Pulmonary fibrosis is a progressive and fatal fibroproliferative disease. The current drugs (nintedanib/pirfenidone) only slow clinical progression. Myofibroblasts are the primary effector cells of PF. We found that CSP7, nintedanib and pirfenidone exert antifibrotic effects through restoring p53-microRNA-34a feedback induction in lung (myo)fibroblasts. We further found that daily treatment of mice with CSP7/nintedanib/pirfenidone between days 14 and 21 post-bleomycin lung fibrosis improve survival, body weight and lung function, and combination therapy had added benefit.

Introduction: Interleukin-17A (IL-17A) signalling disrupts fibrinolysis and drives inflammation and fibrotic remodelling in acute lung injury (ALI). IL-17A signals through a heterodimeric complex of IL-17RA and IL-17RC, initiating a cascade of immunological responses, including the synthesis of chemokines and inflammatory mediators. This leads to compromised epithelial integrity and barrier dysfunction. To determine the therapeutic potential of IL-17RA and IL-17RC neutralising antibodies on inflammation and the fibrinolytic system in a bleomycin (BLM)-induced ALI model. Methods: A549 cells and C57BL/6 mice were used to study the effects of neutralising IL-17RA and IL-17RC. ALI was induced in both models using BLM. A549 cells were subsequently treated with IL-17RA and IL-17RC neutralising antibodies. In mice, ALI was induced via intranasal administration of BLM. Neutralising antibodies against IL-17RA and IL-17RC were administered intranasally. Collected lung tissues and cell pellets were assessed for expression of the fibrinolytic system and inflammation. Results: Our study demonstrates the active involvement of IL-17 receptors, IL-17RA, and IL17RC in ALI. BLM treatment significantly increased PAI-1 expression ~ 3.5-fold, whereas neutralisation of IL-17RA or IL-17RC markedly reduced PAI-1 levels by over 90% compared to the BLM treated group, while restoring the expression of urokinase plasminogen activator (uPA) and its receptor (uPAR) and suppressing pro-inflammatory cytokines TNF-α and IL-6. Discussion: This study reveals that neutralisation of IL-17RA or IL-17RC in BLM-induced ALI reduced inflammation and restored normal fibrinolytic balance. Conclusion: Our study suggests that IL-17RA and IL-17RC play a major role in inflammation and the regulation of fibrinolysis during ALI. Targeting these receptors can mitigate lung injury and restore normal fibrinolytic activity, highlighting a novel receptor-specific IL-17 blockade as a potential therapeutic strategy to limit lung injury and improve ALI and Acute respiratory distress syndrome (ARDS) outcomes.

Alveolar inflammation, elevated interleukin-17A (IL-17A), and fibrin deposition are common features in all forms of lung injury followed by fibrotic repair. Type II alveolar epithelial cell (AEC) viability, regulated by tumor suppressor protein p53 and changes in uPA-mediated fibrinolysis, has been linked to lung injury and pulmonary fibrosis (PF). Nevertheless, mechanistic details linking increased IL-17A with p53 and PAI-1 to lung injury and remodeling remain unclear. We found that IL-17A and its receptor (IL-17RA) are induced during various lung injuries. IL-17A augments IL-17RA, p53 and downstream PAI-1 with a concurrent decrease in uPA and its receptor (uPAR) in AECs. These changes promote AEC apoptosis, alveolar injury and PF. In addition, IL-17A causes a dose-dependent increase in IL-17RA and profibrogenic markers in lung fibroblasts (LFs), suggesting myofibroblast differentiation. We further found that inhibition of IL-17A by caveolin-1 scaffolding domain peptide (CSP) or its 7-mer deletion fragment (CSP7) inhibits AEC apoptosis, lung inflammation, and profibrogenic markers in LFs and PF. Further, treatment of mice with bleomycin-induced lung injury using CSP7, an anti-IL-17A antibody, or an IL-17RA blocking antibody attenuates total lung hydroxyproline and soluble collagen content, as well as levels of profibrogenic markers. These observations support the role of IL-17A/IL-17RA signaling in lung injury and post-injury remodeling.