Potential role for laminin 5 in hypoxia-mediated apoptosis of human corneal epithelial cells

Effects of hypoxia in the diabetic corneal stroma microenvironment

Corneal dysfunctions associated with Diabetes Mellitus (DM), termed diabetic keratopathy (DK), can cause impaired vision and/or blindness. Hypoxia affects both Type 1 (T1DM) and Type 2 (T2DM) surprisingly, the role of hypoxia in DK is unexplored. The aim of this study was to examine the impact of hypoxia in vitro on primary human corneal stromal cells derived from Healthy (HCFs), and diabetic (T1DMs and T2DMs) subjects, by exposing them to normoxic (21% O2) or hypoxic (2% O2) conditions through 2D and 3D in vitro models. Our data revealed that hypoxia affected T2DMs by slowing their wound healing capacity, leading to significant alterations in oxidative stress-related markers, mitochondrial health, cellular homeostasis, and endoplasmic reticulum health (ER) along with fibrotic development. In T1DMs, hypoxia significantly modulated markers related to membrane permeabilization, oxidative stress via apoptotic marker (BAX), and protein degradation. Hypoxic environment induced oxidative stress (NOQ1 mediated reduction of superoxide in T1DMs and Nrf2 mediated oxidative stress in T2DMs), modulation in mitochondrial health (Heat shock protein 27 (HSP27), and dysregulation of cellular homeostasis (HSP90) in both T1DMs and T2DMs. This data underscores the significant impact of hypoxia on the diabetic cornea. Further studies are warranted to delineate the complex interactions.

Thrombospondin 1-induced exosomal proteins attenuate hypoxia-induced paraptosis in corneal epithelial cells and promote wound healing

Thrombospondin-1 (TSP1) is involved in corneal wound healing caused by chemical injury. Herein, we examined the effects of TSP1 on hypoxia-induced damages and wound-healing activity in human corneal epithelial (HCE) cells. Exosomal protein expression was determined using liquid chromatography-tandem mass spectrometry, and HCE cell migration and motility were examined through wound-healing assay and time-lapse microscopy. Reestablishment of cell junctions by TSP1 was assessed through confocal microscopy and 3D image reconstruction. Our results show that CoCl₂ -induced hypoxia promoted HCE cell death by paraptosis. TSP1 protected these cells against paraptosis by attenuating mitochondrial membrane potential depletion, swelling and dilation of endoplasmic reticulum and mitochondria, and mitochondrial fission. Exosomes isolated from HCE cells treated with TSP1 contained wound healing-associated proteins that were taken up by HCE cells to promote tissue remodeling and repair. TSP1 protected HCE cells against hypoxia-induced damages and inhibited paraptosis progression by promoting cell migration, cell-cell adhesion, and extracellular matrix remodeling. These findings indicate that TSP1 ameliorates hypoxia-induced paraptosis in HCE cells and promotes wound healing and remodeling by regulating exosomal protein expression. TSP1 may, therefore, play important roles in the treatment of hypoxia-associated corneal diseases.

Gradients in the in vivo intestinal stem cell compartment and their in vitro recapitulation in mimetic platforms

Intestinal tissue, and specifically its mucosal layer, is a complex and gradient-rich environment. Gradients of soluble factor (BMP, Noggin, Notch, Hedgehog, and Wnt), insoluble extracellular matrix proteins (laminins, collagens, fibronectin, and their cognate receptors), stromal stiffness, oxygenation, and sheer stress induced by luminal fluid flow at the crypt-villus axis controls and supports healthy intestinal tissue homeostasis. However, due to current technological challenges, very few of these features have so far been included in in vitro intestinal tissue mimetic platforms. In this review, the tightly defined and dynamic microenvironment of the intestinal tissue is presented in detail. Additionally, the authors introduce the current state-of-the-art intestinal tissue mimetic platforms, as well as the design drawbacks and challenges they face while attempting to capture the complexity of the intestinal tissue's physiology. Finally, the compositions of an "idealized" mimetic system is presented to guide future developmental efforts.

[Corneal transparency: anatomical basis and evaluation methods]

Being just a relatively small part of the fibrous tunic of the eyeball, the cornea is, nevertheless, unique in terms of the variety of its functions. Because the cornea differs significantly from other protective frames in its structure, it provides the possibility of light transmission and strong refraction that largely contributes to the total refraction of the eye. The development of ophthalmology is impossible without improving methods of adequate anatomical and functional assessment of the eye not only as a whole, but also as a collection of interacting structures.In this regard, examination methods of the cornea have undergone significant advances in recent years. So far, the level of corneal transparency has been judged by biomicroscopy findings or indirect characteristics (thickness, structure, etc.). Confocal microscopy of the cornea and wave-based examinations involving one of the available laser interferometers (OCT or HRT) are also used. However, the data obtained with these methods resembles that of layer-specific reflectometry, i.e. the magnitude of directed reflection of the light beam from corneal corpuscles, which does not completely agree with the classical idea of transparency.

Efficacy, long-term toxicity, and mechanistic studies of gold nanorods photothermal therapy of cancer in xenograft mice

Gold nanorods (AuNRs)-assisted plasmonic photothermal therapy (AuNRs-PPTT) is a promising strategy for combating cancer in which AuNRs absorb near-infrared light and convert it into heat, causing cell death mainly by apoptosis and/or necrosis. Developing a valid PPTT that induces cancer cell apoptosis and avoids necrosis in vivo and exploring its molecular mechanism of action is of great importance. Furthermore, assessment of the long-term fate of the AuNRs after treatment is critical for clinical use. We first optimized the size, surface modification [rifampicin (RF) conjugation], and concentration (2.5 nM) of AuNRs and the PPTT laser power (2 W/cm²) to achieve maximal induction of apoptosis. Second, we studied the potential mechanism of action of AuNRs-PPTT using quantitative proteomic analysis in mouse tumor tissues. Several death pathways were identified, mainly involving apoptosis and cell death by releasing neutrophil extracellular traps (NETs) (NETosis), which were more obvious upon PPTT using RF-conjugated AuNRs (AuNRs@RF) than with polyethylene glycol thiol-conjugated AuNRs. Cytochrome c and p53-related apoptosis mechanisms were identified as contributing to the enhanced effect of PPTT with AuNRs@RF. Furthermore, Pin1 and IL18-related signaling contributed to the observed perturbation of the NETosis pathway by PPTT with AuNRs@RF. Third, we report a 15-month toxicity study that showed no long-term toxicity of AuNRs in vivo. Together, these data demonstrate that our AuNRs-PPTT platform is effective and safe for cancer therapy in mouse models. These findings provide a strong framework for the translation of PPTT to the clinic.

Is there a relationship between sleep apnea and central corneal thickness?

PURPOSE

The objective of this study was to determine the central corneal thickness (CCT) measurements in patients with Sleep Apnea Syndrome (SAS) and the relationship between the severity of SAS and minimal arterial oxygen saturation (min. SpO2) with respect to CCT.

MATERIALS AND METHODS

Two hundred and fourteen eyes of 107 patients (58 males, 49 females) who were diagnosed as SAS and 80 eyes of 40 healthy subjects (20 males, 20 females) were included in the study. The SAS patients were divided into subgroups according to their Apnea-Hypopnea Index (AHI) values as: AHI values between 5 and 15 as subgroup 1, between 15 and 30 as subgroup 2, and the values ≥30 as subgroup 3. The CCT was measured by an ultrasonic pachymetric system. Statistical analyses were an analysis of variance test and, for post-hoc analysis, the Dunnett C test.

RESULTS

Mean age was 52.5 ± 10.96 years in the study group, and 40.7 ± 10.14 years in the control group. There were 58 (54.2%) males and 49 (45.8%) females in the study group, and 20 (50%) males and 20 (50%) females in the control group. Mean CCT values were 526.65 ± 25.06, 525.26 ± 29.25, 512.93 ± 43.20 and 539.90 ± 17.28 in subgroup 1, subgroup 2, subgroup 3 and the control group, respectively. There were no statistically significant differences between gender and age groups with respect to CCT (p > 0.05). When the mean CCT values of each subgroups were compared with the control group, the differences were statistically significant (p < 0.05). There was a negative correlation between CCT and AHI values and a positive correlation between CCT and min. SpO2 values.

CONCLUSIONS

CCT measurements differ significantly in patients with SAS compared with healthy control subjects. It should be taken into consideration that SAS may reduce CCT over time and that CCT should be measured in each ophthalmic examination.

New insights in wound response and repair of epithelium

Epithelial wounds usually heal relatively quickly, but repair may be impaired by environmental stressors, such as hypoxic or diabetic states, rendering patients vulnerable to a number of corneal pathologies. Though this response appears simple, at first, years of research have uncovered the complicated biochemical pathways coordinating the wound healing response. Here, we investigate signaling cascades and individual proteins involved in the corneal epithelium's self-repair. We will explore how an epithelial cell migrates across the wound bed and attaches itself to its new post-injury surroundings, including its neighboring cells and the basement membrane, through focal adhesions and hemidesmosomes. We will also discuss how the cell coordinates this motion physiologically, through calcium signaling and protein phosphorylation, focusing on the communication through purinergic, glutamatergic, and growth factor receptors. Many of these aspects reflect and can be extended to similar epithelial surfaces, and can be used to facilitate wound healing in patients with various underlying pathologies. The collective library of laboratory and clinical research done around the world has demonstrated how important precise regulation of these processes is in order for the injured corneal epithelium to properly heal.

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.

Morphological evidences indicate that the interference of cimetidine on the peritubular components is responsible for detachment and apoptosis of Sertoli cells

Cimetidine, referred as antiandrogenic agent, has caused alterations in the seminiferous tubules, including alterations in the peritubular tissue and death of myoid cells by apoptosis. Regarding the structural and functional importance of the peritubular tissue for the maintenance of Sertoli cells (SC), we purpose to investigate the SC-basement membrane interface, focusing the morphological features of SC and their interaction with the basement membrane in the affected tubules by cimetidine. Ten animals were distributed into two groups, control (CG) and cimetidine (CmG) which received saline solution and 50 mg of cimetidine per kg of body weight, respectively, for 52 days. The testes were fixed, dehydrated and embedded for analyses under light and transmission electron microscopy. Paraffin sections were submitted to the TUNEL method; sections of testes embedded in glycol methacrylate were submitted to PAS method and stained by H&E for morphological and quantitative analyses of Sertoli Cells. In the CmG, the SC nuclei were positive to the TUNEL method and showed typical morphological alterations of cell death by apoptosis (from early to advanced stages). A significant reduction in the number of Sertoli Cells was probably due to death of these cells by apoptosis. A close relationship between SC nuclear alterations (including a high frequency of dislocated nuclei from the basal portion) and damage in the peritubular tissue was observed. The ultrastructural analysis showed a parallelism between the gradual advancement of apoptotic process in SC and detachment of the anchoring sites (hemidesmosomes) of SC plasma membrane from the lamina densa. The presence of portions of lamina densa underlying the detached hemidesmosomes indicates a continuous deposition of lamina densa, resulting in the thickening of the basal lamina. The results indicate a possible disarrangement of the SC cytoskeleton, including the focal adhesion structure. These alterations are related to SC apoptosis and probably result from disturbs induced by cimetidine on the peritubular tissue.

Effects of ambient oxygen concentration on the proliferation and viability of cultured human corneal epithelial cells

Ambient oxygen (O(2)) affects the metabolism and other functions of corneal epithelial cells. The effects of O(2) concentration on the proliferation and viability of corneal epithelial cells in culture were investigated. Simian virus 40-transformed human corneal epithelial (HCE) cells were maintained at 37 degrees C in a humidified incubator containing 5% CO(2) and 95% air. The cells were subsequently transferred to a multigas incubator and exposed to 5% CO(2) and either 1, 21, or 60% O(2) plus 94, 74, or 35% N(2), respectively. Cell proliferation was evaluated by determination of cell number and measurement of the incorporation of bromodeoxyuridine. Cell lysis was quantified by measurement of the release of lactate dehydrogenase. Apoptosis was evaluated by flow cytometric analysis of cells stained with annexin V and propidium iodide as well as by immunoblot analysis of cleavage of caspase-7. The phosphorylation (activation) of Akt was also detected by immunoblot analysis. Hyperoxia (60% O(2)) inhibited the increase in cell number and the incorporation of bromodeoxyuridine apparent in HCE cells exposed to normoxia (21% O(2)). It also induced the release of lactate dehydrogenase, an increase in the proportion of apoptotic (annexin V(+), propidium iodide(-)) cells, the cleavage of caspase-7, and the phosphorylation of Akt. None of these effects was observed in cells exposed to hypoxia (1% O(2)). The amounts of the cleaved forms of caspase-3, 6, and 9 did not differ among HCE cells cultured under 1, 21, or 60% O(2). These results indicate that hyperoxia inhibited the proliferation of, and induced death by apoptosis in, cultured human corneal epithelial cells. The antiapoptotic protein Akt was also activated in cells exposed to hyperoxia, possibly reflecting a protective response to oxygen toxicity.

An in vivo study of common carp (Cyprinus carpio L.) liver during prolonged hypoxia

Hypoxia induced apoptosis has been studied extensively in many mammalian cell lines but there are only a few studies using whole animal models. We investigated the response of the intact liver to hypoxia in a hypoxia tolerant fish, the carp (Cyprinus carpio, L). We exposed carp to hypoxia for up to 42 days, using oxygen level (0.5 mgO(2)/L) that were slightly higher than the critical oxygen level of carp. There was extensive DNA damage in liver cells, especially during the first week of exposure, indicated by a massive TUNEL signal. However there was no change in cell proliferation, cell number or size, no increase in caspase-3 activity, no increase in single stranded DNA and this, combined with a number of other observations, led us to conclude there was no increase in apoptosis in the liver during hypoxia. There was up-regulation of some anti-apoptotic genes and proteins (Bcl-2, HSP70, p27) and down-regulation of some pro-apoptotic genes (Tetraspanin 5 and Cell death activator). The cells appeared to enter cell cycle arrest, presumably to allow repair of damaged DNA. As there was no change in cell proliferation and cell number, the damaged cells were not entering apoptosis and must have recovered during prolonged hypoxia.

The extracellular matrix in oral squamous cell carcinoma: friend or foe?

Oral squamous cell carcinoma is a disfiguring, highly invasive and metastatic cancer. Despite advances in detection and therapy, many patients will continue to face a poor prognosis. It is well established that the predominate factor determining overall survival in patients with oral squamous cell carcinoma is lymph node involvement. Tumor growth and progression to invasive cancer requires tumor cell interactions with the extracellular matrix. An understanding of how the extracellular matrix influences tumor development and invasion is fundamental in the development of new prognostic indicators and treatment strategies for oral squamous cell carcinoma. In this review, we summarize how changes in the extracellular matrix contribute to oral cancer development.

Plasminogen activator inhibitor-1 (PAI-1) stimulates human corneal epithelial cell adhesion and migration in vitro

In addition to its role as an inhibitor of urokinase plasminogen activator (uPA), plasminogen activator inhibitor-1 (PAI-1) is hypothesized to regulate epithelial cell adhesion and migration. We have previously reported that PAI-1 may be an important regulatory factor of the uPA system in cornea. The purpose of this study was to extend those observations by determining the effect of exogenous PAI-1 on the migration and adhesion of human corneal epithelial cells (HCEC) in vitro. The expression of PAI-1 in non-transformed early passage HCEC was confirmed by immunofluorescence microscopy and Western blot analysis. Colorimetric assays coupled with function-inhibiting antibody studies using the matrix assembled in situ by cultured cells demonstrate that immobilized PAI-1 serves as an efficient substrate for HCEC adhesion. HCEC attachment to PAI-1 is comparable to that of laminin-10, a known strong adhesion protein for epithelial cells. In addition to serving as an adhesion substrate, PAI-1 also functions as a chemotactic agent for corneal epithelium. Additionally it promotes the random migration of HCEC, from an initial cell cluster, along a culture substrate. Our results in corneal epithelium are consistent with reports from other investigators showing that PAI-1 facilitates both epithelial adhesion and migration. From our studies we conclude that PAI-1 may play a dual role in corneal wound healing. Initially PAI-1 may function to stimulate migration and facilitate the reepithelialization of the wound bed. Post-reepithelization, PAI-1 may ensure corneal epithelial cell adhesion to matrix to promote successful wound healing.

The developing mouse dentition: a new tool for apoptosis study

Developing limb or differentiating neural and blood cells are traditional models used to study programmed cell death in mammals. The developing mouse dentition can also be an attractive model for studying apoptosis regulation. Apoptosis is most extant during early odontogenesis in mice. The embryonic tooth pattern is comprised not only of anlagen of functional teeth (incisor, molars), but also of vestiges of ancestral tooth primordia that must be suppressed. Apoptosis is involved in (a) the elimination of vestigial tooth primordia in the prospective toothless gap (diastema) between the incisor and molars and (b) the shaping of germs in functional teeth. This type of apoptosis occurs in the dental epithelium according to a characteristic temporo-spatial pattern. Where apoptosis concentrates, specific signaling is also found. We proposed a hypothesis to explain the stimulation of apoptosis in the dental epithelium by integrating two concepts: (1) The regulation of epithelial budding by positional information generated from interactions between growth-activating and growth-inhibiting signals, and (2) apoptosis stimulation by the failure of death-suppressing signals. During the budding of the dental epithelium, local excess in growth inhibitors (e.g., Bmps) might lead to the epithelial cells' failure to receive adequate growth-activating (apoptosis-suppressing) signals (e.g., Fgfs). The resulting signal imbalance leads to cell "suicide" by apoptosis. Understanding of apoptosis regulation in the vestigial tooth primordia can help to elucidate the mechanism of their suppression during evolution and to identify factors essential for tooth survival. The latter knowledge will be important for developing a technology of tooth engineering.

Myosin-mediated cytoskeleton contraction and Rho GTPases regulate laminin-5 matrix assembly

Laminin-5 is a major structural element of epithelial tissue basement membranes. In the matrix of cultured epithelial cells, laminin-5 is arranged into intricate patterns. Here we tested a hypothesis that myosin II-mediated actin contraction is necessary for the proper assembly of a laminin-5 matrix by cultured SCC12 epithelial cells. To do so, the cells were treated with ML-7, a myosin II light chain kinase inhibitor, or Y-27632, an inhibitor of Rho-kinase (ROCK), both of which block actomyosin contraction. Under these conditions, laminin-5 shows an aberrant localization in dense patches at the cell periphery. Since ROCK activity is regulated by the small GTPase Rho, this suggests that members of the Rho family of GTPases may also be important for laminin-5 matrix assembly by SCC12 cells. We confirmed this hypothesis since SCC12 cells expressing mutant proteins that inhibit RhoA, Rac, and Cdc42 assemble the same aberrant laminin-5 protein arrays as drug-treated cells. We have also evaluated the organization of the laminin-5 receptors alpha3beta1 and alpha6beta4 integrin and hemidesmosome proteins in ML-7- and Y-27632-treated cells or in cells in which RhoA, Rac, and Cdc42 activity were inhibited. In all instances, alpha3beta1 and alpha6beta4 integrin heterodimers, as well as hemidesmosome proteins, localize precisely with laminin-5 in the matrix of the cells. In summary, our results provide evidence that myosin II-mediated actin contraction and the activity of Rho GTPases are necessary for the proper organization of a laminin-5 matrix and localization of hemidesmosome protein arrays in epithelial cells.

Thymosin beta 4 stimulates laminin-5 production independent of TGF-beta

Thymosin beta 4 (Tbeta(4)) stimulates epithelial cell migration and promotes laminin-5 (LM-5) expression. Using gene expression analysis with human corneal epithelial cells treated with Tbeta(4), we find that both LM-5 gamma2 chain and transforming growth factor beta 1 (TGFbeta-1) are increased by more than 2-fold over untreated cells. These findings were confirmed by RT-PCR and at the protein level. Although TGFbeta-1 increases LM-5 synthesis in a dose-dependent manner, it does not appear to be the mechanism by which Tbeta(4) acts on LM-5 gamma2 chain synthesis based on three independent experiments. In a time-course analysis, Tbeta(4) increases LM-5 gamma2 chain expression at 2 h and peaks at 6 h, while TGFbeta-1 increases LM-5 gamma2 chain expression only at 4 h and peaks at 8 h. When Tbeta(4)-induced LM-5 gamma2 chain expression is blocked with neutralizing antibodies to TGFbeta-1, LM-5 gamma2 chain expression is increased. Finally, in TGFbeta-1 knock-out mice, Tbeta(4) increases LM-5 gamma2 chain expression to levels higher than that observed in wild-type mice treated with Tbeta(4). These findings demonstrate that Tbeta(4) induces both TGFbeta-1 and LM-5 gamma2 chain expression in corneal epithelial cells. Tbeta(4) and TGFbeta-1 increase LM-5 gamma2 chain expression by independent pathways. Suppression of TGFbeta-1 further increases LM-5 gamma2 chain expression.

Laminin-5 γ2Chain in Cryptogenic Organizing Pneumonia and Idiopathic Pulmonary Fibrosis

Insufficient reepithelialization of injured alveolar walls may be important in the pathogenesis of idiopathic pulmonary fibrosis (IPF). Laminin-5 is expressed in epithelial cells of healing wounds, promoting cell attachment and migration. In this study we have studied the extent of reepithelialization of newly formed intraluminal connective tissue, the immunohistochemical expression and ultrastructural localization of the laminin-5 gamma2 chain protein, and the synthesis of the laminin-5 gamma2 chain mRNA in regenerating epithelial cells in cryptogenic organizing pneumonia (COP) and IPF. The results show that the mean extent of reepithelialization of intraluminal connective tissue lesions was 76% (SD, +/- 27%) in COP, and 54% (SD, +/- 23%) in IPF (p < 0.025). The laminin-5 gamma2 chain was synthesized and widely expressed in regenerating epithelial cells in both diseases. Immunohistochemistry for surfactant-associated protein A suggests a pneumocyte origin for the regenerating epithelial cells in IPF. It is concluded that both in COP and IPF, regenerating epithelial cells are capable of synthesizing the laminin-5 gamma2 chain needed for adhesive connections to the underlying basement membrane. However, in IPF, the reepithelialization seems to be disturbed or delayed.

Targeted inactivation of murine laminin gamma2-chain gene recapitulates human junctional epidermolysis bullosa

Junctional forms of epidermolysis bullosa (JEB) are associated with mutations in six distinct genes expressed in the cutaneous basement membrane zone; these include LAMA3, LAMB3, and LAMC2, which encode laminin 5 subunit polypeptides, the alpha3-, beta3-, and gamma2-chains, respectively. Here we generated a mouse model for JEB by inactivating the laminin gamma2-chain gene by targeted frameshift deletion of exon 8 in Lamc2. Heterozygous mice were phenotypically normal, whereas the majority of Lamc2-/- mice showed blistering phenotype on days 1 to 2 and died within 5 days of birth. The Lamc2-/- mice demonstrated absent expression of laminin gamma2-chain on the basement membrane zone as well as attenuated expression of alpha3- and beta3-chains of laminin. Transmission electron microscopy revealed rudimentary, poorly developed hemidesmosomes. The epidermis of the Lamc2-/- mice revealed induced apoptosis in the basal cells of the blistered skin, suggesting that cell-matrix adhesion provided by laminin 5 plays a role in cell survival in vivo. Cultured Lamc2-/- keratinocytes demonstrated slightly positive staining with gamma2-chain-specific antibodies, which could be explained by the presence of a transcript with partial restoration of the reading frame owing to alternative splicing in vitro. These cells proliferated in different matrices and attached to type IV collagen and Matrigel as efficiently as the wild-type keratinocytes, whereas their attachment on plastic and laminin was significantly weaker. In summary, Lamc2-/- mouse recapitulates human JEB and provides novel insight into the role of laminin 5 in keratinocyte biology.

Hydrogen sulfide induces serum-independent cell cycle entry in nontransformed rat intestinal epithelial cells

Hydrogen sulfide (H2S), produced by commensal sulfate-reducing bacteria, is an environmental insult that potentially contributes to chronic intestinal epithelial disorders. We tested the hypothesis that exposure of nontransformed intestinal epithelial cells (IEC-18) to the reducing agent sodium hydrogen sulfide (NaHS) activates molecular pathways that underlie epithelial hyperplasia, a phenotype common to both ulcerative colitis (UC) and colorectal cancer. Exposure of IEC-18 cells to NaHS rapidly increased the NADPH/NADP ratio, reduced the intracellular redox environment, and inhibited mitochondrial respiratory activity. The addition of 0.2-5 mM NaHS for 4 h increased the IEC-18 proliferative cell fraction (P<0.05), as evidenced by analysis of the cell cycle and proliferating cell nuclear antigen expression, while apoptosis occurred only at the highest concentration of NaHS. Thirty minutes of NaHS exposure increased (P<0.05) c-Jun mRNA concentrations, consistent with the observed activation of mitogen activated protein kinases (MAPK). Microarray analysis confirmed an increase (P<0.05) in MAPK-mediated proliferative activity, likely reflecting the reduced redox environment of NaHS-treated cells. These data identify functional pathways by which H2S may initiate epithelial dysregulation and thereby contribute to UC or colorectal cancer. Thus, it becomes crucial to understand how genetic background may affect epithelial responsiveness to this bacterial-derived environmental insult.

Decreased plasminogen activator inhibitor-1 secretion in hypoxic corneal epithelial cells is associated with increased urokinase plasminogen activator activity

The aim of this study was to determine the effects of hypoxia on mRNA levels, cell-associated and -secreted protein concentration, activity, and protein complex formation of urokinase-type plasminogen activator, its receptor, and plasminogen activator inhibitor type-1 in corneal epithelium. Non-transformed human corneal epithelial cells were cultured in 20% oxygen (normoxic conditions) or 2% oxygen (hypoxic conditions) for 1, 3, 5, or 7 days. Relative changes in mRNA levels of plasminogen activator, receptor, and plasminogen activator inhibitor-1 were determined using a cDNA expression array, chemiluminescence, and densitometry. Protein concentrations were determined using enzyme linked immunosorbent assays. Activity assays were also used. Protein complex formation was assayed using cell surface biotinylation, immunoprecipitation, and Western blot analysis. Hypoxic corneal epithelial cells demonstrated no significant differences in plasminogen activator or receptor mRNA. Cell-associated plasminogen activator and membrane-associated receptor protein levels were unchanged. In contrast decreases in mRNA and secreted plasminogen activator inhibitor-1 protein were observed in hypoxic cells. Concurrently, increased cell-associated plasminogen activator activity was observed in hypoxic cells. The formation of plasminogen activator/receptor/plasminogen activator inhibitor-1 complex at the cell surface was not inhibited by hypoxia. However, in hypoxic cells less plasminogen activator inhibitor-1 was associated with receptor. It is concluded that in corneal epithelium cultured in 2% oxygen plasminogen activator inhibitor-1 may be an important regulatory factor of the plasminogen activator system resulting in increased urokinase plasminogen activator activity.