Phosphatidylinositol 4,5-Bisphosphate-Dependent Interaction of Myelin Basic Protein with the Plasma Membrane in Oligodendroglial Cells and Its Rapid Perturbation by Elevated Calcium

Abstract

Myelin basic protein (MBP) is an essential structural component of CNS myelin. The electrostatic association of this positively charged protein with myelin-forming membranes is a crucial step in myelination, but the mechanism that regulates myelin membrane targeting is not known. Here, we demonstrate that phosphatidylinositol 4,5-bisphosphate (PIP2) is important for the stable association of MBP with cellular membranes. In oligodendrocytes, overexpression of synaptojanin 1-derived phosphoinositide 5-phosphatase, which selectively hydrolyzes membrane PIP2, causes the detachment of MBP from the plasma membrane. In addition, constitutively active Arf6/ Q67L induces the formation of PIP2-enriched endosomal vacuoles, leading to the redistribution of MBP to intracellular vesicles. Fluorescence resonance energy transfer imaging revealed an interaction of the PIP2 sensing probe PH-PLC␦1 with wild-type MBP, but not with a mutant MBP isoform that fails to associate with the plasma membrane. Moreover, increasing intracellular Ca 2ϩ , followed by phospholipase C-mediated PIP2 hydrolysis, as well as reduction of the membrane charge by ATP depletion, resulted in the dissociation of MBP from the glial plasma membrane. When the corpus callosum of mice was analyzed in acute brain slices by electron microscopy, the reduction of membrane surface charge led to the loss of myelin compaction and rapid vesiculation. Together, these results establish that PIP2 is an essential determinant for stable membrane binding of MBP and provide a novel link between glial phosphoinositol metabolism and MBP function in development and disease.

Pals1 Is a Major Regulator of the Epithelial-Like Polarization and the Extension of the Myelin Sheath in Peripheral Nerves

“…However, their distributions were not exclusive, probably because of their limited specificity (Várnai and Balla, 2007) and because of their toxicity, which limited their use to less mature myelinating cells. Recently, the compact myelin protein MBP has been shown to interact with the plasma membrane via PIP2 binding (Nawaz et al, 2009), suggesting that the compact myelin may contain PIP2. In our experiments, the PIP2 probe was not detected in compact myelin.…”

“…Interestingly, compact myelin proteins such as PMP22 and P0 are expressed in tight or tight-like junctions of the apical domain of epithelial cells (D'Urso et al, 1990;Doyle et al, 1995;Notterpek et al, 2001). In addition, the compact myelin protein MBP binds to PIP2 (Nawaz et al, 2009), which is a marker of the apical domain (MartinBelmonte et al, 2007). Together these data indicate that the compact myelin, which is the largest and the most characteristic compartment of myelinating cells, belongs to the apical-like domain of myelinating SCs.…”

Phosphoinositide Control of Membrane Protein Function: A Frontier Led by Studies on Ion Channels

“…These mutations are linked to a form of long-QT syndrome, causing debilitating cardiac arrhythmias and the potential for sudden cardiac death (9). Notable examples involving the nervous system are neurodegenerative disorders [such as Alzheimer’s disease (AD), in which the oligomeric amyloid-β peptide that accumulates in AD patients decreases PI(4,5)P 2 levels (10)], mental retardation [such as Down’s syndrome, or trisomy 21, in which the gene coding for the lipid phosphatase synaptojanin is localized to chromosome 21q and is overexpressed (11)], and demyelinating diseases [such as multiple sclerosis, in which the myelin basic protein, an essential component of the myelination pathway, fails to localize to the membrane when its interactions with PI(4,5)P 2 are disrupted (12)].…”

MOBP levels are regulated by Fyn kinase and affect the morphological differentiation of oligodendrocytes

“…It has been proposed that the ability of MBP to polymerize is stimulated by structural changes upon contact with the membrane, which could then lead to the formation of a growing protein meshwork that develops into membrane sheets in cultured cells, resembling compact myelin structures in vivo (Aggarwal et al, 2011;Bakhti et al, 2014). MBP binds to the membrane in a phosphatidylinositol 4,5-bisphosphate [PI(4,5)P 2 ]-dependent way (Nawaz et al, 2009), but it is not known where exactly MBP initially associates with the membrane and how this is controlled. Fyn is localized in lipid raft membrane microdomains (Krämer et al, 1999) and PI(4,5)P2-enriched lipid rafts have been connected to surface motility (Golub and Caroni, 2005).…”