Bacterial peptidoglycans as novel signaling molecules from microbiota to brain

Mounting evidence indicates that gut microbiota exerts a broad range of effects on host physiology and development beyond the gastrointestinal tract, including the modulation of brain development. However, the mechanisms mediating the interactions between the microbiota and the developing brain are still poorly understood. Pattern recognition receptors of the innate immune system that recognize microbial products, such as peptidoglycans have emerged as potential key regulators of gut microbiome-brain interactions. Peptidoglycan-sensing molecules are expressed in the placenta and brain during specific time windows of development. Moreover, peptidoglycans are ubiquitously present in circulation and can cross the blood brain barrier. This review brings together the current evidence supporting a broad function of peptidoglycans well beyond host's immunity, extending to neurodevelopment and behavior.