Recent advances in understanding inflammatory acne: Deciphering the relationship between Cutibacterium acnes and Th17 inflammatory pathway

Acne vulgaris is a common chronic inflammatory skin disease of the pilosebaceous units. Four factors contribute to acne: hyperseborrhea and dysseborrhea, follicular hyperkeratinisation, skin microbiome dysbiosis and local immuno-inflammation. Recent key studies have highlighted a better understanding of the important role of Cutibacterium acnes (C. acnes) in the development of acne. Three major findings in the last decade include: (1) the ability of C. acnes to self-organize in a biofilm associated with a more virulent activity, (2) the loss of the C. acnes phylotype diversity and (3) the central role of the Th17 pathway in acne inflammation. Indeed, there is a close link between C. acnes and the activation of the Th17 immuno-inflammatory pathway at the initiation of acne development. These mechanisms are directly linked to the loss of C. acnes phylotype diversity during acne, with a predominance of the pro-pathogenic phylotype IA1. This specifically contributes to the induction of the Th17-mediated immuno-inflammatory response involving skin cells, such as keratinocytes, monocytes and sebocytes. These advancements have led to new insights into the underlying mechanisms which can be harnessed to develop novel treatments and diagnostic biomarkers. A major disadvantage of traditional treatment with topical antibiotics is that they induce cutaneous dysbiosis and antimicrobial resistance. Thus, future treatments would no longer aim to 'kill' C. acnes, but to maintain the skin microbiota balance allowing for tissue homeostasis, specifically, the restoration of C. acnes phylotype diversity. Here, we provide an overview of some of the key processes involved in the pathogenesis of acne, with a focus on the prominent role of C. acnes and the Th17-inflammatory pathways involved.

Change in Cutibacterium acnes phylotype abundance and improvement of clinical parameters using a new dermocosmetic product containing Myrtus communis and Celastrol enriched plant cell culture extracts in patients with acne vulgaris

BACKGROUND

Acne is a multifactorial chronic inflammatory disease of the pilosebaceous unit, where Cutibacterium acnes plays a main role. Recent papers demonstrated that specific C. acnes phylotypes were correlated with the severity of inflammatory acne and reported a specific loss of C. acnes phylotype diversity in this context.

OBJECTIVES

The aim of this exploratory study was to evaluate the efficacy of a new dermocosmetic product containing Myrtus communis and Celastrol-enriched plant cell culture extracts on C. acnes phylotype abundance and clinical parameters in subjects with mild to moderate acne vulgaris.

METHODS

Cutibacterium acnes phylotype diversity was evaluated by single-locus sequence typing sequencing on the nonlesional areas of the forehead, that is, areas excluding inflammatory lesions (papules and pustules) on day 1 (D1) and after 56 days (D57) of twice daily application of the dermocosmetic product on the whole face. Clinical efficacy on acne was also assessed by acne lesion counting and Global Evaluation Acne (GEA) score on D1 and D57.

RESULTS

Our study confirmed the link between the presence of some C. acnes phylotypes and acne severity. The dermocosmetic cream was linked to a positive impact on C. acnes phylotypes: a significant decrease in pro-pathogen phylotype IC and increase in nonpathogen phylotype IB were observed in the nonlesional areas of acne on D57 compared to D1. In parallel, the clinical results showed a significant decrease in inflammatory and comedonal acne lesions and a significant improvement in the acne severity according to the GEA score.

CONCLUSIONS

This study showed that the application of a new dermocosmetic product containing M. communis and Celastrol-enriched plant cell culture extracts was linked to a change in the C. acnes phylotype abundance and an improvement in acne severity.

Myrtus communis and Celastrol enriched plant cell culture extracts control together the pivotal role of Cutibacterium acnes and inflammatory pathways in acne

INTRODUCTION

Acne is a multifactorial inflammatory disease of the pilosebaceous unit in which Cutibacterium acnes is one of the main triggers. A strong predominance of C. acnes phylotype IA1 is present in acne skin with higher biofilm organization and virulence, promoting local immuno-inflammation, especially the Th17 pathway.

OBJECTIVES

We evaluated the single and combined pharmacological properties of the plant extracts, Myrtus communis (Myrtacine®) and Celastrol enriched plant cell culture (CEE) extracts on the C. acnes/Th17 pathway.

METHODS

The effect of Myrtacine® on the virulence of C. acnes phylotype IA1 was quantified according to the expression of several related genes. The activity of Myrtacine® and CEE on the inflammatory cascade was assessed using monocytes-derived dendritic cells (Mo-DC) stimulated with membranes or biofilms of the C. acnes phylotype IA1. Finally, the effect of CEE on the Th17 pathway was studied using C. acnes stimulated sebocyte 2D cultures and 3D skin tissue models containing preactivated Th17 cells.

RESULTS

Myrtacine® had an anti-virulence effect, evident as a significant and strong inhibition of the expression of several virulence factor genes by 60%-95% compared to untreated controls. Myrtacine® and CEE significantly inhibited proinflammatory cytokine (IL-6, IL-8, IL-12p40 and TNF-α) production by Mo-DC in response to C. acnes phylotype IA1. Interestingly, these two ingredients resulted in synergistic inhibition of most cytokines when used in combination. Finally, we demonstrated an inhibitory effect of CEE, in solution or formulated at 0.3%, specifically on IL-17 release by Th17 lymphocytes in a C. acnes-stimulated sebocyte 2D cultures and by Th17-lymphocytes integrated in a 3D skin models.

CONCLUSIONS

2D and 3D models were developed to represent relevant and specific pathways involved in acne. Myrtacine® and CEE were shown to alter one or more of these pathways, indicating their potential beneficial effects on this disease.

Specific protection of sensitive skin against environmental stress by maintenance and improvement of barrier function

BACKGROUND

Sensitive skin is a common condition that can severely impact quality of life. Several mechanisms are thought to be involved, including those affecting the skin barrier function, hydration and skin innervation.

OBJECTIVES

To investigate the benefit of cream and balm formulations dedicated to sensitive skin and containing Aquaphilus dolomiae extract-G3 (ADE-G3) on skin barrier functions (lipid composition, pH, TEWL), as well as protective responses to dry and pollution stresses.

METHODS

In vitro sensitized (using histamine) reconstructed human epidermis (RHE) were subjected to dehydration and pollution stress in the absence and presence of the formulations. Endpoint measurements included transepithelial electric resistance (TEER), stratum corneum protein expression and lipid contents. Clinical measurements included transepithelial water loss (TEWL), skin pH and the lipid index.

RESULTS

When applied in cream and balm formulations, ADE-G3, increased the TEER in sensitized RHEs. In non-sensitized dehydrated RHEs, both formulations increased recovery of skin barrier integrity after dehydration, evident as a return of the ratios of filaggrin/profilaggrin and caspase-14/procaspase-14 to values measured in control non-stressed RHEs, as well as reducing the 'natural moisturizing factor' to control levels. In clinical studies performed on dry human skin, the formulations helped to maintain and improve the skin barrier function. This was evident as an intense and sustained moisturization (total lipids and lipid esters were increased), an increase in pH and a decrease in the TEWL by both formulations. When exposed to pollution stress by treating the models with benzo[a]pyrene and airborne particulate matter (PM10), application of both formulations prior to exposure attenuated the induction of CYP1A1, CYP1B1 and UGT1A7 expression, indicating a protective effect.

CONCLUSIONS

ADE-G3 cream and balm formulations increased the hydration of the skin but also protected and improved the skin barrier integrity of sensitive skin exposed to dry and cold and airborne pollutant-induced stress environments.

Protective properties of Avène Thermal Spring Water on biomechanical, ultrastructural and clinical parameters of human skin

BACKGROUND

Thermal Spring Water (TSW) has been recognized to have beneficial effects on skin; however, the mechanisms underlying these are not completely elucidated.

AIMS

We compared the effects of Avène TSW with mineral-rich (MR) TSW on the biomechanical properties of the skin using mechanistic ex vivo assays and clinical studies.

METHODS

Ex vivo studies included the effect of both TSWs on the structure of the surface of human skin explants using scanning electron microscopy (SEM); mineral elemental content on the skin surface using SEM coupled to energy dispersing X-ray spectroscopy; and the stress properties of the stratum corneum (SC) when exposed to dehydration. Human clinical studies were conducted to compare the soothing effect of TSWs after a dermatological chemical peeling of face skin and to evaluate the overall sensitive scale of consumers using Avène TSW for 7 days.

RESULTS

Both TSWs preserved surface skin ultrastructure; however, crystals formed from MR-TSW were needle-like and formed small grains, present in clusters heterogeneously spread over the surface. Needle crystals were mainly composed of calcium, while small clusters were mainly composed of sulphur. By contrast, Avène TSW-formed crystals composed of sodium and chlorine only were regular in shape and homogeneously distributed across the skin surface. Peak stress of SC layers was increased by MR-TSW, whereas Avène TSW showed a comparatively reduced effect on dehydration and stress. The difference in the two TSW types was reflected in clinical findings comparing postpeeling redness after TSW application. Avène TSW significantly decreased postpeeling redness, while MR-TSW increased it. The overall sensitive scale of consumers was decreased by 47% using Avène TSW for 7 days.

CONCLUSIONS

Avène TSW decreases postpeeling redness and soothes sensitive skin in human volunteers. Mechanistic studies suggested that differences in biomechanical effects could be linked to differences in calcium content of the TSW.

Protective effect of Aquaphilus dolomiae extract-G1, ADE-G1, on tight junction barrier function in a Staphylococcus aureus-infected atopic dermatitis model

BACKGROUND

Atopic dermatitis (AD) is a common skin disease characterized by recurrent pruritic inflammatory skin lesions and defects of the skin barrier. Bacterial infection with Staphylococcus aureus contributes to increased severity of AD by compromising the barrier further. A microorganism component of Avène Thermal Spring Water, Aquaphilus dolomiae, is thought to contribute to some of its beneficial effects to skin, eg AD alleviation.

AIMS

Here, we have investigated the effects of an extract of A. dolomiae, A. dolomiae extract-G1 (ADE-G1), on the structural barrier function of keratinocytes, tight junction (TJ) protein expression and the expression of several genes altered in AD patients.

METHODS

An epidermal cell culture model mimicking the AD environment and phenotype was used, in which S. aureus-infected cell cultures of normal human epidermal keratinocytes were exposed to a proinflammatory environment. Endpoints measured included the transepithelial electrical resistance (TER) and immunohistological staining of the epidermal TJ proteins, claudin and occludin. Additional analysis was made of several genes known to be differentially regulated in skin from AD patients (C-C motif chemokine ligand 20 (CCL20), interleukin-8 (IL-8), S100 calcium binding protein A7 (S100A7), defensin beta 4 (DEFB4) and filaggrin).

RESULTS

Aquaphilus dolomiae extract-G1 strongly increased TER in non-infected cells and provided protection against infection by overcoming the decrease in TER induced by the infection with S. aureus. In infected cells exposed to a pro-inflammatory environment - depicting AD-like conditions - TER protection by ADE-G1 was still observed. Gene expression analysis of infected and pro-inflammatory stimulated cells indicated that ADE-G1 modulated the inflammatory response (induced IL-8 and attenuated CCL20 expression), increased antimicrobial activities (induced DEFB4 and A100A7) and strengthened barrier function (restored filaggrin expression).

CONCLUSIONS

ADE-G1 reinforces barrier function and strongly protects TJ barrier disruption induced by bacterial infection and inflammation.

High bacterial colonization and lipase activity in microcomedones

BACKGROUND

Although acne vulgaris has a multifactorial aetiology, comedogenesis and bacteria colonization of the pilosebaceous unit are known to play a major role in the onset of inflammatory acne lesions. However, many aspects remain poorly understood such as where and when is the early stage of the Propionibacterium acnes colonization in follicular unit? Our research aimed at providing a precise analysis of microcomedone's structure to better understand the interplay between Propionibacterium acnes and follicular units, and therefore, the role of its interplay in the formation of acne lesions.

METHODS

Microcomedones were sampled using cyanoacrylate skin surface stripping (CSSS). Their morphology was investigated with multiphoton imaging and their ultrastructure with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Bacterial lipase activity in the microcomedones was quantified using a dedicated enzymatic test as well as a Fourier Transform Infra-Red (FTIR) analysis. The porphyrin produced by bacteria was analysed with HPTLC and fluorescence spectroscopy.

RESULTS

The imaging analysis showed that microcomedones' structure resembles a pouch, whose interior is mostly composed of lipids with clusters of bacteria and whose outer shell is made up of corneocyte layers. The extensive bacteria colonization is clearly visible using TEM. Even after sampling, clear lipase activity was still seen in the microcomedone. A high correlation, r = .85, was observed between porphyrin content measured with HPTLC and with fluorescence spectroscopy. These observations show that microcomedones, which are generally barely visible clinically, already contain a bacterial colonization.

Visualization of dendritic cells' responses in atopic dermatitis: Preventing effect of emollient

Atopic dermatitis (AD) is a chronic and multifactorial inflammatory skin disease involving various dendritic cells such as epidermal Langerhans cells (LC) and inflammatory dendritic epidermal cells (IDECs). Most of the clinical studies was performed on isolated cells, and thus, it would be useful to characterize directly on the human epidermal tissue the first cellular events occurred during the AD. The suction blister method was used to obtain whole epidermis samples and interstitial cutaneous fluids. Employing multiphoton microscopy, we analyzed the early dynamic behavior of inflammatory cells using Dermatophagoides pteronyssinus atopy patch test (Derp-APT) and evaluated the effects of emollient pre-application. Derp-APT application provoked rapid and strong infiltration of IDECs, and proliferation and activation of LC in the AD subjects' epidermis. Moreover, emollient pre-application strengthened the defective skin barrier and had positive effects on inflammatory cells' behavior, characterized by the complete inhibition of IDEC influx and the presence of immature LC.

Optical coherence tomography: An efficient imaging method for the visualization of human epidermis orientation

Recently, it has been shown that epidermal sheets taken from suction blisters are very appropriate skin samples for Multi-Photon (MP) microscopy. However, we observed that image quality was much better when the sample was visualized through the basale side. Thus, the epidermis orientation needs to be controlled before MP imaging. We observed that the use of standard laboratory binoculars led to a high rate of false results. In this context, we showed that optical coherence tomography provided clear images of the epidermis orientation without loss of sample integrity and thus represents an effective technique before slide sealing and MP analysis.

Intraocular pressure reduction and neuroprotection conferred by bone marrow-derived mesenchymal stem cells in an animal model of glaucoma

INTRODUCTION

Glaucoma is a sight-threatening retinal neuropathy associated with elevated intraocular pressure (IOP) due to degeneration and fibrosis of the trabecular meshwork (TM). Glaucoma medications aim to reduce IOP without targeting the specific TM pathology, Bone-marrow mesenchymal stem cells (MSCs) are used today in various clinical studies. Here, we investigated the potential of MSCs therapy in an glaucoma-like ocular hypertension (OHT) model and decipher in vitro the effects of MSCs on primary human trabecular meshwork cells.

METHODS

Ocular hypertension model was performed by cauterization of 3 episcleral veins (EVC) of Long-Evans male rat eyes. MSCs were isolated from rat bone marrow, amplified in vitro and tagged with quantum dot nanocrystals. Animals were distributed as 1) MSCs group receiving 5.10(5)cells/6μl Minimum Essential Medium and 2) MEM group receiving 6μl MEM (n = 10 each). Injections were performed into the anterior chamber of 20 days-hypertensive eyes and IOP was monitored twice a week for 4 weeks. At the end of experiment, cell distribution in the anterior segment was examined in confocal microscopy on flat mounted corneas. Moreover, we tested in vitro effects of MSCs conditioned medium (MSC-CM) on primary human trabecular meshwork cells (hTM cells) using Akt activation, myosin phosphorylation and TGF-β2-dependent profibrotic phenotype in hTM cells.

RESULTS

We demonstrated a rapid and long-lasting in vivo effect of MSCs transplantation that significantly reduced IOP in hypertensive eyes induced by EVC. MSCs were located to the ciliary processes and the TM. Enumeration of RGCs on whole flat-mounted retina highlighted a protective effect of MSCs on RGCs death. In vitro, MSC-CM promotes: (i) hTM cells survival by activating the antiapoptotic pathway, Akt, (ii) hTM cells relaxation as analyzed by the decrease in myosin phosphorylation and (iii) inhibition of TGF-β2-dependent profibrotic phenotype acquisition in hTM cells.

CONCLUSIONS

MSCs injection in the ocular anterior chamber in a rat model of OHT provides neuroprotective effect in the glaucoma pathophysiology via TM protection. These results demonstrate that MSCs constitute promising tool for treating ocular hypertension and retinal cell degeneration.

Atomic force and electron microscopic-based study of sarcolemmal surface of living cardiomyocytes unveils unexpected mitochondrial shift in heart failure

Loss of T-tubules (TT), sarcolemmal invaginations of cardiomyocytes (CMs), was recently identified as a general heart failure (HF) hallmark. However, whether TT per se or the overall sarcolemma is altered during HF process is still unknown. In this study, we directly examined sarcolemmal surface topography and physical properties using Atomic Force Microscopy (AFM) in living CMs from healthy and failing mice hearts. We confirmed the presence of highly organized crests and hollows along myofilaments in isolated healthy CMs. Sarcolemma topography was tightly correlated with elasticity, with crests stiffer than hollows and related to the presence of few packed subsarcolemmal mitochondria (SSM) as evidenced by electron microscopy. Three days after myocardial infarction (MI), CMs already exhibit an overall sarcolemma disorganization with general loss of crests topography thus becoming smooth and correlating with a decreased elasticity while interfibrillar mitochondria (IFM), myofilaments alignment and TT network were unaltered. End-stage post-ischemic condition (15days post-MI) exacerbates overall sarcolemma disorganization with, in addition to general loss of crest/hollow periodicity, a significant increase of cell surface stiffness. Strikingly, electron microscopy revealed the total depletion of SSM while some IFM heaps could be visualized beneath the membrane. Accordingly, mitochondrial Ca(2+) studies showed a heterogeneous pattern between SSM and IFM in healthy CMs which disappeared in HF. In vitro, formamide-induced sarcolemmal stress on healthy CMs phenocopied post-ischemic kinetics abnormalities and revealed initial SSM death and crest/hollow disorganization followed by IFM later disarray which moved toward the cell surface and structured heaps correlating with TT loss. This study demonstrates that the loss of crest/hollow organization of CM surface in HF occurs early and precedes disruption of the TT network. It also highlights a general stiffness increased of the CM surface most likely related to atypical IFM heaps while SSM died during HF process. Overall, these results indicate that initial sarcolemmal stress leading to SSM death could underlie subsequent TT disarray and HF setting.

[Adult resident cardiomyocytes wake up: new axis for cardiac tissue regeneration]

All cardiomyopathies and more specifically myocardial infarction always evolve to cardiomyocytes death and the ensuing heart failure setting. So far, cardiac regenerative medicine has focused on the use of stem cells and completely ignored the resident cardiomyocytes, assumed in a postmitotic state. However, recent findings in zebrafish and mammalians challenge this view and suggest that these cells have some capacity to proliferate and can contribute to heart regeneration. In this review, we propose an overall synthesis about knowledge of the proliferative and regenerative capacities of resident cardiomyocytes, dealing with some mechanistic aspects. In the future, the accurate identification of molecular mechanisms allowing wake-up of resident cardiomyocyte proliferation will certainly open new therapeutic avenues in cardiac regeneration.

Role of endothelial AADC in cardiac synthesis of serotonin and nitrates accumulation

Serotonin (5-HT) regulates different cardiac functions by acting directly on cardiomyocytes, fibroblasts and endothelial cells. Today, it is widely accepted that activated platelets represent a major source of 5-HT. In contrast, a supposed production of 5-HT in the heart is still controversial. To address this issue, we investigated the expression and localization of 5-HT synthesizing enzyme tryptophan hydroxylase (TPH) and L-aromatic amino acid decarboxylase (AADC) in the heart. We also evaluated their involvement in cardiac production of 5-HT. TPH1 was weakly expressed in mouse and rat heart and appeared restricted to mast cells. Degranulation of mast cells by compound 48/80 did not modify 5-HT cardiac content in mice. Western blots and immunolabelling experiments showed an abundant expression of AADC in the mouse and rat heart and its co-localization with endothelial cells. Incubation of cardiac homogenate with the AADC substrate (5-hydroxy-L-tryptophan) 5-HTP or intraperitoneal injection of 5-HTP in mice significantly increased cardiac 5-HT. These effects were prevented by the AADC inhibitor benserazide. Finally, 5-HTP administration in mice increased phosphorylation of aortic nitric oxide synthase 3 at Ser (1177) as well as accumulation of nitrates in cardiac tissue. This suggests that the increase in 5-HT production by AADC leads to activation of endothelial and cardiac nitric oxide pathway. These data show that endothelial AADC plays an important role in cardiac synthesis of 5-HT and possibly in 5-HT-dependent regulation of nitric oxide generation.

Intraparenchymal injection of bone marrow mesenchymal stem cells reduces kidney fibrosis after ischemia-reperfusion in cyclosporine-immunosuppressed rats

Ischemia-reperfusion and immunosuppressive therapy are a major cause of progressive renal failure after kidney transplantation. Recent studies have shown that administration of bone marrow mesenchymal stem cells (MSCs) improves kidney functional recovery in the acute phase of post ischemia-reperfusion injury. In the present study, we used an original model of renal ischemia-reperfusion in immunosuppressed rats (NIRC) to investigate the effects of bone marrow MSCs on progression of chronic renal failure and the mechanisms potentially involved. Left renal ischemia-reperfusion (IR) was induced in unilateral nephrectomized Lewis rats. After IR, rats were treated daily with cyclosporine (10 mg/kg SC) for 28 days. MSCs were injected into the kidney at day 7 after IR. At day 28 after IR, kidneys were removed for histomorphological, biochemical, and gene expression analysis. The effect of conditioned media from MSCs on epithelial-mesenchymal transition was studied in vitro on HK2 cells. Our results show that, as compared to untreated NIRC rats, rats treated by intrarenal injection of MSCs 7 days after IR displayed improvement in renal function, reduction of interstitial fibrosis, and decrease in chronic tubule injury. These effects were associated with a decrease in interstitial α-SMA accumulation and MMP2 activity, markers of fibroblast/fibroblast-like cell activation, and renal remodeling, respectively. Finally, experiments in vitro showed that MSC-conditioned medium prevented epithelial-mesenchymal transition induced by TGF-β in HK2 cells. In conclusion, our results show that, in immunosuppressed animals, a single intrarenal administration of MSCs reduced renal fibrosis and promoted the recovery of renal function.

Evaluation of alginate microspheres for mesenchymal stem cell engraftment on solid organ

Mesenchymal stem cells (MSCs) may be used as a cell source for cell therapy of solid organs due to their differentiation potential and paracrine effect. Nevertheless, optimization of MSC-based therapy needs to develop alternative strategies to improve cell administration and efficiency. One option is the use of alginate microencapsulation, which presents an excellent biocompatibility and an in vivo stability. As MSCs are hypoimmunogenic, it was conceivable to produce microparticles with [alginate-poly-L-lysine-alginate (APA) microcapsules] or without (alginate microspheres) a surrounding protective membrane. Therefore, the aim of this study was to determine the most suitable microparticles to encapsulate MSCs for engraftment on solid organ. First, we compared the two types of microparticles with 4 × 10(6) MSCs/ml of alginate. Results showed that each microparticle has distinct morphology and mechanical resistance but both remained stable over time. However, as MSCs exhibited a better viability in microspheres than in microcapsules, the study was pursued with microspheres. We demonstrated that viable MSCs were still able to produce the paracrine factor bFGF and did not present any chondrogenic or osteogenic differentiation, processes sometimes reported with the use of polymers. We then proved that microspheres could be implanted under the renal capsule without degradation with time or inducing impairment of renal function. In conclusion, these microspheres behave as an implantable scaffold whose biological and functional properties could be adapted to fit with clinical applications.

Mesenchymal stem cells promote matrix metalloproteinase secretion by cardiac fibroblasts and reduce cardiac ventricular fibrosis after myocardial infarction

Recent studies showed that mesenchymal stem cells (MSCs) transplantation significantly decreased cardiac fibrosis; however, the mechanisms involved in these effects are still poorly understood. In this work, we investigated whether the antifibrotic properties of MSCs involve the regulation of matrix metalloproteinases (MMPs) and matrix metalloproteinase endogenous inhibitor (TIMP) production by cardiac fibroblasts. In vitro experiments showed that conditioned medium from MSCs decreased viability, alpha-smooth muscle actin expression, and collagen secretion of cardiac fibroblasts. These effects were concomitant with the stimulation of MMP-2/MMP-9 activities and membrane type 1 MMP expression. Experiments performed with fibroblasts from MMP2-knockout mice demonstrated that MMP-2 plays a preponderant role in preventing collagen accumulation upon incubation with conditioned medium from MSCs. We found that MSC-conditioned medium also decreased the expression of TIMP2 in cardiac fibroblasts. In vivo studies showed that intracardiac injection of MSCs in a rat model of postischemic heart failure induced a significant decrease in ventricular fibrosis. This effect was associated with the improvement of morphological and functional cardiac parameters. In conclusion, we showed that MSCs modulate the phenotype of cardiac fibroblasts and their ability to degrade extracellular matrix. These properties of MSCs open new perspectives for understanding the mechanisms of action of MSCs and anticipate their potential therapeutic or side effects.

Ex vivo pretreatment with melatonin improves survival, proangiogenic/mitogenic activity, and efficiency of mesenchymal stem cells injected into ischemic kidney

Bone marrow mesenchymal stem cells (MSCs) have shown great potential in cell therapy of solid organs. Approaches to improving the ability of grafted MSCs to survive and secrete paracrine factors represent one of the challenges for the further development of this novel therapy. In the present study, we designed a strategy of ex vivo pretreatment with the pineal hormone melatonin to improve survival, paracrine activity, and efficiency of MSCs. Using a rat model of acute renal failure, we showed that melatonin pretreatment strongly increased survival of MSCs after intraparenchymal injection. This effect was concomitant with overstimulation of angiogenesis, proliferation of renal cells, and accelerated recovery of renal function. To gain insight into the mechanisms involved in the effects observed in vivo, melatonin was tested in vitro on cultured MSCs. Our results show that through stimulation of specific melatonin receptors, melatonin induced an overexpression of the antioxidant enzyme catalase and superoxide dismutase-1 and increased the resistance of MSCs to hydrogen peroxide-dependent apoptosis. Compared with untreated cells, MSCs incubated with melatonin displayed a higher expression of basic fibroblast growth factor and hepatocyte growth factor. In addition, conditioned culture media from melatonin-treated MSCs stimulated tube formation by endothelial progenitor cells and proliferation of proximal tubule cells in culture. In conclusion, our results show that melatonin behaves as a preconditioning agent increasing survival, paracrine activity, and efficiency of MSCs. The use of this molecule for pretreatment of stem cells may represent a novel and safe approach to improving the beneficial effects of cell therapy of solid organs.