CERTL reduces C16 ceramide, amyloid-β levels, and inflammation in a model of Alzheimer’s disease

Abstract

Background Dysregulation of ceramide and sphingomyelin levels have been suggested to contribute to the pathogenesis of Alzheimer’s disease (AD). Ceramide transfer proteins (CERTs) are ceramide carriers which are 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 A plasmid expressing CERTL, the long isoform of CERTs, was used to study the interaction of CERTL with amyloid precursor protein (APP) by co-immunoprecipitation and immunofluorescence in HEK cells. The recombinant CERTL protein was employed to study interaction of CERTL with amyloid-β (Aβ), Aβ aggregation process in presence of CERTL, and the resulting changes in Aβ toxicity in neuroblastoma cells. CERTL was overexpressed in neurons by adeno-associated virus (AAV) in a mouse model of familial AD (5xFAD). Ten weeks after transduction, animals were challenged with behavior tests for memory, anxiety, and locomotion. At week 12, 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 5xFAD mice. CERTL in vivo over-expression has a mild effect on animal locomotion, decreases Aβ formation, and modulates microglia by decreasing their pro-inflammatory phenotype. Conclusion Our results demonstrate a crucial role of CERTL in regulating ceramide levels in the brain, in amyloid plaque formation and neuroinflammation, thereby opening research avenues for therapeutic targets of AD and other neurodegenerative diseases.

Ceramide Transfer Protein (CERT): An Overlooked Molecular Player in Cancer

“…The embryonic cells in CERT knockout mice exhibit a reduced level of sphingomyelin in the plasma membrane and an increased level of ceramide in the ER and mitochondria [160,161]. Consistently, adeno-associated virus-mediated overexpression of CERT L decreases ceramide but increases sphingomyelin in the cortex of mice [162].…”

“…Thus, the CERT might be a determinant of cancer development by dictating the ratio of ceramide to sphingomyelin. In addition to regulating ceramide and sphingomyelin, CERT L is also implicated in several cellular and physiological functions via physical interaction with other proteins [162,191,192]. Here we summarize the biological functions of both short and long-form of CERT (Figure 4).…”

“…CERT L is highly expressed in neurons of the cerebral cortex, formation of the hippocampus, basal ganglia and the olfactory and nuclei of the thalamus than other regions of the adult rat brain, suggesting it might play a critical role in neuron functions of the central nervous system [213]. CERT L can physically interact with amyloid precursor protein [162]. CERT L inhibits the spontaneous fibrillization of amyloid β in vitro and protects SHSY-5Y human neuroblastoma cells from amyloid β-induced toxicity [162].…”

Disentangling Mitochondria in Alzheimer’s Disease

“…A cell-permeable analog of ceramide, C6-ceramide, was shown to increase the generation of Aβ by post-translationally stabilizing BACE1 [ 250 ]. Ceramide transfer proteins bind to APP and reduce Aβ aggregation and neurotoxicity in vitro and in vivo [ 251 ]. Astrocyte-derived extracellular vesicles in AD mice and AD patients were shown to be enriched in ceramide and associated with Aβ [ 252 ].…”

Ceramide Metabolism Enzymes—Therapeutic Targets against Cancer

“…CerS is a family of six different isoforms, each of which synthesizes ceramides with different chain lengths of fatty acyl-CoA, resulting in a specific activity. This fact is important, since, for example, CerS1 generates 18-carbon Cer (C 18:0 -Ceramide) that inhibits tumor growth [ 73 ], whereas CerS5/6 produces C 16:0 -Ceramide, an anti-apoptotic metabolite in human head and neck squamous cell carcinomas [ 74 ] that is also involved in type II diabetes [ 17 , 33 , 75 ] and that has proinflammatory properties [ 76 ]. Interestingly, a specific inhibitor of CerS1, called P053, has been described to reduce the levels of C 18:0 -Ceramide in renal HEK 293 cancer cells [ 77 ].…”