The human oral microbiome refers to an ecological community of symbiotic and pathogenic microorganisms found in the oral cavity. The oral cavity is an environment that provides various biological niches, such as the teeth, tongue, and oral mucosa. The oral cavity is the gateway between the external environment and the human body, maintaining oral homeostasis, protecting the mouth, and preventing disease. On the flip side, the oral microbiome also plays an important role in the triggering, development, and progression of oral and systemic diseases. In recent years, disease diagnosis through the analysis of the human oral microbiome has been realized with the recent development of innovative detection technology and is overwhelmingly promising compared to the previous era. It has been found that patients with oral and systemic diseases have variations in their oral microbiome compared to normal subjects. This narrative review provides insight into the pathophysiological role that the oral microbiome plays in influencing oral and systemic diseases and furthers the knowledge related to the oral microbiome produced over the past 30 years. A wide range of updates were provided with the latest knowledge of the oral microbiome to help researchers and clinicians in both academic and clinical aspects. The microbial community information can be utilized in non-invasive diagnosis and can help to develop a new paradigm in precision medicine, which will benefit human health in the era of post-metagenomics.

Recent studies have reported that changes in gut microbiota composition could induce neuropsychiatric problems. In this study, we investigated alterations in gut microbiota induced by early-life stress (ELS) in rats subjected to maternal separation (MS; 6 h a day, postnatal days (PNDs) 1–21), along with changes in inflammatory cytokines and tryptophan-kynurenine (TRP-KYN) metabolism, and assessed the differences between sexes. High-throughput sequencing of the bacterial 16S rRNA gene showed that the relative abundance of the Bacteroides genus was increased and that of the Lachnospiraceae family was decreased in the feces of MS rats of both sexes (PND 56). By comparison, MS increased the relative abundance of the Streptococcus genus and decreased that of the Staphylococcus genus only in males, whereas the abundance of the Sporobacter genus was enhanced and that of the Mucispirillum genus was reduced by MS only in females. In addition, the levels of proinflammatory cytokines were increased in the colons (IFN-γ and IL-6) and sera (IL-1β) of the male MS rats, together with the elevation of the KYN/TRP ratio in the sera, but not in females. In the hippocampus, MS elevated the level of IL-1β and the KYN/TRP ratio in both male and female rats. These results indicate that MS induces peripheral and central inflammation and TRP-KYN metabolism in a sex-dependent manner, together with sex-specific changes in gut microbes.

Postmortem studies reveal that the brain pH in schizophrenia patients is lower than normal. The exact cause of this low pH is unclear, but increased lactate levels due to abnormal energy metabolism appear to be involved. Schizophrenia patients display distinct changes in mitochondria number, morphology, and function, and such changes promote anaerobic glycolysis, elevating lactate levels. pH can affect neuronal activity as H⁺ binds to numerous proteins in the nervous system and alters the structure and function of the bound proteins. There is growing evidence of pH change associated with cognition, emotion, and psychotic behaviors. Brain has delicate pH regulatory mechanisms to maintain normal pH in neurons/glia and extracellular fluid, and a change in these mechanisms can affect, or be affected by, neuronal activities associated with schizophrenia. In this review, we discuss the current understanding of the cause and effect of decreased brain pH in schizophrenia based on postmortem human brains, animal models, and cellular studies. The topic includes the factors causing decreased brain pH in schizophrenia, mitochondria dysfunction leading to altered energy metabolism, and pH effects on the pathophysiology of schizophrenia. We also review the acid/base transporters regulating pH in the nervous system and discuss the potential contribution of the major transporters, sodium hydrogen exchangers (NHEs), and sodium-coupled bicarbonate transporters (NCBTs), to schizophrenia.

The human oral microbiome refers to an ecological community of symbiotic and pathogenic microorganisms found in the oral cavity. The oral cavity is a suitable environment that provides various kinds of biological niches such as teeth, tongue, and oral mucosa. The oral cavity is the gateway between the external environment and the human body, maintaining oral homeostasis, protecting the mouth, and preventing disease. On the flip side, the oral microbiome plays an important role in triggering, development, and progression of oral and systemic diseases. Currently, disease diagnosis through the analysis of the human oral microbiome has been realized with the recent development of innovative detection technology, and is overwhelmingly promising compared to the previous era. It has been found that patients with oral diseases and systemic diseases have variations in the oral microbiome compared to normal subjects. This narrative review provides insight into the pathophysiological role that oral microbiome plays in influencing oral and systemic diseases, and updates the knowledge related to the oral microbiome over the past 30 years. A wide range of updates was provided with the latest knowledge of the oral microbiome to help researchers and clinicians in both academic and clinical aspects. The microbial community information can be utilized in non-invasive diagnosis and help develop a new paradigm in precision medicine, which will benefit human health in the era of post-metagenomics.

Background/Aim: Sleep loss is proposed as a trigger for manic episodes in bipolar disorder in humans. It has been shown that sleep and wakefulness can affect changes in mitochondrial gene expression, oxidative phosphorylation (OXPHOS) activity, and morphology in the brain. In this study, we investigated alterations in mitochondrial bioenergetic function in the brain of rats after 72-h rapid eye movement sleep deprivation (REM-SD). Materials and Methods: Alterations in the mitochondrial DNA (mtDNA) copy number were detected in the prefrontal cortex and hippocampus through amplification of mitochondrially encoded NADH dehydrogenase 1 (mt-Nd1) gene using quantitative real-time polymerase chain reaction. The expression levels of mitochondrial biogenesis-related proteins such as peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PPARGC1A), cytochrome c oxidase subunit 4I1 (COX4I1) and sirtuin 3 (SIRT3) were assessed using western blot analysis and immunohistochemistry. Results: We found that REM-SD significantly increased the mtDNA copy number in the hippocampus but not in the prefrontal cortex. In addition, REM-SD increased the protein expression of COX4I1 in the hippocampus. Furthermore, we observed manic-like behaviors in rats exposed to 72-h REM-SD. REM-SD increased locomotion in the open-field test and the time spent in open arms in the elevated plus-maze test. Conclusion: REM-SD may induce mitochondrial dysfunction in the brain, which may be involved in the induction of mania.

FOS has been implicated in the progression of renal disease including IgAN. In this study, we investigated whether polymorphisms of FOS family genes [FOS, FOSB, FOS-like antigen 1 (FOSL1), and FOSL2] were associated with immunoglobulin A nephropathy (IgAN) and the clinical phenotypes of IgAN patients. We genotyped single nucleotide polymorphisms (SNPs) of FOS family genes (rs2239615 and rs7101 for FOS, rs12373539 and rs2282695 for FOSB, rs637571 for FOSL1, and rs925255 for FOSL2) using direct sequencing in 198 IgAN patients and 290 control subjects. No SNPs were associated with IgAN; however, in the analysis of clinical phenotypes, we found that rs637571 of FOSL1 was associated with podocyte foot process effacement of IgAN in additive (CT vs. TT vs. CC, P = 0.0031, OR = 2.08, 95% CI = 1.27-3.40) and dominant models (CT/TT vs. CC, P = 0.0034, OR = 2.50, 95% CI = 1.35-4.64). The frequency of genotypes containing the T allele was increased in IgAN patients with podocyte foot process effacement, compared to those without podocyte foot process effacement. These results suggest that FOSL1 may be related to IgAN severity.