PTPα Is a Regulator of Fibroproliferation During ARDS

Rationale: Acute Respiratory Distress Syndrome (ARDS) is a major healthcare issue resulting in high morbidity and mortality. Up to 25% of patients with ARDS will develop pathological fibrosis, termed Fibroproliferative ARDS (FP-ARDS). In this subset of patients, ongoing injury and dysregulated repair results in persistence of inflammatory infiltrates, myofibroblast differentiation, and dysregulated deposition of extracellular matrix. The consequences of this pathologic fibroproliferation include increased mortality, prolonged ventilator dependence, and diminished quality of life for survivors. This is especially relevant in the context of the COVID-19 pandemic, during which fibroproliferation following ARDS is an increasingly recognized entity. We demonstrate that a tyrosine phosphatase, PTPα, plays an important role in promoting fibroproliferation following ARDS. Methods: Mice deficient in PTPα and littermate controls were treated with intratracheal hydrochloric acid;histological, biochemical, and gene expression endpoint analyses were performed. NIH 3T3 (murine) fibroblasts or normal human lung fibroblasts (NLHFs) were stimulated with BAL fluid from these mice, or from ARDS patients and healthy controls, respectively. Human lung fibroblasts in which PTPα was deleted via CRISPR-cas9 targeted guide RNA were treated with exogenous TGF-β. Analysis of gene expression by qPCR was performed. Results: Mice deficient in PTPα demonstrated reduced fibrotic outcomes after lung injury. A fibrosis-focused qPCR array showed significant attenuation of key pro-fibrotic genes in PTPα-null mice, even at early timepoints during which inflammatory outcomes were unchanged. BAL fluid from PTPα-null mice treated with HCl induced less fibroproliferative gene expression in murine fibroblasts than BAL fluid from littermate controls. Human fibroblasts lacking PTPα (generated via CRISPR-cas9 deletion) showed reduced pro-fibrotic gene expression responses following stimulation with exogenous TGF-β. NHLFs stimulated with ARDS patient BAL fluid demonstrated increased pro-fibrotic gene expression as compared to BAL fluid from control patients. Conclusions: We conclude that absence of PTPα is protective in a model of FP-ARDS, through mechanisms that result in reduced TGF-β-dependent gene expression. The alveolar milieu of mice lacking PTPα has reduced fibroproliferative potential than those that express PTPα. Similarly, human fibroblasts that have been genetically modified to delete PTPα are less responsive to stimulation with TGF-β, suggesting that this pathway is relevant to human pathology. Since human ARDS BAL fluid induces the same changes in normal human lung fibroblasts that are attenuated by the absence of PTPα in experimental models, this suggests that targeting of this protein could be a strategy to alleviate pathologic fibroproliferation following lung injury.