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Alveolar Lipid Accumulation in GMCSFRβ KO Mice Involves Epithelial Steatosis as well as Macrophage Lipotoxicity and is Not Associated with Altered Surfactant Lipid Synthesis
Author(s) -
Corkill Dominic John,
Hunt Alan N,
Hinrichs Mary Jane,
Rebellato Marlon C,
Ryan Patricia,
Scott Alison,
Sleeman Matthew A,
Postle Anthony D
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.921.2
Subject(s) - pulmonary surfactant , pulmonary alveolar proteinosis , alveolar macrophage , lung , pathology , lamellar granule , chemistry , dipalmitoylphosphatidylcholine , pulmonary alveolus , macrophage , endocrinology , medicine , immunology , biology , phosphatidylcholine , phospholipid , respiratory disease , biochemistry , in vitro , membrane
In human subjects, auto‐antibodies to granulocyte macrophage colony stimulating factor (GM‐CSF) are associated with the development of pulmonary alveolar proteinosis (PAP), a lung disease characterised by alveolar accumulation of surfactant resulting in respiratory failure and increased infection risk. GM‐CSF receptor β‐chain deficient (GMCSFRβ KO) mice develop an equivalent phenotype. Although GMCSF‐dependent defective alveolar macrophage (AM) clearance of surfactant is believed to be the underlying mechanism for this pathology, the role of surfactant lipid synthesis and catabolism is less clear. At 6, 12 and 16 weeks of age, alveolar lipid content was determined in GMCSFRβ KO and wild‐type (WT) mice following deuterium labelled choline administration and subsequent analysis of broncho‐alveolar lavage fluid (BALF) and lung tissue homogenates by mass spectrometry (MS). This approach permitted, for the first time, determination of the synthetic rates of alveolar lipid molecular species in vivo at 12 weeks of age. At each endpoint, lung function, gross pathology and histopathological assessment of lung tissue was performed. In GMCSFRβ KO mice there was clear development of a PAP‐like phenotype with accumulation of PAS stained material in the alveoli and significantly increased BALF surfactant recovered compared to WT mice. Histologically, alveolar proteinaceous material and perivascular inflammatory cell infiltrates were seen in the lung of KO mice only, which increased over time. Additionally, surfactant lipids were present within the alveolar epithelia. In 16 week mice, the major surfactant species, dipalmitoylphosphatidylcholine (DPPC), increased in the BALF of GMCSFRβ KO mice versus WT mice (185±19.49 vs 48±2.36 nmol in KO vs WT (mean±SEM), p<0.001). Tissue homogenate DPPC was also increased at 16 weeks (85.2± 6.39 vs 15.55±0.91 nmol in KO vs WT (mean±SEM)), p<0.001. These increases were not associated with enhanced DPPC synthesis at 12 weeks (estimated rate of synthesis 0.19 vs 0.14nmol/h/lung in WT vs KO), suggesting defective AM clearance from the lung alone is sufficient to explain this pathology. Deficiency of GM‐CSF signalling in knock‐out mice results in a PAP‐like phenotype, and we showed by MS that whole lung lipid accumulation was not due to enhanced lipid synthesis. Clinical studies using an anti‐GMCSFRα antibody (Mavrilimumab) for the treatment of rheumatoid arthritis are currently underway, and further studies to determine the effect of neutralising antibodies on alveolar lipid biology will be important. Use of sensitive MS methods to quantitate lung surfactant lipid turnover will enable greater understanding of the interactions between the GM‐CSF axis and airway lipid physiology.