Sven Pettersson

Host-Gut Microbiota Metabolic Interactions

The composition and activity of the gut microbiota codevelop with the host from birth and is subject to a complex interplay that depends on the host genome, nutrition, and life-style. The gut microbiota is involved in the regulation of multiple host metabolic pathways, giving rise to interactive host-microbiota metabolic, signaling, and immune-inflammatory axes that physiologically connect the gut, liver, muscle, and brain. A deeper understanding of these axes is a prerequisite for optimizing therapeutic strategies to manipulate the gut microbiota to combat disease and improve health.

Normal gut microbiota modulates brain development and behavior

Microbial colonization of mammals is an evolution-driven process that modulate host physiology, many of which are associated with immunity and nutrient intake. Here, we report that colonization by gut microbiota impacts mammalian brain development and subsequent adult behavior. Using measures of motor activity and anxiety-like behavior, we demonstrate that germ free (GF) mice display increased motor activity and reduced anxiety, compared with specific pathogen free (SPF) mice with a normal gut microbiota. This behavioral phenotype is associated with altered expression of genes known to be involved in second messenger pathways and synaptic long-term potentiation in brain regions implicated in motor control and anxiety-like behavior. GF mice exposed to gut microbiota early in life display similar characteristics as SPF mice, including reduced expression of PSD-95 and synaptophysin in the striatum. Hence, our results suggest that the microbial colonization process initiates signaling mechanisms that affect neuronal circuits involved in motor control and anxiety behavior.

Commensal anaerobic gut bacteria attenuate inflammation by regulating nuclear-cytoplasmic shuttling of PPAR-gamma and RelA.

The human gut microflora is important in regulating host inflammatory responses and in maintaining immune homeostasis. The cellular and molecular bases of these actions are unknown. Here we describe a unique anti-inflammatory mechanism, activated by nonpathogenic bacteria, that selectively antagonizes transcription factor NF-κB. Bacteroides thetaiotaomicron targets transcriptionally active NF-κB subunit RelA, enhancing its nuclear export through a mechanism independent of nuclear export receptor Crm-1. Peroxisome proliferator activated receptor-γ (PPAR-γ), in complex with nuclear RelA, also undergoes nucleocytoplasmic redistribution in response to B. thetaiotaomicron. A decrease in PPAR-γ abolishes both the nuclear export of RelA and the anti-inflammatory activity of B. thetaiotaomicron. This PPAR-γ-dependent anti-inflammatory mechanism defines new cellular targets for therapeutic drug design and interventions for the treatment of chronic inflammation.

Local administration of antisense phosphorothiate olignucleotides to the p65 subunit of NF–κB abrogates established experimental colitis in mice

Chronic intestinal inflammation induced by 2,4,6,–trinitrobenzene sulfonic acid (TNBS) is characterized by a transmural granulomatous colitis that mimics some characteristics of human Crohns disease. Here, we show that the transcription factor NF–κB p65 was strongly activated in TNBS–induced colitis and in colitis of interleukin–10–deficient mice. Local administration of p65 antisense phosphorothioate oligonucleotides abrogated clinical and histological signs of colitis and was more effective in treating TNBS–induced colitis than single or daily administration of glucocorticoids. The data provide direct evidence for the central importance of p65 in chronic intestinal inflammation and suggest a potential therapeutic utility of p65 antisense oligonucleotides as a novel molecular approach for the treatment of patients with Crohns disease.

Genome-wide association identifies multiple ulcerative colitis susceptibility loci

Ulcerative colitis is a chronic, relapsing inflammatory condition of the gastrointestinal tract with a complex genetic and environmental etiology. In an effort to identify genetic variation underlying ulcerative colitis risk, we present two distinct genome-wide association studies of ulcerative colitis and their joint analysis with a previously published scan, comprising, in aggregate, 2,693 individuals with ulcerative colitis and 6,791 control subjects. Fifty-nine SNPs from 14 independent loci attained an association significance of P < 10−5. Seven of these loci exceeded genome-wide significance (P < 5 × 10−8). After testing an independent cohort of 2,009 cases of ulcerative colitis and 1,580 controls, we identified 13 loci that were significantly associated with ulcerative colitis (P < 5 × 10−8), including the immunoglobulin receptor gene FCGR2A, 5p15, 2p16 and ORMDL3 (orosomucoid1-like 3). We confirmed association with 14 previously identified ulcerative colitis susceptibility loci, and an analysis of acknowledged Crohns disease loci showed that roughly half of the known Crohns disease associations are shared with ulcerative colitis. These data implicate approximately 30 loci in ulcerative colitis, thereby providing insight into disease pathogenesis.

The gut microbiota influences blood-brain barrier permeability in mice

The intestinal microbiota helps to maintain the integrity of the blood-brain barrier in fetal and adult mice. The Gut Microbiota and the Blood-Brain Barrier The blood-brain barrier is an important gateway that controls the passage of molecules and nutrients in and out of the brain. An intact blood-brain barrier is a crucial checkpoint for appropriate development and function of the brain. Braniste et al. now show that germ-free pregnant dams, devoid of maternal microbes, have offspring that show increased permeability of the blood-brain barrier. This elevated permeability was also observed in adult germ-free mice. However, fecal transplants from mice exposed to bacteria into adult germ-free mice reduced blood-brain barrier permeability, possibly through the regulation of tight junction proteins. These findings suggest that crosstalk between the gut microbiota and the brain, initiated during the intrauterine period, is perpetuated throughout life. Pivotal to brain development and function is an intact blood-brain barrier (BBB), which acts as a gatekeeper to control the passage and exchange of molecules and nutrients between the circulatory system and the brain parenchyma. The BBB also ensures homeostasis of the central nervous system (CNS). We report that germ-free mice, beginning with intrauterine life, displayed increased BBB permeability compared to pathogen-free mice with a normal gut flora. The increased BBB permeability was maintained in germ-free mice after birth and during adulthood and was associated with reduced expression of the tight junction proteins occludin and claudin-5, which are known to regulate barrier function in endothelial tissues. Exposure of germ-free adult mice to a pathogen-free gut microbiota decreased BBB permeability and up-regulated the expression of tight junction proteins. Our results suggest that gut microbiota–BBB communication is initiated during gestation and propagated throughout life.

Impaired expression of peroxisome proliferator-activated receptor γ in ulcerative colitis

Abstract Background & Aims: The peroxisome proliferator-activated receptor γ (PPARγ) has been proposed as a key inhibitor of colitis through attenuation of nuclear factor κB (NF-κB) activity. In inflammatory bowel disease, activators of NF-κB, including the bacterial receptor toll-like receptor (TLR)4, are elevated. We aimed to determine the role of bacteria and their signaling effects on PPARγ regulation during inflammatory bowel disease (IBD). Methods: TLR4-transfected Caco-2 cells, germ-free mice, and mice devoid of functional TLR4 ( Lps d /Lps d mice) were assessed for their expression of PPARγ in colonic tissues in the presence or absence of bacteria. This nuclear receptor expression and the polymorphisms of gene also were assessed in patients with Crohns disease (CD) and ulcerative colitis (UC), 2 inflammatory bowel diseases resulting from an abnormal immune response to bacterial antigens. Results: TLR4-transfected Caco-2 cells showed that the TLR4 signaling pathway elevated PPARγ expression and a PPARγ-dependent reporter in an Iκκβ dependent fashion. Murine and human intestinal flora induced PPARγ expression in colonic epithelial cells of control mice. PPARγ expression was significantly higher in the colon of control compared with Lps d /Lps d mice. Although PPARγ levels appeared normal in patients with CD and controls, UC patients displayed a reduced expression of PPARγ confined to colonic epithelial cells, without any mutation in the PPARγ gene. Conclusions: These data showed that the commensal intestinal flora affects the expression of PPARγ and that PPARγ expression is considerably impaired in patients with UC.

The yopJ locus is required for Yersinia‐mediated inhibition of NF‐κB activation and cytokine expression: YopJ contains a eukaryotic SH2‐like domain that is essential for its repressive activity

Upon exposure to bacteria, eukaryotic cells activate signalling pathways that result in the increased expression of several defence‐related genes. Here, we report that the yopJ locus of the enteropathogen Yersinia pseudotuberculosis encodes a protein that inhibits the activation of NF‐κB transcription factors by a mechanism(s), which prevents the phosphorylation and subsequent degradation of the inhibitor protein IκB. Consequently, eukaryotic cells infected with YopJ‐expressing Yersinia become impaired in NF‐κB‐dependent cytokine expression. In addition, the blockage of inducible cytokine production coincides with yopJ‐dependent induction of apoptosis. Interestingly, the YopJ protein contains a region that resembles a src homology domain 2 (SH2), and we show that a wild‐type version of this motif is required for YopJ activity in suppressing cytokine expression and inducing apoptosis. As SH2 domains are found in several eukaryotic signalling proteins, we propose that YopJ, which we show is delivered into the cytoplasm of infected cells, interacts directly with signalling proteins involved in inductive cytokine expression. The repressive activity of YopJ on the expression of inflammatory mediators may account for the lack of an inflammatory host response observed in experimental yersiniosis. YopJ‐like activity may also be a common feature of commensal bacteria that, like Yersinia, do not provoke a host inflammatory response.

A constitutively active dioxin/aryl hydrocarbon receptor induces stomach tumors

The dioxin/aryl hydrocarbon receptor (AhR) functions as a ligand-activated transcription factor regulating transcription of a battery of genes encoding xenobiotic metabolizing enzymes. Known receptor ligands are environmental pollutants including polycyclic aromatic hydrocarbons and polychlorinated dioxins. Loss-of-function (gene-disruption) studies in mice have demonstrated that the AhR is involved in toxic effects of dioxins but have not yielded unequivocal results concerning the physiological function of the receptor. Gain-of-function studies therefore were performed to unravel the biological functions of the AhR. A constitutively active AhR expressed in transgenic mice reduced the life span of the mice and induced tumors in the glandular part of the stomach, demonstrating the oncogenic potential of the AhR and implicating the receptor in regulation of cell proliferation.

Cytokine Gene Transcription By NF-κB Family Members in Patients with Inflammatory Bowel Disease

ABSTRACT: We examined the expression of the transcription factor NF‐κB, a nuclear trans‐acting factor known to play a key role in cytokine gene regulation, in patients with inflammatory bowel disease (IBD). It was found that LP macrophages in Crohns disease (CD) and ulcerative colitis (UC) display high levels of NF‐κB DNA‐binding activity accompanied by an increased production of interleukin (IL)‐1, IL‐6, and tumor necrosis factor (TNF)α. Western blot studies showed an increased expression of the p50 and c‐rel subunits of NF‐κB; however, the most striking finding was an increased expression level of NF‐κB p65 in patients with CD and UC. Selective downregulation of p65 in IBD macrophages by a specific antisense phosphorothioate oligonucleotide was sufficient to considerably reduce production of proinflammatory cytokines. These results demonstrate a characteristic increase of NF‐κB binding levels in patients with IBD. The data suggest that antisense DNA targeting NF‐κB p65 can be used as a novel molecular approach for the treatment of patients with IBD.