Bioactivities of pneumococcal cell wall in neuropathogenesis

Using the pneumococcus as a model, our lab has revealed many features of the biochemical basis of the inflammatory response to bacteria in the brain. The important discovery of this application is the opening of a new area of pathogenesis at the maternal/fetal interface that will inform newly discovered cell wall/TLR2 effects as a morphogen in the brain. We have determined that cell wall, a universal pathogen associated molecular pattern, circulates in the bloodstream of pregnant mice and traverses the placenta to the fetal brain. The response of fetal neurons is not the well characterized inflammation and neuronal death of the postnatal setting but the exact opposite: neuroproliferation without inflammation. This response involves two new activities of cell wall: 1) induction of cell proliferation via TLR2 without inflammatory signaling, and 2) remodeling of embryonic brain anatomy and changes in postnatal behavior. We will further determine the relevance of these findings to the human brain using organoids. An understanding of the details of this new biology, to be investigated in this application, represents both novel bacterial pathogenesis and an avenue of high potential for tangible medical impact. Using single cell spatial RNASeq and knock out animal models, we propose to identify the signaling cascade initiated by cell wall to modulate brain structure, including determining the links between TLR2/6, the signaling node of the neuronal cilium and the neuronal transcription factor FoxG1. This will connect innate immune receptors to nuclear transcription factors for the first time and define a new activity of TLRs as morphogens. The involvement of the LANDO autophagy pathway will be characterized as a cell wall trafficking/removal pathway associated with defects in cognitive function.