Mesenchymal Stromal Cell Therapy in Ischemia/Reperfusion Injury

Low intensity ultrasound targeted microbubble destruction assists MSCs delivery and improves neural function in brain ischaemic rats

Background and purpose: The present study aimed to explore the feasibility and efficacy of the targeted non-invasive implantation of mesenchymal stromal cells (MSCs) by low-intensity ultrasound-targeted microbubble destruction (LI-UTMD) assisted blood-brain barrier (BBB) opening and its improvement on neurobehavioural outcomes in brain ischaemic rats.Methods: A transcranial irradiation of low-intensity ultrasound by diagnostic devices was performed, and lipid microbubbles (MBs) and MSCs were simultaneously infused. Then, the MSC transmigration from brain vessels to parenchyma was demonstrated, and MSCs were statistically analysed on days 1, 4, 7 and 14. Behavioural function was statistically analysed.Results: The extra-vascular leakage of lanthanum and EB was observed at the brain ischaemic area receiving ultrasound. MSCs were observed at the ultrasound irradiated brain hemisphere, and the number of MSCs in LI-UTMD assisted MSCs group was significantly higher than that in the MSCs group (p < .01). The attachment, traversing and trans-migration of MSCs across the BBB were recorded. Neuro-behavioural function was improved with this approach.Conclusions: The transcranial irradiation of low intensity ultrasound targeted MBs destruction on brain ischaemic rats might be a safe and efficient BBB opening approach to prompt the successful delivery of MSCs into the targeted area of brain ischaemia, and ameliorate neurological function.

Mesenchymal stem cell-derived extracellular vesicles improve the molecular phenotype of isolated rat lungs during ischemia/reperfusion injury

BACKGROUND

Lung ischemia/reperfusion (IR) injury contributes to the development of severe complications in patients undergoing transplantation. Mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs) exert beneficial actions comparable to those of MSCs without the risks of the cell-based strategy. This research investigated EV effects during IR injury in isolated rat lungs.

METHODS

An established model of 180-minutes ex vivo lung perfusion (EVLP) was used. At 60 minutes EVs (n = 5) or saline (n = 5) were administered. Parallel experiments used labeled EVs to determine EV biodistribution (n = 4). Perfusate samples were collected to perform gas analysis and to assess the concentration of nitric oxide (NO), hyaluronan (HA), inflammatory mediators, and leukocytes. Lung biopsies were taken at 180 minutes to evaluate HA, adenosine triphosphate (ATP), gene expression, and histology.

RESULTS

Compared with untreated lungs, EV-treated organs showed decreased vascular resistance and a rise of perfusate NO metabolites. EVs prevented the reduction in pulmonary ATP caused by IR. Increased medium-high-molecular-weight HA was detected in the perfusate and in the lung tissue of the IR + EV group. Significant differences in cell count on perfusate and tissue samples, together with induction of transcription and synthesis of chemokines, suggested EV-dependent modulation of leukocyte recruitment. EVs upregulated genes involved in the resolution of inflammation and oxidative stress. Biodistribution analysis showed that EVs were retained in the lung tissue and internalized within pulmonary cells.

CONCLUSIONS

This study shows multiple novel EV influences on pulmonary energetics, tissue integrity, and gene expression during IR. The use of cell-free therapies during EVLP could constitute a valuable strategy for reconditioning and repair of injured lungs before transplantation.

The Anti-Inflammatory, Anti-Oxidative, and Anti-Apoptotic Benefits of Stem Cells in Acute Ischemic Kidney Injury

Ischemia-reperfusion injury (IRI) plays a significant role in the pathogenesis of acute kidney injury (AKI). The complicated interaction between injured tubular cells, activated endothelial cells, and the immune system leads to oxidative stress and systemic inflammation, thereby exacerbating the apoptosis of renal tubular cells and impeding the process of tissue repair. Stem cell therapy is an innovative approach to ameliorate IRI due to its antioxidative, immunomodulatory, and anti-apoptotic properties. Therefore, it is crucial to understand the biological effects and mechanisms of action of stem cell therapy in the context of acute ischemic AKI to improve its therapeutic benefits. The recent finding that treatment with conditioned medium (CM) derived from stem cells is likely an effective alternative to conventional stem cell transplantation increases the potential for future therapeutic uses of stem cell therapy. In this review, we discuss the recent findings regarding stem cell-mediated cytoprotection, with a focus on the anti-inflammatory effects via suppression of oxidative stress and uncompromised immune responses following AKI. Stem cell-derived CM represents a favorable approach to stem cell-based therapy and may serve as a potential therapeutic strategy against acute ischemic AKI.

Silencing of SNHG12 Enhanced the Effectiveness of MSCs in Alleviating Ischemia/Reperfusion Injuries via the PI3K/AKT/mTOR Signaling Pathway

Previous studies have reported that the long non-coding RNA SNHG12 (lncRNA SNHG12) plays a critical role in regulating the function of mesenchymal stem cells (MSCs); however, the effect of lncRNA SNHG12 on MSCs in injured brain tissue has rarely been reported. We studied the effect and mechanism of lncRNA SNHG12-modified mesenchymal stem cells (MSCs) in treating brain injuries caused by ischemia/reperfusion (I/R). I/R treated rat brain microvascular endothelial cells (BMECs) were co-cultured with MSCs or I/R pretreated MSCs. Next, BMEC proliferation was detected by using CCK-8 and EdU assays, and cell apoptosis was determined by using flow cytometry and the Hoechst staining method. Autophagy of BMECs was determined using immunofluorescence and expression of associated pathway proteins were measured by western blotting. Moreover, BMEC proliferation, apoptosis, and autophagy were also determined after the BMECs had been co-cultured with shSNHG12-MSCs. In addition, a rat model of middle cerebral artery occlusion (MCAO) was used to further confirm the findings obtained with cells. I/R treatment significantly decreased the proliferation of BMECs, but increased their levels of SNHG12 expression, apoptosis, and autophagy. However, co-culturing of BMECs with MSCs markedly alleviated the reduction in BMEC proliferation and the increases in BMEC apoptosis and autophagy, as well as the phosphorylation of PI3K, AKT, and mTOR proteins in BMECs that had been induced by I/R. Furthermore, shSNHG12 remarkably enhanced the effects of MSCs. In addition, an injection MSCs reduced the infarct areas and rates of cell apoptosis in MACO rats, and reduced the phosphorylation of PI3K, AKT, and mTOR proteins. Moreover, shSNHG12 enhanced the ameliorative effect of MSCs in treating brain injuries in the MACO rats. In conclusion, silencing of SNHG12 enhanced the effects of MSCs in reducing apoptosis and autophagy of BMECs by activating the PI3K/AKT/mTOR signaling pathway.

Concise Review: Stem Cell Therapy for Stroke Patients: Are We There Yet?

Four decades of preclinical research demonstrating survival, functional integration, and behavioral effects of transplanted stem cells in experimental stroke models have provided ample scientific basis for initiating limited clinical trials of stem cell therapy in stroke patients. Although safety of the grafted cells has been overwhelmingly documented, efficacy has not been forthcoming. Two recently concluded stroke clinical trials on mesenchymal stem cells (MSCs) highlight the importance of strict adherence to the basic science findings of optimal transplant regimen of cell dose, timing, and route of delivery in enhancing the functional outcomes of cell therapy. Echoing the Stem Cell Therapeutics as an Emerging Paradigm for Stroke and Stroke Treatment Academic Industry Roundtable call for an NIH‐guided collaborative consortium of multiple laboratories in testing the safety and efficacy of stem cells and their derivatives, not just as stand‐alone but preferably in combination with approved thrombolytic or thrombectomy, may further increase the likelihood of successful fruition of translating stem cell therapy for stroke clinical application. The laboratory and clinical experience with MSC therapy for stroke may guide the future translational research on stem cell‐based regenerative medicine in neurological disorders. stem cells translational medicine2019;8:983&988

Potential role of stem cells in disease prevention based on a murine model of experimental necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is a devastating disease of newborns, and despite years of research, there is no known cure. The mortality rate of infants with NEC remains as high as 20%-30%. Babies who survive NEC frequently have long term complications including short gut syndrome, developmental delays and neurological sequelae. Unfortunately, despite much research over the past years, the precise pathogenesis of the disease is still not completely understood.

METHODS

Our laboratory has focused on identifying novel therapies to prevent the disease, including the use of stem cells (SC), heparin-binding epidermal growth factor-like growth factor (HB-EGF) and recently, stem cell derived-exosomes, a type of nanovesicle, to combat this illness.

RESULTS

We have outlined the major SC lines and data suggesting potential benefit as a curative or preventive approach for NEC as well as describing several new therapeutic strategies, including stem cell derived- exosomes and HB-EGF for decreasing the incidence and severity of this disease in rat models in our lab.

CONCLUSION

Overall, our lab has demonstrated that these different types of SC equivalently reduce the incidence and severity of NEC and equally preserve intestinal barrier function during NEC. We have previously demonstrated that AF-MSC can protect the intestines from intestinal injury and may therefore hold strong therapeutic potential for the prevention of NEC. Most recently, our work with stem cell derived-exosomes has shown them to be equivalent to their derived SC lines in decreasing the incidence of this disease.

From deceased to bioengineered graft: New frontiers in liver transplantation

In the worldwide context of graft shortage, several strategies have been explored to increase the number of grafts available for liver transplantation (LT). These include the use of marginal and living donors, split livers, and the improvement of marginal donor grafts (machine perfusion). However, recent advances in the understanding of liver organogenesis, stem cells, and matrix biology provide novel insights in tissue engineering. Today, the newest technologies and discoveries open the door to the development of new methods for organ implementation such as the recellularization of natural scaffolds, liver organoids, bio-printing, and tissue or generation of chimeric organs. These approaches might potentially to generate an unlimited source of grafts (allogenic or chimeric) which will be used in the near future for LT or as a temporary bridge toward LT. This qualitative review focuses on all methods of organ implementation and highlights the newest developments in tissue engineering and regenerative medicine.

Mesenchymal Stem Cells Ameliorate Hepatic Ischemia/Reperfusion Injury via Inhibition of Neutrophil Recruitment

Ischemia/reperfusion injury (IRI) remains a major problem in organ transplantation, which represents the main cause of graft dysfunction posttransplantation. Hepatic IRI is characterized by an excessive inflammatory response within the liver. Mesenchymal stem cells (MSCs) have been shown to be immunomodulatory cells and have the therapeutic action on IRI in several organs. However, the mechanism of regulatory effect of MSCs on IRI remains unclear. In the present study, we examined the impact of MSCs on hepatic inflammatory response such as neutrophil influx and liver damage in a rat model of 70% hepatic IRI. Treatment with MSCs protected rat against hepatic IRI, with significantly decreased serum levels of liver enzymes, attenuated hepatic neutrophil infiltration, reduced expression of apoptosis-associated proteins, and ameliorated liver pathological injury. MSCs also significantly enhanced the intracellular activation of p38 MAPK phosphorylation, which led to decreased expression of CXCR2 on the surface of neutrophils. In addition, MSCs significantly diminished neutrophil chemoattractant CXCL2 production by inhibiting NF-κB p65 phosphorylation in macrophages. These results demonstrate that MSCs significantly ameliorate hepatic IRI predominantly through its inhibitory effect on hepatic neutrophil migration and infiltration.

Regulation of microglial process elongation, a featured characteristic of microglial plasticity

Microglia, a type of glia within the brain characterized by a ramified morphology, are essential for removing neuronal debris and restricting the expansion of a lesion site. Upon moderate activation, they undergo a transformation in morphology inducing beneficial responses. However, upon strong stimulation, they mediate neuronal damage via production of pro-inflammatory cytokines. The inhibition of this cascade is considered an effective strategy for neuroinflammation-associated disorder therapy. During this pathological activation microglia also undergo a shortening of process length which contributes to the pathogenesis of such disorders. Thus, microglial plasticity should be considered to have two components: one is the production of inflammatory mediators, and the other is the dynamic changes in their processes. The former role has been well-documented in previous studies, while the latter one remains largely unknown. Recently, we and others have reported that the elongation of microglial process is associated with the transformation of microglia from a pro-inflammatory to an anti-inflammatory state, suggesting that the shortening of process length would make the microglia lose their ability to restrict pathological injury, while the elongation of microglial process would help attenuate neuroinflammation. Compared with the traditional anti-neuroinflammatory strategy, stimulating elongation of microglial process not only reduces the production of pro-inflammatory cytokines, but restores the ability of microglia to scan their surrounding environments, thus rendering their homeostasis regulation more effective. In this review, we provide a discussion of the factors that regulate microglial process elongation in vitro and in vivo, aiming to further drive the understanding of microglial process plasticity.

Mesenchymal stromal cell potency to treat acute kidney injury increased by ultrasound-activated interferon-γ/interleukin-10 axis

Mesenchymal stromal cell (MSC) therapies combined with renal pulsed focused ultrasound (pFUS) pretreatment increase MSC homing and improve cisplatin-induced acute kidney injury (AKI) better than MSC alone. However, mechanisms underlying improved outcomes remain unknown. We hypothesize pFUS up-regulates renal interferon-γ (IFNγ) and stimulates MSC to produce interleukin-10 (IL-10) after migrating to kidneys. To demonstrate initially, MSC cultured with IFNγ up-regulated IL-10. More MSC-derived IL-10 was detected in kidneys when IFNγ-stimulated MSC were infused and they improved AKI better than unstimulated MSC. Next, IFNγ-knockout mice with AKI received pFUS+MSC, but MSC-derived IL-10 expression and AKI were similar to using MSC alone. AKI in wild-type mice receiving pFUS and IL-10-deficient MSC was also unimproved compared to administering IL-10-deficient MSC alone. Indoleamine 2,3-dioxygenase (IDO), an anti-inflammatory enzyme up-regulated in MSC by IFNγ, was up-regulated during AKI, but was not further elevated in MSC from pFUS-treated kidneys, suggesting that IDO is not involved in improved AKI healing by pFUS+MSC. These data suggest IFNγ is up-regulated by pFUS and after i.v.-infused MSC home to pFUS-treated kidneys, IFNγ stimulates additional IL-10 production by MSC to improve AKI. Analogous mechanisms of ultrasound-treated tissue microenvironments stimulating therapeutic MSC may exist in other pathologies where adjuvant ultrasound techniques are successful.

KRT1 gene silencing ameliorates myocardial ischemia-reperfusion injury via the activation of the Notch signaling pathway in mouse models

Myocardial ischemia and reperfusion injury (MIRI) includes major drawbacks, such as excessive formation of free radicals and also overload of calcium, which lead to cell death, tissue scarring, and remodeling. The current study aims to explore whether KRT1 silencing may ameliorate MIRI via the Notch signaling pathway in mouse models. Myocardial tissues were used for the determination of the positive rate of KRT1 protein expression, apoptosis of myocardial cells, creatine kinase (CK) and lactate dehydrogenase (LDH) expression, expression of related biomarkers as well as myocardial infarction area. The transfected myocardial cells were treated with KRT1-siRNA, Jagged1, and DAPT (inhibitor of Notch-1 signaling pathway). The expression of KRT1, NICD, Hes1, Bcl-2, and Bax protein was detected. The MTT assay was applied for cell proliferation and flow cytometry was used for cell apoptosis. Mice with MIRI had a higher positive rate of KRT1 protein expression, apoptosis of myocardial cells, CK and LDH expression, myocardial infarction area, increased expression of MDA, NO, SDH, IL-1, IL-6, TNF-α, CRP, KRT1, Bax protein, CK, and LDH, and decreased expression of SOD, NICD, Hes1, and Bcl-2. The downregulation of KRT1 led to decreased expression of KRT1 and Bax protein, increased expression of NICD, Hes1, and Bcl-2, decreased cell apoptosis, and improved cell proliferation. The inhibition of the Notch signaling pathway leads to reduced expression of Bax, increased expression of NICD, Hes1, and Bcl 2, and also decreased cell apoptosis and increased cell proliferation. Our data conclude that KRT1 silencing is able to make MIRI better by activating the Notch signaling pathway in mice.

Stem/Stromal Cells for Treatment of Kidney Injuries With Focus on Preclinical Models

Within the last years, the use of stem cells (embryonic, induced pluripotent stem cells, or hematopoietic stem cells), Progenitor cells (e.g., endothelial progenitor cells), and most intensely mesenchymal stromal cells (MSC) has emerged as a promising cell-based therapy for several diseases including nephropathy. For patients with end-stage renal disease (ESRD), dialysis or finally organ transplantation are the only therapeutic modalities available. Since ESRD is associated with a high healthcare expenditure, MSC therapy represents an innovative approach. In a variety of preclinical and clinical studies, MSC have shown to exert renoprotective properties, mediated mainly by paracrine effects, immunomodulation, regulation of inflammation, secretion of several trophic factors, and possibly differentiation to renal precursors. However, studies are highly diverse; thus, knowledge is still limited regarding the exact mode of action, source of MSC in comparison to other stem cell types, administration route and dose, tracking of cells and documentation of therapeutic efficacy by new imaging techniques and tissue visualization. The aim of this review is to provide a summary of published studies of stem cell therapy in acute and chronic kidney injury, diabetic nephropathy, polycystic kidney disease, and kidney transplantation. Preclinical studies with allogeneic or xenogeneic cell therapy were first addressed, followed by a summary of clinical trials carried out with autologous or allogeneic hMSC. Studies were analyzed with respect to source of cell type, mechanism of action etc.

Treatment of experimental necrotizing enterocolitis with stem cell-derived exosomes

PURPOSE

Necrotizing enterocolitis (NEC) remains a devastating disease in premature infants. We previously showed that four stem cell (SC) types equivalently improve experimental NEC. Exosomes are intercellular nanovesicles containing RNA, miRNA, DNA, and protein. Because SC therapy faces challenges, our aim was to determine if the beneficial effects of SC are achievable with cell-free exosomes.

METHODS

Exosomes from four SC types were compared: (1) amniotic fluid-derived mesenchymal SC (AF-MSC); (2) bone marrow-derived MSC (BM-MSC); (3) amniotic fluid-derived neural SC (AF-NSC); and (4) neonatal enteric NSC (E-NSC). Rat pups exposed to NEC received a varying concentration of a single type of exosome with control pups receiving PBS only. Intestinal damage was graded histologically.

RESULTS

The incidence of NEC was 0% in unstressed pups and 60.7% in control pups subjected to NEC. Exosomes (4.0×10⁸) reduced NEC incidence to: AF-MSC 25.0%; BM-MSC 23.1%; AF-NSC 11.1%; E-NSC 27.3%. When administered at a concentration of at least 4.0×10⁸, all groups demonstrated a significant reduction in NEC compared to untreated pups. At this minimum concentration, there was no difference in treatment efficacy between exosomes and the SC from which they were derived.

CONCLUSION

Stem cell-derived exosomes reduce the incidence and severity of experimental NEC as effectively as the stem cells from which they are derived, supporting the potential for novel cell-free exosome therapy for NEC.

TYPE OF STUDY

Basic science.

Mesenchymal stem cells attenuate blood-brain barrier leakage after cerebral ischemia in mice

Background

Ischemic stroke induced matrixmetallo-proteinase-9 (MMP-9) upregulation, which increased blood-brain barrier permeability. Studies demonstrated that mesenchymal stem cell therapy protected blood-brain barrier disruption from several cerebrovascular diseases. However, the underlying mechanism was largely unknown. We therefore hypothesized that mesenchymal stem cells reduced blood-brain barrier destruction by inhibiting matrixmetallo-proteinase-9 and it was related to intercellular adhesion molecule-1 (ICAM-1).

Methods

Adult ICR male mice (n = 118) underwent 90-min middle cerebral artery occlusion and received 2 × 10⁵ mesenchymal stem cell transplantation. Neurobehavioral outcome, infarct volume, and blood-brain barrier permeability were measured after ischemia. The relationship between myeloperoxidase (MPO) activity and ICAM-1 release was further determined.

Results

We found that intracranial injection of mesenchymal stem cells reduced infarct volume and improved behavioral function in experimental stroke models (p < 0.05). IgG leakage, tight junction protein loss, and inflammatory cytokines IL-1β, IL-6, and TNF-α reduced in mesenchymal stem cell-treated mice compared to the control group following ischemia (p < 0.05). After transplantation, MMP-9 was decreased in protein and activity levels as compared with controls (p < 0.05). Furthermore, myeloperoxidase-positive cells and myeloperoxidase activity were decreased in mesenchymal stem cell-treated mice (p < 0.05).

Conclusion

The results showed that mesenchymal stem cell therapy attenuated blood-brain barrier disruption in mice after ischemia. Mesenchymal stem cells attenuated the upward trend of MMP-9 and potentially via downregulating ICAM-1 in endothelial cells. Adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK) pathway may influence MMP-9 expression of neutrophils and resident cells, and ICAM-1 acted as a key factor in the paracrine actions of mesenchymal stem cell.

Biomaterials for revascularization and immunomodulation after spinal cord injury

Spinal cord injury (SCI) causes immediate damage to the nervous tissue accompanied by loss of motor and sensory function. The limited self-repair competence of injured nervous tissue underscores the need for reparative interventions to recover function after SCI. The vasculature of the spinal cord plays a crucial role in SCI and repair. Ruptured and sheared blood vessels in the injury epicenter and blood vessels with a breached blood-spinal cord barrier (BSCB) in the surrounding tissue cause bleeding and inflammation, which contribute to the overall tissue damage. The insufficient formation of new functional vasculature in and near the injury impedes endogenous tissue repair and limits the prospect of repair approaches. Limiting the loss of blood vessels, stabilizing the BSCB, and promoting the formation of new blood vessels are therapeutic targets for spinal cord repair. Inflammation is an integral part of injury-mediated vascular damage, which has deleterious and reparative consequences. Inflammation and the formation of new blood vessels are intricately interwoven. Biomaterials can be effectively used for promoting and guiding blood vessel formation or modulating the inflammatory response after SCI, thereby governing the extent of damage and the success of reparative interventions. This review deals with the vasculature after SCI, the reciprocal interactions between inflammation and blood vessel formation, and the potential of biomaterials to support revascularization and immunomodulation in damaged spinal cord nervous tissue.

Genetic susceptibility to delayed graft function following kidney transplantation: a systematic review of the literature

Delayed graft function (DGF) is defined as the need for dialysis within 7 days following kidney transplantation (KTx). DGF is associated with increased costs, higher risk for acute rejection and decreased long-term graft function. Renal ischaemia/reperfusion (I/R) injury plays a major role in DGF occurrence. Single nucleotide polymorphisms (SNPs) in certain genes may aggravate kidney susceptibility to I/R injury, thereby worsening post-transplant outcomes. The present article proposes an extensive review of the literature about the putative impact of donor or recipient SNPs on DGF occurrence in kidney transplant recipients (KTRs). Among 30 relevant PubMed reports, 16 articles identified an association between 18 SNPs and DGF. These polymorphisms concern 14 different well-known genes and one not-yet-identified gene located on chromosome 18. They have been categorized into five groups according to the role of the corresponding proteins in I/R cascade: (i) oxidative stress, (ii) telomere shortening, (iii) chemokines, (iv) T-cell homeostasis and (v) metabolism of anti-inflammatory molecules. The remaining 14 studies failed to demonstrate any association between the studied SNPs and the occurrence of DGF. A better understanding of the genetic susceptibility to renal I/R injury may help prevent DGF and improve clinical outcomes in KTRs.

Neuroprotective Effects of Bioactive Compounds and MAPK Pathway Modulation in "Ischemia"-Stressed PC12 Pheochromocytoma Cells

This review surveys the efforts taken to investigate in vitro neuroprotective features of synthetic compounds and cell-released growth factors on PC12 clonal cell line temporarily deprived of oxygen and glucose followed by reoxygenation (OGD/R). These cells have been used previously to mimic some of the properties of in vivo brain ischemia-reperfusion-injury (IRI) and have been instrumental in identifying common mechanisms such as calcium overload, redox potential, lipid peroxidation and MAPKs modulation. In addition, they were useful for establishing the role of certain membrane penetrable cocktails of antioxidants as well as potential growth factors which may act in neuroprotection. Pharmacological mechanisms of neuroprotection addressing modulation of the MAPK cascade and increased redox potential by natural products, drugs and growth factors secreted by stem cells, in either undifferentiated or nerve growth factor-differentiated PC12 cells exposed to ischemic conditions are discussed for future prospects in neuroprotection studies.

Spheroid-cultured human umbilical cord-derived mesenchymal stem cells attenuate hepatic ischemia-reperfusion injury in rats

Mesenchymal stem cell (MSC) transplantation is a promising treatment for ischemia-reperfusion injury (IRI). However, its effects on hepatic IRI were not consistent in the previous studies. 3D spheroid-cultured MSCs enhance their production of trophic and anti-inflammatory properties, but their effects on hepatic IRI remain unclear. In this study, we compared the 3D spheroid-cultured human umbilical derived MSCs (3D UC-MSCs) with 2D-cultured UC-MSCs (2D UC-MSCs) on treating hepatic IRI. The RNA sequencing data showed that suppression of cell mitosis, response to hypoxia, inflammation, and angiogenesis were the top genetic changes in 3D UC-MSCs compared with 2D UC-MSCs. Although both pro-inflammatory and anti-inflammatory genes were upregulated in the 3D UC-MSCs, the mRNA and protein of an RNase (ZC3H12A), which turnovers the mRNA of pro-inflammatory genes at the post-transcript level, were significantly upregulated in 3D UC-MSCs. 3D UC-MSCs reduced the secretion of many chemokines and growth factors, but increased the secretion of vascular endothelial growth factor. Compared with the vehicle and 2D UC-MSCs, 3D UC-MSCs significantly reduced hepatic IRI in rats, based on the plasma aminotransferase levels, liver damage scores, neutrophil infiltration, hepatocyte apoptosis and expression of inflammation-associated genes. These findings suggest that 3D UC-MSCs therapy is a promising treatment for hepatic IRI.

Stem cell therapy in necrotizing enterocolitis: Current state and future directions

Stem cell therapy is a promising treatment modality for necrotizing enterocolitis. Among the many promising stem cells identified to date, it is likely that mesenchymal stem cells will be the most useful and practical cell-based therapies for this condition. Using acellular components such as exosomes or other paracrine mediators are promising as well. Multiple mechanisms are likely at play in the positive effects provided by these cells, and further research is underway to further elucidate these effects.

Where's the Leak in Vascular Barriers? A Review

Edema is typically presented as a secondary effect from injury, illness, disease, or medication, and its impact on patient wellness is nested within the underlying etiology. Therefore, it is often thought of more as an amplifier to current preexisting conditions. Edema, however, can be an independent risk factor for patient deterioration. Improper management of edema is costly not only to the patient, but also to treatment and care facilities, as mismanagement of edema results in increased lengths of hospital stay. Direct tissue trauma, disease, or inappropriate resuscitation and/or ventilation strategies result in edema formation through physical disruption and chemical messenger-based structural modifications of the microvascular barrier. Derangements in microvascular barrier function limit tissue oxygenation, nutrient flow, and cellular waste removal. Recent studies have sought to elucidate cellular signaling and structural alterations that result in vascular hyperpermeability in a variety of critical care conditions to include hemorrhage, burn trauma, and sepsis. These studies and many others have highlighted how multiple mechanisms alter paracellular and/or transcellular pathways promoting hyperpermeability. Roles for endothelial glycocalyx, extracellular matrix and basement membrane, vesiculo-vacuolar organelles, cellular junction and cytoskeletal proteins, and vascular pericytes have been described, demonstrating the complexity of microvascular barrier regulation. Understanding these basic mechanisms inside and out of microvessels aid in developing better treatment strategies to mitigate the harmful effects of excessive edema formation.

Mesenchymal stem cell conditioned medium alleviates oxidative stress injury induced by hydrogen peroxide via regulating miR143 and its target protein in hepatocytes

BACKGROUND

To investigate the impact of miRNA (microRNA) on hepatic oxidative stress damage under the human mesenchymal stem cell conditioned medium (MSC-CM) and explore the roles of the beta-1 adrenergic receptor (ADRB1) and hexokinase 2 (HK2) in this process.

METHODS

Hydrogen peroxide was used to induce oxidative stress injury in the human normal liver cell line L02. MSC-CM was separately prepared. After treatment with MSC-CM, the protective effects of MSC-CM on oxidative stress injury were assessed by changes in apoptosis, cell viability, cell cycle, and mitochondrial membrane potential. According to the microarray analysis, 19 disparately expressed miRNAs were selected for RT-PCR and miR143 identified as having significant differential expression in MSC-CM against oxidative stress injury. Subsequently, the predicted target proteins of miR143 were selected by bioinformatics software, and verified by western blot. In addition, down-regulation and up-regulation of miR143 expression and hydrogen peroxide induced hypoxia injury were carried out on L02 cells to study the role of miR143.

RESULTS

MSC-CM significantly attenuated H₂O₂ induced oxidative stress injury. The expression of miR143 was increased following oxidative stress injury whereas it decreased after MSC-CM treatment. The expression levels of HK2 and ADRB1 regulated by miR143 and Bcl-2 decreased under H₂O₂ treatment but were restored following MSC-CM treatment. However the expression levels of Bax and BMF increased after H₂O₂ injury and decreased after MSC-CM treatment. Moreover over-expression or down-regulation of miR143 aggravated or alleviated hepatocyte apoptosis respectively.

CONCLUSIONS

MSC-CM may alleviate H₂O₂ induced oxidative stress injury by inhibiting apoptosis and adjusting miRNA expression. Moreover down-regulation of miR143 protects L02 cells from apoptosis and initiates an adaptive process by adjusting the expression of HK2 ADRB1 and apoptosis-related proteins.

Clinical Translation of Mesenchymal Stromal Cell Therapies in Nephrology

Mesenchymal stromal cells have emerged as potential candidates for cell-based therapies to modulate the immune response in organ transplantation and repair tissues after acute or chronic injury. Preclinical studies have shown convincingly in rodent models that mesenchymal stromal cells can prolong solid organ graft survival and that they can induce immune tolerance, accelerate recovery from AKI, and promote functional improvement in chronic nephropathies. Multiple complex properties of the cells, including immunomodulatory, anti-inflammatory, and proregenerative effects, seem to contribute. The promising preclinical studies have encouraged investigators to explore the safety, tolerability, and efficacy of mesenchymal stromal cell-based therapy in pilot clinical trials, including those for bone marrow and solid organ transplantation, autoimmune diseases, and tissue and organ repair. Here, we review the available data on culture-expanded mesenchymal stromal cells tested in renal transplantation, AKI, and CKD. We also briefly discuss the relevant issues that must be addressed to ensure rigorous assessment of the safety and efficacy of mesenchymal stromal cell therapies to allow the translation of this research into the practice of clinical nephrology.

Administration of mesenchymal stromal cells before renal ischemia/reperfusion attenuates kidney injury and may modulate renal lipid metabolism in rats

Mesenchymal stromal cells (MSC) have been demonstrated to attenuate renal ischemia/reperfusion (I/R) damage in rodent models. The mechanisms of such nephro-protection remain largely unknown. Furthermore, the optimal timing of MSC administration has been poorly investigated. Here, we compare the impact of MSC injection 7 days before (MSCD - 7) versus 1 day after (MSCD + 1) renal I/R in rats. Control groups received equivalent volumes of saline at similar time-points (SD - 7 and SD + 1). Right nephrectomy was performed, and left renal ischemia lasted 45 min. After 48-hour reperfusion, we observed significantly improved renal function parameters, reduced apoptotic index and neutrophil/macrophage infiltration in kidney parenchyma, and lower expression of tubular damage markers and pro-inflammatory cytokines in MSCD - 7 in comparison to MSCD + 1 and saline control groups. Next, comparative high-throughput RNA sequencing of MSCD - 7 vs. SD - 7 non-ischemic right kidneys highlighted significant down-regulation of fatty acid biosynthesis and up-regulation of PPAR-α pathway. Such a preferential regulation towards lipid catabolism was associated with decreased levels of lipid peroxidation products, i.e. malondialdehyde and 4-hydroxy-2-nonenal, in MSCD - 7 versus SD - 7 ischemic kidneys. Our findings suggest that MSC pretreatment may exert protective effects against renal I/R by modulating lipid metabolism in rats.

Mesenchymal Stromal Cells Accelerate Epithelial Tight Junction Assembly via the AMP-Activated Protein Kinase Pathway, Independently of Liver Kinase B1

BACKGROUND

Mesenchymal stromal cells (MSC) are fibroblast-like multipotent cells capable of tissue-repair properties. Given the essentiality of tight junctions (TJ) in epithelial integrity, we hypothesized that MSC modulate TJ formation, via the AMP-activated kinase (AMPK) pathway. Liver kinase-β1 (LKB1) and Ca²⁺-calmodulin-dependent protein kinase kinase (CaMKK) represent the main kinases that activate AMPK.

METHODS

The in vitro Ca²⁺ switch from 5 μM to 1.8 mM was performed using epithelial Madin-Darby canine kidney (MDCK) cells cultured alone or cocultured with rat bone marrow-derived MSC or preexposed to MSC-conditioned medium. TJ assembly was measured by assessing ZO-1 relocation to cell-cell contacts. Experiments were conducted using MDCK stably expressing short-hairpin-RNA (shRNA) against LKB1 or luciferase (LUC, as controls). Compound STO-609 (50 μM) was used as CaMKK inhibitor.

RESULTS

Following Ca²⁺ switch, ZO-1 relocation and phosphorylation/activation of AMPK were significantly higher in MDCK/MSC compared to MDCK. No difference in AMPK phosphorylation was observed between LKB1-shRNA and Luc-shRNA MDCK following Ca²⁺ switch. Conversely, incubation with STO-609 prior to Ca²⁺ switch prevented AMPK phosphorylation and ZO-1 relocation. MSC-conditioned medium slightly but significantly increased AMPK activation and accelerated TJ-associated distribution of ZO-1 post Ca²⁺ switch in comparison to regular medium.

CONCLUSIONS

MSC modulate the assembly of epithelial TJ, via the CaMKK/AMPK pathway independently of LKB1.

Infusion of mesenchymal stromal cells after deceased liver transplantation: A phase I-II, open-label, clinical study

BACKGROUND & AIMS

Mesenchymal stromal cell (MSC) infusion could be a means to establish tolerance in solid organ recipients. The aim of this prospective, controlled, phase I study was to evaluate the feasibility, safety and tolerability of a single infusion of MSCs in liver transplant recipients.

METHODS

Ten liver transplant recipients under standard immunosuppression received 1.5-3×10⁶/kg third-party unrelated MSCs on postoperative day 3±2, and were prospectively compared to a control group of ten liver transplant recipients. As primary endpoints, MSC infusion toxicity was evaluated, and infectious and cancerous complications were prospectively recorded until month 12 in both groups. As secondary endpoints, rejection rate, month-6 graft biopsies, and peripheral blood lymphocyte phenotyping were compared. Progressive immunosuppression weaning was attempted from month 6 to 12 in MSC recipients.

RESULTS

No variation in vital parameters or cytokine release syndrome could be detected during and after MSC infusion. No patient developed impairment of organ functions (including liver graft function) following MSC infusion. No increased rate of opportunistic infection or de novo cancer was detected. As secondary endpoints, there was no difference in overall rates of rejection or graft survival. Month-6 biopsies did not demonstrate a difference between groups in the evaluation of rejection according to the Banff criteria, in the fibrosis score or in immunohistochemistry (including Tregs). No difference in peripheral blood lymphocyte typing could be detected. The immunosuppression weaning in MSC recipients was not successful.

CONCLUSIONS

No side effect of MSC infusion at day 3 after liver transplant could be detected, but this infusion did not promote tolerance. This study opens the way for further MSC or Treg-based trials in liver transplant recipients.

LAY SUMMARY

Therapy with mesenchymal stromal cells (MSCs) has been proposed as a means to improve results of solid organ transplantation. One of the potential MSC role could be to induce tolerance after liver transplantation, i.e. allowing the cessation of several medications with severe side effects. This study is the first-in-man use of MSC therapy in ten liver transplant recipients. This study did not show toxicity after a single MSC infusion but it was not sufficient to allow withdrawal of immunosuppression.

CLINICAL TRIAL REGISTRATION NUMBER

Eudract: # 2011-001822-81, ClinicalTrials.gov: # NCT 01429038.

Safety and Tolerance of Donor-Derived Mesenchymal Stem Cells in Pediatric Living-Donor Liver Transplantation: The MYSTEP1 Study

Background

Calcineurin inhibitors (CNI) have significantly improved patient and graft survival in pediatric liver transplantation (pLT). However, CNI toxicity leads to significant morbidity. Moreover, CNIs cannot prevent long-term allograft injury. Mesenchymal stem (stromal) cells (MSC) have potent immunomodulatory properties, which may promote allograft tolerance and ameliorate toxicity of high-dose CNI. The MYSTEP1 trial aims to investigate safety and feasibility of donor-derived MSCs in pLT.

Methods/Design

7 to 10 children undergoing living-donor pLT will be included in this open-label, prospective pilot trial. A dose of 1 × 10⁶ MSCs/kg body weight will be given at two time points: first by intraportal infusion intraoperatively and second by intravenous infusion on postoperative day 2. In addition, participants will receive standard immunosuppressive treatment. Our primary objective is to assess the safety of intraportal and intravenous MSC infusion in pLT recipients. Our secondary objective is to evaluate efficacy of MSC treatment as measured by the individual need for immunosuppression and the incidence of biopsy-proven acute rejection. We will perform detailed immune monitoring to investigate immunomodulatory effects.

Discussion

Our study will provide information on the safety of donor-derived MSCs in pediatric living-donor liver transplantation and their effect on immunomodulation and graft survival.

Mesenchymal stem cells sense mitochondria released from damaged cells as danger signals to activate their rescue properties

Mesenchymal stem cells (MSCs) protect tissues against cell death induced by ischemia/reperfusion insults. This therapeutic effect seems to be controlled by physiological cues released by the local microenvironment following injury. Recent lines of evidence indicate that MSC can communicate with their microenvironment through bidirectional exchanges of mitochondria. In particular, in vitro and in vivo studies report that MSCs rescue injured cells through delivery of their own mitochondria. However, the role of mitochondria conveyed from somatic cells to MSC remains unknown. By using a co-culture system consisting of MSC and distressed somatic cells such as cardiomyocytes or endothelial cells, we showed that mitochondria from suffering cells acted as danger-signaling organelles that triggered the anti-apoptotic function of MSC. We demonstrated that foreign somatic-derived mitochondria were engulfed and degraded by MSC, leading to induction of the cytoprotective enzyme heme oxygenase-1 (HO-1) and stimulation of mitochondrial biogenesis. As a result, the capacity of MSC to donate their mitochondria to injured cells to combat oxidative stress injury was enhanced. We found that similar mechanisms - activation of autophagy, HO-1 and mitochondrial biogenesis - occurred after exposure of MSC to exogenous mitochondria isolated from somatic cells, strengthening the idea that somatic mitochondria alert MSC of a danger situation and subsequently promote an adaptive reparative response. In addition, the cascade of events triggered by the transfer of somatic mitochondria into MSC was recapitulated in a model of myocardial infarction in vivo. Specifically, MSC engrafted into infarcted hearts of mice reduced damage, upregulated HO-1 and increased mitochondrial biogenesis, while inhibition of mitophagy or HO-1 failed to protect against cardiac apoptosis. In conclusion, our study reveals a new facet about the role of mitochondria released from dying cells as a key environmental cue that controls the cytoprotective function of MSC and opens novel avenues to improve the effectiveness of MSC-based therapies.

Recent Advances in Stem Cell-Based Therapeutics for Stroke

Regenerative medicine for central nervous system disorders, including stroke, has challenged the non-regenerative capacity of the brain. Among the many treatment strategies tailored towards repairing the injured brain, stem cell-based therapeutics have been demonstrated as safe and effective in animal models of stroke, and are being tested in limited clinical trials. We address here key lab-to-clinic translational research that relate to efficacy, safety, and mechanism of action underlying stem cell therapy. Recognizing the multi-pronged cell death processes associated with stroke that will likely require combination therapies, we next discuss potent drugs and novel technologies directed at improving the functional outcomes of stem cell-based therapeutics. We also examine discrepant transplant regimens between preclinical studies and clinical trials, as well as missing appropriate control arm (i.e., stroke subjects undergoing rehabilitation) on which to directly compare the therapeutic benefits of cell therapy. Finally, the bioethics of cell therapy is presented in order to assess its prevailing social status. With preliminary results now being reported from on-going clinical trials of stem cell therapy for stroke, a careful assessment of the true functional benefits of this novel treatment will further direct the future of regenerative medicine for neurological disorders.

Hypoxic Preconditioning Augments the Therapeutic Efficacy of Bone Marrow Stromal Cells in a Rat Ischemic Stroke Model

Transplantation of bone marrow stromal cells (BMSCs) is a promising therapy for ischemic stroke, but the poor oxygen environment in brain lesions limits the efficacy of cell-based therapies. Here, we tested whether hypoxic preconditioning (HP) could augment the efficacy of BMSC transplantation in a rat ischemic stroke model and investigated the underlying mechanism of the effect of HP. In vitro, BMSCs were divided into five passage (P0, P1, P2, P3, and P4) groups, and HP was applied to the groups by incubating the cells with 1% oxygen for 0, 4, 8, 12, and 24 h, respectively. We demonstrated that the expression of hypoxia-inducible factor-1α (HIF-1α) was increased in the HP-treated BMSCs, while their viability was unchanged. We also found that HP decreased the apoptosis of BMSCs during subsequent simulated ischemia-reperfusion (I/R) injury, especially in the 8-h HP group. In vivo, a rat transient focal cerebral ischemia model was established. These rats were administered normal cultured BMSCs (N-BMSCs), HP-treated BMSCs (H-BMSCs), or DMEM cell culture medium (control) at 24 h after the ischemic insult. Compared with the DMEM control group, the two BMSC-transplanted groups exhibited significantly improved functional recovery and reduced infarct volume, especially the H-BMSC group. Moreover, HP decreased neuronal apoptosis and enhanced the expression of BDNF and VEGF in the ischemic brain. Survival and differentiation of transplanted BMSCs were also increased by HP, and the quantity of engrafted BMSCs was significantly correlated with neurological function improvement. These results suggest that HP may enhance the therapeutic efficacy of BMSCs in an ischemic stroke model. The underlying mechanism likely involves the inhibition of caspase-3 activation and an increasing expression of HIF-1α, which promotes angiogenesis and neurogenesis and thereby reduces neuronal death and improves neurological function.

Nuclear Magnetic Resonance Metabolomic Profiling of Mouse Kidney, Urine and Serum Following Renal Ischemia/Reperfusion Injury

Background

Ischemia/reperfusion (I/R) is the most common cause of acute kidney injury (AKI). Its pathophysiology remains unclear. Metabolomics is dedicated to identify metabolites involved in (patho)physiological changes of integrated living systems. Here, we performed ¹H-Nuclear Magnetic Resonance metabolomics using urine, serum and kidney samples from a mouse model of renal I/R.

Methods

Renal 30-min ischemia was induced in 12-week-old C57BL/6J male mice by bilaterally clamping vascular pedicles, and was followed by 6, 24 or 48-hour reperfusion (n = 12/group). Sham-operated mice were used as controls. Statistical discriminant analyses, i.e. principal component analysis and orthogonal projections to latent structures (OPLS-DA), were performed on urine, serum and kidney lysates at each time-point. Multivariate receiver operating characteristic (ROC) curves were drawn, and sensitivity and specificity were calculated from ROC confusion matrix (with averaged class probabilities across 100 cross-validations).

Results

Urine OPLS-DA analysis showed a net separation between I/R and sham groups, with significant variations in levels of taurine, di- and tri-methylamine, creatine and lactate. Such changes were observed as early as 6 hours post reperfusion. Major metabolome modifications occurred at 24h post reperfusion. At this time-point, correlation coefficients between urine spectra and conventional AKI biomarkers, i.e. serum creatinine and urea levels, reached 0.94 and 0.95, respectively. The area under ROC curve at 6h, 24h and 48h post surgery were 0.73, 0.98 and 0.97, respectively. Similar discriminations were found in kidney samples, with changes in levels of lactate, fatty acids, choline and taurine. By contrast, serum OPLS-DA analysis could not discriminate sham-operated from I/R-exposed animals.

Conclusions

Our study demonstrates that renal I/R in mouse causes early and sustained metabolomic changes in urine and kidney composition. The most implicated pathways at 6h and 24h post reperfusion include gluconeogenesis, taurine and hypotaurine metabolism, whereas protein biosynthesis, glycolysis, and galactose and arginine metabolism are key at 48h post reperfusion.

Autologous Cells for Kidney Bioengineering

Worldwide, increasing numbers of patients are developing end-stage renal disease, and at present, the only treatment options are dialysis or kidney transplantation. Dialysis is associated with increased morbidity and mortality, poor life quality and high economic costs. Transplantation is by far the better option, but there are insufficient numbers of donor kidneys available. Therefore, there is an urgent need to explore alternative approaches. In this review, we discuss how this problem could potentially be addressed by using autologous cells and appropriate scaffolds to develop 'bioengineered' kidneys for transplantation. In particular, we will highlight recent breakthroughs in pluripotent stem cell biology that have led to the development of autologous renal progenitor cells capable of differentiating to all renal cell types and will discuss how these cells could be combined with appropriate scaffolds to develop a bioengineered kidney.

Extracardiac-Lodged Mesenchymal Stromal Cells Propel an Inflammatory Response against Myocardial Infarction via Paracrine Effects

Transplantation of stem cells, including mesenchymal stromal cells (MSCs), improves the recovery of cardiac function after myocardial infarction (MI) in experimental studies using animal models and in patients. However, the improvement of cardiac function following MSC transplantation remains suboptimal in both preclinical and clinical studies. Understanding the mechanism of cell therapy may improve its therapeutic outcomes, but the mode of action mediating stem cell promotion of cardiac repair is complex and not fully understood. Recent studies suggest that the immunomodulatory effects of MSCs on the macrophage M1/M2 subtype transition allow the transplanted stem cells to inhibit inflammation-induced injury and promote cardiac repair in acute MI. However, equally compelling evidence shows that there is poor survival and minimal graft persistence of transplanted MSCs within the infarcted heart tissues, negating the view that graft survival per se is required for the observed high rate and long duration of the transition from proinflammatory M1 to reparative M2 macrophages in the infarcted myocardium. Therefore, we raised a novel hypothesis that the therapeutic effects of MSC transplantation for acute MI depends not primarily on the grafted cells in infarct myocardium, but that MSCs migrating to and being lodged in the extracardiac organs, demonstrating good graft survival and persistence, may render the therapeutic effects in MI. More specifically, MSC transplantation promotes the transition from M1 to M2 in extracardiac organs, such as spleen and bone marrow, and therapeutic effects are conferred to the infarcted myocardium via paracrine effects. In MSC transplantation, the conversion from proinflammatory M1 to anti-inflammatory M2 monocytes may occur remotely from the heart and may serve as one of the major pathways in regulating the dual effects of inflammation. This hypothesis, if proven valid, may represent an important new mechanism of action to be considered for the future of MSC transplantation in the treatment of MI.

Stem cell death and survival in heart regeneration and repair

Cardiovascular diseases are major causes of mortality and morbidity. Cardiomyocyte apoptosis disrupts cardiac function and leads to cardiac decompensation and terminal heart failure. Delineating the regulatory signaling pathways that orchestrate cell survival in the heart has significant therapeutic implications. Cardiac tissue has limited capacity to regenerate and repair. Stem cell therapy is a successful approach for repairing and regenerating ischemic cardiac tissue; however, transplanted cells display very high death percentage, a problem that affects success of tissue regeneration. Stem cells display multipotency or pluripotency and undergo self-renewal, however these events are negatively influenced by upregulation of cell death machinery that induces the significant decrease in survival and differentiation signals upon cardiovascular injury. While efforts to identify cell types and molecular pathways that promote cardiac tissue regeneration have been productive, studies that focus on blocking the extensive cell death after transplantation are limited. The control of cell death includes multiple networks rather than one crucial pathway, which underlies the challenge of identifying the interaction between various cellular and biochemical components. This review is aimed at exploiting the molecular mechanisms by which stem cells resist death signals to develop into mature and healthy cardiac cells. Specifically, we focus on a number of factors that control death and survival of stem cells upon transplantation and ultimately affect cardiac regeneration. We also discuss potential survival enhancing strategies and how they could be meaningful in the design of targeted therapies that improve cardiac function.

Insight into SUCNR1 (GPR91) structure and function

SUCNR1 (or GPR91) belongs to the family of G protein-coupled receptors (GPCR), which represents the largest group of membrane proteins in human genome. The majority of marketed drugs targets GPCRs, directly or indirectly. SUCNR1 has been classified as an orphan receptor until a landmark study paired it with succinate, a citric acid cycle intermediate. According to the current paradigm, succinate triggers SUCNR1 signaling pathways to indicate local stress that may affect cellular metabolism. SUCNR1 implication has been well documented in renin-induced hypertension, ischemia/reperfusion injury, inflammation and immune response, platelet aggregation and retinal angiogenesis. In addition, the SUCNR1-induced increase of blood pressure may contribute to diabetic nephropathy or cardiac hypertrophy. The understanding of SUCNR1 activation, signaling pathways and functions remains largely elusive, which calls for deeper investigations. SUCNR1 shows a high potential as an innovative drug target and is probably an important regulator of basic physiology. In order to achieve the full characterization of this receptor, more specific pharmacological tools such as small-molecules modulators will represent an important asset. In this review, we describe the structural features of SUCNR1, its current ligands and putative binding pocket. We give an exhaustive overview of the known and hypothetical signaling partners of the receptor in different in vitro and in vivo systems. The link between SUCNR1 intracellular pathways and its pathophysiological roles are also extensively discussed.