Upregulation of sphingomyelin and ABCA8 in response to TDP-43 pathology in amyotrophic lateral sclerosis brain

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing neurodegenerative disease characterized by the degeneration of motor neurons and the presence of TAR DNA-binding protein 43 (TDP-43) aggregation in the brain. Dyslipidemia is a common feature of ALS, and increasing evidence indicates that lipid dysregulation in the central nervous system underlies ALS pathology. Sphingomyelin is a sphingolipid that is highly enriched in the human brain. However, very little is known about changes in sphingomyelin in the context of ALS brain. We therefore undertook a comprehensive analysis of sphingomyelin in the disease-affected motor cortex and disease-unaffected cerebellum in sporadic ALS with TDP-43 pathology using liquid chromatography-mass spectrometry. We found that sphingomyelin was significantly increased in the ALS motor cortex compared to controls and was strongly associated with disease duration. In contrast, sphingomyelin was unaltered in the cerebellum. The increase in sphingomyelin was associated with an upregulation of ATP-binding cassette subfamily A member 8 (ABCA8), a sphingomyelin transporter, only in the motor cortex of ALS. Importantly, both sphingomyelin and ABCA8 were associated with TDP-43 only in the motor cortex. These results suggest that increases in sphingomyelin and ABCA8 could be a protective response against TDP-43 pathology.