Melissa E. Gove

Interleukin-18, together with interleukin-12, induces severe acute pancreatitis in obese but not in nonobese leptin-deficient mice.

Obesity is associated with increased severity of acute pancreatitis (AP). The cytokines IL-18 and IL-12 are elevated in patients with AP, and IL-18 levels are high in obesity. We aimed to develop a pathologically relevant model to study obesity-associated severe AP. Lean WT and obese leptin-deficient ob/ob mice received two injections of IL-12 plus IL-18. Survival, pancreatic inflammation, and biochemical markers of AP were measured. Dosing with IL-12 plus IL-18 induced 100% lethality in ob/ob mice; no lethality was observed in WT mice. Disruption of pancreatic exocrine tissue and acinar cell death as well as serum amylase and lipase levels were significantly higher in ob/ob than in WT mice. Edematous AP developed in WT mice, whereas obese ob/ob mice developed necrotizing AP. Adipose tissue necrosis and saponification were present in cytokine-injected ob/ob but not in WT mice. Severe hypocalcemia and elevated acute-phase response developed in ob/ob mice. The cytokine combination induced high levels of regenerating protein 1 and pancreatitis-associated protein expression in the pancreas of WT but not of ob/ob mice. To differentiate the contribution of obesity to that of leptin deficiency, mice received short- and long-term leptin replacement therapy. Short-term leptin reconstitution in the absence of major weight loss did not protect ob/ob mice, whereas leptin deficiency in the absence of obesity resulted in a significant reduction in the severity of the pancreatitis. In conclusion, we developed a pathologically relevant model of AP in which obesity per se is associated with increased severity.

Role of leptin receptor-induced STAT3 signaling in modulation of intestinal and hepatic inflammation in mice

Leptin‐deficient ob/ob mice are resistant to dextran sulfate sodium (DSS)‐induced colitis and Concanavalin A (Con A)‐induced hepatitis. However, the signal transduction pathways involved have not been identified. The present study investigated the effect of leptin‐induced STAT3 signaling in the DSS and Con A models. Mice carrying a leptin receptor (LEPR) gene mutant for Y1138 (s/s mice), with abrogated leptin‐induced STAT3 signaling, were compared with wild‐type (WT) and LEPR‐deficient db/db mice. Administration of DSS to s/s mice resulted in a clinical score and colon shortening of intermediate severity compared with disease induced in WT and db/db mice—the latter group having the lowest disease severity. A comparable degree of inflammatory infiltrate and epithelial damage was observed in the colon of WT and s/s mice, and these parameters were reduced in db/db mice. Levels of IFN‐γ, IL‐6, IL‐10, and TNF‐α were comparable in the colon of s/s and db/db mice, and a similar trend was observed for CXCL2. s/s and WT mice developed severe liver disease in response to Con A, whereas db/db mice were protected. However, Con A‐induced serum IL‐6 and TNF‐α levels in s/s mice mimicked levels observed in db/db rather than WT mice. In conclusion, lack of leptin‐induced STAT3 signaling is associated with reduced cytokine production following DSS and Con A administration, but it appears to sensitize mice to the effects of proinflammatory mediators.

Role and Regulation of Adipokines during Zymosan-Induced Peritoneal Inflammation in Mice

Adipokines, cytokines mainly produced by adipocytes, are active participants in the regulation of inflammation. Administration of zymosan (ZY) was used to investigate the regulation and role of adipokines during peritonitis in mice. Injection of ZY led to a significant increase in leptin levels in both serum and peritoneal lavage fluid, whereas a differential trend in local vs. systemic levels was observed for both resistin and adiponectin. The role of leptin in ZY-induced peritonitis was investigated using leptin-deficient ob/ob mice, with and without reconstitution with exogenous leptin. Leptin deficiency was associated with delayed resolution of peritoneal inflammation induced by ZY, because ob/ob mice had a more pronounced cellular infiltrate in the peritoneum as well as higher and prolonged local and systemic levels of IL-6, TNFalpha, IL-10, and chemokine (C-X-C motif) ligand 2 compared with wild-type mice. Reconstitution with exogenous leptin exacerbated the inflammatory infiltrate and systemic IL-6 levels in ob/ob mice while inhibiting production of TNFalpha, IL-10, and chemokine (C-X-C motif) ligand 2. In contrast with the important role of leptin in regulating each aspect of ZY-induced peritonitis, adiponectin deficiency was associated only with a decreased inflammatory infiltrate, without affecting cytokine levels. These findings point to a complex role for adipokines in ZY-induced peritonitis and further emphasize the interplay between obesity and inflammation.

Adiponectin deficiency does not affect development and progression of spontaneous colitis in IL-10 knockout mice

The goal of this study was to investigate the role of the adipokine adiponectin (APN) in development of spontaneous colitis in IL-10 knockout (KO) mice. To this aim, we generated double IL-10 APN KO mice and compared their disease development to that of single IL-10 KO mice. Both IL-10 KO and double IL-10 APN KO mice spontaneously developed colitis of comparable severity. No significant differences in inflammatory infiltrate or crypt elongation were observed in colonic tissue obtained from IL-10 KO and double IL-10 APN KO mice at either 12 or 20 wk of age. A comparable increase in circulating levels of serum amyloid A and IFN-gamma was observed in IL-10 KO and double IL-10 APN KO mice as disease progressed. In vitro stimulation of lymphocytes from mesenteric lymph nodes with anti-CD3 and anti-CD28 induced a significantly higher production of IL-17 and TNF-alpha in IL-10 KO and double IL-10 APN KO mice compared with their healthy littermates. No significant differences in cytokine production from lymphocytes or colonic mRNA expression of cytokines were observed between IL-10 KO and double IL-10 APN KO mice. Both IL-10 KO and double IL-10 APN KO mice had a similar decrease in body weight and bone mass compared with their respective healthy littermates. Finally, APN deficiency did not lead to development of insulin resistance, either in APN KO or double IL-10 APN KO mice. In conclusion, lack of APN does not play a significant role in the pathogenesis of spontaneous colonic inflammation in the IL-10 KO model.

Generation of leptin receptor bone marrow chimeras: Recovery from irradiation, immune cellularity, cytokine expression, and metabolic parameters

Leptin regulates appetite and metabolism but also immunity and inflammation. Although functional leptin receptors (LepR) are expressed on hematopoietic cells, the role of these receptors in regulating immune function in vivo remains controversial. To clarify this issue, we performed bone marrow (BM) transplantation between obese db/db mice, lacking LepR, and wild‐type (WT) mice. Results indicate that expression of LepR on BM‐derived cells directly, though partially, regulates spleen and thymus cellularity, although the environment of db mice contributes to maintaining reduced cellularity of these organs. Selective expression of LepR on BM‐derived cells also modulates leptin and adiponectin levels, with induction of a more favorable adipokine environment in the WT→db/db group. However, LepR signaling in BM‐derived cells is not involved in regulation of body weight (BW) and composition, glycemia, hepatosteatosis or adipose tissue inflammation, although it modulates expression of interleukin (IL)‐1β in the brain. Finally, data indicate that db mice have an increased susceptibility to irradiation compared to WT mice in terms of BW loss and recovery of leukocyte counts in peripheral blood. Therefore, interpretation of results obtained using BM chimeras between WT and db mice should take into account the difference in radiation sensitivity between the two types of animals.

Adiponectin deficiency modulates adhesion molecules expression and cytokine production but does not affect disease severity in the transfer model of colitis

We investigated the effect of adiponectin (APN) deficiency in the CD4(+)CD45RB(high) transfer model of colitis. Recombination activating gene (Rag)-1 knockout (KO) and Rag-1 APN KO mice receiving CD4(+)CD45RB(high) cells developed colitis of comparable severity. Colonic mRNA expression of IL-6 and IL-17 was lower in Rag-1 APN KO mice compared to Rag-1 KO mice. Rag-1 APN KO and Rag-1 KO mice released comparable amounts of IL-6 from colon cultures, whereas release of IL-17 was higher in Rag-1 APN KO compared to Rag-1 KO mice. Expression of TNFalpha mRNA was comparable in Rag-1 KO and Rag-1 APN KO mice, but protein release was lower in Rag-1 APN KO mice compared to Rag-1 KO mice. Levels of IFNgamma and IL-10 at mRNA and protein were comparable in Rag-1 KO and Rag-1 APN KO mice. Higher mRNA expression of VCAM-1 was observed in the colon of healthy APN KO compared to WT mice, while induction of colitis resulted in a comparable increase in VCAM-1 expression in Rag-1 KO and Rag-1 APN KO mice. In conclusion, although APN regulates expression of cytokines and adhesion molecules in the colon, this does not result in alteration of overall colitis severity in the CD4(+)CD45RB(high) transfer model.

Effect of adiponectin deficiency on intestinal damage and hematopoietic responses of mice exposed to gamma radiation.

Adiponectin (APN) is an adipose tissue-derived cytokine that regulates insulin sensitivity and inflammation. It is also involved in modulation of cell proliferation by binding to various growth factors. Based on its known effects in modulating cell proliferation and oxidative stress, APN may potentially be involved in regulating tissue damage and repair following irradiation. Adiponectin KO mice and their WT littermates were exposed to a single whole-body dose of 3 or 6Gy gamma radiation. Radiation-induced alterations were studied in jejunum, blood, bone marrow and thymus at days 1 and 5 post-irradiation and compared with sham-irradiated groups. In WT mice, irradiation did not significantly alter serum APN levels while inducing a significant decrease in serum leptin. Irradiation caused a significant reduction in thymocyte cellularity, with concomitant decrease in CD4(+), CD8(+) and CD4(+)CD8(+) T cell populations, with no significant differences between WT and APN KO mice. Irradiation resulted in a significantly higher increase in the frequency of micronucleated reticulocytes in the blood of APN KO compared with WT mice, whereas frequency of micronucleated normochromatic erythrocytes in the bone marrow at day 5 was significantly higher in WT compared with APN KO mice. Finally, irradiation induced similar alterations in villus height and crypt cell proliferation in the jejunum of WT and APN KO mice. Jejunum explants from sham-irradiated APN KO mice produced higher levels of IL-6 compared with tissue from WT animals, but the difference was no longer apparent following irradiation. Our data indicate that APN deficiency does not play a significant role in modulating radiation-induced gastrointestinal injury in mice, while it may participate in regulation of damage to the hematopoietic system.

Adipokines, Nutrition, and Obesity

The traditional view of white adipose tissue (WAT) existing solely as an energy reservoir is no longer true. Although predominantly consisting of adipocytes, WAT is also composed of preadipocytes, endothelial cells, fibroblasts, and macrophages located in the stromovascular fraction. As a result, WAT is a complex and highly active secretory organ capable of modulating appetite, energy expenditure, insulin sensitivity, endocrine and reproductive systems, bone metabolism, inflammation, and immunity. The release of adipokines and cytokines by WAT is one of the most important ways this tissue influences physiological and pathological processes throughout the body. Adipokines are biologically active mediators released from adipocytes and include proteins such as leptin, adiponectin (APN), resistin, adipsin, and visfatin, as well as factors traditionally considered as cytokines such as interleukin (IL)-6, tumor necrosis factor (TNF)-α, and others. Obesity is characterized by an increase in fat mass, which is associated with a state of chronic inflammation with macrophage infiltration of WAT and abnormal production of adipokines and cytokines. Leptin, APN, resistin, visfatin, IL-6, and TNF-α help provide a link between obesity and development of insulin resistance, impaired glucose tolerance, and Type 2 diabetes (T2D) commonly associated with obesity. How specific nutrients affect production and secretion of adipokines and WAT-derived cytokines is currentlycontroversial