Human adipose tissue-derived stromal cells act as functional pericytes in mice and suppress high-glucose-induced proinflammatory activation of bovine retinal endothelial cells.

AIMS/HYPOTHESIS: The immunomodulatory capacity of adipose tissue-derived stromal cells (ASCs) is relevant for next-generation cell therapies that aim to reverse tissue dysfunction such as that caused by diabetes. Pericyte dropout from retinal capillaries underlies diabetic retinopathy and the subsequent aberrant angiogenesis. METHODS: We investigated the pericytic function of ASCs after intravitreal injection of ASCs in mice with retinopathy of prematurity as a model for clinical diabetic retinopathy. In addition, ASCs influence their environment by paracrine signalling. For this, we assessed the immunomodulatory capacity of conditioned medium from cultured ASCs (ASC-Cme) on high glucose (HG)-stimulated bovine retinal endothelial cells (BRECs). RESULTS: ASCs augmented and stabilised retinal angiogenesis and co-localised with capillaries at a pericyte-specific position. This indicates that cultured ASCs exert juxtacrine signalling in retinal microvessels. ASC-Cme alleviated HG-induced oxidative stress and its subsequent upregulation of downstream targets in an NF-κB dependent fashion in cultured BRECs. Functionally, monocyte adhesion to the monolayers of activated BRECs was also decreased by treatment with ASC-Cme and correlated with a decline in expression of adhesion-related genes such as SELE, ICAM1 and VCAM1. CONCLUSIONS/INTERPRETATION: The ability of ASC-Cme to immunomodulate HG-challenged BRECs is related to the length of time for which ASCs were preconditioned in HG medium. Conditioned medium from ASCs that had been chronically exposed to HG medium was able to normalise the HG-challenged BRECs to normal glucose levels. In contrast, conditioned medium from ASCs that had been exposed to HG medium for a shorter time did not have this effect. Our results show that the manner of HG preconditioning of ASCs dictates their immunoregulatory properties and thus the potential outcome of treatment of diabetic retinopathy.

A global downregulation of microRNAs occurs in human quiescent satellite cells during myogenesis.

During myogenesis, human satellite cells differentiate and form multinucleated myotubes, while a fraction of the human satellite cells enter quiescence. These quiescent satellite cells are able to activate, proliferate and contribute to muscle regeneration. Post-transcriptional regulation of myogenesis occurs through specific myogenic microRNAs, also known as myomiRs. Although many microRNAs are involved in myotube formation, little is known on the involvement of microRNAs in satellite cells entering quiescence. This current study aims to investigate microRNA involvement during differentiation of human satellite cells, specifically proliferating satellite cells entering quiescence. For this, clonally expanded human satellite cells were differentiated for 5 days, after which myotubes and quiescent satellite cells were separated through FACS sorting. Next, a microRNA microarray comparison of proliferating satellite cells, myotubes and quiescent satellite cells was performed and verified through qRT-PCR. We show that during human satellite cell differentiation, microRNAs are globally downregulated in quiescent satellite cells compared to proliferating satellite cells, in particular microRNA-106b, microRNA-25, microRNA-29c and microRNA-320c. Furthermore, we show that during myogenesis microRNA-1, microRNA-133, microRNA-206 and microRNA-486 are involved in myotube formation rather than satellite cells entering quiescence. Finally, we show an overall decrease in total mRNA in quiescent satellite cells, and an indication that RNaseL regulation plays a role in promoting and maintaining quiescence. Given the importance of quiescent satellite cells in skeletal muscle development and regenerative medicine, it is imperative to distinguish between myotubes and quiescent satellite cells when investigating skeletal muscle development, especially in microRNA studies, since we show that microRNAs are globally downregulated in quiescent human satellite cells.

Epicardium-derived cells enhance proliferation, cellular maturation and alignment of cardiomyocytes.

During heart development, cells from the proepicardial organ spread over the naked heart tube to form the epicardium. From here, epicardium-derived cells (EPDCs) migrate into the myocardium. EPDCs proved to be indispensable for the formation of the ventricular compact zone and myocardial maturation, by largely unknown mechanisms. In this study we investigated in vitro how EPDCs affect cardiomyocyte proliferation, cellular alignment and contraction, as well as the expression and cellular distribution of proteins involved in myocardial maturation. Embryonic quail EPDCs induced proliferation of neonatal mouse cardiomyocytes. This required cell-cell interactions, as proliferation was not observed in transwell cocultures. Western blot analysis showed elevated levels of electrical and mechanical junctions (connexin43, N-cadherin), sarcomeric proteins (Troponin-I, alpha-actinin), extracellular matrix (collagen I and periostin) in cocultures of EPDCs and cardiomyocytes. Immunohistochemistry indicated more membrane-bound expression of Cx43, N-cadherin, the mechanotransduction molecule focal adhesion kinase, and higher expression of the sarcoplasmic reticulum Ca(2+) ATPase (SERCA2a). Newly developed software for analysis of directionality in immunofluorescent stainings showed a quantitatively determined enhanced cellular alignment of cardiomyocytes. This was functionally related to increased contraction. The in vitro effects of EPDCs on cardiomyocytes were confirmed in three reciprocal in vivo models for EPDC-depletion (chicken and mice) in which downregulation of myocardial N-cadherin, Cx43, and FAK were observed. In conclusion, direct interaction of EPDCs with cardiomyocytes induced proliferation, correct mechanical and electrical coupling of cardiomyocytes, ECM-deposition and concurrent establishment of cellular array. These findings implicate that EPDCs are ideal candidates as adjuvant cells for cardiomyocyte integration during cardiac (stem) cell therapy.

Endothelial progenitor cell-based neovascularization: implications for therapy.

Ischemic cardiovascular events are a major cause of death globally. Endothelial progenitor cell (EPC)-based approaches can result in improvement of vascular perfusion and might offer clinical benefit. However, although functional improvement is observed, the lack of long-term engraftment of EPCs into neovessels has raised controversy regarding their mechanism of action. We and others have hypothesized that after ischemic injury, EPCs induce neovascularization through the secretion of cytokines and growth factors, which act in a paracrine fashion and induce sprouting angiogenesis by the surrounding endothelium. In this concise review, we discuss the (patho)physiology of EPC-induced neovascularization and focus on the paracrine signals secreted by EPCs and the effects they elicit. In future therapies, clinical administration of these paracrine modulators using slow-release depots might induce neovascularization and might therefore hold promise for vascular regenerative medicine.

Ciclosporin does not influence bone marrow-derived cell differentiation to myofibroblasts early after renal ischemia/reperfusion.

BACKGROUND: Ischemia/reperfusion injury (IRI) is a risk factor for the development of interstitial fibrosis. Previously we had shown that after renal IRI, bone marrow-derived cells (BMDC) can differentiate to interstitial myofibroblasts. Here we hypothesized that the immunosuppressant ciclosporin A (CsA), known for its profibrotic side effect, promotes myofibroblast differentiation of BMDC in the postischemic kidney. METHODS: Using a model of unilateral renal IRI in rats reconstituted with R26-human placental alkaline phosphatase transgenic bone marrow, CsA was administered in a previously defined critical window for differentiation of BMDC to myofibroblasts. We evaluated fibrotic changes in the kidney and myofibroblast differentiation of BMDC on day 14 after CsA treatment. RESULTS: CsA treatment for 14 days led to increased transforming growth factor-beta transcript levels and collagen III deposition in the postischemic kidney. However, neither the total number of alpha-smooth-muscle-actin-positive interstitial myofibroblasts, nor the bone marrow-derived fraction thereof was affected by CsA administration, irrespective of dosage and duration of treatment. CONCLUSIONS: In the critical postischemic window of BMDC differentiation to myofibroblasts, CsA did not promote BMDC differentiation to myofibroblasts, suggesting that, in the clinical setting, CsA is not involved in myofibroblastic differentiation of BMDC.

Human retinal Müller cells synthesize collagens of the vitreous and vitreoretinal interface in vitro.

PURPOSE: To investigate the capacity of cultured Müller cells to synthesize collagens, since previous studies indicated that Müller cells could be involved in collagen remodeling at the vitreoretinal border in adult human eyes. METHODS: Spontaneously immortalized cultured human Müller cells were analyzed for the presence of mRNA of types I-VII, IX, XI, and XVII collagen by RT-PCR. Furthermore, Müller cells were immunocytochemically stained for light microscopic (LM) evaluation of these collagens and their main characteristics. Finally, cell extracts and culture medium were evaluated by western blot (WB) analysis using anticollagen antibodies. RESULTS: Cultured Müller cells contained mRNA for types I-VII, IX, and XI collagen, but not for type XVII collagen. LM and WB confirmed the intracellular expression of all the above-mentioned collagens with the exception of type XVII. Collagen secretion into the medium was established for types I-VII, IX, and XI collagen. CONCLUSIONS: Cultured Müller cells can synthesize internal limiting lamina and vitreous collagens. Possible collagen production by Müller cells could explain and expand on previous in vivo morphological findings in the embryonic and postnatal period and in pathologic conditions.

Vascular smooth muscle cells for use in vascular tissue engineering obtained by endothelial-to-mesenchymal transdifferentiation (EnMT) on collagen matrices.

The discovery of the endothelial progenitor cell (EPC) has led to an intensive research effort into progenitor cell-based tissue engineering of (small-diameter) blood vessels. Herein, EPC are differentiated to vascular endothelial cells and serve as the inner lining of bioartificial vessels. As yet, a reliable source of vascular smooth muscle progenitor cells has not been identified. Currently, smooth muscle cells (SMC) are obtained from vascular tissue biopsies and introduce new vascular pathologies to the patient. However, since SMC are mesenchymal cells, endothelial-to-mesenchymal transdifferentiation (EnMT) may be a novel source of SMC. Here we describe the differentiation of smooth muscle-like cells through EnMT. Human umbilical cord endothelial cells (HUVEC) were cultured either under conditions favoring endothelial cell growth or under conditions favoring mesenchymal differentiation (TGF-beta and PDGF-BB). Expression of smooth muscle protein 22alpha and alpha-smooth muscle actin was induced in HUVEC cultured in mesenchymal differentiation media, whereas hardly any expression of these markers was found on genuine HUVEC. Transdifferentiated endothelial cells lost the ability to prevent thrombin formation in an in vitro coagulation assay, had increased migratory capacity towards PDGF-BB and gained contractile behavior similar to genuine vascular smooth muscle cells. Furthermore, we showed that EnMT could be induced in three-dimensional (3D) collagen sponges. In conclusion, we show that HUVEC can efficiently transdifferentiate into smooth muscle-like cells through endothelial-to-mesenchymal transdifferentiation. Therefore, EnMT might be used in future progenitor cell-based vascular tissue engineering approaches to obtain vascular smooth muscle cells, and circumvent a number of limitations encountered in current vascular tissue engineering strategies.

Cryoinjury: a model of myocardial regeneration.

INTRODUCTION: Although traditionally adult cardiomyocytes are thought to be unable to divide, recent observations provide evidence for cardiomyocyte proliferation after myocardial injury. Myocardial cryoinjury has been shown to be followed by neovascularization. We hypothesize that, in addition to neovascularization, cardiomyocyte proliferation after myocardial cryoinjury contributes to regeneration. METHOD: Cryolesions were applied to the left ventricle of mouse hearts. Inflammatory cell infiltration (F4/80, neutrophils), neovascularization (CD31), and cardiomyocyte proliferation (5-bromo-2-deoxyuridine, Ki-67, mitotic spindle) were determined at different time points (2-70 days) after cryoinjury. RESULTS: Between Days 7 and 14 after injury, a 150- and 280-fold increase in number of proliferating cardiomyocytes was observed, as compared to controls. At the same time, numerous proliferating capillaries were found in between the proliferating cardiomyocytes. Presence of high numbers of macrophages in the cryolesion preceded and coincided with this proliferation. The area of cryolesion decreased significantly between Days 7 (23+/-5%) and 14 (8+/-2%) after cryoinjury. Moreover, regeneration of viable, nonhypertrophied myocardium was observed. After 14 days, cardiomyocyte proliferation decreased to numbers observed in controls, and concomitantly, the number of macrophages strongly decreased. CONCLUSION: Our data show that adult cardiomyocytes proliferate in sufficiently high numbers to effectuate myocardial regeneration after left ventricular cryoinjury in mice.

Trimethylene carbonate and epsilon-caprolactone based (co)polymer networks: mechanical properties and enzymatic degradation.

High molecular weight trimethylene carbonate (TMC) and epsilon-caprolactone (CL) (co)polymers were synthesized. Melt pressed (co)polymer films were cross-linked by gamma irradiation (25 kGy or 50 kGy) in vacuum, yielding gel fractions of up to 70%. The effects of copolymer composition and irradiation dose on the cytotoxicity, surface properties, degradation behavior, and mechanical and thermal properties of these (co)polymers and networks were investigated. Upon incubation with cell culture medium containing extracts of (co)polymers and networks, human foreskin fibroblasts remained viable. For all (co)polymers and networks, cell viabilities were determined to be higher than 94%. The formed networks were flexible, with elastic moduli ranging from 2.7 to 5.8 MPa. Moreover, these form-stable networks were creep resistant under dynamic conditions. The permanent deformation after 2 h relaxation was as low as 1% after elongating to 50% strain for 20 times. The in vitro enzymatic erosion behavior of these hydrophobic (co)polymers and networks was investigated using aqueous lipase solutions. The erosion rates in lipase solution could be tuned linearly from 0.8 to 45 mg/(cm (2) x day) by varying the TMC to CL ratio and the irradiation dose. The copolymers and networks degraded essentially by a surface erosion mechanism.

Should in the treatment of osteochondritis dissecans biodegradable or metallic fixation devices be used? A comparative study in goat knees.

Most of the metallic devices have to be removed, treating osteochondritis dissecans lesions. This animal study describes the biological and mechanical behavior of screws and pins, made of commercially available PGA/PLA and PLA96 and metallic screws and pins, used for fragment fixation. A sham operation served as control. A tissue reaction with cavity formation was observed around every PGA/PLA screw, beginning at 12 weeks following insertion, in contrast to once around a PLA96 screw (p < 0.001), once around one of the 16 PGA/PLA pins and never around those, made of PLA96 (no significance). Disintegration of the PGA/PLA devices started 6 weeks following implantation against 34 weeks for the PLA96 implants. The gap between the fragment and the recipient cartilage disappeared only in the sham group. Many fragments of PGA/PLA material were found in the synovia, in contrast with just a few fragments in the PLA96 group, causing a mild cellular reaction. No polymer particles were found in the draining lymph nodes at any interval. In conclusion, the tested biodegradable screws should not be used for fragment fixation in the treatment of osteochondritis dissecans. Either an undesirable tissue reaction can be expected (PGAPLA), or, because of the slow degradation (PLLA), a screw might damage the opposite cartilage during weight bearing. Two biodegradable pins provide a safe rotational stability and should be combined with one metallic screw, providing compression. This screw has to be removed before loading the limb to prevent cartilage wear of the opposite tibia plateau.

Heparin coating of poly(ethylene terephthalate) decreases hydrophobicity, monocyte/leukocyte interaction and tissue interaction.

Woven poly(ethylene terephthalate) (PET) is widely used in implantable medical devices. Upon implantation, fibrinogen interacts with the PET and changes conformation, such that the fibrinogen P2 epitope may become exposed. This allows inflammatory cells to interact with the material. In this study we have coated PET with heparin and show that this decreases PET hydrophobicity and the presence of the fibrinogen P2 epitope on the material surface. In addition, we show that heparin-induced reduction of PET hydrophobicity correlates with decreased exposure of the fibrinogen P2 epitope and reduced adhesion of monocytes. Reduction of PET hydrophobicity was furthermore associated with reduced PMN elastase production and decreased interaction between PET and embryonic chicken tissue. We conclude that the heparin coating-induced decrease in PET hydrophobicity is associated with decreased interaction between PET and inflammatory cells. Independent of this interaction, the hydrophobic nature of the heparin coating is related to tissue interaction as demonstrated by a reduction in adhesion, growth and spreading of tissue on PET. The combination of these properties makes heparin coating a candidate for improving biocompatibility of PET.

Stem cell-related cardiac gene expression early after murine myocardial infarction.

OBJECTIVE: Clinical experimental stem cell therapy after myocardial infarction appears feasible, but its use has preceded the understanding of the working mechanism. The ischemic recipient cardiac environment is determinative for the attraction and subsequent fate of stem cells. Here, we studied expression levels of genes that are anticipated to be essential for adequate stem cell-based cardiac repair at various time-points during the 1 month period following myocardial infarction (MI). METHODS: Gene expression in the hearts of mice that underwent MI by permanent or transient (30 min) ligation of the coronary artery was monitored using quantitative RT-PCR analysis of mRNA isolated from whole heart sections as well as from specific, laser micro-dissected, regions of sections. Protein expression was performed by immunohistochemical stainings and Western blot analysis. RESULTS: Many inflammatory genes were highly expressed for at least 1 week after MI. The expression of pro-angiogenic genes such as bFGF, VEGF-A and VEGF-R2 changed only marginally post-MI. Markers used to test stem cell gene expression remained unchanged post-MI with the exception of G-CSF and GM-CSF, which are genes that are also known to enhance the inflammatory response. Analysis of micro-dissected regions revealed that SDF-1, SCF (both stem cell attractants) and VEGF-R2 (involved in angiogenesis) gene expression was slightly decreased especially in the infarcted region. CONCLUSION: Genes that are generally considered to participate in stem cell-related processes and angiogenesis were not upregulated after MI, whereas the inflammatory gene expression dominated. Modulation of this imbalance might be of value for stem cell-mediated therapy.

Tubular engraftment and myofibroblast differentiation of recipient-derived cells after experimental kidney transplantation.

BACKGROUND: In human renal allografts, recipient-derived cells engrafted in various kidney substructures, have been detected in the long term after transplantation. Here we investigated tubular engraftment and myofibroblast differentiation of recipient-derived cells at short term after experimental kidney transplantation, during a previously described window of regeneration and possible onset of renal interstitial fibrosis. METHODS: Fisher (F344, syngeneic) and Dark Agouti (DA, allogeneic) kidneys were transplanted into F344-hPAP transgenic recipient rats, which allowed tracing of recipient-derived cells in nontransgenic donor kidneys. We evaluated tubular engraftment and myofibroblast differentiation of recipient-derived cells on day 14 after kidney transplantation. RESULTS: Kidney transplantation resulted in tubular engraftment of recipient-derived cells. After allogeneic kidney transplantation, 9.7% of tubular cross-sections contained at least one recipient-derived cell, which represented a significant increase in comparison to syngeneic transplantation (4.0%, P<0.05). Moreover, recipient-derived myofibroblasts were present in the renal interstitium of the transplanted kidney. These cells contributed 39% of the total interstitial myofibroblast population in allografts, which was comparable to the syngeneic situation (28%, P=0.25). CONCLUSIONS: In a defined early window of regeneration and possible onset of renal interstitial fibrosis after kidney transplantation, rejection-associated injury, superimposed on ischemic damage, increases tubular engraftment of recipient-derived cells, although it does not affect their relative contribution to the renal interstitial myofibroblast population.

Efficient differentiation of CD14+ monocytic cells into endothelial cells on degradable biomaterials.

Vascular tissue engineering aims at creating self-renewing, anti-thrombogenic, vascular grafts, which can be based on endothelial progenitor cells (EPC). EPC harbor essential features such as plasticity and longevity. Unfortunately, the archetype CD34(+) EPC is rare in peripheral blood. Monocytes, i.e. CD14(+) cells also have the ability to differentiate into endothelial-like cells and are by far more abundant in peripheral blood than are CD34(+) EPC. Therefore, CD14(+) cells would seem appropriate candidates for tissue engineering of small-diameter blood vessels. In this study, we investigated the differentiation of CD14(+) cells on three biodegradable biomaterials under angiogenic conditions. Morphological analyses, gene transcript analyses, endothelial marker (i.e. VE-Cadherin and eNOS) and macrophage marker (i.e. CD68 and CD163) expression analyses, revealed that a small fraction (15-25%) of cultured CD14(+) cells differentiated into macrophages after 21 days of culture. The majority of CD14(+) cells (>75%) differentiated into endothelial-like cells (ELC) on all biomaterials used. The expression of endothelial markers was similar to their expression on HUVEC. Since CD14(+) cells are present in high numbers in adult peripheral blood, easy to isolate and because they easily differentiate into ELC on biomaterials, we conclude that CD14(+) cells are a suitable cell source for progenitor-based vascular tissue engineering.

Dependence of neovascularization mechanisms on the molecular microenvironment.

In vivo vascularization of implanted (bio)artificial constructs is essential for their proper function. Vascularization may rely on sprouting angiogenesis, vascular incorporation of bone marrow-derived endothelial cells (BMDECs), or both. Here we investigated the relative contribution of these 2 mechanisms to neovascularization in a mouse model of a foreign body reaction (FBR) to subcutaneously implanted Dacron and in hind limb ischemia (HLI) in relation to the molecular microenvironment at these neovascularization sites. Neovascularization was studied in C57Bl/6 mice reconstituted with enhanced green fluorescent protein (EGFP) transgenic bone marrow. Sprouting angiogenesis, detected using nuclear incorporation of bromodeoxyuridine in endothelial cells was present in both models, whereas vascular incorporation of EGFP(+) BMDECs was restricted to HLI. In HLI, the presence of a pro-angiogenic molecular microenvironment comprising vascular endothelial growth factor, fibroblast growth factor 2, and granulocyte colony-stimulating factor corroborated the importance of these factors for vascular BMDEC incorporation, whereas this microenvironment was absent in FBR. Enhanced mobilization of BMDECs by granulocyte-macrophage colony-stimulating factor administration or by combining HLI and FBR with Dacron did not induce incorporation of BMDECs in FBR neovessels. We conclude that the efficacy of BMDEC-based therapy is not generally warranted, but it depends on the molecular microenvironment in the targeted tissue.

The enzymatic degradation of scaffolds and their replacement by vascularized extracellular matrix in the murine myocardium.

Replacement of injured myocardium by cell-based degradable scaffolds is a novel approach to regenerate myocardium. Understanding the foreign body reaction (FBR) induced by the scaffold is requisite to predict unwanted site effects or implant failure. We evaluated the FBR against a biodegradable scaffold applied on injured myocardium in mice. Cryolesions and collagen type I scaffolds (Col-I) were applied to the left ventricle of mice. Cell infiltration, neovascularization, collagen deposition, matrix metalloproteinase (MMP-8) expression, enzymatic activity and scaffold degradation were determined at different time points (2-70 days). Infiltration of mainly macrophages, neutrophils and blood vessels was completed within 14 days. High numbers of neutrophils accumulated around the Col-I fibers and degradation of Col-I fibers into small fragments was observed on day 14. Active MMP-8 co-localized with the neutrophils on day 14, indicating enzymatic degradation of Col-I by neutrophil collagenase. Highly vascularized extracellular matrix remained at day 70. No differences were observed in the FBR to Col-I after application on healthy or injured myocardium. The FBR had no adverse effects on the adjacent myocardial tissue. In conclusion, cardiac scaffolds are degraded by MMP-8 and replaced by vascularized extracellular matrix during the FBR on injured myocardium.

The correlation between difference in foreign body reaction between implant locations and cytokine and MMP expression.

The foreign body reaction (FBR) differs between subcutaneously and supra-epicardially implanted materials. We hypothesize that this is a result of differences in cytokine, chemokine and matrix metalloproteinase (MMP) dynamics. Therefore we applied collagen disks subcutaneously and on the epicardium in mice and analyzed the FBR from day 1 to 21. Both the influx of leukocytes and implant degradation were higher in supra-epicardially implanted collagen than in subcutaneously implanted material. This correlated with a higher gene expression of pro-inflammatory cytokines such as IL-1 and IL-6, and a lower expression of the anti-inflammatory cytokine IL-10. Furthermore, the higher supra-epicardial expression of PMN attractants CXCL1/KC and CXCL2/MIP2 correlated with a higher and prolonged PMN influx. The gene expression levels of collagen degrading MMPs, i.e. MMP8, MMP13 and MMP14 were similar in subcutaneous and supra-epicardial disks. However, the activity of these enzymes was markedly higher supra-epicardially. In addition, the MMP9 expression was higher supra-epicardially, suggesting a role for this enzyme in the degradation process. In conclusion, a strong pro-inflammatory milieu is generated after supra-epicardial implantation that enables prolonged PMN presence and activation. This, together with the high supra-epicardial MMP9 level, could explain the observed difference in Col-I degradation between locations.

Chemical and biological properties of supramolecular polymer systems based on oligocaprolactones.

We show that materials with a diverse range of mechanical and biological properties can be obtained using a modular approach by simply mixing different ratios of oligocaprolactones that are either end-functionalized or chain-extended with quadruple hydrogen bonding ureido-pyrimidinone (UPy) moieties. The use of two UPy-synthons allows for easy synthesis of UPy-modified polymers resulting in high yields. Comparison of end-functionalized UPy-polymers with chain-extended UPy-polymers shows that these polymers behave distinctively different regarding their material and biological properties. The end-modified UPy-polymer is rather stiff and brittle due to its high crystallinity. Disks made of this material fractures after subcutaneous implantation. The material shows a low inflammatory response which is accompanied by the formation of a fibrous capsule, reflecting the inertness of the material. The chain-extended UPy-material on the contrary is practically free of crystalline domains and shows clear flexible properties. This material deforms after in-vivo implantation, accompanied with cellular infiltration. By mixing both polymers, materials with intermediate properties concerning their mechanical and biological behaviour can be obtained. Surprisingly, a 20:80 mixture of both polymers with the chain-extended UPy-polymer in excess shows flexible properties without visible deformation upon implantation for 42 days. This mixture, a blend formed by intimate mixing through UPy-UPy interaction, also shows a mild tissue response accompanied with the formation of a thin capsule. The material does not become more crystalline upon implantation. Hence, this mixture might be an ideal scaffold material for soft tissue engineering due to its flexibility and diminished fibrous tissue formation, and illustrates the strength of the modular approach.

Cellular and molecular dynamics in the foreign body reaction.

Intracorporally implanted materials, such as medical devices, will provoke the body to initiate an inflammatory reaction. This inflammatory reaction to implanted materials is known as the foreign body reaction (FBR) and is characterized by 3 distinct phases: onset, progression, and resolution. The FBR proceeds in the creation of a dynamic microenvironment that is spatially well organized. The progression of the FBR is regulated by soluble mediators, such as cytokines, chemokines, and matrix metalloproteinases (MMPs), which are produced locally by tissue cells and infiltrated inflammatory cells. These soluble mediators orchestrate the cascade of cellular processes in the microenvironment that accompanies the FBR, consisting of cellular activation, angiogenesis, extravasation, migration, phagocytosis, and, finally, fibrosis. The nature of the FBR requires that the soluble mediators act in a spatial and temporally regulated manner as well. This regulation is well known for several inflammatory processes, but scarce knowledge exists about the intricate relationship between the FBR and the expression of soluble mediators. This review discusses the key processes during the initiation, progression, and resolution phase, with emphasis on the role of soluble mediators. Besides other sites of implantation, we focus on the subcutaneous implantation model.

Increased inflammatory response and neovascularization in reperfused vs. non-reperfused murine myocardial infarction.

INTRODUCTION: Fundamental knowledge of the inflammatory response after myocardial infarction (MI) is indispensable for intervention toward cardiac regeneration. Although reperfusion is preferred as clinical therapy, for basic research, also permanent ligation MI models are widely used. METHODS: In this report, we pathohistologically compared the kinetics of the inflammatory and angiogenic response after MI induced by permanent ligation or ligation followed by reperfusion of the left anterior descending coronary artery in mice. RESULTS: Permanent ligation resulted in a higher mortality rate accompanied by increased left ventricular dilatation and more progressive wall thinning. However, reperfused infarcts showed higher inflammatory cell influx. Neutrophil numbers were higher after reperfusion post-MI, although their presence was prolonged after ligation. Also, the number of macrophages after reperfusion was continuously higher, but the course of macrophage influx was comparable in both models. The number of lymphocytes was low in both models. Only the peak in myofibroblast numbers at 7 days was higher after ligation than after reperfusion. Moreover, cardiomyocyte remnants were cleared faster, and collagen deposition started earlier after reperfusion. In addition, reperfusion resulted in an increased angiogenic response, as was reflected in increased numbers of medium-sized and large vessels at 7 and 14 days post-MI. CONCLUSION: We show less adverse remodeling together with a higher presence of inflammatory cells and enhanced neovascularization in reperfused MI. These differences between non-reperfused and reperfused MI should be taken into consideration for experimental use of MI models.