Bioengineering Hematopoietic Stem Cell Niche toward Regenerative Medicine

Development and application of nanomaterials, nanotechnology and nanomedicine for treating hematological malignancies

Hematologic malignancies (HMs) pose a serious threat to patients' health and life, and the five-year overall survival of HMs remains low. The lack of understanding of the pathogenesis and the complex clinical symptoms brings immense challenges to the diagnosis and treatment of HMs. Traditional therapeutic strategies for HMs include radiotherapy, chemotherapy, targeted therapy and hematopoietic stem cell transplantation. Although immunotherapy and cell therapy have made considerable progress in the last decade, nearly half of patients still relapse or suffer from drug resistance. Recently, studies have emerged that nanomaterials, nanotechnology and nanomedicine show great promise in cancer therapy by enhancing drug targeting, reducing toxicity and side effects and boosting the immune response to promote durable immunological memory. In this review, we summarized the strategies of recently developed nanomaterials, nanotechnology and nanomedicines against HMs and then proposed emerging strategies for the future designment of nanomedicines to treat HMs based on urgent clinical needs and technological progress.

Rebuilding the hematopoietic stem cell niche: Recent developments and future prospects

Hematopoietic stem cells (HSCs) have proven their clinical relevance in stem cell transplantation to cure patients with hematological disorders. Key to their regenerative potential is their natural microenvironment - their niche - in the bone marrow (BM). Developments in the field of biomaterials enable the recreation of such environments with increasing preciseness in the laboratory. Such artificial niches help to gain a fundamental understanding of the biophysical and biochemical processes underlying the interaction of HSCs with the materials in their environment and the disturbance of this interplay during diseases affecting the BM. Artificial niches also have the potential to multiply HSCs in vitro, to enable the targeted differentiation of HSCs into mature blood cells or to serve as drug-testing platforms. In this review, we will introduce the importance of artificial niches followed by the biology and biophysics of the natural archetype. We will outline how 2D biomaterials can be used to dissect the complexity of the natural niche into individual parameters for fundamental research and how 3D systems evolved from them. We will present commonly used biomaterials for HSC research and their applications. Finally, we will highlight two areas in the field of HSC research, which just started to unlock the possibilities provided by novel biomaterials, in vitro blood production and studying the pathophysiology of the niche in vitro. With these contents, the review aims to give a broad overview of the different biomaterials applied for HSC research and to discuss their potentials, challenges and future directions in the field. STATEMENT OF SIGNIFICANCE: Hematopoietic stem cells (HSCs) are multipotent cells responsible for maintaining the turnover of all blood cells. They are routinely applied to treat patients with hematological diseases. This high clinical relevance explains the necessity of multiplication or differentiation of HSCs in the laboratory, which is hampered by the missing natural microenvironment - the so called niche. Biomaterials offer the possibility to mimic the niche and thus overcome this hurdle. The review introduces the HSC niche in the bone marrow and discusses the utility of biomaterials in creating artificial niches. It outlines how 2D systems evolved into sophisticated 3D platforms, which opened the gateway to applications such as, expansion of clinically relevant HSCs, in vitro blood production, studying niche pathologies and drug testing.

Emerging Biofabrication Techniques: A Review on Natural Polymers for Biomedical Applications

Natural polymers have been widely used for biomedical applications in recent decades. They offer the advantages of resembling the extracellular matrix of native tissues and retaining biochemical cues and properties necessary to enhance their biocompatibility, so they usually improve the cellular attachment and behavior and avoid immunological reactions. Moreover, they offer a rapid degradability through natural enzymatic or chemical processes. However, natural polymers present poor mechanical strength, which frequently makes the manipulation processes difficult. Recent advances in biofabrication, 3D printing, microfluidics, and cell-electrospinning allow the manufacturing of complex natural polymer matrixes with biophysical and structural properties similar to those of the extracellular matrix. In addition, these techniques offer the possibility of incorporating different cell lines into the fabrication process, a revolutionary strategy broadly explored in recent years to produce cell-laden scaffolds that can better mimic the properties of functional tissues. In this review, the use of 3D printing, microfluidics, and electrospinning approaches has been extensively investigated for the biofabrication of naturally derived polymer scaffolds with encapsulated cells intended for biomedical applications (e.g., cell therapies, bone and dental grafts, cardiovascular or musculoskeletal tissue regeneration, and wound healing).

[Effects of nicotinamide mononucleotide adenylyl transferase 3 on mitochondrial function and anti-oxidative stress of rabbit bone marrow mesenchymal stem cells via regulating nicotinamide adenine dinucleotide levels]

OBJECTIVE

To investigate the effect of nicotinamide mononucleotide adenosyl transferase 3 (NMNAT3) on the mitochondrial function and anti-oxidative stress of rabbit bone marrow mesenchymal stem cells (BMSCs) under oxidative stress in vitro by regulating nicotinamide adenine dinucleotide (NAD +) levels.

METHODS

The bone marrow of femur and tibia of New Zealand white rabbits were extracted. BMSCs were isolated and cultured in vitro by density gradient centrifugation combined with adherent culture. The third generation cells were identified by flow cytometry and multi-directional induction. Overexpression of NMNAT3 gene was transfected into rabbit BMSCs by enhanced green fluorescent protein (EGFP) labeled lentivirus (BMSCs/Lv-NMNAT3-EGFP), and then the expression of NMNAT3 was detected by real-time fluorescence quantitative PCR (qRT-PCR) and Western blot and cell proliferation by cell counting kit 8 (CCK-8) method. BMSCs transfected with negative lentivirus (BMSCs/Lv-EGFP) and untransfected BMSCs were used as controls. The oxidative stress injury cell model was established by using H 2O 2 to treat rabbit BMSCs. According to the experimental treatment conditions, they were divided into 4 groups: Group A was normal BMSCs without H 2O 2 treatment; untransfected BMSCs, BMSCs/Lv-EGFP, and BMSCs/Lv-NMNAT3-EGFP in groups B, C, and D were treated with H 2O 2 simulated oxidative stress, respectively. The effects of NMNAT3 on the mitochondrial function of BMSCs under oxidative stress [changes of mitochondrial membrane potential, NAD + and adenosine triphosphate (ATP) levels], the changes of anti-oxidative stress ability of BMSCs [reactive oxygen species (ROS) and malondialdehyde (MDA) levels, manganese superoxide dismutase (Mn-SOD) and catalase (CAT) activities], and the effects of BMSCs on senescence and apoptosis [senescence associated-β-galactosidase (SA-β-gal) staining and TUNEL staining] were detected after 24 hours of treatment.

RESULTS

The rabbit BMSCs were successfully isolated and cultured in vitro. The stable strain of rabbit BMSCs with high expression of NMNAT3 gene was successfully obtained by lentiviral transfection, and the expressions of NMNAT3 gene and protein significantly increased ( P<0.05). There was no significant difference in the trend of cell proliferation compared with normal BMSCs. After treatment with H 2O 2, the function of mitochondria was damaged and apoptosis increased in all groups. However, compared with groups B and C, the group D showed that the mitochondrial function of BMSCs improved, the membrane potential increased, the level of NAD + and ATP synthesis of mitochondria increased; the anti-oxidative stress ability of BMSCs enhanced, the levels of ROS and MDA decreased, and the activities of antioxidant enzymes (Mn-SOD, CAT) increased; and the proportion of SA-β-gal positive cells and the rate of apoptosis decreased. The differences in all indicators between group D and groups B and C were significant ( P<0.05).

CONCLUSION

NMNAT3 can effectively improve the mitochondrial function of rabbit BMSCs via increasing the NAD + levels, and enhance its anti-oxidative stress and improve the survival of BMSCs under oxidative stress conditions.

Umbilical cord blood mesenchymal stem cells application in hematopoietic stem cells expansion on nanofiber three-dimensional scaffold

Umbilical cord blood (UCB) hematopoietic stem cells (HSCs) transplantation (HSCTs) is considered as a therapeutic strategy for malignant and nonmalignant hematologic disorders. Nevertheless, the low number of HSCs obtained from each unit of UCB can be a major challenge for using these cells in adults. In addition, UCB is a rich source of mesenchymal stem cells (MSCs) creating hopes for nonaggressive and painless treatment in tissue engineering compared with bone marrow MSCs. This study was designed to evaluate the effects of UCB-MSCs application in UCB-HSCs expansion on the nanoscaffold that mimics the cell's natural niche. To achieve this goal, after flow cytometry confirmation of isolated HSCs from UCB, they were expanded on three-dimensional (3D) poly-l-lactic acid (PLLA) scaffolds fabricated by electrospinning and two-dimensional (2D)-culture systems, such as (1) HSCs-MSCs culturing on the scaffold, (2) HSCs culturing on the scaffold, (3) HSCs-MSCs culturing on 2D, and (4) HSCs culturing on 2D. After 7 days, real-time polymerase chain reaction (PCR) was performed to evaluate the CXCR4 gene expression in the mentioned groups. Moreover, for the next validation, the number of total HSCs, 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide assay, scanning electron microscopy imaging, and colony-forming unit assay were evaluated as well. The results of the study indicated that UCB-MSCs interaction with HSCs in 3D-culture systems led to the highest expansion of UCB-HSCs on day 7. Flow cytometry results showed the highest purity of HSCs cocultured with MSCs. Real-time PCR showed a significant increase in gene expression of CXCR4 in the mentioned group. The highest viability and clonogenicity were detected in the mentioned group too. Considered together, our results suggest that UCB-HSCs and MSCs coculturing on PLLA scaffold could provide a proper microenvironment that efficiently promotes UCB-HSCs expansion and UCB-MSCs can also be considered as a promising candidate for UCB-HSCTs.

Liver Sinusoidal Endothelial Cells Promote the Expansion of Human Cord Blood Hematopoietic Stem and Progenitor Cells

Cord blood (CB) is an attractive source of hematopoietic stem cells (HSCs) for hematopoietic cell transplantation. However, its application remains limited due to the low number of HSCs/progenitors in a single CB unit and its notoriously difficulty in expanding ex vivo. Here, we demonstrated that the human fetal liver sinusoidal endothelial cells engineered to constitutively express the adenoviral E4orf1 gene (hFLSECs-E4orf1) is capable of efficient expansion ex vivo for human CB hematopoietic stem and progenitor cells (HSPCs). Coculture of CD34⁺ hCB cells with hFLSECs-E4orf1 resulted in generation of substantially more total nucleated cells, CD34⁺CD38⁻ and CD34⁺ CD38⁻CD90⁺ HSPCs in comparison with that of cytokines alone after 14 days. The multilineage differentiation potential of the expanded hematopoietic cells in coculture condition, as assessed by in vitro colony formation, was also significantly heightened. The CD34⁺ hCB cells amplified on hFLSECs-E4orf1 were capable of engraftment in vivo. Furthermore, hFLSECs-E4orf1 highly expressed hematopoiesis related growth factor and Notch receptors. Accordingly, the CD34⁺ hCB cells amplified on hFLSECs-E4orf1 exhibited Notch signaling activation. Taken together, our findings indicated that FLSECs may potentially be the crucial component of the microenvironment to support recapitulation of embryonic HSC amplification in vitro and allow identification of new growth factors responsible for collective regulation of hematopoiesis.

Tracing Hematopoietic Progenitor Cell Neutrophilic Differentiation via Raman Spectroscopy

A major challenge to experimental studies and therapeutic uses of hematopoietic stem cells (HSC) is the limited options for analytical tools that can reliably resolve functional differences in heterogeneous HSC subpopulations at the single cell level. Currently available methods require the use of external labels and/or separate clonogenic and transplantation assays to identify bona fide stem cells, necessitating the harvest of bulk cell populations and long incubation times that obscure how individual HSCs dynamically respond to exogenous and endogenous stimuli. In this study, we employ Raman spectroscopy to noninvasively resolve the dynamics of individual differentiating hematopoietic progenitor cells during the course of neutrophilic differentiation. We collected Raman peaks of individual cells daily over the course of 14-day neutrophilic differentiation. Principal component analysis (PCA) of the Raman peaks revealed spectral differences between individual cells during differentiation that were strongly correlated with changes in the nucleus shape and surface antigen expression, the primary traditional means of monitoring neutrophilic differentiation. Additionally, our results were consistently reproducible in independent rounds of neutrophilic differentiation, as demonstrated by our partial least-squares discriminant analysis (PLS-DA) of the Raman spectral information that predicted the degree of neutrophilic differentiation with high sensitivity and specificity. Our findings highlight the utility and reliability of Raman spectroscopy as a robust molecular imaging tool to monitor the kinetics of HSC differentiation patterns.

The significance and application of vascular niche in the development and maintenance of hematopoietic stem cells

Deriving hematopoietic stem cells (HSCs) from human pluripotent stem cells is one of major goals in stem cell and hematological research. To induce HSCs from human pluripotent stem cells, many attempts to mimic embryonic development through stepwise exposure to morphogens. HSCs arise from dorsal aorta of embryos then migrate and settle in the bone marrow. Development and maintenance of HSCs are controlled by the microenvironmental cues around the blood vessels (called vascular niche) through morphogens and cytokines. Vascular niche serves as a common mechanism from embryo development to life-long maintenance of HSCs. In this chapter, I discuss that how vascular niche regulates development and maintenance of HSCs and exemplify the role of vascular niche to exquisitely induce HSCs from human pluripotent stem cells.

Effects of oral implants with miR‑122‑modified cell sheets on rat bone marrow mesenchymal stem cells

The aim of the present study was to regulate the transformation of bone marrow mesenchymal stem cells (BMMSCs) to osteoblasts to promote bone formation and osseointegration surrounding oral implants. BMMSCs were cultured using the whole bone marrow adherence method. Cell surface markers were detected by flow cytometry, and multi‑lineage differentiation potential was detected by osteogenic and adipogenic tests. miR‑122‑modified cell sheets were prepared by non‑viral transfection and complexed with micro‑arc titanium oxide implants to construct a gene‑modified tissue‑engineered implant, with its surface morphology observed by scanning electron microscopy (SEM). In vitro osteogenic activity of the implant was determined by alkaline phosphatase (ALP), Sirius Red, alizarin red staining, polymerase chain reaction and western blot analysis. The BMMSCs were spindle‑ or triangular‑shaped. Surface markers, cluster of differentiation 29 (CD29), CD90 and CD105 were positively expressed, whereas blood cell markers CD34, CD45 and CD31 were negatively expressed. Osteogenic staining exhibited deposition of calcified nodules, while adipogenic staining demonstrated the formation of lipid droplets. miR‑122 modification significantly enhanced the in vitro osteogenic activity of the sheets. On day 3 of osteogenic induction, runt-related transcription factor 2, osterix, osteocalcin, collagen I, ALP and bone morphogenetic protein 2 expression levels of the experimental group were 2.0, 3.1, 4.6, 3.2, 10.5 and 4.5 times those of the blank control group, respectively. SEM imaging of the modified sheet demonstrated close adhesion and fitting between abundant cellular and extracellular matrices, and the porous surface of the implant. In vitro osteogenesis of the complex was promoted and accelerated. Thus, miR‑122 effectively promoted osteogenic differentiation of the BMMSC sheet. Therefore, it is feasible to construct gene‑modified tissue‑engineered implants by complexing miR‑122‑modified sheets with micro‑arc titanium oxide implants.

ECM-based macroporous sponges release essential factors to support the growth of hematopoietic cells

The success of hematopoietic stem cells (HSCs) transplantation is limited due to the low number of HSCs received from donors. In vivo, HSCs reside within a specialized niche inside the 3D porous spongy bone. The natural environment in the niche is composed of structural proteins, glycosaminoglycans (GAGs) and soluble factors that control cells fate. However, the designed scaffolds for in vitro culture do not fairly recapitulate this microenvironment and cannot efficiently control HSCs fate. Here we report on the development of new omental ECM-based 3D macroporous sponges for hematopoietic cell culture. The scaffolds' structure, porosity and stability were characterized and optimized. Analysis of the biochemical content revealed that they were composed of collagens and GAGs, including sulfated GAGs. This morphology and composition enabled growth factors interaction with the sulfated GAGs, as indicated by the high loading capacity and release profile of three different hematopoietic niche factors. Finally, the ability of the ECM-based scaffolds to efficiently support the growth of hematopoietic cells by releasing stem cell factor (SCF) was demonstrated.

New insights into the regulation by RUNX1 and GFI1(s) proteins of the endothelial to hematopoietic transition generating primordial hematopoietic cells

The first hematopoietic cells are generated very early in ontogeny to support the growth of the embryo and to provide the foundation to the adult hematopoietic system. There is a considerable therapeutic interest in understanding how these first blood cells are generated in order to try to reproduce this process in vitro. This would allow generating blood products, or hematopoietic cell populations from embryonic stem (ES) cells, induced pluripotent stem cells or through directed reprogramming. Recent studies have clearly established that the first hematopoietic cells originate from a hemogenic endothelium (HE) through an endothelial to hematopoietic transition (EHT). The molecular mechanisms underlining this transition remain largely unknown with the exception that the transcription factor RUNX1 is critical for this process. In this Extra Views report, we discuss our recent studies demonstrating that the transcriptional repressors GFI1 and GFI1B have a critical role in the EHT. We established that these RUNX1 transcriptional targets are actively implicated in the downregulation of the endothelial program and the loss of endothelial identity during the formation of the first blood cells. In addition, our results suggest that GFI1 expression provides an ideal novel marker to identify, isolate and study the HE cell population.

From discovery to approval of an advanced therapy medicinal product-containing stem cells, in the EU

In 1997, the human corneal epithelium was reconstructed in vitro and transplanted on patients. Later, it became a routine treatment, before regulations considered advanced therapy medicinal products and drugs on the same lines. Manufacturing, before and after good manufacturing practice setting, was established in different facilities and the clinical application in several hospitals. Advanced therapy medicinal products, including stem cells, are unique products with different challenges than other drugs: some uncertainties, in addition to benefit, cannot be avoided. This review will focus on all recent developments in the stem cell-based corneal therapy.

Challenges and Opportunities to Harnessing the (Hematopoietic) Stem Cell Niche

In our body, stem cells reside in a microenvironment termed the niche. While the exact composition and therefore the level of complexity of a stem cell niche can vary significantly tissue-to-tissue, the stem cell niche microenvironment is dynamic, typically containing spatial and temporal variations in both cellular, extracellular matrix, and biomolecular components. This complex flow of secreted or bound biomolecules, cytokines, extracellular matrix components, and cellular constituents all contribute to the regulation of stem cell fate specification events, making engineering approaches at the nano- and micro-scale of particular interest for creating an artificial niche environment in vitro. Recent advances in fabrication approaches have enabled biomedical researchers to capture and recreate the complexity of stem cell niche microenvironments in vitro. Such engineered platforms show promise as a means to enhance our understanding of the mechanisms underlying niche-mediated stem cell regulation as well as offer opportunities to precisely control stem cell expansion and differentiation events for clinical applications. While these principles generally apply to all adult stem cells and niches, in this review, we focus on recent developments in engineering synthetic niche microenvironments for one of the best-characterized stem cell populations, hematopoietic stem cells (HSC). Specifically, we highlight recent advances in platforms designed to facilitate the extrinsic control of HSC fate decisions.

Bone-marrow mimicking biomaterial niches for studying hematopoietic stem and progenitor cells

This review discusses the considerations and approaches that have been employed for designing biomaterial based cultures for replicating the hematopoietic stem and progenitor cell niche.