellular response to ischemia. Mitophagy is activated in both cardiomyocytes and platelets during ischemia/reperfusion (I/R) and heart disease conditions. We focus on the molecular regulation of mitophagy and highlight the role of mitophagy in cardioprotection.

Dopamine induces platelet production from megakaryocytes via oxidative stress-mediated signaling pathways

Dopamine (DA), a catecholamine neurotransmitter, is known to for its diverse roles on hematopoiesis, yet its function in thrombopoiesis remains poorly understood. This study shows that DA stimulation can directly induce platelet production from megakaryocytes (MKs) in the final stages of thrombopoiesis via a reactive oxygen species (ROS)-dependent pathway. The mechanism was suggested by the results that DA treatment could significantly elevate the ROS levels in MKs, and time-dependently activate oxidative stress-mediated signaling, including p38 mitogen-activated protein kinase, c-Jun NH2-terminal kinase, and caspase-3 signaling pathways, while the antioxidants N-acetylcysteine and L-glutathione could effectively inhibit the activation of these signaling pathways, as well as the ROS increase and platelet production triggered by DA. Therefore, our data revealed that the direct role and mechanism of DA in thrombopoiesis, which provides new insights into the function recognition of DA in hematopoiesis.

Tetrandrine antagonizes acute megakaryoblastic leukaemia growth by forcing autophagy-mediated differentiation

BACKGROUND AND PURPOSE

The poor prognosis of acute megakaryoblastic leukaemia (AMKL) means there is a need to develop novel therapeutic methods to treat this condition. It was recently shown that inducing megakaryoblasts to undergo terminal differentiation is effective as a treatment for AMKL. This encouraged us to identify a compound that induces megakaryocyte differentiation, which could then act as a potent anti-leukaemia agent.

EXPERIMENTAL APPROACH

The effects of tetrandrine on the expression of CD41 and cell morphology were investigated in AMKL cells. We used CRISPR/Cas9 knockout system to knock out ATG7 and verify the role of autophagy in tetrandrine-induced megakaryocyte differentiation. shNotch1 and CA-Akt were transfected into K562 cells to examine the downstream pathways of ROS signalling and the mechanistic basis of the tetrandrine-induced megakaryocyte differentiation. The anti-leukaemia effects of tetrandrine were analysed both in vitro and in vivo.

KEY RESULTS

A low dose of tetrandrine induced cell cycle arrest and megakaryocyte differentiation in AMKL cells via activation of autophagy. Molecularly, we demonstrated that this effect is mediated by activation of Notch1 and Akt and subsequent accumulation of ROS. In contrast, in normal mouse fetal liver cells, although tetrandrine induced autophagy, it did not affect cell proliferation or promote megakaryocyte differentiation, suggesting a specific effect of tetrandrine in malignant megakaryoblasts. Finally, tetrandrine also showed in vivo efficacy in an AMKL xenograft mouse model.

CONCLUSIONS AND IMPLICATIONS

Modulating autophagy-mediated differentiation may be a novel strategy for treating AMKL, and tetrandrine has the potential to be developed as a differentiation-inducing agent for AMKL chemotherapy.

Suppressive effect of dengue virus envelope protein domain III on megakaryopoiesis

Dengue virus (DENV) infection can cause severe, life-threatening events, and no specific treatments of DENV infection are currently approved. Although thrombocytopenia is frequently observed in dengue patients, its pathogenesis is still not fully understood. Previous studies have suggested that DENV-induced thrombocytopenia occurs through viral-replication-mediated megakaryopoiesis inhibition in the bone marrow; however, the exact mechanism for megakaryopoiesis suppression remains elusive. In this study, a reductionist approach was applied, in which C57B/6J mice were inoculated with recombinant DENV-envelope protein domain III (DENV-EIII) instead of the full viral particle. Our results demonstrated that DENV-EIII-suppressed megakaryopoiesis is similar to those observed with DENV infection. Furthermore, in agreement with our in vivo analyses, DENV-EIII sufficiently suppressed the megakaryopoiesis of progenitor cells from murine bone marrow and human cord blood in vitro. Additional analyses suggested that autophagy impairment and apoptosis are involved in DENV-EIII-mediated suppression of megakaryopoiesis. These data suggest that, even without viral replication, the binding of DENV-EIII to the cell surface is sufficient to suppress megakaryopoiesis.

NPM1 Mutant Mediated PML Delocalization and Stabilization Enhances Autophagy and Cell Survival in Leukemic Cells

Accumulating evidence has defined nucleophosmin 1 (NPM1) mutation as a driver genetic event in acute myeloid leukemia (AML), whereas the pathogenesis of NPM1-mutated AML remains to be fully elucidated. In this study, we showed that mutant NPM1 elevated autophagic activity and autophagic activation contributed to leukemic cell survival in vitro. Meanwhile, we also found high expression of promyelocytic leukemia gene (PML) and its cytoplasmic dislocation in primary NPM1-mutated AML blasts and NPM1-mA positive OCI-AML3 cells. Mechanically, mutant NPM1 interacted with PML and mediated it delocalization as well as stabilization. Notably, NPM1-mA knockdown impaired autophagic activity, while induced expression of PML reversed this effect. Finally, we confirmed that PML modulated autophagic activity via AKT signal. These findings suggest that aberrant PML expression and autophagy are beneficial to the leukemic transformation driven by NPM1 mutations. This indicates an attractive therapeutic avenue for PML targeting and/or autophagy inhibition in the treatment of NPM1-mutated AML.

Autophagy Promotes the Repair of Radiation-Induced DNA Damage in Bone Marrow Hematopoietic Cells via Enhanced STAT3 Signaling

Autophagy protects hematopoietic cells from radiation damage in part by promoting DNA damage repair. However, the molecular mechanisms by which autophagy regulates DNA damage repair remain largely elusive. Here, we report that this radioprotective effect of autophagy depends on STAT3 signaling in murine bone marrow mononuclear cells (BM-MNCs). Specifically, we found that STAT3 activation and nuclear translocation in BM-MNCs were increased by activation of autophagy with an mTOR inhibitor and decreased by knockout of the autophagy gene Atg7. The autophagic regulation of STAT3 activation is likely mediated by induction of KAP1 degradation, because we showed that KAP1 directly interacted with STAT3 in the cytoplasm and knockdown of KAP1 increased the phosphorylation and nuclear translocation of STAT3. Subsequently, activated STAT3 transcriptionally upregulated the expression of BRCA1, which increased the ability of BM-MNCs to repair radiation-induced DNA damage. This novel finding that activation of autophagy can promote DNA damage repair in BM-MNCs via the ATG-KAP1-STAT3-BRCA1 pathway suggests that autophagy plays an important role in maintaining genomic integrity of BM-MNCs and its activation may confer protection of BM-MNCs against radiation-induced genotoxic stress.

Macrothrombocytopenia and dense granule deficiency associated with FLI1 variants: ultrastructural and pathogenic features

Congenital macrothrombocytopenia is a family of rare diseases, of which a significant fraction remains to be genetically characterized. To analyze cases of unexplained thrombocytopenia, 27 individuals from a patient cohort of the Bleeding and Thrombosis Exploration Center of the University Hospital of Marseille were recruited for a high-throughput gene sequencing study. This strategy led to the identification of two novel FLI1 variants (c.1010G>A and c.1033A>G) responsible for macrothrombocytopenia. The FLI1 variant carriers’ platelets exhibited a defect in aggregation induced by low-dose adenosine diphosphate (ADP), collagen and thrombin receptor-activating peptide (TRAP), a defect in adenosine triphosphate (ATP) secretion, a reduced mepacrine uptake and release and a reduced CD63 expression upon TRAP stimulation. Precise ultrastructural analysis of platelet content was performed using transmission electron microscopy and focused ion beam scanning electron microscopy. Remarkably, dense granules were nearly absent in the carriers’ platelets, presumably due to a biogenesis defect. Additionally, 25–29% of the platelets displayed giant α-granules, while a smaller proportion displayed vacuoles (7–9%) and autophagosome-like structures (0–3%). In vitro study of megakaryocytes derived from circulating CD34⁺ cells of the carriers revealed a maturation defect and reduced proplatelet formation potential. The study of the FLI1 variants revealed a significant reduction in protein nuclear accumulation and transcriptional activity properties. Intraplatelet flow cytometry efficiently detected the biomarker MYH10 in FLI1 variant carriers. Overall, this study provides new insights into the phenotype, pathophysiology and diagnosis of FLI1 variant-associated thrombocytopenia.

Hypoxic mitophagy regulates mitochondrial quality and platelet activation and determines severity of I/R heart injury

Mitochondrial dysfunction underlies many prevalent diseases including heart disease arising from acute ischemia/reperfusion (I/R) injury. Here, we demonstrate that mitophagy, which selectively removes damaged or unwanted mitochondria, regulated mitochondrial quality and quantity in vivo. Hypoxia induced extensive mitochondrial degradation in a FUNDC1-dependent manner in platelets, and this was blocked by in vivo administration of a cell-penetrating peptide encompassing the LIR motif of FUNDC1 only in wild-type mice. Genetic ablation of Fundc1 impaired mitochondrial quality and increased mitochondrial mass in platelets and rendered the platelets insensitive to hypoxia and the peptide. Moreover, hypoxic mitophagy in platelets protected the heart from worsening of I/R injury. This represents a new mechanism of the hypoxic preconditioning effect which reduces I/R injury. Our results demonstrate a critical role of mitophagy in mitochondrial quality control and platelet activation, and suggest that manipulation of mitophagy by hypoxia or pharmacological approaches may be a novel strategy for cardioprotection.

Photodynamic N-TiO2 Nanoparticle Treatment Induces Controlled ROS-mediated Autophagy and Terminal Differentiation of Leukemia Cells

In this study, we used nitrogen-doped titanium dioxide (N-TiO₂) NPs in conjugation with visible light, and show that both reactive oxygen species (ROS) and autophagy are induced by this novel NP-based photodynamic therapy (PDT) system. While well-dispersed N-TiO₂ NPs (≤100 μg/ml) were inert, their photo-activation with visible light led to ROS-mediated autophagy in leukemia K562 cells and normal peripheral lymphocytes, and this increased in parallel with increasing NP concentrations and light doses. At a constant light energy (12 J/cm²), increasing N-TiO₂ NP concentrations increased ROS levels to trigger autophagy-dependent megakaryocytic terminal differentiation in K562 cells. By contrast, an ROS challenge induced by high N-TiO₂ NP concentrations led to autophagy-associated apoptotic cell death. Using chemical autophagy inhibitors (3-methyladenine and Bafilomycin A1), we confirmed that autophagy is required for both terminal differentiation and apoptosis induced by photo-activated N-TiO₂. Pre-incubation of leukemic cells with ROS scavengers muted the effect of N-TiO₂ NP-based PDT on cell fate, highlighting the upstream role of ROS in our system. In summary, PDT using N-TiO₂ NPs provides an effective method of priming autophagy by ROS induction. The capability of photo-activated N-TiO₂ NPs in obtaining desirable cellular outcomes represents a novel therapeutic strategy of cancer cells.

Atg5-dependent autophagy contributes to the development of acute myeloid leukemia in an MLL-AF9-driven mouse model

Acute myeloid leukemia (AML) is a hierarchical hematopoietic malignancy originating from leukemic stem cells (LSCs). Autophagy is a lysosomal degradation pathway that is hypothesized to be important for the maintenance of AML as well as contribute to chemotherapy response. Here we employ a mouse model of AML expressing the fusion oncogene MLL-AF9 and explore the effects of Atg5 deletion, a key autophagy protein, on the malignant transformation and progression of AML. Consistent with a transient decrease in colony-forming potential in vitro, the in vivo deletion of Atg5 in MLL-AF9-transduced bone marrow cells during primary transplantation prolonged the survival of recipient mice, suggesting that autophagy has a role in MLL-AF9-driven leukemia initiation. In contrast, deletion of Atg5 in malignant AML cells during secondary transplantation did not influence the survival or chemotherapeutic response of leukemic mice. Interestingly, autophagy was found to be involved in the survival of differentiated myeloid cells originating from MLL-AF9-driven LSCs. Taken together, our data suggest that Atg5-dependent autophagy may contribute to the development but not chemotherapy sensitivity of murine AML induced by MLL-AF9.