Quantitative Profiling of Brain Lipid Raft Proteome in a Mouse Model of Fragile X Syndrome

Abstract

Fragile X Syndrome, a leading cause of inherited intellectual disability and autism, arises from transcriptional silencing of the FMR1 gene encoding an RNA-binding protein, Fragile X Mental Retardation Protein (FMRP). FMRP can regulate the expression of approximately 4% of brain transcripts through its role in regulation of mRNA transport, stability and translation, thus providing a molecular rationale for its potential pleiotropic effects on neuronal and brain circuitry function. Several intracellular signaling pathways are dysregulated in the absence of FMRP suggesting that cellular deficits may be broad and could result in homeostatic changes. Lipid rafts are specialized regions of the plasma membrane, enriched in cholesterol and glycosphingolipids, involved in regulation of intracellular signaling. Among transcripts targeted by FMRP, a subset encodes proteins involved in lipid biosynthesis and homeostasis, dysregulation of which could affect the integrity and function of lipid rafts. Using a quantitative mass spectrometry-based approach we analyzed the lipid raft proteome of Fmr1 knockout mice, an animal model of Fragile X syndrome, and identified candidate proteins that are differentially represented in Fmr1 knockout mice lipid rafts. Furthermore, network analysis of these candidate proteins reveals connectivity between them and predicts functional connectivity with genes encoding components of myelin sheath, axonal processes and growth cones. Our findings provide insight to aid identification of molecular and cellular dysfunctions arising from Fmr1 silencing and for uncovering shared pathologies between Fragile X syndrome and other autism spectrum disorders.

SMN affects membrane remodelling and anchoring of the protein synthesis machinery

“…In particular, the netrin receptor DCC, which anchors protein synthesis machinery in neurons (Tcherkezian et al, 2010), partially localizes at lipid rafts and this association is required for axon outgrowth (Hérincs et al, 2005). Importantly, deficiency of the RNAbinding protein FMRP changes lipid rafts properties (Kalinowska et al, 2015). In contrast to SMN, ribosomal subunits are present only in plasma membrane preparations from unstimulated fibroblasts.…”

Of Men and Mice: Modeling the Fragile X Syndrome

“…FXS is associated with a vast misregulation of protein expression, not only in the context of mGluR signaling, but also with respect to proteins regulating other aspects of neuronal excitability such as Calmodulin or Neuroligin for instance (Liao et al, 2008 ; Matic et al, 2014 ; Kalinowska et al, 2015 ; Tang et al, 2015 ). Although it is not clear yet whether abnormal mGluR-LTD directly impacts on the balance of excitatory and inhibitory activity in neuronal networks (E/I balance), mGluR signaling is able to alter the excitability of neurons by increasing the intrinsic conductance (Bianchi et al, 2009 ; Tang and Alger, 2015 ).…”

The role of cholesterol metabolism and various steroid abnormalities in autism spectrum disorders: A hypothesis paper

“…The largest pool of cholesterol exists in myelin membranes and disorders that interfere with sterol and cholesterol synthesis cause hypomyelination [Saher & Stumpf, ]. In addition, myelination abnormalities have been detected in patients with Fragile X syndrome suggesting that dysfunctions of myelination at the cellular and/or circuitry level may play a role in the pathological manifestations of this syndrome [Kalinowska, Castillo, & Francesconi, ]. Also, in autism in general, abnormalities in white matter integrity and in functional connectivity have been demonstrated [Kana, Libero, Hu, Deshpande, & Colburn, ; Travers et al, ] supporting the interdependence of sterol/lipid metabolism and autism.…”