[Injury patterns in interstitial lung diseases]

The role of vascularity and the fibrovascular interface in interstitial lung diseases

Interstitial lung disease (ILD) is a clinical term that refers to a diverse group of non-neoplastic lung diseases. This group includes idiopathic and secondary pulmonary entities that are often associated with progressive pulmonary fibrosis. Currently, therapeutic approaches based on specific structural targeting of pulmonary fibrosis are limited to nintedanib and pirfenidone, which can only slow down disease progression leading to a lower mortality rate. Lung transplantation is currently the only available curative treatment, but it is associated with high perioperative mortality. The pulmonary vasculature plays a central role in physiological lung function, and vascular remodelling is considered a hallmark of the initiation and progression of pulmonary fibrosis. Different patterns of pulmonary fibrosis commonly exhibit detectable pathological features such as morphomolecular changes, including intussusceptive and sprouting angiogenesis, vascular morphometry, broncho-systemic anastomoses, and aberrant angiogenesis-related gene expression patterns. Dynamic cellular interactions within the fibrovascular interface, such as endothelial activation and endothelial-mesenchymal transition, are also observed. This review aims to summarise the current clinical, radiological and pathological diagnostic algorithm for different ILDs, including usual interstitial pneumonia/idiopathic pulmonary fibrosis, non-specific interstitial pneumonia, alveolar fibroelastosis/pleuroparenchymal fibroelastosis, hypersensitivity pneumonitis, systemic sclerosis-related ILD and coronavirus disease 2019 injury. It emphasises an interdisciplinary clinicopathological perspective. Additionally, the review covers current therapeutic strategies and knowledge about associated vascular abnormalities.

[Interstitial lung diseases : From imaging to treatment]

BACKGROUND

The role of radiology in the diagnosis of interstitial lung diseases (ILDs) has evolved over time, in part replacing histology. Radiology now represents a pillar of diagnostics and monitoring in ILDs.

OBJECTIVE

To what extent does radiology influence diagnostics and treatment in ILDs?

MATERIALS AND METHODS

A literature review was conducted, and current findings were discussed in the context of clinical data.

RESULTS

Radiology plays a crucial role in the diagnosis of ILDs. Within the framework of the multidisciplinary conference, it provides specific CT patterns such as usual interstitial pneumonia (UIP), nonspecific interstitial pneumonia (NSIP), and organizing pneumonia (OP), or helps in identifying cystic lung diseases. Multicompartment diseases can be detected, and pulmonary hypertension or extrapulmonary involvement of the respective diseases can be suspected. Progressive pulmonary fibrosis requires radiologic assessment as one of the required criteria. Interstitial lung abnormalities are usually detected by radiological studies performed for an unrelated indication.

CONCLUSION

Radiology plays an important role within the multidisciplinary conference to determine both diagnosis and treatment with antifibrotic or anti-inflammatory drugs, or a combination of both.

[Consensus guideline on the interdisciplinary diagnosis of interstitial lung diseases]

The evaluation of a patient with interstitial lung disease (ILD) includes assessment of clinical, radiological, and often histopathological data. As there were no specific recommendations to guide the evaluation of patients under the suspicion of an ILD within the German practice landscape, this position statement from an interdisciplinary panel of ILD experts provides guidance related to the diagnostic modalities which should be used in the evaluation of ILD. This includes clinical assessment rheumatological evaluation, radiological examinations, histopathologic sampling and the need for a final discussion in a multidisciplinary team.

Comparative Analysis of Gene Expression in Fibroblastic Foci in Patients with Idiopathic Pulmonary Fibrosis and Pulmonary Sarcoidosis

Background: Fibroblastic foci (FF) are characteristic features of usual interstitial pneumonia (UIP)/idiopathic pulmonary fibrosis (IPF) and one cardinal feature thought to represent a key mechanism of pathogenesis. Hence, FF have a high impact on UIP/IPF diagnosis in current guidelines. However, although less frequent, these histomorphological hallmarks also occur in other fibrotic pulmonary diseases. Currently, there is therefore a gap in knowledge regarding the underlying molecular similarities and differences of FF in different disease entities. Methods: In this work, we analyzed the compartment-specific gene expression profiles of FF in IPF and sarcoidosis in order to elucidate similarities and differences as well as shared pathomechanisms. For this purpose, we used laser capture microdissection, mRNA and protein expression analysis. Biological pathway analysis was performed using two different gene expression databases. As control samples, we used healthy lung tissue that was donated but not used for lung transplantation. Results: Based on Holm Bonferroni corrected expression data, mRNA expression analysis revealed a significantly altered expression signature for 136 out of 760 genes compared to healthy controls while half of these showed a similar regulation in both groups. Immunostaining of selected markers from each group corroborated these results. However, when comparing all differentially expressed genes with the fdr-based expression data, only 2 of these genes were differentially expressed between sarcoidosis and IPF compared to controls, i.e., calcium transport protein 1 (CAT1) and SMAD specific E3 ubiquitin protein ligase 1 (SMURF1), both in the sarcoidosis group. Direct comparison of sarcoidosis and IPF did not show any differentially regulated genes independent from the statistical methodology. Biological pathway analysis revealed a number of fibrosis-related pathways pronounced in IPF without differences in the regulatory direction. Conclusions: These results demonstrate that FF of end-stage IPF and sarcoidosis lungs, although different in initiation, are similar in gene and protein expression, encouraging further studies on the use of antifibrotic agents in sarcoidosis.

Genetic Deletion of Polo-Like Kinase 2 Induces a Pro-Fibrotic Pulmonary Phenotype

Pulmonary fibrosis is the chronic-progressive replacement of healthy lung tissue by extracellular matrix, leading to the destruction of the alveolar architecture and ultimately death. Due to limited pathophysiological knowledge, causal therapies are still missing and consequently the prognosis is poor. Thus, there is an urgent clinical need for models to derive effective therapies. Polo-like kinase 2 (PLK2) is an emerging regulator of fibroblast function and fibrosis. We found a significant downregulation of PLK2 in four different entities of human pulmonary fibrosis. Therefore, we characterized the pulmonary phenotype of PLK2 knockout (KO) mice. Isolated pulmonary PLK2 KO fibroblasts displayed a pronounced myofibroblast phenotype reflected by increased expression of αSMA, reduced proliferation rates and enhanced ERK1/2 and SMAD2/3 phosphorylation. In PLK2 KO, the expression of the fibrotic cytokines osteopontin and IL18 was elevated compared to controls. Histological analysis of PLK2 KO lungs revealed early stage remodeling in terms of alveolar wall thickening, increased alveolar collagen deposition and myofibroblast foci. Our results prompt further investigation of PLK2 function in pulmonary fibrosis and suggest that the PLK2 KO model displays a genetic predisposition towards pulmonary fibrosis, which could be leveraged in future research on this topic.

The Diagnosis and Treatment of Pulmonary Fibrosis

BACKGROUND

The different types of pulmonary fibrosis are a subgroup of the interstitial lung diseases (ILDs). They are associated with a chronic and often progressive course.

METHODS

This review is based on pertinent publications retrieved by a selective search in the EMBASE and PubMed databases, with an emphasis on articles published from 2000 to 2020.

RESULTS

The most common type of pulmonary fibrosis is idiopathic pulmonary fibrosis (IPF). Among other relevant types, the most important ones are fibrosing hypersensitivity pneumonitis (fHP) and ILDs associated with systemic diseases, all of which are rare and generally carry a poor prognosis. The essential prerequisite to accurate diagnosis is aninterdisciplinary approach, taking account of the clinical, histological, and radiological aspects. The main complications of pulmonary fibrosis are acute exacerbations and pulmonary hypertension; comorbidities are also of prognostic relevance. Treatment of pulmonary fibrosis depends on the subtype and clinical behavior. For IPF, antifibrotic therapy is indicated; fHP, on the other hand, is mainly treated by antigen avoidance and immune modulation. The predominant mode of treatment for systemic disease-associated pulmonary fibrosis is immune suppression. Antifibrotic agents can also be useful in the treatment of other types of progressivepulmonary fibrosis besides IPF.

CONCLUSION

The differential diagnosis of pulmonary fibrosis, though complex, is clinically essential, as different types of pulmonary fibrosis are treated differently.

[The updated S2k guideline for the diagnosis of idiopathic pulmonary fibrosis : Essential aspects for pathology]

Idiopathic pulmonary fibrosis (IPF) is a specific form of chronic progressive fibrosing nonreversible interstitial lung disease of largely unknown origin. In high-resolution computer tomography (HRCT) and histopathology it presents with a UIP pattern. To diagnose IPF, (i) an ILD of known origin must be excluded (e.g., hypersensitivity pneumonitis, lung involvement in autoimmune or other systemic disease, and drug-induced ILD) and either (ii) the presence of a UIP pattern in HRCT or (iii) specific combinations of HRCT and histopathology is necessary. The diagnosis of IPF requires interdisciplinary collaboration and a structured procedure. The updated S2k guideline focuses on the IPF diagnostic process and describes the criteria of a UIP pattern in HRCT and histopathology that are differentiated into the categories "UIP pattern," "probable UIP pattern," "indetermined for UIP," and "alternative pattern." Depending on the anamnestic, clinical and serologic findings, HRCT, and - if acquired - histomorphology features, an algorithm to diagnose the IPF is recommended. If a UIP pattern in HRCT is present, IPF can still be diagnosed without further bioptic examination. Additionally, recommendations for the use of surgical lung biopsy (SLB), transbronchial lung biopsy, and the relatively new transbronchial lung cryobiopsy (TBLC) procedure are provided. In contrast to the international guideline, the S2k guideline group evaluated TBLC based on recent studies to be advantageous compared to the SLB, as the diagnostic value and the side-effect rate was assessed to be acceptable and more patients with progressed ILD can be biopsied by TBLC. It is therefore expected that by using TBLC the rate of unclassifiable ILDs can be reduced.

[Fibrotic remodeling of the lung following lung and stem-cell transplantation]

Transplantation of solid organs and hematopoietic stem cells represents an important therapeutic option for a variety of end-stage pulmonary diseases, aggressive hematopoietic neoplasms, or severe immunodeficiencies. Although the overall survival following transplantation has generally improved over recent decades, long-time survival of lung and stem-cell transplant recipients is still alarmingly low with an average 5‑year survival rate of only 50-60%. Chronic allo-immunoreactions in general and pulmonary allo-immunoreactions with subsequent fibrosis in particular are major reasons for this poor outcome. Comparable patterns of fibrotic lung remodeling are observed following both lung and hematopoietic stem-cell transplantation. Besides the meanwhile well-established obliterative and functionally obstructive remodeling of the small airways - obliterative bronchiolitis - a specific restrictive subform of fibrosis, namely alveolar fibroelastosis, has been identified. Despite their crucial impact on patient outcome, both entities can be very challenging to detect by conventional histopathological analysis. Their underlying mechanisms are considered overreaching aberrant repair attempts to acute lung injuries with overactivation of (myo-) fibroblasts and excessive and irreversible deposition of extracellular matrix. Of note, the underlying molecular mechanisms are widely divergent between these two morphological entities and are independent of the underlying clinical setting.Further comprehensive investigations of these fibrotic alterations are key to the development of much-needed predictive diagnostics and curative concepts, considering the high mortality of pulmonary fibrosis following transplantation.

Molecular Profiling of Vascular Remodeling in Chronic Pulmonary Disease

Pulmonary hypertension and pulmonary vascular remodeling (PVR) are common in many lung diseases leading to right ventricular dysfunction and death. Differences in PVR result in significant prognostic divergences in both the pulmonary arterial and venous compartments, as in pulmonary arterial hypertension (PAH) and pulmonary veno-occlusive disease (PVOD), respectively. Our goal was to identify compartment-specific molecular hallmarks of PVR, considering the risk of life-threatening pulmonary edema in PVOD, if treated by conventional pulmonary hypertension therapy. Formalin-fixed and paraffin-embedded tissues from fresh explanted human lungs of patients with PVOD (n = 19), PAH (n = 20), idiopathic pulmonary fibrosis (n = 13), and chronic obstructive pulmonary disease (n = 15), were analyzed for inflammation and kinome-related gene regulation. The generated neuronal network differentiated PVOD from PAH samples with a sensitivity of 100% and a specificity of 92% in a randomly chosen validation set, a level far superior to established diagnostic algorithms. Further, various alterations were identified regarding the gene expression of explanted lungs with PVR, compared with controls. Specifically, the dysregulation of microtubule-associated serine/threonine kinase 2 and protein-o-mannose kinase SGK196 in all disease groups suggests a key role in pulmonary vasculopathy for the first time. Our findings promise to help develop novel target-specific interventions and innovative approaches to facilitate clinical diagnostics in an elusive group of diseases.

Comprehensive three-dimensional morphology of neoangiogenesis in pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis

Pulmonary veno‐occlusive disease (PVOD) is a rare lung disease characterized by fibrotic narrowing of pulmonary veins leading to pulmonary hypertension (PH) and finally to death by right heart failure. PVOD is often accompanied by pulmonary capillary hemangiomatosis (PCH), a marked abnormal proliferation of pulmonary capillaries. Both morphological patterns often occur together and are thought to be distinct manifestations of the same disease process and accordingly are classified together in group 1′ of the Nice classification of PH. The underlying mechanisms of these aberrant remodeling processes remain poorly understood. In this study, we investigated the three‐dimensional structure of these vascular lesions in the lung explant of a patient diagnosed with PVOD by μ‐computed tomography, microvascular corrosion casting, electron microscopy, immunohistochemistry, correlative light microscopy and gene expression analysis. We were able to describe multifocal intussusceptive neoangiogenesis and vascular sprouting as the three‐dimensional correlate of progressive PCH, a process dividing pre‐existing vessels by intravascular pillar formation previously only known from embryogenesis and tumor neoangiogenesis. Our findings suggest that venous occlusions in PVOD increase shear and stretching forces in the pulmonary capillary bloodstream and thereby induce intussusceptive neoangiogenesis. These findings can serve as a basis for novel approaches to the analysis of PVOD.