Microbial Species that Initially Colonize the Human Gut at Birth or in Early Childhood Can Stay in Human Body for Lifetime

High-fat diet, microbiome-gut-brain axis signaling, and anxiety-like behavior in male rats

Obesity, associated with the intake of a high-fat diet (HFD), and anxiety are common among those living in modern urban societies. Recent studies suggest a role of microbiome-gut-brain axis signaling, including a role for brain serotonergic systems in the relationship between HFD and anxiety. Evidence suggests the gut microbiome and the serotonergic brain system together may play an important role in this response. Here we conducted a nine-week HFD protocol in male rats, followed by an analysis of the gut microbiome diversity and community composition, brainstem serotonergic gene expression (tph2, htr1a, and slc6a4), and anxiety-related defensive behavioral responses. We show that HFD intake decreased alpha diversity and altered the community composition of the gut microbiome in association with obesity, increased brainstem tph2, htr1a and slc6a4 mRNA expression, including in the caudal part of the dorsomedial dorsal raphe nucleus (cDRD), a subregion previously associated with stress- and anxiety-related behavioral responses, and, finally, increased anxiety-related defensive behavioral responses. The HFD increased the Firmicutes/Bacteroidetes ratio relative to control diet, as well as higher relative abundances of Blautia, and decreases in Prevotella. We found that tph2, htr1a and slc6a4 mRNA expression were increased in subregions of the dorsal raphe nucleus in the HFD, relative to control diet. Specific bacterial taxa were associated with increased serotonergic gene expression in the cDRD. Thus, we propose that HFD-induced obesity is associated with altered microbiome-gut-serotonergic brain axis signaling, leading to increased anxiety-related defensive behavioral responses in rats.

The re-emerging role of linoleic acid in paediatric asthma

Asthma is the most common chronic disease within the paediatric population. Although it is multifactorial, its onset may be linked to early-life exposures with subsequent impact on immune system development. Microbial and dietary metabolic products have been implicated in the development and exacerbation of paediatric asthma. Linoleic acid is the most common omega-6 polyunsaturated fatty acid in the Western diet. In this review, we summarise the literature regarding the involvement of linoleic acid in the development of and its impact on existing paediatric asthma. First, we summarise the existing knowledge surrounding the relationship between human microbial metabolism and allergic diseases in children. Next, we examine cellular or animal model-based mechanistic studies that investigated the impact of dietary- and microbial-derived linoleic acid metabolites on asthma. Finally, we review the literature investigating the impact of linoleic acid metabolites on the development and exacerbation of childhood asthma. While there is conflicting evidence, there is growing support for a role of linoleic acid in the onset and pathophysiology of asthma. We recommend that additional cellular, animal, and longitudinal studies are performed that target linoleic acid and its metabolites.

Contribution of HLA DRB1, PTPN22, and CTLA4, to RA dysbiosis

This narrative review gathers current evidence for a contribution of rheumatoid arthritis (RA) HLA-DRB1, PTPN22 and CTLA4 polymorphisms to the gut dysbiosis observed in RA, especially at its onset (transient excess of Prevotella). The gut microbiome contains elements which are 30% heritable, including genera like Bacteroides and Veillonella, and to a lesser extent Prevotella. The first months/year seems a critical period for the selection of a core of microbiota, that should be considered as a second self by the immune system, and tolerized by regulatory T and B cells. Imperfect tolerization may increase the risk of RA following further repeated silent translocations of various gut microorganisms, including Prevotella copri, from gut to joints (fostered by a concurrent loss in gut mucosa of protective bacteria like Faecalibacterium prausnitzii). Genetics studies confirmed that Prevotella copri was partly heritable, and strong associations were observed between the overall microbial composition of stools and the HLA-DRB1 RA risk allele, either in a US cohort (P=0.00001), or the Twins UK cohort (P=0.033). This finding also stands for persons still free from RA, and was replicated in the Swiss SCREEN-RA cohort. Gene variants of PTPN22 also modify intestinal microbiota composition, compromise granulocyte-mediated antibacterial defence in gut, and reduce the suppressive effect of gut regulatory B cells. CTLA4 variants may similarly contribute to RA dysbiosis, since immunotherapy by CTLA-4 blockade depends on microbiota, and CTLA4 activates T follicular regulatory cells to reduce immune responses to segmented filamentous bacteria. Suggestions for future works are made.

Disentangling Diet- and Medium-Associated Microbes in Shaping Daphnia Gut Microbiome

Host genotype and environment are considered crucial factors in shaping Daphnia gut microbiome composition. Among the environmental factors, diet is an important factor that regulates Daphnia microbiome. Most of the studies only focused on the use of axenic diet and non-sterile medium to investigate their effects on Daphnia microbiome. However, in natural environment, Daphnia diets such as phytoplankton are associated with microbes and could affect Daphnia microbiome composition and fitness, but remain relatively poorly understood compared to that of axenic diet. To test this, we cultured two Daphnia magna genotypes (genotype-1 and genotype-2) in sterile medium and fed with axenic diet. To check the effects of algal diet-associated microbes versus free water-related microbes, Daphnia were respectively inoculated with three different inoculums: medium microbial inoculum, diet-associated microbial inoculum, and medium and diet-mixed microbial inoculum. Daphnia were cultured for 3 weeks and their gut microbiome and life history traits were recorded. Results showed that Daphnia inoculated with medium microbial inoculum were dominated by Comamonadaceae in both genotypes. In Daphnia inoculated with mixed inoculum, genotype-1 microbiome was highly changed, whereas genotype-2 microbiome was slightly altered. Daphnia inoculated with diet microbial inoculum has almost the same microbiome in both genotypes. The total number of neonates and body size were significantly reduced in Daphnia inoculated with diet microbial inoculum regardless of genotype compared to all other treatments. Overall, this study shows that the microbiome of Daphnia is flexible and varies with genotype and diet- and medium-associated microbes, but not every bacteria is beneficial to Daphnia, and only symbionts can increase Daphnia performance.

Microbiome-Immune Interactions in Allergy and Asthma

The human microbiota has been established as a key regulator of host health, in large part owing to its constant interaction with and impact on host immunity. A range of environmental exposures spanning from the prenatal period through adulthood are known to affect the composition and molecular productivity of microbiomes across mucosal and dermal tissues with short- and long-term consequences for host immune function. Here we review recent findings in the field that provide insights into how microbial-immune interactions promote and sustain immune dysfunction associated with allergy and asthma. We consider both early life microbiome perturbation and the molecular underpinnings of immune dysfunction associated with subsequent allergy and asthma development in childhood, as well as microbiome features that relate to phenotypic attributes of allergy and asthma in older patients with established disease.

Heritable vaginal bacteria influence immune tolerance and relate to early-life markers of allergic sensitization in infancy

Maternal asthma status, prenatal exposures, and infant gut microbiota perturbation are associated with heightened risk of atopy and asthma risk in childhood, observations hypothetically linked by intergenerational microbial transmission. Using maternal vaginal (n = 184) and paired infant stool (n = 172) samples, we identify four compositionally and functionally distinct Lactobacillus-dominated vaginal microbiota clusters (VCs) that relate to prenatal maternal health and exposures and infant serum immunoglobulin E (IgE) status at 1 year. Variance in bacteria shared between mother and infant pairs relate to VCs, maternal allergy/asthma status, and infant IgE levels. Heritable bacterial gene pathways associated with infant IgE include fatty acid synthesis and histamine and tryptophan degradation. In vitro, vertically transmitted Lactobacillus jensenii strains induce immunosuppressive phenotypes on human antigen-presenting cells. Murine supplementation with L. jensenii reduces lung eosinophils, neutrophilic expansion, and the proportion of interleukin-4 (IL-4)⁺ CD4⁺ T cells. Thus, bacterial and atopy heritability are intimately linked, suggesting a microbial component of intergenerational disease transmission.