IL-17 signaling accelerates the progression of nonalcoholic fatty liver disease in mice

Inflammation plays a central pathogenic role in the pernicious metabolic and end-organ sequelae of obesity. Among these sequelae, nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease in the developed world. The twinned observations that obesity is associated with increased activation of the interleukin (IL)-17 axis and that this axis can regulate liver damage in diverse contexts prompted us to address the role of IL-17RA signaling in the progression of NAFLD. We further examined whether microbe-driven IL-17A regulated NAFLD development and progression. We show here that IL-17RA−/− mice respond to high-fat diet stress with significantly greater weight gain, visceral adiposity, and hepatic steatosis than wild-type controls. However, obesity-driven lipid accumulation was uncoupled from its end-organ consequences in IL-17RA−/− mice, which exhibited decreased steatohepatitis, nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase enzyme expression, and hepatocellular damage. Neutralization of IL-17A significantly reduced obesity-driven hepatocellular damage in wild-type mice. Further, colonization of mice with segmented filamentous bacteria (SFB), a commensal that induces IL-17A production, exacerbated obesity-induced hepatocellular damage. In contrast, SFB depletion protected from obesity-induced hepatocellular damage. Conclusion: These data indicate that obesity-driven activation of the IL-17 axis is central to the development and progression of NAFLD to steatohepatitis and identify the IL-17 pathway as a novel therapeutic target in this condition. (Hepatology 2014;59:1830–1839

Differential colonization with segmented filamentous bacteria and Lactobacillus murinus do not drive divergent development of diet-induced obesity in C57BL/6 mice

Alterations in the gut microbiota have been proposed to modify the development and maintenance of obesity and its sequelae. Definition of underlying mechanisms has lagged, although the ability of commensal gut microbes to drive pathways involved in inflammation and metabolism has generated compelling, testable hypotheses. We studied C57BL/6 mice from two vendors that differ in their obesogenic response and in their colonization by specific members of the gut microbiota having well-described roles in regulating gut immune responses. We confirmed the presence of robust differences in weight gain in mice from these different vendors during high fat diet stress. However, neither specific, highly divergent members of the gut microbiota (Lactobacillus murinus, segmented filamentous bacteria) nor the horizontally transmissible gut microbiota were found to be responsible. Constitutive differences in locomotor activity were observed, however. These data underscore the importance of selecting appropriate controls in this widely used model of human obesity

An examination of the effects of simvastatin on innate immune responses to S. aureus

Staphylococcus aureus is one of the most prevalent etiologic agents causing sepsis, a systemic inflammatory response to foreign pathogenic invasion. S. aureus infections have become increasingly common. Alternative therapies are needed since prevention of S. aureus-induced sepsis requires aggressive medical treatments that are not entirely effective. Simvastatin may be one such treatment. Studies from our collaborator’s lab show that simvastatin pre-treatment increases survival of S. aureus-infected C57BL/6 mice. The goal of these studies is to examine the effect of simvastatin pre-treatment on the activation of the inflammatory, coagulation, and complement pathways to elicit a mechanism explaining the increased survival of simvastatin-treated, S. aureus-infected mice. Thus far, we have examined bacterial clearance and TNF production, and found that mice pretreated with simvastatin have comparable bacterial clearance and serum TNF levels when compared to non-treated controls. Establishing the role of simvastatin in these innate immune pathways is important to determining the possibility of simvastatin being used as an adjunctive therapeutic agent for the treatment of sepsis.Department of BiologyThesis (M.A.

An examination of the effects of simvastatin on innate immune responses to S. aureus

Staphylococcus aureus is one of the most prevalent etiologic agents causing sepsis, a systemic inflammatory response to foreign pathogenic invasion. S. aureus infections have become increasingly common. Alternative therapies are needed since prevention of S. aureus-induced sepsis requires aggressive medical treatments that are not entirely effective. Simvastatin may be one such treatment. Studies from our collaborator’s lab show that simvastatin pre-treatment increases survival of S. aureus-infected C57BL/6 mice. The goal of these studies is to examine the effect of simvastatin pre-treatment on the activation of the inflammatory, coagulation, and complement pathways to elicit a mechanism explaining the increased survival of simvastatin-treated, S. aureus-infected mice. Thus far, we have examined bacterial clearance and TNF production, and found that mice pretreated with simvastatin have comparable bacterial clearance and serum TNF levels when compared to non-treated controls. Establishing the role of simvastatin in these innate immune pathways is important to determining the possibility of simvastatin being used as an adjunctive therapeutic agent for the treatment of sepsis.Thesis (M.A.)Department of Biolog

Regulation of Inflammation by IL-17A and IL-17F Modulates Non-Alcoholic Fatty Liver Disease Pathogenesis.

Non-alcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide. While it is well-accepted that inflammation is central to NAFLD pathogenesis, the immune pathway(s) orchestrating disease progression are poorly defined. Notably, IL-17RA signaling, via IL-17A, plays an important role in obesity-driven NAFLD pathogenesis. However, the role of the IL-17F, another IL-17RA ligand, in NAFLD pathogenesis has not been examined. Further, the cell types expressing IL-17RA and producing IL-17RA ligands in the pathogenesis of NAFLD have not been defined. Here, IL-17RA-/-, IL-17A-/-, IL-17F-/- and wild-type (WT) mice were fed either standard chow diet or methionine and choline deficient diet (MCDD)--a diet known to induce steatosis and hepatic inflammation through beta-oxidation dysfunction--and hepatic inflammation and NAFLD progression were subsequently quantified. MCDD feeding augmented hepatic IL-17RA expression and significantly increased hepatic infiltration of macrophages and IL-17A and IL-17F producing CD4+ and CD8+ T cells in WT mice. In contrast, IL-17RA-/-, IL-17A-/-, and IL-17F-/- mice, despite increased steatosis, exhibited significant protection from hepatocellular damage compared to WT controls. Protection from hepatocellular damage correlated with decreased levels of hepatic T-cell and macrophage infiltration and decreased expression of inflammatory mediators associated with NAFLD. In sum, our results indicate that the IL-17 axis also plays a role in a MCDD-induced model of NAFLD pathogenesis. Further, we show for the first time that IL-17F, and not only IL-17A, plays an important role in NAFLD driven inflammation

Maternal regulation of inflammatory cues is required for induction of preterm birth

Infection-driven inflammation in pregnancy is a major cause of spontaneous preterm birth (PTB). Both systemic infection and bacterial ascension through the vagina/cervix to the amniotic cavity are strongly associated with PTB. However, the contribution of maternal or fetal inflammatory responses in the context of systemic or localized models of infection-driven PTB is not well defined. Here, using intraperitoneal or intraamniotic LPS challenge, we examined the necessity and sufficiency of maternal and fetal Toll-like receptor (TLR) 4 signaling in induction of inflammatory vigor and PTB. Both systemic and local LPS challenge promoted induction of inflammatory pathways in uteroplacental tissues and induced PTB. Restriction of TLR4 expression to the maternal compartment was sufficient for induction of LPS-driven PTB in either systemic or intraamniotic challenge models. In contrast, restriction of TLR4 expression to the fetal compartment failed to induce LPS-driven PTB. Vav1-Cre–mediated genetic deletion of TLR4 suggested a critical role for maternal immune cells in inflammation-driven PTB. Further, passive transfer of WT in vitro–derived macrophages and dendritic cells to TLR4-null gravid females was sufficient to induce an inflammatory response and drive PTB. Cumulatively, these findings highlight the critical role for maternal regulation of inflammatory cues in induction of inflammation-driven parturition

Modulation of ambient temperature promotes inflammation and initiates atherosclerosis in wild type C57BL/6 mice

Objectives: Obesity and obesity-associated inflammation is central to a variety of end-organ sequelae including atherosclerosis, a leading cause of death worldwide. Although mouse models have provided important insights into the immunopathogenesis of various diseases, modeling atherosclerosis in mice has proven difficult. Specifically, wild-type (WT) mice are resistant to developing atherosclerosis, while commonly used genetically modified mouse models of atherosclerosis are poor mimics of human disease. The lack of a physiologically relevant experimental model of atherosclerosis has hindered the understanding of mechanisms regulating disease development and progression as well as the development of translational therapies. Recent evidence suggests that housing mice within their thermoneutral zone profoundly alters murine physiology, including both metabolic and immune processes. We hypothesized that thermoneutral housing would allow for augmentation of atherosclerosis induction and progression in mice. Methods: ApoE−/− and WT mice were housed at either standard (TS) or thermoneutral (TN) temperatures and fed either a chow or obesogenic “Western” diet. Analysis included quantification of (i) obesity and obesity-associated downstream sequelae, (ii) the development and progression of atherosclerosis, and (iii) inflammatory gene expression pathways related to atherosclerosis. Results: Housing mice at TN, in combination with an obesogenic “Western” diet, profoundly augmented obesity development, exacerbated atherosclerosis in ApoE−/− mice, and initiated atherosclerosis development in WT mice. This increased disease burden was associated with altered lipid profiles, including cholesterol levels and fractions, and increased aortic plaque size. In addition to the mild induction of atherosclerosis, we similarly observed increased levels of aortic and white adipose tissue inflammation and increased circulating immune cell expression of pathways related to adverse cardiovascular outcome. Conclusions: In sum, our novel data in WT C57Bl/6 mice suggest that modulation of a single environmental variable, temperature, dramatically alters mouse physiology, metabolism, and inflammation, allowing for an improved mouse model of atherosclerosis. Thus, thermoneutral housing of mice shows promise in yielding a better understanding of the cellular and molecular pathways underlying the pathogenesis of diverse diseases. Keywords: Atherosclerosis, Thermoneutrality, Inflammatio

Aging mitigates the severity of obesity-associated metabolic sequelae in a gender independent manner

Abstract Background Understanding gender-associated bias in aging and obesity-driven metabolic derangements has been hindered by the inability to model severe obesity in female mice. Methods Here, using chow- or high fat diet (HFD)-feeding regimens at standard (TS) and thermoneutral (TN) housing temperatures, the latter to model obesity in female mice, we examined the impact of gender and aging on obesity-associated metabolic derangements and immune responsiveness. Analysis included quantification of: (i) weight gain and adiposity; (ii) the development and severity of glucose dysmetabolism and non-alcoholic fatty liver disease (NAFLD); and (iii) induction of inflammatory pathways related to metabolic dysfunction. Results We show that under chow diet feeding regimen, aging was accompanied by increased body weight and white adipose tissue (WAT) expansion in a gender independent manner. HFD feeding regimen in aged, compared to young, male mice at TS, resulted in attenuated glucose dysmetabolism and hepatic steatosis. However, under TS housing conditions only aged, but not young, HFD fed female mice developed obesity. At TN however, both young and aged HFD fed female mice developed severe obesity. Independent of gender or housing conditions, aging attenuated the severity of metabolic derangements in HFD-fed obese mice. Tempered severity of metabolic derangements in aged mice was associated with increased splenic frequency of regulatory T (Treg) cells, Type I regulatory (Tr1)-like cells and circulating IL-10 levels and decreased vigor of HFD-driven induction of inflammatory pathways in adipose and liver tissues. Conclusion Our findings suggest that aging-associated altered immunological profile and inflammatory vigor may play a dominant role in the attenuation of obesogenic diet-driven metabolic dysfunction

BAFF and APRIL counterregulate susceptibility to inflammation-induced preterm birth

Summary: Clinical evidence points to a function for B cell-activating factor (BAFF) in pregnancy. However, direct roles for BAFF-axis members in pregnancy have not been examined. Here, via utility of genetically modified mice, we report that BAFF promotes inflammatory responsiveness and increases susceptibility to inflammation-induced preterm birth (PTB). In contrast, we show that the closely related A proliferation-inducing ligand (APRIL) decreases inflammatory responsiveness and susceptibility to PTB. Known BAFF-axis receptors serve a redundant function in signaling BAFF/APRIL presence in pregnancy. Treatment with anti-BAFF/APRIL monoclonal antibodies or BAFF/APRIL recombinant proteins is sufficient to manipulate susceptibility to PTB. Notably, macrophages at the maternal-fetal interface produce BAFF, while BAFF and APRIL presence divergently shape macrophage gene expression and inflammatory function. Overall, our findings demonstrate that BAFF and APRIL play divergent inflammatory roles in pregnancy and provide therapeutic targets for mitigating risk of inflammation-induced PTB

MCDD-driven NAFLD alters hepatic levels of IL-17A and IL-17F production.

<p>8 week old male C57BL/6 mice (<i>n</i> = 4/condition) were placed on MCDD or chow diet for 4 weeks. (<b>A</b>) IL-17A and IL-17F production was determined in cells following the gating on: CD45⁺, TCRβ⁺, NK1.1^-, CD4⁺ or CD8⁺. (<b>B</b>) Percent of hepatic immune cells (CD45⁺) producing IL-17A. (<b>C</b>) Percent of hepatic immune cells (CD45⁺) producing IL-17F. (<b>D</b>) Percent of hepatic TCRβ⁺ cells (CD4⁺ or CD8⁺ T cells) producing IL-17A. (<b>E</b>) Percent of hepatic TCRβ⁺ cells (CD4⁺ or CD8⁺ T cells) producing IL-17F. (<b>F</b>) Mean fluorescent intensity of IL-17A in TCRβ⁺ cells (CD4⁺ or CD8⁺ T cells). (<b>G</b>) Mean fluorescent intensity of IL-17F in TCRβ⁺ cells (CD4⁺ or CD8⁺ T cells). (<b>H</b>) Percent of hepatic immune cells (CD45⁺) expressing GR-1 and CD11b. Data represent means + SE; a representative of two separate experiments. Student <i>t</i> test **<i>P</i> < 0.01.</p