Precision cut lung slices #3: PCLS for specific respiratory disease research

Using precision-cut lung slices (PCLS) as an experimental model has revolutionized the study of respiratory diseases. PCLS offer a unique platform to investigate disease mechanisms, explore cellular and molecular interactions, and evaluate potential therapeutic interventions. With their preserved tissue architecture, cellular diversity, and physiological relevance, PCLS enable researchers to dissect complex respiratory pathologies, such as asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. By providing a representative ex vivo model that closely mimics the native lung microenvironment, PCLS have become invaluable tools in unraveling the intricacies of respiratory diseases and paving the way for the development of targeted treatments and improved patient outcomes.

PCLS in Asthma

Asthma, a prevalent chronic respiratory disease affecting millions worldwide, is characterized by airway inflammation, hyperresponsiveness, bronchoconstriction, and airflow obstruction, with marked heterogeneity among individuals. Animal models, such as mice and rats, have been utilized to mimic certain aspects of allergen-induced asthma, but translatability to human disease remains a challenge. To overcome these limitations and improve disease understanding, precision-cut lung slices (PCLS) derived from healthy and diseased patients have been employed as an ex vivo tool for studying asthma.

PCLS obtained from healthy and diseased lungs exhibit altered responses to stimulation, including bronchoconstriction and hyperresponsiveness, aligning with clinical observations and various animal models. This physiological mimicry of the whole lung suggests that PCLS provide a representative system for studying asthma. Notably, PCLS from asthmatic patients demonstrate significantly enhanced airway inflammation and hyperresponsiveness following rhinovirus stimulation, further reflecting disease-specific characteristics. Additionally, increased expression of genes, such as Il25, Tslp, and Il13, implicated in asthma pathogenesis, is detected in asthmatic human PCLS. These findings support the utility of PCLS as a promising model for investigating asthma, offering correlations with findings in asthmatic patients and enabling mechanistic investigations into disease pathogenesis and potential therapeutic strategies.

PCLS in COPD

Chronic obstructive pulmonary disease (COPD) is a progressive inflammatory disease of the airways characterized by irreversible airflow limitation, immune dysfunction, and significant morbidity and mortality. With approximately 400 million affected individuals worldwide, COPD is projected to become the third leading cause of death by 2030. Immune dysregulation and persistent pulmonary inflammation are key factors contributing to COPD pathogenesis, primarily driven by excessive inflammatory responses to tobacco smoke and infections.

While animal models have been instrumental in studying certain aspects of COPD pathology, there is no single model that fully encompasses the complexity of the disease. Animal models of cigarette smoke exposure, elastase-induced emphysema, and lipopolysaccharide (LPS) challenge have provided insights into specific aspects of COPD, such as emphysema and airway remodeling. However, these models have limitations in terms of replicating the full spectrum of clinical disease and may not fully mimic human COPD.

To address these limitations and gain a better understanding of COPD, precision-cut lung slices (PCLS) derived from animal models have proven valuable. PCLS from smoke-exposed mice have shown elevated expression of chemokines upon stimulation with viral mimics or influenza A virus, providing insights into the interplay between smoking and viral infections in COPD. Furthermore, murine PCLS have demonstrated impaired bronchodilator responsiveness to β2-adrenoceptor agonists following influenza A infection and cigarette smoke exposure. The use of PCLS from COPD patients in future studies holds great potential for characterizing functional and phenotypic immune cell responses, allowing for a comprehensive understanding of disease heterogeneity and molecular mechanisms.

In summary, PCLS derived from animal models and potentially from COPD patients offer a valuable ex vivo platform for modeling and investigating COPD. These models provide opportunities for functional and phenotypic characterization of immune cells, enabling a more integrated and comprehensive analysis of COPD mechanisms and facilitating the development of targeted therapies for specific patient subsets.

PCLS in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease characterized by progressive interstitial fibrosis. It is associated with shortness of breath, chronic dry cough, and nail clubbing, and is influenced by various genetic and environmental risk factors. Animal models have contributed significantly to our understanding of IPF mechanisms; however, they do not fully replicate the human disease. Nevertheless, these models have been used to evaluate therapeutic agents and understand early molecular changes.

Precision-cut lung slices (PCLS) have emerged as a successful tool for studying early-onset lung fibrosis in IPF. PCLS exposed to factors like TGF-β1 and cadmium chloride exhibit pathohistological changes similar to early lung fibrosis, including upregulation of pro-fibrotic genes, increased thickness of alveolar septa, and abnormal activation of pulmonary cells. A recent study by Alsafadi et al. established an ex vivo human PCLS model of early fibrosis by exposing PCLS to a combination of pro-fibrotic growth factors and signaling molecules, enabling the investigation of early-stage IPF mechanisms and novel therapies.

PCLS have also shown promise in evaluating novel therapies for IPF. Caffeine, known for inhibiting TGF-β-induced increases in pro-fibrotic gene expression, significantly reduces fibrosis in PCLS from bleomycin-treated mice. Furthermore, targeting the PI3K signaling pathway has shown potential as an anti-fibrotic treatment strategy using PCLS derived from IPF patients.

In summary, PCLS has proven to be a valuable tool for studying early lung fibrosis in IPF. Their ability to replicate relevant pathohistological changes, upregulate pro-fibrotic genes, and evaluate potential therapeutic agents makes them a promising ex vivo model for advancing our understanding of IPF pathogenesis and exploring novel treatment approaches.

PCLS in Infection and Inflammation

The precision-cut lung slices (PCLS) system has been utilized effectively to investigate innate responses to viral, bacterial, and bacterial component challenges. By studying cells within their physiological environment, PCLS studies have provided insights into the infectability of differentiated airway epithelial cells and the influence of cellular associations and structural architecture on infection. Notably, studies have shown that the epithelium, when in its proper physiological structure, exhibits resistance to infection.

PCLS has proven to be a valuable tool for understanding the inflammatory response, ranging from investigations into the innate response to bacterial wall components like LPS to complex studies involving mixed infections with multiple viruses or viral and bacterial combinations. Through careful analysis, researchers have been able to examine immune responses to each stimulus and evaluate the effects of immunomodulators on innate signaling.

Moreover, the ability to obtain PCLS from diseased lungs, such as those affected by COPD or asthma, offers a robust model system to explore how respiratory diseases influence infectivity and host responses. This is particularly relevant to diseases like COPD and asthma, which are associated with pathogen-induced exacerbations.

In summary, the PCLS system provides a valuable platform for studying infection and inflammation, enabling investigations into innate responses, the influence of cellular associations, and the impact of respiratory diseases on infectivity and host responses. By studying cells within their physiological context, PCLS offers a more comprehensive understanding of immune interactions and facilitates the evaluation of potential therapeutic interventions.

PCLS for Testing New Therapeutic Targets

The use of precision-cut lung slices (PCLS) has shown promise in the evaluation of new therapeutic targets, especially in the context of respiratory diseases like asthma. While regulatory toxicology testing traditionally relies on in vivo experiments in animals to identify organ toxicities, in vitro methods are now being implemented in earlier stages of drug discovery to mitigate potential safety concerns and increase pharmaceutical research and development productivity. However, current in vitro models, such as air-liquid interface (ALI) cultures, have limitations in replicating the complex architecture and cellular associations of the lung.

PCLS offer a more representative and translatable system that bridges the gap between cell line or primary cell culture systems and the in vivo situation. These slices can be used to investigate the efficacy and safety of drug candidates. In the context of asthma, PCLS have successfully modeled the response to inhaled corticosteroids and bronchodilators, effectively reducing airway constriction and mimicking the performance observed in animal models and clinical trials.

Additionally, PCLS have facilitated the evaluation of alternative targets for asthma treatment, as tolerance to current therapies necessitates the development of novel therapeutic strategies. PCLS studies have explored targets relevant to asthma pathogenesis, such as histone deacetylase inhibitors and activation of soluble guanylate cyclase, demonstrating their potential as bronchodilators and modulators of airway hyperresponsiveness.

Furthermore, PCLS provide an opportunity to assess the impact of therapeutics on the immune system in the lung. By incorporating immune cell components into ALI cultures and utilizing PCLS derived from diseased human lungs, researchers can better evaluate the adverse effects on host defense and immune cell function, providing insights into the potential risks associated with immunomodulatory drug candidates.

In summary, PCLS have emerged as a valuable tool for testing new therapeutic targets, offering a more representative model system that captures the complexity of the lung. Their use in drug development facilitates the evaluation of efficacy, safety, and potential immune-related adverse effects, enabling researchers to advance the understanding and treatment of respiratory diseases like asthma.