Transcriptionally and Functionally Distinct Mesenchymal Subpopulations Are Generated from Human Pluripotent Stem Cells

Mesenchymal stem/stromal cells from human pluripotent stem cell-derived brain organoid enhance the ex vivo expansion and maintenance of hematopoietic stem/progenitor cells

BACKGROUND

Mesenchymal stem/stromal cells (MSCs) are of great therapeutic value due to their role in maintaining the function of hematopoietic stem/progenitor cells (HSPCs). MSCs derived from human pluripotent stem cells represent an ideal alternative because of their unlimited supply. However, the role of MSCs with neural crest origin derived from HPSCs on the maintenance of HSPCs has not been reported.

METHODS

Flow cytometric analysis, RNA sequencing and differentiation ability were applied to detect the characteristics of stromal cells from 3D human brain organoids. Human umbilical cord blood CD34+ (UCB-CD34+) cells were cultured in different coculture conditions composed of stromal cells and umbilical cord MSCs (UC-MSCs) with or without a cytokine cocktail. The hematopoietic stroma capacity of stromal cells was tested in vitro with the LTC-IC assay and in vivo by cotransplantation of cord blood nucleated cells and stroma cells into immunodeficient mice. RNA and proteomic sequencing were used to detect the role of MSCs on HSPCs.

RESULTS

The stromal cells, derived from both H1-hESCs and human induced pluripotent stem cells forebrain organoids, were capable of differentiating into the classical mesenchymal-derived cells (osteoblasts, chondrocytes, and adipocytes). These cells expressed MSC markers, thus named pluripotent stem cell-derived MSCs (pMSCs). The pMSCs showed neural crest origin with CD271 expression in the early stage. When human UCB-CD34+ HSPCs were cocultured on UC-MSCs or pMSCs, the latter resulted in robust expansion of UCB-CD34+ HSPCs in long-term culture and efficient maintenance of their transplantability. Comparison by RNA sequencing indicated that coculture of human UCB-CD34+ HSPCs with pMSCs provided an improved microenvironment for HSC maintenance. The pMSCs highly expressed the Wnt signaling inhibitors SFRP1 and SFRP2, indicating that they may help to modulate the cell cycle to promote the maintenance of UCB-CD34+ HSPCs by antagonizing Wnt activation.

CONCLUSIONS

A novel method for harvesting MSCs with neural crest origin from 3D human brain organoids under serum-free culture conditions was reported. We demonstrate that the pMSCs support human UCB-HSPC expansion in vitro in a long-term culture and the maintenance of their transplantable ability. RNA and proteomic sequencing indicated that pMSCs provided an improved microenvironment for HSC maintenance via mechanisms involving cell-cell contact and secreted factors and suppression of Wnt signaling. This represents a novel method for large-scale production of MSCs of neural crest origin and provides a potential approach for development of human hematopoietic stromal cell therapy for treatment of dyshematopoiesis.

Single-cell characterization of monolayer cultured human dental pulp stem cells with enhanced differentiation capacity

Human dental pulp stem cells (hDPSCs) are easily obtained multipotent cells, however, their potential value in regenerative medicine is hindered by the phenotypic and functional changes after conventional monolayer expansion. Here, we employed single-cell RNA sequencing (scRNA-seq) to comprehensively study the transcriptional difference between the freshly isolated and monolayer cultured DPSCs. The cell cluster analysis based on our scRNA-seq data showed that monolayer culture resulted in a significant cellular composition switch compared to the freshly isolated DPSCs. However, one subpopulation, characterized as MCAM(+)JAG(+)PDGFRA(-), maintained the most transcriptional characteristics compared to their freshly isolated counterparts. Notably, immunofluorescent staining revealed that the MCAM(+)JAG(+)PDGFRA(-) hDPSCs uniquely located in the perivascular region of human dental pulp tissue. Flow-cytometry analysis confirmed that their proportion remained relatively stable (~2%) regardless of physiological senescence or dental caries. Consistent with the annotation of scRNA-seq data, MCAM(+)JAG(+)PDGFRA(-) hDPSCs showed higher proliferation capacity and enhanced in vitro multilineage differentiation potentials (osteogenic, chondrogenic and adipogenic) compared with their counterparts PDGFRA(+) subpopulation. Furthermore, the MCAM(+)JAG(+)PDGFRA(-) hDPSCs showed enhanced bone tissue formation and adipose tissue formation after 4-week subcutaneous implantation in nude mice. Taken together, our study for the first time revealed the cellular composition switch of monolayer cultured hDPSCs compared to the freshly isolated hDPSCs. After in vitro expansion, the MCAM(+)JAG(+)PDGFRA(-) subpopulation resembled the most transcriptional characteristics of fresh hDPSCs which may be beneficial for further tissue regeneration applications.

Pluripotent-derived Mesenchymal Stem/stromal Cells: an Overview of the Derivation Protocol Efficacies and the Differences Among the Derived Cells

Mesenchymal stem/stromal cells (MSCs) are remarkable tools for regenerative medicine. Therapeutic approaches using these cells can promote increased activity and viability in several cell types through diverse mechanisms such as paracrine and immunomodulatory activities, contributing substantially to tissue regeneration and functional recovery. However, biological samples of human MSCs, usually obtained from adult tissues, often exhibit variable behavior during in vitro culture, especially with respect to cell population heterogeneity, replicative senescence, and consequent loss of functionality. Accordingly, it is necessary to establish standard protocols to generate high-quality, stable cell cultures, for example, by using pluripotent stem cells (PSCs) in derivation protocols of MSC-like cells since PSCs maintain their characteristics consistently during culture. However, the available protocols seem to generate distinct populations of PSC-derivedMSCs (PSC-MSCs) with peculiar attributes, which do not always resemble bona fide primary MSCs. The present review addresses the developmental basis behind some of these derivation protocols, exposing the differences among them and discussing the functional properties of PSC-MSCs, shedding light on elements that may help determine standard characterizations and criteria to evaluate and define these cells.

CD73+ Mesenchymal Stem Cells Ameliorate Myocardial Infarction by Promoting Angiogenesis

With multipotent differentiation potential and paracrine capacity, mesenchymal stem cells (MSCs) have been widely applied in clinical practice for the treatment of ischemic heart disease. MSCs are a heterogeneous population and the specific population of MSCs may exhibit a selective ability for tissue repair. The aim of our research was to adapt the CD73⁺ subgroup of adipose derived MSCs (AD-MSCs) for the therapy of myocardial infarction (MI). In this research, AD-MSCs were isolated from adipose tissue surrounding the groin of mice and CD73⁺ AD-MSCs were sorted using flow cytometry. To investigate the therapeutic effects of CD73⁺ AD-MSCs, 1.2 × 10⁶ CD73⁺ AD-MSCs were transplanted into rat model of MI, and CD73^– AD-MSCs, normal AD-MSCs transplantation served as control. Our results revealed that CD73⁺ AD-MSCs played a more effective role in the acceleration function of cardiac recovery by promoting angiogenesis in a rat model of MI compared with mixed AD-MSCs and CD73^– AD-MSCs. Moreover, with the expression of CD73 in AD-MSCs, the secretion of VEGF, SDF-1α, and HGF factors could be promoted. It also shows differences between CD73⁺ and CD73^– AD-MSCs when the transcription profiles of these two subgroups were compared, especially in VEGF pathway. These findings raise an attractive outlook on CD73⁺ AD-MSCs as a dominant subgroup for treating MI-induced myocardial injury. CD73, a surface marker, can be used as a MSCs cell quality control for the recovery of MI by accelerating angiogenesis.

Therapeutic Efficacy of Human Embryonic Stem Cell-Derived Multipotent Stem/Stromal Cells in Diabetic Detrusor Underactivity: A Preclinical Study

Mesenchymal stem/stromal cell (MSC) therapy is a promising approach for treatment of as yet incurable detrusor underactivity (DUA), which is characterized by decreased detrusor contraction strength and/or duration, leading to prolonged bladder emptying. In the present study, we demonstrated the therapeutic potential of human embryonic stem cell (ESC)-derived multipotent MSCs (M-MSCs) in a diabetic rat model of DUA. Diabetes mellitus (DM) was induced by intraperitoneal injection of streptozotocin (STZ) (50 mg/kg) into 8-week-old female Sprague-Dawley rats. Three weeks later, various doses of M-MSCs (0.25, 0.5, and 1 × 10⁶ cells) or an equivalent volume of PBS were injected into the outer layer of the bladder. Awake cystometry, organ bath, histological, and gene expression analyses were evaluated 1 week (short-term) or 2 and 4 weeks (long-term) after M-MSC transplantation. STZ-induced diabetic rats developed DUA, including phenotypes with significantly longer micturition intervals, increased residual urine amounts and bladder capacity, decreased micturition pressure on awake cystometry, and contractile responses to various stimuli in organ bath studies. Muscle degeneration, mast cell infiltration, fibrosis, and apoptosis were present in the bladders of DM animals. A single local transplantation of M-MSCs ameliorated DUA bladder pathology, including functional changes and histological evaluation, and caused few adverse outcomes. Immunostaining and gene expression analysis revealed that the transplanted M-MSCs supported myogenic restoration primarily by engrafting into bladder tissue via pericytes, and subsequently exerting paracrine effects to prevent apoptotic cell death in bladder tissue. The therapeutic efficacy of M-MSCs was superior to that of human umbilical cord-derived MSCs at the early time point (1 week). However, the difference in efficacy between M-MSCs and human umbilical cord-derived MSCs was statistically insignificant at the later time points (2 and 4 weeks). Collectively, the present study provides the first evidence for improved therapeutic efficacy of a human ESC derivative in a preclinical model of DM-associated DUA.

Practical choice for robust and efficient differentiation of human pluripotent stem cells

Human pluripotent stem cells (hPSCs) have the distinct advantage of being able to differentiate into cells of all three germ layers. Target cells or tissues derived from hPSCs have many uses such as drug screening, disease modeling, and transplantation therapy. There are currently a wide variety of differentiation methods available. However, most of the existing differentiation methods are unreliable, with uneven differentiation efficiency and poor reproducibility. At the same time, it is difficult to choose the optimal method when faced with so many differentiation schemes, and it is time-consuming and costly to explore a new differentiation approach. Thus, it is critical to design a robust and efficient method of differentiation. In this review article, we summarize a comprehensive approach in which hPSCs are differentiated into target cells or organoids including brain, liver, blood, melanocytes, and mesenchymal cells. This was accomplished by employing an embryoid body-based three-dimensional (3D) suspension culture system with multiple cells co-cultured. The method has high stable differentiation efficiency compared to the conventional 2D culture and can meet the requirements of clinical application. Additionally, ex vivo co-culture models might be able to constitute organoids that are highly similar or mimic human organs for potential organ transplantation in the future.

Engineering Brain-Specific Pericytes from Human Pluripotent Stem Cells

Pericytes (PCs) are a type of perivascular cells that surround endothelial cells of small blood vessels. In the brain, PCs show heterogeneity depending on their position within the vasculature. As a result, PC interactions with surrounding endothelial cells, astrocytes, and neuron cells play a key role in a wide array of neurovascular functions such as regulating blood-brain barrier (BBB) permeability, cerebral blood flow, and helping to facilitate the clearance of toxic cellular molecules. Therefore, a reliable method of engineering brain-specific PCs from human induced pluripotent stem cells (hiPSCs) is critical in neurodegenerative disease modeling. This review summarizes brain-specific PC differentiation of hiPSCs through mesoderm and neural crest induction. Key signaling pathways (platelet-derived growth factor-B [PDGF-B], transforming growth factor [TGF]-β, and Notch signaling) regulating PC function, PC interactions with adjacent cells, and PC differentiation from hiPSCs are also discussed. Specifically, PDGF-BB-platelet-derived growth factor receptor β signaling promotes PC cell survival, TGF-β signal transduction facilitates PC attachment to endothelial cells, and Notch signaling is critical in vascular development and arterial-venous specification. Furthermore, current challenges facing the use of hiPSC-derived PCs are discussed, and their ongoing uses in neurodegenerative disease modeling are identified. Further investigations into PCs and surrounding cell interactions are needed to characterize the roles of brain PCs in various neurodegenerative disorders. Impact statement This article summarizes the work related to brain-specific pericytes (PCs) derived from human pluripotent stem cells (hPSCs). In particular, key signaling pathways regulating PC function, PC interactions with adjacent cells, and PC differentiation from hPSCs were discussed. Furthermore, current challenges facing the use of hPSC-derived PCs were identified, and their ongoing uses in neurodegenerative disease modeling were discussed. The review highlights the important role of cell-cell interactions in blood-brain barrier (BBB) models and neurodegeneration. The summarized findings are significant for establishing pluripotent stem cell-based BBB models toward the applications in drug screening and disease modeling.

Unleashing the cure: Overcoming persistent obstacles in the translation and expanded use of hematopoietic stem cell-based therapies

Hematopoietic stem cell transplantation (HSCT) is broadly used for treating and curing hematological cancers and various disorders of the blood and immune system. However, its true therapeutic potential remains vastly constrained by significant scientific and technical hurdles that preclude expansion to new indications and limit the number of patients who could benefit from, gain access to, or financially afford the procedure. To define and overcome these challenges, the California Institute for Regenerative Medicine (CIRM) held multiple workshops related to HSCT and has subsequently invested in a new generation of approaches to address the most compelling needs of the field, including new sources of healthy and immunologically compatible hematopoietic stem cells for transplant; safe and efficient genome modification technologies for correction of inherited genetic defects and other forms of gene therapy; safer and more tractable transplantation procedures such as nongenotoxic conditioning regimens, methods to accelerate immune reconstitution and recovery of immune function, and innovations to minimize the risk of immune rejection; and other life‐threatening complications from transplant. This Perspective serves to highlight these needs through examples from the recent CIRM‐funded and other notable investigations, presents rationale for comprehensive, systematic, and focused strategies to unleash the full potential of HSCT, thereby enabling cures for a greatly expanded number of disorders and making HSCT feasible, accessible, and affordable to all who could benefit.

Non-fibro-adipogenic pericytes from human embryonic stem cells attenuate degeneration of the chronically injured mouse muscle

Massive tears of the rotator cuff (RC) are associated with chronic muscle degeneration due to fibrosis, fatty infiltration, and muscle atrophy. The microenvironment of diseased muscle often impairs efficient engraftment and regenerative activity of transplanted myogenic precursors. Accumulating myofibroblasts and fat cells disrupt the muscle stem cell niche and myogenic cell signaling and deposit excess disorganized connective tissue. Therefore, restoration of the damaged stromal niche with non-fibro-adipogenic cells is a prerequisite to successful repair of an injured RC. We generated from human embryonic stem cells (hES) a potentially novel subset of PDGFR-β+CD146+CD34-CD56- pericytes that lack expression of the fibro-adipogenic cell marker PDGFR-α. Accordingly, the PDGFR-β+PDGFR-α- phenotype typified non-fibro-adipogenic, non-myogenic, pericyte-like derivatives that maintained non-fibro-adipogenic properties when transplanted into chronically injured murine RCs. Although administered hES pericytes inhibited developing fibrosis at early and late stages of progressive muscle degeneration, transplanted PDGFR-β+PDGFR-α+ human muscle-derived fibro-adipogenic progenitors contributed to adipogenesis and greater fibrosis. Additionally, transplanted hES pericytes substantially attenuated muscle atrophy at all tested injection time points after injury. Coinciding with this observation, conditioned medium from cultured hES pericytes rescued atrophic myotubes in vitro. These findings imply that non-fibro-adipogenic hES pericytes recapitulate the myogenic stromal niche and may be used to improve cell-based treatments for chronic muscle disorders.

Pericytes for Therapeutic Bone Repair

Besides seminal functions in angiogenesis and blood pressure regulation, microvascular pericytes possess a latent tissue regenerative potential that can be revealed in culture following transition into mesenchymal stem cells. Endowed with robust osteogenic potential, pericytes and other related perivascular cells extracted from adipose tissue represent a potent and abundant cell source for refined bone tissue engineering and improved cell therapies of fractures and other bone defects. The use of diverse bone formation assays in vivo, which include mouse muscle pocket osteogenesis and calvaria replenishment, rat and dog spine fusion, and rat non-union fracture healing, has confirmed the superiority of purified perivascular cells for skeletal (re)generation. As a surprising observation though, despite strong endogenous bone-forming potential, perivascular cells drive bone regeneration essentially indirectly, via recruitment by secreted factors of local osteo-progenitors.

Metabolomics Analysis of Mesenchymal Stem Cells

Various mesenchymal stem cells as easily accessible and multipotent cells can share different essential signaling pathways related to their stemness ability. Understanding the mechanism of stemness ability can be useful for controlling the stem cells for regenerative medicine targets. In this context, OMICs studies can analyze the mechanism of different stem cell properties or stemness ability via a broad range of current high-throughput techniques. This field is fundamentally directed toward the analysis of whole genome (genomics), mRNAs (transcriptomics), proteins (proteomics) and metabolites (metabolomics) in biological samples. According to several studies, metabolomics is more effective than other OMICs ّfor various system biology concerns. Metabolomics can elucidate the biological mechanisms of various mesenchymal stem cell function by measuring their metabolites such as their secretome components. Analyzing the metabolic alteration of mesenchymal stem cells can be useful to promote their regenerative medicine application.

Quantifying Ca2+ signaling and contraction in vascular pericytes and smooth muscle cells

Vascular pericytes and smooth muscle cells surround many blood vessels of the body. Their primary roles include vessel stabilization and regulation of the blood flow. The high degree of heterogeneity among these cells is dictated by (1) differences in their developmental origin and (2) their location in the vascular bed. Phenotype switching contributes to this heterogeneity especially following in vitro culture. In the absence of distinguishing molecular markers, functional assays that capture their heterogeneity in vitro are needed. Spatiotemporal changes in intracellular Ca²⁺ levels and contraction in response to vasoconstrictors reflect the differences between vascular pericyte and smooth muscle cell. In order to capture this heterogeneity in vitro, large ensembles of cells need to be analyzed. Here we developed an automated image processing method to measure intracellular Ca²⁺ and contraction in large cell groups which in combination with a computational approach for integrative analysis allowed vascular pericytes and smooth muscle cells to be distinguished without knowledge of their anatomical origin.

Advanced in vitro models of vascular biology: Human induced pluripotent stem cells and organ-on-chip technology

The vascular system is one of the first to develop during embryogenesis and is essential for all organs and tissues in our body to develop and function. It has many essential roles including controlling the absorption, distribution and excretion of compounds and therefore determines the pharmacokinetics of drugs and therapeutics. Vascular homeostasis is under tight physiological control which is essential for maintaining tissues in a healthy state. Consequently, disruption of vascular homeostasis plays an integral role in many disease processes, making cells of the vessel wall attractive targets for therapeutic intervention. Experimental models of blood vessels can therefore contribute significantly to drug development and aid in predicting the biological effects of new drug entities. The increasing availability of human induced pluripotent stem cells (hiPSC) derived from healthy individuals and patients have accelerated advances in developing experimental in vitro models of the vasculature: human endothelial cells (ECs), pericytes and vascular smooth muscle cells (VSMCs), can now be generated with high efficiency from hiPSC and used in 'microfluidic chips' (also known as 'organ-on-chip' technology) as a basis for in vitro models of blood vessels. These near physiological scaffolds allow the controlled integration of fluid flow and three-dimensional (3D) co-cultures with perivascular cells to mimic tissue- or organ-level physiology and dysfunction in vitro. Here, we review recent multidisciplinary developments in these advanced experimental models of blood vessels that combine hiPSC with microfluidic organ-on-chip technology. We provide examples of their utility in various research areas and discuss steps necessary for further integration in biomedical applications so that they can be contribute effectively to the evaluation and development of new drugs and other therapeutics as well as personalized (patient-specific) treatments.

Pericytes in Muscular Dystrophies

The muscular dystrophies are an heterogeneous group of inherited myopathies characterised by the progressive wasting of skeletal muscle tissue. Pericytes have been shown to make muscle in vitro and to contribute to skeletal muscle regeneration in several animal models, although recent data has shown this to be controversial. In fact, some pericyte subpopulations have been shown to contribute to fibrosis and adipose deposition in muscle. In this chapter, we explore the identity and the multifaceted role of pericytes in dystrophic muscle, potential therapeutic applications and the current need to overcome the hurdles of characterisation (both to identify pericyte subpopulations and track cell fate), to prevent deleterious differentiation towards myogenic-inhibiting subpopulations, and to improve cell proliferation and engraftment efficacy.

The mesenchymoangioblast, mesodermal precursor for mesenchymal and endothelial cells

Mesenchymoangioblast (MB) is the earliest precursor for endothelial and mesenchymal cells originating from APLNR+PDGFRα+KDR+ mesoderm in human pluripotent stem cell cultures. MBs are identified based on their capacity to form FGF2-dependent compact spheroid colonies in a serum-free semisolid medium. MBs colonies are composed of PDGFRβ+CD271+EMCN+DLK1+CD73- primitive mesenchymal cells which are generated through endothelial/angioblastic intermediates (cores) formed during first 3-4 days of clonogenic cultures. MB-derived primitive mesenchymal cells have potential to differentiate into mesenchymal stromal/stem cells (MSCs), pericytes, and smooth muscle cells. In this review, we summarize the specification and developmental potential of MBs, emphasize features that distinguish MBs from other mesenchymal progenitors described in the literature and discuss the value of these findings for identifying molecular pathways leading to MSC and vasculogenic cell specification, and developing cellular therapies using MB-derived progeny.

Mesenchymal Stromal/Stem Cells in Regenerative Medicine and Tissue Engineering

As a result of over five decades of investigation, mesenchymal stromal/stem cells (MSCs) have emerged as a versatile and frequently utilized cell source in the fields of regenerative medicine and tissue engineering. In this review, we summarize the history of MSC research from the initial discovery of their multipotency to the more recent recognition of their perivascular identity in vivo and their extraordinary capacity for immunomodulation and angiogenic signaling. As well, we discuss long-standing questions regarding their developmental origins and their capacity for differentiation toward a range of cell lineages. We also highlight important considerations and potential risks involved with their isolation, ex vivo expansion, and clinical use. Overall, this review aims to serve as an overview of the breadth of research that has demonstrated the utility of MSCs in a wide range of clinical contexts and continues to unravel the mechanisms by which these cells exert their therapeutic effects.

Pericytes in Tissue Engineering

Pericytes have crucial roles in blood-brain barrier function, blood vessel function/stability, angiogenesis, endothelial cell proliferation/differentiation, wound healing, and hematopoietic stem cells maintenance. They can be isolated from fetal and adult tissues and have multipotential differentiation capacity as mesenchymal stem cells (MSCs). All of these properties make pericytes as preferred cells in the field of tissue engineering. Current developments have shown that tissue-engineered three-dimensional (3D) systems including multiple cell layers (or types) and a supporting biological matrix represent the in vivo environment better than those monolayers on plastic dishes. Tissue-engineered models are also more ethical and cheaper systems than animal models. This chapter describes the role of pericytes in tissue engineering for regenerative medicine.