Endoplasmic reticulum stress in alveolar epithelial cells is prominent in IPF: association with altered surfactant protein processing and herpesvirus infection.
Recent evidence suggests that dysfunctional type II alveolar epithelial cells (AECs) contribute to the pathogenesis of idiopathic pulmonary fibrosis (IPF). Based on the hypothesis that disease-causing mutations in surfactant protein C (SFTPC) provide an important paradigm for studying IPF, we investigated a potential mechanism of AEC dysfunction suggested to result from mutant SFTPC expression: induction of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). We evaluated biopsies from 23 IPF patients (including 3 family members with L188Q SFTPC mutations, 10 individuals with familial interstitial pneumonia without SFTPC mutations, and 10 individuals with sporadic IPF) and sections from 10 control lungs. After demonstrating UPR activation in cultured A549 cells expressing mutant SFTPC, we identified prominent expression of UPR markers in AECs in the lungs of patients with SFTPC mutation-associated fibrosis. In individuals with familial interstitial pneumonia without SFTPC mutations and patients with sporadic IPF, we also found UPR activation selectively in AECs lining areas of fibrotic remodeling. Because herpesviruses are found frequently in IPF lungs and can induce ER stress, we investigated expression of viral proteins in lung biopsies. Herpesvirus protein expression was found in AECs from 15/23 IPF patients and colocalized with UPR markers in AECs from these patients. ER stress and UPR activation are found in the alveolar epithelium in patients with IPF and could contribute to disease progression. Activation of these pathways may result from altered surfactant protein processing or chronic herpesvirus infection.
Lawson
William E
WE
Department of Medicine, Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2650, USA. william.lawson@vanderbilt.edu
Crossno
Peter F
PF
Polosukhin
Vasiliy V
VV
Roldan
Juan
J
Cheng
Dong-Sheng
DS
Lane
Kirk B
KB
Blackwell
Thomas R
TR
Xu
Carol
C
Markin
Cheryl
C
Ware
Lorraine B
LB
Miller
Geraldine G
GG
Loyd
James E
JE
Blackwell
Timothy S
TS
D000956:Antigens, Viral / Q000096:biosynthesis; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D004721:Endoplasmic Reticulum / Q000502:physiology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006023:Glycoproteins / Q000096:biosynthesis; D006360:Heat-Shock Proteins / Q000096:biosynthesis; D006566:Herpesviridae Infections / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D007150:Immunohistochemistry; D018832:Molecular Chaperones / Q000096:biosynthesis; D009687:Nuclear Proteins / Q000096:biosynthesis; D017510:Protein Folding; D011650:Pulmonary Alveoli / Q000648:ultrastructure*; D011658:Pulmonary Fibrosis / Q000150:complications / Q000503:physiopathology*; D037721:Pulmonary Surfactant-Associated Protein C / Q000235:genetics / Q000502:physiology*; D000071701:Regulatory Factor X Transcription Factors; D013312:Stress, Physiological / Q000503:physiopathology*; D014157:Transcription Factors; D043323:alpha-Mannosidase / Q000096:biosynthesis
D000956:Antigens, Viral; D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006023:Glycoproteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D037721:Pulmonary Surfactant-Associated Protein C; D000071701:Regulatory Factor X Transcription Factors; C489679:SFTPC protein, human; D014157:Transcription Factors; C497155:EDEM2 protein, human; D043323:alpha-Mannosidase