Background: Inflammatory myopathies are characterized by infiltration of inflammatory cells into muscle. Typically, immune-mediated disorders such as polymyositis, dermatomyositis and inclusion body myositis are diagnosed. Objective: A small family of dogs with early onset muscle weakness and inflammatory muscle biopsies were investigated for an underlying genetic cause. Methods: Following the histopathological diagnosis of inflammatory myopathy, mutational analysis including whole genome sequencing, functional transport studies of the mutated and wild-type proteins, and metabolomic analysis were performed. Results: Whole genome resequencing identified a pathological variant in the SLC25A12 gene, resulting in a leucine to proline substitution at amino acid 349 in the mitochondrial aspartate-glutamate transporter known as the neuron and muscle specific aspartate glutamate carrier 1 (AGC1). Functionally reconstituting recombinant wild-type and mutant AGC1 into liposomes demonstrated a dramatic decrease in AGC1 transport activity and inability to transfer reducing equivalents from the cytosol into mitochondria. Targeted, broad-spectrum metabolomic analysis from affected and control muscles demonstrated a proinflammatory milieu and strong support for oxidative stress. Conclusions: This study provides the first description of a metabolic mechanism in which ablated mitochondrial glutamate transport markedly reduced the import of reducing equivalents into mitochondria and produced a highly oxidizing and proinflammatory muscle environment and an inflammatory myopathy.
Bibliographical noteFunding Information:
Table S1. Discriminating metabolites. (XLS) Table S2. Raw metabolomic data. (CSV) Support for this study was provided by grant GGP11139 from Comitato Telethon Fondazione Onlus and the MFAxMCD InterOmics Flag Project of the Consiglio Nazionale delle Ricerche. Support for the metabolomic analysis was provided in part by the UCSD Christini Fund. The authors thank Karen Wroblewski DVM, Allen Animal Hospital, Livonia, MI for bringing this family of dogs to our attention.
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- Mitochondrial transporter