Dysregulation of SELENOI Is Associated with TDP-43 Neuropathology in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease, is characterized by progressive degeneration of motor neurons and accumulation of TAR DNA-binding protein 43 (TDP-43) in the brain. Increasing evidence indicates that aberration in lipid synthesis or regulation underlies neuronal dysfunction and degeneration. Phosphatidylethanolmine (PE) is an abundant phospholipid in the brain and is synthesized by the SELENOI gene. SELENOI is important in motor neuron development and function, as demonstrated in hereditary spastic paraplegia, a neurological disorder in which SELENOI is mutated. Despite this, virtually nothing was known about SELENOI in the context of ALS neuropathology. We therefore undertook a comprehensive assessment of PE in ALS brain tissues, using sophisticated liquid chromatography-mass spectrometry, and investigated how SELENOI regulates TDP-43 expression. PE levels were significantly decreased in the disease-affected motor cortex of ALS compared to controls and were inversely associated with disease duration. In contrast, PE levels were unaltered in the disease-unaffected cerebellum. Consistent with this, SELENOI expression was dysregulated only in the motor cortex of ALS. The correlation between SELENOI and TDP-43 was also lost in the motor cortex of ALS. A knockdown of SELENOI expression in neuronal cells caused an upregulation of TDP-43 expression. When put together, these results suggest that SELENOI dysregulation may contribute to TDP-43 pathology in ALS brain. Our study has provided new insights into an unrecognized pathway in ALS brain and revealed new targets for controlling TDP-43 pathology in ALS brain.