Human Breast Milk-derived Exosomes Attenuate Lipopolysaccharide-induced Activation in Microglia

Microglia mediate the immune response in the central nervous system to many insults, including lipopolysaccharide (LPS), a bacterial endotoxin that initiates neuroinflammation in the neonatal population, especially preterm infants. The synthesis of the proinflammatory proteins CD40 and NLRP3 depends on the canonical NF-κB cascade as the genes encoding CD40 and NLRP3 are transcribed by the phosphorylated NF-κB p50/p65 heterodimer in LPS-induced microglia. Exosomes, which are nanosized vesicles (40-150 nm) involved in intercellular communication, are implicated in many pathophysiological processes. Human breast milk, which is rich in exosomes, plays a vital role in neonatal immune system maturation and adaptation. Activated microglia may cause brain-associated injuries or disorders; therefore, we hypothesize that human breast milk-derived exosomes (HBME) attenuate LPS-induced activation of CD40 and NLRP3 by decreasing p38 MAPK and NF-κB p50/p65 activation/phosphorylation downstream of TLR4 in murine microglia (BV2). Human microglia (HMC3) showed a significant decrease in p65 phosphorylation. We isolated purified HBME and characterized them using nanoparticle tracking analysis, transmission electron microscopy, fluorescence-activated cell sorting, and western blots. Analysis of microglia exposed to LPS and HBME indicated that HBME modulated the expression of signaling molecules in the canonical NF-κB pathway, including MyD88, IκBα, p38 MAPK, NF-κB p65, and their products CD40, NLRP3, and cytokines IL-1β and IL-10. Thus, HBMEs have great potential for attenuating the microglial response to LPS.