Unrevealing mechanisms of gabaergic control of neuro-schwann cell interaction in peripheral neuropathies

The peripheral neuropathies are a health problem of heterogenuos etiology for which reliable treatments are still not available. The GABAergic ligands might be novel promising factors for such a therapy. Indeed, the importance of the GABAergic system has been demonstrated in the PNS. GABA and its receptors (GABA-A and GABA-B) are functionally active in the Schwann cells, where they participate in the control of cell proliferation, myelination and cell functions. In particular, the study of GABA-B1 total deficient mice showed that several biochemical (myelin proteins expression), morphological [number of small myelinated fibers and small dorsal root ganglia (DRG) neurons] and functional (nociception sensitivity and locomotor control) parameters of the PNS depend on GABA-B receptors. Therefore, GABA-B1 deficient mice showed altered myelin sheaths, suggesting a specific Schwann cell autonomous effect, although a specific involvement of the peripheral neuronal compartment (e.g. the small DRG neurons) was also hypothesized. To address this assumption we analyzed the conditional mice in which the GABA-B1 receptor was specifically missing in the Schwann cells. Biochemical, morphologic and morphometric evaluations as well as behavioral and nociceptive analysis were performed on the PNS of the conditional knockout mice. Our findings clearly indicated myelin changes with increased myelin proteins and myelin abnormalities, but also increased number of small unmyelinated fibers and Remak bundles. The mice were hyperalgesic, allodynic a presented gait alterations. Altogether the changes observed emphasized a cell autonomous effect consequent to the specific GABA-B1 knockout in Schwann cells. However, the axon modifications also suggested Schwann cell non-autonomous effects, through the neuronal compartment. Moreover, given these findings, that partially differ from data previously obtained in GABA-B1 total knockout mice, we propose that some compensation mechanisms occur in the neuronal compartment. Further investigations to determine the fine mechanisms regulating these processes are needed.



In the present RENEWAL we propose to study
in vitro
preparations of primary pure culture of sensitive DRG neurons and Schwann cells from P0-CRE/GABA-B1fl/fl (experimental) and GABA-B1fl/fl (control) mice, which will be analyzed separately or in co-culture system. The co-culture system is a helpful method which allows the manipulation of the microenvironment in a way that is not possible
in vivo.
Parameters of cell morphology, vitality, proliferation and
in vitro
myelination will be assessed. This research will be particularly relevant for the identification of novel therapeutic strategies for the treatment of peripheral neuropathies (such as CMT diseases), handling of associated chronic pain and managing of the phenotype. This is a challenge for basic neurologists since a reliable therapy of these pathologies is still not available. Thus, our project may contribute to the understanding of the mechanisms related to the neuromuscular diseases and is of relevance to the purposes of AFM association.