The effects of plasma gelsolin on human erythroblast maturation for erythrocyte production

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.

Emerging roles of plasma gelsolin in tumorigenesis and modulating the tumor microenvironment

The protein expression of gelsolin, an actin scavenger controlling cytoskeletal remodeling, cell morphology, differentiation, movement, and apoptosis, has been found to be significantly decreased in several pathological conditions including neurodegenerative diseases, inflammatory disorders, and cancers. Its extracellular isoform, called plasma gelsolin (pGSN), is one of the most abundant plasma proteins in the circulation, and has emerged as a novel diagnostic biomarker for early disease detection. Current evidence reveals that gelsolin can function as either an oncoprotein or a tumor suppressor depending on the carcinoma type. Interestingly, recent studies have shown that pGSN is also involved in immunomodulation, revealing the multifunctional roles of pGSN in tumor progression. In this review, we discuss the current knowledge focusing on the roles of gelsolin in inflammation and wound healing, cancers, and tumor microenvironment. Future prospects of pGSN related studies and clinical application are also addressed.

Erythroid enucleation: a gateway into a "bloody" world

Erythropoiesis is an intricate process starting in hematopoietic stem cells and leading to the daily production of 200 billion red blood cells (RBCs). Enucleation is a greatly complex and rate-limiting step during terminal maturation of mammalian RBC production involving expulsion of the nucleus from the orthochromatic erythroblasts, resulting in the formation of reticulocytes. The dynamic enucleation process involves many factors ranging from cytoskeletal proteins to transcription factors to microRNAs. Lack of optimum terminal erythroid maturation and enucleation has been an impediment to optimum RBC production ex vivo. Major efforts in the past two decades have exposed some of the mechanisms that govern the enucleation process. This review focuses in detail on mechanisms implicated in enucleation and discusses the future perspectives of this fascinating process.

Red cell manufacturing using parallel stirred-tank bioreactors at the final stages of differentiation enhances reticulocyte maturation

The aim of this study was to develop a robust, quality controlled, and reproducible erythroid culture system to obtain high numbers of mature erythroblasts and red blood cells (RBCs). This was achieved using a fully controlled stirred-tank bioreactor by the design of experiments (DOE) methods in the serum-free medium by defining the appropriate culture parameters. Human cord blood CD34+ cells were first cultured in static flasks and then inoculated to stirred-tank bioreactors. Cell diameter was gradually decreased and final RBC yields were significantly higher when cells were inoculated at sizes smaller than 12 μm. The larger immature cells in the basophilic stage did not survive, while smaller mature erythroid cells were successfully expanded at high agitation speeds, demonstrating that appropriate seeding timing is critical. A high inoculation cell density of 5 × 10⁶  cells/ml was achieved reaching 1.5 × 10⁷  cells/ml. By using DOE analysis fitted to precise stages of erythropoiesis, we were able to acquire the optimal culture parameters for pH (7.5), temperature (37°C), dissolved oxygen, agitation speed (500 rpm), inoculation timing (cell diameter 12-13 μm), media feeding regimen, and cell seeding density (5 × 10⁶  cells/ml). The final pure RBCs showed appropriate functions compared with fresh donor RBCs, confirming that manufacturing mature RBCs with reproducibility is possible.

CAP1, a target of miR-144/451, negatively regulates erythroid differentiation and enucleation

The exact molecular mechanism underlying erythroblast enucleation has been a fundamental biological question for decades. In this study, we found that miR-144/451 critically regulated erythroid differentiation and enucleation. We further identified CAP1, a G-actin-binding protein, as a direct target of miR-144/451 in these processes. During terminal erythropoiesis, CAP1 expression declines along with gradually increased miR-144/451 levels. Enforced CAP1 up-regulation inhibits the formation of contractile actin rings in erythroblasts and prevents their terminal differentiation and enucleation. Our findings reveal a negative regulatory role of CAP1 in miR-144/451-mediated erythropoiesis and thus shed light on how microRNAs fine-tune terminal erythroid development through regulating actin dynamics.

Role of Plasma Gelsolin Protein in the Final Stage of Erythropoiesis and in Correction of Erythroid Dysplasia In Vitro

Gelsolin, an actin-remodeling protein, is involved in cell motility, cytoskeletal remodeling, and cytokinesis and is abnormally expressed in many cancers. Recently, human recombinant plasma gelsolin protein (pGSN) was reported to have important roles in cell cycle and maturation of primary erythroblasts. However, the role of human plasma gelsolin in late stage erythroblasts prior to enucleation and putative clinical relevance in patients with myelodysplastic syndrome (MDS) and hemato-oncologic diseases have not been reported. Polychromatic and orthochromatic erythroblasts differentiated from human cord blood CD34+ cells, and human bone marrow (BM) cells derived from patients with MDS, were cultured in serum-free medium containing pGSN. Effects of pGSN on mitochondria, erythroid dysplasia, and enucleation were assessed in cellular and transcriptional levels. With pGSN treatment, terminal maturation at the stage of poly- and ortho-chromatic erythroblasts was enhanced, with higher numbers of orthochromatic erythroblasts and enucleated red blood cells (RBCs). pGSN also significantly decreased dysplastic features of cell morphology. Moreover, we found that patients with MDS with multi-lineage dysplasia or with excess blasts-1 showed significantly decreased expression of gelsolin mRNA (GSN) in their peripheral blood. When BM erythroblasts of MDS patients were cultured with pGSN, levels of mRNA transcripts related to terminal erythropoiesis and enucleation were markedly increased, with significantly decreased erythroid dysplasia. Moreover, pGSN treatment enhanced mitochondrial transmembrane potential that is unregulated in MDS and cultured cells. Our findings demonstrate a key role for plasma gelsolin in erythropoiesis and in gelsolin-depleted MDS patients, and raises the possibility that pGSN administration may promote erythropoiesis in erythroid dysplasia.