engleski

Compositional changes of brain gangliosides lead to dispersal of cell adhesion molecule neuroplastin from the lipid raft fractions

Lipid rafts are membrane microdomains characterized by high content of cholesterol, sphingomyelin and glycosphingolipids, particularly gangliosides. Gangliosides are especially important for modulating various cellular events in mammalian brain, such as signal transduction, adhesion, and cellular recognition. There is strong evidence that ganglioside composition ensures correct positioning and functions of specific membrane proteins through interactions of gangliosides and proteins within membrane subdomains. In addition, any disturbance of ganglioside composition leads to changes in lipid raft integrity. In our previous work, we have reported altered expression and distribution of transmembrane glycoprotein neuroplastin (Np) in hippocampus of mice lacking complex gangliosides. Np is a cell adhesion molecule involved in promoting neurite outgrowth, regulation of structure and function of synapses and synaptic plasticity. The aim of this study was to analyze membrane positioning of Np within specific membrane subdomains - lipid rafts and non-rafts, in cortical tissue of mice with aberrant ganglioside synthesis. Cortical tissue was dissected from brains of B4galnt1 knock-out (KO) and St3gal2/3 double knock-out (DKO) mice and their corresponding wild-type (WT) controls. The phenotype of KO mice includes demyelination and motor deficits, and is characterized by complete absence of all complex brain gangliosides. DKO mice have a distinctly different brain ganglioside composition with overexpression of complex gangliosides GM1 and GD1b and lack of GD1a and GT1b, which leads to more severe phenotype including neurological and motor deficits. In our study membrane proteins were isolated from brain tissue homogenates and segregated in lipid raft and non-raft domains using a procedure for lipid raft isolation modified in our laboratory. Neuroplastin distribution within the specific membrane fractions was analyzed using Western blotting and quantification by ImageJ. We report changed total cortical Np expression in both mouse models with aberrant ganglioside composition as compared to WT mice, more prominently in KO mice. Also, we show different positioning of Np within membrane subdomains depending on ganglioside composition. Specifically, Np is redistributed and dispersed from lipid raft to non-raft domains in analyzed cortical tissue of both KO and DKO mice when compared to WT animals. Observed alteration of Np expression and positioning within the membrane is related to documented specific changes in ganglioside composition in brain tissue of mouse models with disrupted ganglioside biosynthesis. Our results clearly demonstrate that Np expression and submembrane distribution depends on specific ganglioside milieu. Further investigation is needed in order to clarify the exact interaction of Np and gangliosides as well as functional consequences of Np redistribution caused by changed ganglioside environment.

Neuroplastin ; Gangliosides ; Lipid rafts

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