Azetidine-2-carboxylic acid-induced oligodendrogliopathy in vitro and the pathogenesis of multiple sclerosis

Azetidine 2-carboxylic acid (Aze) is consumed by humans and can be misincorporated in place of proline (Pro) in myelin basic protein (MBP). In systemically treated mice Aze induced distinct oligodendroglial (OL) alterations mimicking those in multiple sclerosis (MS) patient normal-appearing white matter. Here, Aze induced an unfolded protein response (UPR), cytoplasmic MBP aggregation, apoptosis and tumor necrosis factor secretion in the human OL lineage MO13.3 cell line. These alterations were counteracted by equimolar Pro suggesting that they are due to Aze substitution for Pro in OL proteins. Gene set enrichment analysis demonstrated extensive Aze-induced alterations of cell cycle, cytoskeletal, organelle, transport, developmental, inflammation-associated and myelination pathways that are altered in OL in MS patients and in toxin and inflammatory MS animal models. These data provide mechanistic support for the hypothesis that Aze protein misincorporation during early life myelinogenesis might over time result in a progressive UPR culminating in a pro-inflammatory/immunomodulatory phenotype, intracytoplasmic MBP aggregation, accelerated senescence and apoptosis in OL. This could occur prior to and independent of an external immune stimulus such as a viral infection. Aze-induced pathological alterations might enhance subsequent antiviral and autoimmune responses and contribute to MS susceptibility, lesion pathogenesis, remyelination failure, neurodegeneration and clinical progression.