The development of the nervous system depends on dynamic processes that require intense, spatially and temporally regulated cross talk between neurons and their surrounding glial cells. In particular, during both development and nerve fiber repair, motor and sensory axons grow and differentiate in close association with Schwann cells (SCs) that proliferate and migrate along the nerve fibers and drive growth cones to their specific targets. The factors responsible for the interaction between axons and SCs have been only in part identified. Neurotransmitters and their receptors are early expressed during nervous system development suggesting their involvement also in the modulation of axon-glia interaction. The study of the modulation of SC proliferation and differentiation appears relevant to identify new molecules that may play strategic roles in the treatment of nerve regeneration and of acquired peripheral neuropathies.
Recently we demonstrated that Acetylcholine (ACh) via M2 muscarinic receptor activation, inhibited SC proliferation and enhanced differentiation. Our data suggest that M2 receptor may promote SC progression into a differentiated myelinating phenotype, also contributing to the compact myelin organization. Furthermore, it has also been demonstrated the existence of an axo-glial signaling pathway between axonal Neurexins and Neuroligin 3 expressed on oligodendrocytes (OL) and that this contact may contribute to myelinogenesis, to the maintenance of established myelination and to differentiation state of the OL.
In order to better characterize the signals involved in myelinating processes, in particular in peripheral nervous system, we propose to investigate the role of ACh and Neurolighins in regulating peripheral myelination using different in vitro models
Our project proposes to investigate new mechanisms and signalling pathways involved in myelin formation in peripheral nervous system. The neuron-glia co-cultures will allow to have an in vitro system for studying myelination. The model proposes to use purified cultures of Dorsal root ganglia explants and Schwann cells obtained from sciatic nerves. Myelination can be observed in co-cultures after a period of at least 20 days, in the presence of a specific cocktail of growth factors. This experimental approach may be use to analyse the effects of cholinergic mimetics in the control of myelination processes. Another important novelty is the use of a new cell model system, the dASC, that may represent an alternative therapeutic tool for peripheral injuries. These cells can be obtained by adipose mesenchymal stem cells through a differentiation protocol published by Kingham et al, 2011 and Razavi et al, 2012. They proliferate rapidly in culture, can be transplanted, and successfully integrate into the host tissue. These cells are able to myelinate and may represent an interesting alternative to study the effects of cholinergic mimetics in vitro.
Neuronal cell adhesion proteins are emerging as multiple organizers in the central nervous system mainly in the formation of neuron-neuron synapses (Mackowiak et al., 2014) and with a possible role in the process of myelination (Proctor et al, 2015). Here we propose to explore new functions for the Neuroligins, specifically NL3, in the myelination process in the peripheral nervous system. We propose to dissect DRG from the NL3 R451C Knock-in mouse, a consolidated mouse model of a monogenic form of autism, expressing a mutation (R451C), found in humans, and characterized by impaired cell surface expression. This mouse strain is already available in our departmental animal house.
We believe this project to be innovative for the topic and the model systems that we propose to use. The results obtained may offer new information on the mechanisms modulating the myelin formation that may have a relevant impact on the study and therapeutic treatment of de-myelinating pathologies.
References
De Jaco A, Lin MZ, Dubi N, Comoletti D, Miller MT, Camp S, Ellisman M, Butko MT, Tsien RY, Taylor P. Neuroligin trafficking deficiencies arising from mutations in the alpha/beta-hydrolase fold protein family. J Biol Chem. 2010; 285:28674-82.
Gilbert M, Smith J, Roskams AJ, Auld VJ. Neuroligin 3 is a vertebrate gliotactin expressed in the olfactory ensheathing glia, a growth-promoting class of macroglia. Glia 2001; 34:151¿164.
Kingham PJ, Mantovani C, Terenghi G. Stem cell and neuron co-cultures for the study of nerveregeneration. Methods Mol Biol. 2011;695:115-27.
Loreti S., Ricordy R., De Stefano M.E.,Augusti-Tocco G. and Tata A.M. Acetylcholine inhibits cell cycle progression in cultured rat Schwann cells by activation of M2 receptor subtype. Neuron Glia Biology, 2007, 3 : 269-279.
Mackowiak M, Mordalska P, W¿dzony K. Neuroligins, synapse balance and neuropsychiatric disorders. Pharmacol Rep. 2014; 66:830-5.
Proctor DT, Stotz SC, Scott LO, de la Hoz CL, Poon KW, Stys PK, Colicos MA. Axo-glial communication through neurexin-neuroligin signaling regulates myelination and oligodendrocyte differentiation. Glia 2015; 63:2023¿2039
Razavi S, Ahmadi N, Kazemi M, Mardani M, Esfandiari E Efficient transdifferentiation of human adipose-derived stem cells into Schwann-like cells: A promise for treatment of demyelinating diseases. Adv Biomed Res. 2012;1:12.
R. Douglas Fields, Dipankar J. Dutta, Jillian Belgrad, and Maya Robnett. Cholinergic Signaling in Myelination. Glia, 2017, DOI: 10.1002/glia.23101
S. Loreti, M. T. Vilaró, S. Visentin; H. Rees, A. I. Levey and A. M. Tata. Rat Schwann cells express M1-M4 muscarinic receptor subtypes. J. Neurosci. Res. 2006, 84: 97-105
Sudhof TC. Neuroligins and neurexins link synaptic function to cognitive disease. Nature. 2008;455:903-11.
Tabuchi K, Blundell J, Etherton MR, Hammer RE, Liu X, Powell CM, Südhof TC. A neuroligin-3 mutation implicated in autism increases inhibitory synaptic transmission in mice. Science. 2007; 318:71-6.
Taveggia C, Feltri L, Wrabetz L.(2010). Signals to promote myelin formation and repair: Nature Rev Neurobiol 2010, 6: 276-287.
Uggenti C, De Stefano ME, Costantino M, Loreti S, Pisano A, Avallone B, Talora C, Magnaghi V, Tata AM. M2 muscarinic receptor activation regulates Schwann cell differentiation and myelin organization. Dev Neurobiol. 2014 Jul;74(7):676-91.
V. Magnaghi, P. Procacci, A.M.Tata. Novel pharmacological approaches to Schwann cells as neuroprotective agents for peripheral nerve regeneration. Int. Rev Neurobiol 2009, 87:295-315.