Via Luigi Vanvitelli 32
Membrane trafficking in oligodendrocyte differentiation
The present work of the laboratory exploits our documented expertise in cell biology and protein trafficking to investigate the cellular and molecular mechanisms involved in oligodendrocyte (OL) development. OLs are the myelinating cells of the central nervous system (CNS) and their malfunctioning accompanies defective myelination associated to a number of neurological disorders.
Immature OL (green) and myelinating OLs (blue) that enwrap axons (red)
Current research interests include the following topics:
Analysis of GPR17 trafficking in differentiating OLs.
Deciphering the mechanisms of myelination defects linked to Trisomy 21 and additional pathologies associated to OL dysfunction.
Detailed research activity
The OL developmental program begins with specification of oligodendrocyte progenitor cells (OPCs) during late embryonic gestation. Postnatally, OPCs differentiate through pre-myelinating stages to become mature OLs with many branched processes that wrap around axons and form membrane sheaths of myelin. OL differentiation is regulated by a complex interplay of intrinsic, epigenetic and extrinsic factors, including the G protein-coupled receptor (GPCR)referred to as GPR17 an intrinsic timer of OL differentiation.
Analysis of GPR17 trafficking
GPR17 is highly expressed in the early phase of OL differentiation but must be down regulated to allow immature-OL to differentiate into myelinating cells (Fig. 1, immature OL expressing GPR17, but not the myelin protein MBP).
One aim of our work is to understand the mechanisms underlying the tightly regulation of GPR17. Recently we focused our attention on the receptor endocytic trafficking and demonstrated that in differentiating OLs, GPR17 can be sorted to lysosomes or recycled to the plasma membrane via a Rab4-dependent pathway.
Since balance between degradation and recycling is expected to modulate the levels of GPR17 at the cell surface with implications for OL differentiation, we have further characterized the mechanisms of the receptor sorting in the endosomes by focusing on the role of its C-terminal PDZ binding motif. We demonstrated that i) the PDZ binding motif is required for receptor recycling to the cell surface by means of interaction with the retromer complex-associated protein SNX27 (Fig. 2: co-localisation of native internalized GPR17 with SNX27 in endocytic vesicles) and ii) SNX27 knockdown determines an accelerated sorting of GPR17 into lysosomes. Interestingly, the increased degradation of GPR17 in pre-myelinating cells determines a premature OL maturation.
Myelination defects in trisomy 21 brain
The above data suggest that pathologies altering the levels of SNX27/retromer complexes may affect myelination in brain. Since SNX27 is down regulated in Down’s syndrome, we decide to investigate OL maturation and myelination in a mouse model of Trisomy 21.
While it is well known that trisomy 21 causes various neuro-anatomical abnormalities, including impaired neurogenesis and neuronal differentiation, less information is available on myelin and OL differentiation. Our Analysis of brain sections demonstrated a decrease in GPR17+ immature-OL paralleled by an increase in more mature CC1+OL. However, we detected a decrease in myelinated fibers in various regions of Ts65Dn brains, including cortex (CTX) and corpus callosum (CC) (Fig. 3). Altogether this data indicate a defective myelination in Down syndrome brain potentially mediated by multiple mechanisms.
Abbracchio Maria Pia e Stefania Ceruti, Universita degli Studi di Milano
Bartesaghi Renata, Università degli Studi di Bologna
Buffo Annalisa , Università degli Studi di Torino
Meraviglia V, Ulivi AF, Boccazzi M, Valenza F, Fratangeli A, Passafaro M, Lecca D, Stagni F, Giacomini A, Bartesaghi R, Abbracchio MP, Ceruti S, Rosa P. 2016. SNX27, a protein involved in down syndrome, regulates GPR17 trafficking and oligodendrocyte differentiation. Glia. 64:1437-1460. doi: 10.1002/glia.23015.
Boda E, Di Maria S, Rosa P, Taylor V, Abbracchio MP, Buffo A. 2015. Early phenotypic asymmetry of sister oligodendrocyte progenitor cells after mitosis and its modulation by aging and extrinsic factors. Glia 63:271-86. doi: 10.1002/glia.22750.
Condliffe SB, Fratangeli A, Munasinghe NR, Saba E, Passafaro M, Montrasio C, Ferrari M, Rosa P, Carrera P. 2013. The E1015K variant in the synprint region of the CaV2.1 channel alters channel function and is associated with different migraine phenotypes. J Biol Chem.
Knospe M, Müller CE, Rosa P, Abdelrahman A, von Kügelgen I, Thimm D, Schiedel AC. (2013) The rat adenine receptor: pharmacological characterization and mutagenesis studies to investigate its putative ligand binding site.Purinergic Signal. 9:367-381. doi: 10.1007/s11302-013-9355-6.
Fratangeli A, Parmigiani E, Fumagalli M, Lecca D, Benfante R, Passafaro M, Buffo A, Abbracchio MP, Rosa P. (2013). The regulated expression, intracellular trafficking and membrane recycling of the P2Y-like receptor GPR17 in Oli-neu oligodendroglial cells. J Biol Chem. 288:5241-5246.
Boda E, Viganò F, Rosa P, Fumagalli M, Labat-Gest V, Tempia F, Abbracchio MP, Dimou L, Buffo A. (2011).The GPR17 receptor in NG2 expressing cells: Focus on in vivo cell maturation and participation in acute trauma and chronic damage. Glia. 59, 1958-1973
Rosa P, Fratangeli A. 2010 Cholesterol and synaptic vesicle exocytosis. Commun Integr Biol. 3:352-353.
Linetti A, Fratangeli A, Taverna E, Valnegri P, Francolini M, Cappello V, Matteoli M, Passafaro M, Rosa P. (2010). Cholesterol reduction impairs exocytosis of synaptic Vesicles. J Cell Sci. 123, 595-605