Studio della funzionalità del sistema GABAergico nel Sistema nervoso Periferico mediante l'utilizzo di topi transgenici con mutazione condizionale per il recettore GABA-B1 nelle cellule di Schwan

The peripheral neuropathies are a health problem of heterogeneous etiology for which reliable treatments are still not available. Based on our results, the GABAergic ligands might be novel promising factors for therapy.



The relevance of GABAergic system, indeed, has been recently demonstrated in the PNS. In particular, the GABA-A and GABA-B receptors are functionally active in the Schwann cells, where participate in the control of cell proliferation and myelination. Very recent studies performed in GABA-B1-deficient mice revealed that several biochemical, morphological and functional parameters of the PNS depend on GABA-B receptors. For instance GABA-B1-deficient mice show morphological and molecular alterations in myelin, including changes in the expression of the myelin proteins PMP22 and P0. Moreover, small myelinated fibers and small DRG neurons were more abundant in GABA-B1-deficient mice. Therefore, GABA-B1 deficient mice showed altered myelin sheaths, although an involvement of the neuronal PNS compartment (e.g. the small DRG neurons or motoneurons) might be also hypothesized. Altogether our data evidenced the importance of GABA-B receptors in PNS myelination. However, these mice presented changes in sensory functions, supporting the role of GABA-B receptors also in the peripheral nociception. With regard to nociception, it is well known that CMT patients do experience symptoms of neuropathic pain, including burning or pain dysesthesias of their feet and hands.



In order to consider the different aspects of this novel GABAergic system, the role of GABA-B receptor in PNS physiology will be further analyzed in conditional mice that specifically lack the GABA-B1 receptor in Schwann cells or in motoneurons. The conditional gene knockout represents a powerful approach to study the function of single genes in the nervous system (Gavériaux-Ruff C., 2007). The Cre-LoxP system is a technology for spatial and temporal control of genetic inactivation. By this approach, mice with LoxP sites flanking the GABA-B gene, floxed GABA-B1, will be crossed respectively with P0-Cre mice (for specific GABA-B1 knockout in the Schwann cells) or with Hb9-Cre (for specific knockout in motoneurons). These mice will be studied for biochemical, morphologic and morphometric, behavioral and nociceptive analysis of the PNS.



The preliminary data already obtained in the first breed of conditional P0-Cre/GABA-B1 fl/fl null mice in Schwann cells strongly suggest that these cells are affected. These conditional mice showed a decrease in myelin thickness, with high myelin abnormalities, delaminations and apoptotic Schwann cells. The increase in unmyelinated fibers strongly relies on a correlation with the hyperalgesic state observed. The data, however, indicate that the morphology in P0-CRE/GABA-B1 null mice is different from that previously published for total null GABA-B1 -/- mice and deserves further investigation.



Our research will be addressed to identify new possible 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.