Hypoxia and transforming growth factor-beta 1 act independently to increase extracellular matrix production by placental fibroblasts

Engineering placental trophoblast fusion: A potential role for biomechanics in syncytialization

The process by which placental trophoblasts fuse to form the syncytiotrophoblast around the chorionic villi is not fully understood. Mechanical features of the in vivo and in vitro culture environments have recently emerged as having the potential to influence fusion efficiency, and considering these mechanical cues may ultimately allow predictive control of trophoblast syncytialization. Here, we review recent studies that suggest that biomechanical factors such as shear stress, tissue stiffness, and dimensionally-related stresses affect villous trophoblast fusion efficiency. We then discuss how these stimuli might arise in vivo and how they can be incorporated in cultures to study and enhance villous trophoblast fusion. We believe that this mechanical paradigm will provide novel insight into manipulating the syncytialization process to better engineer improved models, understand disease progression, and ultimately develop novel therapeutic strategies.

JMJD6 Dysfunction Due to Iron Deficiency in Preeclampsia Disrupts Fibronectin Homeostasis Resulting in Diminished Trophoblast Migration

The mechanisms contributing to excessive fibronectin in preeclampsia, a pregnancy-related disorder, remain unknown. Herein, we investigated the role of JMJD6, an O₂- and Fe²⁺-dependent enzyme, in mediating placental fibronectin processing and function. MALDI-TOF identified fibronectin as a novel target of JMJD6-mediated lysyl hydroxylation, preceding fibronectin glycosylation, deposition, and degradation. In preeclamptic placentae, fibronectin accumulated primarily in lysosomes of the mesenchyme. Using primary placental mesenchymal cells (pMSCs), we found that fibronectin fibril formation and turnover were markedly impeded in preeclamptic pMSCs, partly due to impaired lysosomal degradation. JMJD6 knockdown in control pMSCs recapitulated the preeclamptic FN phenotype. Importantly, preeclamptic pMSCs had less total and labile Fe²⁺ and Hinokitiol treatment rescued fibronectin assembly and promoted lysosomal degradation. Time-lapse imaging demonstrated that defective ECM deposition by preeclamptic pMSCs impeded HTR-8/SVneo cell migration, which was rescued upon Hinokitiol exposure. Our findings reveal new Fe²⁺-dependent mechanisms controlling fibronectin homeostasis/function in the placenta that go awry in preeclampsia.

Techniques to Assess Collagen Synthesis, Deposition, and Cross-Linking In Vitro

Synthesis, deposition, and cross-linking of collagen are hallmarks of fibroblast to myofibroblast differentiation. Standard methods for determining collagen from tissue samples are not directly applicable to cell culture conditions, where the overall synthesis and deposition of collagen is clearly unfavorable, mainly due to quantity limitations and dilution of required extracellular remodeling factors. In this chapter, we describe the methods we have established to analyze collagen production and deposition into the extracellular matrix by cultured myo/fibroblasts, as well as to determine lysyl oxidase (LOX) activity in cell supernatants as an index of the capacity of the cell to cross-link collagen in vitro.

Developmental programming: Prenatal bisphenol A treatment disrupts mediators of placental function in sheep

Gestational Bisphenol A (BPA) exposure is associated with low birth weight. We hypothesized that the low birth weight is the consequence of reduced placental efficiency and a function of BPA-induced inflammatory, oxidative, lipotoxic, angiogenic, steroidal and fibrotic changes involving epigenetic alterations. Placentomes were collected during early (day 65) and mid (day 90) gestation (term ∼147 days) from control and BPA (gestational day 30-90)-treated pregnant sheep. BPA treatment: reduced placental efficiency and fetal weight; increased interleukin 8, lipid peroxidation marker, antioxidants, aromatase, 17 alpha-hydroxylase, estrogen receptor 2, insulin like growth factor (IGF) 2 receptor and IGF binding proteins (IGFBP), and histone deacetylase 1 and 2; reduced tumor necrosis factor alpha and IGF1 receptor at early gestation (Day 65). Gestational BPA-induced mid-gestational changes include: reduced angiogenic factor hypoxia inducible factor 1 alpha; increased IL1beta, oxidative stress markers, triglyceride, 17alpha hydroxylase, IGFBP 1, DNA methyltransferase 3 A and histone deacetylase 1. These findings indicate that gestational BPA, either acting directly or by altering steroidal input, produces early/mid-gestational-specific epigenetic changes culminating in placental disruptions at several levels, in keeping with time-specific/time-lagged pregnancy-associated changes in placental efficiency and fetal weight. The reduced early-gestational placental efficiency may be a function of increased inflammation/oxidative stress and reduced IGF bioavailability with the mid-gestational restoration of placental efficiency likely driven by improved IGF bioavailability and the time-lagged response to antioxidant increase. This compensation, the result of time-lagged response to increases in negative mediators of placental function must have failed with pregnancy advancement to explain the low birthweight outcome.

A hierarchical network of hypoxia-inducible factor and SMAD proteins governs procollagen lysyl hydroxylase 2 induction by hypoxia and transforming growth factor β1

Collagens are extracellular matrix (ECM) proteins that support the structural and biomechanical integrity of many tissues. Procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2) encodes the only lysyl hydroxylase (LH) isoform that specifically hydroxylates lysine residues in collagen telopeptides, a post-translational modification required for the formation of stabilized cross-links. PLOD2 expression is induced by hypoxia and transforming growth factor-β1 (TGF-β1), well-known stimuli for the formation of a fibrotic ECM, which can lead to pathological fibrosis underlying several diseases. Here, using human and murine fibroblasts, we studied the molecular determinants underlying hypoxia- and TGF-β1-induced PLOD2 expression and its impact on collagen biosynthesis. Deletion mapping and mutagenesis analysis identified specific binding sites for hypoxia-inducible factors (HIF) and TGF-β1-activated SMAD proteins on the human PLOD2 gene promoter that were required for these stimuli to induce PLOD2 expression. Interestingly, our experiments also revealed that HIF signaling plays a preponderant role in the SMAD pathway, as intact HIF sites were absolutely required for TGF-β1 to exert its effect on SMAD-binding sites. We also found that silencing PLOD2 expression did not alter soluble collagen accumulation in the extracellular medium, but it effectively abolished the deposition into the insoluble collagen matrix. Taken together, our findings reveal the existence of a hierarchical relationship between the HIF and SMAD signaling pathways for hypoxia- and TGF-β1-mediated regulation of PLOD2 expression, a key event in the deposition of collagen into the ECM.

Relevant biological processes for tissue development with stem cells and their mechanistic modeling: A review

A potential alternative for tissue transplants is tissue engineering, in which the interaction of cells and biomaterials can be optimized. Tissue development in vitro depends on the complex interaction of several biological processes such as extracellular matrix synthesis, vascularization and cell proliferation, adhesion, migration, death, and differentiation. The complexity of an individual phenomenon or of the combination of these processes can be studied with phenomenological modeling techniques. This work reviews the main biological phenomena in tissue development and their mathematical modeling, focusing on mesenchymal stem cell growth in three-dimensional scaffolds.

Hypoxia-inducible factor-1α activates transforming growth factor-β1/Smad signaling and increases collagen deposition in dermal fibroblasts

Hypoxia of local tissue occurs during the scar formation; however, the degree of ischemia and hypoxia in the central areas of keloids is more serious than those in normal scars. Hypoxia-induced factor (HIF), is one of the main cellular responses to hypoxia, allowing cells to adapt to low-oxygen conditions. We investigated the correlation among hypoxia, transforming growth factor-β1/Smad signaling and collagen deposition. Hypoxia up-regulated TGF-β1, Smad2/3, p-Smad2/3, Smad4, and total collagen in both normal and keloid fibroblasts via HIF-1α, which was attenuated by HIF-1α inhibition, but TβRII levels were not significantly altered. Silencing Smad4 under hypoxia decreased the mRNA and protein levels of HIF-1α, suggesting up-regulated Smad4 may also plays a role in promoting HIF-1α. Finally, we examined the role of the TGF-β1/Smad pathway in collagen deposition. When TβRII was inhibited by ITD-1 under hypoxic conditions, p-Smad2/3 levels and collagen deposition decreased. When inhibited TβRII by siRNA under normoxia, the levels of p-Smad2/3, Smad4 and collagen deposition also decreased. This result demonstrated that hypoxia promoted TGF-β1/Smad signaling via HIF-1α and that both HIF-1α and the TGF-β1/Smad signaling promotes collagen deposition in hypoxia, which is an important mechanism of keloid formation.

Fibroblasts in Hypoxic Conditions Mimic Laryngotracheal Stenosis

Objective To elucidate the role of hypoxia and inflammatory pathways in the pathogenesis of iatrogenic laryngotracheal stenosis (iLTS). Study Design (1) Examination of mucosal surface gene expression in human iLTS. (2) In vitro comparison of normal and scar laryngotracheal fibroblasts under normoxic and hypoxic conditions. Setting Tertiary care hospital in a research university (2012-2016). Subjects and Methods Brush biopsies were obtained from normal laryngotracheal tissue and scar in iLTS patients; gene expression was compared. Fibroblasts were isolated from normal and scarred trachea and grown in vitro in either a 1% O₂ or normoxic environment. Cell growth and gene and protein expression were compared. Statistical analysis utilized a multilevel mixed effects model. Results Expression of IL-6 (fold change = 2.8, P < .01), myofibroblast marker αSMA (fold change = 3.0, P = .01), and MMP13 (fold change = 5.4, P = .02) was significantly increased in scar biopsy samples as compared to normal. Under hypoxic conditions in vitro, normal laryngotracheal fibroblasts proliferated significantly faster (n = 8, P < .01 each day). Expression of IL-6 (n = 8, fold change = 2.6, P < .01) increased significantly after 12 hours under hypoxia. Expression of αSMA (n = 8, fold change= 2.0, P = .03), COL1 (n = 8, fold change = 1.1, P = .03), and MMP13 (n = 8, fold change = 1.6, P = .01) increased significantly after 48 hours under hypoxia. Scar fibroblasts also proliferated significantly faster under hypoxic conditions but did not display the same expression profile. Conclusion Human iLTS scar has a myofibroblast phenotype. Under hypoxic conditions in vitro, normal laryngotracheal fibroblasts can transdifferentiate into a similar phenotype. These changes may be mediated by IL-6, a fibrosis-related cytokine.

Hypoxia-increased expression of genes involved in inflammation, dedifferentiation, pro-fibrosis, and extracellular matrix remodeling of human bladder smooth muscle cells

Partial bladder outlet obstruction (pBOO) is characterized by exaggerated stretch, hydrodynamic pressure, and inflammation which cause significant damage and fibrosis to the bladder wall. Several studies have implicated hypoxia in its pathophysiology. However, the isolated progressive effects of hypoxia on bladder cells are not yet defined. Sub-confluent normal human bladder smooth muscle cells (hbSMC) were cultured in 3% O₂ tension for 2, 24, 48, and 72 h. RNA, cellular proteins, and secreted proteins were used for gene expression analysis, immunoblotting, and ELISA, respectively. Transcription of hypoxia-inducible factor (HIF)1α and HIF2α were transiently induced after 2 h of hypoxia (p < 0.05), whereas HIF3 was upregulated after 72 h (p < 0.005). HIF1 and HIF3α proteins were significantly induced after 2 and 72 h, respectively. VEGF mRNA increased significantly after 24 and 72 h (p < 0.005). The inflammatory cytokines, TGFB (protein and mRNA), IL 1β, 1L6, and TNFα (mRNA) demonstrated a time-dependent increased expression. Furthermore, the anti-inflammatory cytokine IL-10 was downregulated after 72 h (p < 0.05). Evidence of smooth muscle cell dedifferentiation included increased αSMA, vimentin, and desmin. Evidence of pro-fibrotic changes included increased CTGF, SMAD 2, and SMAD 3 as well as collagens 1, 2, 3, and 4, fibronectin, aggrecan, and TIMP 1 transcripts (p < 0.05). Total collagen proteins also increased time-dependently (p < 0.05). Together, these results show that exposure of hbSMC to low oxygen tension results in intense hypoxic cascade, including inflammation, de-differentiation, pro-fibrotic changes, and increased extracellular matrix expression. This elucidates mechanisms of hypoxia-driven bladder deterioration in bladder cells, which is important in tailoring in vivo experiments and may ultimately translate into improved clinical outcomes.

Adrenomedullin alleviates pulmonary artery collagen accumulation in rats with pulmonary hypertension induced by high blood flow

Collagen accumulation is one of the important pathologic changes in the development of pulmonary hypertension. Previous research showed that adrenomedullin (ADM) mitigates the development of pulmonary hypertension. The present study explored the role of ADM in the development of pulmonary artery collagen accumulation induced by high pulmonary blood flow, by investigating the effect of ADM [1.5 μg/(kg h)] subcutaneously administered by mini-osmotic pump on pulmonary hemodynamics, pulmonary vascular structure and pulmonary artery collagen accumulation and synthesis in rats with high pulmonary blood flow induced by aortocaval shunting. The results showed that ADM significantly decreased mean pulmonary artery pressure (mPAP) and the ratio of right ventricular mass to left ventricular plus septal mass [RV/(LV+SP)], attenuated the muscularization of small pulmonary vessels and relative medial thickness (RMT) of pulmonary arteries in rats with high pulmonary blood flow. Meanwhile, ADM ameliorated pulmonary artery collagen deposition represented by a decrease in lung tissue hydroxyproline, collagens I and III content and pulmonary artery collagens I and III expression, reduced collagen synthesis represented by a decrease in lung tissue procollagens I and III mRNA expression. The results suggest that ADM plays a protective role in the development of pulmonary hypertension induced by high blood flow, by inhibiting pulmonary procollagen synthesis and alleviating pulmonary artery collagen accumulation.

Hyperoxia accelerates progression of hepatic fibrosis by up-regulation of transforming growth factor-β expression

AIM: To investigate the effect of hypoxia or hyperoxia on the progression of hepatic fibrosis and to examine the role of transforming growth factor-β (TGF-β) in the livers of rats exposed to hypoxic or hyperoxic conditions.

METHODS: Male Sprague-Dawley rats were injected intraperitoneally with thioacetamide to induce hepatic fibrosis and were randomly divided into a hypoxia group, a hyperoxia group and an untreated control group. Ten rats in the hypoxia group were exposed to an altitude of 20000 ft for 1 h/d during 7 wk. Ten rats in the hyperoxia group were exposed to a water depth of 20 m with 100% oxygen supply for 1 h/d during 7 wk. We evaluated the degree of hepatic fibrosis using Masson trichrome stain and examined the expression level of hepatic TGF-β mRNA using quantitative real-time reverse transcriptase-polymerase chain reaction analysis.

RESULTS: Eight of 10 rats exposed to hypoxia showed diffuse and confluent fibrosis with the formation of structurally abnormal parenchymal nodules involving the entire liver, consistent with hepatic cirrhosis. Nine of 10 rats exposed to hyperoxia also demonstrated obvious histological findings of hepatic cirrhosis identical to those in hypoxic rat livers. In contrast, 8 of 10 untreated rats had periportal or septal fibrosis only. The frequency of hepatic cirrhosis in hypoxic rats (P = 0.009) and hyperoxic rats (P = 0.003) was significantly higher than that in untreated rats. In addition, hepatic TGF-β mRNA levels in hyperoxic rats were significantly higher than those in untreated rats. The mean value of the normalized TGF-β mRNA/β-actin expression ratio in the hyperoxic rats was 1.9-fold higher than that in the untreated rats (P = 0.027).

CONCLUSION: We demonstrated that both hypoxia and hyperoxia accelerated the progression of hepatic fibrosis in rats. Significant up-regulation of hepatic TGF-β in hyperoxic rats suggests that TGF-β is involved in the acceleration of hepatic fibrosis under hyperoxic conditions.

Rapamycin inhibits transforming growth factor β-induced peritoneal angiogenesis by blocking the secondary hypoxic response

Patients with end-stage kidney disease on peritoneal dialysis often develop progressive scarring of the peritoneal tissues. This manifests as submesothelial thickening and is associated with increased vascularization that leads to ultrafiltration dysfunction. Hypoxia induces a characteristic series of responses including angiogenesis and fibrosis. We investigated the role of hypoxia in peritoneal membrane damage. An adenovirus expressing transforming growth factor (TGF) β was used to induce peritoneal fibrosis. We evaluated the effect of the mTOR inhibitor rapamycin, which has been previously shown to block hypoxia-inducible factor (HIF) 1α. We also assessed the effect of HIF1α independently using an adenovirus expressing active HIF1α. To identify the TGFβ1-independent effects of HIF1α, we expressed HIF1α in the peritoneum of mice lacking the TGFβ signalling molecule Smad3. We demonstrate that TGFβ-induced fibroproliferative tissue is hypoxic. Rapamycin did not affect the early angiogenic response, but inhibited angiogenesis and submesothelial thickening 21 days after induction of fibrosis. In primary mesothelial cell culture, rapamycin had no effect on TGFβ-induced vascular endothelial growth factor (VEGF) but did suppress hypoxia-induced VEGF. HIF1α induced submesothelial thickening and angiogenesis in peritoneal tissue. The fibrogenic effects of HIF1α were Smad3 dependent. In summary, submesothelial hypoxia may be an important secondary factor, which augments TGFβ-induced peritoneal injury. The hypoxic response is mediated partly through HIF1α and the mTOR inhibitor rapamycin blocks the hypoxic-induced angiogenic effects but does not affect the direct TGFβ-mediated fibrosis and angiogenesis.

Oxygen tension and formation of cervical-like tissue in two-dimensional and three-dimensional culture

Cervical dysfunction contributes to a significant number of preterm births and is a common cause of morbidity and mortality in newborn infants. Cervical dysfunction is related to weakened load bearing properties of the collagen-rich cervical stroma. However, the mechanisms responsible for cervical collagen changes during pregnancy are not well defined. It is known that blood flow and oxygen tension significantly increase in reproductive tissues during pregnancy. To examine the effect of oxygen tension, a key mediator of tissue homeostasis, on the formation of cervical-like tissue in vitro, we grew primary human cervical cells in both two-dimensional (2D) and three-dimensional (3D) culture systems at 5% and 20% oxygen. Immunofluorescence studies revealed a stable fibroblast phenotype across six passages in all subjects studied (n=5). In 2D culture for 2 weeks, 20% oxygen was associated with significantly increased collagen gene expression (p<0.01), increased tissue wet weight (p<0.01), and increased collagen concentration (p=0.046). 3D cultures could be followed for significantly longer time frames than 2D cultures (12 weeks vs. 2 weeks). In contrast to 2D cultures, 20% oxygen in 3D cultures was associated with decreased collagen concentration (p<0.01) and unchanged collagen gene expression, which is similar to cervical collagen changes seen during pregnancy. We infer that 3D culture is more relevant for studying cervical collagen changes in vitro. The data suggest that increased oxygen tension may be related to significant cervical collagen changes seen in pregnancy.

Integrative network analysis identifies key genes and pathways in the progression of hepatitis C virus induced hepatocellular carcinoma

Background

Incidence of hepatitis C virus (HCV) induced hepatocellular carcinoma (HCC) has been increasing in the United States and Europe during recent years. Although HCV-associated HCC shares many pathological characteristics with other types of HCC, its molecular mechanisms of progression remain elusive.

Methods

To investigate the underlying pathology, we developed a systematic approach to identify deregulated biological networks in HCC by integrating gene expression profiles with high-throughput protein-protein interaction data. We examined five stages including normal (control) liver, cirrhotic liver, dysplasia, early HCC and advanced HCC.

Results

Among the five consecutive pathological stages, we identified four networks including precancerous networks (Normal-Cirrhosis and Cirrhosis-Dysplasia) and cancerous networks (Dysplasia-Early HCC, Early-Advanced HCC). We found little overlap between precancerous and cancerous networks, opposite to a substantial overlap within precancerous or cancerous networks. We further found that the hub proteins interacted with HCV proteins, suggesting direct interventions of these networks by the virus. The functional annotation of each network demonstrates a high degree of consistency with current knowledge in HCC. By assembling these functions into a module map, we could depict the stepwise biological functions that are deregulated in HCV-induced hepatocarcinogenesis. Additionally, these networks enable us to identify important genes and pathways by developmental stage, such as LCK signalling pathways in cirrhosis, MMP genes and TIMP genes in dysplastic liver, and CDC2-mediated cell cycle signalling in early and advanced HCC. CDC2 (alternative symbol CDK1), a cell cycle regulatory gene, is particularly interesting due to its topological position in temporally deregulated networks.

Conclusions

Our study uncovers a temporal spectrum of functional deregulation and prioritizes key genes and pathways in the progression of HCV induced HCC. These findings present a wealth of information for further investigation.

Growth factor production from fibrin-encapsulated human keratinocytes

Fibrin has been used extensively in cell encapsulation because it has important biological properties. Keratinocyte encapsulation in fibrin is a widely used technique in skin tissue engineering. The production of growth factors (EGF, TGF-beta1 and PDGF-BB) was evaluated when keratinocytes are encapsulated in fibrin. Secretions of TGF-beta1 and PDGF-BB increased more than five times compared to monolayer cultures. Encapsulated cells secreted about 80% active form of TGF-beta1 (monolayer cells only secreted inactive form). An enhanced secretion of TGF-beta1 and PDGF-BB was found in encapsulated cells, showing that fibrin capsules are favourable for the production of these growth factors.

Mediators of neovascularization and the hypoxic cornea

The maintenance of corneal avascularity is essential to vision. The mechanisms by which the cornea becomes vascularized in response to inflammation or hypoxic stress are beginning to be elucidated. A detailed understanding of the molecular responses of the cornea to hypoxia is critical for prevention and development of novel treatments for neovascularization in a range of disease states. Here, we have examined the current literature on the major mediators of angiogenesis, which have previously been reported during hypoxia in the cornea in order to better understand the mechanisms by which corneal angiogenesis occurs in circumstances where the available oxygen is reduced. The normal cornea produces angiogenic factors that are regulated by the production of anti-angiogenic molecules. The various cell types of the cornea respond differentially to inflammatory and hypoxic stimuli. An understanding of the factors that may predispose patients to development of corneal blood vessels may provide an opportunity to develop novel prophylactic strategies. The difficulties with extrapolating data from other cell types and animal models to the cornea are also examined.

A gel-free quantitative proteomics analysis of factors released from hypoxic-conditioned placentae

Characterizing the protein factors released from placentae during pathogenesis remains a key objective toward understanding preeclampsia and related pregnancy disorders. Gel-free proteomics technologies applied to placental explant-conditioned media offers the potential of identifying these factors. Relative quantification mass spectrometry using isobaric tagging for relative and absolute quantification (iTRAQ) labeling was employed to compare the ''secretome'' between healthy term placental tissue cultured under both normoxic and hypoxic oxygen tensions. Of the 499 proteins identified, 45 were differentially expressed (P < .01 level), including interleukin 8 (IL-8) which was significantly upregulated under hypoxia. Global protein level changes are suggestive of decreased extracellular matrix remodeling under the same conditions. A significant enrichment of soluble liberated placental factors is achieved using this model system. Identifying these changes resulting from hypoxic conditioning is hypothesis generating and may provide new mechanistic insights into preeclampsia.

Hypoxia/reoxygenation induces CTGF and PAI-1 in cultured human retinal pigment epithelium cells

Early age-related macular degeneration (AMD) is characterized by thickening of Bruch's membrane due to the accumulation of extracellular matrix (ECM). This finding could be related to hypoxia of the retinal pigment epithelium (RPE). In the present study, we investigated the effects of hypoxia and reoxygenation on the expression of connective tissue growth factor (CTGF), plasminogen activator inhibitor-1 (PAI-1), collagen type IV (Col IV) and fibronectin (Fn) in cultured human RPE cells. Cultured human RPE cells were kept for 12-36h under hypoxic conditions (1% O(2)). Reoxygenation was conducted for 24h. Hypoxia-mediated CTGF and PAI-1 expression were analyzed by using immunohistochemistry, Northern and Western blot analysis. Actinomycin D was added to examine whether hypoxia induces the transcription of CTGF and PAI-1 mRNA. Furthermore, cells were transfected with siRNA against hypoxia-inducible factor-1alpha (HIF-1alpha) and kept under hypoxic conditions. The effects of antioxidants on hypoxia/reoxygenation-mediated CTGF and PAI-1 expression were tested by real-time PCR analysis. Production of Col IV and Fn were investigated by real-time PCR and Western blot analysis. Both hypoxia and hypoxia/reoxygenation increased the expression of CTGF, PAI-1, Col IV and Fn. Actinomycin D prevented the new transcription of CTGF and PAI-1 mRNA by hypoxia. Using siRNA against HIF-1alpha, the hypoxia-mediated increase of CTGF and PAI-1 was inhibited. Antioxidants attenuated the reoxygenation-mediated increase of CTGF and PAI-1. The process of hypoxia/reoxygenation in the RPE may lead to an increase of ECM in the RPE and thus may contribute to the accumulation of ECM in Bruch's membrane.

Selective induction of integrin beta1 by hypoxia-inducible factor: implications for wound healing

Because of localized vascular damage and increased tissue oxygen demand, wound healing occurs in a relatively hypoxic microenvironment. These features are particularly relevant to wound healing and fibrosis in chronic inflammatory conditions, such as Crohn's disease and ulcerative colitis. In these studies, we sought to identify the contribution of hypoxia to mechanisms of wound repair in a model of the intestinal submucosa. Initial studies revealed that hypoxia promotes wound healing, as modeled by an increase in intestinal fibroblast-mediated collagen gel contraction. Guided by results from transcriptional profiling, we identified the selective induction of fibroblast integrin beta1 (ITGB1) by hypoxia. Further analysis revealed that hypoxia, as well as pharmacological activators of hypoxia-inducible factor (HIF), induce fibroblast beta1 integrin mRNA, protein, and function by as much as 4-fold. Cloning and analysis of the beta1 integrin gene promoter revealed a 10 +/- 0.8-fold increase in promoter activity in response to hypoxia, and subsequent studies identified a functional DNA binding region for HIF in the ITGB1 gene promoter. Mutational analysis of the HIF binding site within the ITGB1 promoter resulted in a significant loss of ITGB1 hypoxia-inducibility. As proof of principle, studies in a murine model of colitis revealed a correlation between colitic disease severity and tissue ITGB1 expression (R(2)=0.80). Taken together, these results demonstrate that hypoxia induces fibroblast ITGB1 expression and function by transcriptional mechanisms dependent on HIF.

Regulation of angiotensin II receptors and extracellular matrix turnover in human retinal pigment epithelium: role of angiotensin II

The early stage of age-related macular degeneration (AMD) is characterized by the formation of subretinal pigment epithelium (RPE) deposits as a result of the dysregulation in the turnover of extracellular matrix (ECM) molecules. However, the mechanism involved remains unclear. Hypertension (HTN) is an important risk factor for AMD, and angiotensin II (ANG II) is the most important hormone associated with HTN. However, the relevance of ANG II receptors and ANG II effects on RPE have not been investigated yet. Therefore, the expression and regulation of ANG II receptors as well as the ECM turnover were studied in human RPE. ANG II receptors were expressed and upregulated by ANG II in human RPE. This regulation resulted in functional receptor expression, since an increase in intracellular concentration of calcium was observed upon ANG II stimulation. ANG II also increased matrix metalloproteinase (MMP)-2 activity and MMP-14 at the mRNA and protein levels as well as type IV collagen degradation. These ANG II effects were abolished in the presence of the ANG II receptor subtype 1 (AT1) receptor antagonist candesartan. In contrast, ANG II decreased type IV collagen via both AT1 and AT2 receptors, suggesting a synergistic effect of the two receptor subtypes. In conclusion, we have confirmed the presence of ANG II receptors in human RPE and their regulation by ANG II as well as the regulation of ECM molecules via ANG II receptors. Our data support the hypothesis that ANG II may exert biological function in RPE through ANG II receptors and that ANG II may cause dysregulation of molecules that play a major role in the turnover of ECM in RPE basement membrane and Bruch's membrane, suggesting a pathogenic mechanism to explain the link between HTN and AMD.

Regulation of angiotensin II receptors and extracellular matrix turnover in human retinal pigment epithelium: role of angiotensin II

The early stage of age-related macular degeneration (AMD) is characterized by the formation of subretinal pigment epithelium (RPE) deposits as a result of the dysregulation in the turnover of extracellular matrix (ECM) molecules. However, the mechanism involved remains unclear. Hypertension (HTN) is an important risk factor for AMD, and angiotensin II (ANG II) is the most important hormone associated with HTN. However, the relevance of ANG II receptors and ANG II effects on RPE have not been investigated yet. Therefore, the expression and regulation of ANG II receptors as well as the ECM turnover were studied in human RPE. ANG II receptors were expressed and upregulated by ANG II in human RPE. This regulation resulted in functional receptor expression, since an increase in intracellular concentration of calcium was observed upon ANG II stimulation. ANG II also increased matrix metalloproteinase (MMP)-2 activity and MMP-14 at the mRNA and protein levels as well as type IV collagen degradation. These ANG II effects were abolished in the presence of the ANG II receptor subtype 1 (AT1) receptor antagonist candesartan. In contrast, ANG II decreased type IV collagen via both AT1 and AT2 receptors, suggesting a synergistic effect of the two receptor subtypes. In conclusion, we have confirmed the presence of ANG II receptors in human RPE and their regulation by ANG II as well as the regulation of ECM molecules via ANG II receptors. Our data support the hypothesis that ANG II may exert biological function in RPE through ANG II receptors and that ANG II may cause dysregulation of molecules that play a major role in the turnover of ECM in RPE basement membrane and Bruch's membrane, suggesting a pathogenic mechanism to explain the link between HTN and AMD.

Hyperactivity of fibroblasts and functional regression of endothelial cells contribute to microvessel occlusion in hypertrophic scarring

Hypertrophic scars (HSc) have an excess of microvessels, most of which are partially or totally occluded. The mechanisms underlying microvessel endothelial cell accumulation and microvessel occlusion are poorly understood. In this study, we observed the microvessels with H&E staining and electron microscopy, and detected the cytokine expression with immunochemistry. In addition, we isolated fibroblasts and endothelial cells from both human HSc tissue and normal skin and studied their cytokine expression. Furthermore, we assayed the endothelial cell proliferation when co-cultured with normal endothelial cells and blocked with anti-VEGF and anti-bFGF neutralizing. The results revealed that more endothelial cells in HSc microvessels and the cells were swollen. The cultured HSc fibroblasts secreted significantly more while HSc endothelial cells secreted significantly less cytokines, and the same trend was found with cytokines and collagen mRNAs, which was also confirmed by immunochemistry finding. In addition, endothelial cells proliferated faster when co-cultured with HSc fibroblasts, and reduced by anti-VEGF and anti-bFGF neutralizing. This is the first report regarding the function of endothelial cells in hypertrophic scars. The hyperactivity in cytokine secretion and collagen production is largely responsible for over-proliferation and functional regression of endothelial cells, and the malfunctioning of both cell types contributes to microvessel occlusion.

Developmental Changes in Extracellular Matrix Messenger RNAs in the Mouse Placenta During the Second Half of Pregnancy: Possible Factors Involved in the Regulation of Placental Extracellular Matrix Expression1

Expression of procollagens (Col1a1/2, Col3a1, Col4a1/2, Col5a1/2) and fibronectin 1 (Fn1) in the mouse fetal placental tissue was examined during the second half of pregnancy. Ribonuclease protection assays (RPAs) revealed that levels of these mRNAs noticeably increased between Days 10 and 14 of pregnancy, and they remained at relatively constant levels thereafter. In situ hyridization showed that Col1a1 and Col4a1 mainly localized in the labyrinth, whereas Fn1 was expressed mainly in the spongiotrophoblast. Since members of the transforming growth factor-beta (TGFB) superfamily are involved in the regulation of extracellular matrix (ECM) expression in various tissues, mRNA levels of TGFB family members and their binding proteins were also examined by RPAs. Transforming growth factor-beta1-3 (Tgfb1-3), activin subunits (Inhba, Inhbb), follistatin (Fst), and follistatin-like 3 (Fstl3) were expressed in the placenta, whereas significant expression of myostatin (Mstn) was not detected. Although the expression patterns of Tgfb1-3 and Inhba in the placenta suggest possible involvement of TGFBs and activin A in the regulation of placental ECM expression, neither TGFBs nor activin A affected ECM mRNA levels in vitro. On the other hand, hypoxia significantly decreased Col1a1/2 and Col4a1/2 mRNAs in cultured placental cells, and a high-glucose condition significantly increased Col1a1 and Col3a1 mRNAs. Fn1 expression was increased under the high-glucose condition, although hypoxia also increased Fn1 expression to a lesser degree. These data suggest that an increase in oxygen tension and nutrient supply during placentation rather than TGFB family members may be responsible for the increase in the placental ECM mRNA expression.

In vitro wounding: effects of hypoxia and transforming growth factor β1 on proliferation, migration and myofibroblastic differentiation in an endothelial cell-fibroblast co-culture model

The adequate reconstitution of human soft tissue wounds requires the coordinated interaction of endothelial cells and fibroblasts during the proliferation phase of healing. Endothelial cells assure neoangiogenesis, fibroblasts fill the defect and provide extracellular matrix proteins, and myofibroblasts are believed to support the reconstitution of microvessels. In the present study, we combined in vitro-wound size measurement and multicolour immunocytochemical staining of co-cultured human dermal microvascular endothelial cells and normal human dermal fibroblasts, recently introduced as co-culture scratch-wound migration assay. Applying antibodies for alpha-smooth-muscle actin, von Willebrand factor, extra domain A fibronectin and endothelin-1, we were able to monitor proliferation, migration and the differentiation process from fibroblasts to myofibroblasts as a response to hypoxia. Furthermore, we verified, whether transforming growth factor beta1 (TGFbeta1) and endothelin-1 are able to mediate this response. We show, that proliferation and migration of endothelial cells and fibroblasts decreased under hypoxia. The additional administration of TGFbeta1 did not significantly attenuate this decrease. Solely the myofibroblast population in co-culture adapted well to hypoxia, when cultures were supplemented with TGFbeta1. Considerating the data concerning TGFbeta1 and endothelin-1, we propose a model explaining the cellular interaction during early and late proliferation phase of human wound healing.

Hypoxia-induced pulmonary vascular remodeling: cellular and molecular mechanisms

Chronic hypoxic exposure induces changes in the structure of pulmonary arteries, as well as in the biochemical and functional phenotypes of each of the vascular cell types, from the hilum of the lung to the most peripheral vessels in the alveolar wall. The magnitude and the specific profile of the changes depend on the species, sex, and the developmental stage at which the exposure to hypoxia occurred. Further, hypoxia-induced changes are site specific, such that the remodeling process in the large vessels differs from that in the smallest vessels. The cellular and molecular mechanisms vary and depend on the cellular composition of vessels at particular sites along the longitudinal axis of the pulmonary vasculature, as well as on local environmental factors. Each of the resident vascular cell types (ie, endothelial, smooth muscle, adventitial fibroblast) undergo site- and time-dependent alterations in proliferation, matrix protein production, expression of growth factors, cytokines, and receptors, and each resident cell type plays a specific role in the overall remodeling response. In addition, hypoxic exposure induces an inflammatory response within the vessel wall, and the recruited circulating progenitor cells contribute significantly to the structural remodeling and persistent vasoconstriction of the pulmonary circulation. The possibility exists that the lung or lung vessels also contain resident progenitor cells that participate in the remodeling process. Thus the hypoxia-induced remodeling of the pulmonary circulation is a highly complex process where numerous interactive events must be taken into account as we search for newer, more effective therapeutic interventions. This review provides perspectives on each of the aforementioned areas.

Genetic relationship between placental and fetal weights and markers of the metabolic syndrome in rat recombinant inbred strains

Epidemiological studies have shown a clear link between fetal growth retardation and an increased propensity for later cardiovascular disease in adults. It has been hypothesized that such early fetal deprivation “programs” individuals toward a life-long metabolical “thrifty phenotype” that predisposes adults to such diseases. Here we test this hypothesis, and its possible genetic basis, in rat recombinant inbred (RI) strains that uniquely allow the longitudinal studies necessary for its testing. Placental and fetal weights were determined on day 20 of pregnancy in (at least) 6 litters from each of 25 available BXH/HXB RI strains and from their SHR and BN-Lx progenitors and were correlated with metabolic traits determined in adult rats from the same inbred lines. Quantitative trait loci (QTLs) associated with placental and fetal weights were identified by total genome scanning of RI strains using the Map Manager QTX program. Heritabilities of placental and fetal weights were 56% and 62%, respectively, and total genome scanning of RI strains revealed QTLs near the D1Rat266 marker on chromosome 1 and near the D15Rat101 marker on chromosome 15 that were significantly associated with fetal and placental weights respectively. Placental weights correlated with fetal weights ( r = 0.60, P = 0.001), while reduced fetal weights correlated with increased insulin concentrations during glucose tolerance test ( r = −0.71, P = 0.0001) and with increased serum triglycerides ( r = −0.54, P = 0.006) in adult rats. Our results suggest that predisposition toward a thrifty phenotype associated with decreased placental weight and restricted fetal growth is in part genetically determined.

An imbalance between vascular endothelial growth factor and its soluble receptor in placental villous explants of intrauterine growth-restricted pregnancies

OBJECTIVES

Human umbilical vascular endothelial cells (HUVECs), seeded on Matrigel (BD Biosciences, Bedford, UK), undergo an angiogenic-like process. We hypothesized that placental explants from normal pregnancies, maintained in cultures of different oxygen, would liberate factors that could be measured in this system. We further tested the angiogenic potential of placentae from intrauterine growth-restricted (IUGR) pregnancies and the effects of vascular endothelial growth factor (VEGF) blockade.

METHODS

Placental villous explants were maintained in culture at 3% and 20% O2. The resultant media was added to HUVECs seeded on 80% Matrigel. Cells were incubated at 6% O2 in accordance with the natural placental environment. After 6 hours, cells were fixed and stained and the length and number of tubules measured by morphometric imaging. Finally, VEGF and soluble VEGF receptor (sVEGFR-1) were recorded in the explant conditioned media.

RESULTS

Within the angiogenic assay, recombinant human VEGF significantly enhanced tubule outgrowth (branching and elongation) and this effect was blocked with neutralising antibody. Compared to 20% O2, media of placental explants conditioned at 3% O2 significantly encouraged tubule length and numbers. Again this affect was ablated by VEGF blockade. In cases of IUGR, conditioned media at 3% O2 showed a significant reduction in tubule growth. This was paralleled by a decline in available VEGF brought about an exaggeration in liberated sVEGFR-1. Notably, venous cord serum from IUGR pregnancies showed a similar elevation in sVEGFR-1.

CONCLUSION

Under restricted oxygen, placental angiogenic potential is suppressed in IUGR pregnancies through the overproduction of placental sVEGFR-1. This reduction may discourage normal placental vascularization and impact on fetal development.

Identification and relative quantification of membrane proteins by surface biotinylation and two-dimensional peptide mapping

Membrane proteins play a central role in biological processes, but their separation and quantification using two-dimensional gel electrophoresis is often limited by their poor solubility and relatively low abundance. We now present a method for the simultaneous recovery, separation, identification, and relative quantification of membrane proteins, following their selective covalent modification with a cleavable biotin derivative. After cell lysis, biotinylated proteins are purified on streptavidin-coated resin and proteolytically digested. The resulting peptides are analyzed by high-pressure liquid chromatography and mass spectrometry, thus yielding a two-dimensional peptide map. Matrix assisted laser desorption/ionization-time of flight signal intensity of peptides, in the presence of internal standards, is used to quantify the relative abundance of membrane proteins from cells treated in different experimental conditions. As experimental examples, we present (i) an analysis of a BSA-spiked human embryonic kidney membrane protein extract, and (ii) an analysis of membrane proteins of human umbilical vein endothelial cells cultured in normoxic and hypoxic conditions. This last study allowed the recovery of the vascular endothelial-cadherin/actin/catenin complex, revealing an increased accumulation of beta-catenin at 2% O(2) concentration.