Muscarinic receptor activation modulates proliferation and neurotrophic factors production in rat Schwann-like cells: implication in nerve regeneration

Peripheral nerve injury is commonly caused by direct mechanical trauma. Regeneration depends on the ability of Schwann cells (SCs) to create a favourable environment, by producing neurotrophic factors. Although SCs are effective in promoting nerve regeneration, they are not a convenient source of transplantable cells to improve outcomes after injury. Mesenchymal Stem Cells derived from adipose tissue (ASCs) seem to be a promising alternative source considering their ability to differentiate towards SC phenotype (Schwann-like). SCs express different receptors for neurotransmitters. In particular cholinergic stimulation of M2 muscarinic receptor decreases SCs proliferation whilst upregulating myelination. Previously, we demonstrated that Schwann-like cells express muscarinic receptors; in particular the M2 receptor activation resulted in decreased proliferation and reduced migration. In present work, we have characterised the effects mediated by muscarinic receptors on neurotrophic factors (NFs) expression and production. The selective activation of M2 receptors by arecaidine propargyl ester (APE) caused a significant decrease of the transcript levels for NFs (NGF, BDNF and GDNF), while the non-selective agonist muscarine did not influence NFs mRNA expression. By custom made Elisa Assay, we analysed the production of two different NGF forms, precursor (proNGF) and mature NGF (mNGF). APE treatment induced a decreased release of both NGF forms, whereas muscarine treatment stimulated an increased release of mNGF. Western blot analysis indicated that both agonists caused a significant decrease in the expression of the proNGF isoform at 25 kDa, which is likely involved in the modulation of apoptotic processes. The data obtained suggest a relevant role of muscarinic receptors in the modulation of NFs production in Schwann-like cells. In particular the ability of both muscarinic agonists to negatively modulate the proNGF isoform, thereby suggesting a neuroprotective role of muscarinic receptors towards regenerating axons.