The opposing roles of the mTOR signaling pathway in different phases of human umbilical cord blood-derived CD34+ cell erythropoiesis

Accessory-cell-free differentiation of hematopoietic stem and progenitor cells into mature red blood cells

BACKGROUND AIMS

The culture and ex vivo engineering of red blood cells (RBCs) can help characterize genetic variants, model diseases, and may eventually spur the development of applications in transfusion medicine. In the last decade, improvements to the in vitro production of RBCs have enabled efficient erythroid progenitor proliferation and high enucleation levels from several sources of hematopoietic stem and progenitor cells (HSPCs). Despite these advances, there remains a need for refining the terminal step of in vitro human erythropoiesis, i.e., the terminal maturation of reticulocytes into erythrocytes, so that it can occur without feeder or accessory cells and animal-derived components.

METHODS

Here, we describe the near-complete erythroid differentiation of cultured RBCs (cRBCs) from adult HSPCs in accessory-cell-free and xeno-free conditions.

RESULTS

The approach improves post-enucleation cell integrity and cell survival, and it enables subsequent storage of cRBCs for up to 42 days in classical additive solution conditions without any specialized equipment.

CONCLUSIONS

We foresee that these improvements will facilitate the characterization of RBCs derived from gene-edited HSPCs.

DNA methylation status of DNAJA4 is essential for human erythropoiesis

Aims: To investigate DNA methylation patterns in early and terminal stages of erythropoiesis, and to explore the function of differentially methylated genes in erythropoiesis and erythroid disorders. Materials & methods: Differential analysis of DNA methylation and gene expression during erythropoiesis, as well as weighted gene coexpression network analysis of acute myeloid leukemia was performed. Results: We identified four candidate genes that possessed differential methylation in the promoter regions. DNAJA4 affected proliferation, apoptosis and enucleation during terminal erythropoiesis and was associated with the prognosis of acute myeloid leukemia.  DNAJA4 was specifically highly expressed in erythroleukemia and is associated with DNA methylation. Conclusion: DNAJA4 plays a crucial role for erythropoiesis and is regulated via DNA methylation. Dysregulation of DNAJA4 expression is associated with erythroid disorders.

Autophagy regulated by the HIF/REDD1/mTORC1 signaling is progressively increased during erythroid differentiation under hypoxia

For hematopoietic stem and progenitor cells (HSPCs), hypoxia is a specific microenvironment known as the hypoxic niche. How hypoxia regulates erythroid differentiation of HSPCs remains unclear. In this study, we show that hypoxia evidently accelerates erythroid differentiation, and autophagy plays a pivotal role in this process. We further determine that mTORC1 signaling is suppressed by hypoxia to relieve its inhibition of autophagy, and with the process of erythroid differentiation, mTORC1 activity gradually decreases and autophagy activity increases accordingly. Moreover, we provide evidence that the HIF-1 target gene REDD1 is upregulated to suppress mTORC1 signaling and enhance autophagy, thereby promoting erythroid differentiation under hypoxia. Together, our study identifies that the enhanced autophagy by hypoxia favors erythroid maturation and elucidates a new regulatory pattern whereby autophagy is progressively increased during erythroid differentiation, which is driven by the HIF-1/REDD1/mTORC1 signaling in a hypoxic niche.

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.

Fine-Tuning of Cholesterol Homeostasis Controls Erythroid Differentiation

Lipid metabolism is essential for stemness maintenance, self-renewal, and differentiation of stem cells, however, the regulatory function of cholesterol metabolism in erythroid differentiation is poorly studied. In the present study, a critical role for cholesterol homeostasis in terminal erythropoiesis is uncovered. The master transcriptional factor GATA1 binds to Sterol-regulatory element binding protein 2 (SREBP2) to downregulate cholesterol biosynthesis, leading to a gradual reduction in intracellular cholesterol levels. It is further shown that reduced cholesterol functions to block erythroid proliferation via the cholesterol/mTORC1/ribosome biogenesis axis, which coordinates cell cycle exit in the late stages of erythroid differentiation. The interaction of GATA1 and SREBP2 also provides a feedback loop for regulating globin expression through the transcriptional control of NFE2 by SREBP2. Importantly, it is shown that disrupting intracellular cholesterol hemostasis resulted in defect of terminal erythroid differentiation in vivo. These findings demonstrate that fine-tuning of cholesterol homeostasis emerges as a key mechanism for regulating erythropoiesis.

TMEA, a Polyphenol in Sanguisorba officinalis, Promotes Thrombocytopoiesis by Upregulating PI3K/Akt Signaling

Thrombocytopenia is closely linked with hemorrhagic diseases, for which induction of thrombopoiesis shows promise as an effective treatment. Polyphenols widely exist in plants and manifest antioxidation and antitumour activities. In this study, we investigated the thrombopoietic effect and mechanism of 3,3′,4′-trimethylellagic acid (TMEA, a polyphenol in Sanguisorba officinalis L.) using in silico prediction and experimental validation. A KEGG analysis indicated that PI3K/Akt signalling functioned as a crucial pathway. Furthermore, the virtual molecular docking results showed high-affinity binding (a docking score of 6.65) between TMEA and mTOR, suggesting that TMEA might target the mTOR protein to modulate signalling activity. After isolation of TMEA, in vitro and in vivo validation revealed that this compound could promote megakaryocyte differentiation/maturation and platelet formation. In addition, it enhanced the phosphorylation of PI3K, Akt, mTOR, and P70S6K and increased the expression of GATA-1 and NF-E2, which confirmed the mechanism prediction. In conclusion, our findings are the first to demonstrate that TMEA may provide a novel therapeutic strategy that relies on the PI3K/Akt/mTOR pathway to facilitate megakaryocyte differentiation and platelet production.

New Insights into Red Blood Cell Microcytosis upon mTOR Inhibitor Administration

The aim of this study was to evaluate the effect of everolimus, a mammalian target of rapamycin (mTOR) inhibitor, on red blood cell parameters in the context of iron homeostasis in patients with tuberous sclerosis complex (TSC) and evaluate its effect on cell size in vitro. Everolimus has a significant impact on red blood cell parameters in patients with TSC. The most common alteration was microcytosis. The mean MCV value decreased by 9.2%, 12%, and 11.8% after 3, 6, and 12 months of everolimus treatment. The iron level declined during the first 3 months, and human soluble transferrin receptor concentration increased during 6 months of therapy. The size of K562 cells decreased when cultured in the presence of 5 μM everolimus by approximately 8%. The addition of hemin to the cell culture with 5 μM everolimus did not prevent any decrease in cell size. The stage of erythroid maturation did not affect the response to everolimus. Our results showed that the mTOR inhibitor everolimus caused red blood cell microcytosis in vivo and in vitro. This effect is not clearly related to a deficit of iron and erythroid maturation. This observation confirms that mTOR signaling plays a complex role in the control of cell size.

Dihydroartemisinin Inhibits TGF-β-Induced Fibrosis in Human Tenon Fibroblasts via Inducing Autophagy

Background

The formation of hypertrophic scars (HS) can result in the failure of glaucoma surgery, and fibrosis is known to be closely associated with the progression of HS. Dihydroartemisinin (DHA) has been reported to inhibit the progression of fibrosis; however, whether DHA can alleviate the formation of HS remains unclear.

Methods

In the present study, in order to examine the effects of DHA on the progression of HS, human Tenon's capsule fibroblasts (HTFs) were isolated from patients who underwent glaucoma surgery. In addition, Western blot analysis, microtubule associated protein 1 light chain 3 α staining and reverse transcription-quantitative PCR were performed to detect protein and mRNA expression levels in the HTFs, respectively. Cell proliferation was detected by Ki67 staining. Flow cytometry was used to examine apoptosis and reactive oxygen species (ROS) levels in the HTFs.

Results

The results revealed that TGF-β promoted the proliferation and fibrosis of HTFs; however, DHA significantly reversed the effects of TGF-β by increasing cell autophagy. In addition, DHA notably induced the apoptosis of TGF-β-stimulated HTFs by increasing the ROS levels, while these increases were partially reversed by 3-methyladenine. Furthermore, DHA notably increased the expression of microRNA (miR)-145-5p in HTFs in a dose-dependent manner.

Conclusion

The present study demonstrated that DHA inhibits the TGF-β-induced fibrosis of HTFs by inducing autophagy. These findings may aid in the development of novel agents for the prevention of the formation of HS following glaucoma surgery.

The opposing roles of the mTOR signaling pathway in different phases of human umbilical cord blood-derived CD34+ cell erythropoiesis

As an indispensable, even lifesaving practice, red blood cell (RBC) transfusion is challenging due to several issues, including supply shortage, immune incompatibility, and blood-borne infections since donated blood is the only source of RBCs. Although large-scale in vitro production of functional RBCs from human stem cells is a promising alternative, so far, no such system has been reported to produce clinically transfusable RBCs due to the poor understanding of mechanisms of human erythropoiesis, which is essential for the optimization of in vitro erythrocyte generation system. We previously reported that inhibition of mammalian target of rapamycin (mTOR) signaling significantly decreased the percentage of erythroid progenitor cells in the bone marrow of wild-type mice. In contrast, rapamycin treatment remarkably improved terminal maturation of erythroblasts and anemia in a mouse model of β-thalassemia. In the present study, we investigated the effect of mTOR inhibition with rapamycin from different time points on human umbilical cord blood-derived CD34⁺ cell erythropoiesis in vitro and the underlying mechanisms. Our data showed that rapamycin treatment significantly suppressed erythroid colony formation in the commitment/proliferation phase of erythropoiesis through inhibition of cell-cycle progression and proliferation. In contrast, during the maturation phase of erythropoiesis, mTOR inhibition dramatically promoted enucleation and mitochondrial clearance by enhancing autophagy. Collectively, our results suggest contrasting roles for mTOR in regulating different phases of human erythropoiesis.