Human Mesenchymal stem cells program macrophage plasticity by altering their metabolic status via a PGE2-dependent mechanism

Current understanding of the immunosuppressive properties of mesenchymal stromal cells

Several studies have demonstrated the anti-inflammatory potential of mesenchymal stromal cells (MSCs) isolated from bone marrow, adipose tissue, placenta, and other sources. Nevertheless, MSCs may also induce immunosuppression when administered systemically or directly to injured environments, as shown in different preclinical disease models. MSCs express certain receptors, including toll-like receptors and the aryl-hydrocarbon receptor, that are activated by the surrounding environment, thus leading to modulation of their immunosuppressive activity. Once MSCs are activated, they can affect a wide range of immune cells (e.g., neutrophils, monocytes/macrophages, dendritic cells, natural killer cells, T and B lymphocytes), a phenomenon that has been correlated to secretion of several mediators (e.g., indolamine 2,3-dioxygenase, galectins, prostaglandin E₂, nitric oxide, and damage- and pathogen-associated molecular patterns) and stimulation of certain signaling pathways (e.g., protein kinase R, signal transducer and activator of transcription-1, nuclear factor-κB). Additionally, MSC manipulation and culture conditions, as well as the number of passages, duration of cryopreservation, and O₂ content available, can significantly affect the immunosuppressive properties of MSCs. This review sheds light on current knowledge regarding the mechanisms by which MSCs exert immunosuppressive effects both in vitro and in vivo, focusing on the receptors expressed by MSCs, the correlation between soluble factors secreted by MSCs and their immunosuppressive effects, and interactions between MSCs and immune cells.

Promising effects of exosomes isolated from menstrual blood-derived mesenchymal stem cell on wound-healing process in diabetic mouse model

Wound healing is a complicated process that contains a number of overlapping and consecutive phases, disruption in each of which can cause chronic nonhealing wounds. In the current study, we investigated the effects of exosomes as paracrine factors released from menstrual blood-derived mesenchymal stem cells (MenSCs) on wound-healing process in diabetic mice. The exosomes were isolated from MenSCs conditioned media using ultracentrifugation and were characterized by scanning electron microscope and western blotting assay. A full thickness excisional wound was created on the dorsal skin of each streptozotocin-induced diabetic mouse. The mice were divided into three groups as follows: phosphate buffered saline, exosomes, and MenSC groups. We found that MenSC-derived exosomes can resolve inflammation via induced M1-M2 macrophage polarization. It was observed that exosomes enhance neoangiogenesis through vascular endothelial growth factor A upregulation. Re-epithelialization accelerated in the exosome-treated mice, most likely through NF-κB p65 subunit upregulation and activation of the NF-κB signaling pathway. The results demonstrated that exosomes possibly cause less scar formation through decreased Col1:Col3 ratio. These notable results showed that the MenSC-derived exosomes effectively ameliorated cutaneous nonhealing wounds. We suggest that exosomes can be employed in regenerative medicine for skin repair in difficult-to-heal conditions such as diabetic foot ulcer.

Extracellular Vesicle-Educated Macrophages Promote Early Achilles Tendon Healing

Tendon healing follows a complex series of coordinated events, which ultimately produces a mechanically inferior tissue more scar‐like than native tendon. More regenerative healing occurs when anti‐inflammatory M2 macrophages play a more dominant role. Mesenchymal stromal/stem cells (MSCs) are able to polarize macrophages to an M2 immunophenotype via paracrine mechanisms. We previously reported that coculture of CD14+ macrophages (MQs) with MSCs resulted in a unique M2‐like macrophage. More recently, we generated M2‐like macrophages using only extracellular vesicles (EVs) isolated from MSCs creating “EV‐educated macrophages” (also called exosome‐educated macrophages [EEMs]), thereby foregoing direct use of MSCs. For the current study, we hypothesized that cell therapy with EEMs would improve in vivo tendon healing by modulating tissue inflammation and endogenous macrophage immunophenotypes. We evaluated effects of EEMs using a mouse Achilles tendon rupture model and compared results to normal tendon healing (without any biologic intervention), MSCs, MQs, or EVs. We found that exogenous administration of EEMs directly into the wound promoted a healing response that was significantly more functional and more regenerative. Injured tendons treated with exogenous EEMs exhibited (a) improved mechanical properties, (b) reduced inflammation, and (c) earlier angiogenesis. Treatment with MSC‐derived EVs alone were less effective functionally but stimulated a biological response as evidenced by an increased number of endothelial cells and decreased M1/M2 ratio. Because of their regenerative and immunomodulatory effects, EEM treament could provide a novel strategy to promote wound healing in this and various other musculoskeletal injuries or pathologies where inflammation and inadequate healing is problematic. Stem Cells2019;37:652–662

Immunoregulatory potential of mesenchymal stem cells following activation by macrophage-derived soluble factors

BACKGROUND

Immunoregulatory capacity of mesenchymal stem cells (MSC) is triggered by the inflammatory environment, which changes during tissue repair. Macrophages are essential in mediating the inflammatory response after injury and can adopt a range of functional phenotypes, exhibiting pro-inflammatory and anti-inflammatory activities. An accurate characterization of MSC activation by the inflammatory milieu is needed for improving the efficacy of regenerative therapies. In this work, we investigated the immunomodulatory functions of MSC primed with factors secreted from macrophages polarized toward a pro-inflammatory or an anti-inflammatory phenotype. We focused on the role of TNF-α and IL-10, prototypic pro-inflammatory and anti-inflammatory cytokines, respectively, as priming factors for MSC.

METHODS

Secretion of immunoregulatory mediators from human MSC primed with media conditioned by human macrophages polarized toward a pro-inflammatory or an anti-inflammatory phenotype was determined. Immunomodulatory potential of primed MSC on polarized macrophages was studied using indirect co-cultures. Involvement of TNF-α and IL-10 in priming MSC and of PGE2 in MSC-mediated immunomodulation was investigated employing neutralizing antibodies. Collagen hydrogels were used to study MSC and macrophages interactions in a more physiological environment.

RESULTS

Priming MSC with media conditioned by pro-inflammatory or anti-inflammatory macrophages enhanced their immunomodulatory potential through increased PGE2 secretion. We identified the pro-inflammatory cytokine TNF-α as a priming factor for MSC. Notably, the anti-inflammatory IL-10, mainly produced by pro-resolving macrophages, potentiated the priming effect of TNF-α. Collagen hydrogels acted as instructive microenvironments for MSC and macrophages functions and their crosstalk. Culturing macrophages on hydrogels stimulated anti-inflammatory versus pro-inflammatory cytokine secretion. Encapsulation of MSC within hydrogels increased PGE2 secretion and potentiated immunomodulation on macrophages, attenuating macrophage pro-inflammatory state and sustaining anti-inflammatory activation. Priming with inflammatory factors conferred to MSC loaded in hydrogels greater immunomodulatory potential, promoting anti-inflammatory activity of macrophages.

CONCLUSIONS

Factors secreted by pro-inflammatory and anti-inflammatory macrophages activated the immunomodulatory potential of MSC. This was partially attributed to the priming effect of TNF-α and IL-10. Immunoregulatory functions of primed MSC were enhanced after encapsulation in hydrogels. These findings may provide insight into novel strategies to enhance MSC immunoregulatory potency.

Periodontal ligament-derived mesenchymal stem cells modulate neutrophil responses via paracrine mechanisms

BACKGROUND

Mesenchymal stem cells differentiate into distinct mesenchymal cell lineages and regulate the immune response. The aim of this study was to determine whether periodontal ligament-derived mesenchymal stem cells (PDLSCs) have the ability to modulate neutrophil responses via paracrine mechanisms.

METHODS

CD105-enriched PDLSCs were seeded for 24 h and challenged with Porphyromonas gingivalis total protein extract (PgPE) (0 or 2 ug/mL) for 3 h. Cells were then washed and further cultured for 18 h and the supernatants were collected and stored. Next, neutrophil-differentiated human promyelocytic leukemia HL-60 cells (HL60D) were treated with PDLSCs supernatants and HL-60D activation and functional responses were determined.

RESULTS

PgPE treatment induced higher secretion of inflammatory markers and chemokines by PDLSCs, including RANTES, eotaxin, interferon (IFN)-γ- inducible protein 10 (IP-10), monocyte chemoattractant protein-1 (MCP-1), IFN-γ, interleukin (IL)-6, IL-8 and IL-1ra (P < 0.05). HL-60D recruitment rate was increased by 4.7 ± 1.09-fold when exposed to PgPE-treated PDLSCs supernatants. PgPE-treated PDLSCs supernatants promoted a 1.78 ± 1.04-fold increase in the production of intracellular reactive oxygen species (ROS) by PMA-stimulated HL-60D, whereas PgPE-untreated PDLSCs supernatants led to a 16% reduction in intracellular ROS. In sharp contrast, neither PgPE-untreated nor PgPE-treated PDLSCs supernatants altered tumor necrosis factor (TNF)-α and IL-1β secretion by HL-60D cells.

CONCLUSION

Together, these findings suggest an important role of PDLSCs in the recognition of P. gingivalis, paracrine recruitment and activation of antimicrobial mechanisms in innate immune cells, without interfering in cytokine responses.

Adipose-derived stem cell therapy inhibits the deterioration of cerebral infarction by altering macrophage kinetics

INTRODUCTION

We previously established a method to isolate and culture human adipose-derived stem cells (hADSCs) using fetal bovine serum and showed the therapeutic impact on cerebral infarction. Recently, we modified the culture method with the use of serum-free media for future clinical applications. This study aims to evaluate whether intravenous administration of hADSCs induced by the serum-free culture method would improve neurobehavioral deficits in mice with cerebral infarction.

RESULTS

Induced hADSCs possessed the characteristics of mesenchymal stem cells and withstood a freeze-thaw process. hADSC administration improved neurobehavioral deficits in MCAO-treated mice and suppressed brain atrophy at the chronic phase. Although hADSC administration did not affect serum cytokine profiles, it decreased the number of CD11b⁺ monocytes in the spleen. Concomitantly, hADSC administration increased the local accumulation of CD11b⁺CD163⁺ M2 macrophages into the border zone of the cerebral infarction at 4 days post-MCAO (the acute phase).

DISCUSSION

Our data indicate that the systemic administration of hADSCs can improve the neurobehavioral deficits that occur after cerebral infarction by modulating the acute immune response mediated by CD11b⁺CD163⁺ M2 macrophages in infarcted lesions.

Concise review: The challenges and opportunities of employing mesenchymal stromal cells in the treatment of acute pancreatitis

To date only small animal models have been employed to assess the effect of mesenchymal stromal cell (MSC) therapy on acute pancreatitis (AP), the most common cause of hospitalization for gastrointestinal diseases worldwide. We outline the challenges inherent in the small animal models of AP. We also point to specific benefits afforded by the adoption of larger animal models. The potential for MSC therapeutics in the treatment of AP was recognized over a decade ago. With sharper focus on the form of AP and development of new MSC delivery routes in larger animals, we believe the challenge can be engaged.

The mesenchymal stem cell secretome as an acellular regenerative therapy for liver disease

The use of mesenchymal stem cells (MSC) for tissue repair has garnered much interest and has been evaluated in several disease settings. Recent evidence indicates that the beneficial effects observed with MSC-based therapy can be mediated through the paracrine release of extracellular vesicles and other soluble proteins or biologically active molecules, which collectively constitute the MSC secretome. In this concise overview, we highlight results from preclinical and other studies that demonstrate the therapeutic efficacy of the MSC secretome for diseases that are characterized by liver injury or fibrosis. The potential for the use of the MSC secretome as an acellular regenerative therapy and approaches for the isolation of a secretome product for therapeutic applications are highlighted. The use of the MSC secretome as an acellular therapeutic agent could provide several advantages over the use of cell-based therapies for liver diseases.

Platelet Lysate Activates Human Subcutaneous Adipose Tissue Cells by Promoting Cell Proliferation and Their Paracrine Activity Toward Epidermal Keratinocytes

Skin chronic wounds are non-healing ulcerative defects, which arise in association with a morbidity state, such as diabetes and vascular insufficiency or as the consequence of systemic factors including advanced age. Platelet Rich Plasma, a platelet-rich blood fraction, can significantly improve the healing of human skin chronic ulcers. Given that the subcutaneous adipose tissue is located beneath the skin and plays a role in the skin homeostasis, in this study, we investigated the in vitro response of human subcutaneous adipose tissue cells to platelet content in a model mimicking in vitro the in situ milieu of a deep skin injury. Considering that, at the wound site, plasma turn to serum, platelets are activated and inflammation occurs, human adipose-derived stromal cells (hASC) were cultured with Human Serum (HS) supplemented or not with Platelet Lysate (PL) and/or IL-1α. We observed that HS sustained hASC proliferation more efficiently than FBS and induced a spontaneous adipogenic differentiation in the cells. PL added to HS enhanced hASC proliferation, regardless the presence of IL-1α. In the presence of PL, hASC progressively lessened the adipogenic phenotype, possibly because the proliferation of less committed cells was induced. However, these cells resumed adipogenesis in permissive conditions. Accordingly, PL induced in quiescent cells activation of the proliferation-related pathways ERK, Akt, and STAT-3 and expression of Cyclin D1. Moreover, PL induced an early and transient increase of the pro-inflammatory response triggered by IL-1α, by inducing COX-2 expression and secretion of a large amount of PGE₂, IL-6, and IL-8. Media conditioned by PL-stimulated hASC exerted a chemotactic activity on human keratinocytes and favored the healing of an in vitro scratch wound. In order to bridge the gap between in vitro results and possible in vivo events, the stimuli were also tested in ex vivo cultures of in toto human adipose tissue biopsies (hAT). PL induced cell proliferation in hAT and outgrowth of committed progenitor cells able to differentiate in permissive conditions. In conclusion, we report that the adipose tissue responds to the wound microenvironment by activating the proliferation of adipose tissue progenitor cells and promoting the release of factors favoring wound healing.

Bone physiology as inspiration for tissue regenerative therapies

The development, maintenance of healthy bone and regeneration of injured tissue in the human body comprise a set of intricate and finely coordinated processes. However, an analysis of current bone regeneration strategies shows that only a small fraction of well-reported bone biology aspects has been used as inspiration and transposed into the development of therapeutic products. Specific topics that include inter-scale bone structural organization, developmental aspects of bone morphogenesis, bone repair mechanisms, role of specific cells and heterotypic cell contact in the bone niche (including vascularization networks and immune system cells), cell-cell direct and soluble-mediated contact, extracellular matrix composition (with particular focus on the non-soluble fraction of proteins), as well as mechanical aspects of native bone will be the main reviewed topics. In this Review we suggest a systematic parallelization of (i) fundamental well-established biology of bone, (ii) updated and recent advances on the understanding of biological phenomena occurring in native and injured tissue, and (iii) critical discussion of how those individual aspects have been translated into tissue regeneration strategies using biomaterials and other tissue engineering approaches. We aim at presenting a perspective on unexplored aspects of bone physiology and how they could be translated into innovative regeneration-driven concepts.

Serum from Asthmatic Mice Potentiates the Therapeutic Effects of Mesenchymal Stromal Cells in Experimental Allergic Asthma

Asthma is a chronic inflammatory disease characterized by airway inflammation and remodeling, which can lead to progressive decline of lung function. Although mesenchymal stromal cells (MSCs) have shown beneficial immunomodulatory properties in preclinical models of allergic asthma, effects on airway remodeling have been limited. Mounting evidence suggests that prior exposure of MSCs to specific inflammatory stimuli or environments can enhance their immunomodulatory properties. Therefore, we investigated whether stimulating MSCs with bronchoalveolar lavage fluid (BALF) or serum from asthmatic mice could potentiate their therapeutic properties in experimental asthma. In a house dust mite (HDM) extract asthma model in mice, unstimulated, asthmatic BALF‐stimulated, or asthmatic serum‐stimulated MSCs were administered intratracheally 24 hours after the final HDM challenge. Lung mechanics and histology; BALF protein, cellularity, and biomarker levels; and lymph‐node and bone marrow cellularity were assessed. Compared with unstimulated or BALF‐stimulated MSCs, serum‐stimulated MSCs further reduced BALF levels of interleukin (IL)‐4, IL‐13, and eotaxin, total and differential cellularity in BALF, bone marrow and lymph nodes, and collagen fiber content, while increasing BALF IL‐10 levels and improving lung function. Serum stimulation led to higher MSC apoptosis, expression of various mediators (transforming growth factor‐β, interferon‐γ, IL‐10, tumor necrosis factor‐α‐stimulated gene 6 protein, indoleamine 2,3‐dioxygenase‐1, and IL‐1 receptor antagonist), and polarization of macrophages to M2 phenotype. In conclusion, asthmatic serum may be a novel strategy to potentiate therapeutic effects of MSCs in experimental asthma, leading to further reductions in both inflammation and remodeling than can be achieved with unstimulated MSCs. stem cells translational medicine2019;8:301&312

Hydroxychloroquine induced lung cancer suppression by enhancing chemo-sensitization and promoting the transition of M2-TAMs to M1-like macrophages

BACKGROUND

Lysosome-associated agents have been implicated as possible chemo-sensitizers and immune regulators for cancer chemotherapy. We investigated the potential roles and mechanisms of hydroxychloroquine (HCQ) in combination with chemotherapy in lung cancer treatment.

METHODS

The effects of combined treatment on non-small cell lung cancer (NSCLC) were investigated using cell viability assays and animal models. The influence of HCQ on lysosomal pH was evaluated by lysosomal sensors and confocal microscopy. The effects of HCQ on the tumour immune microenvironment were analysed by flow cytometry.

RESULTS

HCQ elevates the lysosomal pH of cancer cells to inactivate P-gp while increasing drug release from the lysosome into the nucleus. Furthermore, single HCQ therapy inhibits lung cancer by inducing macrophage-modulated anti-tumour CD8⁺ T cell immunity. Moreover, HCQ could promote the transition of M2 tumour-associated macrophages (TAMs) into M1-like macrophages, leading to CD8⁺ T cell infiltration into the tumour microenvironment.

CONCLUSIONS

HCQ exerts anti-NSCLC cells effects by reversing the drug sequestration in lysosomes and enhancing the CD8⁺ T cell immune response. These findings suggest that HCQ could act as a promising chemo-sensitizer and immune regulator for lung cancer chemotherapy in the clinic.

Mesenchymal Stem Cells in Primary Sjögren's Syndrome: Prospective and Challenges

Primary Sjögren's syndrome (pSS) is a chronic systemic inflammatory autoimmune disease characterized by lymphocytic infiltrates in exocrine glands. Current approaches do not control harmful autoimmune attacks or prevent irreversible damage and have considerable side effects. Mesenchymal stem cells (MSCs) have been effective in the treatment of several autoimmune diseases. The objective of this review is to illustrate the potential therapeutic role of MSCs in pSS. We summarize the recent advances in what is known about their immunomodulatory function and therapeutic applications in pSS. MSC transfusion can suppress autoimmunity and restore salivary gland secretory function in mouse models and patients with pSS by inducing regulatory T cells, suppressing Th1, Th17, and T follicular helper cell responses. In addition, MSCs can differentiate into salivary epithelial cells, presenting an option as a suitable alternative treatment. We also discuss current bioengineering methods which improve functions of MSCs for pSS. However, there remain many challenges to overcome before their wide clinical application.

Cell therapy in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is driven by a severe pro-inflammatory response resulting in lung damage, impaired gas exchange and severe respiratory failure. There is no specific treatment that effectively improves outcome in ARDS. However, in recent years, cell therapy has shown great promise in preclinical ARDS studies. A wide range of cells have been identified as potential candidates for use, among these are mesenchymal stromal cells (MSCs), which are adult multi-lineage cells that can modulate the immune response and enhance repair of damaged tissue. The therapeutic potential of MSC therapy for sepsis and ARDS has been demonstrated in multiple in vivo models. The therapeutic effect of these cells seems to be due to two different mechanisms; direct cellular interaction, and paracrine release of different soluble products such as extracellular vesicles (EVs)/exosomes. Different approaches have also been studied to enhance the therapeutic effect of these cells, such as the over-expression of anti-inflammatory or pro-reparative molecules. Several clinical trials (phase I and II) have already shown safety of MSCs in ARDS and other diseases. However, several translational issues still need to be addressed, such as the large-scale production of cells, and their potentiality and variability, before the therapeutic potential of stem cells therapies can be realized.

Splenic involvement in umbilical cord matrix-derived mesenchymal stromal cell-mediated effects following traumatic spinal cord injury

Background

The spleen plays an important role in erythrocyte turnover, adaptive immunity, antibody production, and the mobilization of monocytes/macrophages (Mφ) following tissue injury. In response to trauma, the spleen initiates production of inflammatory cytokines, which in turn recruit immune cells to the inflamed tissue, exacerbating damage. Our previous work has shown that intravenous mesenchymal stromal cell (MSC) infusion has potent immunomodulatory effects following spinal cord injury (SCI), associated with the transplanted cells homing to and persisting within the spleen. Therefore, this work aimed to characterize the relationship between the splenic inflammatory response and SCI pathophysiology, emphasizing splenic involvement in MSC-mediated effects.

Methods

Using a rodent model of cervical clip-compression SCI, secondary tissue damage and functional recovery were compared between splenectomised rodents and those with a sham procedure. Subsequently, 2.5 million MSCs from the term human umbilical cord matrix cells (HUCMCs) were infused via tail vein at 1-h post-SCI and the effects were assessed in the presence or absence of a spleen.

Results

Splenectomy alone had no effect on lesion volume, hemorrhage, or inflammation. There was also no significant difference between the groups in functional recovery and those in lesion morphometry. Yet, while the infusion of HUCMCs reduced spinal cord hemorrhage and increased systemic levels of IL-10 in the presence of a spleen, these effects were lost with splenectomy. Further, HUCMC infusion was shown to alter the expression levels of splenic cytokines, suggesting that the spleen is an important target and site of MSC effects.

Conclusions

Our results provide a link between MSC function and splenic inflammation, a finding that can help tailor the cells/transplantation approach to enhance therapeutic efficacy.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1243-0) contains supplementary material, which is available to authorized users.

Eicosapentaenoic Acid Enhances the Effects of Mesenchymal Stromal Cell Therapy in Experimental Allergic Asthma

Asthma is characterized by chronic lung inflammation and airway hyperresponsiveness. Despite recent advances in the understanding of its pathophysiology, asthma remains a major public health problem and, at present, there are no effective interventions capable of reversing airway remodeling. Mesenchymal stromal cell (MSC)-based therapy mitigates lung inflammation in experimental allergic asthma; however, its ability to reduce airway remodeling is limited. We aimed to investigate whether pre-treatment with eicosapentaenoic acid (EPA) potentiates the therapeutic properties of MSCs in experimental allergic asthma. Seventy-two C57BL/6 mice were used. House dust mite (HDM) extract was intranasally administered to induce severe allergic asthma in mice. Unstimulated or EPA-stimulated MSCs were administered intratracheally 24 h after final HDM challenge. Lung mechanics, histology, protein levels of biomarkers, and cellularity in bronchoalveolar lavage fluid (BALF), thymus, lymph nodes, and bone marrow were analyzed. Furthermore, the effects of EPA on lipid body formation and secretion of resolvin-D₁ (RvD₁), prostaglandin E₂ (PGE₂), interleukin (IL)-10, and transforming growth factor (TGF)-β1 by MSCs were evaluated in vitro. EPA-stimulated MSCs, compared to unstimulated MSCs, yielded greater therapeutic effects by further reducing bronchoconstriction, alveolar collapse, total cell counts (in BALF, bone marrow, and lymph nodes), and collagen fiber content in airways, while increasing IL-10 levels in BALF and M2 macrophage counts in lungs. In conclusion, EPA potentiated MSC-based therapy in experimental allergic asthma, leading to increased secretion of pro-resolution and anti-inflammatory mediators (RvD₁, PGE₂, IL-10, and TGF-β), modulation of macrophages toward an anti-inflammatory phenotype, and reduction in the remodeling process. Taken together, these modifications may explain the greater improvement in lung mechanics obtained. This may be a promising novel strategy to potentiate MSCs effects.

Analysis of skeletal muscle microcirculation in a porcine polytrauma model with haemorrhagic shock

Polytraumatised patients with haemorrhagic shock are prone to develop systemic complications, such as SIRS (systemic inflammatory response syndrome), ARDS (acute respiratory distress syndrome) and MOF (multiple organ failure). The pathomechanism of severe complications following trauma is multifactorial, and it is believed that microcirculatory dysfunction plays an important role. The aim of this study was to determine the changes in the microcirculation in musculature over time during shock and subsequent resuscitation in a porcine model of haemorrhagic shock and polytrauma. Twelve pigs (German Landrace) underwent femur fracture, liver laceration, blunt chest trauma, and haemorrhagic shock under standard anaesthesia and intensive care monitoring. Microcirculation data were measured from the vastus lateralis muscle using a combined white light spectrometry and laser spectroscopy system every 15 min during the shock and resuscitation period, and at 24, 48, and 72 h. Oxygen delivery and oxygen consumption were calculated and compared to baseline. The relative haemoglobin, local oxygen consumption, and saturation values in the microcirculation were observed significantly lower during shock, however, no changes in the microcirculatory blood flow and microcirculatory oxygen delivery were observed. After resuscitation, the microcirculatory blood flow and relative haemoglobin increased and remained elevated during the whole observation period (72 h). In this study, we observed changes in microcirculation during the trauma and shock phases. Furthermore, we also measured persistent dysfunction of the microcirculation over the observation period of 3 days after resuscitation and haemorrhagic shock. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1377-1382, 2018.

Mesenchymal stem cells enhance NOX2-dependent reactive oxygen species production and bacterial killing in macrophages during sepsis

Human mesenchymal stem/stromal cells (MSCs) have been reported to produce an M2-like, alternatively activated phenotype in macrophages. In addition, MSCs mediate effective bacterial clearance in pre-clinical sepsis models. Thus, MSCs have a paradoxical antimicrobial and anti-inflammatory response that is not understood.Here, we studied the phenotypic and functional response of monocyte-derived human macrophages to MSC exposure in vitroMSCs induced two distinct, coexistent phenotypes: M2-like macrophages (generally elongated morphology, CD163⁺, acute phagosomal acidification, low NOX2 expression and limited phagosomal superoxide production) and M1-like macrophages characterised by high levels of phagosomal superoxide production. Enhanced phagosomal reactive oxygen species production was also observed in alveolar macrophages from a rodent model of pneumonia-induced sepsis. The production of M1-like macrophages was dependent on prostaglandin E₂ and phosphatidylinositol 3-kinase. MSCs enhanced human macrophage phagocytosis of unopsonised bacteria and enhanced bacterial killing compared with untreated macrophages. Bacterial killing was significantly reduced by blockade of NOX2 using diphenyleneiodonium, suggesting that M1-like cells are primarily responsible for this effect. MSCs also enhanced phagocytosis and polarisation of M1-like macrophages derived from patients with severe sepsis.The enhanced antimicrobial capacity (M1-like) and inflammation resolving phenotype (M2-like) may account for the paradoxical effect of these cells in sepsis in vivo.

Mesenchymal Stromal Cells and Their Extracellular Vesicles Enhance the Anti-Inflammatory Phenotype of Regulatory Macrophages by Downregulating the Production of Interleukin (IL)-23 and IL-22

Resolution-phase macrophage population orchestrates active dampening of the inflammation by secreting anti-inflammatory and proresolving products including interleukin (IL)-10 and lipid mediators (LMs). We investigated the effects of both human bone marrow-derived mesenchymal stromal cells (MSCs) and MSC-derived extracellular vesicles (MSC-EVs) on mature human regulatory macrophages (Mregs). The cytokines and LMs were determined from cell culture media of Mregs cultivated with MSCs and MSC-EVs. In addition, the alterations in the expression of cell surface markers and the phagocytic ability of Mregs were investigated. Our novel findings indicate that both MSC coculture and MSC-EVs downregulated the production of IL-23 and IL-22 enhancing the anti-inflammatory phenotype of Mregs and amplifying proresolving properties. The levels of prostaglandin E2 (PGE2) were substantially upregulated in MSC coculture media, which may endorse proresolving LM class switching. In addition, our results manifest, for the first time, that MSC-EVs mediate the Mreg phenotype change via PGE2. These data suggest that both human MSC and MSC-EVs may potentiate tolerance-promoting proresolving phenotype of human Mregs.

TSG-6 released from intraperitoneally injected canine adipose tissue-derived mesenchymal stem cells ameliorate inflammatory bowel disease by inducing M2 macrophage switch in mice

BACKGROUND

Inflammatory bowel disease (IBD) is an intractable autoimmune disorder that markedly deteriorates one's quality of life. Mesenchymal stem cells (MSCs) alleviate inflammation by modulating inflammatory cytokines in inflamed tissues, and have been suggested as a promising alternative for IBD treatment in human and veterinary cases. Furthermore, tumor necrosis factor-α-induced gene/protein 6 (TSG-6) is a key factor influencing MSC immunomodulatory properties; however, the precise mechanism of TSG-6 release from canine MSCs in IBD remains unclear. This study aimed to assess the therapeutic effects of canine adipose tissue-derived (cAT)-MSC-produced TSG-6 in an IBD mouse model and to explore the mechanisms underlying the immunomodulatory properties.

METHODS

Mice with dextran sulfate sodium-induced colitis were administered cAT-MSCs intraperitoneally; colon tissues were collected on day 10 for histopathological, quantitative real-time polymerase chain reaction, and immunofluorescence analyses.

RESULTS

cAT-MSC-secreted TSG-6 ameliorated IBD and regulated colonic expression of pro- and anti-inflammatory cytokines such as tumor necrosis factor-α, interleukin-6, and interleukin-10. To investigate the effect of cAT-MSC-secreted TSG-6 on activated macrophages in vitro, a transwell coculture system was used; TSG-6 released by cAT-MSCs induced a macrophage phenotypic switch from M1 to M2. The cAT-MSC-secreted TSG-6 increased M2 macrophages in the inflamed colon in vivo.

CONCLUSIONS

TSG-6 released from cAT-MSCs can alleviate dextran sulfate sodium-induced colitis by inducing a macrophage phenotypic switch to M2 in mice.

Can a Conversation Between Mesenchymal Stromal Cells and Macrophages Solve the Crisis in the Inflamed Intestine?

Inflammatory bowel disease (IBD) is a group of chronic inflammatory conditions of the gastrointestinal tract characterized by an exacerbated mucosal immune response. Macrophages play pivotal roles in the maintenance of gut homeostasis but they are also implicated in the pathogenesis of IBD. They are highly plastic cells and their activation state depends on the local environment. In the healthy intestine, resident macrophages display an M2 phenotype characterized by inflammatory energy, while inflammatory M1 macrophages dominate in the inflamed intestinal mucosa. In this regard, modifying the balance of macrophage populations into an M2 phenotype has emerged as a new therapeutic approach in IBD. Multipotent mesenchymal stromal cells (MSCs) have been proposed as a promising cell-therapy for the treatment of IBD, considering their immunomodulatory and tissue regenerative potential. Numerous preclinical studies have shown that MSCs can induce immunomodulatory macrophages and have demonstrated that their therapeutic efficacy in experimental colitis is mediated by macrophages with an M2-like phenotype. However, some issues have not been clarified yet, including the importance of MSC homing to the inflamed colon and/or lymphoid organs, their optimal route of administration or whether they are effective as living or dead cells. In contrast, the mechanisms behind the effect of MSCs in human IBD are not known and more data are needed regarding the effect of MSCs on macrophage polarization that would support the observation reported in the experimental models. Nevertheless, MSCs have emerged as a novel method to treat IBD that has already been proven safe and with clinical benefits that could be administered in combination with the currently used pharmacological treatments.

Macrophage-Derived Extracellular Succinate Licenses Neural Stem Cells to Suppress Chronic Neuroinflammation

Neural stem cell (NSC) transplantation can influence immune responses and suppress inflammation in the CNS. Metabolites, such as succinate, modulate the phenotype and function of immune cells, but whether and how NSCs are also activated by such immunometabolites to control immunoreactivity and inflammatory responses is unclear. Here, we show that transplanted somatic and directly induced NSCs ameliorate chronic CNS inflammation by reducing succinate levels in the cerebrospinal fluid, thereby decreasing mononuclear phagocyte (MP) infiltration and secondary CNS damage. Inflammatory MPs release succinate, which activates succinate receptor 1 (SUCNR1)/GPR91 on NSCs, leading them to secrete prostaglandin E2 and scavenge extracellular succinate with consequential anti-inflammatory effects. Thus, our work reveals an unexpected role for the succinate-SUCNR1 axis in somatic and directly induced NSCs, which controls the response of stem cells to inflammatory metabolic signals released by type 1 MPs in the chronically inflamed brain.

Immunomodulatory plasticity of mesenchymal stem cells: a potential key to successful solid organ transplantation

Organ transplantation remains to be a treatment of choice for patients suffering from irreversible organ failure. Immunosuppressive (IS) drugs employed to maintain the allograft have shown excellent short-term graft survival, but, their long-term use could contribute to immunological and non-immunological risk factors, resulting in graft dysfunctionalities. Upcoming IS regimes have highlighted the use of cell-based therapies, which can eliminate the risk of drug-borne toxicities while maintaining efficacy of the treatment. Mesenchymal stem cells (MSCs) have been considered as an invaluable cell type, owing to their unique immunomodulatory properties, which makes them desirable for application in transplant settings, where hyper-activation of the immune system is evident. The immunoregulatory potential of MSCs holds true for preclinical studies while achieving it in clinical studies continues to be a challenge. Understanding the biological factors responsible for subdued responses of MSCs in vivo would allow uninhibited use of this therapy for countless conditions. In this review, we summarize the variations in the preclinical and clinical studies utilizing MSCs, discuss the factors which might be responsible for variability in outcome and propose the advancements likely to occur in future for using this as a "boutique/personalised therapy" for patient care.

Stem Cells for Cartilage Repair: Preclinical Studies and Insights in Translational Animal Models and Outcome Measures

Due to the restricted intrinsic capacity of resident chondrocytes to regenerate the lost cartilage postinjury, stem cell-based therapies have been proposed as a novel therapeutic approach for cartilage repair. Moreover, stem cell-based therapies using mesenchymal stem cells (MSCs) or induced pluripotent stem cells (iPSCs) have been used successfully in preclinical and clinical settings. Despite these promising reports, the exact mechanisms underlying stem cell-mediated cartilage repair remain uncertain. Stem cells can contribute to cartilage repair via chondrogenic differentiation, via immunomodulation, or by the production of paracrine factors and extracellular vesicles. But before novel cell-based therapies for cartilage repair can be introduced into the clinic, rigorous testing in preclinical animal models is required. Preclinical models used in regenerative cartilage studies include murine, lapine, caprine, ovine, porcine, canine, and equine models, each associated with its specific advantages and limitations. This review presents a summary of recent in vitro data and from in vivo preclinical studies justifying the use of MSCs and iPSCs in cartilage tissue engineering. Moreover, the advantages and disadvantages of utilizing small and large animals will be discussed, while also describing suitable outcome measures for evaluating cartilage repair.

Preconditioning of murine mesenchymal stem cells synergistically enhanced immunomodulation and osteogenesis

Background

Mesenchymal stem cells (MSCs) are capable of immunomodulation and tissue regeneration, highlighting their potential translational application for treating inflammatory bone disorders. MSC-mediated immunomodulation is regulated by proinflammatory cytokines and pathogen-associated molecular patterns such as lipopolysaccharide (LPS). Previous studies showed that MSCs exposed to interferon gamma (IFN-γ) and the proinflammatory cytokine tumor necrosis factor alpha (TNF-α) synergistically suppressed T-cell activation.

Methods

In the current study, we developed a novel preconditioning strategy for MSCs using LPS plus TNF-α to optimize the immunomodulating ability of MSCs on macrophage polarization.

Results

Preconditioned MSCs enhanced anti-inflammatory M2 macrophage marker expression (Arginase 1 and CD206) and decreased inflammatory M1 macrophage marker (TNF-α/IL-1Ra) expression using an in-vitro coculture model. Immunomodulation of MSCs on macrophages was significantly increased compared to the combination of IFN-γ plus TNF-α or single treatment controls. Increased osteogenic differentiation including alkaline phosphate activity and matrix mineralization was only observed in the LPS plus TNF-α preconditioned MSCs. Mechanistic studies showed that increased prostaglandin E2 (PGE2) production was associated with enhanced Arginase 1 expression. Selective cyclooxygenase-2 inhibition by Celecoxib decreased PGE2 production and Arginase 1 expression in cocultured macrophages.

Conclusions

The novel preconditioned MSCs have increased immunomodulation and bone regeneration potential and could be applied to the treatment of inflammatory bone disorders including periprosthetic osteolysis, fracture healing/nonunions, and osteonecrosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0730-z) contains supplementary material, which is available to authorized users.

Strategies to retain properties of bone marrow-derived mesenchymal stem cells ex vivo

Mesenchymal stem cells (MSCs) have been extensively used for cell therapies and tissue engineering. The current MSC strategy requires a large quantity of cells for such applications, which can be achieved through cell expansion in culture. In the body, stem cell fate is largely determined by their microenvironment, known as the niche. The complex and dynamic stem cell niche provides physical, mechanical, and chemical cues to collaboratively regulate cell activities. It remains a great challenge to maintain the properties of MSCs in culture. Constructing a microenvironment as an engineered stem cell niche in culture to maintain MSC phenotypes, properties, and functions is a viable strategy to address the issue. Here, we review the current understanding of MSC behavior in the bone marrow niche, describe different strategies to engineer an in vitro microenvironment for maintaining MSC properties and functions, and discuss previous findings on environmental factors critical to the modulation of MSC activities in engineered microenvironments.

Mesenchymal Stem Cell Injections for the Treatment of Perianal Crohn's Disease: What We Have Accomplished and What We Still Need to Do

Perianal Crohn's disease [CD] is found in a quarter of patients with CD and remains notoriously difficult to treat. Several medical and surgical therapies are available. However, none is particularly effective nor reliably provides sustained remission. In addition, surgical intervention is complicated by poor healing and the potential for incontinence. Mesenchymal stem cell-based therapies provide a promising treatment alternative for perianal CD, with demonstrated safety, improved efficacy, and a decreased side effect profile. Several phase I, II, and now III randomised controlled trials have now reported safety and efficacy in treating perianal CD. The aim of this review is to discusses the outcomes of conventional treatment approaches, outcomes of mesenchymal stem cell therapies, considerations specific to stem cell-based therapies, and future directions for research.

The role of secreted factors in stem cells-mediated immune regulation

Stem cells are characterized by self-renew and multipotent differentiation abilities. Besides their roles in cell compensation, stem cells are also rich sources of growth factors, cytokines, chemokines, micro-RNAs and exosomes and serve as drug stores to maintain tissue homeostasis. Recent studies have revealed that the secretome of stem cells is regulated by the local inflammatory cues and highlighted the roles of these secretory factors in stem cell based therapies. Importantly, stem cell conditioned medium, in the absence of stem cell engraftment, have shown efficiency in treating diseases involves immune disorders. In this review, we summarize the recent advances in understanding the regulatory effects of stem cells secreted factors on different immune cells including macrophages, dendritic cells, neutrophils, NK cells, T cells, and B cells. We also discuss how stem cells released factors participate in the initiation, maintenance and resolution of inflammation. The in depth understanding of interaction between stem cells secreted factors and immune system would lead to new strategies to restore tissue homeostasis and improve the efficiency of stem cell therapies.

TSG-6 Secreted by Human Adipose Tissue-derived Mesenchymal Stem Cells Ameliorates DSS-induced colitis by Inducing M2 Macrophage Polarization in Mice

Previous studies have revealed that mesenchymal stem cells (MSCs) alleviate inflammatory bowel disease (IBD) by modulating inflammatory cytokines in the inflamed intestine. However, the mechanisms underlying these effects are not completely understood. We sought to investigate the therapeutic effects of human adipose tissue-derived (hAT)-MSCs in an IBD mouse model and to explore the mechanisms of the regulation of inflammation. Dextran sulfate sodium-induced colitis mice were infused with hAT-MSCs intraperitoneally and colon tissues were collected on day 10. hAT-MSCs were shown to induce the expression of M2 macrophage markers and to regulate the expression of pro- and anti-inflammatory cytokines in the colon. Quantitative real time-PCR analyses demonstrated that less than 20 hAT-MSCs, 0.001% of all intraperitoneally injected hAT-MSCs, were detected in the inflamed colon. To investigate the effects of hAT-MSC-secreted factors in vitro, transwell co-culture system was used, demonstrating that tumour necrosis factor-α-induced gene/protein 6 (TSG-6) released by hAT-MSCs induces M2 macrophages. In vivo, hAT-MSCs transfected with TSG-6 small interfering RNA, administered intraperitoneally, were not able to induce M2 macrophage phenotype switch in the inflamed colon and had no significant effects on IBD severity. In conclusion, hAT-MSC-produced TSG-6 can ameliorate IBD by inducing M2 macrophage switch in mice.

Mesenchymal stem cell-mediated immunomodulation in cell therapy of neurodegenerative diseases

Dysfunction of immune responses has been identified to involve in the pathogenesis of various neurodegenerative diseases. Abnormal activation of glia cells and/or infiltration of peripheral adaptive immune cells always sustains neuroinflammation and the disease progression. Obviously, the regulation of neuroinflammation has become a potential therapeutic strategy against neurodegenerative diseases. Mesenchymal stem cells (MSCs) exhibit complex interactions with various immune cells including T cells, macrophages and especially resident glia cells in the central nervous system. In response to tissue injury signals, MSCs adopt specific phenotype to suppress or promote immune responses depending on the inflammatory microenvironment they reside. Therefore, manipulation of MSCs may hold great potentials to improve MSC-based therapy on neurodegenerative diseases. Here we review MSC-mediated immunomodulation in cell therapy of neurodegenerative diseases, providing fundamental information for guiding appropriate applications of MSCs in clinical settings.

Mesenchymal Stromal Cells as Anti-Inflammatory and Regenerative Mediators for Donor Kidneys During Normothermic Machine Perfusion

There is great demand for transplant kidneys for the treatment of end-stage kidney disease patients. To expand the donor pool, organs from older and comorbid brain death donors, so-called expanded criteria donors (ECD), as well as donation after circulatory death donors, are considered for transplantation. However, the quality of these organs may be inferior to standard donor organs. A major issue affecting graft function and survival is ischemia/reperfusion injury, which particularly affects kidneys from deceased donors. The development of hypothermic machine perfusion has been introduced in kidney transplantation as a preservation technique and has improved outcomes in ECD and marginal organs compared to static cold storage. Normothermic machine perfusion (NMP) is the most recent evolution of perfusion technology and allows assessment of the donor organ before transplantation. The possibility to control the content of the perfusion fluid offers opportunities for damage control and reparative therapies during machine perfusion. Mesenchymal stromal cells (MSC) have been demonstrated to possess potent regenerative properties via the release of paracrine effectors. The combination of NMP and MSC administration at the same time is a promising procedure in the field of transplantation. Therefore, the MePEP consortium has been created to study this novel modality of treatment in preparation for human trials. MePEP aims to assess the therapeutic effects of MSC administered ex vivo by NMP in the mechanisms of injury and repair in a porcine kidney autotransplantation model.

Data against a Common Assumption: Xenogeneic Mouse Models Can Be Used to Assay Suppression of Immunity by Human MSCs

Much of what we know about immunology suggests that little is to be gained from experiments in which human cells are administered to immunocompetent mice. Multiple reports have demonstrated that this common assumption does not hold for experiments with human mesenchymal stem/stromal cells (hMSCs). The data demonstrate that hMSCs can suppress immune responses to a variety of stimuli in immunocompetent mice by a range of different mechanisms that are similar to those employed by mouse MSCs. Therefore, further experiments with hMSCs in mice will make it possible to generate preclinical data that will improve both the efficacy and safety of the clinical trials with the cells that are now in progress.