Epithelial stress and apoptosis underlie Hermansky-Pudlak syndrome-associated interstitial pneumonia.
BACKGROUND
The molecular mechanisms underlying Hermansky-Pudlak syndrome-associated interstitial pneumonia (HPSIP) are poorly understood but, as in idiopathic pulmonary fibrosis, may be linked to chronic alveolar epithelial type II cell (AECII) injury.


OBJECTIVE
We studied the development of fibrosis and the role of AECII injury in various murine models of HPS.


METHODS
HPS1, HPS2, and HPS6 monomutant mice, and HPS1/2 and HPS1/6 double-mutant and genetic background mice, were killed at 3 and 9 months of age. Quantitative morphometry was undertaken in lung sections stained with hemalaun-eosin. The extent of lung fibrosis was assessed by trichrome staining and hydroxyproline measurement. Surfactant lipids were analyzed by electrospray ionization mass spectrometry. Surfactant proteins, apoptosis, and lysosomal and endoplasmic reticulum stress markers were studied by Western blotting and immunohistochemistry. Cell proliferation was measured by water-soluble tetrazolium salt-1 and bromodeoxyuridine assays.


RESULTS
Spontaneous and slowly progressive HPSIP was observed in HPS1/2 double mutants, but not in other HPS mutants, with subpleural onset at 3 months and full-blown fibrosis at 9 months. In these mice, extensive surfactant abnormalities were encountered in AECII and were paralleled by early lysosomal stress (cathepsin D induction), late endoplasmic reticulum stress (activating transcription factor-4 [ATF4], C/EBP homologous protein [CHOP] induction), and marked apoptosis. These findings were fully corroborated in human HPSIP. In addition, cathepsin D overexpression resulted in apoptosis of MLE-12 cells and increased proliferation of NIH 3T3 fibroblasts incubated with conditioned medium of the transfected cells.


CONCLUSIONS
Extensively impaired surfactant trafficking and secretion underlie lysosomal and endoplasmic reticulum stress with apoptosis of AECII in HPSIP, thereby causing the development of HPSIP.
Mahavadi
Poornima
P
Department of Internal Medicine II, University of Giessen Lung Center (UGLC), Klinikstrasse 36, 35392 Giessen, Germany.
Korfei
Martina
M
Henneke
Ingrid
I
Liebisch
Gerhard
G
Schmitz
Gerd
G
Gochuico
Bernadette R
BR
Markart
Philipp
P
Bellusci
Saverio
S
Seeger
Werner
W
Ruppert
Clemens
C
Guenther
Andreas
A
D000818:Animals; D017209:Apoptosis; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001992:Bronchoalveolar Lavage Fluid; D002402:Cathepsin D / Q000378:metabolism; D004195:Disease Models, Animal; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004847:Epithelial Cells / Q000473:pathology; D005355:Fibrosis; D022861:Hermanski-Pudlak Syndrome / Q000473:pathology*; D036341:Intercellular Signaling Peptides and Proteins; D008168:Lung / Q000378:metabolism / Q000473:pathology*; D017563:Lung Diseases, Interstitial / Q000473:pathology*; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D010455:Peptides / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology; D037701:Pulmonary Surfactant-Associated Protein B / Q000378:metabolism; D037721:Pulmonary Surfactant-Associated Protein C; D000073940:Transcription Factor 4; D051742:Transcription Factor CHOP / Q000378:metabolism; D015854:Up-Regulation
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; C497250:Ddit3 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010743:Phospholipids; D037701:Pulmonary Surfactant-Associated Protein B; D037721:Pulmonary Surfactant-Associated Protein C; C489680:Sftpc protein, mouse; C090743:Tcf4 protein, mouse; D000073940:Transcription Factor 4; D051742:Transcription Factor CHOP; D002402:Cathepsin D; C533923:Ctsd protein, mouse