Phd in CELL AND DEVELOPMENTAL BIOLOGY

Thesis title: Peripheral Sensorimotor Nerve Alterations in Duchenne Muscular Dystrophy: Insights From the mdx Mouse Model

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disorder characterized by the absence of dystrophin (Dp427), a cytoskeletal protein expressed in skeletal muscles and various other tissues. In the peripheral nervous system (PNS), myelinating Schwann cells (SCs) express a shorter isoform, Dp116, which associates with the dystrophin-glycoprotein complex (DGC), analogous to the muscle DGC and organized around the α/β-dystroglycan (DG) dimer. Dp116 plays a crucial role in the integrity of myelin and nerve conduction. The functional and structural integrity of nerve fibers depends on the crosstalk between axons and SCs, where the neurotransmitter GABA is a well-known mediator. To investigate the effects of DMD on peripheral sensorimotor nerves, we analyzed the sciatic nerve of mdx mice, a DMD model, assessing the expression and localization of Dp116, DGC proteins (α-DG, β-DG,-dystrobrevin), and α3, α7, β4 nicotinic (nAChR) and M2 muscarinic (mAChR) acetylcholine receptor subunits. Moreover, our previous studies have reported a significant reduction in GABA receptors in the dystrophic sciatic nerve, a finding that may indicate impaired crosstalk between Schwann cells and axons, thereby compromising the neurochemical communication essential for nerve function. To further explore this observation, we analyzed the levels of enzymes involved in GABA synthesis (glutamate decarboxylase, glutamine synthetase), associated signaling pathways, and the expression of GABAA receptor subunits (α4, β3) and the metabotropic GABAB-1b receptor in the sciatic nerve and spinal cord. Compared to wild type mice, mdx mice showed a significant reduction in the levels, distribution, and immunostaining intensity of all analyzed proteins, except for Dp116, further suggesting an alteration in myelin integrity and the crosstalk between SCs and axons. We also examined the activation of matrix metalloproteinases (MMPs), which are responsible for DG degradation, suggesting that retrograde inflammation from muscle to nerve may represent a key factor in the destabilization of the Dp116-DGC complex and the subsequent dysfunction of SC-axon signaling. These findings highlight significant alterations in neuron-SC crosstalk in peripheral nerves affected by DMD, an important aspect to consider for the development of therapeutic strategies.