Purpose: The increasing amounts of evidence with abnormal aging process have been involved in the pathogenesis of chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Mice with deficient protein L-isoaspartate (D-aspartate) O-methyl transferase 1 (PCMT1) expression reveal acceleration of aging and result in the increased proportion of D-aspartate (D-Asp) residues and dysfunction in proteins. Furthermore, mitochondrial morphology and functions are associated with COPD and IPF pathogenesis. The purpose of the current study was to investigate the role of PCMT1 on mitochondrial morphology using A549 cells.
Materials and methods: We investigated PCMT1, prohibitin1 (PHB1), mitochondrial membrane proteins expression, mitochondrial morphology, and the proportion of D-Asp residues in PHB1 in A549 cells with (PCMT1-KD) and without the context of decreased PCMT1 expression (PCMT1-Cont) using electron microscopy, fluorescence staining, Western blot analysis, and the ATP content per cells. To investigate the effects of the PCMT1-KD cells, we developed double-transfected cell lines containing either the cytosolic or the endoplasmic isoform of PCMT1.
Results: We found a significantly higher proportion of D-Asp residues in PHB1 in PCMT1-KD cells than that in PCMT1-Cont cells. The PCMT1-KD cells without cigarette smoke extract exposure were characterized by a significantly increased proportion of the D-Asp residues in PHB1, damaged mitochondrial ultrastructure, and a tendency toward the fission direction of the mitochondrial dynamics followed by a significant decrease in the cellular ATP content.
Conclusions: The increased proportion of the D-Asp residues may contribute to COPD pathogenesis, via irreversible protein conformational changes, followed by mitochondrial dysfunction.
Keywords: d-aspartic acid residue; isomerization; protein damage.