ApoE4 disrupts interaction of sortilin with fatty acid-binding protein 7 essential to promote lipid signaling

Abstract

Sortilin is a receptor for neuronal uptake of apolipoprotein E. Sortilin-dependent uptake of lipidated apoE promotes conversion of polyunsaturated fatty acids (PUFA) into neuromodulators that induce anti-inflammatory gene expression in the brain. This neuroprotective pathway works with apoE3 but is lost with apoE4, the main risk factor for Alzheimers disease (AD). Here, we elucidated steps in cellular handling of lipids through sortilin, and why they are disrupted by apoE4. Combining unbiased proteome screens with analyses in mouse models, we uncover interaction of sortilin with fatty acid-binding protein (FABP) 7, the intracellular carrier for PUFA in the brain. In the presence of apoE3, sortilin promotes functional expression of FABP7 and its ability to elicit lipid-dependent gene transcription. By contrast, apoE4 binding blocks sortilin sorting, causing catabolism of FABP7 and impairing lipid signaling. Reduced FABP7 levels in the brain of AD patients expressing apoE4 substantiate the relevance of these interactions for neuronal lipid homeostasis. Taken together, we document interaction of sortilin with mediators of extracellular and intracellular lipid transport that provides a mechanistic explanation for loss of a neuroprotective lipid metabolism in AD. SUMMARY STATEMENTLipids are central to brain health and defects in brain lipid homeostasis are causal to neurodegenerative processes in Alzheimers disease. Here, we uncovered how the neuronal lipoprotein receptor sortilin interacts with apoE and FABP7, the carriers for extra- and intracellular transport of lipids in the brain, respectively. We show that this interaction enables lipids to control gene transcription via nuclear receptors; and why this presumed neuroprotective lipid action is disturbed in humans who carry the {varepsilon}4 variant of apoE, the most important risk factor for sporadic Alzheimers disease.