Silica-related diseases in the modern world: A role for self-DNA sensing in lung inflammatory diseases

Lung inflammation and interstitial fibrosis by targeted alveolar epithelial type I cell death

Introduction

The pathogenesis of chronic lung diseases is multifaceted with a major role of recurrent micro-injuries of the epithelium. While several reports clearly indicated a prominent role for surfactant-producing alveolar epithelial type 2 (AT2) cells, the contribution of gas exchange-permissive alveolar epithelial type 1 (AT1) cells has not been addressed yet. Here, we investigated whether repeated injury of AT1 cells leads to inflammation and interstitial fibrosis.

Methods

We chose an inducible model of AT1 cell depletion following local diphtheria toxin (DT) administration using an iDTR flox/flox (idTRfl/fl) X Aquaporin 5CRE (Aqp5CRE) transgenic mouse strain.

Results

We investigated repeated doses and intervals of DT to induce cell death of AT1 cells causing inflammation and interstitial fibrosis. We found that repeated DT administrations at 1ng in iDTRfl/fl X Aqp5CRE mice cause AT1 cell death leading to inflammation, increased tissue repair markers and interstitial pulmonary fibrosis.

Discussion

Together, we demonstrate that depletion of AT1 cells using repeated injury represents a novel approach to investigate chronic lung inflammatory diseases and to identify new therapeutic targets.

Think Beyond Particle Cytotoxicity: When Self-Cellular Components Released After Immunogenic Cell Death Explain Chronic Disease Development

The prolonged perturbation of the immune system following the release of a plethora of self-molecules (known as damage-associated molecular patterns, DAMPs) by stressed or dying cells triggers acute and chronic pathological responses. DAMPs are commonly released after plasma membrane damage or complete rupture due to immunogenic cell death (ICD), upon numerous stressors including infectious and toxic agents. The set of DAMPs released after ICD include mature proinflammatory cytokines and alarmins, but also polymeric macromolecules. These self-intracellular components are recognized by injured and healthy surrounding cells via innate receptors, and induce upregulation of stress-response mechanisms, including inflammation. In this review, by overstepping the simple toxicological evaluation, we apply ICD and DAMP concepts to silica cytotoxicity, providing new insights on the mechanisms driving the progress and/or the exacerbation of certain SiO2–related pathologies. Finally, by proposing self-DNA as new crucial DAMP, we aim to pave the way for the development of innovative and easy-to-perform predictive tests to better identify the hazard of fine and ultrafine silica particles. Importantly, such mechanisms could be extended to nano/micro plastics and diesel particles, providing strategic advice and reports on their health issues.