Obesity-associated hepatosteatosis and impairment of glucose homeostasis are attenuated by haptoglobin deficiency.

OBJECTIVE: Haptoglobin (Hp) is upregulated in both inflammation and obesity. The low chronic inflammatory state, caused by massive adipose tissue macrophage (ATM) infiltration found in obesity, and low adiponectin have been implicated in the development of insulin resistance and hepatosteatosis. The aim of this work was to investigate whether and how Hp interferes with the onset of obesity-associated complications. RESEARCH DESIGN AND METHODS: Hp-null (Hp(-/-)) and wild-type (WT) mice were metabolically profiled under chow-food diet (CFD) and high-fat diet (HFD) feeding by assessing physical parameters, glucose tolerance, insulin sensitivity, insulin response to glucose load, liver triglyceride content, plasma levels of leptin, insulin, glucose, and adiponectin. ATM content was evaluated by using immunohistochemistry (anti-F4/80 antibody). Adiponectin expression was measured in Hp-treated, cultured 3T3-L1 and human adipocytes. RESULTS: No genotype-related difference was found in CFD animals. HFD-Hp(-/-) mice revealed significantly higher glucose tolerance, insulin sensitivity, glucose-stimulated insulin secretion, and adiponectin expression and reduced hepatomegaly/steatosis compared with HFD-WT mice. White adipose tissue (WAT) of HFD-Hp(-/-) mice showed higher activation of insulin signaling cascade, lower ATM, and higher adiponectin expression. Hp was able to inhibit adiponectin expression in cultured adipocytes. CONCLUSIONS: We demonstrated that in the absence of Hp, obesity-associated insulin resistance and hepatosteatosis are attenuated, which is associated with reduced ATM content, increased plasma adiponectin, and higher WAT insulin sensitivity.

A sensitive period for environmental regulation of eating behavior and leptin sensitivity.

Western lifestyle contributes to body weight dysregulation. Leptin down-regulates food intake by modulating the activity of neural circuits in the hypothalamic arcuate nucleus (ARC), and resistance to this hormone constitutes a permissive condition for obesity. Physical exercise modulates leptin sensitivity in diet-induced obese rats. The role of other lifestyle components in modulating leptin sensitivity remains elusive. Environmentally enriched mice were used to explore the effects of lifestyle change on leptin production/action and other metabolic parameters. We analyzed adult mice exposed to environmental enrichment (EE), which showed decreased leptin, reduced adipose mass, and increased food intake. We also analyzed 50-d-old mice exposed to either EE (YEE) or physical exercise (YW) since birth, both of which showed decreased leptin. YEE mice showed no change in food intake, increased response to leptin administration, increased activation of STAT3 in the ARC. The YW leptin-induced food intake response was intermediate between young mice kept in standard conditions and YEE. YEE exhibited increased and decreased ratios of excitatory/inhibitory synapses onto α-melanocyte-stimulating hormone and agouti-related peptide neurons of the ARC, respectively. We also analyzed animals as described for YEE and then placed in standard cages for 1 mo. They showed no altered leptin production/action but demonstrated changes in excitatory/inhibitory synaptic contacts in the ARC similar to YEE. EE and physical activity resulted in improved insulin sensitivity. In conclusion, EE and physical activity had an impact on feeding behavior, leptin production/action, and insulin sensitivity, and EE affected ARC circuitry. The leptin-hypothalamic axis is maximally enhanced if environmental stimulation is applied during development.

The obesity and inflammatory marker haptoglobin attracts monocytes via interaction with chemokine (C-C motif) receptor 2 (CCR2).

BACKGROUND: Obesity is a chronic low inflammatory state. In the obesity condition the white adipose tissue (WAT) is massively infiltrated with monocytes/macrophages, and the nature of the signals recruiting these inflammatory cells has yet to be fully elucidated. Haptoglobin (Hp) is an inflammatory marker and its expression is induced in the WAT of obese subjects. In an effort to elucidate the biological significance of Hp presence in the WAT and of its upregulation in obesity we formulated the hypothesis that Hp may serve as a macrophage chemoattractant. RESULTS: We demonstrated by chemotaxis assay that Hp is able to attract chemokine (C-C motif) receptor 2 (CCR2)-transfected pre-B lymphocytes and monocytes in a dose-dependent manner. Moreover, Hp-mediated migration of monocytes is impaired by CCR2-specific inhibition or previous cell exposure to monocyte chemoattractant protein 1 (MCP1) (also known as CCR2 ligand or chemokine (C-C motif) ligand 2 (CCL2)). Downstream effects of Hp/CCR2 interaction were also investigated: flow cytometry proved that monocytes treated with Hp show reduced CCR2 expression on their surface; Hp interaction induces calcium release that is reduced upon pretreatment with CCR2 antagonist; extracellular signal-regulated kinase (ERK)1/2, a signal transducer activated by CCR2, is phosphorylated following Hp treatment and this phosphorylation is reduced when cells are pretreated with a specific CCR2 inhibitor. Consistently, blocking the ERK1/2 pathway with U0126, the selective inhibitor of the ERK upstream mitogen-activated protein (MAP)-ERK kinase (MEK), results in a dramatic reduction (by almost 100%) of the capability of Hp to induce monocyte migration. CONCLUSIONS: Our data show that Hp is a novel monocyte chemoattractant and that its chemotactic potential is mediated, at least in part. by its interaction with CCR2.

Cathepsin K null mice show reduced adiposity during the rapid accumulation of fat stores.

Growing evidences indicate that proteases are implicated in adipogenesis and in the onset of obesity. We previously reported that the cysteine protease cathepsin K (ctsk) is overexpressed in the white adipose tissue (WAT) of obese individuals. We herein characterized the WAT and the metabolic phenotype of ctsk deficient animals (ctsk-/-). When the growth rate of ctsk-/- was compared to that of the wild type animals (WT), we could establish a time window (5-8 weeks of age) within which ctsk-/-display significantly lower body weight and WAT size as compared to WT. Such a difference was not observable in older mice. Upon treatment with high fat diet (HFD) for 12 weeks ctsk-/- gained significantly less weight than WT and showed reduced brown adipose tissue, liver mass and a lower percentage of body fat. Plasma triglycerides, cholesterol and leptin were significantly lower in HFD-fed-ctsk-/- as compared to HFD-fed WT animals. Adipocyte lipolysis rates were increased in both young and HFD-fed-ctsk-/-, as compared to WT. Carnitine palmitoyl transferase-1 activity, was higher in mitochondria isolated from the WAT of HFD treated ctsk-/- as compared to WT. Together, these data indicate that ctsk ablation in mice results in reduced body fat content under conditions requiring a rapid accumulation of fat stores. This observation could be partly explained by an increased release and/or utilization of FFA and by an augmented ratio of lipolysis/lipogenesis. These results also demonstrate that under a HFD, ctsk deficiency confers a partial resistance to the development of dyslipidemia.

The homeobox gene Xbh1 cooperates with proneural genes to specify ganglion cell fate within the Xenopus neural retina.

Recent studies on vertebrate eye development have focused on the molecular mechanisms of specification of different retinal cell types during development. Only a limited number of genes involved in this process has been identified. In Drosophila, BarH genes are necessary for the correct specification of R1/R6 eye photoreceptors. Vertebrate Bar homologues have been identified and are expressed in vertebrate retinal ganglion cells during differentiation; however, their retinal function has not yet been addressed. In this study, we report on the role of the Xenopus Bar homologue Xbh1 in retinal ganglion cell development and its interaction with the proneural genes Xath5 and Xath3, whose ability to promote ganglion cell fate has been demonstrated. We show that XHB1 plays a crucial role in retinal cell determination, acting as a switch towards ganglion cell fate. Detailed expression analysis, animal cap assays and in vivo lipofection assays, indicate that Xbh1 acts as a late transcriptional repressor downstream of the atonal genes Xath3 and Xath5. However, the action of Xbh1 on ganglion cell development is different and more specific than that of the Xath genes, and accounts for only a part of their activities during retinogenesis.