Altered autophagy in the development of Hermansky-Pudlak syndrome associated Interstitial pneumonia

Introduction: Hermansky-Pudlak syndrome (HPS) is a lysosome realated disorder. Patients with HPS types -1, -2 & -4 develop pulmonary fibrosis called Hermansky-Pudlak syndrome associated Interstitial Pneumonia (HPSIP). HPSIP lungs show enlarged alveolar typeII cells (AECII) with giant lamellar bodies. We previously reported lung fibrosis in a HPSIP mouse model (HPS1/2), defective surfactant accumulation and apoptosis of AECII due to severe lysosomal stress and ER stress in these mice as well as in human HPS1. Here, we aim to analyze autophagy, an important lysosomal degradation pathway, under HPSIP conditions.

Methods: Immunohistochemistry was performed and on serial paraffin lung sections from mouse HPS1, HPS2, HPS1/2 and WT controls and lungs from human HPS1 patients and healthy donors for autophagy related proteins LC3, p62 and TFEB and for AECII marker, pro SP-C. Immunogold labelling for LC3B was performed on mice lungs fixed in paraformaldehyde and gluteraldehyde.

Results: Immunohistochemistry revealed that the AECII of HPS1/2 mice and human HPS1 did not stain for LC3B, while a convincing signal was observed within macrophages of the same sections and within AECII & macrophages of WT mice and healthy donors. Electron microscopy results confirm the qualitative observation of less labelling of the LC3B on the limiting membrane of lamellar bodies in HPS mice compared to WT mice. Immunohistochemistry showed decreased staining for p62 and TFEB within AECII of HPS1/2 compared to WT mice.

Conclusion: Our results point towards defective autophagy under HPSIP conditions. An indepth analysis of this pathway is underway to further understand the disease pathomechanisms.