Sigmar1 Deficiency Results in Pulmonary Fibrosis Associated with Increased Pulmonary Inflammation and Surfactant Protein Levels in Mice Lung.

Sigmar1 is a ubiquitously expressed multifunctional molecular chaperone protein. Extensive studies demonstrated Sigmar1's molecular functions in the central nervous system, and mutations in the Sigmar1 gene showed association with different neurodegenerative diseases, including amyotrophic lateral sclerosis and distal hereditary motor neuropathy. Studies also showed the protective roles of Sigmar1 in cardiovascular diseases in animal models of cardiac hypertrophy and heart failure. Recent studies focused on Sigmar1 in COVID-19 drug repurposing as Sigmar1 was identified to interact with SARS-Cov-2 replication proteins using proteomic screening and Sigmar1 ligands showed promising protective effects in clinical trials. Despite all these studies showing a function of Sigmar1 in the respiratory system, the Sigmar1's expression, localization, molecular and physiological functions in the lung remained unknown. The main objective of this study was to characterize the expression and localization of Sigmar1 in human and mouse lungs. We also investigated the pathophysiological role of Sigmar1 in the lung using Sigmar1 null mice. Using a combination of immunohistochemistry, immunofluorescence, and biochemical experiments, we confirmed the expression of Sigmar1 in rodent and human lungs. Hematoxylin and Eosin staining showed that Sigmar1 global knockout (Sigmar1-/- ) mice lungs develop altered alveolar structure and organization and higher immune-cells infiltration compared to Wildtype (Wt) littermate controls. This was associated with an upregulated protein level of phospho-NFκB in Sigmar1-/- mice lungs. Sirius red and Masson's trichrome staining of lung tissue sections showed increased collagen deposition, pulmonary fibrotic remodeling associated with elevated fibronectin and phospho-SMAD2 protein levels in Sigmar1-/- mice lungs. Ultrastructural analysis by transmission electron microscopy (TEM) showed structural alteration in the multilamellar bodies with partial loss of lipid lamellae in alveolar-type II epithelial cells (AV-II) in Sigmar1-/- mice lungs. Multilamellar bodies in AV-II cells serve as secretory organelles releasing pulmonary surfactants into the extracellular space. Elevated levels of surfactant proteins (SP), SP-A and SP-D, were reported to serve as biomarkers for acute respiratory failure and lung inflammation. Consistent with the TEM data, we also found increased SP (A, B, C, and D) protein levels in the lungs indicating the AV-II pneumocytes dysfunction in Sigmar1-/- mice. Our findings suggested that Sigmar1's lack of function leads to increased pulmonary inflammation, pulmonary fibrotic remodeling, altered structure and functions of multilamellar bodies, and AV-II pneumocytes dysfunction in Sigmar1-/- mice. © FASEB.

Citation

Naznin S Remex, Chowdhury S Abdullah, Richa Aishwarya, Mohammed M Morshed, Sadia Nitu, James Traylor, Brandon Hartman, Judy King, Christopher Kevil, Anthony W Orr, Md S Bhuiyan. Sigmar1 Deficiency Results in Pulmonary Fibrosis Associated with Increased Pulmonary Inflammation and Surfactant Protein Levels in Mice Lung. FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 2022 May;36 Suppl 1

PMID: 35560592

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