Microglial cells (MC) are phagocytes in the central nervous system (CNS) that become activated in pathological conditions, resulting in microgliosis, manifested by increased cell numbers and inflammation in the affected regions. Thus, controlling microgliosis is important to prevent pathological damage to the brain. We previously observed that activation of MC with peptidoglycan (PGN) from S. aureus and another synthetic Toll-like receptor 2 (TLR2) ligand (Pam3CSK4) results in the induction of autophagy. Due to the potential of TLR2 to act as up-regulator of autophagy in MC, here, we examined if the activation of this receptor can regulate the production of pro-inflammatory molecules in brain MC by inducing autophagy. We observed that PGN or Pam3CSK4 induced nitric oxide production in MC, was significantly reduced in the presence of autophagy inhibitors (3-MA or LY294002)(p<0,05). Moreover, we found that IL1beta production in MC cells stimulated with PGN or Pam3CSK4 was reduced in the presence of both inhibitors (p<0,05). However, the TLR2-induced production of TNFalfa was not affected by the inhibition of autophagy.
In another set of experiments, we evaluated the frecuency of myeloid cells in the mouse brain parenchyma (CPU) after intracerebral injection of PGN. We observed, by flow cytometry, an increase in the frecuency CD11b/CD45+ cells (and particularly in the CD11b/CD45high fraction) in the CPU of mice injected with PGN compared to controls (p<0.05). In addition, we observed, by confocal microscopy, increased number of CD45high cells around of site injection. Currently, we are evaluating if the autophagy response play a role in the regulation of the activation and the recruitment of myeloid cells to the brain. Our results suggest that autophagy induction by TLR2 agonists may selectively regulate the production of pro-inflammatory molecules by MC.
