Mechanisms regulating fetal membrane and neutrophil responses to infection

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Summary/Abstract Chorioamnionitis - inflammation of the fetal membranes (FM) - is characterized by neutrophil infiltration and is a major risk factor for preterm birth. Even in the absence of prematurity, chorioamnionitis can be detrimental to the fetus. Despite a strong association between bacterial infection, chorioamnionitis, and preterm birth, the mechanisms involved are not fully understood. Through expression of the innate immune pattern recognition receptors (PRR), Toll-like receptors (TLRs) and Nod-like receptors (NLRs), FMs have strategies to evade and protect against infection. However, depending upon the nature of signaling and regulation, these protective immune mechanisms may create an inflammatory milieu that can contribute to pathology. In particular, IL-8 is a major neutrophil chemoattractant and inflammasome-mediated IL-1b is a major inducer of tissue injury and mediator of preterm birth. We have found that the chorionic compartment is the primary site of FM IL-8 and IL- 1b production in response to bacterial lipopolysaccharide (LPS), peptidoglycan (PDG), and muramyl dipeptide (MDP) which activate TLR4, TLR2, and Nod2, respectively. While TLRs and NLRs can directly activate signaling pathways leading to inflammatory cytokine/chemokine production, there is the potential for far more complex modulation, regulation, and fine-tuning of these processes and the type of responses generated, particularly for IL-1b. This grant focusses on the requirement of two or more PRRs to be activated sequentially in FMs exposed to bacterial triggers via novel intermediates. A non-classical family of microRNAs (miRs) activate the ssRNA sensors, TLR7 and TLR8, to elicit an inflammatory response. These miRs can also be carried in exosomes and delivered to TLR7 or TLR8 in target cells. Our preliminary data supports the concept that TLR8-activating miR-146a-3p may acts as a novel intermediate signal that drives FM chemotactic and inflammatory responses to bacterial TLR and NLR agonists. We also have preliminary data demonstrating that FM-derived exosomes containing TLR8-activating miRs trigger neutrophil activation and release of neutrophil extracellular traps. Finally, we found that FM tissue and circulating exosomal TLR8-activating miR-146a-3p is elevated in women with preterm birth. Based on this, our central hypothesis is that TLR8-activating miRs mediate FM chemotactic IL-8 and inflammasome-mediated inflammatory IL-1b in response to bacterial triggers, and through their release and delivery via exosomes active maternal neutrophils. This leads to inflammation at the maternal-fetal interface, increasing the risk for chorioamnionitis. To test this, our specific aims are to determine if: Aim 1. TLR8-activating miRs mediate a FM chemotactic IL-8 response after exposure to bacterial triggers. Aim 2. TLR8-activating miRs contribute to FM inflammasome activation and inflammatory IL-1b production. Aim 3. FM exosomes containing TLR8-activating miRs induce neutrophil activation.