Phosphatidyl-Inositol-3 Kinase Inhibitors Regulate Peptidoglycan-Induced Myeloid Leukocyte Recruitment, Inflammation, and Neurotoxicity in Mouse Brain

Abstract

Acute brain injury leads to the recruitment and activation of immune cells including resident microglia and infiltrating peripheral myeloid cells (MC), which contribute to the inflammatory response involved in neuronal damage. We previously reported that TLR2 stimulation by peptidoglycan (PGN) from Staphylococcus aureus, in vitro and in vivo, induced microglial cell activation followed by autophagy induction. In this report, we evaluated if phosphatidyl-inositol-3 kinase (PI3K) pharmacological inhibitors LY294200 and 3-methyladenine (3-MA) can modulate the innate immune response to PGN in the central nervous system. We found that injection of PGN into the mouse brain parenchyma (caudate putamen) triggered an inflammatory reaction, which involved activation of microglial cells, recruitment of infiltrating MC to injection site, production of pro-inflammatory mediators, and neuronal injury. In addition, we observed the accumulation of LC3B+ CD45+ cells and colocalization of LC3B and lysosomal-associated membrane protein 1 in brain cells. Besides, we found that pharmacological inhibitors of PI3K, including the classical autophagy inhibitor 3-MA, reduced the recruitment of MC, microglial cell activation, and neurotoxicity induced by brain PGN injection. Collectively, our results suggest that PI3K pathways and autophagic response may participate in the PGN-induced microglial activation and MC recruitment to the brain. Thus, inhibition of these pathways could be therapeutically targeted to control acute brain inflammatory conditions.

Plasmalogens, the Vinyl Ether-Linked Glycerophospholipids, Enhance Learning and Memory by Regulating Brain-Derived Neurotrophic Factor

“…To confirm the regulatory effects of ERK and Akt phosphorylation on the expression of BDNF, synapsin-1, and SYT-1, we injected either ERK (U0126, 20 μM) or PI3K/Akt inhibitor (LY294002, 0.19 nmol) into the hippocampus (0.5 µL of 50 μM solution/site) stereotaxically in normal mice. It has been reported that these doses of U0126 and LY294002 were effective in blocking the signaling pathways in the brain tissues ( Arroyo et al, 2018 ; Wang et al, 2018 ). Twenty-four hours after the injection we found a significant decrease in the mRNA expression of Bdnf , synapsin-1, and SYT-1 in the hippocampus ( Supplementary Figure S2 ).…”

Peptidoglycan-Mediated Bone Marrow Autonomic Neuropathy Impairs Hematopoietic Stem/Progenitor Cells via a NOD1-Dependent Pathway in db/db Mice

“…PGN receptors were reported to be highly expressed in neurons, and a transgenic mouse model of PGN-sensing molecules showed altered expression levels of synaptic-related genes and behavioral disorders, suggesting a possible association between PGN and the central neuron system [ 45 , 46 ]. Direct PGN injection into the mouse brain parenchyma induced microglial cell activation and neurotoxicity via the PI3K-dependent signaling pathway [ 47 ]. We investigated whether the in vivo injection of PGN could impair HSPC function by compromising bone marrow autonomic neuropathy, as we did not observe a direct effect of PGN on HSPCs ex vivo.…”

Molecular Regulation Mechanism of Microglial Autophagy in the Pathology of Alzheimer's Disease

“…Furthermore, several studies have demonstrated novel roles for TLR2 and TLR4 in regulating microglial autophagy. Arroyo et al [101,102] reported that TLR2 stimulation enhances microglial autophagy via PI3K. TLR4 activation by lipopolysaccharide (LPS) reduces autophagic flux and Atg gene expression in microglia by inhibiting the PI3K-FOXO3 pathway.…”