Therapeutic induction of Bcl2‐associated athanogene 3‐mediated autophagy in idiopathic pulmonary fibrosis

BACKGROUND: Exaggerated fibroblast proliferation is a well‐known feature in idiopathic pulmonary fibrosis (IPF) which may be – in part – due to insufficient autophagy, a lysosome dependent cellular surveillance pathway. Bcl2‐associated athanogene 3 (BAG3) is a pivotal co‐chaperone of the autophagy pathway. Here, we studied whether therapeutic modulation of BAG3‐mediated autophagy can rescue insufficient autophagy and impact IPF fibroblast proliferation. METHODS: Primary interstitial fibroblasts or precision cut lung slices (PCLS) of IPF lungs were treated with (1) the antifibrotic drug pirfenidone (Pirf), (2) the demethylating agent 5‐azacytidine (Aza), (3) the BAG3 modulator cantharidin (Ctd). Autophagy flux was measured following pretreatment with the autophagy inhibitors or by GFP‐RFP‐LC3B transfection followed by drug treatments. Proliferation was measured by 5‐bromo‐2′‐deoxyuridine assay. BAG3, filamin C (FLNC), proliferating‐cell‐nuclear‐antigen (PCNA), collagen1A1 (COL1A1) and autophagy proteins were assessed by immunoblotting or immunofluorescence. Loss of function experiments were performed by siRNA mediated knockdown of BAG3. RESULTS: In comparison with healthy donors, increased BAG3 protein was observed in IPF lung homogenates and IPF fibroblasts. In addition, the substrate of BAG3‐mediated autophagy, FLNC, was increased in IPF fibroblasts, implying insufficient activation of BAG3‐dependent autophagy. Therapeutic modulation of this pathway using Aza and Ctd alone or in combination with the IPF therapy drug Pirf rescued the insufficient BAG3‐mediated autophagy and decreased fibroblast proliferation. Such effects were observed upon therapeutic modulation of BAG3 but not upon knock down of BAG3 per se in IPF fibroblasts. Similarly, PCLS of IPF patients showed a significant decrease in collagen deposition in response to these drugs, either alone or in a more potent form in combination with Pirf. CONCLUSIONS: Our study reveals that repurposing drugs that modulate autophagy regulating proteins render therapeutic benefits in IPF. Fine tuning of this pathway may hence signify a promising therapeutic strategy to ameliorate antifibrotic properties and augment the efficacy of current IPF therapy.