What is the rationale for mesenchymal stromal cells based therapies in the management of hemophilic arthropathies?

Hemophilia A and B are rare X-linked genetic bleeding disorders due to a complete or partial deficiency in the coagulation factors VIII or IX, respectively. The main treatment for hemophilia is prophylactic and based on coagulation factor replacement therapies. These treatments have significantly reduced bleeding and improved the patients' quality of life. Nevertheless, repeated joint bleedings (hemarthroses), even subclinical hemarthroses, can lead to hemophilic arthropathy (HA). This disabling condition is characterized by chronic pain due to synovial inflammation, cartilage and bone destruction requiring ultimately joint replacement. HA resembles to rheumatoid arthritis because of synovitis but HA is considered as having similarities with osteoarthritis as illustrated by the migration of immune cells, production of inflammatory cytokines, synovial hypertrophy and cartilage damage. Various drugs have been evaluated for the management of HA with limited success. The objective of the review is to discuss new therapeutic approaches with a special focus on the studies that have investigated the potential of using mesenchymal stromal cells (MSCs) in the management of HA. A systematic review of the literature has been made. Most of the studies have focused on the interest of MSCs for the delivery of missing factors VIII or IX but in some studies, more insight on the effect of MSC injection on synovial inflammation or cartilage structure were provided and put in perspective for possible clinical applications.

Extracellular vesicles from senescent mesenchymal stromal cells are defective and cannot prevent osteoarthritis.

Age is the most important risk factor in degenerative diseases such as osteoarthritis (OA), which is associated with the accumulation of senescent cells in the joints. Here, we aimed to assess the impact of senescence on the therapeutic properties of extracellular vesicles (EVs) from human fat mesenchymal stromal cells (ASCs) in OA. We generated a model of DNA damage-induced senescence in ASCs using etoposide and characterized EVs isolated from their conditioned medium (CM). Senescent ASCs (S-ASCs) produced 3-fold more EVs (S-EVs) with a slightly bigger size and that contain 2-fold less total RNA. Coculture experiments showed that S-ASCs were as efficient as healthy ASCs (H-ASCs) in improving the phenotype of OA chondrocytes cultured in resting conditions but were defective when chondrocytes were proliferating. S-EVs were also impaired in their capacity to polarize synovial macrophages towards an anti-inflammatory phenotype. A differential protein cargo mainly related to inflammation and senescence was detected in S-EVs and H-EVs. Using the collagenase-induced OA model, we found that contrary to H-EVs, S-EVs could not protect mice from cartilage damage and joint calcifications, and were less efficient in protecting subchondral bone degradation. In addition, S-EVs induced a pro-catabolic and pro-inflammatory gene signature in the joints of mice shortly after injection, while H-EVs decreased hypertrophic, catabolic and inflammatory pathways. In conclusion, S-EVs are functionally impaired and cannot protect mice from developing OA.

Mesenchymal stromal cells-derived extracellular vesicles alleviate systemic sclerosis via miR-29a-3p.

Systemic sclerosis (SSc) is a potentially lethal disease with no curative treatment. Mesenchymal stromal cells (MSCs) have proved efficacy in SSc but no data is available on MSC-derived extracellular vesicles (EVs) in this multi-organ fibrosis disease. Small size (ssEVs) and large size EVs (lsEVs) were isolated from murine MSCs or human adipose tissue-derived MSCs (ASCs). Control antagomiR (Ct) or antagomiR-29a-3p (A29a) were transfected in MSCs and ASCs before EV production. EVs were injected in the HOCl-induced SSc model at day 21 and euthanasized at day 42. We found that both ssEVs and lsEVs were effective to slow-down the course of the disease. All disease parameters improved in skin and lungs. Interestingly, down-regulating miR-29a-3p in MSCs totally abolished therapeutic efficacy. Besides, we demonstrated a similar efficacy of human ASC-EVs and importantly, EVs from A29a-transfected ASCs failed to improve skin fibrosis. We identified Dnmt3a, Pdgfrbb, Bcl2, Bcl-xl as target genes of miR-29a-3p whose regulation was associated with skin fibrosis improvement. Our study highlights the therapeutic role of miR-29a-3p in SSc and the importance of regulating methylation and apoptosis.

Extracellular Vesicles Are More Potent Than Adipose Mesenchymal Stromal Cells to Exert an Anti-Fibrotic Effect in an In Vitro Model of Systemic Sclerosis.

Systemic sclerosis (SSc) is a complex disorder resulting from dysregulated interactions between the three main pathophysiological axes: fibrosis, immune dysfunction, and vasculopathy, with no specific treatment available to date. Adipose tissue-derived mesenchymal stromal cells (ASCs) and their extracellular vesicles (EVs) have proved efficacy in pre-clinical murine models of SSc. However, their precise action mechanism is still not fully understood. Because of the lack of availability of fibroblasts isolated from SSc patients (SSc-Fb), our aim was to determine whether a TGFß1-induced model of human myofibroblasts (Tß-Fb) could reproduce the characteristics of SSc-Fb and be used to evaluate the anti-fibrotic function of ASCs and their EVs. We found out that Tß-Fb displayed the main morphological and molecular features of SSc-Fb, including the enlarged hypertrophic morphology and expression of several markers associated with the myofibroblastic phenotype. Using this model, we showed that ASCs were able to regulate the expression of most myofibroblastic markers on Tß-Fb and SSc-Fb, but only when pre-stimulated with TGFß1. Of interest, ASC-derived EVs were more effective than parental cells for improving the myofibroblastic phenotype. In conclusion, we provided evidence that Tß-Fb are a relevant model to mimic the main characteristics of SSc fibroblasts and investigate the mechanism of action of ASCs. We further reported that ASC-EVs are more effective than parental cells suggesting that the TGFß1-induced pro-fibrotic environment may alter the function of ASCs.

Pathogenic or Therapeutic Extracellular Vesicles in Rheumatic Diseases: Role of Mesenchymal Stem Cell-Derived Vesicles.

Extracellular vesicles (EVs) are important mediators of cell-to-cell communication pathways via the transport of proteins, mRNA, miRNA and lipids. There are three main types of EVs, exosomes, microparticles and apoptotic bodies, which are classified according to their size and biogenesis. EVs are secreted by all cell types and their function reproduces that of the parental cell. They are involved in many biological processes that regulate tissue homeostasis and physiopathology of diseases. In rheumatic diseases, namely osteoarthritis (OA) and rheumatoid arthritis (RA), EVs have been isolated from synovial fluid and shown to play pathogenic roles contributing to progression of both diseases. By contrast, EVs may have therapeutic effect via the delivery of molecules that may stop disease evolution. In particular, EVs derived from mesenchymal stem cells (MSCs) reproduce the main functions of the parental cells and therefore represent the ideal type of EVs for modulating the course of either disease. The aim of this review is to discuss the role of EVs in OA and RA focusing on their potential pathogenic effect and possible therapeutic options. Special attention is given to MSCs and MSC-derived EVs for modulating OA and RA progression with the perspective of developing innovative therapeutic strategies.

Human adipose mesenchymal stem cells as potent anti-fibrosis therapy for systemic sclerosis.

OBJECTIVES: Displaying immunosuppressive and trophic properties, mesenchymal stem/stromal cells (MSC) are being evaluated as promising therapeutic options in a variety of autoimmune and degenerative diseases. Although benefits may be expected in systemic sclerosis (SSc), a rare autoimmune disease with fibrosis-related mortality, MSC have yet to be evaluated in this specific condition. While autologous approaches could be inappropriate because of functional alterations in MSC from patients, the objective of the present study was to evaluate allogeneic and xenogeneic MSC in the HOCl-induced model of diffuse SSc. We also questioned the source of human MSC and compared bone marrow- (hBM-MSC) and adipose-derived MSC (hASC). METHODS: HOCl-challenged BALB/c mice received intravenous injection of BM-MSC from syngeneic BALB/c or allogeneic C57BL/6 mice, and xenogeneic hBM-MSC or hASC (3 donors each). Skin thickness was measured during the experiment. At euthanasia, histology, immunostaining, collagen determination and RT-qPCR were performed in skin and lungs. RESULTS: Xenogeneic hBM-MSC were as effective as allogeneic or syngeneic BM-MSC in decreasing skin thickness, expression of Col1, Col3, α-Sma transcripts, and collagen content in skin and lungs. This anti-fibrotic effect was not associated with MSC migration to injured skin or with long-term MSC survival. Interestingly, compared with hBM-MSC, hASC were significantly more efficient in reducing skin fibrosis, which was related to a stronger reduction of TNFα, IL1ß, and enhanced ratio of Mmp1/Timp1 in skin and lung tissues. CONCLUSIONS: Using primary cells isolated from 3 murine and 6 human individuals, this preclinical study demonstrated similar therapeutic effects using allogeneic or xenogeneic BM-MSC while ASC exerted potent anti-inflammatory and remodeling properties. This sets the proof-of-concept prompting to evaluate the therapeutic efficacy of allogeneic ASC in SSc patients.

Native adipose stromal cells egress from adipose tissue in vivo: evidence during lymph node activation.

Adipose tissue (AT) has become accepted as a source of multipotent progenitor cells, the adipose stromal cells (ASCs). In this regard, considerable work has been performed to harvest and characterize this cell population as well as to investigate the mechanisms by which transplanted ASCs mediate tissue regeneration. In contrast the endogenous release of native ASCs by AT has been poorly investigated. In this work, we show that native ASCs egress from murine AT. Indeed, we demonstrated that the release of native ASCs from AT can be evidenced both using an ex vivo perfusion model that we set up and in vivo. Such a mobilization process is controlled by CXCR4 chemokine receptor. In addition, once mobilized from AT, circulating ASCs were found to navigate through lymph fluid and to home into lymph nodes (LN). Therefore, we demonstrated that, during the LN activation, the fat depot encapsulating the activated LN releases native ASCs, which in turn invade the activated LN. Moreover, the ASCs invading the LN were visualized in close physical interaction with podoplanin and ER-TR7 positive structures corresponding to the stromal network composing the LN. This dynamic was impaired with CXCR4 neutralizing antibody. Taken together, these data provide robust evidences that native ASCs can traffic in vivo and that AT might provide stromal cells to activated LNs.

Adipose-derived mesenchymal stem cells exert antiinflammatory effects on chondrocytes and synoviocytes from osteoarthritis patients through prostaglandin E2.

OBJECTIVE: To examine the effect of different sources of good manufacturing practice clinical grade adipose-derived mesenchymal stem cells (AD-MSCs) on inflammatory factors in osteoarthritic (OA) chondrocytes and synoviocytes. METHODS: AD-MSCs from infrapatellar Hoffa fat, subcutaneous (SC) hip fat, and SC abdominal fat were cocultured in Transwells with chondrocytes or synoviocytes. Inflammatory factors (interleukin-1ß [IL-1ß], tumor necrosis factor α, IL-6, CXCL1/growth-related oncogene α, CXCL8/IL-8, CCL2/monocyte chemotactic protein 1, CCL3/macrophage inflammatory protein 1α, and CCL5/RANTES) were evaluated by quantitative reverse transcription-polymerase chain reaction or multiplex bead-based immunoassay. The role of different immunomodulators was analyzed. RESULTS: All the inflammatory factors analyzed were down-modulated at the messenger RNA or protein level independently by all 3 AD-MSC sources or by allogeneic AD-MSCs used in coculture with chondrocytes or synoviocytes. Inflammatory factor down-modulation was observed only when AD-MSCs were cocultured with chondrocytes or synoviocytes that produced high levels of inflammatory factors, but no effect was observed in cells that produced low levels of those factors, thus highlighting a dependence of the AD-MSC effect on existing inflammation. The immunomodulators IL-10, IL-1 receptor antagonist, fibroblast growth factor 2, indoleamine 2,3-dioxygenase 1, and galectin 1 were not involved in AD-MSC effects, whereas the cyclooxygenase 2 (COX-2)/prostaglandin E2 (PGE2 ) pathway exerted a role in the mechanism of antiinflammatory AD-MSC action. CONCLUSION: The antiinflammatory effects of AD-MSCs are probably not dependent on AD-MSC adipose tissue sources and donors but rather on the inflammatory status of OA chondrocytes and synoviocytes. AD-MSCs seem to be able to sense and respond to the local environment. Even though a combination of different molecules may be involved in AD-MSC effects, the COX-2/PGE2 pathway may play a role, suggesting that AD-MSCs may be useful for therapies in osteoarticular diseases.

Long-term detection of human adipose-derived mesenchymal stem cells after intraarticular injection in SCID mice.

OBJECTIVE: Mesenchymal stem cells (MSCs) represent a promising tool for cell therapy for several disorders, among them the osteoarticular diseases. For such clinical applications, intraarticular (IA) injection of MSCs may be favored for higher levels of safety and targeting of specific joints. Although the safety of intravenous (IV) administration of MSCs has been reported in a number of clinical trials, the safety and biodistribution of MSCs after IA injection have not been tested. Our objective was to assess the toxicity of clinical-grade human adipose-derived MSCs (AD-MSCs), as well as their biodistribution, after IA injection into SCID mice. METHODS: SCID mice received IA or IV administration of 10(6) human AD-MSCs. Several tissues were recovered at different time points and processed for histologic assessment or real-time polymerase chain reaction (PCR) analysis. A highly sensitive assay was used to monitor the distribution of AD-MSCs, based on amplification of human-specific Alu sequences. RESULTS: Absence of toxicity was observed after AD-MSC infusion. Alu PCR assay revealed a high sensitivity (1 human AD-MSC/10(5) murine cells), with a large linear range (1-5 × 10(4) /10(5) murine cells). Importantly, 15% of the IA-injected AD-MSCs were detectable in the joint for the first month and 1.5% of the AD-MSCs engrafted over the long term, at least 6 months. AD-MSCs were observed in the injected joints and in areas of tissue referred to as stem cell niches, such as the bone marrow, adipose tissue, and muscle. CONCLUSION: These data support the feasibility and safety of using IA delivery of human AD-MSCs in the treatment of rheumatic diseases that affect the joints.

Therapeutic potential in rheumatic diseases of extracellular vesicles derived from mesenchymal stromal cells.

The incidence of rheumatic diseases such as rheumatoid arthritis and osteoarthritis and injuries to articular cartilage that lead to osteochondral defects is predicted to rise as a result of population ageing and the increase in high-intensity physical activities among young and middle-aged people. Current treatments focus on the management of pain and joint functionality to improve the patient's quality of life, but curative strategies are greatly desired. In the past two decades, the therapeutic value of mesenchymal stromal cells (MSCs) has been evaluated because of their regenerative potential, which is mainly attributed to the secretion of paracrine factors. Many of these factors are enclosed in extracellular vesicles (EVs) that reproduce the main functions of parental cells. MSC-derived EVs have anti-inflammatory, anti-apoptotic as well as pro-regenerative activities. Research on EVs has gained considerable attention as they are a potential cell-free therapy with lower immunogenicity and easier management than whole cells. MSC-derived EVs can rescue the pathogenetic phenotypes of chondrocytes and exert a protective effect in animal models of rheumatic disease. To facilitate the therapeutic use of EVs, appropriate cell sources for the production of EVs with the desired biological effects in each disease should be identified. Production and isolation of EVs should be optimized, and pre-isolation and post-isolation modifications should be considered to maximize the disease-modifying potential of the EVs.

Mesenchymal Stromal Cells Prevent Blood-induced Degeneration of Chondrocytes in a New Model of Murine Hemarthrosis.

Hemophilia is a rare congenital bleeding disorder caused by deficiency in coagulation factors VIII or IX, which is treated with prophylactic clotting factor concentrates. Nevertheless despite prophylaxis, spontaneous joint bleedings or hemarthroses still occur. The recurrent hemarthroses lead to progressive degradation of the joints and severe hemophilic arthropathy (HA) in patients with moderate and even mild forms of the disease. In absence of disease modifying treatment to stop or even delay HA progression, we aimed at evaluating the therapeutic potential of mesenchymal stromal cells (MSCs)-based therapy. We first developed a relevant and reproducible in vitro model of hemarthrosis relying on blood exposure of primary murine chondrocytes. We found that 30% whole blood for 4 days allowed to induce the characteristic features of hemarthrosis including low survival of chondrocytes, apoptosis induction, and dysregulation of chondrocyte markers in favor of a catabolic and inflammatory phenotype. We then evaluated the potential therapeutic effects of MSCs in this model using different conditions of coculture. Addition of MSCs improved the survival of chondrocytes when added either during the resolution or the acute phases of hemarthrosis and exerted a chondroprotective effect by enhancing the expression of anabolic markers, and reducing the expression of catabolic and inflammatory markers. We here provide the first proof-of-concept that MSCs may exert a therapeutic effect on chondrocytes under hemarthrosis conditions using a relevant in vitro model, thereby confirming a potential therapeutic interest for patients with recurrent joint bleedings.

Gelatin modified with alkoxysilanes (GelmSi) forms hybrid hydrogels for bioengineering applications.

Biopolymers are ideal candidates for the development of hydrogels for tissue engineering applications. However, chemical modifications are required to further improve their mechanical properties, in particular to cross-link them for long-lasting applications or biofabrication. Herein, we developed a novel gelatin-based hydrogel precursor, "GelmSi" which consist on modified gelatin with triethoxysilyl groups. Gelatin was chosen as starting material because of its biocompatibility and bioactivity, favouring cell adhesion and migration. Alkoxysilane moieties were introduced in a controlled manner on the lysine side chains of gelatin to obtain a hybrid precursor which reacts in physiological conditions, forming covalent siloxane bonds and allowing the formation of a three-dimensional chemical network. On the contrary to unmodified gelatin, siloxane covalent network dramatically increases the stiffness and the thermal stability of the resulting gelatin-based hydrogel, making it suitable for cell encapsulation and cell culture. The biorthogonality and versatility of the GelmSi hybrid hydrogel unlock a broad range of gelatin-based bioengineering applications.

Recent Advances in Extracellular Vesicle-Based Therapies Using Induced Pluripotent Stem Cell-Derived Mesenchymal Stromal Cells.

Extracellular vesicles (EVs) are being widely investigated as acellular therapeutics in regenerative medicine applications. EVs isolated from mesenchymal stromal cells (MSCs) are by far the most frequently used in preclinical models for diverse therapeutic applications, including inflammatory, degenerative, or acute diseases. Although they represent promising tools as cell-free therapeutic agents, one limitation to their use is related to the batch-to-batch unreliability that may arise from the heterogeneity between MSC donors. Isolating EVs from MSCs derived from induced pluripotent stem cells (iMSCs) might allow unlimited access to cells with a more stable phenotype and function. In the present review, we first present the latest findings regarding the functional aspects of EVs isolated from iMSCs and their interest in regenerative medicine for the treatment of various diseases. We will then discuss future directions for their translation to clinics with good manufacturing practice implementation.

Extracellular vesicles from mesenchymal stromal cells: Therapeutic perspectives for targeting senescence in osteoarthritis.

Osteoarthritis (OA) is a common age-related disease that correlates with a high number of senescent cells in joint tissues. Senescence has been reported to be one of the main drivers of OA pathogenesis, in particular via the release of senescence-associated secretory phenotype (SASP) factors. SASP factors are secreted as single molecules and/or packaged within extracellular vesicles (EVs), thereby contributing to senescent phenotype dissemination. Targeting senescent cells using senolytics or senomorphics has therefore been tested and improvement of OA-associated features has been reported in murine models. Mesenchymal stromal cells (MSCs) and their derived EVs (MSC-EVs) are promising treatments for OA, exerting pleiotropic functions by producing a variety of factors. However, functions of MSCs and MSC-EVs are affected by aging. In this review, we discuss on the impact of the senescent environment on functions of aged MSC-EVs and on the anti-aging properties of MSC-EVs in the context of OA.

Neuromedin B promotes chondrocyte differentiation of mesenchymal stromal cells via calcineurin and calcium signaling.

BACKGROUND: Articular cartilage is a complex tissue with poor healing capacities. Current approaches for cartilage repair based on mesenchymal stromal cells (MSCs) are often disappointing because of the lack of relevant differentiation factors that could drive MSC differentiation towards a stable mature chondrocyte phenotype. RESULTS: We used a large-scale transcriptomic approach to identify genes that are modulated at early stages of chondrogenic differentiation using the reference cartilage micropellet model. We identified several modulated genes and selected neuromedin B (NMB) as one of the early and transiently modulated genes. We found that the timely regulated increase of NMB was specific for chondrogenesis and not observed during osteogenesis or adipogenesis. Furthermore, NMB expression levels correlated with the differentiation capacity of MSCs and its inhibition resulted in impaired chondrogenic differentiation indicating that NMB is required for chondrogenesis. We further showed that NMB activated the calcineurin activity through a Ca2+-dependent signaling pathway. CONCLUSION: NMB is a newly described chondroinductive bioactive factor that upregulates the key chondrogenic transcription factor Sox9 through the modulation of Ca2+ signaling pathway and calcineurin activity.

Lung Fibrosis Is Improved by Extracellular Vesicles from IFNγ-Primed Mesenchymal Stromal Cells in Murine Systemic Sclerosis.

BACKGROUND: Systemic sclerosis (SSc) is a severe autoimmune disease for which mesenchymal stromal cells (MSCs)-based therapy was reported to reduce SSc-related symptoms in pre-clinical studies. Recently, extracellular vesicles released by MSCs (MSC-EVs) were shown to mediate most of their therapeutic effect. Here, we aimed at improving their efficacy by increasing the MSC-EV dose or by IFNγ-priming of MSCs. METHODS: small size (ssEVs) and large size EVs (lsEVs) were recovered from murine MSCs that were pre-activated using 1 or 20 ng/mL of IFNγ. In the HOCl-induced model of SSc, mice were treated with EVs at day 21 and sacrificed at day 42. Lung and skin samples were collected for histological and molecular analyses. RESULTS: increasing the dose of MSC-EVs did not add benefit to the dose previously reported to be efficient in SSc. By contrast, IFNγ pre-activation improved MSC-EVs-based treatment, essentially in the lungs. Low doses of IFNγ decreased the expression of fibrotic markers, while high doses improved remodeling and anti-inflammatory markers. IFNγ pre-activation upregulated iNos, IL1ra and Il6 in MSCs and ssEVs and the PGE2 protein in lsEVs. CONCLUSION: IFNγ-pre-activation improved the therapeutic effect of MSC-EVs preferentially in the lungs of SSc mice by modulating anti-inflammatory and anti-fibrotic markers.

miR-155 Contributes to the Immunoregulatory Function of Human Mesenchymal Stem Cells.

Objectives: Mesenchymal stem/stromal cells (MSCs) are widely investigated in regenerative medicine thanks to their immunomodulatory properties. They exert their anti-inflammatory function thanks to the secretion of a number of mediators, including proteins and miRNAs, which can be released in the extracellular environment or in the cargo of extracellular vesicles (EVs). However, the role of miRNAs in the suppressive function of MSCs is controversial. The aim of the study was to identify miRNAs that contribute to the immunomodulatory function of human bone marrow-derived MSCs (BM-MSCs). Methods: Human BM-MSCs were primed by coculture with activated peripheral blood mononuclear cells (aPBMCs). High throughput miRNA transcriptomic analysis was performed using Human MicroRNA TaqMan® Array Cards. The immunosuppressive function of miRNAs was investigated in mixed lymphocyte reactions and the delayed type hypersensitivity (DTH) murine model. Results: Upon priming, 21 out of 377 tested miRNAs were significantly modulated in primed MSCs. We validated the up-regulation of miR-29a, miR-146a, miR-155 and the down-regulation of miR-149, miR-221 and miR-361 in additional samples of primed MSCs. We showed that miR-155 significantly reduced the proliferation of aPBMCs in vitro and inflammation in vivo, using the DTH model. Analysis of miRNA-mRNA interactions revealed miR-221 as a potential target gene that is down-regulated by miR-155 both in primed MSCs and in aPBMCs. Conclusion: Here, we present evidence that miR-155 participates to the immunosuppressive function of human BM-MSCs and down-regulates the expression of miR-221 as a possible inflammatory mediator.

A Collagen-Mimetic Organic-Inorganic Hydrogel for Cartilage Engineering.

Promising strategies for cartilage regeneration rely on the encapsulation of mesenchymal stromal cells (MSCs) in a hydrogel followed by an injection into the injured joint. Preclinical and clinical data using MSCs embedded in a collagen gel have demonstrated improvements in patients with focal lesions and osteoarthritis. However, an improvement is often observed in the short or medium term due to the loss of the chondrocyte capacity to produce the correct extracellular matrix and to respond to mechanical stimulation. Developing novel biomimetic materials with better chondroconductive and mechanical properties is still a challenge for cartilage engineering. Herein, we have designed a biomimetic chemical hydrogel based on silylated collagen-mimetic synthetic peptides having the ability to encapsulate MSCs using a biorthogonal sol-gel cross-linking reaction. By tuning the hydrogel composition using both mono- and bi-functional peptides, we succeeded in improving its mechanical properties, yielding a more elastic scaffold and achieving the survival of embedded MSCs for 21 days as well as the up-regulation of chondrocyte markers. This biomimetic long-standing hybrid hydrogel is of interest as a synthetic and modular scaffold for cartilage tissue engineering.

Interplay between human adipocytes and T lymphocytes in obesity: CCL20 as an adipochemokine and T lymphocytes as lipogenic modulators.

OBJECTIVE: Adipose tissue (AT) plays a major role in the low-grade inflammatory state associated with obesity. The aim of the present study was to characterize the human AT lymphocytes (ATLs) and to analyze their interactions with adipocytes. METHODS AND RESULTS: Human ATL subsets were characterized by flow cytometry in subcutaneous ATs from 92 individuals with body mass index (BMI) ranging from 19 to 43 kg/m(2) and in paired biopsies of subcutaneous and visceral AT from 45 class II/III obese patients. CD3(+) ATLs were composed of effector and memory CD4(+) helper and CD8(+) cytotoxic T cells. The number of ATLs correlated positively with BMI and was higher in visceral than subcutaneous AT. Mature adipocytes stimulated the migration of ATLs and released the chemokine CCL20, the receptor of which (CCR6) was expressed in ATLs. The expression of adipocyte CCL20 was positively correlated with BMI and increased in visceral compared to subcutaneous adipocytes. ATLs expressed inflammatory markers and released interferon gamma (IFN gamma). Progenitor and adipocyte treatment with ATL-conditioned media reduced the insulin-mediated upregulation of lipogenic enzymes, an effect involving IFN gamma. CONCLUSIONS: Therefore, crosstalk occurs between adipocytes and lymphocytes within human AT involving T cell chemoattraction by adipocytes and modulation of lipogenesis by ATLs.