Revascularization of ischemic limbs after transplantation of human bone marrow cells with high aldehyde dehydrogenase activity

Sex-related differences in efficacy of bone marrow-derived high aldehyde dehydrogenase activity cells against pulmonary fibrosis

BACKGROUND

Although bone marrow-derived cells with high aldehyde dehydrogenase activity (ALDHbr) have shown therapeutic potential against various diseases in animal studies, clinical trials have failed to show concurrent findings. We aimed to clarify the optimal conditions for the efficacy of ALDHbr cells by using a murine bleomycin-induced pulmonary fibrosis model.

METHODS

We intravenously transferred male or female donor C57BL/6 mice-derived ALDHbr cells into recipient C57BL/6 mice under various conditions, and used mCherry-expressing mice as a donor to trace the transferred ALDHbr cells.

RESULTS

Pulmonary fibrosis improved significantly when (1) female-derived, not male-derived, and (2) lineage (Lin)-negative, not lineage-positive, ALDHbr cells were transferred during the (3) fibrotic, not inflammatory, phase. Consistent with the RNA-sequencing results, female-derived Lin-/ALDHbr cells were more resistant to oxidative stress than male-derived cells in vitro, and transferred female-derived Lin-/ALDHbr cells were more viable than male-derived cells in the fibrotic lung. The mechanism underlying the antifibrotic effects of Lin-/ALDHbr cells was strongly associated with reduction of oxidative stress.

CONCLUSIONS

Our results indicated that Lin-/ALDHbr cell therapy could ameliorate pulmonary fibrosis by reducing oxidative stress and suggested that their efficacy was mediated by sex-related differences. Thus, sex-awareness strategies may be important for clinical application of bone marrow ALDHbr cells as a therapeutic tool.

Vascular regenerative cell content in South Asians: the key learnings

PURPOSE OF REVIEW

We aim to provide a comprehensive examination of the literature linking elevated rates of cardiovascular disease (CVD) in individuals of South Asian ethnicity with the severity of circulating vascular regenerative cell exhaustion.

RECENT FINDINGS

Recent findings have demonstrated reduced bioavailability of pro-vascular progenitor cell subsets in individuals with T2D and obesity. Depletion of vascular regenerative cells in the bone marrow - coupled with decreased mobilization into circulation - can negatively impact the capacity for vascular repair and exacerbate CVD risk. Several recent studies have established that although South Asian individuals possess similar inflammatory cell burden compared with other ethnicities, they exhibit marked decreases in vessel regenerative hematopoietic progenitor cells and monocyte subsets. Validation of these findings and investigation the functional capacity of vascular regenerative cell subsets to mediate vessel repair is highly warranted.

SUMMARY

Vascular regenerative cells play a key role coordinating angiogenic and arteriogenic vessel remodelling. Recent studies have demonstrated that South Asian individuals with T2D show severe depletion in circulating vascular regenerative cell subsets. Because the reversal of vascular regenerative cell exhaustion by current glucose-lowering pharmaceutical agents has recently been documented, early intervention to bolster vascular regenerative cell content may prevent CVD co-morbidities in South Asian individuals with cardiometabolic disease.

GLP-1RA therapy increases circulating vascular regenerative cell content in people living with type 2 diabetes

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) and sodium-glucose cotransporter-2 (SGLT2) inhibitors are guideline-recommended therapies for the management of type 2 diabetes (T2D), atherosclerotic cardiovascular disease, heart failure, and chronic kidney disease. We previously observed in people living with T2D and coronary artery disease that circulating vascular regenerative (VR) progenitor cell content increased following 6-mo use of the SGLT2 inhibitor empagliflozin. In this post hoc subanalysis of the ORIGINS-RCE CardioLink-13 study (ClinicalTrials.gov Identifier NCT05253521), we analyzed the circulating VR progenitor cell content of 92 individuals living with T2D, among whom 20 were on a GLP-1RA, 42 were on an SGLT2 inhibitor but not a GLP-1RA, and 30 were on neither of these vascular protective therapies. In the GLP-1RA group, the mean absolute count of circulating VR progenitor cells defined by high aldehyde dehydrogenase (ALDH) activity (ALDHhiSSClow) and VR progenitor cells further characterized by surface expression of the proangiogenic marker CD133 (ALDHhiSSClowCD133+) was higher than the group receiving neither a GLP-1RA nor an SGLT2 inhibitor (P = 0.02) and comparable with that in the SGLT2 inhibitor group (P = 0.25). The absolute count of proinflammatory, granulocyte-restricted precursor cells (ALDHhiSSChi) was significantly lower in the GLP-1RA group compared with the group on neither therapy (P = 0.031). Augmented vessel repair initiated by VR cells with previously documented proangiogenic activity, alongside a reduction in systemic, granulocyte precursor-driven inflammation, may represent novel mechanisms responsible for the cardiovascular-metabolic benefits of GLP-1RA therapy. Prospective, randomized clinical trials are now warranted to establish the value of recovering circulating VR progenitor cell content with blood vessel regenerative functions.NEW & NOTEWORTHY In this post hoc subanalysis of 92 individuals living with T2D and at high cardiovascular risk, the authors summarize the differences in circulating vascular regenerative (VR) progenitor cell content between those on GLP-1RA therapy, on SGLT2 inhibitor without GLP-1RA therapy, and on neither therapy. Those on GLP-1RA therapy demonstrated greater circulating VR progenitor cell content and reduced proinflammatory granulocyte precursor content. These results offer novel mechanistic insights into the cardiometabolic benefits associated with GLP-1RA therapy.

Icosapent ethyl modulates circulating vascular regenerative cell content: The IPE-PREVENTION CardioLink-14 trial

BACKGROUND

REDUCE-IT (Reduction of Cardiovascular Events with Icosapent Ethyl-Intervention Trial) showed that icosapent ethyl (IPE) reduced major adverse cardiovascular events by 25%. Since the underlying mechanisms for these benefits are not fully understood, the IPE-PREVENTION CardioLink-14 trial (ClinicalTrials.gov: NCT04562467) sought to determine if IPE regulates vascular regenerative (VR) cell content in people with mild to moderate hypertriglyceridemia.

METHODS

Seventy statin-treated individuals with triglycerides ≥1.50 and <5.6 mmol/L and either atherosclerotic cardiovascular disease or type 2 diabetes with additional cardiovascular risk factors were randomized to IPE (4 g/day) or usual care. VR cells with high aldehyde dehydrogenase activity (ALDHhi) were isolated from blood collected at the baseline and 3-month visits and characterized with lineage-specific cell surface markers. The primary endpoint was the change in frequency of pro-vascular ALDHhiside scatter (SSC)lowCD133+ progenitor cells. Change in frequencies of ALDHhiSSCmid monocyte and ALDHhiSSChi granulocyte precursor subsets, reactive oxygen species production, serum biomarkers, and omega-3 levels were also evaluated.

FINDINGS

Baseline characteristics, cardiovascular risk factors, and medications were balanced between the groups. Compared to usual care, IPE increased the mean frequency of ALDHhiSSClowCD133+ cells (-1.00% ± 2.45% vs. +7.79% ± 1.70%; p = 0.02), despite decreasing overall ALDHhiSSClow cell frequency. IPE assignment also reduced oxidative stress in ALDHhiSSClow progenitors and increased ALDHhiSSChi granulocyte precursor cell content.

CONCLUSIONS

IPE-PREVENTION CardioLink-14 provides the first translational evidence that IPE can modulate VR cell content and suggests a novel mechanism that may underlie the cardioprotective effects observed with IPE in REDUCE-IT.

FUNDING

HLS Therapeutics provided the IPE in kind and had no role in the study design, conduct, analyses, or interpretation.

Modalities to Deliver Cell Therapy for Treatment of Chronic Limb Threatening Ischemia

Significance: Chronic limb threatening ischemia (CLTI) is a severe form of peripheral arterial disease (PAD) that is associated with high rates of morbidity and mortality, and especially limb loss. In patients with no options for revascularization, stem cell therapy is a promising treatment option. Recent Advances: Cell therapy directly delivered to the affected ischemic limb has been shown to be a safe, effective, and feasible therapeutic alternative for patients with severe PAD. Multiple methods for cell delivery, including local, regional, and combination approaches, have been examined in both pre-clinical studies and clinical trials. This review focuses on delivery modalities used in clinical trials that deliver cell therapy to patients with severe PAD. Critical Issues: Patients with CLTI are at high risk for complications of the disease, such as amputations, leading to a poor quality of life. Many of these patients do not have viable options for revascularization using traditional interventional or surgical methods. Clinical trials have shown therapeutic benefit for cell therapy in these patients, but methods of cell treatment are not standardized, including the method of cell delivery to the ischemic limb. Future Directions: The ideal delivery approach for stem cell therapy in PAD patients remains unclear. Further studies are needed to determine the best modality of cell delivery to maximize clinical benefits.

Systematic review and meta-analysis of the effect of bone marrow-derived cell therapies on hind limb perfusion

Preclinical and clinical studies on the administration of bone marrow-derived cells to restore perfusion show conflicting results. We conducted a systematic review and meta-analysis on preclinical studies to assess the efficacy of bone marrow-derived cells in the hind limb ischemia model and identify possible determinants of therapeutic efficacy. In vivo animal studies were identified using a systematic search in PubMed and EMBASE on 10 January 2022. 85 studies were included for systematic review and meta-analysis. Study characteristics and outcome data on relative perfusion were extracted. The pooled mean difference was estimated using a random effects model. Risk of bias was assessed for all included studies. We found a significant increase in perfusion in the affected limb after administration of bone marrow-derived cells compared to that in the control groups. However, there was a high heterogeneity between studies, which could not be explained. There was a high degree of incomplete reporting across studies. We therefore conclude that the current quality of preclinical research is insufficient (low certainty level as per GRADE assessment) to identify specific factors that might improve human clinical trials.

Effect of acidosis on adipose-derived stem cell impairment and gene expression

Based on disappointing results of stem cell-based application in clinical trials for patients with critical limb ischemia, we hypothesized that the acidic environment might be the key factor limiting cell survival and function. In the present study, we used microdialysis to determine presence of acidosis and metabolic imbalance in critical ischemia. Moreover, we explored the effect of extracellular acidosis on adipose-derived stem cells (ADSCs) at molecular and transcriptional level. Our data demonstrate that low pH negatively regulates cell proliferation and survival, also, it results in cell cycle arrest, mitochondrial dynamics disorder, DNA damage as well as the impairment of proangiogenic function in a pH-dependent manner. Further transcriptome profiling identified the pivotal signaling pathways and hub genes in response to acidosis. Collectively, these findings provide strong evidences for a critical role of acidosis in ADSCs impairment with ischemic condition and suggest treatments focus on tissue pH balance and acidosis-mediated hub genes may have therapeutic potential in stem cell-based application.

Bioengineering Cell Therapy for Treatment of Peripheral Artery Disease

Peripheral artery disease is an atherosclerotic disease associated with limb ischemia that necessitates limb amputation in severe cases. Cell therapies comprised of adult mononuclear or stromal cells have been clinically tested and show moderate benefits. Bioengineering strategies can be applied to modify cell behavior and function in a controllable fashion. Using mechanically tunable or spatially controllable biomaterials, we highlight examples in which biomaterials can increase the survival and function of the transplanted cells to improve their revascularization efficacy in preclinical models. Biomaterials can be used in conjunction with soluble factors or genetic approaches to further modulate the behavior of transplanted cells and the locally implanted tissue environment in vivo. We critically assess the advances in bioengineering strategies such as 3-dimensional bioprinting and immunomodulatory biomaterials that can be applied to the treatment of peripheral artery disease and then discuss the current challenges and future directions in the implementation of bioengineering strategies.

Vascular Regenerative Cell Deficiencies in South Asian Adults

BACKGROUND

South Asian individuals shoulder a disproportionate burden of cardiometabolic diseases.

OBJECTIVES

The purpose of this study was to determine if vascular regenerative cell content varies significantly between South Asian and White European people.

METHODS

Between January 2022 and January 2023, 60 South Asian and 60 White European adults with either documented cardiovascular disease or established diabetes with ≥1 other cardiovascular risk factor were prospectively enrolled. Vascular regenerative cell content in venous blood was enumerated using a flow cytometry assay that is based on high aldehyde dehydrogenase (ALDHhi) activity and cell surface marker phenotyping. The primary outcome was the difference in frequency of circulating ALDHhi progenitor cells, monocytes, and granulocytes between the 2 groups.

RESULTS

Compared with White European participants, those of South Asian ethnicity were younger (69 ± 10 years vs 66 ± 9 years; P < 0.05), had lower weight (88 ± 19 kg vs 75 ± 13 kg; P < 0.001), and exhibited a greater prevalence of type 2 diabetes (62% vs 92%). South Asian individuals had markedly lower circulating frequencies of pro-angiogenic ALDHhiSSClowCD133+ progenitor cells (P < 0.001) and ALDHhiSSCmidCD14+CD163+ monocytes with vessel-reparative capacity (P < 0.001), as well as proportionally more ALDHhi progenitor cells with high reactive oxygen species content (P < 0.05). After correction for sex, age, body mass index, and glycated hemoglobin, South Asian ethnicity was independently associated with lower ALDHhiSSClowCD133+ cell count.

CONCLUSIONS

South Asian people with cardiometabolic disease had less vascular regenerative and reparative cells suggesting compromised vessel repair capabilities that may contribute to the excess vascular risk in this population. (The Role of South Asian vs European Origins on Circulating Regenerative Cell Exhaustion [ORIGINS-RCE]; NCT05253521).

Vascular regenerative cells in cardiometabolic disease

PURPOSE OF REVIEW

This review will provide an overview of the recent literature linking the pathophysiology of cardiometabolic disease with the depletion and dysfunction of circulating vascular regenerative (VR) cell content. Moreover, we provide rationale for the use of VR cells as a biomarker for cardiovascular risk and the use of pharmacological agents to improve VR cell content.

RECENT FINDINGS

Recent studies demonstrate the potential of VR cells as a biomarker of cardiovascular risk and as a therapeutic target. Notably, lipid-lowering agents, antihyperglycemic therapies such as sodium-glucose cotransporter-2 inhibitors and glucagon-like peptide-1 receptor agonists, as well as exercise and weight loss, have all been found to improve VR cell content, providing mechanistic evidence supporting a role in mitigating adverse cardiovascular outcomes in people with cardiometabolic-based disease.

SUMMARY

The importance of VR cells as a biomarker in assessing cardiovascular risk is becoming increasingly apparent. This review highlights recent literature supporting the accurate use of VR cell characterization to monitor the capacity for vessel repair and novel strategies to improve vessel health. Future research is required to validate and optimize these emerging approaches.

Aldehyde Dehydrogenase, a Marker of Normal and Malignant Stem Cells, Typifies Mesenchymal Progenitors in Perivascular Niches

Innate mesenchymal stem cells exhibiting multilineage differentiation and tissue (re)generative-or pathogenic-properties reside in perivascular niches. Subsets of these progenitors are committed to either osteo-, adipo-, or fibrogenesis, suggesting the existence of a developmental organization in blood vessel walls. We evaluated herein the activity of aldehyde dehydrogenase, a family of enzymes catalyzing the oxidation of aldehydes into carboxylic acids and a reported biomarker of normal and malignant stem cells, within human adipose tissue perivascular areas. A progression of ALDHLow to ALDHHigh CD34+ cells was identified in the tunica adventitia. Mesenchymal stem cell potential was confined to ALDHHigh cells, as assessed by proliferation and multilineage differentiation in vitro of cells sorted by flow cytometry with a fluorescent ALDH substrate. RNA sequencing confirmed and validated that ALDHHigh cells have a progenitor cell phenotype and provided evidence that the main isoform in this fraction is ALDH1A1, which was confirmed by immunohistochemistry. This demonstrates that ALDH activity, which marks hematopoietic progenitors and stem cells in diverse malignant tumors, also typifies native, blood vessel resident mesenchymal stem cells.

Mitochondria in endothelial cells angiogenesis and function: current understanding and future perspectives

Endothelial cells (ECs) angiogenesis is the process of sprouting new vessels from the existing ones, playing critical roles in physiological and pathological processes such as wound healing, placentation, ischemia/reperfusion, cardiovascular diseases and cancer metastasis. Although mitochondria are not the major sites of energy source in ECs, they function as important biosynthetic and signaling hubs to regulate ECs metabolism and adaptations to local environment, thus affecting ECs migration, proliferation and angiogenic process. The understanding of the importance and potential mechanisms of mitochondria in regulating ECs metabolism, function and the process of angiogenesis has developed in the past decades. Thus, in this review, we discuss the current understanding of mitochondrial proteins and signaling molecules in ECs metabolism, function and angiogeneic signaling, to provide new and therapeutic targets for treatment of diverse cardiovascular and angiogenesis-dependent diseases.

Pathological features of tissues and cell populations during cancer cachexia

Cancers remain among the most devastating diseases in the human population in spite of considerable advances in limiting their impact on lifespan and healthspan. The multifactorial nature of cancers, as well as the number of tissues and organs that are affected, have exposed a considerable diversity in mechanistic features that are reflected in the wide array of therapeutic strategies that have been adopted. Cachexia is manifested in a number of diseases ranging from cancers to diabetes and ageing. In the context of cancers, a majority of patients experience cachexia and succumb to death due to the indirect effects of tumorigenesis that drain the energy reserves of different organs. Considerable information is available on the pathophysiological features of cancer cachexia, however limited knowledge has been acquired on the resident stem cell populations, and their function in the context of these diseases. Here we review current knowledge on cancer cachexia and focus on how tissues and their resident stem and progenitor cell populations are individually affected.

Lessons from bariatric surgery: Can increased GLP-1 enhance vascular repair during cardiometabolic-based chronic disease?

Type 2 diabetes (T2D) and obesity represent entangled pandemics that accelerate the development of cardiovascular disease (CVD). Given the immense burden of CVD in society, non-invasive prevention and treatment strategies to promote cardiovascular health are desperately needed. During T2D and obesity, chronic dysglycemia and abnormal adiposity result in systemic oxidative stress and inflammation that deplete the vascular regenerative cell reservoir in the bone marrow that impairs blood vessel repair and exacerbates the penetrance of CVD co-morbidities. This novel translational paradigm, termed 'regenerative cell exhaustion' (RCE), can be detected as the depletion and dysfunction of hematopoietic and endothelial progenitor cell lineages in the peripheral blood of individuals with established T2D and/or obesity. The reversal of vascular RCE has been observed after administration of the sodium-glucose cotransporter-2 inhibitor (SGLT2i), empagliflozin, or after bariatric surgery for severe obesity. In this review, we explore emerging evidence that links improved dysglycemia to a reduction in systemic oxidative stress and recovery of circulating pro-vascular progenitor cell content required for blood vessel repair. Given that bariatric surgery consistently increases systemic glucagon-like-peptide 1 (GLP-1) release, we also focus on evidence that the use of GLP-1 receptor agonists (GLP-1RA) during obesity may act to inhibit the progression of systemic dysglycemia and adiposity, and indirectly reduce inflammation and oxidative stress, thereby limiting the impact of RCE. Therefore, therapeutic intervention with currently-available GLP-1RA may provide a less-invasive modality to reverse RCE, bolster vascular repair mechanisms, and improve cardiometabolic risk in individuals living with T2D and obesity.

Vascular repair and regeneration in cardiometabolic diseases

Chronic cardiometabolic assaults during type 2 diabetes (T2D) and obesity induce a progenitor cell imbalance in the circulation characterized by overproduction and release of pro-inflammatory monocytes and granulocytes from the bone marrow alongside aberrant differentiation and mobilization of pro-vascular progenitor cells that generate downstream progeny for the coordination of blood vessel repair. This imbalance can be detected in the peripheral blood of individuals with established T2D and severe obesity using multiparametric flow cytometry analyses to discern pro-inflammatory vs. pro-angiogenic progenitor cell subsets identified by high aldehyde dehydrogenase activity, a conserved progenitor cell protective function, combined with lineage-restricted cell surface marker analyses. Recent evidence suggests that progenitor cell imbalance can be reversed by treatment with pharmacological agents or surgical interventions that reduce hyperglycaemia or excess adiposity. In this state-of-the-art review, we present current strategies to assess the progression of pro-vascular regenerative cell depletion in peripheral blood samples of individuals with T2D and obesity and we summarize novel clinical data that intervention using sodium-glucose co-transporter 2 inhibition or gastric bypass surgery can efficiently restore cell-mediated vascular repair mechanisms associated with profound cardiovascular benefits in recent outcome trials. Collectively, this thesis generates a compelling argument for early intervention using current pharmacological agents to prevent or restore imbalanced circulating progenitor content and maintain vascular regenerative cell trafficking to sites of ischaemic damage. This conceptual advancement may lead to the design of novel therapeutic approaches to prevent or reverse the devastating cardiovascular comorbidities currently associated with T2D and obesity.

Effect of Static Compressive Force on Aldehyde Dehydrogenase Activity in Periodontal Ligament Fibroblasts

Background:

The application of static compressive forces to periodontal ligament fibroblasts (PDLFs) in vivo or in vitro has been linked to the expression of biochemical agents and local tissue modifications that could be involved in maintaining homeostasis during orthodontic movement. An approach used for identifying mesenchymal cells, or a subpopulation of progenitor cells in both tumoral and normal tissues, involves determining the activity of aldehyde dehydrogenase (ALDH). However, the role of subpopulations of PDLF-derived undifferentiated cells in maintaining homeostasis during tooth movement remains unclear.

Objective:

This study aimed at analyzing the effect of applying a static compressive force to PDLFs on the activity of ALDH in these cells.

Methods:

PDLFs were distributed into two groups: control group (CG), where fibroblasts were not submitted to compression, and experimental group (EG), where fibroblasts were submitted to a static compressive force of 4 g/mm2 for 6 hours. The compressive force was applied directly to the cells using a custom-built device. ALDH activity in the PDLFs was evaluated by a flow cytometry assay.

Results:

ALDH activity was observed in both groups, but was significantly lower in EG than in CG after the application of a static compressive force in the former.

Conclusion:

Application of a static compressive force to PDLFs decreased ALDH activity.

Antifibrotic effect of lung-resident progenitor cells with high aldehyde dehydrogenase activity

Background

Aldehyde dehydrogenase (ALDH) is highly expressed in stem/progenitor cells in various tissues, and cell populations with high ALDH activity (ALDH^br) are associated with tissue repair. However, little is known about lung-resident ALDH^br. This study was performed to clarify the characteristics of lung-resident ALDH^br cells and to evaluate their possible use as a tool for cell therapy using a mouse model of bleomycin-induced pulmonary fibrosis.

Methods

The characteristics of lung-resident/nonhematopoietic (CD45⁻) ALDH^br cells were assessed in control C57BL/6 mice. The kinetics and the potential usage of CD45⁻/ALDH^br for cell therapy were investigated in bleomycin-induced pulmonary fibrosis. Localization of transferred CD45⁻/ALDH^br cells was determined using mCherry-expressing mice as donors. The effects of aging on ALDH expression were also assessed using aged mice.

Results

Lung CD45⁻/ALDH^br showed higher proliferative and colony-forming potential than cell populations with low ALDH activity. The CD45⁻/ALDH^br cell population, and especially its CD45⁻/ALDH^br/PDGFRα⁺ subpopulation, was significantly reduced in the lung during bleomycin-induced pulmonary fibrosis. Furthermore, mRNA expression of ALDH isoforms was significantly reduced in the fibrotic lung. When transferred in vivo into bleomycin-pretreated mice, CD45⁻/ALDH^br cells reached the site of injury, ameliorated pulmonary fibrosis, recovered the reduced expression of ALDH mRNA, and prolonged survival, which was associated with the upregulation of the retinol-metabolizing pathway and the suppression of profibrotic cytokines. The reduction in CD45⁻/ALDH^br/PDGFRα⁺ population was more remarkable in aged mice than in young mice.

Conclusions

Our results strongly suggest that the lung expression of ALDH and lung-resident CD45⁻/ALDH^br cells are involved in pulmonary fibrosis. The current study signified the possibility that CD45⁻/ALDH^br cells could find application as novel and useful cell therapy tools in pulmonary fibrosis treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02549-6.

Decellularized adipose tissue scaffolds guide hematopoietic differentiation and stimulate vascular regeneration in a hindlimb ischemia model

Cellular therapies to stimulate therapeutic angiogenesis in individuals with critical limb ischemia (CLI) remain under intense investigation. In this context, the efficacy of cell therapy is dependent on the survival, biodistribution, and pro-angiogenic paracrine signaling of the cells transplanted. Hematopoietic progenitor cells (HPC) purified from human umbilical cord blood using high aldehyde dehydrogenase-activity (ALDH^hi cells) and expanded ex vivo, represent a heterogeneous mixture of progenitor cells previously shown to support limb revascularization in mouse models of CLI. The objectives of this study were to investigate the utility of bioscaffolds derived from human decellularized adipose tissue (DAT) to guide the differentiation of seeded HPC in vitro and harness the pro-angiogenic capacity of HPC at the site of ischemia after implantation in vivo. Probing whether the DAT scaffolds altered HPC differentiation, label-free quantitative mass spectrometry and flow cytometric phenotype analyses indicated that culturing the HPC on the DAT scaffolds supported their differentiation towards the pro-angiogenic monocyte/macrophage lineage at the expense of megakaryopoiesis. Moreover, implantation of HPC in DAT scaffolds within a unilateral hindlimb ischemia model in NOD/SCID mice increased cell retention at the site of ischemia relative to intramuscular injection, and accelerated the recovery of limb perfusion, improved functional limb use and augmented CD31⁺ capillary density when compared to DAT implantation alone or saline-injected controls. Collectively, these data indicate that cell-instructive DAT scaffolds can direct therapeutic HPC differentiation towards the monocyte/macrophage lineage and represent a promising delivery platform for improving the efficacy of cell therapies for CLI.

Embryonic protein NODAL regulates the breast tumor microenvironment by reprogramming cancer-derived secretomes

The tumor microenvironment (TME) is an important mediator of breast cancer progression. Cancer-associated fibroblasts constitute a major component of the TME and may originate from tissue-associated fibroblasts or infiltrating mesenchymal stromal cells (MSCs). The mechanisms by which cancer cells activate fibroblasts and recruit MSCs to the TME are largely unknown, but likely include deposition of a pro-tumorigenic secretome. The secreted embryonic protein NODAL is clinically associated with breast cancer stage and promotes tumor growth, metastasis, and vascularization. Herein, we show that NODAL expression correlates with the presence of activated fibroblasts in human triple-negative breast cancers and that it directly induces Cancer-associated fibroblasts phenotypes. We further show that NODAL reprograms cancer cell secretomes by simultaneously altering levels of chemokines (e.g., CXCL1), cytokines (e.g., IL-6) and growth factors (e.g., PDGFRA), leading to alterations in MSC chemotaxis. We therefore demonstrate a hitherto unappreciated mechanism underlying the dynamic regulation of the TME.

Current Status of Angiogenic Cell Therapy and Related Strategies Applied in Critical Limb Ischemia

Critical limb ischemia (CLI) constitutes the most severe form of peripheral arterial disease (PAD), it is characterized by progressive blockade of arterial vessels, commonly correlated to atherosclerosis. Currently, revascularization strategies (bypass grafting, angioplasty) remain the first option for CLI patients, although less than 45% of them are eligible for surgical intervention mainly due to associated comorbidities. Moreover, patients usually require amputation in the short-term. Angiogenic cell therapy has arisen as a promising alternative for these "no-option" patients, with many studies demonstrating the potential of stem cells to enhance revascularization by promoting vessel formation and blood flow recovery in ischemic tissues. Herein, we provide an overview of studies focused on the use of angiogenic cell therapies in CLI in the last years, from approaches testing different cell types in animal/pre-clinical models of CLI, to the clinical trials currently under evaluation. Furthermore, recent alternatives related to stem cell therapies such as the use of secretomes, exosomes, or even microRNA, will be also described.

Isolation and characterization of circulating pro-vascular progenitor cell subsets from human whole blood samples

The examination of circulating pro-vascular progenitor cell frequency and function is integral in understanding aberrant blood vessel homeostasis in individuals with cardiometabolic disease. Here, we outline the characterization of progenitor cell subsets from peripheral blood using high aldehyde dehydrogenase (ALDH) activity, an intracellular detoxification enzyme previously associated with pro-vascular progenitor cell status. Using this protocol, cells can be examined by flow cytometry for ALDH activity and lineage restricted cell surface markers simultaneously.

For complete details on the use and execution of this protocol, please refer to Terenzi et al. (2019) and Hess et al. (2019, 2020).

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Aldehyde dehydrogenase is superior in the isolation of progenitor cells

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Flow cytometry is an effective method to characterize pro-vascular cells

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Aggressive gating strategies allows for in-depth progenitor cell characterization

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The use of fresh blood samples will yield most accurate cell prevalence

Platelet-derived growth factor receptor-β (PDGFRβ) lineage tracing highlights perivascular cell to myofibroblast transdifferentiation during post-traumatic osteoarthritis

Pericytes ubiquitously surround capillaries and microvessels within vascularized tissues and have diverse functions after tissue injury. In addition to regulation of angiogenesis and tissue regeneration after injury, pericytes also contribute to organ fibrosis. Destabilization of the medial meniscus (DMM) phenocopies post-traumatic osteoarthritis, yet little is known regarding the impact of DMM surgery on knee joint-associated pericytes and their cellular descendants. Here, inducible platelet-derived growth factor receptor-β (PDGFRβ)-CreER^T2 reporter mice were subjected to DMM surgery, and lineage tracing studies performed over an 8-week period. Results showed that at baseline PDGFRβ reporter activity highlights abluminal perivascular cells within synovial and infrapatellar fat pad (IFP) tissues. DMM induces a temporospatially patterned increase in vascular density within synovial and subsynovial tissues. Marked vasculogenesis within IFP was accompanied by expansion of PDGFRβ reporter⁺ perivascular cell numbers, detachment of mGFP⁺ descendants from vessel walls, and aberrant adoption of myofibroblastic markers among mGFP⁺ cells including α-SMA, ED-A, and TGF-β1. At later timepoints, fibrotic changes and vascular maturation occurred within subsynovial tissues, with the redistribution of PDGFRβ⁺ cellular descendants back to their perivascular niche. In sum, PDGFRβ lineage tracing allows for tracing of perivascular cell fate within the diarthrodial joint. Further, destabilization of the joint induces vascular and fibrogenic changes of the IFP accompanied by perivascular to myofibroblast transdifferentiation.

[Problems and prospects of cell therapy for critical ischaemia of lower limbs]

BACKGROUND

Cell therapy was proposed as a procedure of indirect revascularization for patients with critical ischaemia of lower extremities for whom endovascular and surgical revascularization is impossible. We present herein a review of the state of the art of studies in the field of cell therapy of this cohort of patients.

BASIC PROVISIONS

Cell therapy has proved safe, however, the results of studies of efficacy are relatively ambiguous and unconvincing. The number of patients in separately taken clinical trials is minimal. The reviewed studies differed not only by heterogeneity of the cell types used but by the routes of administration of cells (cells were delivered either intramuscularly (predominantly) or intraarterially) and the duration of follow up (time of assessment and duration of follow up varied from 1 month to 2 years). One of the problems became the lack of the routine study of the angiogenic potential of stem cells prior to their clinical application. It is known that the angiogenic activity of multipotent cells of apparently healthy patients may differ from that of patients suffering from atherosclerosis, chronic renal failure, diabetes.

CONCLUSIONS

It is supposed that treatment with stem cells or precursor cells is more efficient as compared to protein or gene therapy not only owing to direct vasculogenic properties but a paracrine action through excretion of proangiogenic biologically active substances. More studies with larger cohorts are necessary to provide stronger safety and efficacy data on cell therapy. Besides, a promising trend in the field of cellular approaches is modulation of regenerative capability of stem cells, which may help overcome difficulties in understanding the place of cell therapy in therapeutic angiogenesis.

Vascular Risk Reduction in Obesity through Reduced Granulocyte Burden and Improved Angiogenic Monocyte Content following Bariatric Surgery

Bariatric surgery, in addition to the benefit of sustained weight loss, can also reduce cardiometabolic risk and mortality. Lifelong vessel maintenance is integral to the prevention of cardiovascular disease. Using aldehyde dehydrogenase activity, an intracellular detoxifying enzyme present at high levels within pro-vascular progenitor cells, we observed an association between chronic obesity and “regenerative cell exhaustion” (RCE), a pathology whereby chronic assault on circulating regenerative cell types can result in adverse inflammation and diminished vessel repair. We also describe that, at 3 months following bariatric surgery, systemic inflammatory burden was reduced and pro-angiogenic macrophage precursor content was improved in subjects with severe obesity, suggesting the restoration of a microenvironment to support vessel homeostasis. These data suggest that bariatric surgery may reverse deleterious events that predispose patients with morbid obesity to cardiovascular risk.

Obesity features a low frequency of ALDH and CD133 co-expressing cells

Bariatric surgery results in lower granulocyte precursors expressing ALDH

Macrophage balance favors M2 polarization following bariatric surgery

Cellular changes after bariatric surgery give insight into reducing CV risk

SGLT-2 Inhibitors and Regenerative Cell Exhaustion

In response to the Letter by Fadini, Hess et al. discuss the interpretation of their data and the details of the multiparametric analyses employed to measure the changes in circulating provascular cell content in patients with type 2 diabetes receiving empagliflozin compared to placebo treatment.

All-in-One Hydrogel Realizing Adipose-Derived Stem Cell Spheroid Production and In Vivo Injection via "Gel-Sol" Transition for Angiogenesis in Hind Limb Ischemia

Adipose-derived stem cell (ASC) spheroids exhibit enhanced angiogenic efficacy toward ischemia treatment. Thus, it is necessary to develop an all-in-one platform that enables efficient spheroid production, collection, and injectable implantation in vivo. The present study fabricated a poly(l-glutamic acid) (PLGA)-based porous hydrogel that can not only produce ASC spheroids but also conveniently collect spheroids for in vivo implantation via minimally invasive injection to treat hind limb ischemia. PLGA was cross-linked with cystamine (Cys), which contains disulfide bonds, to form a porous hydrogel that could realize "gel-sol" transition by the reduction effect of glutathione (GSH). For one thing, it was found that the introduction of the disulfide bond in the PLGA hydrogel promoted cellular adhesion via combining fibronectin, preventing the formation of spheroids, while the introduction of polyethylene glycol monomethyl ether (mPEG) could disturb the effect of the disulfide bond on cellular adhesion, supporting spheroid formation inside the porous hydrogel. For another, the porous hydrogel transferred into a syringe could turn into liquid polymer solution within about 40 min for collection of the produced spheroids and in vivo injection. In addition, because of the lubrication of polymer solution, the spheroids were protected during the injection of the spheroids/polymer suspensoid through a 25G syringe needle, avoiding damages from shearing. After the in vivo injection, the enhanced paracrine secretion of ASC spheroids resulted in promoted angiogenesis and muscle regeneration, exhibiting obvious therapeutic effect on limb ischemia in mice after 21 days. At the same time, PLGA-based material exhibited well-performed biocompatibility in vivo.

Five Decades Later, Are Mesenchymal Stem Cells Still Relevant?

Mesenchymal stem cells are culture-derived mesodermal progenitors isolatable from all vascularized tissues. In spite of multiple fundamental, pre-clinical and clinical studies, the native identity and role in tissue repair of MSCs have long remained elusive, with MSC selection in vitro from total cell suspensions essentially unchanged as a mere primary culture for half a century. Recent investigations have helped understand the tissue origin of these progenitor cells, and uncover alternative effects of MSCs on tissue healing via growth factor secretion and interaction with the immune system. In this review, we describe current trends in MSC biology and discuss how these may improve the use of these therapeutic cells in tissue engineering and regenerative medicine.

SGLT2 Inhibition with Empagliflozin Increases Circulating Provascular Progenitor Cells in People with Type 2 Diabetes Mellitus

Hess et al. quantified circulating aldehyde dehydrogenase-expressing (ALDH^hi) cell subsets in people with T2DM given either empagliflozin (EMPA) or placebo. EMPA treatment increased circulating pro-angiogenic CD133⁺ progenitor cells, decreased pro-inflammatory ALDH^hi granulocyte precursors, and increased ALDH^hi monocytes with M2 polarization. EMPA treatment improved T2DM-associated "regenerative cell depletion" contributing to enhanced vascular health.

Cell therapy of critical limb ischemia-problems and prospects

Cell therapy is proposed for indirect revascularization for the patient's incurable by endovascular or surgical revascularization. The therapy with stem cells (SCs) or progenitor cells is assumed to be more efficient as compared with protein or gene therapy not only because of their direct vasculogenic properties, but also thanks to their paracrine effect via secretion of manifold biologically active substances. This review gives an overview of the potential of SC-based therapy for critical limb ischemia (CLI), putative mechanism underlying cell therapy, and comparison of cell therapy to angiogenesis gene therapy in CLI treatment. Human trial data and meta-analysis, as well as some problems of clinical trials and considerations for future SC-based therapy in CLI are also discussed.

Exosomes Derived from Human Primed Mesenchymal Stem Cells Induce Mitosis and Potentiate Growth Factor Secretion

Mesenchymal stem cells (MSCs) facilitate functional recovery in numerous animal models of inflammatory and ischemic tissue-related diseases with a growing body of research suggesting that exosomes mediate many of these therapeutic effects. It remains unclear, however, which types of proteins are packaged into exosomes compared with the cells from which they are derived. In this study, using comprehensive proteomic analysis, we demonstrated that human primed MSCs secrete exosomes (pMEX) that are packaged with markedly higher fractions of specific protein subclasses compared with their cells of origin, indicating regulation of their contents. Notably, we found that pMEX are also packaged with substantially elevated levels of extracellular-associated proteins. Fibronectin was the most abundant protein detected, and data established that fibronectin mediates the mitogenic properties of pMEX. In addition, treatment of SHSY5Y cells with pMEX induced the secretion of growth factors known to possess mitogenic and neurotrophic properties. Taken together, our comprehensive analysis indicates that pMEX are packaged with specific protein subtypes, which may provide a molecular basis for their distinct functional properties.

Aldehyde Dehydrogenases: Not Just Markers, but Functional Regulators of Stem Cells

Aldehyde dehydrogenase (ALDH) is a superfamily of enzymes that detoxify a variety of endogenous and exogenous aldehydes and are required for the biosynthesis of retinoic acid (RA) and other molecular regulators of cellular function. Over the past decade, high ALDH activity has been increasingly used as a selectable marker for normal cell populations enriched in stem and progenitor cells, as well as for cell populations from cancer tissues enriched in tumor-initiating stem-like cells. Mounting evidence suggests that ALDH not only may be used as a marker for stem cells but also may well regulate cellular functions related to self-renewal, expansion, differentiation, and resistance to drugs and radiation. ALDH exerts its functional actions partly through RA biosynthesis, as all-trans RA reverses the functional effects of pharmacological inhibition or genetic suppression of ALDH activity in many cell types in vitro. There is substantial evidence to suggest that the role of ALDH as a stem cell marker comes down to the specific isoform(s) expressed in a particular tissue. Much emphasis has been placed on the ALDH1A1 and ALDH1A3 members of the ALDH1 family of cytosolic enzymes required for RA biosynthesis. ALDH1A1 and ALDH1A3 regulate cellular function in both normal stem cells and tumor-initiating stem-like cells, promoting tumor growth and resistance to drugs and radiation. An improved understanding of the molecular mechanisms by which ALDH regulates cellular function will likely open new avenues in many fields, especially in tissue regeneration and oncology.

Circulating Pro-Vascular Progenitor Cell Depletion During Type 2 Diabetes: Translational Insights Into the Prevention of Ischemic Complications in Diabetes

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This study combined ALDH activity with cell surface marker expression to develop a multiparametric flow cytometry assay to assess proangiogenic progenitor and proinflammatory cell content in the peripheral blood of patients with T2D compared with age-matched control subjects.

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Patients with T2D exhibited an increased frequency of proinflammatory ALDH^hi cells with granulocyte side scatter properties and a decreased frequency of circulating monocytes with an M2 phenotype that is associated with proangiogenic and anti-inflammatory functions.

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Patients with T2D exhibited significant depletion of circulating provascular ALDH^hiCD34+ progenitor cells with primitive, migratory, endothelial, and pericyte phenotypes.

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Subgroup analyses that stratified patients with T2D according to age, duration of T2D, insulin requirement, and glycosylated hemoglobin levels revealed that only the duration of T2D correlated with vascular progenitor cell depletion.

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Flow cytometric assessment of circulating ALDH^hi cell subsets represents a promising translational approach for identifying patients with T2D at increased risk for cardiovascular comorbidities.

Detection of vascular regenerative cell exhaustion is required to combat ischemic complications during type 2 diabetes mellitus (T2D). We used high aldehyde dehydrogenase (ALDH) activity and surface marker co-expression to develop a high-throughput flow cytometry–based assay to quantify circulating proangiogenic and proinflammatory cell content in the peripheral blood of individuals with T2D. Circulating proangiogenic monocytes expressing anti-inflammatory M2 markers were decreased in patients with T2D. Individuals with longer duration of T2D exhibited reduced frequencies of circulating proangiogenic ALDH^hiCD34+ progenitor cells with primitive (CD133) and migratory (CXCR4) phenotypes. This approach consistently detected increased inflammatory cell burden and decreased provascular progenitor content in individuals with T2D.

ALDH1A3 Is the Key Isoform That Contributes to Aldehyde Dehydrogenase Activity and Affects in Vitro Proliferation in Cardiac Atrial Appendage Progenitor Cells

High aldehyde dehydrogenase (ALDH^hi) activity has been reported in normal and cancer stem cells. We and others have shown previously that human ALDH^hi cardiac atrial appendage cells are enriched with stem/progenitor cells. The role of ALDH in these cells is poorly understood but it may come down to the specific ALDH isoform(s) expressed. This study aimed to compare ALDH^hi and ALDH^lo atrial cells and to identify the isoform(s) that contribute to ALDH activity, and their functional role.

Methods and Results: Cells were isolated from atrial appendage specimens from patients with ischemic and/or valvular heart disease undergoing heart surgery. ALDH^hi activity assessed with the Aldefluor reagent coincided with primitive surface marker expression (CD34⁺). Depending on their ALDH activity, RT-PCR analysis of ALDH^hi and ALDH^lo cells demonstrated a differential pattern of pluripotency genes (Oct 4, Nanog) and genes for more established cardiac lineages (Nkx2.5, Tbx5, Mef2c, GATA4). ALDH^hi cells, but not ALDH^lo cells, formed clones and were culture-expanded. When cultured under cardiac differentiation conditions, ALDH^hi cells gave rise to a higher number of cardiomyocytes compared with ALDH^lo cells. Among 19 ALDH isoforms known in human, ALDH1A3 was most highly expressed in ALDH^hi atrial cells. Knocking down ALDH1A3, but not ALDH1A1, ALDH1A2, ALDH2, ALDH4A1, or ALDH8A1 using siRNA decreased ALDH activity and cell proliferation in ALDH^hi cells. Conversely, overexpressing ALDH1A3 with a retroviral vector increased proliferation in ALDH^lo cells.

Conclusions: ALDH1A3 is the key isoform responsible for ALDH activity in ALDH^hi atrial appendage cells, which have a propensity to differentiate into cardiomyocytes. ALDH1A3 affects in vitro proliferation of these cells.

Foreskin-derived mesenchymal stromal cells with aldehyde dehydrogenase activity: isolation and gene profiling

Background

Mesenchymal stromal cells (MSCs) become an attractive research topic because of their crucial roles in tissue repair and regenerative medicine. Foreskin is considered as a valuable tissue source containing immunotherapeutic MSCs (FSK-MSCs).

Results

In this work, we used aldehyde dehydrogenase activity (ALDH) assay (ALDEFLUOR™) to isolate and therefore characterize subsets of FSK-MSCs. According to their ALDH activity, we were able to distinguish and sort by fluorescence activated cell sorting (FACS) two subsets of FSK-MSCs (referred as ALDH⁺ and ALDH⁻). Consequently, these subsets were characterized by profiling the gene expression related to the main properties of MSCs (proliferation, response to hypoxia, angiogenesis, phenotype, stemness, multilineage, hematopoiesis and immunomodulation). We thus demonstrated by Real Time PCR several relevant differences in gene expression based on their ALDH activity.

Conclusion

Taken together, this preliminary study suggests that distinct subsets of FSK-MSCs with differential gene expression profiles depending of ALDH activity could be identified. These populations could differ in terms of biological functionalities involving the selection by ALDH activity as useful tool for potent therapeutic applications. However, functional studies should be conducted to confirm their therapeutic relevance.

Electronic supplementary material

The online version of this article (10.1186/s12860-018-0157-0) contains supplementary material, which is available to authorized users.

Mechanically resilient injectable scaffolds for intramuscular stem cell delivery and cytokine release

A promising strategy for treating peripheral ischemia involves the delivery of stem cells to promote angiogenesis through paracrine signaling. Treatment success depends on cell localization, retention, and survival within the mechanically dynamic intramuscular (IM) environment. Herein we describe an injectable, in situ-gelling hydrogel for the IM delivery of adipose-derived stem/stromal cells (ASCs), specifically designed to withstand the dynamic loading conditions of the lower limb and facilitate cytokine release from encapsulated cells. Copolymers of poly(trimethylene carbonate)-b-poly(ethylene glycol)-b-poly(trimethylene carbonate) diacrylate were used to modulate the properties of methacrylated glycol chitosan hydrogels crosslinked by thermally-initiated polymerization using ammonium persulfate and N,N,N',N'-tetramethylethylenediamine. The scaffolds had an ultimate compressive strain over 75% and maintained mechanical properties during compressive fatigue testing at physiological levels. Rapid crosslinking (<3 min) was achieved at low initiator concentration (5 mM). Following injection and crosslinking within the scaffolds, human ASCs demonstrated high viability (>90%) over two weeks in culture under both normoxia and hypoxia. Release of angiogenic and chemotactic cytokines was enhanced from encapsulated cells under sustained hypoxia, in comparison to normoxic and tissue culture polystyrene controls. When delivered by IM injection in a mouse model of hindlimb ischemia, human ASCs were well retained in the scaffold over 28 days and significantly increased the IM vascular density compared to untreated controls.

Different Effects of Insulin-Like Growth Factor-1 and Insulin-Like Growth Factor-2 on Myogenic Differentiation of Human Mesenchymal Stem Cells

Insulin-like growth factors (IGFs) are critical components of the stem cell niche, as they regulate proliferation and differentiation of stem cells into different lineages, including skeletal muscle. We have previously reported that insulin-like growth factor binding protein-6 (IGFBP-6), which has high affinity for IGF-2, alters the differentiation process of placental mesenchymal stem cells (PMSCs) into skeletal muscle. In this study, we determined the roles of IGF-1 and IGF-2 and their interactions with IGFBP-6. We showed that IGF-1 increased IGFBP-6 levels within 24 hours but decreased after 3 days, while IGF-2 maintained higher levels of IGFBP-6 throughout myogenesis. IGF-1 increased IGFBP-6 in the early phase as a requirement for muscle commitment. In contrast, IGF-2 enhanced muscle differentiation as shown by the expression of muscle differentiation markers MyoD, MyoG, and MHC. IGF-1 and IGF-2 had different effects on muscle differentiation with IGF-1 promoting early commitment to muscle and IGF-2 promoting complete muscle differentiation. We also showed that PMSCs acquired increasing capacity to synthesize IGF-2 during muscle differentiation, and the capacity increased as the differentiation progressed suggesting an autocrine and/or paracrine effect. Additionally, we demonstrated that IGFBP-6 could enhance the muscle differentiation process in the absence of IGF-2.

Stem cell-based peripheral vascular regeneration

Chronic critical limb ischemia (CLI) represents an end-stage manifestation of peripheral arterial disease (PAD). CLI patients are at very high risk of amputation and cardiovascular complications, leading to severe morbidity and mortality. Because many patients with CLI are ineligible for conventional revascularization procedures, it is urgently needed to explore alternative strategies to improve blood supply in the ischemic tissue. Although researchers initially focused on gene/protein therapy using proangiogenic growth factors/cytokines, recent discovery of somatic stem/progenitor cells including bone marrow (BM)-derived endothelial progenitor cells (EPCs) and mesenchymal stem cells (MSCs) has drastically developed the field of therapeutic angiogenesis for CLI. Overall, early phase clinical trials demonstrated that stem/progenitor cell therapies may be safe, feasible and potentially effective. However, only few late-phase clinical trials have been conducted. This review provides an overview of the preclinical and clinical reports to demonstrate the usefulness and the current limitations of the cell-based therapies.

Insulin-Like Growth Factor Binding Protein-6 Alters Skeletal Muscle Differentiation of Human Mesenchymal Stem Cells

Insulin-like growth factor binding protein-6 (IGFBP-6), the main regulator of insulin-like growth factor-2 (IGF-2), is a component of the stem cell niche in developing muscle cells. However, its role in muscle development has not been clearly defined. In this study, we investigated the role of IGFBP-6 in muscle commitment and differentiation of human mesenchymal stem cells derived from the placenta. We showed that placental mesenchymal stem cells (PMSCs) have the ability to differentiate into muscle cells when exposed to a specific culture medium by expressing muscle markers Pax3/7, MyoD, myogenin, and myosin heavy chain in a stage-dependent manner with the ultimate formation of multinucleated fibers and losing pluripotency-associated markers, OCT4 and SOX2. The addition of IGFBP-6 significantly increased pluripotency-associated markers as well as muscle differentiation markers at earlier time points, but the latter decreased with time. On the other hand, silencing IGFBP-6 decreased both pluripotent and differentiation markers at early time points. The levels of these markers increased as IGFBP-6 levels were restored. These findings indicate that IGFBP-6 influences MSC pluripotency and myogenic differentiation, with more prominent effects observed at the beginning of the differentiation process before muscle commitment.

Targeted antitumor therapy mediated by prodrug-activating mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) were introduced as tumor-targeted vehicles suitable for delivery of the gene-directed enzyme/prodrug therapy more than 10 years ago. Over these years key properties of tumor cells and MSCs, which are crucial for the treatment efficiency, were examined; and there are some critical issues to be considered for the maximum antitumor effect. Moreover, engineered MSCs expressing enzymes capable of activating non-toxic prodrugs achieved long-term curative effect even in metastatic and hard-to-treat tumor types in pre-clinical scenario(s). These gene-modified MSCs are termed prodrug-activating MSCs throughout the text and represent promising approach for further clinical application. This review summarizes major determinants to be considered for the application of the prodrug-activating MSCs in antitumor therapy in order to maximize therapeutic efficiency.

Hypoxia Inducible Factor-1α Potentiates Jagged 1-Mediated Angiogenesis by Mesenchymal Stem Cell-Derived Exosomes

Insufficient vessel growth associated with ischemia remains an unresolved issue in vascular medicine. Mesenchymal stem cells (MSCs) have been shown to promote angiogenesis via a mechanism that is potentiated by hypoxia. Overexpression of hypoxia inducible factor (HIF)-1α in MSCs improves their therapeutic potential by inducing angiogenesis in transplanted tissues. Here, we studied the contribution of exosomes released by HIF-1α-overexpressing donor MSCs (HIF-MSC) to angiogenesis by endothelial cells. Exosome secretion was enhanced in HIF-MSC. Omics analysis of miRNAs and proteins incorporated into exosomes pointed to the Notch pathway as a candidate mediator of exosome communication. Interestingly, we found that Jagged1 was the sole Notch ligand packaged into MSC exosomes and was more abundant in HIF-MSC than in MSC controls. The addition of Jagged1-containing exosomes from MSC and HIF-MSC cultures to endothelial cells triggered transcriptional changes in Notch target genes and induced angiogenesis in an in vitro model of capillary-like tube formation, and both processes were stimulated by HIF-1α. Finally, subcutaneous injection of Jagged 1-containing exosomes from MSC and HIF-MSC cultures in the Matrigel plug assay induced angiogenesis in vivo, which was more robust when they were derived from HIF-MSC cultures. All Jagged1-mediated effects could be blocked by prior incubation of exosomes with an anti-Jagged 1 antibody. All together, the results indicate that exosomes derived from MSCs stably overexpressing HIF-1α have an increased angiogenic capacity in part via an increase in the packaging of Jagged1, which could have potential applications for the treatment of ischemia-related disease. Stem Cells 2017;35:1747-1759.

Expansion of Umbilical Cord Blood Aldehyde Dehydrogenase Expressing Cells Generates Myeloid Progenitor Cells that Stimulate Limb Revascularization

Uncompromised by chronic disease‐related comorbidities, human umbilical cord blood (UCB) progenitor cells with high aldehyde dehydrogenase activity (ALDH^hi cells) stimulate blood vessel regeneration after intra‐muscular transplantation. However, implementation of cellular therapies using UCB ALDH^hi cells for critical limb ischemia, the most severe form of severe peripheral artery disease, is limited by the rarity (<0.5%) of these cells. Our goal was to generate a clinically‐translatable, allogeneic cell population for vessel regenerative therapies, via ex vivo expansion of UCB ALDH^hi cells without loss of pro‐angiogenic potency. Purified UCB ALDH^hi cells were expanded >18‐fold over 6‐days under serum‐free conditions. Consistent with the concept that ALDH‐activity is decreased as progenitor cells differentiate, only 15.1% ± 1.3% of progeny maintained high ALDH‐activity after culture. However, compared to fresh UCB cells, expansion increased the total number of ALDH^hi cells (2.7‐fold), CD34⁺/CD133⁺ cells (2.8‐fold), and hematopoietic colony forming cells (7.7‐fold). Remarkably, injection of expanded progeny accelerated recovery of perfusion and improved limb usage in immunodeficient mice with femoral artery ligation‐induced limb ischemia. At 7 or 28 days post‐transplantation, mice transplanted with expanded ALDH^hi cells showed augmented endothelial cell proliferation and increased capillary density compared to controls. Expanded cells maintained pro‐angiogenic mRNA expression and secreted angiogenesis‐associated growth factors, chemokines, and matrix modifying proteins. Coculture with expanded cells augmented human microvascular endothelial cell survival and tubule formation under serum‐starved, growth factor‐reduced conditions. Expanded UCB‐derived ALDH^hi cells represent an alternative to autologous bone marrow as an accessible source of pro‐angiogenic hematopoietic progenitor cells for the refinement of vascular regeneration‐inductive therapies. Stem Cells Translational Medicine2017;6:1607–1619

Aldehyde dehydrogenase activity identifies a subpopulation of canine adipose-derived stem cells with higher differentiation potential

Adipose-derived stem cells (ADSCs) are abundant and readily obtained, and have been studied for their clinical applicability in regenerative medicine. Some surface antigens have been identified as markers of different ADSC subpopulations in mice and humans. However, it is unclear whether functionally distinct subpopulations exist in dogs. To address this issue, we evaluated aldehyde dehydrogenase (ALDH) activity—a widely used stem cell marker in mice and humans—by flow cytometry. Approximately 20% of bulk ADSCs showed high ALDH activity. Compared to cells with low activity (ALDH^Lo), the high-activity (ALDH^Hi) subpopulation exhibited a higher capacity for adipogenic and osteogenic differentiation. This is the first report of distinct ADSC subpopulations in dogs that differ in terms of adipogenic and osteogenic differentiation potential.

Mitochondrial aldehyde dehydrogenase-2 deficiency compromises therapeutic effect of ALDH bright cell on peripheral ischemia

The autologous ALDH bright (ALDH^br) cell therapy for ischemic injury is clinically safe and effective, while the underlying mechanism remains elusive. Here, we demonstrated that the glycolysis dominant metabolism of ALDH^br cells is permissive to restore blood flow in an ischemic hind limb model compared with bone marrow mononuclear cells (BMNCs). PCR array analysis showed overtly elevated Aldh2 expression of ALDH^br cells following hypoxic challenge. Notably, ALDH^br cells therapy induced blood flow recovery in this model was reduced in case of ALDH2 deficiency. Moreover, significantly reduced glycolysis flux and increased reactive oxygen species (ROS) levels were detected in ALDH^br cell from Aldh2-/- mice. Compromised effect on blood flow recovery was also noticed post transplanting the human ALDH^br cell from ALDH2 deficient patients (GA or AA genotypes) in this ischemic hindlimb mice model. Taken together, our findings illustrate the indispensable role of ALDH2 in maintaining glycolysis dominant metabolism of ALDH^br cell and advocate that patient's Aldh2 genotype is a prerequisite for the efficacy of ALDH^br cell therapy for peripheral ischemia.

Marrow-isolated adult multilineage inducible cells embedded within a biologically-inspired construct promote recovery in a mouse model of peripheral vascular disease

Peripheral vascular disease is one of the major vascular complications in individuals suffering from diabetes and in the elderly that is associated with significant burden in terms of morbidity and mortality. Stem cell therapy is being tested as an attractive alternative to traditional surgery to prevent and treat this disorder. The goal of this study was to enhance the protective and reparative potential of marrow-isolated adult multilineage inducible (MIAMI) cells by incorporating them within a bio-inspired construct (BIC) made of two layers of gelatin B electrospun nanofibers. We hypothesized that the BIC would enhance MIAMI cell survival and engraftment, ultimately leading to a better functional recovery of the injured limb in our mouse model of critical limb ischemia compared to MIAMI cells used alone. Our study demonstrated that MIAMI cell-seeded BIC resulted in a wide range of positive outcomes with an almost full recovery of blood flow in the injured limb, thereby limiting the extent of ischemia and necrosis. Functional recovery was also the greatest when MIAMI cells were combined with BICs, compared to MIAMI cells alone or BICs in the absence of cells. Histology was performed 28 days after grafting the animals to explore the mechanisms at the source of these positive outcomes. We observed that our critical limb ischemia model induces an extensive loss of muscular fibers that are replaced by intermuscular adipose tissue (IMAT), together with a highly disorganized vascular structure. The use of MIAMI cells-seeded BIC prevented IMAT infiltration with some clear evidence of muscular fibers regeneration.