Mitochondrial Oxidative Stress Reduces the Immunopotency of Mesenchymal Stromal Cells in Adults With Coronary Artery Disease

Application of adipose-derived stem cells in ischemic heart disease: theory, potency, and advantage

Adipose-derived mesenchymal stem cells (ASCs) represent an innovative candidate to treat ischemic heart disease (IHD) due to their abundance, renewable sources, minor invasiveness to obtain, and no ethical limitations. Compared with other mesenchymal stem cells, ASCs have demonstrated great advantages, especially in the commercialization of stem cell-based therapy. Mechanistically, ASCs exert a cardioprotective effect not only through differentiation into functional cells but also via robust paracrine of various bioactive factors that promote angiogenesis and immunomodulation. Exosomes from ASCs also play an indispensable role in this process. However, due to the distinct biological functions of ASCs from different origins or donors with varing health statuses (such as aging, diabetes, or atherosclerosis), the heterogeneity of ASCs deserves more attention. This prompts scientists to select optimal donors for clinical applications. In addition, to overcome the primary obstacle of poor retention and low survival after transplantation, a variety of studies have been dedicated to the engineering of ASCs with biomaterials. Besides, clinical trials have confirmed the safety and efficacy of ASCs therapy in the context of heart failure or myocardial infarction. This article reviews the theory, efficacy, and advantages of ASCs-based therapy, the factors affecting ASCs function, heterogeneity, engineering strategies and clinical application of ASCs.

Therapeutic Effects of Mesenchymal Stromal Cells Require Mitochondrial Transfer and Quality Control

Due to their beneficial effects in an array of diseases, Mesenchymal Stromal Cells (MSCs) have been the focus of intense preclinical research and clinical implementation for decades. MSCs have multilineage differentiation capacity, support hematopoiesis, secrete pro-regenerative factors and exert immunoregulatory functions promoting homeostasis and the resolution of injury/inflammation. The main effects of MSCs include modulation of immune cells (macrophages, neutrophils, and lymphocytes), secretion of antimicrobial peptides, and transfer of mitochondria (Mt) to injured cells. These actions can be enhanced by priming (i.e., licensing) MSCs prior to exposure to deleterious microenvironments. Preclinical evidence suggests that MSCs can exert therapeutic effects in a variety of pathological states, including cardiac, respiratory, hepatic, renal, and neurological diseases. One of the key emerging beneficial actions of MSCs is the improvement of mitochondrial functions in the injured tissues by enhancing mitochondrial quality control (MQC). Recent advances in the understanding of cellular MQC, including mitochondrial biogenesis, mitophagy, fission, and fusion, helped uncover how MSCs enhance these processes. Specifically, MSCs have been suggested to regulate peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α)-dependent biogenesis, Parkin-dependent mitophagy, and Mitofusins (Mfn1/2) or Dynamin Related Protein-1 (Drp1)-mediated fission/fusion. In addition, previous studies also verified mitochondrial transfer from MSCs through tunneling nanotubes and via microvesicular transport. Combined, these effects improve mitochondrial functions, thereby contributing to the resolution of injury and inflammation. Thus, uncovering how MSCs affect MQC opens new therapeutic avenues for organ injury, and the transplantation of MSC-derived mitochondria to injured tissues might represent an attractive new therapeutic approach.

miR-100a-5p-enriched exosomes derived from mesenchymal stem cells enhance the anti-oxidant effect in a Parkinson's disease model via regulation of Nox4/ROS/Nrf2 signaling

BACKGROUND

The pathogenesis of Parkinson's disease (PD) has not been fully elucidated, and there are no effective disease-modifying drugs for the treatment of PD. Mesenchymal stem cells have been used to treat several diseases, but are not readily available.

METHODS

Here, we used phenotypically uniform trophoblast stage-derived mesenchymal stem cells (T-MSCs) from embryonic stem cells, which are capable of stable production, and their exosomes (T-MSCs-Exo) to explore the molecular mechanisms involved in dopaminergic (DA) neuron protection in PD models using experimental assays (e.g., western blotting, immunofluorescence and immunohistochemistry staining).

RESULTS

We assessed the levels of DA neuron injury and oxidative stress in MPTP-induced PD mice and MPP+-induced MN9D cells after treating them with T-MSCs or T-MSCs-Exo. Furthermore, T-MSCs-Exo miRNA sequencing analysis revealed that miR-100-5p-enriched T-MSCs-Exo directly targeted the 3' UTR of NOX4, which could protect against the loss of DA neurons, maintain nigro-striatal system function, ameliorate motor deficits, and reduce oxidative stress via the Nox4-ROS-Nrf2 axis in PD models.

CONCLUSIONS

The study suggests that miR-100-5p-enriched T-MSCs-Exo may be a promising biological agent for the treatment of PD. Schematic summary of the mechanism underlying the neuroprotective actions of T-MSCs-Exo in PD. T-MSCs Exo may inhibit the expression level of the target gene NOX4 by delivering miR-100-5p, thereby reducing ROS production and alleviating oxidative stress via the Nox4-ROS-Nrf2 axis, thus improving DA neuron damage in PD.

Obesity impairs cardiolipin-dependent mitophagy and therapeutic intercellular mitochondrial transfer ability of mesenchymal stem cells

Mesenchymal stem cell (MSC) transplantation alleviates metabolic defects in diseased recipient cells by intercellular mitochondrial transport (IMT). However, the effect of host metabolic conditions on IMT and thereby on the therapeutic efficacy of MSCs has largely remained unexplored. Here we found impaired mitophagy, and reduced IMT in MSCs derived from high-fat diet (HFD)-induced obese mouse (MSC-Ob). MSC-Ob failed to sequester their damaged mitochondria into LC3-dependent autophagosomes due to decrease in mitochondrial cardiolipin content, which we propose as a putative mitophagy receptor for LC3 in MSCs. Functionally, MSC-Ob exhibited diminished potential to rescue mitochondrial dysfunction and cell death in stress-induced airway epithelial cells. Pharmacological modulation of MSCs enhanced cardiolipin-dependent mitophagy and restored their IMT ability to airway epithelial cells. Therapeutically, these modulated MSCs attenuated features of allergic airway inflammation (AAI) in two independent mouse models by restoring healthy IMT. However, unmodulated MSC-Ob failed to do so. Notably, in human (h)MSCs, induced metabolic stress associated impaired cardiolipin-dependent mitophagy was restored upon pharmacological modulation. In summary, we have provided the first comprehensive molecular understanding of impaired mitophagy in obese-derived MSCs and highlight the importance of pharmacological modulation of these cells for therapeutic intervention. A MSCs obtained from (HFD)-induced obese mice (MSC-Ob) show underlying mitochondrial dysfunction with a concomitant decrease in cardiolipin content. These changes prevent LC3-cardiolipin interaction, thereby reducing dysfunctional mitochondria sequestration into LC3-autophagosomes and thus impaired mitophagy. The impaired mitophagy is associated with reduced intercellular mitochondrial transport (IMT) via tunneling nanotubes (TNTs) between MSC-Ob and epithelial cells in co-culture or in vivo. B Pyrroloquinoline quinone (PQQ) modulation in MSC-Ob restores mitochondrial health, cardiolipin content, and thereby sequestration of depolarized mitochondria into the autophagosomes to alleviate impaired mitophagy. Concomitantly, MSC-Ob shows restoration of mitochondrial health upon PQQ treatment (MSC-ObPQQ). During co-culture with epithelial cells or transplantation in vivo into the mice lungs, MSC-ObPQQ restores IMT and prevents epithelial cell death. C Upon transplantation in two independent allergic airway inflammatory mouse models, MSC-Ob failed to rescue the airway inflammation, hyperactivity, metabolic changes in epithelial cells. D PQQ modulated MSCs restored these metabolic defects and restored lung physiology and airway remodeling parameters.

Thyroid hormone modulates hyperoxic neonatal lung injury and mitochondrial function

Mitochondrial dysfunction at birth predicts bronchopulmonary dysplasia (BPD) in extremely low-birth weight (ELBW) infants. Recently, nebulized thyroid hormone (TH), given as triiodothyronine (T3), was noted to decrease pulmonary fibrosis in adult animals through improved mitochondrial function. In this study, we tested the hypothesis that TH may have similar effects on hyperoxia-induced neonatal lung injury and mitochondrial dysfunction by testing whether i.n. T3 decreases neonatal hyperoxic lung injury in newborn mice; whether T3 improves mitochondrial function in lung homogenates, neonatal murine lung fibroblasts (NMLFs), and umbilical cord-derived mesenchymal stem cells (UC-MSCs) obtained from ELBW infants; and whether neonatal hypothyroxinemia is associated with BPD in ELBW infants. We found that inhaled T3 (given i.n.) attenuated hyperoxia-induced lung injury and mitochondrial dysfunction in newborn mice. T3 also reduced bioenergetic deficits in UC-MSCs obtained from both infants with no or mild BPD and those with moderate to severe BPD. T3 also increased the content of peroxisome proliferator-activated receptor γ coactivator 1α in lung homogenates of mice exposed to hyperoxia as well as mitochondrial potential in both NMLFs and UC-MSCs. ELBW infants who died or developed moderate to severe BPD had lower total T4 (TT4) compared with survivors with no or mild BPD. In conclusion, TH signaling and function may play a critical role in neonatal lung injury, and inhaled T3 supplementation may be useful as a therapeutic strategy for BPD.

Advanced Technologies for Potency Assay Measurement

Crucial for their application, cell products need to be well-characterized in the cell manufacturing facilities and conform to regulatory approval criteria before infusion into the patients. Mesenchymal Stromal Cells (MSCs) are the leading cell therapy candidate in clinical trials worldwide. Early phase clinical trials have demonstrated that MSCs display an excellent safety profile and are well tolerated. However, MSCs have also exhibited contradictory efficacy in later-phase clinical trials with reasons for this discrepancy including poorly understood mechanism of MSC therapeutic action. With likelihood that a number of attributes are involved in MSC derived clinical benefit, an assay that measures a single quality of may not adequately reflect potency, thus a combination of bioassays and analytical methods, collectively called "assay matrix" are favoured for defining the potency of MSC more adequately. This chapter highlights advanced technologies and targets that can achieve quantitative measurement for a range of MSC attributes, including immunological, genomic, secretome, phosphorylation, morphological, biomaterial, angiogenic and metabolic assays.

Mesenchymal stem cell bioenergetics and apoptosis are associated with risk for bronchopulmonary dysplasia in extremely low birth weight infants

Oxidant stress contributes significantly to the pathogenesis of bronchopulmonary dysplasia (BPD) in extremely low birth weight (ELBW) infants. Mitochondrial function regulates oxidant stress responses as well as pluripotency and regenerative ability of mesenchymal stem cells (MSCs) which are critical mediators of lung development. This study was conducted to test whether differences in endogenous MSC mitochondrial bioenergetics, proliferation and survival are associated with BPD risk in ELBW infants. Umbilical cord-derived MSCs of ELBW infants who later died or developed moderate/severe BPD had lower oxygen consumption and aconitase activity but higher extracellular acidification-indicative of mitochondrial dysfunction and increased oxidant stress-when compared to MSCs from infants who survived with no/mild BPD. Hyperoxia-exposed MSCs from infants who died or developed moderate/severe BPD also had lower PINK1 expression but higher TOM20 expression and numbers of mitochondria/cell, indicating that these cells had decreased mitophagy. Finally, these MSCs were also noted to proliferate at lower rates but undergo more apoptosis in cell cultures when compared to MSCs from infants who survived with no/mild BPD. These results indicate that mitochondrial bioenergetic dysfunction and mitophagy deficit induced by oxidant stress may lead to depletion of the endogenous MSC pool and subsequent disruption of lung development in ELBW infants at increased risk for BPD.

CD26 is a senescence marker associated with reduced immunopotency of human adipose tissue-derived multipotent mesenchymal stromal cells

Introduction

Human mesenchymal stromal cells (MSCs) have immunomodulatory, anti-inflammatory, and tolerogenic effects. Long-term in vitro expansion of MSCs to generate clinical grade products results in the accumulation of senescent-functionally impaired MSCs. Markers to assess the ‘senescent load’ of MSC products are needed.

Methods

Early and late passage human adipose tissue (AT) MSCs from pediatric and adult donors were characterized using established senescent markers [i.e., MSC size, granularity, and autofluorescence by flow cytometry; β-galactosidase staining (SA-β-gal); CDKN2A and CDKN1A by qRT-PCR]. In gene set enrichment analysis, DPP4 (also known as adenosine deaminase complexing protein 2 or CD26) was found as a prominent dysregulated transcript that was increased in late passage MSC(AT). This was confirmed in a larger number of MSC samples by PCR, flow cytometry, Western blotting, and immunofluorescence. In vitro immunopotency assays compared the function of CD26^high and CD26^low MSC(AT). The effect of senolytics on the CD26^high subpopulation was evaluated in senescent MSC(AT).

Results

Late passage MSC(AT) had a senescence transcriptome signature. DPP4 was the most differentially enriched gene in senescent MSCs. Late passage senescent MSC(AT) had higher CD26 surface levels and total protein abundance. Moreover, CD26 surface levels were higher in early passage MSC(AT) from adults compared to pediatric donors. CD26 abundance correlated with established senescence markers. CD26^high MSC(AT) had reduced immunopotency compared to CD26^low MSC(AT). Senolytic treatment induced MSC apoptosis, which decreased the frequencies of CD26^high MSC(AT).

Conclusions

DPP4 gene expression and DPP4/CD26 protein abundance are markers of replicative senescence in MSC(AT). Samples enriched in CD26^high MSC(AT) have reduced immunopotency and CD26^high MSCs are reduced with senolytics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03026-4.

Translating MSC Therapy in the Age of Obesity

Mesenchymal stromal cell (MSC) therapy has seen increased attention as a possible option to treat a number of inflammatory conditions including COVID-19 acute respiratory distress syndrome (ARDS). As rates of obesity and metabolic disease continue to rise worldwide, increasing proportions of patients treated with MSC therapy will be living with obesity. The obese environment poses critical challenges for immunomodulatory therapies that should be accounted for during development and testing of MSCs. In this review, we look to cancer immunotherapy as a model for the challenges MSCs may face in obese environments. We then outline current evidence that obesity alters MSC immunomodulatory function, drastically modifies the host immune system, and therefore reshapes interactions between MSCs and immune cells. Finally, we argue that obese environments may alter essential features of allogeneic MSCs and offer potential strategies for licensing of MSCs to enhance their efficacy in the obese microenvironment. Our aim is to combine insights from basic research in MSC biology and clinical trials to inform new strategies to ensure MSC therapy is effective for a broad range of patients.

Mesenchymal Stem Cell-Derived Extracellular Vesicles as Non-Coding RNA Therapeutic Vehicles in Autoimmune Diseases

Autoimmune diseases (ADs) are characterized by the activation of the immune system against self-antigens. More common in women than in men and with an early onset, their incidence is increasing worldwide, and this, combined with their chronic nature, is contributing to an enlarged medical and economic burden. Conventional immunosuppressive agents are designed to alleviate symptoms but do not constitute an effective therapy, highlighting a need to develop new alternatives. In this regard, mesenchymal stem cells (MSCs) have demonstrated powerful immunosuppressive and regenerative effects. MSC-derived extracellular vesicles (MSC-EVs) have shown some advantages, such as less immunogenicity, and are proposed as novel therapies for ADs. In this review, we summarize current perspectives on therapeutic options for ADs based on MSCs and MSC-EVs, focusing particularly on their mechanism of action exerted through their non-coding RNA (ncRNA) cargo. A complete state-of-the-art review was performed, centralized on some of the most severe ADs (rheumatoid arthritis, autoimmune type 1 diabetes mellitus, and systemic lupus erythematosus), giving evidence that a promising field is evolving to overcome the current knowledge and provide new therapeutic possibilities centered on MSC-EVs and their role as ncRNA delivery vehicles for AD gene therapy.

The secretion profile of mesenchymal stem cells and potential applications in treating human diseases

Mesenchymal stromal/stem cells (MSCs) possess multi-lineage differentiation and self-renewal potentials. MSCs-based therapies have been widely utilized for the treatment of diverse inflammatory diseases, due to the potent immunoregulatory functions of MSCs. An increasing body of evidence indicates that MSCs exert their therapeutic effects largely through their paracrine actions. Growth factors, cytokines, chemokines, extracellular matrix components, and metabolic products were all found to be functional molecules of MSCs in various therapeutic paradigms. These secretory factors contribute to immune modulation, tissue remodeling, and cellular homeostasis during regeneration. In this review, we summarize and discuss recent advances in our understanding of the secretory behavior of MSCs and the intracellular communication that accounts for their potential in treating human diseases.

Mesenchymal stem cell-mediated transfer of mitochondria: mechanisms and functional impact

There is a steadily growing interest in the use of mitochondria as therapeutic agents. The use of mitochondria derived from mesenchymal stem/stromal cells (MSCs) for therapeutic purposes represents an innovative approach to treat many diseases (immune deregulation, inflammation-related disorders, wound healing, ischemic events, and aging) with an increasing amount of promising evidence, ranging from preclinical to clinical research. Furthermore, the eventual reversal, induced by the intercellular mitochondrial transfer, of the metabolic and pro-inflammatory profile, opens new avenues to the understanding of diseases' etiology, their relation to both systemic and local risk factors, and also leads to new therapeutic tools for the control of inflammatory and degenerative diseases. To this end, we illustrate in this review, the triggers and mechanisms behind the transfer of mitochondria employed by MSCs and the underlying benefits as well as the possible adverse effects of MSCs mitochondrial exchange. We relay the rationale and opportunities for the use of these organelles in the clinic as cell-based product.

Nanorepairers Rescue Inflammation-Induced Mitochondrial Dysfunction in Mesenchymal Stem Cells

Mitochondrial dysfunction in tissue-specific mesenchymal stem cells (MSCs) plays a critical role in cell fate and the morbidity of chronic inflammation-associated bone diseases, such as periodontitis and osteoarthritis. However, there is still no effective method to cure chronic inflammation-associated bone diseases by physiologically restoring the function of mitochondria and MSCs. Herein, it is first found that chronic inflammation leads to excess Ca2+ transfer from the endoplasmic reticulum to mitochondria, which causes mitochondrial calcium overload and further damage to mitochondria. Furthermore, damaged mitochondria continuously accumulate in MSCs due to the inhibition of mitophagy by activating the Wnt/β-catenin pathway under chronic inflammatory conditions, impairing the differentiation of MSCs. Based on the mechanistic discovery, intracellular microenvironment (esterase and low pH)-responsive nanoparticles are fabricated to capture Ca2+ around mitochondria in MSCs to regulate MSC mitochondrial calcium flux against mitochondrial dysfunction. Furthermore, the same nanoparticles are able to deliver siRNA to MSCs to inhibit the Wnt/β-catenin pathway and regulate mitophagy of the originally dysfunctional mitochondria. These precision-engineered nanoparticles, referred to as "nanorepairers," physiologically restore the function of mitochondria and MSCs, resulting in effective therapy for periodontitis and osteoarthritis. The concept can potentially be expanded to the treatment of other diseases via mitochondrial quality control intervention.

Strategies for improving adipose-derived stem cells for tissue regeneration

Adipose-derived stem cells (ADSCs) have promising applications in tissue regeneration. Currently, there are only a few ADSC products that have been approved for clinical use. The clinical application of ADSCs still faces many challenges. Here, we review emerging strategies to improve the therapeutic efficacy of ADSCs in tissue regeneration. First, a great quantity of cells is often needed for the stem cell therapies, which requires the advanced cell expansion technologies. In addition cell-derived products are also required for the development of ‘cell-free’ therapies to overcome the drawbacks of cell-based therapies. Second, it is necessary to strengthen the regenerative functions of ADSCs, including viability, differentiation and paracrine ability, for the tissue repair and regeneration required for different physiological and pathophysiological conditions. Third, poor delivery efficiency also restricts the therapeutic effect of ADSCs. Effective methods to improve cell delivery include alleviating harsh microenvironments, enhancing targeting ability and prolonging cell retention. Moreover, we also point out some critical issues about the sources, effectiveness and safety of ADSCs. With these advanced strategies to improve the therapeutic efficacy of ADSCs, ADSC-based treatment holds great promise for clinical applications in tissue regeneration.

Myelodysplastic Syndromes and Metabolism

Myelodysplastic syndromes (MDS) are acquired clonal stem cell disorders exhibiting ineffective hematopoiesis, dysplastic cell morphology in the bone marrow, and peripheral cytopenia at early stages; while advanced stages carry a high risk for transformation into acute myeloid leukemia (AML). Genetic alterations are integral to the pathogenesis of MDS. However, it remains unclear how these genetic changes in hematopoietic stem and progenitor cells (HSPCs) occur, and how they confer an expansion advantage to the clones carrying them. Recently, inflammatory processes and changes in cellular metabolism of HSPCs and the surrounding bone marrow microenvironment have been associated with an age-related dysfunction of HSPCs and the emergence of genetic aberrations related to clonal hematopoiesis of indeterminate potential (CHIP). The present review highlights the involvement of metabolic and inflammatory pathways in the regulation of HSPC and niche cell function in MDS in comparison to healthy state and discusses how such pathways may be amenable to therapeutic interventions.

Mechanisms underlying the therapeutic potential of mesenchymal stem cells in atherosclerosis

Atherosclerosis is a chronic inflammatory condition resulting in the formation of fibrofatty plaques within the intimal layer of arterial walls. The identification of resident stem cells in the vascular wall has led to significant investigation into their contributions to health and disease, as well as their therapeutic potential. Of these, mesenchymal stem cells (MSCs) are the most widely studied in human clinical trials, which have demonstrated a modulatory role in vascular physiology and disease. This review highlights the most recent knowledge surrounding the cell biology of MSCs, including their origin, identification markers and differentiation potential. The limitations concerning the implementation of MSC therapy are considered and novel solutions to overcome these are proposed.

MIT-001 Restores Human Placenta-Derived Mesenchymal Stem Cells by Enhancing Mitochondrial Quiescence and Cytoskeletal Organization

Inflammation is a major cause of several chronic diseases and is reported to be recovered by the immuno-modulation of mesenchymal stem cells (MSCs). While most studies have focussed on the anti-inflammatory roles of MSCs in stem cell therapy, the impaired features of MSCs, such as the loss of homeostasis by systemic aging or pathologic conditions, remain incompletely understood. In this study, we investigated whether the altered phenotypes of human placenta-derived MSCs (hPD-MSCs) exposed to inflammatory cytokines, including TNF-α and IFN-γ, could be protected by MIT-001, a small anti-inflammatory and anti-necrotic molecule. MIT-001 promoted the spindle-like shape and cytoskeletal organization extending across the long cell axis, whereas hPD-MSCs exposed to TNF-α/IFN-γ exhibited increased morphological heterogeneity with an abnormal cell shape and cytoskeletal disorganization. Importantly, MIT-001 improved mitochondrial distribution across the cytoplasm. MIT-001 significantly reduced basal respiration, ATP production, and cellular ROS levels and augmented the spare respiratory capacity compared to TNF-α/IFN-γ-exposed hPD-MSCs, indicating enhanced mitochondrial quiescence and homeostasis. In conclusion, while TNF-α/IFN-γ-exposed MSCs lost homeostasis and mitochondrial quiescence by becoming over-activated in response to inflammatory cytokines, MIT-001 was able to rescue mitochondrial features and cellular phenotypes. Therefore, MIT-001 has therapeutic potential for clinical applications to treat mitochondrion-related inflammatory diseases.

SRT1720 Pretreatment Promotes Mitochondrial Biogenesis of Aged Human Mesenchymal Stem Cells and Improves Their Engraftment in Postinfarct Nonhuman Primate Hearts

Declined function of aged mesenchymal stem cells (MSCs) diminishes the benefits of cell therapy for myocardial infarction (MI). Our previous study has demonstrated that SRT1720, a specific SIRT1 activator, could protect aged human MSCs (hMSCs) against apoptosis. The purpose of the present study was to investigate the role of mitochondria in the antiapoptotic effects of SRT1720. In addition, we established a nonhuman primate MI model to evaluate cell engraftment of SRT1720-pretreated aged hMSCs (SRT1720-OMSCs). A hydrogen peroxide (H₂O₂)-induced apoptosis model was established in vitro to mimic MI microenvironment. Compared with vehicle-treated aged hMSCs (Vehicle-OMSCs), SRT1720-OMSCs showed alleviated apoptosis level, significantly decreased caspase-3 and caspase-9 activation, and reduced release of cytochrome c when subjected to H₂O₂ treatment. Mitochondrial contents were compared between young and aged hMSCs and our data showed that aged hMSCs had lower mitochondrial DNA (mtDNA) copy numbers and protein expression levels of components of the mitochondrial electron transport chain (ETC) than young hMSCs. Also, treatment with SRT1720 resulted in enhanced MitoTracker staining, increased mtDNA levels and expression of mitochondrial ETC components in aged hMSCs. Furthermore, SRT1720-OMSCs exhibited elevated mitochondrial respiratory capacity and higher mitochondrial membrane potential. In vivo study demonstrated that SRT1720-OMSCs had higher engraftment rates than Vehicle-OMSCs at 3 days after transplantation into the infarcted nonhuman primate hearts. Taken together, these results suggest that SRT1720 promotes mitochondrial biogenesis and function of aged hMSCs, which is involved in its protective effects against H₂O₂-induced apoptosis. These findings encourage further exploration of the optimization of aged stem cells function via regulating mitochondrial function.

Ex vivo Ikkβ ablation rescues the immunopotency of mesenchymal stromal cells from diabetics with advanced atherosclerosis

AIMS

Diabetes is a conventional risk factor for atherosclerotic cardiovascular disease and myocardial infarction (MI) is the most common cause of death among these patients. Mesenchymal stromal cells (MSCs) in patients with type 2 diabetes mellitus (T2DM) and atherosclerosis have impaired ability to suppress activated T-cells (i.e. reduced immunopotency). This is mediated by an inflammatory shift in MSC-secreted soluble factors (i.e. pro-inflammatory secretome) and can contribute to the reduced therapeutic effects of autologous T2DM and atherosclerosis-MSC post-MI. The signalling pathways driving the altered secretome of atherosclerosis- and T2DM-MSC are unknown. Specifically, the effect of IκB kinase β (IKKβ) modulation, a key regulator of inflammatory responses, on the immunopotency of MSCs from T2DM patients with advanced atherosclerosis has not been studied.

METHODS AND RESULTS

MSCs were isolated from adipose tissue obtained from patients with (i) atherosclerosis and T2DM (atherosclerosis+T2DM MSCs, n = 17) and (ii) atherosclerosis without T2DM (atherosclerosis MSCs, n = 17). MSCs from atherosclerosis+T2DM individuals displayed an inflammatory senescent phenotype and constitutively expressed active forms of effectors of the canonical IKKβ nuclear factor-κB transcription factors inflammatory pathway. Importantly, this constitutive pro-inflammatory IKKβ signature resulted in an altered secretome and impaired in vitro immunopotency and in vivo healing capacity in an acute MI model. Notably, treatment with a selective IKKβ inhibitor or IKKβ knockdown (KD) (clustered regularly interspaced short palindromic repeats/Cas9-mediated IKKβ KD) in atherosclerosis+T2DM MSCs reduced the production of pro-inflammatory secretome, increased survival, and rescued their immunopotency both in vitro and in vivo.

CONCLUSIONS

Constitutively active IKKβ reduces the immunopotency of atherosclerosis+T2DM MSC by changing their secretome composition. Modulation of IKKβ in atherosclerosis+T2DM MSCs enhances their myocardial repair ability.

Mesenchymal stromal cells for systemic sclerosis treatment

Systemic sclerosis (SSc) is a rare chronic autoimmune disease characterized by vasculopathy, dysregulation of innate and adaptive immune responses, and progressive fibrosis. SSc remains an orphan disease, with high morbity and mortality in SSc patients. The mesenchymal stromal cells (MSC) demonstrate in vitro and in vivo pro-angiogenic, immuno-suppressive, and anti-fibrotic properties and appear as a promising stem cell therapy type, that may target the key pathological features of SSc disease. This review aims to summarize acquired knowledge in the field of :1) MSC definition and in vitro and in vivo functional properties, which vary according to the donor type (allogeneic or autologous), the tissue sources (bone marrow, adipose tissue or umbilical cord) or inflammatory micro-environment in the recipient; 2) preclinical studies in various SSc animal models , which showed reduction in skin and lung fibrosis after MSC infusion; 3) first clinical trials in human, with safety and early efficacy results reported in SSc patients or currently tested in several ongoing clinical trials.

Adult mesenchymal stem cell ageing interplays with depressed mitochondrial Ndufs6

Mesenchymal stem cell (MSC)-based therapy has emerged as a novel strategy to treat many degenerative diseases. Accumulating evidence shows that the function of MSCs declines with age, thus limiting their regenerative capacity. Nonetheless, the underlying mechanisms that control MSC ageing are not well understood. We show that compared with bone marrow-MSCs (BM-MSCs) isolated from young and aged samples, NADH dehydrogenase (ubiquinone) iron-sulfur protein 6 (Ndufs6) is depressed in aged MSCs. Similar to that of Ndufs6 knockout (Ndufs6^−/−) mice, MSCs exhibited a reduced self-renewal and differentiation capacity with a tendency to senescence in the presence of an increased p53/p21 level. Downregulation of Ndufs6 by siRNA also accelerated progression of wild-type BM-MSCs to an aged state. In contrast, replenishment of Ndufs6 in Ndufs6^−/−-BM-MSCs significantly rejuvenated senescent cells and restored their proliferative ability. Compared with BM-MSCs, Ndufs6^−/−-BM-MSCs displayed increased intracellular and mitochondrial reactive oxygen species (ROS), and decreased mitochondrial membrane potential. Treatment of Ndufs6^−/−-BM-MSCs with mitochondrial ROS inhibitor Mito-TEMPO notably reversed the cellular senescence and reduced the increased p53/p21 level. We provide direct evidence that impairment of mitochondrial Ndufs6 is a putative accelerator of adult stem cell ageing that is associated with excessive ROS accumulation and upregulation of p53/p21. It also indicates that manipulation of mitochondrial function is critical and can effectively protect adult stem cells against senescence.

Mesenchymal Stem Cells Adaptively Respond to Environmental Cues Thereby Improving Granulation Tissue Formation and Wound Healing

Granulation tissue formation constitutes a key step during wound healing of the skin and other organs. Granulation tissue concomitantly initiates regenerative M2 macrophages polarization, fibroblast proliferation, myofibroblast differentiation with subsequent contraction of the wound, new vessel formation, and matrix deposition. Impaired granulation tissue formation either leads to delayed wound healing or excessive scar formation, conditions with high morbidity and mortality. Accumulating evidence has demonstrated that mesenchymal stem cell (MSC)-based therapy is a promising strategy to ameliorate defects in granulation tissue formation and to successfully treat non-healing chronic wounds. In this review we give an updated overview of how therapeutically administered MSCs ensure a balanced granulation tissue formation, and furthermore discuss the cellular and molecular mechanisms underlying the adaptive responses of MSCs to cue in their direct neighborhood. Improved understanding of the interplay between the exogenous MSCs and their niche in granulation tissue will foster the development of MSC-based therapies tailored for difficult-to-treat non-healing wounds.

The involving progress of MSCs based therapy in atherosclerosis

Atherosclerosis is a chronic progressive vascular inflammation characterized by lipid deposition and plaque formation, for which vascular cell dysfunction and impaired immune responses are involved. Up to now, lipid-lowering drugs remain the main therapy for treating atherosclerosis; however, the surgical or interventional therapy is often applied, and yet, morbidity and mortality of such cardiovascular disease remain high worldwide. Over the past decades, an anti-inflammatory approach has become an important therapeutic target for dealing with atherosclerosis, as altered immune responses have been regarded as an essential player in the pathological process of vascular abnormality induced by hyperlipidemia. Interestingly, mesenchymal stem cells, one type of stem cells with the capabilities of self-renewal and multi-potential, have demonstrated their unique immunomodulatory function in the various pathological process, especially in atherosclerosis. While some controversies remain regarding their therapeutic efficacy and working mechanisms, our present review aims to summarize the current research progress on stem cell-based therapy, focusing on its immunomodulatory effects on the pathogenesis of atherosclerosis and how endothelial cells, smooth muscle cells, and other immune cells are regulated by MSC-based therapy.

Oxidative Phosphorylation Dysfunction Modifies the Cell Secretome

Mitochondrial oxidative phosphorylation disorders are extremely heterogeneous conditions. Their clinical and genetic variability makes the identification of reliable and specific biomarkers very challenging. Until now, only a few studies have focused on the effect of a defective oxidative phosphorylation functioning on the cell’s secretome, although it could be a promising approach for the identification and pre-selection of potential circulating biomarkers for mitochondrial diseases. Here, we review the insights obtained from secretome studies with regard to oxidative phosphorylation dysfunction, and the biomarkers that appear, so far, to be promising to identify mitochondrial diseases. We propose two new biomarkers to be taken into account in future diagnostic trials.

GARP is a key molecule for mesenchymal stromal cell responses to TGF-β and fundamental to control mitochondrial ROS levels

Multipotent mesenchymal stromal cells (MSCs) have emerged as a promising cell therapy in regenerative medicine and for autoimmune/inflammatory diseases. However, a main hurdle for MSCs-based therapies is the loss of their proliferative potential in vitro. Here we report that glycoprotein A repetitions predominant (GARP) is required for the proliferation and survival of adipose-derived MSCs (ASCs) via its regulation of transforming growth factor-β (TGF-β) activation. Silencing of GARP in human ASCs increased their activation of TGF-β which augmented the levels of mitochondrial reactive oxygen species (mtROS), resulting in DNA damage, a block in proliferation and apoptosis. Inhibition of TGF-β signaling reduced the levels of mtROS and DNA damage and restored the ability of GARP-/low ASCs to proliferate. In contrast, overexpression of GARP in ASCs increased their proliferative capacity and rendered them more resistant to etoposide-induced DNA damage and apoptosis, in a TGF-β-dependent manner. In summary, our data show that the presence or absence of GARP on ASCs gives rise to distinct TGF-β responses with diametrically opposing effects on ASC proliferation and survival.

Mesenchymal stromal cells ameliorate acute lung injury induced by LPS mainly through stanniocalcin-2 mediating macrophage polarization

Background

Acute lung injury (ALI) is a devastating syndrome with no effective pharmacological therapies in the clinic. Mesenchymal stromal cells (MSCs) have been demonstrated to promote inflammation resolution and tissue repair in ALI. However, the specific mechanisms of this have not been clearly elucidated. Stanniocalcin-2 (STC2) is a stress-responsive protein that has anti-oxidative properties. Our previous study found that STC2 is a highly expressed stanniocalcin in MSCs, which may be involved in immunomodulatory activities. However, the role of STC2 in MSCs to resolve ALI has never been elucidated.

Methods

Specific shRNA was used to downregulate STC2 in MSCs. We detected ROS, cell apoptosis, and paracrine factors changes in MSCs. STC2-associated antioxidant genes were also investigated by Co-immunoprecipitation (Co-IP) and immunofluorescence. Macrophage (THP1 cells) phenotype transitions were measured by flow cytometry after coculturing with MSCs in vitro. Then, we used MSCs to treat LPS-induced ALI in mice, and assessed injury scores inflammation, and antioxidant activities in the lungs of the mice. Alveolar macrophage (AM) phenotypes and CFSE-labeled MSC apoptosis in collected bronchoalveolar fluids (BALF) were also analyzed by flow cytometry.

Results

After the STC2 knockdown, MSCs increased ROS generation and cell apoptosis after PX12 pretreatment. The antioxidant protein Nrf2 was colocalized with STC2 in the nucleus. A lack of STC2 expression in MSCs produced less interleukin 10 (IL10) and blunted macrophage polarization in THP1 cells. Furthermore, in the murine LPS-induced ALI model, the STC2 knockdown counteracted the inflammatory resolution and antioxidative effect of MSCs in the lungs. MSC^shSTC2-treated mice had a higher lung injury score than the controls, which may be attributed to diminished AM polarization and increased apoptosis of MSCs in vivo.

Conclusions

Collectively, these results suggested that STC2 is essential to the anti-oxidative and anti-inflammation properties of MSCs and could prove to be crucial for stem cell therapies for ALI.

The Influence of Negative Pressure and of the Harvesting Site on the Characteristics of Human Adipose Tissue-Derived Stromal Cells from Lipoaspirates

Background

Adipose tissue-derived stromal cells (ADSCs) have great potential for cell-based therapies, including tissue engineering. However, various factors can influence the characteristics of isolated ADSCs.

Methods

We studied the influence of the harvesting site, i.e., inner thigh (n = 3), outer thigh (n = 3), outer thigh (n = 3), outer thigh (

Results

We revealed higher initial cell yields from the outer thigh region than from the abdomen region. Negative pressure did not influence the cell yields from the outer thigh region, whereas the yields from the abdomen region were higher under high negative pressure than under low negative pressure. In the subsequent passage, in general, no significant relationship was identified between the different negative pressure and ADSC characteristics. No significant difference was observed in the characteristics of thigh ADSCs and abdomen ADSCs. Only on day 1, the diameter was significantly bigger in outer thigh ADSCs than in abdomen ADSCs. Moreover, we noted a tendency of thigh ADSCs (i.e., inner thigh+outer thigh) to reach a higher cell number on day 7. Discussion. The harvesting site and negative pressure can potentially influence initial cell yields from lipoaspirates. However, for subsequent in vitro culturing and for use in tissue engineering, it seems that the harvesting site and the level of negative pressure do not have a crucial or limiting effect on basic ADSC characteristics.in vitro culturing and for use in tissue engineering, it seems that the harvesting site and the level of negative pressure do not have a crucial or limiting effect on basic ADSC characteristics.

Adipose-Derived Mesenchymal Stem Cells Isolated from Patients with Abdominal Aortic Aneurysm Exhibit Senescence Phenomena

Mesenchymal stem cells (MSCs) have shown beneficial effects in the treatment of abdominal aortic aneurysm (AAA). Nonetheless, the biological properties of adipose-derived MSCs (ASCs) from patients with AAA (AAA-ASCs) remain unclear. This study is aimed at investigating the properties of cell phenotype and function of AAA-ASCs compared with ASCs from age-matched healthy donors (H-ASCs). H-ASCs and AAA-ASCs were studied for cell phenotype, differentiation capacity, senescence, and mitochondrial and autophagic functions. Cellular senescence was examined by senescence-associated β-galactosidase (SA-β-gal) staining. Mitochondrial morphology was determined by MitoTracker staining. Despite the similar surface markers of AAA-ASCs and H-ASCs, AAA-ASCs exhibited altered multidifferentiation potential. Compared with H-ASCs, AAA-ASCs displayed enhanced senescence manifested by increased SA-β-gal activity and decreased proliferation and migration ability. Furthermore, AAA-ASCs showed increased mitochondrial fusion, reactive oxygen species (ROS) production, and decreased mitochondrial membrane potential. In addition, AAA-ASCs exhibited decreased autophagy level, upregulation of IL-6 and TNF-α secretion, and downregulation of IL-10 secretion compared with H-ASCs. Nonetheless, treatment of AAA-ASCs with rapamycin (an autophagy activator) dramatically reduced secretion of IL-6 and TNF-α and enhanced secretion of IL-10. In conclusion, our study showed that AAA-ASCs exhibit senescence phenomena and decreased cell function. Understanding the specific alterations in AAA-ASCs will help explore novel strategies to restore cell function for AAA treatment.

O-cyclic phytosphingosine-1-phosphate stimulates HIF1α-dependent glycolytic reprogramming to enhance the therapeutic potential of mesenchymal stem cells

O-cyclic phytosphingosine-1-phosphate (cP1P) is a novel chemically synthesized sphingosine metabolite derived from phytosphingosine-1-phosphate. Although structurally similar to sphingosine-1-phosphate (S1P), its biological properties in stem cells remain to be reported. We investigated the effect of cP1P on the therapeutic potential of mesenchymal stem cells (MSCs) and their regulatory mechanism. We found that, under hypoxia, cP1P suppressed MSC mitochondrial dysfunction and apoptosis. Metabolic data revealed that cP1P stimulated glycolysis via the upregulation of glycolysis-related genes. cP1P-induced hypoxia-inducible factor 1 alpha (HIF1α) plays a key role for MSC glycolytic reprogramming and transplantation efficacy. The intracellular calcium-dependent PKCα/mammalian target of the rapamycin (mTOR) signaling pathway triggered by cP1P regulated HIF1α translation via S6K1, which is critical for HIF1 activation. Furthermore, the cP1P-activated mTOR pathway induced bicaudal D homolog 1 expression, leading to HIF1α nuclear translocation. In conclusion, cP1P enhances the therapeutic potential of MSC through mTOR-dependent HIF1α translation and nuclear translocation.

Inhibition of Mitochondrial Oxidative Damage Improves Reendothelialization Capacity of Endothelial Progenitor Cells via SIRT3 (Sirtuin 3)-Enhanced SOD2 (Superoxide Dismutase 2) Deacetylation in Hypertension

OBJECTIVE

Dysfunction of endothelial progenitor cells (EPCs) leads to impaired endothelial repair capacity in patients with hypertension, but the mechanisms remain incompletely understood. Mitochondrial oxidative stress is involved in endothelial injury in hypertension. In this study, we aim to investigate the role of mitochondrial oxidative stress in the deficient endothelial reparative capacity of EPCs and identify enhanced SIRT3 (sirtuin 3)-mediated SOD2 (superoxide dismutase 2) deacetylation as a novel endothelial protective mechanism in hypertension. Approach and Results: Hypertension-EPCs displayed increased mitochondrial reactive oxygen species and mitochondrial damage, including loss of mitochondrial membrane potential, abnormal mitochondrial ultrastructure, and mtDNA oxidative injury, which was coincided with impaired in vitro function and in vivo reendothelialization capacity. The harmful effects of hypertension on mitochondrial function of EPCs were in vitro mimicked by angiotensin II coincubation. Scavenging of mitochondrial reactive oxygen species with mitoTEMPO attenuated mitochondrial oxidative damage and rescued reendothelialization capacity. Enzymatic activity and deacetylation level of SOD2 were significantly reduced in hypertension-EPCs, which was accompanied with decreased SIRT3 expression. Knockdown of SIRT3 in EPCs resulted in mitochondrial oxidative damage, hyperacetylation of SOD2, and suppression of reendothelialization capacity. SIRT3 physically interacted with SOD2 and eliminated excess mitochondrial reactive oxygen species, restored mitochondrial function through enhancing SOD2 activity by deacetylation of K68. Upregulation of SIRT3/SOD2 signaling improved reendothelialization capability of EPCs.

CONCLUSIONS

The present study demonstrated for the first time that mitochondrial oxidative damage because of deficient SIRT3/SOD2 signaling contributes to the decline in reendothelialization capacity of EPCs in hypertension. Maintenance of mitochondrial redox homeostasis in EPCs may be a novel therapeutic target for endothelial injury.

Asprosin improves the survival of mesenchymal stromal cells in myocardial infarction by inhibiting apoptosis via the activated ERK1/2-SOD2 pathway

AIMS

Several adipokines have been proven to improve the therapeutic efficacy of mesenchymal stromal cells (MSCs) when used to treat ischemic heart disease. Asprosin (ASP) is a newly-discovered adipokine. ASP might also predict the severity of coronary pathology. We investigated the role of ASP on MSCs and the effects of ASP-pretreated MSCs on myocardial infarction (MI).

MAIN METHODS

MSCs were labelled with a lentivirus carrying green fluorescent protein (GFP). For in vivo study, after pretreatment with vehicle or ASP, MSCs were injected into infarcted hearts. Cardiac function and fibrosis were then evaluated 4 weeks after the induction of MI and survival of MSCs evaluated after 1 week. MSCs proliferation and migration were investigated after ASP treatment in vitro. MSCs apoptosis induced by hydrogen peroxide (H₂O₂) was assessed using flow cytometry.

KEY FINDINGS

Compared to vehicle-pretreated MSCs, ASP-pretreated MSCs significantly improved the left ventricular ejection fraction (LVEF), and inhibited myocardial fibrosis 4 weeks after MI. ASP pretreatment may have promoted homing of transplanted MSCs. In vitro results showed that ASP had no significant effect on MSC proliferation and migration, but protected these cells from H₂O₂-induced apoptosis. Among 21 molecules associated with antioxidation and cell death, the antioxidant enzyme SOD2 was significantly upregulated by ASP. Furthermore, ASP treatment inhibited H₂O₂-induced ROS generation and apoptosis via the activated ERK1/2-SOD2 pathway.

SIGNIFICANCE

This is the first evidence that ASP can regulate MSCs function and enhance MSCs therapy for ischemic heart disease. Furthermore, we demonstrate that ASP protects MSCs from oxidative stress-induced apoptosis via the ERK1/2-SOD2 pathway.

Nature vs. Nurture: Defining the Effects of Mesenchymal Stromal Cell Isolation and Culture Conditions on Resiliency to Palmitate Challenge

As MSC products move from early development to clinical translation, culture conditions shift from xeno- to xeno-free systems. However, the impact of isolation and culture-expansion methods on the long-term resiliency of MSCs within challenging transplant environments is not fully understood. Recent work in our lab has shown that palmitate, a saturated fatty acid elevated in the serum of patients with obesity, causes MSCs to convert from an immunosuppressive to an immunostimulatory state at moderate to high physiological levels. This demonstrated that metabolically-diseased environments, like obesity, alter the immunomodulatory efficacy of healthy donor MSCs. In addition, it highlighted the need to test MSC efficacy not only in ideal conditions, but within challenging metabolic environments. To determine how the choice of xeno- vs. xeno-free media during isolation and expansion would affect future immunosuppressive function, umbilical cord explants from seven donors were subdivided and cultured within xeno- (fetal bovine serum, FBS) or xeno-free (human platelet lysate, PLT) medias, creating 14 distinct MSC preparations. After isolation and primary expansion, umbilical cord MSCs (ucMSC) were evaluated according to the ISCT minimal criteria for MSCs. Following baseline characterization, ucMSC were exposed to physiological doses of palmitate and analyzed for metabolic health, apoptotic induction, and immunomodulatory potency in co-cultures with stimulated human peripheral blood mononuclear cells. The paired experimental design (each ucMSC donor grown in two distinct culture environments) allowed us to delineate the contribution of inherent (nature) vs. environmentally-driven (nurture) donor characteristics to the phenotypic response of ucMSC during palmitate exposure. Culturing MSCs in PLT-media led to more consistent growth characteristics during the isolation and expansion for all donors, resulting in faster doubling times and higher cell yields compared to FBS. Upon palmitate challenge, PLT-ucMSCs showed a higher susceptibility to palmitate-induced metabolic disturbance, but less susceptibility to palmitate-induced apoptosis. Most striking however, was that the PLT-ucMSCs resisted the conversion to an immunostimulatory phenotype better than their FBS counterparts. Interestingly, examining MSC suppression of PBMC proliferation at physiologic doses of palmitate magnified the differences between donors, highlighting the utility of evaluating MSC products in stress-based assays that reflect the challenges MSCs may encounter post-transplantation.

Metabolism in Human Mesenchymal Stromal Cells: A Missing Link Between hMSC Biomanufacturing and Therapy?

Human mesenchymal stem cells (hMSCs) are the most commonly-tested adult stem cells in cell therapy. While the initial focus for hMSC clinical applications was to exploit their multi-potentiality for cell replacement therapies, it is now apparent that hMSCs empower tissue repair primarily by secretion of immuno-regulatory and pro-regenerative factors. A growing trend in hMSC clinical trials is the use of allogenic and culture-expanded cells because they are well-characterized and can be produced in large scale from specific donors to compensate for the donor pathological condition(s). However, donor morbidity and large-scale expansion are known to alter hMSC secretory profile and reduce therapeutic potency, which are significant barriers in hMSC clinical translation. Therefore, understanding the regulatory mechanisms underpinning hMSC phenotypic and functional property is crucial for developing novel engineering protocols that maximize yield while preserving therapeutic potency. hMSC are heterogenous at the level of primary metabolism and that energy metabolism plays important roles in regulating hMSC functional properties. This review focuses on energy metabolism in regulating hMSC immunomodulatory properties and its implication in hMSC sourcing and biomanufacturing. The specific characteristics of hMSC metabolism will be discussed with a focus on hMSC metabolic plasticity and donor- and culture-induced changes in immunomodulatory properties. Potential strategies of modulating hMSC metabolism to enhance their immunomodulation and therapeutic efficacy in preclinical models will be reviewed.

Hypoxia Prevents Mitochondrial Dysfunction and Senescence in Human c-Kit+ Cardiac Progenitor Cells

Senescence-associated dysfunction deleteriously affects biological activities of human c-Kit⁺ cardiac progenitor cells (hCPCs), particularly under conditions of in vitro culture. In comparison, preservation of self-renewal and decreases in mitochondrial reactive oxygen species (ROS) are characteristics of murine CPCs in vivo that reside within hypoxic niches. Recapitulating hypoxic niche oxygen tension conditions of ∼1% O₂ in vitro for expansion of hCPCs rather than typical normoxic cell culture conditions (21% O₂ ) could provide significant improvement of functional and biological activities of hCPCs. hCPCs were isolated and expanded under permanent hypoxic (hCPC-1%) or normoxic (hCPC-21%) conditions from left ventricular tissue explants collected during left ventricular assist device implantation. hCPC-1% exhibit increased self-renewal and suppression of senescence characteristics relative to hCPC-21%. Oxidative stress contributed to higher susceptibility to apoptosis, as well as decreased mitochondrial function in hCPC-21%. Hypoxia prevented accumulation of dysfunctional mitochondria, supporting higher oxygen consumption rates and mitochondrial membrane potential. Mitochondrial ROS was an upstream mediator of senescence since treatment of hCPC-1% with mitochondrial inhibitor antimycin A recapitulated mitochondrial dysfunction and senescence observed in hCPC-21%. NAD⁺ /NADH ratio and autophagic flux, which are key factors for mitochondrial function, were higher in hCPC-1%, but hCPC-21% were highly dependent on BNIP3/NIX-mediated mitophagy to maintain mitochondrial function. Overall, results demonstrate that supraphysiological oxygen tension during in vitro expansion initiates a downward spiral of oxidative stress, mitochondrial dysfunction, and cellular energy imbalance culminating in early proliferation arrest of hCPCs. Senescence is inhibited by preventing ROS through hypoxic culture of hCPCs. Stem Cells 2019;37:555-567.

Quantifying Senescence-Associated Phenotypes in Primary Multipotent Mesenchymal Stromal Cell Cultures

Cellular senescence is a tumor suppressor mechanism that removes potentially neoplastic cells from the proliferative pool. Senescent cells naturally accumulate with advancing age; however, excessive/aberrant accumulation of senescent cells can disrupt normal tissue function. Multipotent mesenchymal stromal cells (MSCs), which are actively evaluated as cell-based therapy, can undergo replicative senescence or stress-induced premature senescence. The molecular characterization of MSCs senescence can be useful not only for understanding the clinical correlations between MSCs biology and human age or age-related diseases but also for identifying competent MSCs for therapeutic applications. Because MSCs are involved in regulating the hematopoietic stem cell niche, and MSCs dysfunction has been implicated in age-related diseases, the identification and selective removal of senescent MSC may represent a potential therapeutic target. Cellular senescence is generally defined by senescence-associated (SA) permanent proliferation arrest (SAPA) accompanied by persistent DNA damage response (DDR) signaling emanating from persistent DNA lesions including damaged telomeres. Alongside SA cell cycle arrest and DDR signaling, a plethora of phenotypic hallmarks help define the overall senescent phenotype including a potent SA secretory phenotype (SASP) with many microenvironmental functions. Due to the complexity of the senescence phenotype, no single hallmark is alone capable of identifying senescent MSCs. This protocol highlights strategies to validate MSCs senescence through the measurements of several key SA hallmarks including lysosomal SA Beta-galactosidase activity (SA-βgal), cell cycle arrest, persistent DDR signaling, and the inflammatory SASP.

RPS3A positively regulates the mitochondrial function of human periaortic adipose tissue and is associated with coronary artery diseases

Pericardial adipose tissue, which comprises both epicardial adipose tissue (EAT) and paracardial adipose tissue (PAT), has recently been recognized as a novel factor in the pathophysiology of cardiovascular diseases, especially coronary artery disease (CAD). The goal of this study was to evaluate differences in the brown-like characteristic and proteome among human EAT, PAT, and subcutaneous adipose tissue (SAT) to identify candidate molecules causing CAD. Uncoupling protein 1 (UCP-1) and other brown-related proteins were highly expressed in pericardial adipose tissue but was weakly expressed in SAT from the same non-CAD patient. Moreover, pericardial adipose tissues displayed a higher thermogenesis than SAT. However, brown-related genes were lower in CAD pericardial fat. Remarkably, there were lower levels of metabolic enzymes involved in glycolysis, tricarboxylic acid cycle, and fatty acid metabolism in pericardial adipose tissues of CAD. EAT is an organ adjacent to aortic root without anatomy barriers, which differs from PAT. We found that the expression of ribosomal protein S3A (RPS3A) was decreased in human EAT as well as in mouse perivascular adipose tissue (PVAT). Knockdown of RPS3A significantly inhibited adipocyte differentiation in preadipocytes and impaired the function of mitochondria in mature adipocytes. Moreover, RPS3A knockdown in mouse periaortic adipose tissue impaired browning of PVAT, accelerated vascular inflammation, and atherosclerosis progression. Mechanistically, RPS3A can migrate to the mitochondria to maintain the function of brown adipocytes. These findings provide compelling evidence that RPS3A was a key factor for modulating the brown fat-specific gene UCP-1 and carbon metabolic enzymes in EAT for preventing CAD.