Aggregation of MBP in chronic demyelination

Abstract

ObjectivesMisfolding of key disease proteins to an insoluble state is associated with most neurodegenerative conditions, such as prion, Parkinson, and Alzheimer’s diseases. In this work, and by studying animal models of multiple sclerosis, we asked whether this is also the case for myelin basic protein (MBP) in the late and neurodegenerative phases of demyelinating diseases.MethodsTo this effect, we tested whether MBP, an essential myelin component, present prion-like properties in animal models of MS, as is the case for Cuprizone-induced chronic demyelination or chronic phases of Experimental Autoimmune Encephalomyelitis (EAE).ResultsWe show here that while total levels of MBP were not reduced following extensive demyelination, part of these molecules accumulated thereafter as aggregates inside oligodendrocytes or around neuronal cells. In chronic EAE, MBP precipitated concomitantly with Tau, a marker of diverse neurodegenerative conditions, including MS. Most important, analysis of fractions from Triton X-100 floatation gradients suggest that the lipid composition of brain membranes in chronic EAE differs significantly from that of naïve mice, an effect which may relate to oxidative insults and subsequently prevent the appropriate insertion and compaction of new MBP in the myelin sheath, thereby causing its misfolding and aggregation.InterpretationPrion-like aggregation of MBP following chronic demyelination may result from an aberrant lipid composition accompanying this pathological status. Such aggregation of MBP may contribute to neuronal damage that occurs in the progressive phase of MS.

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“…Along these lines, a recent study also suggested that myelin membrane lipid composition may be altered under two models of demyelination. In this work, MBP surface localization to myelinated processes by immunohistochemistry was diminished, while total MBP levels remained unchanged (88). Additionally, a study investigating the role of mammalian target of rapamycin in oligodendrocyte differentiation observed maintenance of normal myelin protein levels despite a significant reduction in the number of maturing oligodendrocytes (89).…”

“…Thus, our data suggest that PIs inhibit oligodendrocyte maturation through an alternate mechanism. An intriguing possibility is whether PIs disrupt the crucially important myelin-lipid balance, which may result in inappropriate organization of myelin components, as previously reported (87, 88, 92, 93). Because PIs have been shown to cause dyslipidemia in patients and in non-CNS cell types (71, 94, 95), this could contribute to the white matter loss seen in HAND patients (17, 19).…”

Structural adaption of axons during de‐ and remyelination in the Cuprizone mouse model

“…Along these lines, another group showed changes in the protein structure of myelin after cuprizone treatment. Although the amount of myelin basic protein (MBP) in cuprizone‐treated mice was not reduced, the protein aggregated in an insoluble form in the pellet of brain homogenates from cuprizone‐treated mice, which was not observed in control brains or prion‐infected brain . This finding could explain the susceptibility of cuprizone‐treated tissue to detergents (own observations).…”

Short-term fructose ingestion affects the brain independently from establishment of metabolic syndrome

“…In the CNS, myelin basic protein (MBP) found in myelinating oligodendrocytes is indispensable for the formation of myelin sheath [19]. Notable reduction in MBP depicts disruption in myelin stability, causing degradation of myelin sheath and resultant loss [19,20]. Mitochondrial biogenesis is crucial for cell function and its failure can have important implications for the pathogenesis of various neurodegenerative diseases [21]; therefore, we also examined molecular systems associated with mitochondria, notably PGC-1α and COX2 [9].…”