Drug-induced impairment of mitochondrial fatty acid oxidation and steatosis: assessment of causal relationship with 45 pharmaceuticals

Drug-induced liver injury (DILI) represents a major issue for pharmaceutical companies, being a potential cause of black-box warnings on marketed pharmaceuticals, or drug withdrawal from the market. Lipid accumulation in the liver also referred to as steatosis, may be secondary to impaired mitochondrial fatty acid oxidation (mtFAO). However, an overall causal relationship between drug-induced mtFAO inhibition and the occurrence of steatosis in patients has not yet been established with a high number of pharmaceuticals. Hence, 32 steatogenic and 13 non-steatogenic drugs were tested for their ability to inhibit mtFAO in isolated mouse liver mitochondria. To this end, mitochondrial respiration was measured with palmitoyl-L-carnitine, palmitoyl-CoA + L-carnitine, or octanoyl-L-carnitine. This mtFAO tri-parametric assay was able to predict the occurrence of steatosis in patients with a sensitivity and positive predictive value above 88%. To get further information regarding the mechanism of drug-induced mtFAO impairment, mitochondrial respiration was also measured with malate/glutamate or succinate. Drugs such as diclofenac, methotrexate and troglitazone could inhibit mtFAO secondary to an impairment of the mitochondrial respiratory chain, while dexamethasone, olanzapine and zidovudine appeared to impair mtFAO directly. Mitochondrial swelling, transmembrane potential and production of reactive oxygen species were also assessed for all compounds. Only the steatogenic drugs amiodarone, ketoconazole, lovastatin and toremifene altered all these 3 mitochondrial parameters. In conclusion, our tri-parametric mtFAO assay could be useful in predicting the occurrence of steatosis in patients. The combination of this assay with other mitochondrial parameters could also help to better understand the mechanism of drug-induced mtFAO inhibition.

Adipose tissue senescence is mediated by increased ATP content after a short-term high-fat diet exposure

In the context of obesity, senescent cells accumulate in white adipose tissue (WAT). The cellular underpinnings of WAT senescence leading to insulin resistance are not fully elucidated. The objective of the current study was to evaluate the presence of WAT senescence early after initiation of high‐fat diet (HFD, 1–10 weeks) in 5‐month‐old male C57BL/6J mice and the potential role of energy metabolism. We first showed that WAT senescence occurred 2 weeks after HFD as evidenced in whole WAT by increased senescence‐associated ß‐galactosidase activity and cyclin‐dependent kinase inhibitor 1A and 2A expression. WAT senescence affected various WAT cell populations, including preadipocytes, adipose tissue progenitors, and immune cells, together with adipocytes. WAT senescence was associated with higher glycolytic and mitochondrial activity leading to enhanced ATP content in HFD‐derived preadipocytes, as compared with chow diet‐derived preadipocytes. One‐month daily exercise, introduced 5 weeks after HFD, was an effective senostatic strategy, since it reversed WAT cellular senescence, while reducing glycolysis and production of ATP. Interestingly, the beneficial effect of exercise was independent of body weight and fat mass loss. We demonstrated that WAT cellular senescence is one of the earliest events occurring after HFD initiation and is intimately linked to the metabolic state of the cells. Our data uncover a critical role for HFD‐induced elevated ATP as a local danger signal inducing WAT senescence. Exercise exerts beneficial effects on adipose tissue bioenergetics in obesity, reversing cellular senescence, and metabolic abnormalities.

Drug-induced hepatic steatosis in absence of severe mitochondrial dysfunction in HepaRG cells: proof of multiple mechanism-based toxicity

Steatosis is a liver lesion reported with numerous pharmaceuticals. Prior studies showed that severe impairment of mitochondrial fatty acid oxidation (mtFAO) constantly leads to lipid accretion in liver. However, much less is known about the mechanism(s) of drug-induced steatosis in the absence of severe mitochondrial dysfunction, although previous studies suggested the involvement of mild-to-moderate inhibition of mtFAO, increased de novo lipogenesis (DNL), and impairment of very low-density lipoprotein (VLDL) secretion. The objective of our study, mainly carried out in human hepatoma HepaRG cells, was to investigate these 3 mechanisms with 12 drugs able to induce steatosis in human: amiodarone (AMIO, used as positive control), allopurinol (ALLO), D-penicillamine (DPEN), 5-fluorouracil (5FU), indinavir (INDI), indomethacin (INDO), methimazole (METHI), methotrexate (METHO), nifedipine (NIF), rifampicin (RIF), sulindac (SUL), and troglitazone (TRO). Hepatic cells were exposed to drugs for 4 days with concentrations decreasing ATP level by less than 30% as compared to control and not exceeding 100 × Cmax. Among the 12 drugs, AMIO, ALLO, 5FU, INDI, INDO, METHO, RIF, SUL, and TRO induced steatosis in HepaRG cells. AMIO, INDO, and RIF decreased mtFAO. AMIO, INDO, and SUL enhanced DNL. ALLO, 5FU, INDI, INDO, SUL, RIF, and TRO impaired VLDL secretion. These seven drugs reduced the mRNA level of genes playing a major role in VLDL assembly and also induced endoplasmic reticulum (ER) stress. Thus, in the absence of severe mitochondrial dysfunction, drug-induced steatosis can be triggered by different mechanisms, although impairment of VLDL secretion seems more frequently involved, possibly as a consequence of ER stress.

Abstract 788: Identification and optimization of pro-apoptotic molecules targeting adenine nucleotide translocator 2 (hANT2) in tumor mitochondria

The mitochondrial protein ANT2 is one of the four isoforms of the ADP/ATP translocase and is expressed in highly proliferating cells. ANT2 plays a crucial role in the maintenance of transmembrane potential and mitochondrial integrity in tumor cells by importing glycolytic ATP into the mitochondrial matrix. Thus, this protein is required for tumor cell survival and displays anti-apoptotic function. Recently, ANT2 upregulation was shown to be involved in drug resistance process in various cancer types. Considering ANT2 role in tumor cell metabolism, we searched for ANT2-ligand small molecules. Ligands were first identified by virtual screening of chemical library on 3D model of human ANT2 and validated as ADP/ATP translocase inhibitors using our screening platform on isolated mitochondria. Compound specificity for ANT2 isoform was validated by cellular knock-down and pull-down experiments. ANT2-ligands optimization lead to the selection of MTL105 compound that induce characteristic intrinsic apoptotic cell death, specifically in tumor cell lines at sub-µM concentrations with no effect on healthy cells, suggesting a strong safety margin. According to the NCI60 compare analysis, this compound constitutes a first-in-class product in cancer therapy with this MoA and would be particularly interesting to overcome multidrug-resistant cancers.

Citation Format: Nelly Buron, Claire Pertuiset, Roxane Loyant, Cécile Martel, Mathieu Porceddu, Annie Borgne-Sanchez. Identification and optimization of pro-apoptotic molecules targeting adenine nucleotide translocator 2 (hANT2) in tumor mitochondria [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 788.

The Mitochondrion-lysosome Axis in Adaptive and Innate Immunity: Effect of Lupus Regulator Peptide P140 on Mitochondria Autophagy and NETosis

Mitochondria deserve special attention as sensors of cellular energy homeostasis and metabolic state. Moreover, mitochondria integrate intra- and extra-cellular signals to determine appropriate cellular responses that range from proliferation to cell death. In autoimmunity, as in other inflammatory chronic disorders, the metabolism of immune cells may be extensively remodeled, perturbing sensitive tolerogenic mechanisms. Here, we examine the distribution and effects of the therapeutic 21-mer peptide called P140, which shows remarkable efficacy in modulating immune responses in inflammatory settings. We measured P140 and control peptide effects on isolated mitochondria, the distribution of peptides in live cells, and their influence on the levels of key autophagy regulators. Our data indicate that while P140 targets macro- and chaperone-mediated autophagy processes, it has little effect, if any, on mitochondrial autophagy. Remarkably, however, it suppresses NET release from neutrophils exposed to immobilized NET-anti-DNA IgG complexes. Together, our results suggest that in the mitochondrion-lysosome axis, a likely driver of NETosis and inflammation, the P140 peptide does not operate by affecting mitochondria directly.

Chronic and low exposure to a pharmaceutical cocktail induces mitochondrial dysfunction in liver and hyperglycemia: Differential responses between lean and obese mice

Pharmaceuticals are found in the environment but the impact of this contamination on human and animal health is poorly known. The liver could be particularly targeted since a significant number of these drugs are hepatotoxic, in particular via oxidative stress and mitochondrial dysfunction. Notably, the latter events can also be observed in liver diseases linked to obesity, so that the obese liver might be more sensitive to drug toxicity. In this study, we determined the effects of a chronic exposure to low doses of pharmaceuticals in wild-type and obese mice, with a particular focus on mitochondrial function. To this end, wild-type and ob/ob mice were exposed for 4 months to a cocktail of 11 pharmaceuticals provided in drinking water containing 0.01, 0.1, or 1 mg/L of each drug. At the end of the treatment, liver mitochondria were isolated and different parameters were measured. Chronic exposure to the pharmaceuticals reduced mitochondrial respiration driven by succinate and palmitoyl-l-carnitine in wild-type mice and increased antimycin-induced ROS production in ob/ob mice. Hyperglycemia and hepatic histological abnormalities were also observed in treated ob/ob mice. Investigations were also carried out in isolated liver mitochondria incubated with the mixture, or with each individual drug. The mitochondrial effects of the mixture were different from those observed in treated mice and could not be predicted from the results obtained with each drug. Because some of the 11 drugs included in our cocktail can be found in water at relatively high concentrations, our data could be relevant in environmental toxicology. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1375-1389, 2017.

Prediction of liver injury induced by chemicals in human with a multiparametric assay on isolated mouse liver mitochondria

Drug-induced liver injury (DILI) in humans is difficult to predict using classical in vitro cytotoxicity screening and regulatory animal studies. This explains why numerous compounds are stopped during clinical trials or withdrawn from the market due to hepatotoxicity. Thus, it is important to improve early prediction of DILI in human. In this study, we hypothesized that this goal could be achieved by investigating drug-induced mitochondrial dysfunction as this toxic effect is a major mechanism of DILI. To this end, we developed a high-throughput screening platform using isolated mouse liver mitochondria. Our broad spectrum multiparametric assay was designed to detect the global mitochondrial membrane permeabilization (swelling), inner membrane permeabilization (transmembrane potential), outer membrane permeabilization (cytochrome c release), and alteration of mitochondrial respiration driven by succinate or malate/glutamate. A pool of 124 chemicals (mainly drugs) was selected, including 87 with documented DILI and 37 without reported clinical hepatotoxicity. Our screening assay revealed an excellent sensitivity for clinical outcome of DILI (94 or 92% depending on cutoff) and a high positive predictive value (89 or 82%). A highly significant relationship between drug-induced mitochondrial toxicity and DILI occurrence in patients was calculated (p < 0.001). Moreover, this multiparametric assay allowed identifying several compounds for which mitochondrial toxicity had never been described before and even helped to clarify mechanisms with some drugs already known to be mitochondriotoxic. Investigation of drug-induced loss of mitochondrial integrity and function with this multiparametric assay should be considered for integration into basic screening processes at early stage to select drug candidates with lower risk of DILI in human. This assay is also a valuable tool for assessing the mitochondrial toxicity profile and investigating the mechanism of action of new compounds and marketed compounds.

Aftins increase amyloid-β42, lower amyloid-β38, and do not alter amyloid-β40 extracellular production in vitro: toward a chemical model of Alzheimer's disease?

Increased production of amyloid-β (Aβ)42 peptide, derived from the amyloid-β protein precursor, and its subsequent aggregation into oligomers and plaques constitutes a hallmark of Alzheimer's disease (AD). We here report on a family of low molecular weight molecules, the Aftins (Amyloid-β Forty-Two Inducers), which, in cultured cells, dramatically affect the production of extracellular/secreted amyloid peptides. Aftins trigger β-secretase inhibitor and γ-secretase inhibitors (GSIs) sensitive, robust upregulation of Aβ42, and parallel down-regulation of Aβ38, while Aβ40 levels remain stable. In contrast, intracellular levels of these amyloids appear to remain stable. In terms of their effects on Aβ38/Aβ40/Aβ42 relative abundance, Aftins act opposite to γ-secretase modulators (GSMs). Aβ42 upregulation induced by Aftin-5 is unlikely to originate from reduced proteolytic degradation or diminished autophagy. Aftin-5 has little effects on mitochondrial functional parameters (swelling, transmembrane potential loss, cytochrome c release, oxygen consumption) but reversibly alters the ultrastructure of mitochondria. Aftins thus alter the Aβ levels in a fashion similar to that described in the brain of AD patients. Aftins therefore constitute new pharmacological tools to investigate this essential aspect of AD, in cell cultures, allowing (1) the detection of inhibitors of Aftin induced action (potential 'anti-AD compounds', including GSIs and GSMs) but also (2) the identification, in the human chemical exposome, of compounds that, like Aftins, might trigger sustained Aβ42 production and Aβ38 down-regulation (potential 'pro-AD compounds').

Abstract 4078: ANT-ligands small molecules induce apoptosis of cancer cells by inhibiting ATP/ADP translocation

Since fifteen years ago, the mitochondrion has been progressively recognized as an integrator-coordinator of apoptosis. In this context recent anti-cancer drugs in development are targeting mitochondrial apoptotic machinery to induce tumor cell death. By this strategy, drugs can interact with apoptosis-regulating proteins of Bcl-2 family to trigger Bax/Bak oligomerization and mitochondrial membrane permeabilization. This event conducts to the release of pro-apoptotic factors such as cytochrome c into the cytosol that are required for caspases activation and apoptosis process. In this study, we selected another strategy and investigated the effect of ANT-targeting small molecules to induce cancer cells apoptosis. The adenine nucleotide translocator (ANT) is a mitochondrial protein of the inner membrane involved in the exchange of ADP and ATP between the mitochondrial matrix and the cytosol. Medicinal chemistry approach coupled with in silico studies yield to several small organic compounds, which proved to be specific for ANT and fulfill druggability criteria (good cell penetration and biodisponibility). We identified a family of compounds that inhibited ATP translocation and induced apoptosis by a pathway involving Bax-dependent cytochrome c release and caspases activation. One of the hit compound was optimized to obtain molecules able to induce apoptosis of HT-29 and BxPC3 cells at 100 nM. We are currently investigating which ANT isoform(s) is (are) targeted in cells. In vivo tumor regression experiments will be performed to achieve the proof of concept of ANT-ligands small molecules as an interesting anti-cancer strategy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4078. doi:10.1158/1538-7445.AM2011-4078

Abstract 1021: Use of functional tumor cell line mitochondria to explore the mechanisms of BH3 peptides and ABT-737-induced mitochondrial membrane permeabilization

Current limitations of chemotherapy include toxicity on healthy tissues and multidrug resistance on malignant cells. A number of recent anti-cancer strategies are targeting the mitochondrial apoptotic machinery to induce tumor cell death. In this study, we set up protocols to isolate mitochondria from various origins with high purity, quality and functionality. We analyzed the effect of putative Bcl-2 inhibitors on both healthy and tumor isolated mitochondria. We measured mitochondrial membrane permeabilization (swelling), mitochondrial transmembrane potential (ΔΨm) and mitochondrial outer membrane permeabilization (MOMP) in both isolated healthy and tumoral cell mitochondria. Like t-Bid and some BH3 peptides, the molecule ABT-737 was found to present a tumor-specific mitochondrio-toxicity, while compounds like HA-14.1, YC-137, Chelerythrine, Gossypol, TW-37 or EM20-25 did not. We thus demonstrated that ABT-737 can induce a relatively large and targeted MOMP triggering the release of apoptotic proteins from tumoral cell mitochondria (Cytochrome c, Smac/Diablo and Omi/HtrA2 but not AIF) however without any mitochondrial swelling. Furthermore, ABT-737 addition to isolated tumoral cell mitochondria induced specific Bax/Bak channel formation by oligomerizing monomeric Bax and/or Bak already inserted in the mitochondrial membrane. We also provided evidence that tumoral cell mitochondria can be either resistant or sensitive to ABT-737-induced MOMP, depending on their origin and interactions between pro- and anti-apoptotic proteins. Finally, this method based on MOMP is an interesting screening tool, tailored for identifying Bcl-2 antagonists with selective toxicity profile against tumoral cell mitochondria but devoid of toxicity against healthy mitochondria.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1021.

Trefoil factor TFF1-induced protection of conjunctival cells from apoptosis at premitochondrial and postmitochondrial levels

PURPOSE

Goblet cells of the conjunctival epithelium synthesize and secrete TFF1 (Trefoil factor 1), a small protease-resistant peptide that, together with mucins, is responsible for the rheologic properties of the tear film. This study aimed to determine whether TFF1, whose synthesis increases in inflammatory conditions such as pterygium, could protect conjunctival cells from apoptosis.

METHODS

Chang conjunctival cells, either wild-type or expressing TFF1 through stable transfection, were exposed to benzalkonium chloride (BAK) and ultraviolet (UV) irradiation to trigger apoptosis. The authors used cell fractionation to detect lipid raft-associated proteins, coimmunoprecipitation to explore the formation of a death-inducing signaling complex (DISC), and a combination of immunofluorescence, immunoblotting, flow cytometry, siRNA-mediated decrease in gene expression, and electrophoretic mobility shift assay to explore the mechanisms of TFF1-protective effects.

RESULTS

TFF1 protects Chang conjunctival cells from apoptosis induced by UV irradiation and BAK at two levels. First, TFF1 prevents caspase-8 activation at the level of the DISC that involves Fas receptor in plasma membrane rafts, which in turn decreases the mitochondrial release of cytochrome c. Second, TFF1 interferes with caspase-9 and caspase-3 activation through an NF-kappaB-induced increase in the expression of XIAP (X-linked inhibitor of apoptosis protein).

CONCLUSIONS

TFF1 upregulation on inflammatory conditions may be a protective mechanism that limits conjunctival cell loss by inhibiting apoptosis upstream and downstream of the mitochondrial events. These observations suggest a potential interest of TFF1 or related peptides to prevent cell death in ocular surface disorders.

Differential Mechanisms of Conjunctival Cell Death Induction by Ultraviolet Irradiation and Benzalkonium Chloride

PURPOSE

To determine the molecular mechanisms of conjunctival cell death on exposure to the quaternary ammonium preservative benzalkonium chloride (BAC) and ultraviolet (UV) irradiation.

METHODS

Chang conjunctival cells, either wild-type or stably transfected with various constructs encoding antiapoptotic molecules or transiently transfected with siRNA targeting the beclin-1 gene, were exposed to BAC or UV radiation Cell death was analyzed morphologically with fluorescence and electron microscopy, and molecular mechanisms of death were studied by using immunofluorescence, cell fractionation, caspase substrates, and immunoblot analysis, with or without immunoprecipitation. The main results were controlled in IOBA-NHC cells.

RESULTS

Both agents induced cytochrome c release from the mitochondria, caspase activation, and nuclear chromatin condensation, suggesting caspase-dependent apoptosis. These events are prevented by stable expression of Bcl-2 protein. Both agents also induced a redistribution of Fas in plasma membrane rafts and the Fas-ligand-independent formation of a death-inducing complex leading to caspase-8 activation. Stable expression of either a dominant negative construct of Fas-associated death domain (FADD) or the long or short isoform of FADD-like interleukin-1-beta-converting enzyme inhibitory protein (FLIP) inhibited caspase-8 activation in response to both UV radiation and BAC. However, these proteins, as well as permeant peptides and baculovirus p35 caspase-inhibitors, delayed more efficiently the UV irradiation-induced than the BAC-induced nuclear chromatin condensation. BAC specifically activated a caspase-independent pathway by inducing the mitochondrial release of apoptosis-inducing factor. BAC-treated cells contain autophagosomes/autolysosomes, a characteristic feature of autophagy, and siRNA-mediated downregulation of the beclin-1 gene, whose product is crucial for autophagy, increases BAC toxicity.

CONCLUSIONS

UV irradiation induces typical, caspase-dependent cell death, whereas death induced by BAC associates features of caspase-dependent and -independent apoptosis counteracted by an autophagic process.

Trefoil factor family 1, MUC5AC and human leucocyte antigen-DR expression by conjunctival cells in patients with glaucoma treated with chronic drugs: could these markers predict the success of glaucoma surgery?

AIMS

To evaluate conjunctival expression of trefoil factor family (TFF)1, MUC5AC and human leucocyte antigen (HLA)-DR in patients with glaucoma treated with topical drugs, and to determine whether these parameters can predict the outcome of glaucoma surgery.

METHODS

77 conjunctival impression cytology specimens were collected from 77 patients with glaucoma (66 receiving drops with preservative and 11 treated with preservative-free drops) and 43 controls. TFF1, MUC5AC and HLA-DR expression was analysed using flow cytometry. Trabeculectomy was performed in 56 patients; success was defined as an intraocular pressure (IOP) < or =15 mm Hg without any IOP-lowering drug at 6 months.

RESULTS

The expression of TFF1, MUC5AC and HLA-DR was significantly higher in patients than in controls (p = 0.01, 0.05 and 0.004, respectively). A higher expression of MUC5AC was found in patients treated with preserved drops than in those receiving unpreserved drops (p = 0.04). A higher MUC5AC expression and a lower HLA-DR expression was observed in successful glaucoma surgeries than in failures.

CONCLUSIONS

TFF1 and MUC5AC secretions are probably a response to mild ocular surface changes caused by long-term use of topical treatment. Their increased expression could be a predicting factor of further successful glaucoma surgery.

Trefoil factor family mRNA and protein expression in pterygium

Trefoil factor family (TFF) of proteins are involved in mucosal protection and healing and are induced in inflammatory diseases and neoplastic progression. The purpose of this investigation was to determine if expression of the trefoil factor family (TFF) proteins is altered in human pterygium compared to in normal conjunctiva. Fourteen pterygia (P) and 21 biopsies from normal human conjunctiva (NC) were studied. TFF1, TFF2 and TFF3 mRNA levels were measured by semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR), and TFF1 mRNA levels in addition by real-time PCR. The cellular expression of TFF1 (pS2), TFF3 (intestinal trefoil factor) and M1/MUC5AC mucin in ten pterygia and ten normal human conjunctiva specimens was analyzed by immunohistochemistry using specific monoclonal antibodies. TFF1 mRNA levels were higher in P than in NC (p=0.02). Accordingly, intensity of TFF1 and mucin MUC5AC immunostaining was higher in P than in NC. Mucus-secreting goblet cells (GC) were more densely packed in P than in NC. In both cases, TFF1 protein was detected in GC only, but was not systematically expressed in all GC. In addition, TFF3 mRNA levels were similar (p=0.89) in NC and P, while TFF2 (spasmolytic polypeptide) mRNA were not detected. Both TFF3 and MUC5AC proteins were clearly detected in all GC identified in NC and P. Increased expression of TFF1 mRNA and protein is observed in pterygium GC, suggesting that this trefoil protein might exert protective and beneficial roles during the pathogenesis of this benign and inflammatory conjunctival tumor.

Analyzing markers of apoptosis in vitro

Cell death by apoptosis was first identified based on morphological changes reproduced with great fidelity in cells of widely different origin when exposed to a death stimulus. These changes include condensation of the cytosol and the nuclear chromatin, blebbing of the plasma membrane, and cell fragmentation into corpses that are engulfed by neighboring cells. Apoptotic cells demonstrate various levels of DNA fragmentation and exposed phosphatidylserine on the outer leaflet of their plasma membrane. Most apoptotic pathways converge on the mitochondria, inducing the disruption of the mitochondrial trans-membrane potential and the release of soluble molecules from mitochondrial inter-membrane space. One of these molecules is cytochrome c, which, in the cytosol, activates proteases of the caspase family. This chapter suggests methods to identify these characteristic morphological and biochemical events, and cell-free systems that can be used to identify the molecular pathways leading to the death phenotype.

[Trefoil factor family gene and peptide expression in pterygium]

PURPOSE

Trefoil factor family (TFF) peptides (formerly P-domain peptides; trefoil factor) are small (7-12 kDa) protease-resistant secreted peptides designated pS2 (or TFF1), SP (TFF2) and ITF (TFF3). Human conjunctival goblet cells (GCs) are known to synthesize TFF, but TFF expression by these cells has not been studied in pathological conditions. We quantified trefoil factor family (TFF) gene transcripts in pterygium, and we immunolocalized TFF protein.

METHODS

Eleven pterygium specimens were studied, together with 19 biopsy specimens of normal human conjunctiva as controls. TFF1 (pS2), TFF2 (spasmolytic peptide) and TFF3 (intestinal trefoil factor) mRNA expression was semiquantified by means of reverse-transcription polymerase chain reaction amplification (RT-PCR). TFF1, TFF2 and TFF3 mRNA levels were determined individually, relative to beta2 microglobulin housekeeping gene mRNA (internal standard), by coamplification of the target fragments and beta2 microglobulin in the same tube. Five pterygia and five normal human conjunctival biopsy specimens were also analyzed for TFF1 and mucin (MUC5AC) protein expression by immunostaining with monoclonal antibodies. Anti-PS2 (Zymed Laboratories, San Francisco), a mouse monoclonal antibody (MAb) against the 30 C-terminal amino acids of human TFF1, and P2802 (provided by Doctor Marie-Christine Rio, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM, Strasbourg, France), a mouse MAb directed against a synthetic peptide corresponding to the last 28 amino acids of TFF1, were used at 1/20 dilution. A mouse monoclonal antibody directed against the peptidic core of gastric M1 mucin was used as previously described. M1 immunoreactivity is encoded by the MUC5AC gene.

RESULTS

TFF1 and TFF3 mRNA was expressed in all normal conjunctival and pterygium specimens. TFF2 mRNA was not expressed by either sample type, but was expressed by the positive control (human stomach cDNA). TFF1 mRNA expression was stronger in pterygium than in controls (p=0.02). TFF3 mRNA expression was similar in the two sample types (p=0.89). TFF are coexpressed and act in concert with mucins to protect mucous epithelia and trigger wound-healing responses. Inflammation and ulceration of the gastrointestinal tract are associated with increased TFF expression. Conjunctival GCs secrete TFF in both pigs and humans. We found that TFF1 mRNA was overexpressed in pterygium relative to healthy conjunctiva, whereas the TFF1 immunostaining patterns were similar. TFF1 protein expression was confined to goblet cells. However, whereas all GCs were positive for MUC5AC, not all GC were labeled by anti-TFF1 mAbs in either normal conjunctiva or pterygium. The observed TFF1 mRNA overexpression in pterygium was not associated with abnormal TFF1 peptide localization. Increased MUC5AC protein expression would be expected in pterygium, because of increased GC density. Indeed, in conjunctival diseases such as dry-eye syndrome in which GC density is decreased, mucin secretion is also decreased. This could explain the increased expression of TFF1 mRNA in pterygium, although not all GCs expressed TFF1 protein. TFF proteins are copackaged within mucous cell granules; TFF1 preferentially colocalizes with MUC5AC, and TFF3 with MUC2. However, we found some cell granules containing MUC5AC but not TFF1. The proportion of TFF1-negative GCs was similar in pterygium and normal conjunctiva. The normal TFF3 mRNA expression in pterygium was unexpected and suggests that only GCs involved in TFF1 secretion are overrepresented in this pathological tissue. TFF2 mRNA was undetectable in both normal conjunctiva and pterygium, possibly because of its copackaging in mucous cell granules and its preferential cosecretion with MUC6, which is not expressed in the conjunctiva.

CONCLUSION

As in normal conjunctiva, the TFF1 and TFF3 genes are expressed by conjunctival goblet cells in pterygium, contrary to the TFF2 gene. Only TFF1 gene expression was elevated in pterygium compared to normal conjunctiva.