CERTL Reduces C16 Ceramide, Amyloid-β Levels and Inflammation in a Model of Alzheimer's Disease

Abstract

Background: Deregulation of ceramide and sphingomyelinlevels have been suggested tocontribute tothe pathogenesis of Alzheimer’s disease (AD).Ceramide transfer proteins (CERTs) are ceramide carriers, crucial for ceramide and sphingomyelin balance in cells.Extracellular forms of CERTs co-localize with amyloid-β (Aβ) plaques in AD brains. To date, the significance of these observations for the pathophysiology of AD remains uncertain.Methods: The plasmid expressing CERTL, the long isoform of CERTs, was used to study the interaction of CERTLwith amyloid precursor protein (APP) by co-immunoprecipitation and immunofluorescencein HEK cells.The recombinant CERTL protein wasemployed to study interaction of CERTLwith amyloid-β (Aβ), Aβ aggregation process in presence of CERTL, and the resulting changes inAβ toxicity in neuroblastoma cells. CERTLwas overexpressed in neurons by adeno associatedvirus (AAV) in a familial mouse model of familial AD (5xFAD). Ten weeks after transduction animal were challenged with behavior tests for memory, anxiety and locomotion. At week twelve brains were investigated for sphingolipid levels by mass spectrometry, plaques and neuroinflammation by immunohistochemistry, gene expression and/or immunoassay.Results:Here, we report that CERTL, binds to APP, modifies Aβ aggregation and reduces Aβ neurotoxicity in vitro. Furthermore, we show that intracortical injection of AAV, mediating the expression of CERTL, decreases levels of ceramide d18:1/16:0 and increases sphingomyelin levels in the brain of male transgenic mice, modelling familial AD (5xFAD). CERTLin vivo over-expression hasa mild effect on animal locomotion and decreases Aβ formation and modulates microglia by decreasing their pro-inflammatory phenotype.Conclusion: Our results demonstratea crucial role of CERTL in regulatingceramidelevels in the brain, in amyloid plaque formation and neuroinflammation,thereby opening research avenuesfor therapeutic targets of AD and other neurodegenerative diseases.

Sphingomyelin 16:0 is a therapeutic target for neuronal death in acid sphingomyelinase deficiency

“…These enzymes show differences in their levels of expression depending on the tissue, cell type and subcellular compartment [4][5][6][7]. Adding further complexity, numerous SM species exist that differ in the length and degree of unsaturation of their fatty acids, and these different species have distinct subcellular localization, metabolism and properties [8][9][10] .…”

Plasma ceramides relate to mild cognitive impairment in middle‐aged men: The Maastricht Study

“…Nevertheless, lipidomic, metabolomic, and targeted approaches have identified pathways of lipids and enzymes of the sphingolipid metabolism that are altered early in the course of AD and contribute to the neuropathological alterations associated with AD. 1,[4][5][6] Sphingolipid metabolites like sphingosine-1-phosphate (S1P) have additionally been implicated in neuroinflammation and neurodegeneration. 1 Along these lines, previous longitudinal studies examining blood sphingolipids reported that high levels of multiple ceramide species predicted cognitive impairment among cognitively unimpaired individuals, 7 as well as memory decline, hippocampal volume loss, 8 and faster rates of cognitive decline among AD patients.…”

“…Ceramides are produced in the endoplasmic reticulum of neurons and glia, and transported from the endoplasmic reticulum to the trans-Golgi regions of these cells by ceramide transporter proteins (CERTs). 5 CERTs are ubiquitously expressed in the CNS, where they are involved in brain development and homeostasis and transport ceramide to membranes via its steroidogenic acute regulatory protein (StAR)-related lipid transfer domain. 2,5,10,11 Specifically, they are known to transfer ceramide C14, C16, C18, and C20 chains.…”

“…5 CERTs are ubiquitously expressed in the CNS, where they are involved in brain development and homeostasis and transport ceramide to membranes via its steroidogenic acute regulatory protein (StAR)-related lipid transfer domain. 2,5,10,11 Specifically, they are known to transfer ceramide C14, C16, C18, and C20 chains. In the brain, the long isoform (CERTL) containing an additional 26-amino acid domain has been identified in AD to partially co-localize with serum amyloid P component and amyloid beta in plaques.…”

“…12 In a transgenic mouse model of AD, CERTL levels are reduced in the AD brain and overexpression of CERTL in neurons affects plasma ceramide C16 levels. 5 However, the relationship of plasma CERTs with levels of specific ceramide chain lengths in the blood is currently unknown, as well as the associations among plasma CERT levels, cognition, and brain atrophy.…”