Louise Grahnemo

The Gut Microbiota Reduces Leptin Sensitivity and the Expression of the Obesity-Suppressing Neuropeptides Proglucagon (Gcg) and Brain-Derived Neurotrophic Factor (Bdnf) in the Central Nervous System

The gut microbiota contributes to fat mass and the susceptibility to obesity. However, the underlying mechanisms are not completely understood. To investigate whether the gut microbiota affects hypothalamic and brainstem body fat-regulating circuits, we compared gene expression of food intake-regulating neuropeptides between germ-free and conventionally raised (CONV-R) mice. We found that CONV-R mice had decreased expression of the antiobesity neuropeptide glucagon-like peptide-1 (GLP-1) precursor proglucagon (Gcg) in the brainstem. Moreover, in both the hypothalamus and the brainstem, CONV-R mice had decreased expression of the antiobesity neuropeptide brain-derived neurotrophic factor (Bdnf). CONV-R mice had reduced expression of the pro-obesity peptides neuropeptide-Y (Npy) and agouti-related protein (Agrp), and increased expression of the antiobesity peptides proopiomelanocortin (Pomc) and cocaine- and amphetamine-regulated transcript (Cart) in the hypothalamus. The latter changes in neuropeptide expression could be secondary to elevated fat mass in CONV-R mice. Leptin treatment caused less weight reduction and less suppression of orexigenic Npy and Agrp expression in CONV-R mice compared with germ-free mice. The hypothalamic expression of leptin resistance-associated suppressor of cytokine signaling 3 (Socs-3) was increased in CONV-R mice. In conclusion, the gut microbiota reduces the expression of 2 genes coding for body fat-suppressing neuropeptides, Gcg and Bdnf, an alteration that may contribute to fat mass induction by the gut microbiota. Moreover, the presence of body fat-inducing gut microbiota is associated with hypothalamic signs of Socs-3-mediated leptin resistance, which may be linked to failed compensatory body fat reduction.

Estrogen regulates T helper 17 phenotype and localization in experimental autoimmune arthritis

IntroductionThe incidence and progression of many autoimmune diseases are sex-biased, which might be explained by the immunomodulating properties of endocrine hormones. Treatment with estradiol potently inhibits experimental autoimmune arthritis. Interleukin-17-producing T helper cells (Th17) are key players in several autoimmune diseases, particularly in rheumatoid arthritis. The aim of this study was to investigate the effects of estrogen on Th17 cells in experimental arthritis.MethodsOvariectomized DBA/1 mice treated with 17β-estradiol (E2) or placebo were subjected to collagen-induced arthritis (CIA), and arthritis development was assessed. Th17 cells in joints and lymph nodes were studied by flow cytometry. Lymph node Th17 cells were also examined in ovariectomized estrogen receptor α–knockout mice (ERα−/−) and wild-type littermates, treated with E2 or placebo and subjected to antigen-induced arthritis.ResultsE2-treated mice with established CIA showed reduced severity of arthritis and fewer Th17 cells in joints compared with controls. Interestingly, E2-treated mice displayed increased Th17 cells in lymph nodes during the early phase of the disease, dependent on ERα. E2 increased the expression of C-C chemokine receptor 6 (CCR6) on lymph node Th17 cells as well as the expression of the corresponding C-C chemokine ligand 20 (CCL20) within lymph nodes.ConclusionsThis is the first study in which the effects of E2 on Th17 cells have been characterized in experimental autoimmune arthritis. We report that E2 treatment results in an increase of Th17 cells in lymph nodes during the early phase of arthritis development, but leads to a decrease of Th17 in joints during established arthritis. Our data suggest that this may be caused by interference with the CCR6-CCL20 pathway, which is important for Th17 cell migration. This study contributes to the understanding of the role of estrogen in the development of autoimmune arthritis and opens up new fields for research concerning the sex bias in autoimmune disease.

Inter-relation between Interleukin (IL)-1, IL-6 and Body Fat Regulating Circuits of the Hypothalamic Arcuate Nucleus

Interleukin (IL)‐1 and IL‐6 are immune modulating cytokines that also affect metabolic function because both IL‐1 receptor I deficient (IL‐1RI−/−) and IL‐6 deficient (IL‐6−/−) mice develop late‐onset obesity and leptin resistance. Both IL‐1 and IL‐6 appear to target the central nervous system (CNS) to increase energy expenditure. The hypothalamic arcuate nucleus (ARC) is a major relay between the periphery and CNS in body fat regulation (e.g. by being a target of leptin). The present study aimed to investigate the possible mechanisms responsible for the effects exerted by endogenous IL‐1 and IL‐6 on body fat at the level of the ARC, as well as possible interactions between IL‐1 and IL‐6. Therefore, we measured the gene expression of neuropeptides of the ARC involved in energy balance in IL‐1RI−/− and IL‐6−/− mice. We also investigated the interactions between expression of IL‐1 and IL‐6 in these mice, and mapped IL‐6 receptor α (IL‐6Rα) in the ARC. The expression of the obesity promoting peptide neuropeptide Y (NPY), found in the ARC, was increased in IL‐1RI−/− mice. The expression of NPY and agouti‐related peptide (AgRP), known to be co‐expressed with NPY in ARC neurones, was increased in cold exposed IL‐6−/− mice. IL‐6Rα immunoreactivity was densely localised in the ARC, especially in the medial part, and was partly found in NPY positive cell bodies and also α‐melanocyte‐stimulating hormone positive cell bodies. The expression of hypothalamic IL‐6 was decreased in IL‐1RI−/− mice, whereas IL‐1ß expression was increased in IL‐6−/− mice. The results of the present study indicate that depletion of the activity of the fat suppressing cytokines IL‐1 and IL‐6 in knockout mice can increase the expression of the obesity promoting neuropeptide NPY in the ARC. Depletion of IL‐1 activity suppresses IL‐6 expression, and IL‐6Rα‐like immunoreactivity is present in neurones in the medial ARC, including neurones containing NPY. Therefore, IL‐6, IL‐1 and NPY/AgRP could interact at the level of the hypothalamic ARC in the regulation of body fat.

Effects of lasofoxifene and bazedoxifene on B cell development and function.

The third generation selective estrogen receptor modulators lasofoxifene (las) and bazedoxifene (bza) are indicated for treatment of postmenopausal osteoporosis. 17β‐Estradiol (E2) and the second generation SERM raloxifene (ral) have major effects on the immune system, particularly on B cells. Treatment with E2 or ral inhibits B lymphopoiesis and treatment with E2, but not ral, stimulates antibody production. The effects of las and bza on the immune system have not been studied. Therefore, the aim of this study was to investigate their role in B cell development, maturation, and function. C57BL/6 mice were sham‐operated or ovariectomized (ovx) and treated with vehicle, E2, ral, las, or bza. All substances increased total bone mineral density in ovx mice, as measured by peripheral quantitative computed tomography. In uterus, bza alone lacked agonistic effect in ovx mice and even acted as an antagonist in sham mice. As expected, E2 decreased B cell numbers at all developmental stages from pre‐BI cells (in bone marrow) to transitional 1 (T1) B cells (in spleen) and increased marginal zone (MZ) B cells as determined by flow cytometry. However, treatment with las or bza only decreased the last stages of bone marrow B cell development and splenic T1 B cells, but had no effect MZ B cells. E2 increased antibody‐producing cells quantified by ELISPOT, but las or bza did not. In conclusion, las and bza differ from E2 by retaining normal number of cells at most B cell stages during B lymphopoiesis and maturation and by not increasing antibody‐producing cells.

Regulation of body fat mass by the gut microbiota: Possible mediation by the brain

New insight suggests gut microbiota as a component in energy balance. However, the underlying mechanisms by which gut microbiota can impact metabolic regulation is unclear. A recent study from our lab shows, for the first time, a link between gut microbiota and energy balance circuitries in the hypothalamus and brainstem. In this article we will review this study further.

Selective estrogen receptor modulators in T cell development and T cell dependent inflammation.

Lasofoxifene (las) and bazedoxifene (bza) are third generation selective estrogen receptor modulators (SERMs) with minimal estrogenic side effects, approved for treatment of postmenopausal osteoporosis. T cells are involved in the pathology of postmenopausal osteoporosis and previous studies have established an important role for 17β-estradiol (E2) in T cell development and function. E2 causes a drastic thymic atrophy, alters the composition of thymic T cell populations, and inhibits T cell dependent inflammation. In contrast, the second generation SERM raloxifene (ral) lacks these properties. Although las and bza are drugs approved for treatment of postmenopausal bone loss, it is of importance to study their effects on other biological aspects in order to extend the potential use of these compounds. Therefore, the aim of this study was to investigate if treatment with las and bza affects T lymphopoiesis and T cell dependent inflammation. C57Bl6 mice were ovariectomized (ovx) and treated with vehicle, E2, ral, las or bza. As expected, E2 reduced both thymus weight and decreased the proportion of early T cell progenitors while increasing more mature T cell populations in the thymus. E2 also suppressed the T cell dependent delayed-type hypersensitivity (DTH) reaction to oxazolone (OXA). Ral and las, but not bza, decreased thymus weight, while none of the SERMs had any effects on T cell populations in the thymus or on inflammation in DTH. In conclusion, this study shows that treatment with las or bza does not affect T lymphopoiesis or T cell dependent inflammation.

Dietary Polyunsaturated Fatty Acids Increase Survival and Decrease Bacterial Load during Septic Staphylococcus aureus Infection and Improve Neutrophil Function in Mice

ABSTRACT Severe infection, including sepsis, is an increasing clinical problem that causes prolonged morbidity and substantial mortality. At present, antibiotics are essentially the only pharmacological treatment for sepsis. The incidence of resistance to antibiotics is increasing; therefore, it is critical to find new therapies for sepsis. Staphylococcus aureus is a major cause of septic mortality. Neutrophils play an important role in the defense against bacterial infections. We have shown that a diet with high levels of dietary saturated fatty acids decreases survival in septic mice, but the mechanisms behind this remain elusive. The aim of the present study was to investigate how the differences in dietary fat composition affect survival and bacterial load after experimental septic infection and neutrophil function in uninfected mice. We found that, after S. aureus infection, mice fed a polyunsaturated high-fat diet (HFD-P) for 8 weeks had increased survival and decreased bacterial load during sepsis compared with mice fed a saturated high-fat diet (HFD-S), similar to mice fed a low-fat diet (LFD). Uninfected mice fed HFD-P had a higher frequency of neutrophils in bone marrow than mice fed HFD-S. In addition, mice fed HFD-P had a higher frequency of neutrophils recruited to the site of inflammation in response to peritoneal injection of thioglycolate than mice fed HFD-S. Differences between the proportion of dietary protein and carbohydrate did not affect septic survival at all. In conclusion, polyunsaturated dietary fat increased both survival and efficiency of bacterial clearance during septic S. aureus infection. Moreover, this diet increased the frequency and chemotaxis of neutrophils, key components of the immune response to S. aureus infections.

IL-17-producing γδT cells are regulated by estrogen during development of experimental arthritis

Interleukin-17 (IL-17) drives inflammation and destruction of joints in rheumatoid arthritis (RA). The female sex hormone 17β-estradiol (E2) inhibits experimental arthritis. γδT cells are significant producers of IL-17, thus the aim of this study was to investigate if E2 influenced IL-17(+) γδT cells during arthritis development using a variety of experimental RA models: collagen-induced arthritis (CIA); antigen-induced arthritis (AIA); and collagen antibody-induced arthritis (CAIA). We demonstrate that E2 treatment decreases IL-17(+) γδT cell number in joints, but increases IL-17(+) γδT cells in draining lymph nodes, suggesting an E2-mediated prevention of IL-17(+) γδT cell migration from lymph nodes to joints, in concert with our recently reported effects of E2 on Th17 cells (Andersson et al., 2015). E2 did neither influence the general γδT cell population nor IFNγ(+) γδT cells, implying a selective regulation of IL-17-producing cells. In conclusion, this study contributes to the understanding of estrogens role in autoimmune disease.

Six Tissue Transcriptomics Reveals Specific Immune Suppression in Spleen by Dietary Polyunsaturated Fatty Acids.

Dietary polyunsaturated fatty acids (PUFA) are suggested to modulate immune function, but the effects of dietary fatty acids composition on gene expression patterns in immune organs have not been fully characterized. In the current study we investigated how dietary fatty acids composition affects the total transcriptome profile, and especially, immune related genes in two immune organs, spleen (SPL) and bone marrow cells (BMC). Four tissues with metabolic function, skeletal muscle (SKM), white adipose tissue (WAT), brown adipose tissue (BAT), and liver (LIV), were investigated as a comparison. Following 8 weeks on low fat diet (LFD), high fat diet (HFD) rich in saturated fatty acids (HFD-S), or HFD rich in PUFA (HFD-P), tissue transcriptomics were analyzed by microarray and metabolic health assessed by fasting blood glucose level, HOMA-IR index, oral glucose tolerance test as well as quantification of crown-like structures in WAT. HFD-P corrected the metabolic phenotype induced by HFD-S. Interestingly, SKM and BMC were relatively inert to the diets, whereas the two adipose tissues (WAT and BAT) were mainly affected by HFD per se (both HFD-S and HFD-P). In particular, WAT gene expression was driven closer to that of the immune organs SPL and BMC by HFDs. The LIV exhibited different responses to both of the HFDs. Surprisingly, the spleen showed a major response to HFD-P (82 genes differed from LFD, mostly immune genes), while it was not affected at all by HFD-S (0 genes differed from LFD). In conclusion, the quantity and composition of dietary fatty acids affected the transcriptome in distinct manners in different organs. Remarkably, dietary PUFA, but not saturated fat, prompted a specific regulation of immune related genes in the spleen, opening the possibility that PUFA can regulate immune function by influencing gene expression in this organ.

Dietary Omega-3 Fatty Acids Increase Survival and Decrease Bacterial Load in Mice Subjected to Staphylococcus aureus-Induced Sepsis

ABSTRACT Sepsis caused by Staphylococcus aureus is increasing in incidence. With the alarming use of antibiotics, S. aureus is prone to become methicillin resistant. Antibiotics are the only widely used pharmacological treatment for sepsis. Interestingly, mice fed high-fat diet (HFD) rich in polyunsaturated fatty acids have better survival of S. aureus-induced sepsis than mice fed HFD rich in saturated fatty acids (HFD-S). To investigate what component of polyunsaturated fatty acids, i.e., omega-3 or omega-6 fatty acids, exerts beneficial effects on the survival of S. aureus-induced sepsis, mice were fed HFD rich in omega-3 or omega-6 fatty acids for 8 weeks prior to inoculation with S. aureus. Further, mice fed HFD-S were treated with omega-3 fatty acid metabolites known as resolvins. Mice fed HFD rich in omega-3 fatty acids had increased survival and decreased bacterial loads compared to those for mice fed HFD-S after S. aureus-induced sepsis. Furthermore, the bacterial load was decreased in resolvin-treated mice fed HFD-S after S. aureus-induced sepsis compared with that in mice treated with vehicle. Dietary omega-3 fatty acids increase the survival of S. aureus-induced sepsis by reversing the deleterious effect of HFD-S on mouse survival.