Stem Cell Aging Research Articles

Donor cord blood aging accelerates in recipients after transplantation

Cord blood stem cell transplantation is an important alternative for patients needing hematopoietic stem cell transplantation. However, it is unclear how cord blood cells, which are 0 years old, age in the recipient’s body after allogeneic transplantation. We performed DNA methylation (DNAm) age analysis to measure the age of cells using post-transplant peripheral blood in 50 cases of cord blood transplantation. The median chronological age (the time elapsed from the date of the cord blood transplant to the day the sample was taken for DNAm analysis) of donor cells was 4.0 years (0.2–15.0 years), while the median DNAm age was 10.0 years (1.3–30.3 years), and the ratio of DNAm age to chronological age (AgeAccel) was 2.7 (1.2–8.2). When comparing the mean values of AgeAccel in cord blood transplant cases and controls, the values were significantly higher in cord blood transplant cases. The characteristics of patients and transplant procedures were not associated with AgeAccel in this analysis, nor were they associated with the development of graft-versus-host disease. However, this analysis revealed that transplanting 0-year-old cord blood into a recipient resulted in cells aging more than twice as quickly as the elapsed time. The results shed light on the importance of the mismatch between cord blood stem cells and donor environmental factors in stem cell aging.

Wnt Signaling in the Gastrointestinal Tract in Health and Disease

Wnt signaling involves multiple pathways that contribute to organ development, cell fate, inflammation, and normal stem cell renewal and maintenance. Although the homeostasis of stem cells in the gastrointestinal (GI) tract highly depends on the Wnt signaling pathway, this regulation is impaired in cancers and in aging. Overactive (uncontrolled) Wnt signaling can induce GI epithelial cancers such as colon and gastric cancer. Overactive Wnt signaling can also contribute to the initiation and progression of gastrointestinal stromal tumor, which is the most common human sarcoma occurring in the walls of the digestive organs, mainly the stomach and small intestine. Wnt expression is positively associated not only with the progression of oncogenesis but also with resistance to chemotherapy and radiotherapy. Of note, recent reports show that decreased Wnt signaling is related to intestinal stem cell aging and that overactivated Wnt signaling leads to gastric pacemaker stem cell aging in tunica muscularis. These findings indicate that Wnt signaling has different crucial aspects of cell fate determination with age in GI tunica mucosa and muscularis. In this review, we summarize the most recent advances in our understanding of Wnt signaling pathways and their role in regulating key aspects during development, carcinogenesis, inflammation, and aging, with the ultimate goal of identifying novel therapies.

A passage-dependent network for estimating the in vitro senescence of mesenchymal stromal/stem cells using microarray, bulk and single cell RNA sequencing.

Long-term in vitro culture of human mesenchymal stem cells (MSCs) leads to cell lifespan shortening and growth stagnation due to cell senescence. Here, using sequencing data generated in the public domain, we have established a specific regulatory network of "transcription factor (TF)-microRNA (miRNA)-Target" to provide key molecules for evaluating the passage-dependent replicative senescence of mesenchymal stem cells for the quality control and status evaluation of mesenchymal stem cells prepared by different procedures. Short time-series expression miner (STEM) analysis was performed on the RNA-seq and miRNA-seq databases of mesenchymal stem cells from various passages to reveal the dynamic passage-related changes of miRNAs and mRNAs. Potential miRNA targets were predicted using seven miRNA target prediction databases, including TargetScan, miRTarBase, miRDB, miRWalk, RNA22, RNAinter, and TargetMiner. Then use the TransmiR v2.0 database to obtain experimental-supported transcription factor for regulating the selected miRNA. More than ten sequencing data related to mesenchymal stem cells or mesenchymal stem cells reprogramming were used to validate key miRNAs and mRNAs. And gene set variation analysis (GSVA) was performed to calculate the passage-dependent signature. The results showed that during the passage of mesenchymal stem cells, a total of 29 miRNAs were gradually downregulated and 210 mRNA were gradually upregulated. Enrichment analysis showed that the 29 miRNAs acted as multipotent regulatory factors of stem cells and participated in a variety of signaling pathways, including TGF-beta, HIPPO and oxygen related pathways. 210 mRNAs were involved in cell senescence. According to the target prediction results, the targets of these key miRNAs and mRNAs intersect to form a regulatory network of "TF-miRNA-Target" related to replicative senescence of cultured mesenchymal stem cells, across 35 transcription factor, 7 miRNAs (has-mir-454-3p, has-mir-196b-5p, has-mir-130b-5p, has-mir-1271-5p, has-let-7i-5p, has-let-7a-5p, and has-let-7b-5p) and 7 predicted targets (PRUNE2, DIO2, CPA4, PRKAA2, DMD, DDAH1, and GATA6). This network was further validated by analyzing datasets from a variety of mesenchymal stem cells subculture and lineage reprogramming studies, as well as qPCR analysis of early passages mesenchymal stem cells versus mesenchymal stem cells with senescence morphologies (SA-β-Gal+). The "TF-miRNA-Target" regulatory network constructed in this study reveals the functional mechanism of miRNAs in promoting the senescence of MSCs during in vitro expansion and provides indicators for monitoring the quality of functional mesenchymal stem cells during the preparation and clinical application.

Extracellularly Detectable Electrochemical Signals of Living Cells Originate from Metabolic Reactions.

Direct detection of cellular redox signals has shown immense potential as a novel living cell analysis tool. However, the origin of such signals remains unknown, which hinders the widespread use of electrochemical methods for cellular research. In this study, the authors found that intracellular metabolic pathways that generate adenosine triphosphate (ATP) are the main contributors to extracellularly detectable electrochemical signals. This is achieved through the detection of living cells (4,706 cells/chip, linearity: 0.985) at a linear range of 7,466-48,866. Based on this discovery, the authors demonstrated that the cellular signals detected by differential pulse voltammetry (DPV) can be rapidly amplified with a developed medium containing metabolic activator cocktails (MACs). The DPV approach combined with MAC treatment shows a remarkable performance to detect the effects of the anticancer drug CPI-613 on cervical cancer both at a low drug concentration (2µm) and an extremely short treatment time (1hour). Furthermore, the senescence of mesenchymal stem cells could also be sensitively quantified using the DPV+MAC method even at a low passage number (P6). Collectively, their findings unveiled the origin of redox signals in living cells, which has important implications for the characterization of various cellular functions and behaviors using electrochemical approaches.

Three-dimensional chromatin re-organization during muscle stem cell aging.

Age-related skeletal muscle atrophy or sarcopenia is a significant societal problem that is becoming amplified as the world's population continues to increase. The regeneration of damaged skeletal muscle is mediated by muscle stem cells, but in old age muscle stem cells become functionally attenuated. The molecular mechanisms that govern muscle stem cell aging encompass changes across multiple regulatory layers and are integrated by the three-dimensional organization of the genome. To quantitatively understand how hierarchical chromatin architecture changes during muscle stem cell aging, we generated 3D chromatin conformation maps (Hi-C) and integrated these datasets with multi-omic (chromatin accessibility and transcriptome) profiles from bulk populations and single cells. We observed that muscle stem cells display static behavior at global scales of chromatin organization during aging and extensive rewiring of local contacts at finer scales that were associated with variations in transcription factor binding and aberrant gene expression. These data provide insights into genome topology as a regulator of molecular function in stem cell aging.

L-Carnitine Reduced Cellular Aging of Bone Marrow Resident C-Kit+ Hematopoietic Progenitor Cells Through Telomere Dependent Pathways.

Increased oxygen species levels can induce mitochondrial DNA damage and chromosomal aberrations and cause defective stem cell differentiation, leading finally to senescence of stem cells. In recent years, several studies have reported that antioxidants can improve stem cell survival and subsequently affect the potency and differentiation of these cells. Finding factors, which reduce the senescence tendency of stem cells upon expansion, has great potential for cellular therapy in regenerative medicine. This study aimed to evaluate the effects of L-carnitine (LC) on the aging of C-kit+ hematopoietic progenitor cells (HPCs) via examining the expression of some signaling pathway components. For this purpose, bone marrow resident C-kit+ HPCs were enriched by the magnetic-activated cell sorting (MACS) method and were characterized using flow cytometry as well as immunocytochemistry. Cells were treated with LC, and at the end of the treatment period, the cells were subjected to the realtime PCR technique along with a western blotting assay for measurement of the telomere length and assessment of protein expression, respectively. The results showed that 0.2 mM LC caused the elongation of the telomere length and increased the TERT protein expression. In addition, a significant increase was observed in the protein expression of p38, p53, BCL2, and p16 as key components of the telomere-dependent pathway. It can be concluded that LC can increase the telomere length as an effective factor in increasing the cell survival and maintenance of the C-kit+ HPCs via these signaling pathway components.

Mitochondria as biological targets for stem cell and organismal senescence

Organismal aging is impacted by the deterioration of tissue turnover mechanisms due, in part, to the decline in stem cell function. This decline can be related to mitochondrial dysfunction and underlying energetic defects that, in concert, help drive biological aging. Thus, mitochondria have been described as a potential interventional target to hinder the loss of stem cell robustness, and subsequently, decrease tissue turnover decline and age-associated pathologies. In this review, we focused our analysis on the most recent literature on mitochondria and stem cell aging and discuss the potential benefits of targeting mitochondria in preventing stem cell dysfunction and thus influencing aging.

Low oxygen tension affects proliferation and senescence of caprine bone marrow mesenchymal stem cells in in vitro culture condition

The culture system of bone marrow mesenchymal stem cells (bmMSCs) in the normoxic environment does not imitate the hypoxic milieu of typical biological conditions, thus hypoxic culture conditions may improve survival, and growth attributes of bmMSCs during in vitro culture. Therefore, the present study was conducted at ICAR-CIRG, Makhdoom during year 2020 with the objective to investigate the changes in biological characteristics of cultured caprine bmMSCs (cbmMSCs) including the cellular senescence, survival, rate of proliferation, immuno-phenotypic characteristics, and gene expression pattern in a normal and hypoxic microenvironment condition. For this, cbmMSCs isolated from bone marrow collected from iliac crest were enriched and grown under either hypoxic (5% O2) or normoxic (20% O2) conditions. Thereafter, the outcome of hypoxic (5% O2) culturing of cbmMSCs on growth characteristics, proliferation, senescence, and expression profile of important stemness-associated (OCT-4) and oxidative stress [glutathione peroxidase (GPx1) and copper-zinc superoxide dismutase (CuZnSOD)] marker genes was evaluated. cbmMSCs cultivated in hypoxic conditions showed higher proliferation and decreased population doubling time and senescence-associated β-GAL expression; however, the immune-phenotypic characteristics of the cells remain unchanged. Furthermore, the culture of cbmMSCs in hypoxia increased the expression of OCT-4, GPx1, and CuZnSOD, compared with the cells grown under normoxia. In conclusion, the culture condition with low O2 level improved the growth characteristics and proliferation of cbmMSCs. These outcomes would provide information to formulate strategies for the collection and efficient in vitro expansion of bmMSCs from goats and other farm animals before their downstream applications.

Fecal microbiota transplantation from young mice rejuvenates aged hematopoietic stem cells by suppressing inflammation

AbstractHematopoietic stem cell (HSC) aging is accompanied by hematopoietic reconstitution dysfunction, including loss of regenerative and engraftment ability, myeloid differentiation bias, and elevated risks of hematopoietic malignancies. Gut microbiota, a key regulator of host health and immunity, has recently been reported to affect hematopoiesis. However, there is currently limited empirical evidence explaining the direct impact of gut microbiome on aging hematopoiesis. In this study, we performed fecal microbiota transplantation (FMT) from young mice to aged mice and observed a significant increment in lymphoid differentiation and decrease in myeloid differentiation in aged recipient mice. Furthermore, FMT from young mice rejuvenated aged HSCs with enhanced short-term and long-term hematopoietic repopulation capacity. Mechanistically, single-cell RNA sequencing deciphered that FMT from young mice mitigated inflammatory signals, upregulated the FoxO signaling pathway, and promoted lymphoid differentiation of HSCs during aging. Finally, integrated microbiome and metabolome analyses uncovered that FMT reshaped gut microbiota composition and metabolite landscape, and Lachnospiraceae and tryptophan-associated metabolites promoted the recovery of hematopoiesis and rejuvenated aged HSCs. Together, our study highlights the paramount importance of the gut microbiota in HSC aging and provides insights into therapeutic strategies for aging-related hematologic disorders.

Abstract A013: Sex-dependent hematopoietic stem cell aging and leukemogenic potential

Abstract Aging of hematopoietic stem cells (HSCs) is linked to various blood disorders. But how HSC aging and sex co-influence leukemogenesis is poorly understood. By examining HSC aging in young, aging (75% lifespan) and longevity (110% lifespan) mice in males vs females, we have discovered that aging males have a significantly higher HSC frequency than females, and that male HSC aging is characterized by an expansion of Lin-CD150+SP HSCs and a decrease of Lin-CD150-SP HSCs, whereas females show opposite HSC changes towards aging and longevity. In line with HSC changes, aging males exhibit an increase of white blood cell counts that is primarily driven by increased myeloid cells, whereas aging females shows a decrease of white blood cell counts that is primarily driven by reduced lymphoid cells. To understand leukemogenic potential of aging HSCs in the true setting of organismal aging, we generated the first aging mouse model of chronic myeloid leukemia (CML) induced by BCR-ABL1 (Oncogene, 2021, 40: 3152-3163). We found that aging male HSCs are significantly more susceptible to BCR-ABL1 transformation and CML induction in aging male mice than aging female HSCs for CML induction in aging female mice. However, in the absence of oncogenic translocation genes, longevity female but not male mice rapidly develop B/myeloid mixed phenotype acute leukemia, a disease of HSC origin, in primary bone marrow transplantation recipients. Leukemias in our aging mouse models phenocopy those of humans in that the incidence of myeloid leukemia is higher in aging men than in women overall, but longevity women have a higher incidence of myeloid leukemia. Using single cell RNA sequencing analysis of HSCs, we found distinct cell clustering patterns and signaling pathways of aging HSCs between male and female mice. The top pathways seen in male HSC aging involve TGFβ and TNFα signaling that have been linked to poor drug response and persistence of human CML stem cells, while those for female HSC aging involve IFNα/γ signaling pathways that have been associated with good drug response of human CML stem cells. Together, our results demonstrate sex-dependent HSC aging and leukemogenic potential and that molecular changes in aging HSCs can inform drug response of leukemia stem cells. Our findings provide novel insight into the etiology of leukemia in males vs females and suggest potential benefit to use sex-based prevention and therapeutic strategies for leukemia in men vs women. Citation Format: WenYong Chen. Sex-dependent hematopoietic stem cell aging and leukemogenic potential [abstract]. In: Proceedings of the AACR Special Conference: Aging and Cancer; 2022 Nov 17-20; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_1):Abstract nr A013.

Inhibitory effects and molecular mechanisms of ginsenoside Rg1 on the senescence of hematopoietic stem cells.

Hematopoietic stem cells (HSCs) produce all blood cell lineages and maintain life-long hematopoiesis. However, the self-renewal ability and differentiation capacity of HSCs reduces with age. The senescence of HSCs can lead to the imbalance of hematopoietic homeostasis and immune disorder and induce a variety of age-related diseases. Recent studies have shown that therapeutic interventions targeting the senescence of HSCs may prevent disease progression. Ginsenoside Rg1 (Rg1), extracted from roots or stems of ginseng, has beneficial antiaging activities. It has been reported that Rg1 can inhibit the senescence of HSCs. Here, we reviewed recent advances of Rg1 in inhibiting the senescence of HSCs and discussed related molecular mechanisms. Bioinformatics and network databases have been widely applied to drug discoveries. Here, we predicted potential antiaging targets of Rg1 explored by bioinformatic methods, which may help discover new targets of Rg1 and provide novel strategies for delaying the aging process of HSCs.

Compromised osteogenic effect of exosomes internalized by senescent bone marrow stem cells via endocytoses involving clathrin, macropinocytosis and caveolae.

Stem cell senescence leads to progressive functional declines and disrupts the physiological homeostasis of bone environment. Stem cell-derived exosomes are emerging as promising therapeutical approaches to treat diverse aging-related osseous diseases. Herein, a previously reported osteoinductive exosome (OI-exo) was applied as a therapeutic agent for bone repair in aging individuals and its internalization mechanisms in senescent bone marrow stem cells (BMSCs) were explored. The results demonstrated that OI-exos derived from young BMSCs could partially rescue the proliferation, osteogenic differentiation and alleviate aging phenotypes in vitro. OI-exo-delivered hierarchical mesoporous bioactive glass (MBG) scaffold effectively promote in vivo bone formation in aging rat cranial defect model. However, the osteogenic effects of OI-exo both in vitro and in vivo were compromised in senescent individuals and for aging BMSCs compared to younger ones. This study revealed that non-senescent BMSCs internalized exosomes exclusively via clathrin-mediated endocytosis, while senescent BMSCs additionally evoked macropinocytosis and caveolae-mediated endocytosis to mediate the internalization of exosomes. The alteration of endocytic manner of senescent BMSCs and the involvement of macropinocytosis might be responsible for the compromised effects of therapeutical exosomes. The phenomena discovered in this study could also be extended to other scenarios where drugs or treatments exerted compromised effects in aging individuals. The influence of endocytic manner, avoidance of macropinocytosis-related negative effects should be taken into considerations in future therapeutic design for aging populations.

Anti-aging biomaterial sturgeon chondroitin sulfate upregulating anti-oxidant and SIRT-1/c-fos gene expression to reprogram stem cell senescence and prolong longevity.

Aging involves tissue and cell potential dysfunction characterized by stem cell senescence and extracellular matrix microenvironment (ECM) alteration. Chondroitin sulfate (CS), found in the ECM of normal cells and tissues, aids in maintaining tissue homeostasis. Here, CS-derived biomaterial (CSDB) from sturgeon is extracted to investigate its antiaging effect in senescence-accelerated mouse prone-8 (SAMP8) mice and elucidate the underlying mechanism of its action. Although CSDB has been widely extracted from different sources and used as a scaffold, hydrogel, or drug carrier for the treatment of various pathological diseases, CSDB has not yet been used as a biomaterial for the amelioration of senescence and aging features. In this study, the extracted sturgeon CSDB showed a low molecular weight and comprised 59% 4-sulfated CS and 23% 6-sulfated CS. In an in vitro study, sturgeon CSDB promoted cell proliferation and reduced oxidative stress to inhibit stem cell senescence. In an ex vivo study, after oral CSDB treatment of SAMP8 mice, the stem cells were extracted to analyze the p16Ink4a and p19Arf gene-related pathways, which were inhibited and then SIRT-1 gene expression was upregulated to reprogram stem cells from a senescence state for retarding aging. In an in vivo study, CSDB also restored the aging-phenotype-related bone mineral density and skin morphology to prolong longevity. Thus, sturgeon CSDB may be useful for prolonging healthy longevity as an anti-aging drug.

C-Phycocyanin Ameliorates the Senescence of Mesenchymal Stem Cells through ZDHHC5-Mediated Autophagy via PI3K/AKT/mTOR Pathway.

The senescence of mesenchymal stem cells (MSCs) impairs their regenerative capacity to maintain tissue homeostasis. Numerous studies are focusing on the interventions and mechanisms to attenuate the senescence of MSCs. C-phycocyanin (C-PC) is reported to have multiple functions such as antitumor, antioxidation, anti-inflammation and anti-aging roles, but there is little research about the effects of C-PC on the senescence of MSCs. Here we investigated the roles and mechanism of C-PC on MSCs senescence. In vitro results showed that C-PC could reduce senescence, enhance proliferation, promote the adipogenic and osteogenic differentiation in senescent MSCs induced by oxidative stress. In vivo D-Galactose (D-Gal) induced rats aging models showed C-PC also increased the viability and differentiation of intrinsic senescent bone marrow derived MSCs (BMSCs). Furthermore, C-PC also decreased the levels of oxidative stress markers ROS or MDA, elevated the SOD activity, and increased the anti-inflammatory factors. Proteomic chip analysis showed that C-PC interacted with ZDHHC5, and their interaction was verified by pull down assay. Overexpression of ZDHHC5 aggravated the senescence of MSCs and greatly lessened the beneficial effects of C-PC on senescence. In addition, we found ZDHHC5 regulated autophagy by altering LC3, Beclin1 and PI3K/AKT/mTOR pathway. In summary, our data indicated that C-PC ameliorates the senescence of MSCs through zinc finger Asp-His-His-Cys (DHHC) domain-containing protein 5 (ZDHHC5) mediated autophagy via PI3K/AKT/mTOR pathway. The present study uncovered the key role of autophagy in MSCs senescence and PI3K/AKT/mTOR pathway may be a potential target for anti-senescence studies of MSCs.

Treating peripheral nerve injury-induced spinal cord degeneration and neuropathic pain with peripherally administrated stem cells.

Treating peripheral nerve injury-induced spinal cord degeneration and neuropathic pain with peripherally administrated stem cells.

Methods to assess radiation-induced fibrosis in mice.

Therapeutic radiation is used to treat a variety of cancers in organs and tissues throughout the body. Exposure of benign normal tissue to radiation can result in late injury in a subset of patients. Radiation induced fibrosis is one chronic, progressive late toxicity of radiation exposure that can occur in many organs and tissues, including skin and lung. Radiation fibrosis has few effective treatments. The process of radiation fibrosis is known to involve many mitogenic and immunomodulatory cytokines, inflammatory programs, and processes such as stem cell senescence. Murine models of radiation fibrosis can be used to evaluate agents that may prevent, mitigate, or treat this injury. Here, we provide a detailed protocol for the development of radiation induced dermal and pulmonary fibrosis in mice and describe protocols for the measurement of this injury in treated tissue.

Mitochondrial DNA Mutations and Ageing.

Mitochondria are subcellular organelles present in most eukaryotic cells which play a significant role in numerous aspects of cell biology. These include carbohydrate and fatty acid metabolism to generate cellular energy through oxidative phosphorylation, apoptosis, cell signalling, haem biosynthesis and reactive oxygen species production. Mitochondrial dysfunction is a feature of many human ageing tissues, and since the discovery that mitochondrial DNA mutations were a major underlying cause of changes in oxidative phosphorylation capacity, it has been proposed that they have a role in human ageing. However, there is still much debate on whether mitochondrial DNA mutations play a causal role in ageing or are simply a consequence of the ageing process. This chapter describes the structure of mammalian mitochondria, and the unique features of mitochondrial genetics, and reviews the current evidence surrounding the role of mitochondrial DNA mutations in the ageing process. It then focusses on more recent discoveries regarding the role of mitochondrial dysfunction in stem cell ageing and age-related inflammation.

Effect of spermidine on radiation-induced long-term bone marrow cell injury.

Spermidine, a natural polyamine, possesses anti-oxidant, autophagy-regulation, and anti-aging properties. Elevated levels of oxidative stress, which was mediated the senescence of hematopoietic stem cells (HSCs) induced by radiation exposure, may further contribute to long-term myelosuppression. Therefore, this study investigated the protective effect of spermidine on the long-term damage of the hematopoietic system caused by radiation exposure. In vitro experiments, bone marrow mononuclear cells (BMMNCs) of C57BL/6 mice were isolated and incubated with 5mM spermidine for 30min, then irradiated by 2Gy X ray. The survival rate, proliferation, and differentiation ability of BMMNCs were detected. In vivo experiment, mice received 4Gy total body irradiation (TBI), 3mM spermidine were administered in the drinking water every day for 14days prior to irradiation and then continued for 30days after irradiation. Peripheral blood, bone marrow cell typing, level of reactive oxygen species (ROS), colony-forming ability of HSC, and transplantation-reconstitution capability were detected. In vitro experiments, spermidine significantly improved the survival rate of BMMNCs as well as the proliferation and differentiation ability of HSCs exposure to ionizing radiation (IR). In vivo, spermidine reduced levels of ROS in HSCs; spermidine attenuated long-term myeloid differentiation deviation induced by TBI. Spermidine promoted the proliferation and differentiation ability of stem cells, but failed to ameliorate the decreased engraftment capacity of bone marrow cells in mice exposed to TBI. This study demonstrated that spermidine could promote the recovery of IR-induced inhibition of proliferation and differentiation ability of HSCs, partly through antioxidant effects. Whether combining spermidine with other radioprotectants could further increase protective efficacy and reduce the long-term bone marrow injury needs further investigation.

Aging, Causes, and Rejuvenation of Hematopoietic Stem Cells.

Hematopoietic stem cells (HSCs) undergo an age-related functional decline, which leads to a disruption of the blood system and contributes to the development of aging-associated hematopoietic diseases and malignancies. In this section, we provide a summary of the key hallmarks associated with HSC aging. We also examine the causal factors that contribute to HSC aging and emphasize potential approaches to mitigate HSC aging and age-related hematopoietic disorders.

Melatonin, tunneling nanotubes, mesenchymal cells, and tissue regeneration.

Mesenchymal stem cells are multipotent stem cells that reside in many human tissues and organs. Mesenchymal stem cells are widely used in experimental and clinical regenerative medicine due to their capability to transdifferentiate into various lineages. However, when transplanted, they lose part of their multipotency and immunomodulatory properties, and most of them die after injection into the damaged tissue. In this review, we discuss the potential utility of melatonin in preserving mesenchymal stem cells' survival and function after transplantation. Melatonin is a pleiotropic molecule regulating critical cell functions including apoptosis, endoplasmic reticulum stress, and autophagy. Melatonin is also synthesized in the mitochondria where it reduces oxidative stress, the opening of the mitochondrial permeability transition pore and the downstream caspase activation, activates uncoupling proteins, and curtails the proinflammatory response. In addition, recent findings showed that melatonin also promotes the formation of tunneling nanotubes and the transfer of mitochondria between cells through the connecting tubules. As mitochondrial dysfunction is a primary cause of mesenchymal stem cells death and senescence and a critical issue for survival after transplantation, we propose that melatonin by favoring mitochondria functionality and their transfer through tunneling nanotubes from healthy to suffering cells could improve mesenchymal stem cell-based therapy in a large number of diseases for which basic and clinical trials are underway.