Microenvironmental regulation of hematopoietic stem cells and its implications in leukemogenesis

Functions and regulatory mechanisms of resting hematopoietic stem cells: a promising targeted therapeutic strategy

Hematopoietic stem cells (HSCs) are the common and essential precursors of all blood cells, including immune cells, and they are responsible for the lifelong maintenance and damage repair of blood tissue homeostasis. The vast majority (> 95%) of HSCs are in a resting state under physiological conditions and are only activated to play a functional role under stress conditions. This resting state affects their long-term survival and is also closely related to the lifelong maintenance of hematopoietic function; however, abnormal changes may also be an important factor leading to the decline of immune function in the body and the occurrence of diseases in various systems. While the importance of resting HSCs has attracted increasing research attention, our current understanding of this topic remains insufficient, and the direction of clinical targeted treatments is unclear. Here, we describe the functions of HSCs, analyze the regulatory mechanisms that affect their resting state, and discuss the relationship between resting HSCs and different diseases, with a view to providing guidance for the future clinical implementation of related targeted treatments.

Mechanisms of myeloid leukemogenesis: Current perspectives and therapeutic objectives

Acute myeloid leukemia (AML) is a heterogeneous hematopoietic neoplasm which results in clonal proliferation of abnormally differentiated hematopoietic cells. In this review, mechanisms contributing to myeloid leukemogenesis are summarized, highlighting aberrations of epigenetics, transcription factors, signal transduction, cell cycling, and the bone marrow microenvironment. The mechanisms contributing to AML are detailed to spotlight recent findings that convey clinical impact. The applications of current and prospective therapeutic targets are accentuated in addition to reviews of treatment paradigms stratified for each characteristic molecular lesion - with a focus on exploring novel treatment approaches and combinations to improve outcomes in AML.

Prognostic Role of Cell Blood Count in Chronic Myeloid Neoplasm and Acute Myeloid Leukemia and Its Possible Implications in Hematopoietic Stem Cell Transplantation

Numerous prognostic indexes have been developed in hematological diseases based on patient characteristics and genetic or molecular assessment. However, less attention was paid to more accessible parameters, such as neutrophils, lymphocytes, monocytes, and platelet counts. Although many studies have defined the role of neutrophil-to-lymphocyte or platelet-to-lymphocyte in lymphoid malignancies, few applications exist for myeloid neoplasm or hematopoietic stem cell transplantation procedures. In this review, we synthesized literature data on the prognostic value of count blood cells in myeloid malignancies and hematopoietic stem cell transplantation in the context of classical prognostic factors and clinical outcomes.

Mesenchymal stem/stromal cells in breast cancer development and management

Mesenchymal stem/stromal cells (MSCs) encompass a heterogeneous population of fibroblastic progenitor cells that reside in multiple tissues around the body. They are endowed with capacities to differentiate into multiple connective tissue lineages, including chondrocytes, adipocytes, and osteoblasts, and are thought to function as trophic cells recruited to sites of injury and inflammation where they contribute to tissue regeneration. In keeping with these roles, MSCs also to home to sites of breast tumorigenesis, akin to their migration to wounds, and participate in tumor stroma formation. Mounting evidence over the past two decades has described the critical regulatory roles for tumor-associated MSCs in various aspects of breast tumor pathogenesis, be it tumor initiation, growth, angiogenesis, tumor microenvironment formation, immune evasion, cancer cell migration, invasion, survival, therapeutic resistance, dissemination, and metastatic colonization. In this review, we present a brief summary of the role of MSCs in breast tumor development and progression, highlight some of the molecular frameworks underlying their pro-malignant contributions, and present evidence of their promising utility in breast cancer therapy.

Bioengineered 3D microfibrous-matrix modulates osteopontin release from MSCs and facilitates the expansion of hematopoietic stem cells

The osteopontin released from mesenchymal stem cells (MSC) undergoing lineage differentiation can negatively influence the expansion of hematopoietic stem cells (HSCs) in co-culture systems developed for expanding HSCs. Therefore, minimising the amount of osteopontin in the co-culture system is important for the successful ex vivo expansion of HSCs. Towards this goal, a bioengineered 3D microfibrous-matrix that can maintain MSCs in less osteopontin-releasing conditions has been developed, and its influence on the expansion of HSCs has been studied. The newly developed 3D matrix significantly decreased the release of osteopontin, depending on the MSC culture conditions used during the priming period before HSC seeding. The culture system with the lowest amount of osteopontin facilitated a more than 24-fold increase in HSC number in 1 week time period. Interestingly, the viability of expanded cells and the CD34+ pure population of HSCs were found to be the highest in the low osteopontin-containing system. Therefore, bioengineered microfibrous 3D matrices seeded with MSCs, primed under suitable culture conditions, can be an improved ex vivo expansion system for HSC culture. This article is protected by copyright. All rights reserved.

Bioinformatic analysis as a first step to predict the compatibility of hematopoiesis and immune system genes between humans and pigs

The shortage of allogeneic donor organs leaves its supply far short of clinical need. There are great expectations on xenotransplantation, especially with pigs' organs. With the genetic modification of donor pigs, the rejection and cross-species transmission issues have now been widely addressed. However, research on the compatibility of genes between humans and pigs was limited. We performed a systematic screening analysis of predicted incompatible genes between humans and pigs, judged by low protein sequence similarities or different predicted protein domain compositions. By combining with gene set enrichment analysis, we screened out several key genes of hematopoiesis and the immune system with possible incompatibilities, which might be important for establishing chimera and xenotransplantation between humans and pigs. There were seven chemokine genes, including CCL1, CCL5, CCL24, CCL25, CCL28, CXCL12, and CXCL16, that exhibited limited similarity between humans and pigs (similarity < 0.8). Among hematopoiesis process-related genes, 15 genes of adhesion molecules, Notch ligands, and cytokine receptors exhibited differences between humans and pigs. In complement and coagulation cascades, 19 genes showed low similarity and 77 genes had different domain compositions between humans and pigs. Our study provides a good reference for further genetic modification of pigs, which might be beneficial for xenotransplantation.

Irradiation Haematopoiesis Recovery Orchestrated by IL-12/IL-12Rβ1/TYK2/STAT3-Initiated Osteogenic Differentiation of Mouse Bone Marrow-Derived Mesenchymal Stem Cells

Purpose

Repairing the irradiation-induced osteogenic differentiation injury of bone marrow mesenchymal stem cells (BM-MSCs) is beneficial to recovering haematopoiesis injury in radiotherapy; however, its mechanism is elusive. Our study aimed to help meet the needs of understanding the effects of radiotherapy on BM-MSC osteogenic potential.

Methods and Materials

Balb/c mice and the BM-MSCs were used to evaluate the irradiation-induced osteogenic differentiation injury in vivo. The cellular and molecular characterization were applied to determine the mechanism for recovery of irradiation-derived haematopoiesis injuries.

Results

We report a functional role of IL-12 in acute irradiation hematopoietic injury recovery and intend to dissect the possible mechanisms through BM-MSC, other than the direct effect of IL-12 on hematopoietic stem and progenitor cells (HSPCs). Specifically, we show that early use of IL-12 enhanced the osteogenic differentiation of BM-MSCs through IL-12Rβ1/TYK2/STAT3 signaling; furthermore, IL-12 induced osteogenesis facilitated bone formation and irradiation hematopoiesis recovery when transplanted BM-MSCs in the femur of Balb/c mice. For the mechanism of action, we found that IL-12 receptor beta 1 (IL-12Rβ1) expression of irradiated BM-MSCs was upregulated rapidly, coincidentally consistent with early use of IL-12 induced osteogenic differentiation enhancement. IL-12Rβ1 and tyrosine kinase 2 gene (Tyk2) silencing experiments and phosphotyrosine of signal transducer and activator of transcription 3 (p-STAT3) suppression experiments indicated the IL-12Rβ1/TYK2/STAT3 signaling was essential in IL-12-induced osteogenic differentiation enhancement of BM-MSCs.

Conclusion

These findings suggested that IL-12 may exert BM-MSCs-based hematopoietic recovery by repairing osteogenic differentiation abilities damages through IL-12Rβ1/TYK2/STAT3 signaling pathway post-irradiation.

Morphogen signaling by Wnt/β-catenin pathway and microenvironmental alteration in the bone marrow of agricultural pesticide exposure-induced experimental aplastic anemia

The etiologic link between pesticide toxicity and aplastic anemia in agricultural and agro-industrial setting has been frequently reported in epidemiological studies conducted worldwide. Chronic pesticide toxicity causes long-term bone marrow injury and perturbs the normal hematopoietic physiology, including survival of hematopoietic progenitor cells and bone marrow's blood cell forming ability. The purpose of this study is to understand the mechanism of pesticide toxicity-mediated bone marrow aplasia by studying Wnt/β-catenin signaling pathway and microenvironmental stromal components. An agricultural pesticide formulation comprising of cypermethrin, chlorpyriphos, and hexaconazole was used to induce bone marrow aplasia in inbred Swiss albino mice. Marrow failure followed by the onset of aplastic condition was confirmed by pancytopenic peripheral blood and hypocellular bone marrow filled with adipocytes. Significant downregulation of canonical Wnt/β-catenin signaling was identified by expression analysis of Wnt3a, β-catenin, and telomerase reverse transcriptase in the aplastic bone marrow hematopoietic stem/progenitor compartment. Along with signaling deregulation, disruption in both the osteoblastic and vascular stromal components was observed in the pesticide-exposed bone marrow microenvironment when compared to control. In this study, we tried to establish the correlation among disease pathophysiology, signaling deregulation in the hematopoietic cells, and bone marrow microenvironmental alteration during environmental exposure-mediated aplastic hematopoietic catastrophe, which may shed light on the unexplored mechanistic perspective of this fatal blood disease.

Neuropeptide Y is involved in the regulation of quiescence of hematopoietic stem cells

Differentiation, self-renewal and quiescence of Hematopoietic stem cells (HSCs) is tightly regulated in order to protect the HSCs from the strain of constant cell division and depletion of the stem cell pool. The neurotransmitter Neuropeptide Y (NPY) is released from sympathetic nerves in the bone marrow and has been shown to indirectly affect HSC function through effects on bone marrow (BM) multipotent Mesenchymal Stromal Cells (MSCs), osteoblasts (OBs) and macrophages. Although the absence of NPY has been shown to be accompanied by severe BM impairment and delayed engraftment of HSCs, the direct effects of NPY on HSCs have never been assessed. Here, we aimed to explore the effect of NPY on the regulation of HSCs. All NPY receptors Y1, Y2, Y4 and Y5 were found to be highly expressed on most HSCs and mature hematopoietic cell subsets. In culture, in particularly expression of the Y1 receptor was shown to decrease in time. Doses of 300 nM NPY suppressed HSC proliferation in cell cultures, as confirmed by an increase of HSCs in G₀ phase and an increase in the gene expression levels of FOXO3, DICER1, SMARCA2 and PDK1, which all have been shown to play an important role in the regulation of cell quiescence. These data support the idea that NPY may have a direct effect on the regulation of HSC fate by modulating cell quiescence.

Mimicking megakaryopoiesis in vitro using biomaterials: Recent advances and future opportunities

Presently donor-derived platelets used in the clinic are associated with concerns about adequate availability, expense, risk of bacterial contamination and complications due to immunological reaction. To prevail over our dependence on transfusion of donor-derived platelets, efforts are being made to generate them in vitro. Development of biomaterials that support or mimic bone marrow niche micro-environmental cues could improve the in vitro production of platelets from megakaryocytes (MKs) derived from various stem cell sources. In spite of significant advances in the production of MKs from various stem cell sources using 2D as well as 3D culture approaches in vitro and the development of biomaterials-based platelet systems, yield and quality of these platelets remains unsuitable for clinical use. Thus, in vitro production of clinically useful platelets on a large scale remains an unmet target to date. This review summarizes the most frequently used 2D and 3D approaches to generate MKs and platelets in vitro, emphasizing the importance of mimicking in vivo micro-environment. Further, this review proposes the use of interpenetrating network (IPN) biomaterial-based approach as a promising strategy for improving the generation of MK and platelets in sufficient numbers in vitro. STATEMENT OF SIGNIFICANCE: Thrombocytopenia is one of the major global health and socio-economic problems. Transfusion with donor-derived platelets (PLTs) is the only effective treatment for this condition. However, this approach is limited by factors like short shelf-life of PLTs, PLT activation, alloimmunization, risk of bacterial contamination, infection etc. In vitro generated MKs and PLTs derived from non-donor-dependent sources may help to overcome the platelet transfusion concerns. Here we have reviewed various 2D and 3D strategies used for in vitro generation of MKs and PLTs, with special emphasis on various biomaterial platforms and different physico/chemical cues being used for the purpose. We have also proposed a biomaterial-based approach of using interpenetrating network (IPN) for generating clinically relevant numbers of MKs and PLTs.

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.

C3G, through its GEF activity, induces megakaryocytic differentiation and proplatelet formation

BACKGROUND

Megakaryopoiesis allows platelet formation, which is necessary for coagulation, also playing an important role in different pathologies. However, this process remains to be fully characterized. C3G, an activator of Rap1 GTPases, is involved in platelet activation and regulates several differentiation processes.

METHODS

We evaluated C3G function in megakaryopoiesis using transgenic mouse models where C3G and C3GΔCat (mutant lacking the GEF domain) transgenes are expressed exclusively in megakaryocytes and platelets. In addition, we used different clones of K562, HEL and DAMI cell lines with overexpression or silencing of C3G or GATA-1.

RESULTS

We found that C3G participates in the differentiation of immature hematopoietic cells to megakaryocytes. Accordingly, bone marrow cells from transgenic C3G, but not those from transgenic C3GΔCat mice, showed increased expression of the differentiation markers CD41 and CD61, upon thrombopoietin treatment. Furthermore, C3G overexpression increased the number of CD41⁺ megakaryocytes with high DNA content. These results are supported by data obtained in the different models of megakaryocytic cell lines. In addition, it was uncovered GATA-1 as a positive regulator of C3G expression. Moreover, C3G transgenic megakaryocytes from fresh bone marrow explants showed increased migration from the osteoblastic to the vascular niche and an enhanced ability to form proplatelets. Although the transgenic expression of C3G in platelets did not alter basal platelet counts, it did increase slightly those induced by TPO injection in vivo. Moreover, platelet C3G induced adipogenesis in the bone marrow under pathological conditions.

CONCLUSIONS

All these data indicate that C3G plays a significant role in different steps of megakaryopoiesis, acting through a mechanism dependent on its GEF activity.

Development of the Myocardial Interstitium

The space between cardiac myocytes is commonly referred-to as the cardiac interstitium (CI). The CI is a unique, complex and dynamic microenvironment in which multiple cell types, extracellular matrix molecules, and instructive signals interact to crucially support heart homeostasis and promote cardiac responses to normal and pathologic stimuli. Despite the biomedical and clinical relevance of the CI, its detailed cellular structure remains to be elucidated. In this review, we will dissect the organization of the cardiac interstitium by following its changing cellular and molecular composition from embryonic developmental stages to adulthood, providing a systematic analysis of the biological components of the CI. The main goal of this review is to contribute to our understanding of the CI roles in health and disease. Anat Rec, 302:58-68, 2019. © 2018 Wiley Periodicals, Inc.

The role of bone marrow microenvironment in platelet production and their implications for the treatment of thrombocytopenic diseases

OBJECTIVES

Impaired platelet production has been found to be an important pathological mechanism of thrombocytopenia in many diseases. Platelet generation is a complex process that mainly occurs in the bone marrow, and thus is closely regulated by the bone marrow microenvironment. This review attempts to summarize the most current knowledge referring the role of bone marrow microenvironment in the regulation of platelet production.

METHODS

The effects of multiple microenvironment ingredients in regulating megakaryopoiesis and thrombocytopoiesis have been discussed. Abnormalities of these components in thrombocytopenic diseases are also described.

DISCUSSIONS

Thrombocytopenia is a common clinical manifestation of a variety of diseases. The functional importance of platelets has driven the developments of a broad range of studies. Platelet generation mainly occurs within the bone marrow, where the cells, soluble factors, and extracellular matrix proteins collaboratively form a complex regulatory network, directing megakaryocytic proliferation and differentiation. Alteration in any part of the regulating network may result in defective platelet formation, and eventually lead to thrombocytopenia. A variety of thrombocytopenic diseases have been found to be related with the disregulated bone marrow microenvironment. Identification of the variations of these niche ingredients in certain diseases has facilitated the developments of multiple therapeutic regimes. Further studies that can combine these niche factors with their downstream regulatory factors will be beneficial for developing more effective therapies.

CONCLUSIONS

Further definition of the role of bone marrow microenvironment in platelet generation may deepen our understanding of the underlying mechanisms as well as provide new therapeutic targets for thrombocytopenic diseases.

Adipose, Bone, and Myeloma: Contributions from the Microenvironment

Researchers globally are working towards finding a cure for multiple myeloma (MM), a destructive blood cancer diagnosed yearly in ~750,000 people worldwide (Podar et al. in Expert Opin Emerg Drugs 14:99-127, 2009). Although MM targets multiple organ systems, it is the devastating skeletal destruction experienced by over 90 % of patients that often most severely impacts patient morbidity, pain, and quality of life. Preventing bone disease is therefore a priority in MM treatment, and understanding how and why myeloma cells target the bone marrow (BM) is fundamental to this process. This review focuses on a key area of MM research: the contributions of the bone microenvironment to disease origins, progression, and drug resistance. We describe some of the key cell types in the BM niche: osteoclasts, osteoblasts, osteocytes, adipocytes, and mesenchymal stem cells. We then focus on how these key cellular players are, or could be, regulating a range of disease-related processes spanning MM growth, drug resistance, and bone disease (including osteolysis, fracture, and hypercalcemia). We summarize the literature regarding MM-bone cell and MM-adipocyte relationships and subsequent phenotypic changes or adaptations in MM cells, with the aim of providing a deeper understanding of how myeloma cells grow in the skeleton to cause bone destruction. We identify avenues and therapies that intervene in these networks to stop tumor growth and/or induce bone regeneration. Overall, we aim to illustrate how novel therapeutic target molecules, proteins, and cellular mediators may offer new avenues to attack this disease while reviewing currently utilized therapies.

Bone Marrow Blood Vessels: Normal and Neoplastic Niche

Blood vessels are among the most important factors in the transport of materials such as nutrients and oxygen. This study will review the role of blood vessels in normal bone marrow hematopoiesis as well as pathological conditions like leukemia and metastasis. Relevant literature was identified by a Pubmed search (1992-2016) of English-language papers using the terms bone marrow, leukemia, metastasis, and vessel. Given that blood vessels are conduits for the transfer of nutrients, they create a favorable situation for cancer cells and cause their growth and development. On the other hand, blood vessels protect leukemia cells against chemotherapy drugs. Finally, it may be concluded that the vessels are an important factor in the development of malignant diseases.