Unraveling the gut-brain connection: The association of microbiota-linked structural brain biomarkers with behavior and mental health.

AIM: The gut microbiota can influence human behavior. However, due to the massive multiple-testing problem, research into the relationship between microbiome ecosystems and the human brain faces drawbacks. This problem arises when attempting to correlate thousands of gut bacteria with thousands of brain voxels. METHODS: We performed brain magnetic resonance imaging (MRI) scans on 133 participants and applied machine-learning algorithms (Ridge regressions) combined with permutation tests. Using this approach, we were able to correlate specific gut bacterial families with brain MRI signals, circumventing the difficulties of massive multiple testing while considering sex, age, and body mass index as confounding factors. RESULTS: The relative abundance (RA) of the Selenomonadaceae, Clostridiaceae, and Veillonellaceae families in the gut was associated with altered cerebellar, visual, and frontal T2-mapping and diffusion tensor imaging measures. Conversely, decreased relative abundance of the Eubacteriaceae family was also linked to T2-mapping values in the cerebellum. Significantly, the brain regions associated with the gut microbiome were also correlated with depressive symptoms and attentional deficits. CONCLUSIONS: Our analytical strategy offers a promising approach for identifying potential brain biomarkers influenced by gut microbiota. By gathering a deeper understanding of the microbiota-brain connection, we can gain insights into the underlying mechanisms and potentially develop targeted interventions to mitigate the detrimental effects of dysbiosis on brain function and mental health.

Human liver microbiota modeling strategy at the early onset of fibrosis.

BACKGROUND: Gut microbiota is involved in the development of liver diseases such as fibrosis. We and others identified that selected sets of gut bacterial DNA and bacteria translocate to tissues, notably the liver, to establish a non-infectious tissue microbiota composed of microbial DNA and a low frequency live bacteria. However, the precise set of bacterial DNA, and thereby the corresponding taxa associated with the early stages of fibrosis need to be identified. Furthermore, to overcome the impact of different group size and patient origins we adapted innovative statistical approaches. Liver samples with low liver fibrosis scores (F0, F1, F2), to study the early stages of the disease, were collected from Romania(n = 36), Austria(n = 10), Italy(n = 19), and Spain(n = 17). The 16S rRNA gene was sequenced. We considered the frequency, sparsity, unbalanced sample size between cohorts to identify taxonomic profiles and statistical differences. RESULTS: Multivariate analyses, including adapted spectral clustering with L1-penalty fair-discriminant strategies, and predicted metagenomics were used to identify that 50% of liver taxa associated with the early stage fibrosis were Enterobacteriaceae, Pseudomonadaceae, Xanthobacteriaceae and Burkholderiaceae. The Flavobacteriaceae and Xanthobacteriaceae discriminated between F0 and F1. Predicted metagenomics analysis identified that the preQ0 biosynthesis and the potential pathways involving glucoryranose and glycogen degradation were negatively associated with liver fibrosis F1-F2 vs F0. CONCLUSIONS: Without demonstrating causality, our results suggest first a role of bacterial translocation to the liver in the progression of fibrosis, notably at the earliest stages. Second, our statistical approach can identify microbial signatures and overcome issues regarding sample size differences, the impact of environment, and sets of analyses. TRIAL REGISTRATION: TirguMECCH ROLIVER Prospective Cohort for the Identification of Liver Microbiota, registration 4065/2014. Registered 01 01 2014.

The Longitudinal Changes in Subcutaneous Abdominal Tissue and Visceral Adipose Tissue Volumetries Are Associated with Iron Status.

Excess iron is known to trigger adipose tissue dysfunction and insulin resistance. Circulating markers of iron status have been associated with obesity and adipose tissue in cross-sectional studies. We aimed to evaluate whether iron status is linked to changes in abdominal adipose tissue longitudinally. Subcutaneous abdominal tissue (SAT) and visceral adipose tissue (VAT) and its quotient (pSAT) were assessed using magnetic resonance imaging (MRI), at baseline and after one year of follow-up, in 131 (79 in follow-up) apparently healthy subjects, with and without obesity. Insulin sensitivity (euglycemic- hyperinsulinemic clamp) and markers of iron status were also evaluated. Baseline serum hepcidin (p = 0.005 and p = 0.002) and ferritin (p = 0.02 and p = 0.01)) were associated with an increase in VAT and SAT over one year in all subjects, while serum transferrin (p = 0.01 and p = 0.03) and total iron-binding capacity (p = 0.02 and p = 0.04) were negatively associated. These associations were mainly observed in women and in subjects without obesity, and were independent of insulin sensitivity. After controlling for age and sex, serum hepcidin was significantly associated with changes in subcutaneous abdominal tissue index (iSAT) (ß = 0.406, p = 0.007) and visceral adipose tissue index (iVAT) (ß = 0.306, p = 0.04), while changes in insulin sensitivity (ß = 0.287, p = 0.03) and fasting triglycerides (ß = -0.285, p = 0.03) were associated with changes in pSAT. These data indicated that serum hepcidin are associated with longitudinal changes in SAT and VAT, independently of insulin sensitivity. This would be the first prospective study evaluating the redistribution of fat according to iron status and chronic inflammation.

Obesity-associated deficits in inhibitory control are phenocopied to mice through gut microbiota changes in one-carbon and aromatic amino acids metabolic pathways.

BACKGROUND: Inhibitory control (IC) is critical to keep long-term goals in everyday life. Bidirectional relationships between IC deficits and obesity are behind unhealthy eating and physical exercise habits. METHODS: We studied gut microbiome composition and functionality, and plasma and faecal metabolomics in association with cognitive tests evaluating inhibitory control (Stroop test) and brain structure in a discovery (n=156), both cross-sectionally and longitudinally, and in an independent replication cohort (n=970). Faecal microbiota transplantation (FMT) in mice evaluated the impact on reversal learning and medial prefrontal cortex (mPFC) transcriptomics. RESULTS: An interplay among IC, brain structure (in humans) and mPFC transcriptomics (in mice), plasma/faecal metabolomics and the gut metagenome was found. Obesity-dependent alterations in one-carbon metabolism, tryptophan and histidine pathways were associated with IC in the two independent cohorts. Bacterial functions linked to one-carbon metabolism (thyX,dut, exodeoxyribonuclease V), and the anterior cingulate cortex volume were associated with IC, cross-sectionally and longitudinally. FMT from individuals with obesity led to alterations in mice reversal learning. In an independent FMT experiment, human donor's bacterial functions related to IC deficits were associated with mPFC expression of one-carbon metabolism-related genes of recipient's mice. CONCLUSION: These results highlight the importance of targeting obesity-related impulsive behaviour through the induction of gut microbiota shifts.

Morbidly obese subjects show increased serum sulfide in proportion to fat mass.

BACKGROUND AND OBJECTIVES: The importance of hydrogen sulfide is increasingly recognized in the pathophysiology of obesity and type 2 diabetes in animal models. Very few studies have evaluated circulating sulfides in humans, with discrepant results. Here, we aimed to investigate serum sulfide levels according to obesity. SUBJECTS AND METHODS: Serum sulfide levels were analyzed, using a selective fluorescent probe, in two independent cohorts [cross-sectionally in discovery (n = 139) and validation (n = 71) cohorts, and longitudinally in 82 participants from discovery cohort]. In the validation cohort, blood gene expression of enzymes contributing to H2S generation and consumption were also measured. RESULTS: In the discovery cohort, serum sulfide concentration was significantly increased in subjects with morbid obesity at baseline and follow-up, and positively correlated with BMI and fat mass, but negatively with total cholesterol, haemoglobin, serum ferritin, iron and bilirubin after adjusting by age, gender and fat mass. Fat mass (ß = 0.51, t = 3.67, p < 0.0001) contributed independently to age-, gender-, insulin sensitivity- and BMI-adjusted serum sulfide concentration variance. Importantly, receiver operating characteristic analysis demonstrated the relevance of fat mass predicting serum sulfide levels, which was replicated in the validation cohort. In addition, serum sulfide concentration was decreased in morbidly obese subjects with impaired compared to those with normal fasting glucose. Longitudinally, weight gain resulted in increased serum sulfide concentration, whereas weight loss had opposite effects, being the percent change in serum sulfide positively correlated with the percent change in BMI and waist circumference, but negatively with bilirubin. Whole blood CBS, CTH, MPST, SQOR, TST and MPO gene expression was not associated to obesity or serum sulfide concentration. CONCLUSIONS: Altogether these data indicated that serum sulfide concentrations were increased in subjects with morbid obesity in proportion to fat mass and inversely associated with circulating markers of haem degradation.

Microbiota impacts on chronic inflammation and metabolic syndrome - related cognitive dysfunction.

Cognitive dysfunction, one of the major concerns of increased life expectancy, is prevalent in patients with metabolic disorders. Added to the inflammation in the context of aging (inflammaging), low-grade chronic inflammation (metaflammation) accompanies metabolic diseases. Peripheral and central inflammation underlie metabolic syndrome - related cognitive dysfunction. The gut microbiota is increasingly recognized to be linked to both inflammaging and metaflammation in parallel to the pathophysiology of obesity, type 2 diabetes and the metabolic syndrome. Microbiota composition, diversity and diverse metabolites have been related to different metabolic features and cognitive traits. The study of different mouse models has contributed to identify characteristic microbiota profiles and shifts in the microbial gene richness in association with cognitive function. Diet, exercise and prebiotics, probiotics or symbiotics significantly influence cognition and changes in the microbiota. Few studies have analyzed the gut microbiota composition in association with cognitive function in humans. Impaired attention, mental flexibility and executive function have been observed in association with a microbiota ecosystem in cross-sectional and longitudinal studies. Nevertheless, the evidence in humans is still scarce and not causal relationships may be inferred, so larger and long-term studies are required to gain insight into the possible role of microbiota in human cognition.

Lower serum ferritin levels are associated with worse cognitive performance in aging.

OBJECTIVES: Iron is important for neurogenesis, synaptic development, and neurotransmitter synthesis. Serum ferritin (SF) is a reliable marker for assessing iron stores. Therefore, we evaluated the cognitive function associated with SF levels. We also assessed brain iron content using R2* Magnetic Resonance Imaging (MRI) and its association with SF levels. DESIGN: Data from three cross-sectional observational studies were used. Aging Imageomics (n = 1030) was conducted on aged subjects. Health Imageomics (n = 971) and IR0NMET (n = 175) were conducted in middle-aged subjects. SETTING AND PARTICIPANTS: Participants were enrolled at Dr. Josep Trueta University Hospital facilities. The three cohorts included a total of 2176 subjects (mean age, 52 years; 48% men). MEASUREMENTS: SF levels were measured by standard laboratory methods. Total Digits Span (TDS), and Phonemic Verbal Fluency (PVF) were used to assess executive function. Language function was assessed by semantic verbal fluency (SVF), attention by the Symbol Digit Modalities Test, and memory by the Memory Binding Tests - Total Free Recall and Total Delayed Free Recall. MRI was used to assess the iron content of the brain by R2*. RESULTS: In subjects aged 65 years or older, SF levels were associated with increased TDS (ß = 0.003, p = 0.02), PVF (ß = 0.004, p = 0.01), and SVF (ß = 0.004, p = 0.002) scores. After stratification by sex, these findings were significant only in men, where SF was associated with increased TDS (ß = 0.003, p = 0.01), PVF (ß = 0.004, p = 0.03), and SVF (ß = 0.004, p = 0.009) scores. In middle-aged subjects, SF was also associated with increased SVF scores (ß = 0.005, p = 0.011). Lastly, in men, SF levels were negatively associated with R2*, a surrogate marker of brain iron content, in both the left frontal inferior opercular area (r = -0.41, p = 0.005) and the right frontal inferior opercular area (r = -0.44, p = 0.002). CONCLUSIONS: SF is significantly and positively associated with cognition. In older people with low SF levels, iron supplementation may be a promising therapy to improve cognition.

Increased brain fractional perfusion in obesity using intravoxel incoherent motion (IVIM) MRI metrics.

OBJECTIVE: This research seeks to shed light on the associations between brain perfusion, cognitive function, and mental health in individuals with and without obesity. METHODS: In this study, we employed the noninvasive intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) technique to examine brain fractional perfusion (FP) in two groups: individuals with obesity (N = 72) and healthy controls (N = 66). Additionally, we investigated potential associations between FP, cognitive function, and depressive symptoms in the participants with and without obesity. Finally, artificial intelligence algorithms (Boruta analysis) were also used. RESULTS: Participants with obesity exhibited increased FP within dopaminergic brain circuits, particularly involving prefrontal cortex areas, anterior and posterior sections of the cingulate cortex, the right striatum, and the midbrain. Additionally, these individuals demonstrated lower working memory and higher depressive symptoms compared to the control group. Notably, higher FP in the inferior temporal and occipital cortices correlated with greater depressive symptoms, whereas increased FP in the right ventral caudate and the midbrain was associated with better working memory performance. A link between inflammatory and metabolic variables, with a particular emphasis on monocytes, and FP in obesity was also evidenced by Boruta analysis. CONCLUSIONS: Increased brain perfusion in individuals with obesity is associated with cognitive function and mental health through interaction with metabolic and inflammatory factors.

A Simplified Screening Model to Predict the Risk of Gestational Diabetes Mellitus in Caucasian and Latin American Pregnant Women.

The pathophysiology of gestational diabetes mellitus (GDM) comprises clinical and genetic factors. In fact, GDM is associated with several single nucleotide polymorphisms (SNPs). This study aimed to build a prediction model of GDM combining clinical and genetic risk factors. A total of 1588 pregnant women from the San Carlos Cohort participated in the present study, including 1069 (67.3%) Caucasian (CAU) and 519 (32.7%) Latin American (LAT) individuals, and 255 (16.1%) had GDM. The incidence of GDM was similar in both groups (16.1% CAU and 16.0% LAT). Genotyping was performed via IPLEX Mass ARRAY PCR, selecting 110 SNPs based on literature references. SNPs showing the strongest likelihood of developing GDM were rs10830963, rs7651090, and rs1371614 in CAU and rs1387153 and rs9368222 in LAT. Clinical variables, including age, pre-pregnancy body mass index, and fasting plasma glucose (FPG) at 12 gestational weeks, predicted the risk of GDM (AUC 0.648, 95% CI 0.601-0.695 in CAU; AUC 0.688, 95% CI 0.628-9.748 in LAT), and adding SNPs modestly improved prediction (AUC 0.722, 95%CI 0.680-0.764 in CAU; AUC 0.769, 95% CI 0.711-0.826 in LAT). In conclusion, adding genetic variants enhanced the prediction model of GDM risk in CAU and LAT pregnant women.

Gut Microbiota Composition and Functionality Are Associated With REM Sleep Duration and Continuous Glucose Levels.

CONTEXT: Sleep disruption is associated with worse glucose metabolic control and altered gut microbiota in animal models. OBJECTIVE: We aimed to evaluate the possible links among rapid eye movement (REM) sleep duration, continuous glucose levels, and gut microbiota composition. METHODS: This observational, prospective, real-life, cross-sectional case-control study included 118 (60 with obesity), middle-aged (39.1-54.8 years) healthy volunteers recruited at a tertiary hospital. Glucose variability and REM sleep duration were assessed by 10-day continuous glucose monitoring (CGM) (Dexcom G6) and wrist actigraphy (Fitbit Charge 3), respectively. The coefficient of variation (CV), interquartile range (IQR), and SD of glucose variability was assessed and the percentage of time in range (% TIR), at 126-139 mg/dL (TIR2), and 140-199 mg/dL (TIR3) were calculated. Shotgun metagenomics sequencing was applied to study gut microbiota taxonomy and functionality. RESULTS: Increased glycemic variability (SD, CV, and IQR) was observed among subjects with obesity in parallel to increased % TIR2 and % TIR3. REM sleep duration was independently associated with % TIR3 (ß = -.339; P < .001) and glucose variability (SD, ß = -.350; P < .001). Microbial taxa from the Christensenellaceae family (Firmicutes phylum) were positively associated with REM sleep and negatively with CGM levels, while bacteria from Enterobacteriacea family and bacterial functions involved in iron metabolism showed opposite associations. CONCLUSION: Decreased REM sleep duration was independently associated with a worse glucose profile. The associations of species from Christensenellaceae and Enterobacteriaceae families with REM sleep duration and continuous glucose values suggest an integrated picture of metabolic health.

Consumption of ultra-processed foods is associated with depression, mesocorticolimbic volume, and inflammation.

BACKGROUND: The consumption of ultra-processed foods and drinks (UPF) has been associated with depression and inflammation and preclinical studies showed that some UPF components disrupt the amygdala-hippocampal complex. We combine diet, clinical and brain imaging data to investigate the relationship between the UPF consumption, depressive symptoms, and brain volumes in humans, considering interactions with obesity, and the mediation effect of inflammation biomarkers. METHODS: One-hundred fifty-two adults underwent diet, depressive symptoms, anatomic magnetic resonance imaging assessments and laboratory tests. Relationships between the % of UPF consumption (in grams) of the total diet, depressive symptoms, and gray matter brain volumes were explored using several adjusted regression models, and in interaction with the presence of obesity. Whether inflammatory biomarkers (i.e., white blood cell count, lipopolysaccharide-binding protein, c-reactive protein) mediate the previous associations was investigated using R mediation package. RESULTS: High UPF consumption was associated with higher depressive symptoms in all participants (ß = 0.178, CI = 0.008-0.261) and in those with obesity (ß = 0.214, CI = -0.004-0.333). Higher consumption was also associated with lower volumes in the posterior cingulate cortex and the left amygdala, which in the participants with obesity also encompassed the left ventral putamen and the dorsal frontal cortex. White blood count levels mediated the association between UPF consumption and depressive symptoms (p = 0.022). LIMITATIONS: The present study precludes any causal conclusions. CONCLUSIONS: UPF consumption is associated with depressive symptoms and lower volumes within the mesocorticolimbic brain network implicated in reward processes and conflict monitoring. Associations were partially dependent on obesity and white blood cell count.

Adipose tissue coregulates cognitive function.

Obesity is associated with cognitive decline. Recent observations in mice propose an adipose tissue (AT)-brain axis. We identified 188 genes from RNA sequencing of AT in three cohorts that were associated with performance in different cognitive domains. These genes were mostly involved in synaptic function, phosphatidylinositol metabolism, the complement cascade, anti-inflammatory signaling, and vitamin metabolism. These findings were translated into the plasma metabolome. The circulating blood expression levels of most of these genes were also associated with several cognitive domains in a cohort of 816 participants. Targeted misexpression of candidate gene ortholog in the Drosophila fat body significantly altered flies memory and learning. Among them, down-regulation of the neurotransmitter release cycle-associated gene SLC18A2 improved cognitive abilities in Drosophila and in mice. Up-regulation of RIMS1 in Drosophila fat body enhanced cognitive abilities. Current results show previously unidentified connections between AT transcriptome and brain function in humans, providing unprecedented diagnostic/therapeutic targets in AT.

Modifiable Risk Factors and Trends in Changes in Glucose Regulation during the First Three Years Postdelivery: The St Carlos Gestational Diabetes Mellitus Prevention Cohort.

OBJECTIVE: Evaluation of the influence of potential risk factors (RFs) on glycemic changes at 3 years postpartum. METHODS: The glycemic status of 1400 women, in absence of a new pregnancy, was evaluated at 3 months (3 m) and 3 years (3 y) postpartum, after participation in the St. Carlos Gestational Study (2228 normoglycemic pregnant women followed from before gestational week 12 to delivery, from 2015-2017). Abnormal glucose regulation (AGR) was defined as fasting serum glucose ≥ 100 mg/dL and/or HbA1c ≥ 5.7% and/or 2 h 75 g OGTT glucose ≥ 140 mg/dL. In total, 12 modifiable and 3 unmodifiable RFs were analyzed. RESULTS: 3 m postpartum, 110/1400 (7.9%) women had AGR; 3 y postpartum, 137 (9.8%) women exhibited AGR (110 with 3 m normal glucose tolerance [NGT]); 1263 (90.2%) had NGT (83 with 3 m AGR). More women with gestational diabetes mellitus (GDM) progressed to AGR at 3 y (OR: 1.60 [1.33-1.92]) than women without GDM. Yet, most women with 3 m and/or 3 y AGR had no GDM history. Having ≥2 unmodifiable RFs was associated with increased risk for progression to AGR (OR: 1.90 [1.28-2.83]) at 3 y postpartum. Having >5/12 modifiable RFs was associated with increased progression from NGT to AGR (OR: 1.40 [1.00-2.09]) and AGR persistence (OR: 2.57 [1.05-6.31]). Pregestational BMI ≥ 25 kg/m2 (OR: 0.59 [0.41-0.85]), postdelivery weight gain (OR: 0.53 [0.29-0.94]), and waist circumference > 89.5 cm (OR: 0.54 [0.36-0.79]) reduced the likelihood of NGT persisting at 3 y. CONCLUSIONS: 3-month and/or 3-year postpartum AGR can be detected if sought in women with no prior GDM. Modifiable and unmodifiable RF predictors of AGR at 3 y postpartum were identified. Universal screening for glycemic alterations should be considered in all women following delivery, regardless of prior GDM. These findings could be useful to design personalized strategies in women with risk factors for 3 y AGR.

Serum neuregulin 4 is negatively correlated with insulin sensitivity in humans and impairs mitochondrial respiration in HepG2 cells.

Neuregulin 4 (NRG4) has been described to improve metabolic disturbances linked to obesity status in rodent models. The findings in humans are controversial. We aimed to investigate circulating NRG4 in association with insulin action in humans and the possible mechanisms involved. Insulin sensitivity (euglycemic hyperinsulinemic clamp) and serum NRG4 concentration (ELISA) were analysed in subjects with a wide range of adiposity (n = 89). In vitro experiments with human HepG2 cell line were also performed. Serum NRG4 was negatively correlated with insulin sensitivity (r = -0.25, p = 0.02) and positively with the inflammatory marker high-sensitivity C reative protein (hsCRP). In fact, multivariant linear regression analyses showed that insulin sensitivity contributed to BMI-, age-, sex-, and hsCRP-adjusted 7.2% of the variance in serum NRG4 (p = 0.01). No significant associations were found with adiposity measures (BMI, waist circumference or fat mass), plasma lipids (HDL-, LDL-cholesterol, or fasting triglycerides) or markers of liver injury. Cultured hepatocyte HepG2 treated with human recombinant NRG4 had an impact on hepatocyte metabolism, leading to decreased gluconeogenic- and mitochondrial biogenesis-related gene expression, and reduced mitochondrial respiration, without effects on expression of lipid metabolism-related genes. Similar but more pronounced effects were found after neuregulin 1 administration. In conclusion, sustained higher serum levels of neuregulin-4, observed in insulin resistant patients may have deleterious effects on metabolic and mitochondrial function in hepatocytes. However, findings from in vitro experiments should be confirmed in human primary hepatocytes.

Downregulation of peripheral lipopolysaccharide binding protein impacts on perigonadal adipose tissue only in female mice.

BACKGROUND AND AIMS: The sexual dimorphism in fat-mass distribution and circulating leptin and insulin levels is well known, influencing the progression of obesity-associated metabolic disease. Here, we aimed to investigate the possible role of lipopolysaccharide-binding protein (LBP) in this sexual dimorphism. METHODS: The relationship between plasma LBP and fat mass was evaluated in 145 subjects. The effects of Lbp downregulation, using lipid encapsulated unlocked nucleomonomer agent containing chemically modified-siRNA delivery system, were evaluated in mice. RESULTS: Plasma LBP levels were associated with fat mass and leptin levels in women with obesity, but not in men with obesity. In mice, plasma LBP downregulation led to reduced weight, fat mass and leptin gain after a high-fat and high-sucrose diet (HFHS) in females, in parallel to increased expression of adipogenic and thermogenic genes in visceral adipose tissue. This was not observed in males. Plasma LBP downregulation avoided the increase in serum LPS levels in HFHS-fed male and female mice. Serum LPS levels were positively correlated with body weight and fat mass gain, and negatively with markers of adipose tissue function only in female mice. The sexually dimorphic effects were replicated in mice with established obesity. Of note, LBP downregulation led to recovery of estrogen receptor alpha (Esr1) mRNA levels in females but not in males. CONCLUSION: LBP seems to exert a negative feedback on ERα-mediated estrogen action, impacting on genes involved in thermogenesis. The known decreased estrogen action and negative effects of metabolic endotoxemia may be targeted through LBP downregulation.

Presence of Blastocystis in gut microbiota is associated with cognitive traits and decreased executive function.

Growing evidence implicates the gut microbiome in cognition. Blastocystis is a common gut single-cell eukaryote parasite frequently detected in humans but its potential involvement in human pathophysiology has been poorly characterized. Here we describe how the presence of Blastocystis in the gut microbiome was associated with deficits in executive function and altered gut bacterial composition in a discovery (n = 114) and replication cohorts (n = 942). We also found that Blastocystis was linked to bacterial functions related to aromatic amino acids metabolism and folate-mediated pyrimidine and one-carbon metabolism. Blastocystis-associated shifts in bacterial functionality translated into the circulating metabolome. Finally, we evaluated the effects of microbiota transplantation. Donor's Blastocystis subtypes led to altered recipient's mice cognitive function and prefrontal cortex gene expression. In summary, Blastocystis warrant further consideration as a novel actor in the gut microbiome-brain axis.

Caudovirales bacteriophages are associated with improved executive function and memory in flies, mice, and humans.

Growing evidence implicates the gut microbiome in cognition. Viruses, the most abundant life entities on the planet, are a commonly overlooked component of the gut virome, dominated by the Caudovirales and Microviridae bacteriophages. Here, we show in a discovery (n = 114) and a validation cohort (n = 942) that subjects with increased Caudovirales and Siphoviridae levels in the gut microbiome had better performance in executive processes and verbal memory. Conversely, increased Microviridae levels were linked to a greater impairment in executive abilities. Microbiota transplantation from human donors with increased specific Caudovirales (>90% from the Siphoviridae family) levels led to increased scores in the novel object recognition test in mice and up-regulated memory-promoting immediate early genes in the prefrontal cortex. Supplementation of the Drosophila diet with the 936 group of lactococcal Siphoviridae bacteriophages resulted in increased memory scores and upregulation of memory-involved brain genes. Thus, bacteriophages warrant consideration as novel actors in the microbiome-brain axis.

A microRNA Cluster Controls Fat Cell Differentiation and Adipose Tissue Expansion By Regulating SNCG.

The H19X-encoded miR-424(322)/503 cluster regulates multiple cellular functions. Here, it is reported for the first time that it is also a critical linchpin of fat mass expansion. Deletion of this miRNA cluster in mice results in obesity, while increasing the pool of early adipocyte progenitors and hypertrophied adipocytes. Complementary loss and gain of function experiments and RNA sequencing demonstrate that miR-424(322)/503 regulates a conserved genetic program involved in the differentiation and commitment of white adipocytes. Mechanistically, it is demonstrated that miR-424(322)/503 targets γ-Synuclein (SNCG), a factor that mediates this program rearrangement by controlling metabolic functions in fat cells, allowing adipocyte differentiation and adipose tissue enlargement. Accordingly, diminished miR-424(322) in mice and obese humans co-segregate with increased SNCG in fat and peripheral blood as mutually exclusive features of obesity, being normalized upon weight loss. The data unveil a previously unknown regulatory mechanism of fat mass expansion tightly controlled by the miR-424(322)/503 through SNCG.

Orally administered Odoribacter laneus improves glucose control and inflammatory profile in obese mice by depleting circulating succinate.

BACKGROUND: Succinate is produced by both human cells and by gut bacteria and couples metabolism to inflammation as an extracellular signaling transducer. Circulating succinate is elevated in patients with obesity and type 2 diabetes and is linked to numerous complications, yet no studies have specifically addressed the contribution of gut microbiota to systemic succinate or explored the consequences of reducing intestinal succinate levels in this setting. RESULTS: Using germ-free and microbiota-depleted mouse models, we show that the gut microbiota is a significant source of circulating succinate, which is elevated in obesity. We also show in vivo that therapeutic treatments with selected bacteria diminish the levels of circulating succinate in obese mice. Specifically, we demonstrate that Odoribacter laneus is a promising probiotic based on its ability to deplete succinate and improve glucose tolerance and the inflammatory profile in two independent models of obesity (db/db mice and diet-induced obese mice). Mechanistically, this is partly mediated by the succinate receptor 1. Supporting these preclinical findings, we demonstrate an inverse correlation between plasma and fecal levels of succinate in a cohort of patients with severe obesity. We also show that plasma succinate, which is associated with several components of metabolic syndrome including waist circumference, triglycerides, and uric acid, among others, is a primary determinant of insulin sensitivity evaluated by the euglycemic-hyperinsulinemic clamp. CONCLUSIONS: Overall, our work uncovers O. laneus as a promising next-generation probiotic to deplete succinate and improve glucose tolerance and obesity-related inflammation. Video Abstract.

DPP9 as a Potential Novel Mediator in Gastrointestinal Virus Infection.

Dipeptidyl peptidase 9 (DPP9) is a member of the dipeptidyl peptidase IV family. Inhibition of DPP9 has recently been shown to activate the nucleotide-binding domain leucine-rich repeat 1 (NLRP1) inflammasome. NLRP1 is known to bind nucleic acids with high affinity and directly interact with double stranded RNA, which plays a key role in viral replication. DPP9 has also recently emerged as a key gene related to lung-inflammation in critical SARS-CoV-2 infection. Importantly, DPP9 activity is strongly dependent on the oxidative status. Here, we explored the potential role of DPP9 in the gastrointestinal tract. We performed transcriptomics analyses of colon (microarray, n = 37) and jejunal (RNA sequencing, n = 31) biopsies from two independent cohorts as well as plasma metabolomics analyses in two independent cohorts (n = 37 and n = 795). The expression of DPP9 in the jejunum, colon, and blood was significantly associated with circulating biomarkers of oxidative stress (uric acid, bilirubin). It was also associated positively with the expression of transcription factors (NRF-2) and genes (SOD, CAT, GPX) encoding for antioxidant enzymes, but negatively with that of genes (XDH, NOX) and transcription factors (NF-KB) involved in ROS-generating enzymes. Gene co-expression patterns associated with DPP9 identified several genes participating in antiviral pathways in both tissues. Notably, DPP9 expression in the colon and plasma was strongly positively associated with several circulating nucleotide catabolites (hypoxanthine, uric acid, 3-ureidopropionic acid) with important roles in the generation of ROS and viral infection, as well as other metabolites related to oxidative stress (Resolvin D1, glutamate-containing dipeptides). Gene-drug enrichment analyses identified artenimol, puromycin, anisomycin, 3-phenyllactic acid, and linezolid as the most promising drugs targeting these DPP9-associated genes. We have identified a novel potential pathogenic mechanism of viral infection in the digestive tract and promising existing drugs that can be repositioned against viral infection.