Oxytocin plays important roles in reproductive physiology and various behaviors, including maternal behavior and social memory. Its receptor (Oxtr) is present in peripheral tissues and brain, so a conditional knockout (KO, −/−) would be useful to allow elimination of the receptor in specific sites at defined times. We created a line of mice in which loxP sites flank Oxtr coding sequence (floxed) enable Cre recombinase-mediated inactivation of the receptor. We expressed Cre recombinase in these mice either in all tissues (Oxtr^−/−) or the forebrain (Oxtr^FB/FB) using the Ca²⁺/calmodulin-dependent protein kinase IIα promoter. The latter KO has reduced Oxtr binding beginning 21–28 d postnatally, leading to prominent reductions in the lateral septum, hippocampus, and ventral pallidum. The medial amygdala is spared, and there is significant retention of binding within the olfactory bulb and nucleus and neocortex. We did not observe any deficits in the general health, sensorimotor functions, anxiety-like behaviors, or sucrose intake in either Oxtr^−/− or Oxtr^FB/FB mice. Females of both KO types deliver pups, but only the Oxtr^FB/FB mice are able to eject milk. Oxtr^−/− males show impaired social memory for familiar females, whereas the Oxtr^FB/FB males appear to recognize their species but not individuals. Our results confirm the importance of oxytocin in social recognition and demonstrate that spatial and temporal inactivation of the Oxtr will enable finer understanding of the physiological, behavioral, and developmental roles of the receptor.

Among the main bacteria implicated in the pathology of periodontal disease, Aggregatibacter actinomycetemcomitans (Aa) is well known for causing loss of periodontal attachment and systemic disease. Recent studies have suggested that secreted extracellular RNAs (exRNAs) from several bacteria may be important in periodontitis, although their role is unclear. Emerging evidence indicates that exRNAs circulate in nanosized bilayered and membranous extracellular vesicles (EVs) known as outer membrane vesicles (OMVs) in gram‐negative bacteria. In this study, we analyzed the small RNA expression profiles in activated human macrophage‐like cells (U937) infected with OMVs from Aa and investigated whether these cells can harbor exRNAs of bacterial origin that have been loaded into the host RNA‐induced silencing complex, thus regulating host target transcripts. Our results provide evidence for the cytoplasmic delivery and activity of microbial EV‐derived small exRNAs in host gene regulation. The production of TNF‐α was promoted by exRNAs via the TLR‐8 and NF‐κB signaling pathways. Numerous studies have linked periodontal disease to neuroinflammatory diseases but without elucidating specific mechanisms for the connection. We show here that intracardiac injection of Aa OMVs in mice showed successful delivery to the brain after crossing the blood‐brain barrier, the exRNA cargos increasing expression of TNF‐α in the mouse brain. The current study indicates that host gene regulation by microRNAs originating from OMVs of the periodontal pathogen Aa is a novel mechanism for host gene regulation and that the transfer of OMV exRNAs to the brain may cause neuroinflammatory diseases like Alzheimer's.—Han, E.‐C., Choi, S.‐Y., Lee, Y., Park, J.‐W., Hong S.‐H., Lee, H.‐J. Extracellular RNAs in periodontopathogenic outer membrane vesicles promote TNF‐α production in human macrophages and cross the blood‐brain barrier in mice. FASEB J. 33, 13412–13422 (2019). www.fasebj.org

MicroRNAs (miRNAs) have been shown to be major regulators of eukaryotic gene expression. However, bacterial RNAs comparable in size to eukaryotic miRNAs (18–22 nucleotides) have received little attention. Recently, a novel class of small RNAs similar in size to miRNAs (miRNA-size, small RNAs or msRNAs) have also been found in several bacteria. Like miRNAs, msRNAs are approximately 15 to 25 nucleotides in length, and their precursors are predicted to form a hairpin loop secondary structure. Here, we identified msRNAs in the periodontal pathogens Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Treponema denticola. We examined these msRNAs using a deep sequencing method and characterized dozens of msRNAs through bioinformatic analysis. Highly expressed msRNAs were selected for further validation. The findings suggest that this class of small RNAs is well conserved across the domains of life. Indeed, msRNAs secreted via bacterial outer membrane vesicles (OMVs) were detected. The ability of bacterial OMVs to deliver RNAs into eukaryotic cells was also observed. These msRNAs in OMVs allowed us to identify their potential human immune-related target genes. Furthermore, we found that exogenous msRNAs could suppress expression of certain cytokines in Jurkat T cells. We propose msRNAs may function as novel bacterial signaling molecules that mediate bacteria-to-human interactions. Furthermore, this study may provide fresh insight into bacterial pathogenic mechanisms of periodontal diseases.