Characterization of Human Genes Modulated by Porphyromonas gingivalis Highlights the Ribosome, Hypothalamus, and Cholinergic Neurons

Glutamate is a key nutrient for Porphyromonas gingivalis growth and survival during intracellular autophagic life under nutritionally limited conditions

Porphyromonas gingivalis survives in special autophagic vacuoles that serve as major replicative habitats in human primary gingival epithelial cells (GECs). As an asaccharolytic strict anaerobe, P. gingivalis is dependent on amino acids and peptides for nutrient sources. However, it is largely unknown as to P. gingivalis' metabolic processing under the nutritionally limited intracellular environments such the vacuoles, especially the preferred amino acids and associated-metabolic machineries. Here we elucidate that a Glutamate (Glu) catabolic enzyme, glutamate dehydrogenase (GdhA) is highly enriched in the isolated P. gingivalis -containing vacuoles. Interestingly, we found that P. gingivalis induces conversion of intracellular glutamine pool to Glu determined by analyses of the P. gingivalis- containing vacuoles and the whole infected-GECs. Critically, exogenous Glu-Glu dipeptide, a simple precursor of Glu, significantly increases the size of isolated intact P. gingivalis containing-vacuoles and live wild-type P. gingivalis numbers in GECs. In contrast, the isogenic GdhA-deficient-strain, Δ gdhA displayed a significant growth defect with collapsed-vacuoles in GECs. Next, we confirmed that P. gingivalis uptakes 14 C-Glu and it preferentially utilizes Glu-Glu-dipeptide using a nutritionally reduced Tryptic-Soy-Broth (TSB) media supplemented with Glu-Glu. Contrary, Δ gdhA -strain showed no detectable growth especially in nutritionally reduced TSB media with Glu-Glu. Using Atomic-Force-Microscopy, we observed that, wild-type P. gingivalis but not Δ gdhA strain notably increased the cell volume upon Glu-Glu supplementation, an indicator of higher metabolism and growth. Utilization of a human gingiva-mimicking organoid-system further validated the importance of Glu as an essential nutrient for the intramucosal colonization of P. gingivalis via the protected replicative vacuoles in GECs.

Importance

This study reveals that P. gingivalis heavily depends on preferential utilization of Glutamate (Glu) for autophagic vacuolar growth and survival in human GECs. Several novel observations are made to support this: (i) GdhA of P. gingivalis is highly enriched in these vacuoles, (ii) P. gingivalis induces a large conversion of intracellular glutamine to Glu, (iii) size of vacuoles are significantly increased in the presence of Glu-Glu in P. gingivalis wild-type strain infection which is opposite in a Δ gdhA strain, (iv) P. gingivalis uptakes 14 C-Glu and preferentially utilizes Glu-Glu dipeptide, (v) similarly, wild-type strain shows growth increase in a nutritionally reduced bacterial culture media, and (vi) finally, Glu-Glu supplementation increases bacterial cell-volume of P. gingivalis wild-type but not Δ gdhA strain, an indicator of higher metabolism and growth. Taken together, this study highlights the pathophysiological importance of Glu for P. gingivalis growth-rate, biomass induction and survival in nutritionally limited host subcellular environments.

Ethanol extract from Astilbe chinensis inflorescence suppresses inflammation in macrophages and growth of oral pathogenic bacteria

Chronic oral inflammation and biofilm-mediated infections drive diseases such as dental caries and periodontitis. This study investigated the anti-inflammatory and antibacterial potential of an ethanol extract from Astilbe chinensis inflorescence (GA-13-6) as a prominent candidate for natural complex substances (NCS) with therapeutic potential. In LPS-stimulated RAW 264.7 macrophages, GA-13-6 significantly suppressed proinflammatory mediators, including interleukin-6 (IL-6), tumor necrosis factor (TNF), and nitric oxide (NO), surpassing purified astilbin, a known bioactive compound found in A. chinensis. Furthermore, GA-13-6 downregulated the expression of cyclooxygenase-2 (COX2) and inducible nitric oxide synthase (iNOS), indicating an inhibitory effect on the inflammatory cascade. Remarkably, GA-13-6 exhibited selective antibacterial activity against Streptococcus mutans, Streptococcus sanguinis, and Porphyromonas gingivalis, key players in dental caries and periodontitis, respectively. These findings suggest that complex GA-13-6 holds the potential for the treatment or prevention of periodontal and dental diseases, as well as various other inflammation-related conditions, while averting the induction of antibiotic resistance.

Porphyromonas gingivalis activates Heat-Shock-Protein 27 to drive a LC3C-specific probacterial form of select autophagy that is redox sensitive for intracellular bacterial survival in human gingival mucosa

Porphyromonas gingivalis , a major oral pathobiont, evades canonical host pathogen clearance in human primary gingival epithelial cells (GECs) by initiating a non-canonical variant of autophagy consisting of Microtubule-associated protein 1A/1B-light chain 3 (LC3)-rich autophagosomes, which then act as replicative niches. Simultaneously, P. gingivalis inhibits apoptosis and oxidative-stress, including extracellular-ATP (eATP)-mediated reactive-oxygen-species (ROS) production via phosphorylating Heat Shock Protein 27 (HSp27) with the bacterial nucleoside-diphosphate-kinase (Ndk). Here, we have mechanistically identified that P. gingivalis -mediated induction of HSp27 is crucial for the recruitment of the LC3 isoform, LC3C, to drive the formation of live P. gingivalis -containing Beclin1-ATG14-rich autophagosomes that are redox sensitive and non-degrading. HSp27 depletions of both infected GECs and gingiva-mimicking organotypic-culture systems resulted in the collapse of P. gingivalis -mediated autophagosomes, and abolished P. gingivalis -induced LC3C-specific autophagic-flux in a HSp27-dependent manner. Concurrently, HSp27 depletion accompanied by eATP treatment abrogated protracted Beclin 1-ATG14 partnering and decreased live intracellular P. gingivalis levels. These events were only partially restored via treatments with the antioxidant N-acetyl cysteine (NAC), which rescued the cellular redox environment independent of HSp27. Moreover, the temporal phosphorylation of HSp27 by the bacterial Ndk results in HSp27 tightly partnering with LC3C, hindering LC3C canonical cleavage, extending Beclin 1-ATG14 association, and halting canonical maturation. These findings pinpoint how HSp27 pleiotropically serves as a major platform-molecule, redox regulator, and stepwise modulator of LC3C during P. gingivalis -mediated non-canonical autophagy. Thus, our findings can determine specific molecular strategies for interfering with the host-adapted P. gingivalis ' successful mucosal colonization and oral dysbiosis.

AI algorithm combined with RNA editing-based blood biomarkers to discriminate bipolar from major depressive disorders in an external validation multicentric cohort

Bipolar disorder (BD) is a leading cause of disability worldwide, as it can lead to cognitive and functional impairment and premature mortality. The first episode of BD is usually a depressive episode and is often misdiagnosed as major depressive disorder (MDD). Growing evidence indicates that peripheral immune activation and inflammation are involved in the pathophysiology of BD and MDD. Recently, by developing a panel of RNA editing-based blood biomarkers able to discriminate MDD from depressive BD, we have provided clinicians a new tool to reduce the misdiagnosis delay observed in patients suffering from BD. The present study aimed at validating the diagnostic value of this panel in an external independent multicentric Switzerland-based cohort of 143 patients suffering from moderate to major depression. The RNA-editing based blood biomarker (BMK) algorithm developped allowed to accurately discriminate MDD from depressive BD in an external cohort, with high accuracy, sensitivity and specificity values (82.5 %, 86.4 % and 80.8 %, respectively). These findings further confirm the important role of RNA editing in the physiopathology of mental disorders and emphasize the possible clinical usefulness of the biomarker panel for optimization treatment delay in patients suffering from BD.

Population-enriched innate immune variants may identify candidate gene targets at the intersection of cancer and cardio-metabolic disease

Both cancer and cardio-metabolic disease disparities exist among specific populations in the US. For example, African Americans experience the highest rates of breast and prostate cancer mortality and the highest incidence of obesity. Native and Hispanic Americans experience the highest rates of liver cancer mortality. At the same time, Pacific Islanders have the highest death rate attributed to type 2 diabetes (T2D), and Asian Americans experience the highest incidence of non-alcoholic fatty liver disease (NAFLD) and cancers induced by infectious agents. Notably, the pathologic progression of both cancer and cardio-metabolic diseases involves innate immunity and mechanisms of inflammation. Innate immunity in individuals is established through genetic inheritance and external stimuli to respond to environmental threats and stresses such as pathogen exposure. Further, individual genomes contain characteristic genetic markers associated with one or more geographic ancestries (ethnic groups), including protective innate immune genetic programming optimized for survival in their corresponding ancestral environment(s). This perspective explores evidence related to our working hypothesis that genetic variations in innate immune genes, particularly those that are commonly found but unevenly distributed between populations, are associated with disparities between populations in both cancer and cardio-metabolic diseases. Identifying conventional and unconventional innate immune genes that fit this profile may provide critical insights into the underlying mechanisms that connect these two families of complex diseases and offer novel targets for precision-based treatment of cancer and/or cardio-metabolic disease.

The Presence of Periodontitis Exacerbates Non-Alcoholic Fatty Liver Disease via Sphingolipid Metabolism-Associated Insulin Resistance and Hepatic Inflammation in Mice with Metabolic Syndrome

Clinical studies have shown that periodontitis is associated with non-alcoholic fatty liver disease (NAFLD). However, it remains unclear if periodontitis contributes to the progression of NAFLD. In this study, we generated a mouse model with high-fat diet (HFD)-induced metabolic syndrome (MetS) and NAFLD and oral P. gingivalis inoculation-induced periodontitis. Results showed that the presence of periodontitis increased insulin resistance and hepatic inflammation and exacerbated the progression of NAFLD. To determine the role of sphingolipid metabolism in the association between NAFLD and periodontitis, we also treated mice with imipramine, an inhibitor of acid sphingomyelinase (ASMase), and demonstrated that imipramine treatment significantly alleviated insulin resistance and hepatic inflammation, and improved NAFLD. Studies performed in vitro showed that lipopolysaccharide (LPS) and palmitic acid (PA), a major saturated fatty acid associated with MetS and NAFLD, synergistically increased the production of ceramide, a bioactive sphingolipid involved in NAFLD progression in macrophages but imipramine effectively reversed the ceramide production stimulated by LPS and PA. Taken together, this study showed for the first time that the presence of periodontitis contributed to the progression of NAFLD, likely due to alterations in sphingolipid metabolism that led to exacerbated insulin resistance and hepatic inflammation. This study also showed that targeting ASMase with imipramine improves NAFLD by reducing insulin resistance and hepatic inflammation.

Curcumin-Attenuated TREM-1/DAP12/NLRP3/Caspase-1/IL1B, TLR4/NF-κB Pathways, and Tau Hyperphosphorylation Induced by 1,2-Diacetyl Benzene: An in Vitro and in Silico Study

We aimed to evaluate the effects of 1,2-diacetylbenzene (DAB) and curcumin on neuroinflammation induced by DAB via triggering receptor expressed on myeloid cells 1 (TREM-1), Toll-like receptor 4 (TLR4), and NLR family pyrin domain containing 3 (NLP3)/calcium-dependent activator protein for secretion 1 (CAPS1)/interleukin 1 beta (IL1B) pathways; tau hyperphosphorylation; reactive oxygen species (ROS); and advanced glycation end-product (AGE) in microglia cells; and explore the molecular mechanisms involved in the key genes induced by DAB and targeted by curcumin in silico analysis. In this study, Western blot, quantitative polymerase chain reaction, and immunocytochemistry were used as the key methods in vitro. In silico analysis, GeneMANIA, ToppFun feature, Metascape, CHEA3, Cytoscape, Autodock, and MIENTURNET were the core approaches used. Curcumin inhibited both the DAB-induced TREM-1/DAP12/NLRP3/caspase-1/IL1B pathway and the TLR4/NF-κB pathway. In BV2 cells, curcumin inhibited ROS, AGE, hyperphosphorylation, glycogen synthase kinase-3β (GSK-3β), and β-amyloid while activating nuclear factor erythroid 2-related factor 2 (Nrf2) expression. In silico studies showed that tumor necrosis factor (TNF), IL6, NFKB1, IL10, and IL1B, as well as MTF1 and ZNF267, were shown to be important genes and transcription factors in the pathogenesis of cognitive impairment produced by DAB and curcumin. Three significant miRNAs (hsa-miR-26a-5p, hsa-miR-203a-3p, and hsa-miR-155-5p) implicated in the etiology of DAB-induced cognitive impairment and targeted by curcumin were also identified. Inflammation and cytokine-associated pathways, Alzheimer's disease, and cognitive impairment were characterized as the most significant biological processes implicated in genes, miRNAs, and transcription factors induced by DAB and targeted by curcumin. Our findings provide new insight into fundamental molecular mechanisms implicated in the pathogenesis of cognitive impairment caused by DAB, particularly the effects of neuroinflammation. Furthermore, this study suggests that curcumin might be a promising therapeutic molecule for cognitive impairment treatment through modulating neuroinflammatory responses.

Leaky Gum: The Revisited Origin of Systemic Diseases

The oral cavity is the gateway for microorganisms into your body where they disseminate not only to the directly connected respiratory and digestive tracts but also to the many remote organs. Oral microbiota, travelling to the end of the intestine and circulating in our bodies through blood vessels, not only affect a gut microbiome profile but also lead to many systemic diseases. By gathering information accumulated from the era of focal infection theory to the age of revolution in microbiome research, we propose a pivotal role of “leaky gum”, as an analogy of “leaky gut”, to underscore the importance of the oral cavity in systemic health. The oral cavity has unique structures, the gingival sulcus (GS) and the junctional epithelium (JE) below the GS, which are rarely found anywhere else in our body. The JE is attached to the tooth enamel and cementum by hemidesmosome (HD), which is structurally weaker than desmosome and is, thus, vulnerable to microbial infiltration. In the GS, microbial biofilms can build up for life, unlike the biofilms on the skin and intestinal mucosa that fall off by the natural process. Thus, we emphasize that the GS and the JE are the weakest leaky point for microbes to invade the human body, making the leaky gum just as important as, or even more important than, the leaky gut.

Periodontal microorganisms and Alzheimer disease - A causative relationship?

In the initiation or exacerbation of Alzheimer disease, the dissemination of oral microorganisms into the brain tissue or the low‐level systemic inflammation have been speculated to play a role. However, the impact of oral microorganisms, such as Porphyromonas gingivalis, on the pathogenesis of Alzheimer disease and the potential causative relationship is still unclear. The present review has critically reviewed the literature by examining the following aspects: (a) the oral microbiome and the immune response in the elderly population, (b) human studies on the association between periodontal and gut microorganisms and Alzheimer disease, (c) animal and in vitro studies on microorganisms and Alzheimer disease, and (d) preventive and therapeutic approaches. Factors contributing to microbial dysbiosis seem to be aging, local inflammation, systemic diseases, wearing of dentures, living in nursing homes and no access to adequate oral hygiene measures. Porphyromonas gingivalis was detectable in post‐mortem brain samples. Microbiome analyses of saliva samples or oral biofilms showed a decreased microbial diversity and a different composition in Alzheimer disease compared to cognitively healthy subjects. Many in‐vitro and animal studies underline the potential of P gingivalis to induce Alzheimer disease‐related alterations. In animal models, recurring applications of P gingivalis or its components increased pro‐inflammatory mediators and β‐amyloid in the brain and deteriorated the animals' cognitive performance. Since periodontitis is the result of a disturbed microbial homoeostasis, an effect of periodontal therapy on the oral microbiome and host response related to cognitive parameters may be suggested and should be elucidated in further clinical trials.

Knockdown of zinc finger protein 267 suppresses diffuse large B-cell lymphoma progression, metastasis, and cancer stem cell properties

Zinc finger protein 267 (ZNF267) is a member of the Kruppel-like transcription factor family, which regulates various biological processes such as cell proliferation and differentiation. However, the biological significance of ZNF267 and its potential role in diffuse large B-cell lymphoma (DLBCL) remain to be documented. Experiments were herein conducted to study the role of ZNF267 in DLBCL. real-time quantitative reverse transcription PCR and Western blotting assays were conducted to detect the expression of ZNF267 in tissues and cells. Tissue microarray and bioinformatics analyses of public data were also done to detect the expression status and clinical significance of ZNF267. Functional cell experiments including CCK8 assay, colony formation assay, 5-ethynyl-2'-deoxyuridine (EDU) assay, terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) assay, transwell assay, and wound healing assay were conducted to study the effects of ZNF267 knockdown and overexpression on cell proliferation and mobility. Xenograft assay was also conducted to confirm the effects of ZNF267 knockdown in vivo. In the present study, we found ZNF267 was significantly upregulated in DLBCL and predicted a poor survival outcome based on the bioinformatics analysis. Functionally, the knockdown of ZNF267 resulted in less cell proliferation and mobility, whereas the overexpression led to enhanced cell proliferation and mobility. Animal experiments also confirmed that ZNF267 silence contributed to less tumor growth and less lung metastasis. Further analysis showed that ZFN267 knockdown resulted in decreased epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) properties. Our results suggest that ZNF267 is an oncogene in DLBCL and its silence could compromise the aggression of DLBCL, which makes ZNF267 a promising therapeutic target.

RNA Helicases in Microsatellite Repeat Expansion Disorders and Neurodegeneration

Short repeated sequences of 3-6 nucleotides are causing a growing number of over 50 microsatellite expansion disorders, which mainly present with neurodegenerative features. Although considered rare diseases in relation to the relatively low number of cases, these primarily adult-onset conditions, often debilitating and fatal in absence of a cure, collectively pose a large burden on healthcare systems in an ageing world population. The pathological mechanisms driving disease onset are complex implicating several non-exclusive mechanisms of neuronal injury linked to RNA and protein toxic gain- and loss- of functions. Adding to the complexity of pathogenesis, microsatellite repeat expansions are polymorphic and found in coding as well as in non-coding regions of genes. They form secondary and tertiary structures involving G-quadruplexes and atypical helices in repeated GC-rich sequences. Unwinding of these structures by RNA helicases plays multiple roles in the expression of genes including repeat-associated non-AUG (RAN) translation of polymeric-repeat proteins with aggregating and cytotoxic properties. Here, we will briefly review the pathogenic mechanisms mediated by microsatellite repeat expansions prior to focus on the RNA helicases eIF4A, DDX3X and DHX36 which act as modifiers of RAN translation in C9ORF72-linked amyotrophic lateral sclerosis/frontotemporal dementia (C9ORF72-ALS/FTD) and Fragile X-associated tremor/ataxia syndrome (FXTAS). We will further review the RNA helicases DDX5/17, DHX9, Dicer and UPF1 which play additional roles in the dysregulation of RNA metabolism in repeat expansion disorders. In addition, we will contrast these with the roles of other RNA helicases such as DDX19/20, senataxin and others which have been associated with neurodegeneration independently of microsatellite repeat expansions. Finally, we will discuss the challenges and potential opportunities that are associated with the targeting of RNA helicases for the development of future therapeutic approaches.

Porphyromonas gingivalis Outer Membrane Vesicles as the Major Driver of and Explanation for Neuropathogenesis, the Cholinergic Hypothesis, Iron Dyshomeostasis, and Salivary Lactoferrin in Alzheimer's Disease

Porphyromonas gingivalis (Pg) is a primary oral pathogen in the widespread biofilm-induced "chronic" multi-systems inflammatory disease(s) including Alzheimer's disease (AD). It is possibly the only second identified unique example of a biological extremophile in the human body. Having a better understanding of the key microbiological and genetic mechanisms of its pathogenesis and disease induction are central to its future diagnosis, treatment, and possible prevention. The published literature around the role of Pg in AD highlights the bacteria's direct role within the brain to cause disease. The available evidence, although somewhat adopted, does not fully support this as the major process. There are alternative pathogenic/virulence features associated with Pg that have been overlooked and may better explain the pathogenic processes found in the "infection hypothesis" of AD. A better explanation is offered here for the discrepancy in the relatively low amounts of "Pg bacteria" residing in the brain compared to the rather florid amounts and broad distribution of one or more of its major bacterial protein toxins. Related to this, the "Gingipains Hypothesis", AD-related iron dyshomeostasis, and the early reduced salivary lactoferrin, along with the resurrection of the Cholinergic Hypothesis may now be integrated into one working model. The current paper suggests the highly evolved and developed Type IX secretory cargo system of Pg producing outer membrane vesicles may better explain the observed diseases. Thus it is hoped this paper can provide a unifying model for the sporadic form of AD and guide the direction of research, treatment, and possible prevention.

Donor-Specific Transcriptomic Analysis of Alzheimer's Disease-Associated Hypometabolism Highlights a Unique Donor, Ribosomal Proteins and Microglia

Alzheimer's disease (AD) starts decades before clinical symptoms appear. Low-glucose utilization in regions of the cerebral cortex marks early AD. To identify these regions, we conducted a voxel-wise meta-analysis of previous studies conducted with positron emission tomography that compared AD patients with healthy controls. The resulting map marks hypometabolism in the posterior cingulate, middle frontal, angular gyrus, and middle and inferior temporal regions. Using the Allen Human Brain Atlas, we identified genes that show spatial correlation across the cerebral cortex between their expression and this hypometabolism. Of the six brains in the Atlas, one demonstrated a strong spatial correlation between gene expression and hypometabolism. Previous neuropathological assessment of this brain from a 39-year-old male noted a neurofibrillary tangle in the entorhinal cortex. Using the transcriptomic data, we estimate lower proportions of neurons and more microglia in the hypometabolic regions when comparing this donor's brain with the other five donors. Within this single brain, signal recognition particle (SRP)-dependent cotranslational protein targeting genes, which encode primarily cytosolic ribosome proteins, are highly expressed in the hypometabolic regions. Analyses of human and mouse data show that expression of these genes increases progressively across AD-associated states of microglial activation. In addition, genes involved in cell killing, chronic inflammation, ubiquitination, tRNA aminoacylation, and vacuole sorting are associated with the hypometabolism map. These genes suggest disruption of the protein life cycle and neuroimmune activation. Taken together, our molecular characterization reveals a link to AD-associated hypometabolism that may be relevant to preclinical stages of AD.