Methods
We assessed spinal cord microglia in humans and mice with AMN and investigated the role of ABCD1 in microglial activity toward neuronal phagocytosis in cell culture. Because mutations in ABCD1 lead to incorporation of very-long-chain fatty acids into phospholipids, we separately examined the effects of lysophosphatidylcholine (LPC) upon microglia.
Objective
Mutations in ABCD1 cause the neurodegenerative disease, adrenoleukodystrophy, which manifests as the spinal cord axonopathy adrenomyeloneuropathy (AMN) in nearly all males surviving into adulthood. Microglial dysfunction has long been implicated in pathogenesis of brain disease, but its role in the spinal cord is unclear.
Results
Within the spinal cord of humans and mice with AMN, upregulation of several phagocytosis-related markers, such as MFGE8 and TREM2, precedes complement activation and synapse loss. Unexpectedly, this occurs in the absence of overt inflammation. LPC C26:0 added to ABCD1-deficient microglia in culture further enhances MFGE8 expression, aggravates phagocytosis, and leads to neuronal injury. Furthermore, exposure to a MFGE8-blocking antibody reduces phagocytic activity. Interpretation: Spinal cord microglia lacking ABCD1 are primed for phagocytosis, affecting neurons within an altered metabolic milieu. Blocking phagocytosis or specific phagocytic receptors may alleviate synapse loss and axonal degeneration. Ann Neurol 2017;82:813-827.