Alveolar type II cells from ethanol-fed rats produce a fibronectin-enriched extracellular matrix that promotes monocyte activation

Donor factors and risk of primary graft dysfunction and mortality post lung transplantation: A proposed conceptual framework

Lung transplantation remains a therapeutic option in end-stage lung disease. However, despite advances in the field, early allograft function can be compromised by the development of primary graft dysfunction (PGD); this being the leading cause of morbidity and mortality immediately following the lung transplant procedure. Several recipient factors have been associated with increased risk of PGD, but less is known about donor factors. Aging, tobacco, and chronic alcohol use are donor factors implicated, but how these factors promote PGD remains unclear. Herein, we discuss the available clinical data that link these donor factors with outcomes after lung transplantation, and how they might render the recipient susceptible to PGD through a two-hit process.

Nicotine stimulates collagen type I expression in lung via α7 nicotinic acetylcholine receptors

Background

Tobacco-related chronic lung diseases are characterized by alterations in lung architecture leading to decreased lung function. Knowledge of the exact mechanisms involved in tobacco-induced tissue remodeling and inflammation remains incomplete. We hypothesize that nicotine stimulates the expression of extracellular matrix proteins, leading to relative changes in lung matrix composition, which may affect immune cells entering the lung after injury.

Methods

Pulmonary fibroblasts from wildtype and α7 nicotinic acetylcholine receptor knockout (α7KO) mice were exposed to nicotine and examined for collagen type 1 mRNA and protein expression. Testing the potential role on immune cell function, pulmonary fibroblasts were retained in culture for 120 h. The fibroblasts were eliminated by osmotic lysis and the remaining matrix-coated dishes were washed thoroughly. U937 cells were incubated on the matrix-coated dishes for 24 h followed by evaluation of IL-1β gene expression. Wildtype or α7KO C57BL/6 mice (female, 8–12 weeks) were fed normal diet and exposed to nicotine in their drinking water (100 μg/ml) for 8-12weeks. Lungs were processed for mRNA, protein, and histology. Statistical significance was determined at p ≤ .05 by two-tailed test or 2-way ANOVA with Bonferroni posttest.

Results

We found that nicotine stimulated collagen type I mRNA and protein expression in a dose-dependent manner and up to 72 h in primary lung fibroblasts. The stimulatory effect of nicotine was inhibited in α7KO primary lung fibroblasts. Testing the potential role of these events on immune cell function, U937 monocytic cells were cultured atop matrices derived from nicotine-treated lung fibroblasts. These cells expressed more IL-1β than those cultured atop matrices derived from untreated fibroblasts, and antibodies against the α2β1 collagen integrin receptor inhibited the effect. Nicotine also stimulated fibroblast proliferation via MEK-1/ERK, unveiling a potentially amplifying pathway. In vivo, nicotine increased collagen type I expression was detected in wildtype, but not in α7KO mice. Wildtype mice showed increased collagen staining in lung, primarily around the airways.

Conclusions

These observations suggest that nicotine stimulates fibroblast proliferation and their expression of collagen type I through α7 nAChRs, thereby altering the relative composition of the lung matrix without impacting the overall lung architecture; this may influence inflammatory responses after injury.

Potential Role of the Gut/Liver/Lung Axis in Alcohol-Induced Tissue Pathology

Both Alcoholic Liver Disease (ALD) and alcohol-related susceptibility to acute lung injury are estimated to account for the highest morbidity and mortality related to chronic alcohol abuse and, thus, represent a focus of intense investigation. In general, alcohol-induced derangements to both organs are considered to be independent and are often evaluated separately. However, the liver and lung share many general responses to damage, and specific responses to alcohol exposure. For example, both organs possess resident macrophages that play key roles in mediating the immune/inflammatory response. Additionally, alcohol-induced damage to both organs appears to involve oxidative stress that favors tissue injury. Another mechanism that appears to be shared between the organs is that inflammatory injury to both organs is enhanced by alcohol exposure. Lastly, altered extracellular matrix (ECM) deposition appears to be a key step in disease progression in both organs. Indeed, recent studies suggest that early subtle changes in the ECM may predispose the target organ to an inflammatory insult. The purpose of this chapter is to review the parallel mechanisms of liver and lung injury in response to alcohol consumption. This chapter will also explore the potential that these mechanisms are interdependent, as part of a gut-liver-lung axis.

Chronic alcohol ingestion and predisposition to lung "cirrhosis"

BACKGROUND

Although liver is the organ most often associated with the damaging effects of chronic alcohol abuse, other organs may also be affected. In the past decade, data emerged linking chronic alcohol intake to lung dysfunction. However, the mechanisms by which alcohol affects the lung remain incompletely elucidated.

METHODS

In this issue, Sueblinvong and colleagues explore the effect of chronic alcohol intake in the well-known rodent model of bleomycin-induced lung injury. This represents a review of their article and a commentary on its findings in relation to current knowledge in the field.

RESULTS

The investigators found that chronic alcohol intake increased lung fibrosis in the bleomycin-model of lung injury. This effect was related to increased production of transforming growth factor β (TGFβ) and expression of α-smooth muscle actin. Diet supplementation with S-adenosylmethionine greatly reduced the effect. These data strengthen published reports linking chronic alcohol intake with TGFβ overproduction and lung disrepair after injury, while implicating oxidant stress as a critical mediator of these effects.

CONCLUSIONS

A review of Sueblinvong and colleagues' article and the literature strongly suggests that the lung is a target for alcohol, and that chronic alcohol intake may predispose the lung to disrepair after injury. The overexpression of pro-fibrotic growth factors and pro-inflammatory cytokines, and the generation of oxidant stress may lead to lung cellular dysfunction, aberrant tissue remodeling, and loss of lung function. These events may represent targets for intervention, but translational studies evaluating their role in humans are desperately needed.

Chronic alcohol ingestion primes the lung for bleomycin-induced fibrosis in mice

BACKGROUND

Alcohol abuse increases the risk for acute lung injury (ALI). In both experimental models and in clinical studies, chronic alcohol ingestion causes airway oxidative stress and glutathione depletion and increases the expression of transforming growth factor beta-1 (TGFβ1), a potent inducer of fibrosis, in the lung. Therefore, we hypothesized that alcohol ingestion could promote aberrant fibrosis following experimental ALI and that treatment with the glutathione precursor s-adenosylmethionine (SAMe) could mitigate these effects.

METHODS

Three-month-old C57BL/6 mice were fed standard chow ± alcohol (20% v/v) in their drinking water for 8 weeks and ±SAMe (4% w/v) during the last 4 weeks. ALI was induced by intratracheal instillation of bleomycin (2.5 units/kg), and lungs were assessed histologically at 7 and 14 days for fibrosis and at 14 days for the expression of extracellular matrix proteins and TGFβ1.

RESULTS

Alcohol ingestion had no apparent effect on lung inflammation at 7 days, but at 14 days after bleomycin treatment, it increased lung tissue collagen deposition, hydroxyproline content, and the release of activated TGFβ1 into the airway. In contrast, SAMe supplementation completely mitigated alcohol-induced priming of these aberrant fibrotic changes through decreased TGFβ1 expression in the lung. In parallel, SAMe decreased alcohol-induced TGFβ1 and Smad3 mRNA expressions by lung fibroblasts in vitro.

CONCLUSIONS

These new experimental findings demonstrate that chronic alcohol ingestion renders the experimental mouse lung susceptible to fibrosis following bleomycin-induced ALI, and that these effects are likely driven by alcohol-mediated oxidative stress and its induction and activation of TGFβ1.

Alcohol and the Alveolar Epithelium

The distal airways are covered with a heterogeneous layer of cells known as the alveolar epithelium. Alveolar epithelial cells provide the major barrier between the airspace and fluid filled tissue compartments. As such, regulation of the alveolar epithelium is critical to maintain a healthy lung and for optimal gas exchange. In this chapter, we discuss functional roles for alveolar epithelial cells with particular emphasis on intercellular junctions and communication. As a thin layer of cells directly exposed to atmospheric oxygen, alveoli are particularly sensitive to oxidant insults. Alcohol significantly diminishes the normal antioxidant reserves of the alveolar epithelium, thereby rendering it sensitized for an exaggerated damage response to acute and chronic injuries. The effects of alcohol on alveolar epithelia are discussed along with open questions and potential therapeutic targets to prevent the pathophysiology of alcoholic lung disease.

Nicotinic acetylcholine receptors are sensors for ethanol in lung fibroblasts

BACKGROUND

Chronic ethanol (EtOH) abuse in humans is known to independently increase the incidence of and mortality due to acute lung injury in at-risk individuals. However, the mechanisms by which EtOH affects lung cells remain incompletely elucidated. In earlier work, we reported that EtOH increased the expression in lung fibroblasts of fibronectin, a matrix glycoprotein implicated in lung injury and repair. This effect was blocked by α-bungarotoxin, a neurotoxin that binds certain nicotinic acetylcholine receptors (nAChRs) thereby implicating nAChRs in this process. Here, we examine the identity of these receptors.

METHODS

Mouse lung fibroblasts were stimulated with EtOH (60 mM) or acetylcholine (100 to 500 μM) and evaluated for the expression of fibronectin and nAChRs. Inhibitors to nAChRs or the antioxidant N-acetyl cysteine (NAC) were used to assess changes in fibronectin expression. Animals exposed to EtOH for up to 6 weeks were used to evaluate the expression of nAChRs in vivo.

RESULTS

First, in EtOH-treated fibroblasts, we observed increased expression of α4 and α9 nAChR subunits. Second, we found that acetylcholine, a natural ligand for nAChRs, mimicked the effects of EtOH. Dihydro-β-erythroidin hydrobromide, a competitive inhibitor of α4 nAChR, blocked the increase in fibronectin expression and cell proliferation. Furthermore, EtOH-induced fibronectin expression was inhibited in cells silenced for α4 nAChR. However, EtOH-treated cells showed increased α-bungarotoxin binding suggesting that α4 nAChR mediates the effects of EtOH via a ligand-independent pathway. Knowing there are several important cysteine residues near the ligand-binding site of α4 nAChRs, we tested the antioxidant NAC and found that it too blocked the induction of fibronectin expression by EtOH. Also, fibroblasts exposed to oxidant stress showed increased fibronectin expression that was blocked with α-bungarotoxin. Finally, we showed increased expression of α4 nAChRs in the lung tissue of mice and rats exposed to EtOH suggesting a role for these receptors in vivo.

CONCLUSIONS

Altogether, our observations suggest that α4 nAChRs serve as sensors for EtOH-induced oxidant stress in lung fibroblasts, thereby revealing a new mechanism by which EtOH may affect lung cells and tissue remodeling and pointing to nAChRs as potential targets for intervention.

Efeito do treinamento físico no pulmão de ratos submetidos à ingestão alcoólica

O alcoolismo crônico provoca alterações nos tecidos pulmonares caracterizadas por edema pulmonar e formação de extenso infiltrado inflamatório. O objetivo deste trabalho foi avaliar o efeito do exercício físico sobre as lesões pulmonares provocadas por ingestão crônica de álcool em ratos Wistar. MATERIAL E MÉTODOS: Trinta e dois ratos Wistar machos (261,1 ± 1,3 gramas) receberam aguardente de cana-de-açúcar diluída (30%, v/v, grupo alcoolizado) ou água potável (grupo controle) durante 120 dias. Após este período, cinco animais de cada grupo foram sacrificados. Os demais animais receberam apenas água potável até o final do experimento e foram divididos em quatro grupos: alcoolizados sedentários (AS), controle sedentários (CS), alcoolizados treinados (AT) e controles treinados (CT). Os animais AT e CT foram submetidos a protocolo de natação, aumentando gradativamente o tempo de exercício até 20 minutos por dia, cinco vezes por semana, durante um período total de cinco semanas. Neste mesmo período, os animais AS e CS foram mantidos em sedentarismo. RESULTADOS: Após o período de ingestão alcoólica, os animais do grupo alcoolizado apresentaram redução de peso (P < 0,05) e aumento da massa relativa do pulmão (P < 0,05). O pulmão do grupo alcoolizado apresentou edema pulmonar e extenso infiltrado inflamatório. Os animais dos grupos CS e CT não apresentaram diferenças morfológicas. Os animais do grupo AT apresentaram aumento do quadro de edema pulmonar e do número de macrófagos pigmentados em relação ao grupo AC (P < 0,05). CONCLUSÃO: O exercício físico pode acentuar o processo inflamatório pulmonar quando aplicado em animais com lesão pulmonar inflamatória provocada pelo consumo crônico de álcool.

Laboratory models available to study alcohol-induced organ damage and immune variations: choosing the appropriate model

The morbidity and mortality resulting from alcohol-related diseases globally impose a substantive cost to society. To minimize the financial burden on society and improve the quality of life for individuals suffering from the ill effects of alcohol abuse, substantial research in the alcohol field is focused on understanding the mechanisms by which alcohol-related diseases develop and progress. Since ethical concerns and inherent difficulties limit the amount of alcohol abuse research that can be performed in humans, most studies are performed in laboratory animals. This article summarizes the various laboratory models of alcohol abuse that are currently available and are used to study the mechanisms by which alcohol abuse induces organ damage and immune defects. The strengths and weaknesses of each of the models are discussed. Integrated into the review are the presentations that were made in the symposium "Methods of Ethanol Application in Alcohol Model-How Long is Long Enough" at the joint 2008 Research Society on Alcoholism (RSA) and International Society for Biomedical Research on Alcoholism (ISBRA) meeting, Washington, DC, emphasizing the importance not only of selecting the most appropriate laboratory alcohol model to address the specific goals of a project but also of ensuring that the findings can be extrapolated to alcohol-induced diseases in humans.

Alcohol, signaling, and ECM turnover

Alcohol is recognized as a direct hepatotoxin, but the precise molecular pathways that are important for the initiation and progression of alcohol-induced tissue injury are not completely understood. The current understanding of alcohol toxicity to organs suggests that alcohol initiates injury by generation of oxidative and nonoxidative ethanol metabolites and via translocation of gut-derived endotoxin. These processes lead to cellular injury and stimulation of the inflammatory responses mediated through a variety of molecules. With continuing alcohol abuse, the injury progresses through impairment of tissue regeneration and extracellular matrix (ECM) turnover, leading to fibrogenesis and cirrhosis. Several cell types are involved in this process, the predominant being stellate cells, macrophages, and parenchymal cells. In response to alcohol, growth factors and cytokines activate many signaling cascades that regulate fibrogenesis. This mini-review brings together research focusing on the underlying mechanisms of alcohol-mediated injury in a number of organs. It highlights the various processes and molecules that are likely involved in inflammation, immune modulation, susceptibility to infection, ECM turnover and fibrogenesis in the liver, pancreas, and lung triggered by alcohol abuse.

Extracellular matrix influences alveolar epithelial claudin expression and barrier function

The lung is dynamically remodeled in response to injury, which alters extracellular matrix composition, and can lead to either healthy or impaired lung regeneration. To determine how changes in extracellular matrix can influence alveolar epithelial barrier function, we examined the expression and function of tight junction proteins by rat alveolar epithelial type II cells cultured on one of three different matrix components: type I collagen or fibronectin, matrix glycoproteins which are highly expressed in injured lungs, or laminin, a basement membrane matrix component. Of note, alveolar epithelial cells cultured for 2 days on fibronectin formed high-resistance barriers and showed continuous claudin-3 and claudin-18 localization to the plasma membrane, as opposed to cells cultured on either type I collagen or laminin, which had low resistance monolayers and had areas of cell-cell contact that were claudin deficient. The barrier formed by cells cultured on fibronectin also had preferential permeability to chloride as compared with sodium. Regardless of the initial matrix composition, alveolar epithelial cells cultured for 5 days formed high-resistance barriers, which correlated with increased claudin-18 localization to the plasma membrane and an increase in zonula occludens-1. Day 5 cells on laminin had significantly higher resistance than cells on either fibronectin or type I collagen. Thus, although alveolar epithelial cells on fibronectin formed rapid barriers, it was at the expense of producing an optimized barrier.