Diffuse parenchymal lung disease

BAG3: An enticing therapeutic target for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a dreadful and fatal disease of unknown etiology, for which no cure exists. Autophagy, a lysosomal cellular surveillance pathway is insufficiently activated in both alveolar epithelial type II cells and fibroblasts of IPF patient lungs. Fine-tuning this pathway may result in the degradation of the accumulated cargo and influence cell fate. Based on our previous data, we here present our view on modulating autophagy via a unique co-chaperone, namely Bcl2-associated athanogene3 (BAG3) in IPF and discuss about how repurposing drugs that modulate this pathway may emerge as a promising novel therapeutic approach for IPF.

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.

Comparison of Transbronchial and Cryobiopsies in Evaluation of Diffuse Parenchymal Lung Disease

BACKGROUND

Diffuse parenchymal lung diseases (DPLDs) are common. An accurate diagnosis is essential due to differences in etiology, clinicopathologic features, therapeutic options, and prognosis. Transbronchial lung biopsies (TBLBs) are often limited by small specimen size, crush artifact, and other factors. Transbronchial lung cryobiopsies (TBLCs) are under investigation to overcome these limitations.

METHODS

We conducted a retrospective study of 56 patients in a single, tertiary-care academic center to compare the yield of both techniques when performed in the same patient. Patients underwent flexible bronchoscopy using moderate sedation with TBLB followed by TBLC in the most radiographically abnormal areas. Clinical data and postprocedural outcomes were reviewed, with a final diagnosis made utilizing a multidisciplinary approach.

RESULTS

The mean age of patients was 60 years and 54% were male. Comorbidities included COPD (14%) and prior malignancy (48%). The number of TBLB specimens ranged from 1 to 10 per patient (mean 4) and size varied from 0.1 to 0.8 cm. The number of TBLC specimens ranged from 1 to 4 per patient (mean 2) and size ranged from 0.4 to 2.6 cm. Both techniques provided the same diagnosis in 26 patients (46%). An additional 11 (20%) patients had a diagnosis established by adding TBLC to TBLB. Compared with TBLB, TBLC had a higher diagnostic yield in patients with hypersensitivity pneumonitis and interstitial lung disease. Only 2 patients required video-assisted thoracoscopic surgery to establish a diagnosis. Complications included pneumothorax (20%) and massive hemoptysis (2%).

CONCLUSION

TBLC used with TBLB can improve the diagnostic yield of flexible bronchoscopy in patients with DPLD.