Cardiac ischemia and reperfusion lead to tissue damage and subsequent repair during which the necrotic tissue is replaced with a fibrotic scar. Fibroblasts are major actors in cardiac repair. Under the influence of transforming growth factor β (TGFβ) released at the site of injury, fibroblasts become activated and subsequently trans-differentiate into myofibroblasts, which are responsible for extracellular matrix production. ATP plays a crucial role in collagen production. However, the role of Pannexin1 (Panx1) ATP release channels in cardiac repair remains unexplored.

This study aims to understand the involvement of Panx1 channels in cardiac fibroblast activation and trans-differentiation as well as in the mechanism of scar formation.

We used an in vitro model of TGFβ-induced activation and trans-differentiation of human cardiac fibroblasts. Thus, human cardiac fibroblasts were treated with TGFβ (5–20ng/mL) for 48hours. Expression of platelet-derived growth factor receptor α (PDGFRα), collagen1α1 (COL1α1), and of extracellular signal-regulated kinase 1/2 (Erk1/2) was verified by Western blot. Expression of F-actin was assessed by immunofluorescent staining. ATP release from fibroblasts treated with TGFβ was determined by biochemiluminescent assays.

With increasing concentrations of TGFβ treatment, we observed a transient increase in PDGFRα and steady upregulation of COL1α1 expression, confirming the trans-differentiation of quiescent cardiac fibroblasts into activated fibroblasts and myofibroblasts, respectively. F-actin expression was also increased in fibroblasts after exposure to TGFβ, suggesting changes in the organization of actin cytoskeleton. Notably, Panx1 was expressed in human cardiac fibroblasts, and its expression level remained unchanged after exposure to TGFβ. TGFβ is known to activate Erk1/2 pathway, which might subsequently induce Panx1 phosphorylation and stimulate Panx1 channel opening. Time course experiments upon TGFβ treatment showed an increase in Erk1/2 phosphorylation after 5minutes. Basal and stimulated ATP release through Panx1 channels was however unchanged at this time point.

Our results show that TGFβ does not affect Panx1 expression and channel function in human cardiac fibroblasts. Future studies will explore non-canonical functions of Panx1 in cardiac fibroblasts to better understand the interaction of Panx1 with other proteins.