Intercellular Exchange Research Articles

Mesenchymal stem cell-derived exosomes: Toward cell-free therapeutic strategies in regenerative medicine.

Mesenchymal stem cells (MSCs) are multipotent stem cells with marked potential for regenerative medicine because of their strong immunosuppressive and regenerative abilities. The therapeutic effects of MSCs are based in part on their secretion of biologically active factors in extracellular vesicles known as exosomes. Exosomes have a diameter of 30-100 nm and mediate intercellular communication and material exchange. MSC-derived exosomes (MSC-Exos) have potential for cell-free therapy for diseases of, for instance, the kidney, liver, heart, nervous system, and musculoskeletal system. Hence, MSC-Exos are an alternative to MSC-based therapy for regenerative medicine. We review MSC-Exos and their therapeutic potential for a variety of diseases and injuries.

Rho GTPases and the emerging role of tunneling nanotubes in physiology and disease.

Tunneling nanotubes (TNTs) emerged as important specialized actin-rich membrane protrusions for cell-to-cell communication. These structures allow the intercellular exchange of material, such as ions, soluble proteins, receptors, vesicles and organelles, therefore exerting critical roles in normal cell function. Indeed, TNTs participate in a number of physiological processes, including embryogenesis, immune response, and osteoclastogenesis. TNTs have been also shown to contribute to the transmission of retroviruses (e.g., human immunodeficiency virus-1, HIV-1) and coronaviruses. As with other membrane protrusions, the involvement of Rho GTPases in the formation of these elongated structures is undisputable, although the mechanisms involved are not yet fully elucidated. The tight control of Rho GTPase function by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) strongly suggests that localized control of these Rho regulators may contribute to TNT assembly and disassembly. Deciphering the intricacies of the complex signaling mechanisms leading to actin reorganization and TNT development would reveal important information about their involvement in normal cellular physiology as well as unveil potential targets for disease management.

Transfer of metastatic traits via miR-200c in extracellular vesicles derived from colorectal cancer stem cells is inhibited by atractylenolide I.

Cancer stem cells (CSCs) are important factors contributing to tumorigenesis. We examined whether CSCs isolated from colorectal cancer (CRC) cells possess metastatic properties that can be transferred to non‐CSCs via the delivery of miR‐200c enclosed in extracellular vesicles (EVs). The inhibitory effect of atractylenolide I (ATL‐1), a traditional Chinese medicinal compound, on miR‐200c activity and metastatic transfer was investigated. EVs were isolated from colorectal CSCs. The expression of miR‐200c was evaluated in CSCs and CSC‐derived EVs, and horizontal transfer of metastatic properties via EVs to non‐CSCs was investigated in terms of cell behavior and phosphatidylinositol‐4,5‐bisphosphate 3‐kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling. CSCs isolated from metastatic CRC cells exhibited higher levels of miR‐200c than those in nonmetastatic CRC cells. Overexpression of miR‐200c in CSCs enhanced metastatic potential by promoting proliferation and inhibiting apoptosis, in turn leading to the release of EVs carrying an excess of miR‐200c. Non‐CSCs co‐cultured with miR‐200c‐containing EVs exhibited enhanced invasion and stemness maintenance associated with PI3K/Akt/mTOR activation, demonstrating successful metastatic transfer via EV delivery. Furthermore, ATL‐1 impaired the EV‐mediated transfer of metastatic properties by suppressing miR‐200c activity and disrupting EV uptake by non‐CSCs. EVs are critical signal transducers that facilitate intercellular communication and exchange of metastatic properties, which can be controlled by ATL‐1. The findings are useful in the development of microRNA‐based anticancer strategies by targeting EV‐mediated activity, especially using natural compounds.

Neuronal and astroglial monocarboxylate transporters play key but distinct roles in hippocampus-dependent learning and memory formation.

Brain lactate formation, intercellular exchange and utilization has been implicated in memory formation. However, the individual role of either neuronal or astroglial monocarboxylate transporters for the acquisition and consolidation of information remains incomplete. Using novel transgenic mice and a viral vector approach to decrease the expression of each transporter in a cell-specific manner within the dorsal hippocampus, we show that both neuronal MCT2 and astroglial MCT4 are required for spatial information acquisition and retention (at 24 h post-training) in distinct hippocampus-dependent tasks. Intracerebral infusion of lactate rescued spatial learning in mice with reduced levels of astroglial MCT4 but not of neuronal MCT2, suggesting that lactate transfer from astrocytes and utilization in neurons contribute to hippocampal-dependent learning. In contrast, only neuronal MCT2 was shown to be required for long-term (7 days post training) memory formation. Interestingly, reduced MCT2 expression levels in mature neurons result in a heterologous effect as it blunts hippocampal neurogenesis associated with memory consolidation. These results suggest important but distinct contributions of both neuronal MCT2 and astroglial MCT4 in learning and memory processes, going beyond a simple passive role as alternative energy substrate suppliers or in waste product disposal.

T regulatory cells-derived extracellular vesicles and their contribution to the generation of immune tolerance.

T regulatory (Treg) cells have a major role in the maintenance of immune tolerance against self and foreign antigens through the control of harmful inflammation. Treg cells exert immunosuppressive function by several mechanisms, which can be distinguished as contact dependent or independent. Recently, the secretion of extracellular vesicles (EVs) by Treg cells has been reported as a novel suppressive mechanism capable of modulating immunity in a cell-contact independent and targeted manner, which has been identified in different pathologic scenarios. EVs are cell-derived membranous structures involved in physiologic and pathologic processes through protein, lipid, and genetic material exchange, which allow intercellular communication. In this review, we revise and discuss current knowledge on Treg cells-mediated immune tolerance giving special attention to the production and release of EVs. Multiple studies support that Treg cells-derived EVs represent a refined intercellular exchange device with the capacity of modulating immune responses, thus creating a tolerogenic microenvironment in a cell-free manner. The mechanisms proposed encompass miRNAs-induced gene silencing, the action of surface proteins and the transmission of enzymes. These observations gain relevance by the fact that Treg cells are susceptible to converting into effector T cells after exposition to inflammatory environments. Yet, in contrast to their cells of origin, EVs are unlikely to be modified under inflammatory conditions, highlighting the advantage of their use. Moreover, we speculate in the possibility that Treg cells may contribute to infectious tolerance via vesicle secretion, intervening with CD4+ T cells differentiation and/or stability.

Modulation of the Inflammatory Response and Bone Healing.

The optimal treatment for complex fractures and large bone defects is an important unsolved issue in orthopedics and related specialties. Approximately 5–10% of fractures fail to heal and develop non-unions. Bone healing can be characterized by three partially overlapping phases: the inflammatory phase, the repair phase, and the remodeling phase. Eventual healing is highly dependent on the initial inflammatory phase, which is affected by both the local and systemic responses to the injurious stimulus. Furthermore, immune cells and mesenchymal stromal cells (MSCs) participate in critical inter-cellular communication or crosstalk to modulate bone healing. Deficiencies in this inter-cellular exchange, inhibition of the natural processes of acute inflammation, and its resolution, or chronic inflammation due to a persistent adverse stimulus can lead to impaired fracture healing. Thus, an initial and optimal transient stage of acute inflammation is one of the key factors for successful, robust bone healing. Recent studies demonstrated the therapeutic potential of immunomodulation for bone healing by the preconditioning of MSCs to empower their immunosuppressive properties. Preconditioned MSCs (also known as “primed/ licensed/ activated” MSCs) are cultured first with pro-inflammatory cytokines (e.g., TNFα and IL17A) or exposed to hypoxic conditions to mimic the inflammatory environment prior to their intended application. Another approach of immunomodulation for bone healing is the resolution of inflammation with anti-inflammatory cytokines such as IL4, IL10, and IL13. In this review, we summarize the principles of inflammation and bone healing and provide an update on cellular interactions and immunomodulation for optimal bone healing.

The Role of Extracellular Vesicles in the Hallmarks of Cancer and Drug Resistance

Extracellular vesicles (EVs) mediate intercellular signaling and communication, allowing the intercellular exchange of proteins, lipids, and genetic material. Their recognized role in the maintenance of the physiological balance and homeostasis seems to be severely disturbed throughout the carcinogenesis process. Indeed, the modus operandi of cancer implies the highjack of the EV signaling network to support tumor progression in many (if not all) human tumor malignancies. We have reviewed the current evidence for the role of EVs in affecting cancer hallmark traits by: (i) promoting cell proliferation and escape from apoptosis, (ii) sustaining angiogenesis, (iii) contributing to cancer cell invasion and metastasis, (iv) reprogramming energy metabolism, (v) transferring mutations, and (vi) modulating the tumor microenvironment (TME) by evading immune response and promoting inflammation. Special emphasis was given to the role of EVs in the transfer of drug resistant traits and to the EV cargo responsible for this transfer, both between cancer cells or between the microenvironment and tumor cells. Finally, we reviewed evidence for the increased release of EVs by drug resistant cells. A timely and comprehensive understanding of how tumor EVs facilitate tumor initiation, progression, metastasis and drug resistance is instrumental for the development of innovative EV-based therapeutic approaches for cancer.

Intercellular Transmission of a Synthetic Bacterial Cytotoxic Prion-Like Protein in Mammalian Cells.

RepA is a bacterial protein that builds intracellular amyloid oligomers acting as inhibitory complexes of plasmid DNA replication. When carrying a mutation enhancing its amyloidogenesis (A31V), the N-terminal domain (WH1) generates cytosolic amyloid particles that are inheritable within a bacterial lineage. Such amyloids trigger in bacteria a lethal cascade reminiscent of mitochondrial impairment in human cells affected by neurodegeneration. To fulfill all the criteria to qualify as a prion-like protein, horizontal (intercellular) transmissibility remains to be demonstrated for RepA-WH1. Since this is experimentally intractable in bacteria, here we transiently expressed in a murine neuroblastoma cell line the soluble, barely cytotoxic RepA-WH1 wild type [RepA-WH1(WT)] and assayed its response to exposure to in vitro-assembled RepA-WH1(A31V) amyloid fibers. In parallel, murine cells releasing RepA-WH1(A31V) aggregates were cocultured with human neuroblastoma cells expressing RepA-WH1(WT). Both the assembled fibers and donor-derived RepA-WH1(A31V) aggregates induced, in the cytosol of recipient cells, the formation of cytotoxic amyloid particles. Mass spectrometry analyses of the proteomes of both types of injured cells pointed to alterations in mitochondria, protein quality triage, signaling, and intracellular traffic. Thus, a synthetic prion-like protein can be propagated to, and become cytotoxic to, cells of organisms placed at such distant branches of the tree of life as bacteria and mammalia, suggesting that mechanisms of protein aggregate spreading and toxicity follow default pathways.IMPORTANCE Proteotoxic amyloid seeds can be transmitted between mammalian cells, arguing that the intercellular exchange of prion-like protein aggregates can be a common phenomenon. RepA-WH1 is derived from a bacterial intracellular functional amyloid protein, engineered to become cytotoxic in Escherichia coli Here, we have studied if such bacterial aggregates can also be transmitted to, and become cytotoxic to, mammalian cells. We demonstrate that RepA-WH1 is capable of entering naive cells, thereby inducing the cytotoxic aggregation of a soluble RepA-WH1 variant expressed in the cytosol, following the same trend that had been described in bacteria. These findings highlight the universality of one of the central principles underlying prion biology: No matter the biological origin of a given prion-like protein, it can be transmitted to a phylogenetically unrelated recipient cell, provided that the latter expresses a soluble protein onto which the incoming protein can readily template its amyloid conformation.

Cell‐specific heterogeneity of Cx43‐positive gap junctions in the mammalian kidney

ObjectiveConnexin 43 (Cx43) is a gap junction‐forming protein which mediates the intercellular passage of molecules < 1000 Da. In the kidney, Cx43 was reported in glomerular vessels and mesangium. Own results prompted us to reevaluate the distribution of Cx43 and its phosphorylated form, phospho‐S368‐Cx43 (pCx43), within the different zones of the rat kidney and in cultured fibroblasts in more detail.MethodsCx43 and pCx43 were localized by immunofluorescence in rat kidney sections and cultured human fibroblasts. High‐resolution immunostaining of Cx43 was achieved by ultrastructural immunogold labelling on electron microscopy sections. Double‐labelings with anti‐aquaporin 1 (AQP1), aquaporin 2 (AQP2), zonula occludens‐1 (ZO‐1), and cyclooxygenase‐2 (COX‐2) were conducted to clarify Cx43 distribution in the rat renal medulla. Cultured human fibroblasts served to study intercellular transfer of fluorescent lucifer yellow.ResultsCx43 was distributed in renal arterial and arteriolar endothelia, lymphatic vessel walls, peritubular capillaries, and glomerular compartments. In the interstitium, Cx43 was present as linear or punctate signals of the cell membrane of fibroblasts, in colocalization with pCx43. Cx43‐positive medullary fibroblasts co‐expressed COX‐2. No colocalization was detected between Cx43 and AQP1 or AQP2. Ultrastructural analysis showed Cx43 immunoreactivity at membrane contact zones between fibroblasts and in isolated cell processes of inner medullary interstitium. Cultured fibroblasts showed extensive, punctate Cx43 and pCx43 signals between adjacent cells. Signal was further distributed in non‐junctional areas of plasma membrane, suggesting Cx43 hemichannel functions. Lucifer yellow spread rapidly (10 min) between fibroblasts suggesting intercellular exchange via gap junctions, which was blocked by the gap junctional inhibitor, 18β‐glycyrrhetinic acid.ConclusionsCx43 in rat kidney shows prominent glomerular, vascular, and interstitial distribution, while epithelia, with exception of the podocytes, were negative. Focusing on interstitial fibroblasts, Cx43‐mediated information transfer was demonstrated. A constitutive nature of Cx43 phosphorylation was established in these cells. Our data suggest a cell‐specific heterogeneity of Cx43‐positive gap junctions mediating information exchange among renal cell types.

A CRISPR-Cas9-based reporter system for single-cell detection of extracellular vesicle-mediated functional transfer of RNA

Extracellular vesicles (EVs) form an endogenous transport system for intercellular transfer of biological cargo, including RNA, that plays a pivotal role in physiological and pathological processes. Unfortunately, whereas biological effects of EV-mediated RNA transfer are abundantly studied, regulatory pathways and mechanisms remain poorly defined due to a lack of suitable readout systems. Here, we describe a highly-sensitive CRISPR-Cas9-based reporter system that allows direct functional study of EV-mediated transfer of small non-coding RNA molecules at single-cell resolution. Using this CRISPR operated stoplight system for functional intercellular RNA exchange (CROSS-FIRE) we uncover various genes involved in EV subtype biogenesis that play a regulatory role in RNA transfer. Moreover we identify multiple genes involved in endocytosis and intracellular membrane trafficking that strongly regulate EV-mediated functional RNA delivery. Altogether, this approach allows the elucidation of regulatory mechanisms in EV-mediated RNA transfer at the level of EV biogenesis, endocytosis, intracellular trafficking, and RNA delivery.

Uncoupling of the Astrocyte Syncytium Differentially Affects AQP4 Isoforms.

The water channel protein aquaporin-4 (AQP4) and the gap junction forming proteins connexin-43 (Cx43) and connexin-30 (Cx30) are astrocytic proteins critically involved in brain water and ion homeostasis. While AQP4 is mainly involved in water flux across the astrocytic endfeet membranes, astrocytic gap junctions provide syncytial coupling allowing intercellular exchange of water, ions, and other molecules. We have previously shown that mice with targeted deletion of Aqp4 display enhanced gap junctional coupling between astrocytes. Here, we investigate whether uncoupling of the astrocytic syncytium by deletion of the astrocytic connexins Cx43 and Cx30 affects AQP4 membrane localization and expression. By using quantitative immunogold cytochemistry, we show that deletion of astrocytic connexins leads to a substantial reduction of perivascular AQP4, concomitant with a down-regulation of total AQP4 protein and mRNA. Isoform expression analysis shows that while the level of the predominant AQP4 M23 isoform is reduced in Cx43/Cx30 double deficient hippocampal astrocytes, the levels of M1, and the alternative translation AQP4ex isoform protein levels are increased. These findings reveal a complex interdependence between AQP4 and connexins, which are both significantly involved in homeostatic functions and astrogliopathologies.

Gap Junctions in the Bone Marrow Lympho-Hematopoietic Stem Cell Niche, Leukemia Progression, and Chemoresistance.

The crosstalk between hematopoietic stem cells (HSC) and bone marrow (BM) microenvironment is critical for homeostasis and hematopoietic regeneration in response to blood formation emergencies after injury, and has been associated with leukemia transformation and progression. Intercellular signals by the BM stromal cells in the form of cell-bound or secreted factors, or by physical interaction, regulate HSC localization, maintenance, and differentiation within increasingly defined BM HSC niches. Gap junctions (GJ) are comprised of arrays of membrane embedded channels formed by connexin proteins, and control crucial signaling functions, including the transfer of ions, small metabolites, and organelles to adjacent cells which affect intracellular mechanisms of signaling and autophagy. This review will discuss the role of GJ in both normal and leukemic hematopoiesis, and highlight some of the most novel approaches that may improve the efficacy of cytotoxic drugs. Connexin GJ channels exert both cell-intrinsic and cell-extrinsic effects on HSC and BM stromal cells, involved in regenerative hematopoiesis after myelosuppression, and represent an alternative system of cell communication through a combination of electrical and metabolic coupling as well as organelle transfer in the HSC niche. GJ intercellular communication (GJIC) in the HSC niche improves cellular bioenergetics, and rejuvenates damaged recipient cells. Unfortunately, they can also support leukemia proliferation and survival by creating leukemic niches that provide GJIC dependent energy sources and facilitate chemoresistance and relapse. The emergence of new strategies to disrupt self-reinforcing malignant niches and intercellular organelle exchange in leukemic niches, while at the same time conserving normal hematopoietic GJIC function, could synergize the effect of chemotherapy drugs in eradicating minimal residual disease. An improved understanding of the molecular basis of connexin regulation in normal and leukemic hematopoiesis is warranted for the re-establishment of normal hematopoiesis after chemotherapy.

Exosomal Long NonCoding Rnas as Cancer Biomarkers and Therapeutic Targets

Extensive study of extracellular vesicles began about ten years ago. Exosomes are extracellular membrane vesicles 30–100 nm in diameter secreted by various types of cells and present in most biological fluids. For a long time they were considered non-functional cellular components. However, it has been proven that they serve as a means of intercellular exchange of information. They can move bioactive molecules such as proteins, lipids, RNA, and DNA. Several studies have shown that their contents, including proteins and non-coding nucleic acids, may be of particular interest as biomarkers of diseases. The most promising of all these molecules are non-coding RNAs (ncRNAs), including microRNAs and long non-coding RNAs (lncRNAs). LncRNAs are a large group of non-coding RNAs (ncRNAs) longer than 200 nucleotides. As regulatory factors lncRNAs play an important role in complex cellular processes, such as apoptosis, growth, differentiation, proliferation, etc. Despite many advances in diagnosis and treatment (surgery, radiation therapy, chemotherapy), cancer remains one of the most important public healthcare problems worldwide. Every day brings a better understanding of the role of exosomes in the development of cancer and metastases. Liquid biopsy has been developed as a method for the detection of cancer at an early stage. This is a series of minimally invasive tests of bodily fluids offering the advantage of real-time tracking of the tumour development. In fact, circulating exosomal lncRNAs have been found to be closely linked to processes of oncogenesis, metastasis and treatment. In this paper we review current studies into the functional role of exosomal lncRNAs in cancer and discuss their potential clinical use as diagnostic biomarkers and therapeutic targets for cancer.

Interleukin-1Β Induces Intracellular Serum Amyloid A1 Expression In Human Coronary Endothelial Cells And Promotes Its Intercellular Exchange

Interleukin-1Β Induces Intracellular Serum Amyloid A1 Expression In Human Coronary Endothelial Cells And Promotes Its Intercellular Exchange

Multiple Roles of Exosomal Long Noncoding RNAs in Cancers.

Long noncoding RNAs (lncRNAs) are not transcriptional noise, as previously understood, but are currently considered to be multifunctional. Exosomes are derived from the internal multivesicular compartment and are extracellular vesicles (EVs) with diameters of 30–100 nm. Exosomes play significant roles in the intercellular exchange of information and material. Exosomal lncRNAs may be promising biomarkers for cancer diagnosis and potential targets for cancer therapies, since they are increasingly understood to be involved in tumorigenesis, tumor angiogenesis, and chemoresistance. This review mainly focuses on the roles of emerging exosomal lncRNAs in cancer. In addition, the biogenesis of exosomes, the functions of lncRNAs, and the mechanisms of lncRNAs in exosome-mediated cell-cell communication are also summarized.

The research advances of exosomes in esophageal cancer.

Esophageal carcinoma (EC) is one of the most common human digestive tract tumors, with high morbidity and mortality. It is necessary to elucidate the mechanism of cancer progression and seek early EC diagnostic markers for promptdetection and intervention. Exosomes are membrane nanovesicles secreted from many nucleated cells, 30-100nm in diameter, containing various proteins, lipids and nucleic acids. They exist in peripheral blood, urine, ascites and other body fluids, widely engaged withintercellular material exchange and signal communication. Exosomes secreted from EC cells or tissues conduct important functions in tumor growth and progression. The detection and analysis of tumor-derived or tumor-associated exosomes has potential for EC early diagnosis and prognosis assessment. In the present paper, the exosomes' biological behaviors, isolation, detection and functions in EC progression -using as potential biomarkers for EC diagnosis or prognosis - are reviewed.

Intercellular wireless communication network between mother and fetus in rat pregnancy-a study on directed and weighted network

BackgroundThe maternal body forms a wireless communication system with the embryo through the blood circulation system. Obviously, direct sampling from early embryos is damaging. Therefore, we detected changes in the concentrations of 30 signaling molecules in serum from the pregnant rats at the 14 time points, then the intercellular wireless communication network was established, to explore the regularity of signal communication between mother and fetus.Method of studyWe used liquid chip scanning technology to detect 30 signal molecules at 14 time points. Statistical analysis of the data yielded significant change signal molecules. According to the secretory cells and effector cells involved in signal molecules, the communication network of different stages were drawn by using Biograph software.ResultsThe process could be divided into 4 periods including early, middle, late pregnancy, and postpartum. In early pregnancy, two immune transformations occur: (a) interleukin-10 (IL-10), interleukin-13 (IL-13) increased at day 5, which promoted immunoglobin G (IgG) secretion, provided protection through the neonatal Fc receptor for IgG (FcγRn) crossing the placental barrier to reach the embryo, achieved T helper 1 (Th1) transformation into T helper 2 (Th2), reduced maternal innate and cellular immunity, and prevented fetal abortion; (b) the fetal heart was fully developed at day 7, with circulatory system established, which provided a platform for intercellular information exchange. The second transformation corresponded to the maternal immune system providing signaling molecules for the embryo to promote Th2 transformation into Th1, thus activating embryonic innate immune cells, and enabling antibody-mediated immune recognition, response and protection. Days 9–19 was a stable period. After 21 days of pregnancy, the maternal body prepared for delivery. The characteristic signaling molecules in the process were monocyte chemotactic protein-1 (MCP-1), IL-10, IL-13, IL-1ɑ, interferon-inducible protein-10 (IP-10), regulated upon activation normal T cell expressed and secreted (RANTES), thyroid stimulating hormone (TSH), IL-2, IL-6, IL-12p70 and IL-18.ConclusionDetection of concentration changes of the factors in maternal serum could provide a tool for monitoring, diagnosis, prediction and treatment of embryo differentiation, development and health.

Nischarin Regulates Secretion of Exosomes and Cancer Progression.

The intercellular exchange of exosomes may play a regulatory function in tumor progression and metastasis. Maziveyi and colleagues demonstrated that Nischarin regulated the secretion of exosomes from breast cancer cells. Loss of Nischarin expression increased exosome production and promoted tumor cell growth and migration, supporting that Nischarin can influence the behavior of surrounding cancer cells. This study identified a novel function of the tumor suppressor Nischarin in exosome biology and cancer progression.See related article by Maziveyi et al., p. 2152.

Human Bone Marrow Mesenchymal Stem Cells Rescue Endothelial Cells Experiencing Chemotherapy Stress by Mitochondrial Transfer Via Tunneling Nanotubes.

Tunneling nanotubes (TNTs) are newly discovered tubular structures between two distant cells that facilitate the intercellular exchange of signals and components. Recent reports show that mesenchymal stem cells (MSCs) can rescue injured target cells and promote recovery from a variety of stresses via TNT-mediated mitochondrial transfer. In this study, we explored how TNTs form between bone marrow MSCs and endothelial cells (ECs) by using a human umbilical cord vein endothelial cell (HUVEC) model. TNT formation between MSCs and HUVECs could be induced by treating HUVECs with cytarabine (Ara-C), and human bone marrow mesenchymal stem cells (hBMMSCs) could transfer mitochondria to injured HUVECs through TNTs. Mitochondrial transfer from hBMMSCs to HUVECs via TNTs rescued the injured HUVECs by reducing apoptosis, promoting proliferation and restoring the transmembrane migration ability as well as the capillary angiogenic capacity of HUVECs. This study provides novel insights into the cell-cell communication between MSCs and ECs and supports the results of prior studies indicating that ECs promote hematopoietic regeneration. An improved understanding of MSC-EC cross-talk will promote the development of MSC-directed strategies for improving EC function and hematopoietic system regeneration following myelosuppressive and myeloablative injuries.

Interleukin-1β Induces Intracellular Serum Amyloid A1 Expression in Human Coronary Artery Endothelial Cells and Promotes its Intercellular Exchange.

Serum amyloid A (SAA) is an acute-phase protein with important, pathogenic role in the development of atherosclerosis. Since dysfunctional endothelium represents a key early step in atherogenesis, we aimed to determine whether induced human coronary artery endothelial cells (HCAEC) modulate SAA1/2/4 expression and influence intracellular location and intercellular transport of SAA1. HCAEC were stimulated with 1ng/ml IL-1β, 10ng/ml IL-6, and/or 1μM dexamethasone for 24h. QPCR, Western blots, ELISA, and immunofluorescent labeling were performed for detection of SAA1/2/4 mRNA and protein levels, respectively. In SAA1 transport experiments, FITC- or Cy3-labeled SAA1 were added to HCAEC separately, for 24h, followed by a combined incubation of SAA1-FITC and SAA1-Cy3 positive cells, with IL-1β and analysis by flow cytometry. IL-1β upregulated SAA1 (119.9-fold, p < 0.01) and SAA2 (9.3-fold; p < 0.05) mRNA expression levels, while mRNA expression of SAA4 was not affected. Intracellular SAA1 was found mainly as a monomer, while SAA2 and SAA4 formed octamers as analyzed by Western blots. Within HCAEC, SAA1/2/4 located mostly to the perinuclear area and tunneling membrane nanotubes. Co-culturing of SAA1-FITC and SAA1-Cy3 positive cells for 48h showed a significantly higher percentage of double positive cells in IL-1β-stimulated (mean ± SD; 60 ± 4%) vs. non-stimulated cells (48 ± 2%; p < 0.05). IL-1β induces SAA1 expression in HCAEC and promotes its intercellular exchange, suggesting that direct communication between cells in inflammatory conditions could ultimately lead to faster development of atherosclerosis in coronary arteries.