Matrix metalloproteinases in intestinal fibrosis.

Intestinal fibrosis is a common complication in patients with inflammatory bowel disease [IBD], in particular Crohn's disease [CD]. Unfortunately, at present intestinal fibrosis is not yet preventable, and cannot be treated by interventions other than surgical removal. Intestinal fibrosis is characterized by excessive accumulation of extracellular matrix [ECM], which is caused by activated fibroblasts and smooth muscle cells. Accumulation of ECM results from an imbalanced production and degradation of ECM. ECM degradation is mainly performed by matrix metalloproteinases [MMPs], enzymes that are counteracted by tissue inhibitors of MMPs [TIMPs]. In IBD patients, MMP activity [together with other protease activities] is increased. At the same time, CD patients have a generally lower MMP activity compared to ulcerative colitis patients, who usually do not develop intestinal strictures or fibrosis. The exact regulation and role[s] of these MMPs in fibrosis are far from understood. Here, we review the current literature about ECM remodelling by MMPs in intestinal fibrosis and their potential role as biomarkers for disease progression or druggable targets.

Verteporfin ameliorates fibrotic aspects of Dupuytren's disease nodular fibroblasts irrespective the activation state of the cells.

Dupuytren's disease is a chronic, progressive fibroproliferative condition of the hand fascia which results in digital contraction. So far, treatments do not directly interfere with the (myo)fibroblasts that are responsible for the formation of the collagen-rich cords and its contraction. Here we investigated whether verteporfin (VP) is able to inhibit the activation and subsequent differentiation of DD nodular fibroblasts into myofibroblasts. Fibroblasts were isolated from nodules of 7 Dupuytren patients. Cells are treated (1) for 48 h with 5 ng/ml transforming growth factor ß1 (TGF-ß1) followed by 48 h with/without 250 nM VP in the absence of TGF-ß1, or treated (2) for 48 h with TGF-ß1 followed by 48 h with/without VP in the presence of TGF-ß1. mRNA levels were measured by means of Real-Time PCR, and proteins were visualized by means of Western blotting and/or immunofluorescence. Quantitative data were statistically analyzed with GraphPad Prism using the paired t-test. We found that fibroblasts activated for 48 h with TGF-ß1 show a decrease in mRNA levels of COL1A1, COL3A1, COL4A1, PLOD2, FN1EDA, CCN2 and SERPINE1 when exposed for another 48 h with VP, whereas no decrease is seen for ACTA2, YAP1, SMAD2 and SMAD3 mRNA levels. Cells exposed for an additional 48 h with TGF-ß1, but now in the presence of VP, are not further activated anymore, whereas in the absence of VP the cells continue to differentiate into myofibroblasts. Collagen type I, fibronectin-extra domain A, α-smooth muscle actin, YAP1, Smad2 and Smad3 protein levels were attenuated by both VP treatments. We conclude that VP has strong anti-fibrotic properties: it is able to halt the differentiation of fibroblasts into myofibroblasts, and is also able to reverse the activation status of fibroblasts. The decreased protein levels of YAP1, Smad2 and Smad3 in the presence of VP explain in part the strong anti-fibrotic properties of VP. Verteporfin is clinically used as a photosensitizer for photodynamic therapy to eliminate abnormal blood vessels in the eye to attenuate macular degeneration. The antifibrotic properties of VP do not rely on photo-activation, as we used the molecule in its non-photoinduced state.

KRAB-Induced Heterochromatin Effectively Silences PLOD2 Gene Expression in Somatic Cells and is Resilient to TGFß1 Activation.

Epigenetic editing, an emerging technique used for the modulation of gene expression in mammalian cells, is a promising strategy to correct disease-related gene expression. Although epigenetic reprogramming results in sustained transcriptional modulation in several in vivo models, further studies are needed to develop this approach into a straightforward technology for effective and specific interventions. Important goals of current research efforts are understanding the context-dependency of successful epigenetic editing and finding the most effective epigenetic effector(s) for specific tasks. Here we tested whether the fibrosis- and cancer-associated PLOD2 gene can be repressed by the DNA methyltransferase M.SssI, or by the non-catalytic Krüppel associated box (KRAB) repressor directed to the PLOD2 promoter via zinc finger- or CRISPR-dCas9-mediated targeting. M.SssI fusions induced de novo DNA methylation, changed histone modifications in a context-dependent manner, and led to 50%-70% reduction in PLOD2 expression in fibrotic fibroblasts and in MDA-MB-231 cancer cells. Targeting KRAB to PLOD2 resulted in the deposition of repressive histone modifications without DNA methylation and in almost complete PLOD2 silencing. Interestingly, both long-term TGFß1-induced, as well as unstimulated PLOD2 expression, was completely repressed by KRAB, while M.SssI only prevented the TGFß1-induced PLOD2 expression. Targeting transiently expressed dCas9-KRAB resulted in sustained PLOD2 repression in HEK293T and MCF-7 cells. Together, these findings point to KRAB outperforming DNA methylation as a small potent targeting epigenetic effector for silencing TGFß1-induced and uninduced PLOD2 expression.

Glimpses into the molecular pathogenesis of Peyronie's disease.

Peyronie's disease (PD) is a fibroproliferative disease of the penis. Since little is known about the molecular pathogenesis of PD, we compared the biochemical make-up of PD plaques with normal tunica albuginea to clarify pathological processes in the scarred tissue. Protein and mRNA levels were measured in plaques and in unaffected pieces of the tunica albuginea. We investigated the presence of myofibroblasts, the deposition of collagens, and some key elements of Wnt and YAP1 signaling at protein level. The expression of 45 genes, all related to collagen homeostasis and extracellular matrix proteins, was quantified. In plaques, more myofibroblasts were present, and we observed an activation of Wnt signaling and YAP1 signaling. Increased levels of the collagens types I and III confirm the fibrotic nature of plaques. The mRNA ratio of collagen types III, IV, and VI to type I was increased. The expression of lysyl hydroxylase 3 was higher, whereas a decreased expression level was seen for fibronectin and cathepsin K. The biochemical composition of plaques was different from unaffected tunica albuginea: the relative and absolute abundance of various extracellular matrix proteins were changed, as well as the quality of collagen and the level of the collagen-degrading enzyme cathepsin K.

Verteporfin as a Medical Treatment in Peyronie's Disease.

INTRODUCTION: In Europe and the United States, verteporfin (Visudyne; VP) is registered and used in treating macular degeneration. Research showed that VP decreased expression of fibrotic genes in fibroblasts collected from nodules of patients suffering from Dupuytren's disease, plausibly by de-activating transcription in the Yes Activated Protein (YAP) pathway. AIM: To analyze the effect of VP on myofibroblasts cultured from Peyronie's disease (PD) plaques. METHODS: At surgery for PD we took biopsies from the plaques of 5 patients. By immunostaining, the presence of the pathologic myofibroblasts was determined. After culturing cells, VP was dispensed in starvation medium for 24 and 48 hours and messenger(m)RNA levels of COL1A1, ACTA2, COL5A1, EDA-FN, LOXL2, CCN2, SERPINH1, PLOD2, and YAP were quantified and compared with controls with real-time polymerase chain reaction. MAIN OUTCOME MEASURE: mRNA-levels of COL1A1, ACTA2, COL5A1, EDA-FN, LOXL2, CCN2, SERPINH1, PLOD2, and YAP. RESULTS: The pathologic phenotype of cells isolated from PD plaques was confirmed with baseline immunofluorescent stainings that showed considerable levels of α-smooth muscle actin, being a marker for the presence of myofibroblasts. The mRNA ratios of all the genes related to fibrosis (COL1A1, etc.) except YAP decreased significantly after treatment with VP within 24 and 48 hours. These results suggest inhibition of fibrosis in the YAP cascade, downstream of YAP. CONCLUSION: In our opinion, urologists must move the focus to disease before deformity, and the search for new oral or intralesional agents, well-tolerated and effective in both the acute and chronic phase of PD must continue. VP blocked the expression of genes related to fibrosis in the YAP cascade in myofibroblasts derived from PD plaque. Mohede DCJ, de Jong IJ, Bank RA, et al. Verteporfin as a medical treatment in Peyronie's disease. Sex Med 2018;6:302-308.

Biomaterial Encapsulation Is Enhanced in the Early Stages of the Foreign Body Reaction During Conditional Macrophage Depletion in Transgenic Macrophage Fas-Induced Apoptosis Mice.

Macrophages are pivotal cells during the foreign body reaction (FBR), as they orchestrate the proinflammatory microenvironment inside and around biomaterials by secretion of inflammatory mediators. Furthermore, they are responsible for the degradation of biomaterials and are thought to instruct the fibroblasts that generate a fibrous capsule around implanted biomaterials. In this study, we investigated the events during the FBR when macrophages are not present. Hexamethylenediisocyanate crosslinked collagen scaffolds were implanted in "Macrophage Fas-Induced Apoptosis" mice, which allow "on demand" macrophage depletion. We observed that macrophage depletion completely inhibited inflammatory ingrowth into the scaffolds and resulted in an increased capsule size. Quantitative polymerase chain reaction analysis revealed decreased expression levels of proinflammatory mediators such as TNFα and IL1ß, and increased expression levels of collagens and fibroblast-stimulating growth factors such as EGF, FGF1, FGF2, and TGFα. Our results indicate that macrophages are indeed crucial for the generation of a proinflammatory microenvironment inside implanted biomaterials, leading to inflammatory ingrowth. In contrast, macrophages do not appear to be important for the generation of a fibrous capsule around implanted biomaterials. In fact, our data suggest that the macrophages present in the capsule might instruct the surrounding fibroblasts to produce less fibroblast-stimulating factors and less collagens.

Disentangling mechanisms involved in collagen pyridinoline cross-linking: The immunophilin FKBP65 is critical for dimerization of lysyl hydroxylase 2.

Collagens are subjected to extensive posttranslational modifications, such as lysine hydroxylation. Bruck syndrome (BS) is a connective tissue disorder characterized at the molecular level by a loss of telopeptide lysine hydroxylation, resulting in reduced collagen pyridinoline cross-linking. BS results from mutations in the genes coding for lysyl hydroxylase (LH) 2 or peptidyl-prolyl cis-trans isomerase (PPIase) FKBP65. Given that the immunophilin FKBP65 does not exhibit LH activity, it is likely that LH2 activity is somehow dependent on FKPB65. In this report, we provide insights regarding the interplay between LH2 and FKBP65. We found that FKBP65 forms complexes with LH2 splice variants LH2A and LH2B but not with LH1 and LH3. Ablating the catalytic activity of FKBP65 or LH2 did not affect complex formation. Both depletion of FKBP65 and inhibition of FKBP65 PPIase activity reduced the dimeric (active) form of LH2 but did not affect the binding of monomeric (inactive) LH2 to procollagen Iα1. Furthermore, we show that LH2A and LH2B cannot form heterodimers with each other but are able to form heterodimers with LH1 and LH3. Collectively, our results indicate that FKBP65 is linked to pyridinoline cross-linking by specifically mediating the dimerization of LH2. Moreover, FKBP65 does not interact with LH1 and LH3, explaining why in BS triple-helical hydroxylysines are not affected. Our results provide a mechanistic link between FKBP65 and the loss of pyridinolines and may hold the key to future treatments for diseases related to collagen cross-linking anomalies, such as fibrosis and cancer.

Wnt pathway in Dupuytren disease: connecting profibrotic signals.

A role of Wnt signaling in Dupuytren disease, a fibroproliferative disease of the hand and fingers, has not been fully elucidated. We examined a large set of Wnt pathway components and signaling targets and found significant dysregulation of 41 Wnt-related genes in tissue from the Dupuytren nodules compared with patient-matched control tissue. A large proportion of genes coding for Wnt proteins themselves was downregulated. However, both canonical Wnt targets and components of the noncanonical signaling pathway were upregulated. Immunohistochemical analysis revealed that protein expression of Wnt1-inducible secreted protein 1 (WISP1), a known Wnt target, was increased in nodules compared with control tissue, but knockdown of WISP1 using small interfering RNA (siRNA) in the Dupuytren myofibroblasts did not confirm a functional role. The protein expression of noncanonical pathway components Wnt5A and VANGL2 as well as noncanonical coreceptors Ror2 and Ryk was increased in nodules. On the contrary, the strongest downregulated genes in this study were 4 antagonists of Wnt signaling (DKK1, FRZB, SFRP1, and WIF1). Downregulation of these genes in the Dupuytren tissue was mimicked in vitro by treating normal fibroblasts with transforming growth factor ß1 (TGF-ß1), suggesting cross talk between different profibrotic pathways. Furthermore, siRNA-mediated knockdown of these antagonists in normal fibroblasts led to increased nuclear translocation of Wnt target ß-catenin in response to TGF-ß1 treatment. In conclusion, we have shown extensive dysregulation of Wnt signaling in affected tissue from Dupuytren disease patients. Components of both the canonical and the noncanonical pathways are upregulated, whereas endogenous antagonists are downregulated, possibly via interaction with other profibrotic pathways.

YAP1 Is a Driver of Myofibroblast Differentiation in Normal and Diseased Fibroblasts.

Dupuytren disease is a fibrotic disorder characterized by contraction of myofibroblast-rich cords and nodules in the hands. The Hippo member Yes-associated protein 1 (YAP1) is activated by tissue stiffness and the profibrotic transforming growth factor-ß1, but its role in cell fibrogenesis is yet unclear. We hypothesized that YAP1 regulates the differentiation of dermal fibroblasts into highly contractile myofibroblasts and that YAP1 governs the maintenance of a myofibroblast phenotype in primary Dupuytren cells. Knockdown of YAP1 in transforming growth factor-ß1-stimulated dermal fibroblasts decreased the formation of contractile smooth muscle α-actin stress fibers and the deposition of collagen type I, which are hallmark features of myofibroblasts. Translating our findings to a clinically relevant model, we found that YAP1 deficiency in Dupuytren disease myofibroblasts resulted in decreased expression of ACTA2, COL1A1, and CCN2 mRNA, but this did not result in decreased protein levels. YAP1-deficient Dupuytren myofibroblasts showed decreased contraction of a collagen hydrogel. Finally, we showed that YAP1 levels and nuclear localization were elevated in affected Dupuytren disease tissue compared with matched control tissue and partly co-localized with smooth muscle α-actin-positive cells. In conclusion, our data show that YAP1 is a regulator of myofibroblast differentiation and contributes to the maintenance of a synthetic and contractile phenotype, in both transforming growth factor-ß1-induced myofibroblast differentiation and primary Dupuytren myofibroblasts.

The IκB kinase inhibitor ACHP strongly attenuates TGFß1-induced myofibroblast formation and collagen synthesis.

Excessive accumulation of a collagen-rich extracellular matrix (ECM) by myofibroblasts is a characteristic feature of fibrosis, a pathological state leading to serious organ dysfunction. Transforming growth factor beta1 (TGFß1) is a strong inducer of myofibroblast formation and subsequent collagen production. Currently, there are no remedies for the treatment of fibrosis. Activation of the nuclear factor kappa B (NF-κB) pathway by phosphorylating IκB with the enzyme IκB kinase (IKK) plays a major role in the induction of fibrosis. ACHP {2-Amino-6-[2-(cyclopropylmethoxy)-6-hydroxyphenyl]-4-(4-piperidinyl)-3 pyridinecarbonitrile}, a selective inhibitor of IKK, prohibits the activation of the NF-κB pathway. It is not known whether ACHP has potential anti-fibrotic properties. Using adult human dermal and lung fibroblasts we have investigated whether ACHP has the ability to inhibit the TGFß1-induced transition of fibroblasts into myofibroblasts and its excessive synthesis of ECM. The presence of ACHP strongly suppressed the induction of the myofibroblast markers alpha-smooth muscle actin (αSMA) and SM22α, as well as the deposition of the ECM components collagen type I and fibronectin. Furthermore, post-treatment with ACHP partly reversed the expression of αSMA and collagen type I production. Finally, ACHP suppressed the expression of the three collagen-modifying enzymes lysyl hydroxylase (PLOD1, PLOD2 and PLOD3) in dermal fibroblasts, but did not do so in lung fibroblasts. We conclude that the IKK inhibitor ACHP has potent antifibrotic properties, and that the NF-κB pathway plays an important role in myofibroblast biology.

Spinal fusion using adipose stem cells seeded on a radiolucent cage filler: a feasibility study of a single surgical procedure in goats.

PURPOSE: To assess the feasibility of a one-step surgical concept, employing adipose stem cells (ASCs) and a novel degradable radiolucent cage filler (poly-L-lactide-co-caprolactone; PLCL), within polyetheretherketone cages in a stand-alone caprine spinal fusion model. METHODS: A double-level fusion study was performed in 36 goats. Four cage filler groups were defined: (i) acellular PLCL, (ii) PLCL + SVF (freshly harvested stromal vascular fraction highly enriched in ASCs); (iii) PLCL + ASCs (cultured to homogeneity); and (iv) autologous iliac crest bone graft (ABG). Fusion was assessed after 3 and 6 months by radiography, micro-CT, biomechanics, and biochemical analysis of tissue formed inside the cage after 6 months. RESULTS: No adverse effects were observed in all groups. After 3 months, similar and low fusion rates were found. Segmental stability did not differ between groups in all tested directions. Micro-CT imaging revealed significantly higher amounts of mineralized tissue in the ABG group compared to all others. After 6 months, interbody fusion rates were: PLCL 53%, SVF 30%, ASC 43% and ABG 63%. A trend towards higher mineralized tissue content was found for the ABG group. Biochemical and biomechanical analyses revealed equal maturity of collagen cross-links and similar segmental stability between all groups. CONCLUSIONS: This study demonstrates the technical feasibility and safety of the one-step surgical procedure for spinal fusion for the first time. The radiolucent PLCL scaffold allowed in vivo monitoring of bone formation using plain radiography. Addition of stem cells to the PLCL scaffolds did not result in adverse effects, but did not enhance the rate and number of interbody fusions under the current conditions. A trend towards superior results with ABG was found. Further research is warranted to optimize the spinal fusion model for proper evaluation of both PLCL and stem cell therapy.

Interleukin-1ß attenuates myofibroblast formation and extracellular matrix production in dermal and lung fibroblasts exposed to transforming growth factor-ß1.

One of the most potent pro-fibrotic cytokines is transforming growth factor (TGFß). TGFß is involved in the activation of fibroblasts into myofibroblasts, resulting in the hallmark of fibrosis: the pathological accumulation of collagen. Interleukin-1ß (IL1ß) can influence the severity of fibrosis, however much less is known about the direct effects on fibroblasts. Using lung and dermal fibroblasts, we have investigated the effects of IL1ß, TGFß1, and IL1ß in combination with TGFß1 on myofibroblast formation, collagen synthesis and collagen modification (including prolyl hydroxylase, lysyl hydroxylase and lysyl oxidase), and matrix metalloproteinases (MMPs). We found that IL1ß alone has no obvious pro-fibrotic effect on fibroblasts. However, IL1ß is able to inhibit the TGFß1-induced myofibroblast formation as well as collagen synthesis. Glioma-associated oncogene homolog 1 (GLI1), the Hedgehog transcription factor that is involved in the transformation of fibroblasts into myofibroblasts is upregulated by TGFß1. The addition of IL1ß reduced the expression of GLI1 and thereby also indirectly inhibits myofibroblast formation. Other potentially anti-fibrotic effects of IL1ß that were observed are the increased levels of MMP1, -2, -9 and -14 produced by fibroblasts exposed to TGFß1/IL1ß in comparison with fibroblasts exposed to TGFß1 alone. In addition, IL1ß decreased the TGFß1-induced upregulation of lysyl oxidase, an enzyme involved in collagen cross-linking. Furthermore, we found that lung and dermal fibroblasts do not always behave identically towards IL1ß. Suppression of COL1A1 by IL1ß in the presence of TGFß1 is more pronounced in lung fibroblasts compared to dermal fibroblasts, whereas a higher upregulation of MMP1 is seen in dermal fibroblasts. The role of IL1ß in fibrosis should be reconsidered, and the differences in phenotypical properties of fibroblasts derived from different organs should be taken into account in future anti-fibrotic treatment regimes.

TGF-ß induces Lysyl hydroxylase 2b in human synovial osteoarthritic fibroblasts through ALK5 signaling.

Lysyl hydroxylase 2b (LH2b) is known to increase pyridinoline cross-links, making collagen less susceptible to enzymatic degradation. Previously, we observed a relationship between LH2b and osteoarthritis-related fibrosis in murine knee joint. For this study, we investigate if transforming growth factor-beta (TGF-ß) and connective tissue growth factor (CTGF) regulate procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2) (gene encoding LH2b) and LH2b expression differently in osteoarthritic human synovial fibroblasts (hSF). Furthermore, we investigate via which TGF-ß route (Smad2/3P or Smad1/5/8P) LH2b is regulated, to explore options to inhibit LH2b during fibrosis. To answer these questions, fibroblasts were isolated from knee joints of osteoarthritis patients. The hSF were stimulated with TGF-ß with or without a kinase inhibitor of ALK4/5/7 (SB-505124) or ALK1/2/3/6 (dorsomorphin). TGF-ß, CTGF, constitutively active (ca)ALK1 and caALK5 were adenovirally overexpressed in hSF. The gene expression levels of PLOD1/2/3, CTGF and COL1A1 were analyzed with Q-PCR. LH2 protein levels were determined with western blot. As expected, TGF-ß induced PLOD2/LH2 expression in hSF, whereas CTGF did not. PLOD1 and PLOD3 were not affected by either TGF-ß or CTGF. SB-505124 prevented the induction of TGF-ß-induced PLOD2, CTGF and COL1A1. Surprisingly, dorsomorphin completely blocked the induction of CTGF and COL1A1, whereas TGF-ß-induced PLOD2 was only slightly reduced. Overexpression of caALK5 in osteoarthritic hSF significantly induced PLOD2/LH2 expression, whereas caALK1 had no effect. We showed, in osteoarthritic hSF, that TGF-ß induced PLOD2/LH2 via ALK5 Smad2/3P. This elevation of LH2b in osteoarthritic hSF makes LH2b an interesting target to interfere with osteoarthritis-related persistent fibrosis.

Human amniotic fluid-derived mesenchymal cells from fetuses with a neural tube defect do not deposit collagen type i protein after TGF-ß1 stimulation in vitro.

In spina bifida, the neural tube fails to close during the embryonic period. Exposure of the neural tube to the amniotic fluid during pregnancy causes additional neural damage. Intrauterine tissue engineering using a biomaterial seeded with stem cells might prevent this additional damage. For this purpose, autologous cells from the amniotic fluid are an attractive source. To close the defect, it is important that these cells deposit an extracellular matrix. However, it is not known if amniotic fluid mesenchymal cells (AFMCs) from a fetus with a neural tube defect (NTD) share the same characteristics as AFMCs from a healthy fetus. We found that cells derived from fetuses with a NTD, in contrast to healthy human amniotic fluid cells, did not deposit collagen type I. Furthermore, the NTD cells showed, compared with both healthy amniotic fluid cells and fetal fibroblasts, much lower mRNA expression levels of genes that are involved in collagen biosynthesis [procollagen C-endopeptidase enhancer proteins (PCOLCE), PCOLCE2, ADAM metallopeptidase with thrombospondin type 1 motif, 2 (ADAMTS2), ADAMTS14]. This indicates that NTD-AFMCs have different characteristics compared with healthy AFMCs and might not be suitable for fetal therapy to close the defect in spina bifida patients.

Epithelial-to-mesenchymal transition in fibrosis: collagen type I expression is highly upregulated after EMT, but does not contribute to collagen deposition.

The hallmark of fibrosis is an accumulation of fibrillar collagens, especially of collagen type I. There is considerable debate whether in vivo type II epithelial-to-mesenchymal transition (EMT) is involved in organ fibrosis. Lineage tracing experiments by various groups show opposing data concerning the relative contribution of epithelial cells to the pool of myofibroblasts. We hypothesized that EMT-derived cells might directly contribute to collagen deposition. To study this, EMT was induced in human epithelial lung and renal cell lines in vitro by means of TGF-ß1 stimulation, and we compared the collagen type I (COL1A1) expression levels of transdifferentiated cells with that of myofibroblasts obtained by TGF-ß1 stimulation of human dermal and lung fibroblasts. COL1A1 expression levels of transdifferentiated epithelial cells appeared to be at least one to two orders of magnitude lower than that of myofibroblasts. This was confirmed at immunohistochemical level: in contrast to myofibroblasts, collagen type I deposition by EMT-derived cells was not or hardly detectable. We postulate that, even when type II EMT occurs in vivo, the direct contribution of EMT-derived cells to collagen accumulation is rather limited.

Macrophage phenotypes in the collagen-induced foreign body reaction in rats.

Implantation of biomaterials into the body elicits a material-dependent inflammatory response called the foreign body reaction (FBR). Macrophages play a pivotal role in the FBR by orchestrating the pro-inflammatory microenvironment around the biomaterials by secreting cytokines, chemokines and growth factors. When the biomaterial is porous or degradable, macrophages can migrate into the material and continue the generation of a pro-inflammatory microenvironment inside the materials. They also regulate the degradation of biomaterials by secreting proteolytic enzymes and by phagocytosis. We hypothesize that macrophages present in the different microenvironments of the FBR have different phenotypes. Fundamental knowledge of the phenotypes of macrophages and their dynamics during the FBR will contribute to our overall understanding of the mechanisms involved in the FBR, and may provide us with additional tools to modulate the FBR. To investigate the phenotype of macrophages in the FBR, we validated phenotype-specific markers for rat macrophages in vitro by stimulating them with IFNγ/LPS, IL4/IL13 or IL4/dexamethasone to induce classically activated macrophages (M1φ) or alternatively activated macrophages (M2φ). Gene expression analysis, Western blot and immunohistochemistry revealed that iNOS and CD206 are specifically expressed by M1φ and M2φ, respectively. Using these markers, we investigated the distribution of M1φ and M2φ in the FBR induced by subcutaneously implanted hexamethylenediisocyanate cross-linked dermal sheep collagen (HDSC) disks in AO rats. We found that part of the macrophages display an M2 phenotype, whereas the M1phenotype was not detected. Our data suggest that many macrophages in the FBR induced by HDSC do not fit into the classical M1 or M2 dichotomy.

The tissue response to photopolymerized PEG-p(HPMAm-lactate)-based hydrogels.

Hydrogels are three-dimensional networks of crosslinked hydrophilic polymers widely used for protein delivery and tissue engineering. To be eligible for in vivo applications, the hydrogels should not evoke an adverse tissue response. In this study the angiogenic and inflammatory responses in vivo after implantation of photopolymerized thermosensitive poly(hydroxypropyl methacrylamide lactate)-poly(ethyl copolymer hydrogels are investigated. Hydrogels consisting of polymers with different crosslink densities were subcutaneously implanted in Balb/c mice and histological evaluation of the tissue response was performed. The implants showed an acute and localized inflammatory reaction upon implantation, mainly characterized by a strong infiltration of granulocytes. The acute inflammatory reaction was followed by a milder chronic inflammation which was characterized by infiltration of macrophages and persistent but decreasing levels of granulocytes. The number of macrophages and blood vessels was associated with the biodegradation and resorption of the biomaterial and increased in time as the degradation of the materials progressed. The observed degradation rates in vivo correlated well with previously observed in vitro degradation rates, which suggests that hydrolysis is the main mechanism governing the degradation.

Rapid attachment of adipose stromal cells on resorbable polymeric scaffolds facilitates the one-step surgical procedure for cartilage and bone tissue engineering purposes.

The stromal vascular fraction (SVF) of adipose tissue provides an abundant source of mesenchymal stem cells. For clinical application, it would be beneficial to establish treatments in which SVF is obtained, seeded onto a scaffold, and returned into the patient within a single surgical procedure. In this study, we evaluated the suitability of both a macroporous poly(L-lactide-co-caprolactone) and a porous collagen type I/III scaffold for this purpose. Surprisingly, cell attachment was rapid (∼10 min) and sequestered the majority of adipose stem cells, as deduced from colony-forming unit assays. Proliferation occurred in both polymeric scaffolds. Upon chondrogenic induction, up-regulation of chondrogenic genes, production of glycosaminoglycans, and accumulation of collagen type II was observed, indicating differentiation of scaffold-attached SVF cells along the chondrogenic lineage. Osteogenic differentiation was achieved in both scaffold types, as visualized by up-regulation of osteogenic genes, increase of alkaline phosphatase production over time, and accumulation of bone sialoprotein and osteonectin. In conclusion, this study identifies both poly(L-lactide-co-caprolactone) and collagen type I/III as promising scaffold materials for rapid attachment of adipose stem cell-like (stromal) cells, enhancing the development of one-step surgical concepts for cartilage and bone tissue engineering.

The role of collagen receptors Endo180 and DDR-2 in the foreign body reaction against non-crosslinked collagen and gelatin.

Despite the use of collagen-derived scaffolds in regenerative medicine, little is known about the degradation mechanisms of these scaffolds in vivo. Non-crosslinked dermal sheep (NDSC) and gelatin disks were implanted subcutaneously in mice. NDSC disks showed a very low degradation rate, despite the presence of high numbers of macrophages and the influx of neutrophils. This was attributed to the presence of the matrix metalloproteinase inhibitor TIMP-1. The limited degradation occurred mainly in the later stages of the foreign body reaction, and could be attributed to (1) phagocytosis by macrophages due to a co-expression of Endo180 and MT1-MMP on these cells (intracellular degradation) and (2) the presence of MMP-13 due to an upregulation of the expression of the DDR-2 receptor (extracellular degradation). In contrast, gelatin disks degraded quickly, due to the efficient formation of large giant cells as well as the presence of MMP-13; the inhibitor TIMP-1 was absent. The DDR-2 receptor was not expressed in the gelatin disks. Endo180 and MT1-MMP were expressed, but at most times no co-expression was seen. We conclude that the physical state of collagen (native or denatured) had a dramatic outcome on the degradation rate and provoked a completely different foreign body reaction.

Collagen type II enhances chondrogenesis in adipose tissue-derived stem cells by affecting cell shape.

Ideally, biomaterials have inductive properties, favoring specific lineage differentiation. For chondrogenic induction, these properties have been attributed to collagen type II. However, the underlying mechanisms are largely unknown. This study aimed to investigate whether collagen type II favors chondrogenic induction by affecting cell shape through beta1 integrins and Rho A/Rock signaling. For this purpose, adipose tissue-derived stem cells (ASCs) were encapsulated in collagen type I or II gels and cultured in plain and chondrogenic medium. It was demonstrated that (i) ASCs showed more efficient chondrogenic induction (higher collagen X, aggrecan, sox6, sox9, and collagen II gene expression) in both plain and chondrogenic media in collagen type II versus collagen type I gels; (ii) ASCs showed lower Rock 2 gene expression and a more rounded cell shape in collagen type II versus type I gels when grown in plain medium; (iii) Rock inhibitor (Y27632) more effectively enhanced chondrogenic gene expression of ASCs in collagen type I than in collagen type II gels, and diminished differences in chondrogenic gene expression and cell shape of ASCs between the two gel types; and (iv) beta1 integrins blocking not only reduced the differences of chondrogenic gene expression but also eliminated the differences of Rock 1 and Rock 2 gene expressions and cell shape when comparing ASCs embedded in collagen type I and II gels. We conclude that collagen type II provides the inductive signaling for chondrogenic differentiation in ASCs by evoking a round cell shape through beta1 integrin-mediated Rho A/Rock signaling pathway.