Isolation of mesenchymal stem cells (MSCs) from green fluorescent protein positive (GFP+) transgenic rodents: the grass is not always green(er)

Structural and Temporal Dynamics of Mesenchymal Stem Cells in Liver Diseases From 2001 to 2021: A Bibliometric Analysis

Background

Mesenchymal stem cells (MSCs) have important research value and broad application prospects in liver diseases. This study aims to comprehensively review the cooperation and influence of countries, institutions, authors, and journals in the field of MSCs in liver diseases from the perspective of bibliometrics, evaluate the clustering evolution of knowledge structure, and discover hot trends and emerging topics.

Methods

The articles and reviews related to MSCs in liver diseases were retrieved from the Web of Science Core Collection using Topic Search. A bibliometric study was performed using CiteSpace and VOSviewer.

Results

A total of 3404 articles and reviews were included over the period 2001-2021. The number of articles regarding MSCs in liver diseases showed an increasing trend. These publications mainly come from 3251 institutions in 113 countries led by China and the USA. Li L published the most papers among the publications, while Pittenger MF had the most co-citations. Analysis of the most productive journals shows that most are specialized in medical research, experimental medicine and cell biology, and cell & tissue engineering. The macroscopical sketch and micro-representation of the whole knowledge field are realized through co-citation analysis. Liver scaffold, MSC therapy, extracellular vesicle, and others are current and developing areas of the study. The keywords "machine perfusion", "liver transplantation", and "microRNAs" also may be the focus of new trends and future research.

Conclusions

In this study, bibliometrics and visual methods were used to review the research of MSCs in liver diseases comprehensively. This paper will help scholars better understand the dynamic evolution of the application of MSCs in liver diseases and point out the direction for future research.

Molecular and cellular mechanisms of liver fibrosis and its regression

Chronic liver injury leads to liver inflammation and fibrosis, through which activated myofibroblasts in the liver secrete extracellular matrix proteins that generate the fibrous scar. The primary source of these myofibroblasts are the resident hepatic stellate cells. Clinical and experimental liver fibrosis regresses when the causative agent is removed, which is associated with the elimination of these activated myofibroblasts and resorption of the fibrous scar. Understanding the mechanisms of liver fibrosis regression could identify new therapeutic targets to treat liver fibrosis. This Review summarizes studies of the molecular mechanisms underlying the reversibility of liver fibrosis, including apoptosis and the inactivation of hepatic stellate cells, the crosstalk between the liver and the systems that orchestrate the recruitment of bone marrow-derived macrophages (and other inflammatory cells) driving fibrosis resolution, and the interactions between various cell types that lead to the intracellular signalling that induces fibrosis or its regression. We also discuss strategies to target hepatic myofibroblasts (for example, via apoptosis or inactivation) and the myeloid cells that degrade the matrix (for example, via their recruitment to fibrotic liver) to facilitate fibrosis resolution and liver regeneration.

A standard procedure for lentiviral-mediated labeling of murine mesenchymal stromal cells in vitro

Tracking of stem cells after transplantation is effectively performed in vivo with imaging systems, assuming the cells are adequately labeled to facilitate their recognition. This study aimed to optimize a protocol for fluorescent labeling of mesenchymal stromal cells (MSCs) in vitro, by using a third-generation lentiviral system. Basically, 293T cells are seeded in high-glucose Dulbecco's modified Eagle medium with 10% FBS one day before transfection. Transfection is done for 24 h using a mix of transfer, packaging, regulatory, and envelope plasmids, in molar ratio of 4:2:1:1, respectively. After transfection, the cells are further cultured for two days. During this period, the viral medium is harvested two times, at 24-h intervals, with the first round being stored at 4°C until the second round is completed. The pooled viral medium is frozen in single-use aliquots. MSCs are transduced with 25 multiplicity of infection (MOI) and one day later the cells are passaged at standard seeding density and further grown for three days, when the fluorescence reach the maximum level. Our protocol provides particular experimental details for permanent MSC labeling that makes the procedure highly effective for therapeutic purposes, without affecting the functional properties of stem cells.

Ultrasound-targeted microbubble destruction enhances delayed BMC delivery and attenuates post-infarction cardiac remodelling by inducing engraftment signals

Delayed administration of bone marrow cells (BMCs) at 2-4 weeks after successful reperfusion in patients with acute myocardial infarction (MI) does not improve cardiac function. The reduction in engraftment signals observed following this time interval might impair the effects of delayed BMC treatment. In the present study, we aimed to determine whether ultrasound-targeted microbubble destruction (UTMD) treatment could increase engraftment signals, enhance the delivery of delayed BMCs and subsequently attenuate post-infarction cardiac remodelling. A myocardial ischaemia/reperfusion (I/R) model was induced in Wistar rats via left coronary ligation for 45 min followed by reperfusion. Western blotting revealed that engraftment signals peaked at 7 days post-I/R and were dramatically lower at 14 days post-I/R. The lower engraftment signals at 14 days post-I/R could be triggered by UTMD treatment at a mechanical index of 1.0-1.9. The troponin I levels in the 1.9 mechanical index group were higher than in the other groups. Simultaneous haematoxylin and eosin staining and fluorescence revealed that the number of engrafted BMCs in the ischaemic zone was greater in the group treated with both UTMD and delayed BMC transplantation than in the control groups (P<0.05). Both UTMD and delayed BMC transplantation improved cardiac function and decreased cardiac fibrosis at 4 weeks after treatment, as compared with control groups (both P<0.05). Histopathology demonstrated that UTMD combined with delayed BMC transplantation increased capillary density, myocardial cell proliferation and c-kit⁺ cell proliferation. These findings indicated that UTMD treatment could induce engraftment signals and enhance homing of delayed BMCs to ischaemic myocardium, attenuating post-infarction cardiac remodelling by promoting neovascularization, cardiomyogenesis and expansion of cardiac c-kit⁺ cells.

Pre- and postmortem imaging of transplanted cells

Therapeutic interventions based on the transplantation of stem and progenitor cells have garnered increasing interest. This interest is fueled by successful preclinical studies for indications in many diseases, including the cardiovascular, central nervous, and musculoskeletal system. Further progress in this field is contingent upon access to techniques that facilitate an unambiguous identification and characterization of grafted cells. Such methods are invaluable for optimization of cell delivery, improvement of cell survival, and assessment of the functional integration of grafted cells. Following is a focused overview of the currently available cell detection and tracking methodologies that covers the entire spectrum from pre- to postmortem cell identification.

Effects of mesenchymal stem cell therapy, in association with pharmacologically active microcarriers releasing VEGF, in an ischaemic stroke model in the rat

Few effective therapeutic interventions are available to limit brain damage and functional deficits after ischaemic stroke. Within this context, mesenchymal stem cell (MSC) therapy carries minimal risks while remaining efficacious through the secretion of trophic, protective, neurogenic and angiogenic factors. The limited survival rate of MSCs restricts their beneficial effects. The usefulness of a three-dimensional support, such as a pharmacologically active microcarrier (PAM), on the survival of MSCs during hypoxia has been shown in vitro, especially when the PAMs were loaded with vascular endothelial growth factor (VEGF). In the present study, the effect of MSCs attached to laminin-PAMs (LM-PAMs), releasing VEGF or not, was evaluated in vivo in a model of transient stroke. The parameters assessed were infarct volume, functional recovery and endogenous cellular reactions. LM-PAMs induced the expression of neuronal markers by MSCs both in vitro and in vivo. Moreover, the prolonged release of VEGF increased angiogenesis around the site of implantation of the LM-PAMs and facilitated the migration of immature neurons towards the ischaemic tissue. Nonetheless, MSCs/LM-PAMs-VEGF failed to improve sensorimotor functions. The use of LM-PAMs to convey MSCs and to deliver growth factors could be an effective strategy to repair the brain damage caused by a stroke.

Contribution of bone marrow-derived fibrocytes to liver fibrosis

Since the discovery of fibrocytes in 1994 by Dr. Bucala and colleagues, these bone marrow (BM)-derived collagen Type I producing CD45(+) cells remain the most fascinating cells of the hematopoietic system. Despite recent reports on the emerging contribution of fibrocytes to fibrosis of parenchymal and non-parenchymal organs and tissues, fibrocytes remain the most understudied pro-fibrogenic cellular population. In the past years fibrocytes were implicated in the pathogenesis of liver, skin, lung, and kidney fibrosis by giving rise to collagen type I producing cells/myofibroblasts. Hence, the role of fibrocytes in fibrosis is not well defined since different studies often contain controversial results on the number of fibrocytes recruited to the site of injury versus the number of fibrocyte-derived myofibroblasts in the same fibrotic organ. Furthermore, many studies were based on the in vitro characterization of fibrocytes formed after outgrowth of BM and/or peripheral blood cultures. Therefore, the fibrocyte function(s) still remain(s) lack of understanding, mostly due to (I) the lack of mouse models that can provide complimentary in vivo real-time and cell fate mapping studies of the dynamic differentiation of fibrocytes and their progeny into collagen type I producing cells (and/or possibly, other cell types of the hematopoietic system); (II) the complexity of hematopoietic cell differentiation pathways in response to various stimuli; (III) the high plasticity of hematopoietic cells. Here we summarize the current understanding of the role of CD45(+) collagen type I(+) BM-derived cells in the pathogenesis of liver injury. Based on data obtained from various organs undergoing fibrogenesis or other type of chronic injury, here we also discuss the most recent evidence supporting the critical role of fibrocytes in the mediation of pro-fibrogenic and/or pro-inflammatory responses.

Isolation and characterization of a novel strain of mesenchymal stem cells from mouse umbilical cord: potential application in cell-based therapy

Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) have recently been recognized as a potential source for cell-based therapy in various preclinical animal models, such as Parkinson's disease, cerebral ischemia, spinal cord injury, and liver failure; however, the precise cellular and molecular mechanisms underlying the beneficial outcomes remain under investigation. There is a growing concern regarding rejection and alteration of genetic code using this xenotransplantation approach. In this study, a novel strain of murine MSCs derived from the umbilical cord of wild-type and green fluorescent protein (GFP) transgenic mice have been successfully isolated, expanded, and characterized. After 10 passages, the mUC-MSCs developed a rather homogeneous, triangular, spindle-shaped morphology, and were sub-cultured up to 7 months (over 50 passages) without overt changes in morphology and doubling time. Cell surface markers are quite similar to MSCs isolated from other tissue origins as well as hUC-MSCs. These mUC-MSCs can differentiate into osteoblasts, adipocytes, neurons, and astrocytes in vitro, as well as hematopoietic lineage cells in vivo. mUC-MSCs also possess therapeutic potential against two disease models, focal ischemic stroke induced by middle cerebral artery occlusion (MCAo) and acute hepatic failure. Subtle differences in the expression of cytokine-related genes exist between mUC-MSCs and hUC-MSCs, which may retard and jeopardize the advance of cell therapy. Allografts of these newly established mUC-MSCs into various mouse disease models may deepen our insights into the development of more effective cell therapy regimens.

Hepatic stem cell niches

Stem cell niches are special microenvironments that maintain stem cells and control their behavior to ensure tissue homeostasis and regeneration throughout life. The liver has a high regenerative capacity that involves stem/progenitor cells when the proliferation of hepatocytes is impaired. In recent years progress has been made in the identification of potential hepatic stem cell niches. There is evidence that hepatic progenitor cells can originate from niches in the canals of Hering; in addition, the space of Disse may also serve as a stem cell niche during fetal hematopoiesis and constitute a niche for stellate cells in adults.

Intraarticular Administration of Dexamethasone after Mesenchymal Stem Cells Implantation Does Not Improve Significantly the Treatment of Preestablished Full-Thickness Chondral Defect in a Rabbit Model

OBJECTIVE

The aim of this study was to evaluate the contribution to hyaline cartilage regeneration of dexamethasone intraarticular administration after autologous mesenchymal stem cells (MSCs) implantation into a preestablished knee full-thickness chondral defect.

DESIGN

Full-thickness chondral defects of 4.5 × 4.5 mm(2) were surgically made in both medial femoral condyles of adult male New Zealand rabbits. Two weeks later, autologous ex vivo expanded bone marrow-derived MSCs were embedded in hyaluronic acid and implanted into the chondral defects. Immediately and every week after the intervention, dexamethasone 0.25 mg/kg was intraarticularly administered (MSC/dexa-treated group). Six weeks after MSC transplantation, the animals were euthanized and condyles were characterized molecularly according to aggrecan, collagen type II, and collagen type I gene expression (quantitative reverse transcriptase-polymerase chain reaction) and histologically (hematoxylin-eosin staining). Data of MSC/dexa-treated condyles were compared with untreated, dexa-treated, MSC-treated, or normal unlesioned condyles.

RESULTS

The ratio between collagen type II expression versus collagen type I expression in MSC/dexa-treated condyles was higher than one, even though the group mean value was not statistically different from that of untreated defects. Histological changes were observed between MSC/dexa-treated and untreated defects mainly in surface regularity and in hyaline matrix abundance. However, International Cartilage Repair Society score analysis did not support robust differences between those groups.

CONCLUSION

Intraarticular administration of dexamethasone after autologous MSC implantation into a preestablished full-thickness chondral defect does not contribute significantly to the regeneration of a tissue with molecular and histological characteristics identical to hyaline cartilage.

Mesenchymal stem cells combined with an artificial dermal substitute improve repair in full-thickness skin wounds

Autografts represent the gold standard for the treatment of full thickness burns. Factors such as lack of suitable donor sites and poor skin quality, however, have led to the development of artificial dermal substitutes. The investigation of mechanisms leading to enhanced functionality of these skin substitutes has been attracting great attention. This study aimed to investigate the effect of autologous stem cells on the integration and vascularization of a dermal substitute in full-thickness skin wounds, in a murine model. Two cell populations were compared, whole bone marrow cells and cultivated mesenchymal stem cells, isolated from mice transgenic for the enhanced green fluorescent protein, which allowed tracking of the transplanted cells. The number of cells colonizing the dermal substitute, as well as vascular density, were higher in mice receiving total bone marrow and particularly mesenchymal stem cells, than in control animals. The effect was more pronounced in animals treated with mesenchymal stem cells, which located primarily in the wound bed, suggesting a paracrine therapeutic mechanism. These results indicate that combining mesenchymal stem cells with artificial dermal substitutes may represent an important potential modality for treating full thickness burns, even in allogeneic combinations due to the immunoregulatory property of these cells.

Production of somatic chimera chicks by injection of bone marrow cells into recipient blastoderms

Several types of cells, including blastoderm cells, primordial germ cells, and embryonic germ cells were injected into early-stage recipient embryos to produce chimera avians and to gain insights into cell development. However, a limited number of studies of avian adult stem cells have also been conducted. This study is, to the best of our knowledge, the first to evaluate chicken bone marrow cells' (chBMC) ability to differentiate into multiple cell lineages and capability to generate chimera chicks. We induced random differentiation of chBMCs in vitro and injected immunologically selected pluripotent cells in chBMCs into the blastoderms of recipient eggs. The multipotency of BMCs from the barred Plymouth rock (BPR) was confirmed via AP staining, RT-PCR, immunocytochemistry, and FACS using specific markers, such as Oct-4 and SSEA-1, 3 and 4. Isolated chBMCs were found to be able to induce in vitro differentiation to multiple cell lineages. Approximately 5,000 chBMCs were injected into the blastoderms of white leghorn (WL) recipients and proved able to contribute to the generation of somatic chimera chicks with a frequency of 2.7% (2 of 73). Confirmation of chimerism in hatched chicks was achieved via PCR analysis using D-loop-specific primers of BPR and WL. Our study demonstrated the successful production of chimera chicks using chBMC. Therefore, we propose that the use of adult chBMCs may constitute a new possible approach to the production of chimera poultry, and may provide helpful studies in avian developmental biology.

Pelvic organ distribution of mesenchymal stem cells injected intravenously after simulated childbirth injury in female rats

The local route of stem cell administration utilized presently in clinical trials for stress incontinence may not take full advantage of the capabilities of these cells. The goal of this study was to evaluate if intravenously injected mesenchymal stem cells (MSCs) home to pelvic organs after simulated childbirth injury in a rat model. Female rats underwent either vaginal distension (VD) or sham VD. All rats received 2 million GFP-labeled MSCs intravenously 1 hour after injury. Four or 10 days later pelvic organs and muscles were imaged for visualization of GFP-positive cells. Significantly more MSCs home to the urethra, vagina, rectum, and levator ani muscle 4 days after VD than after sham VD. MSCs were present 10 days after injection but GFP intensity had decreased. This study provides basic science evidence that intravenous administration of MSCs could provide an effective route for cell-based therapy to facilitate repair after injury and treat stress incontinence.

Bone marrow cell-mediated production of transgenic chickens

The transplantation of adult stem cells into recipients is a method used widely in mammals to determine the fate of transferred cells, and for the production of progenies. This study is the first report, to our knowledge, to demonstrate the successful production of chickens using cells transdifferentiated from adult chicken bone marrow cells (BMCs) transplanted into the testes. BMCs from the enhanced green fluorescent protein (eGFP) transgenic (Tg) chickens were induced via in vitro transdifferentiation to male germ cells and injected into the testes of normal recipients. The multipotency of BMC was found with RT-PCR, immunocytochemistry, and FACS using specific markers, such as OCT4 and SSEA-1, -3, and -4. Localization and in vivo transdifferentiation of injected cells in the seminiferous tubules of recipients were traced for up to 40 days' post-injection by GFP expression and immunocytochemical analyses. The integration of the eGFP and the neo(R) genes in sperm gDNAs of recipient was confirmed via PCR analysis. A subsequent testcross of the recipient roosters with non-Tg hens resulted in the production of eGFP Tg progenies, demonstrating the successful transdifferentiation of the adult BMC to the germ cells in the testis. Therefore, we suggest that the use of adult BMCs is a new and promising approach to the production of Tg poultry, and may prove helpful in the study of avian developmental biology.

Isolation and culture of rodent bone marrow-derived multipotent mesenchymal stromal cells

Initial attempts to cultivate mesenchymal stem cells (MSCs) were more successful from human than murine tissues. Methods for the in vitro expansion of murine MSCs were described more recently, but are now well established. Despite limitations such as a poor equivalence to be expected between cultured stem cells and their in vivo counterparts, MSC culture allows the expansion of a cell population capable of providing important information on the biology of stem cells and their therapeutic application. Murine MSCs may be obtained from the bone marrow and virtually from any other organ or tissue. This chapter describes the most widely used method, which involves the preparation of single-cell suspension followed by incubation for 1-3 days and removal of nonadherent cells. The adherent fraction is then expanded by continuous culture and may be maintained for prolonged periods of time.

Progenitor cell therapies for traumatic brain injury: barriers and opportunities in translation

Traumatic brain injury (TBI) directly affects nearly 1.5 million new patients per year in the USA, adding to the almost 6 million cases in patients who are permanently affected by the irreversible physical, cognitive and psychosocial deficits from a prior injury. Adult stem cell therapy has shown preliminary promise as an option for treatment, much of which is limited currently to supportive care. Preclinical research focused on cell therapy has grown significantly over the last decade. One of the challenges in the translation of this burgeoning field is interpretation of the promising experimental results obtained from a variety of cell types, injury models and techniques. Although these variables can become barriers to a collective understanding and to evidence-based translation, they provide crucial information that, when correctly placed, offers the opportunity for discovery. Here, we review the preclinical evidence that is currently guiding the translation of adult stem cell therapy for TBI.