Didier J. Colin

Gut Microbiota Orchestrates Energy Homeostasis during Cold

Microbial functions in the host physiology are a result of the microbiota-host co-evolution. We show that cold exposure leads to marked shift of the microbiota composition, referred to as cold microbiota. Transplantation of the cold microbiota to germ-free mice is sufficient to increase insulin sensitivity of the host and enable tolerance to cold partly by promoting the white fat browning, leading to increased energy expenditure and fat loss. During prolonged cold, however, the body weight loss is attenuated, caused by adaptive mechanisms maximizing caloric uptake and increasing intestinal, villi, and microvilli lengths. This increased absorptive surface is transferable with the cold microbiota, leading to altered intestinal gene expression promoting tissue remodeling and suppression of apoptosis-the effect diminished by co-transplanting the most cold-downregulated strain Akkermansia muciniphila during the cold microbiota transfer. Our results demonstrate the microbiota as a key factor orchestrating the overall energy homeostasis during increased demand.

Microbiota depletion promotes browning of white adipose tissue and reduces obesity

Brown adipose tissue (BAT) promotes a lean and healthy phenotype and improves insulin sensitivity. In response to cold or exercise, brown fat cells also emerge in the white adipose tissue (WAT; also known as beige cells), a process known as browning. Here we show that the development of functional beige fat in the inguinal subcutaneous adipose tissue (ingSAT) and perigonadal visceral adipose tissue (pgVAT) is promoted by the depletion of microbiota either by means of antibiotic treatment or in germ-free mice. This leads to improved glucose tolerance and insulin sensitivity and decreased white fat and adipocyte size in lean mice, obese leptin-deficient (ob/ob) mice and high-fat diet (HFD)-fed mice. Such metabolic improvements are mediated by eosinophil infiltration, enhanced type 2 cytokine signaling and M2 macrophage polarization in the subcutaneous white fat depots of microbiota-depleted animals. The metabolic phenotype and the browning of the subcutaneous fat are impaired by the suppression of type 2 cytokine signaling, and they are reversed by recolonization of the antibiotic-treated or germ-free mice with microbes. These results provide insight into the microbiota-fat signaling axis and beige-fat development in health and metabolic disease.

Caloric Restriction Leads to Browning of White Adipose Tissue through Type 2 Immune Signaling

Caloric restriction (CR) extends lifespan from yeast to mammals, delays onset of age-associated diseases, and improves metabolic health. We show that CR stimulates development of functional beige fat within the subcutaneous and visceral adipose tissue, contributing to decreased white fat and adipocyte size in lean C57BL/6 and BALB/c mice kept at room temperature or at thermoneutrality and in obese leptin-deficient mice. These metabolic changes are mediated by increased eosinophil infiltration, type 2 cytokine signaling, and M2 macrophage polarization in fat of CR animals. Suppression of the type 2 signaling, using Il4ra(-/-), Stat6(-/-), or mice transplanted with Stat6(-/-) bone marrow-derived hematopoietic cells, prevents the CR-induced browning and abrogates the subcutaneous fat loss and the metabolic improvements induced by CR. These results provide insights into the overall energy homeostasis during CR, and they suggest beige fat development as a common feature in conditions of negative energy balance.

Ectopic UCP1 Overexpression in White Adipose Tissue Improves Insulin Sensitivity in Lou/C Rats, a Model of Obesity Resistance

Brown adipose tissue (BAT), characterized by the presence of uncoupling protein 1 (UCP1), has been described as metabolically active in humans. Lou/C rats, originating from the Wistar strain, are resistant to obesity. We previously demonstrated that Lou/C animals express UCP1 in beige adipocytes in inguinal white adipose tissue (iWAT), suggesting a role of this protein in processes such as the control of body weight and the observed improved insulin sensitivity. A β3 adrenergic agonist was administered for 2 weeks in Wistar and Lou/C rats to activate UCP1 and delineate its metabolic impact. The treatment brought about decreases in fat mass and improvements in insulin sensitivity in both groups. In BAT, UCP1 expression increased similarly in response to the treatment in the two groups. However, the intervention induced the appearance of beige cells in iWAT, associated with a marked increase in UCP1 expression, in Lou/C rats only. This increase was correlated with a markedly enhanced glucose uptake measured during euglycemic-hyperinsulinemic clamps, suggesting a role of beige cells in this process. Activation of UCP1 in ectopic tissues, such as beige cells in iWAT, may be an interesting therapeutic approach to prevent body weight gain, decrease fat mass, and improve insulin sensitivity.

Role of MIF/CD74 signaling pathway in the development of pleural mesothelioma

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine implicated in acute and chronic inflammatory diseases. MIF is overexpressed in various tumors. It displays a number of functions that provide a direct link between the process of inflammation and tumor growth. Our group recently identified the MIF-receptor CD74 as an independent prognostic factor for overall survival in patients with malignant pleural mesothelioma. In the present study, we compared the levels of expression of MIF and CD74 in different human mesothelioma cell lines and investigated their physiopathological functions in vitro and in vivo. Human mesothelioma cells expressed more CD74 and secreted less MIF than non tumoral MeT5A cells, suggesting a higher sensitivity to MIF. In mesothelioma cells, high MIF levels were associated with a high multiplication rate of cells. In vitro, reduction of MIF or CD74 levels in both mesothelioma cell lines showed that the MIF/CD74 signaling pathway promoted tumor cell proliferation and protected MPM cells from apoptosis. Finally, mesothelioma cell lines expressing high CD74 levels had a low tumorigenic potential after xenogeneic implantation in athymic nude mice. All these data highlight the complexity of the MIF/CD74 signaling pathway in the development of mesothelioma.

Experimental Model of Human Malignant Mesothelioma in Athymic Mice

Malignant pleural mesothelioma (MPM) is a thoracic aggressive cancer caused by asbestos exposure, which is difficult to diagnose and treat. Here, we characterized an in vivo orthotopic xenograft model consisting of human mesothelioma cells (designed as H2052/484) derived from a pleural NCI-H2052 tumor injected in partially immunodeficient athymic mice. We assessed tumor formation and tumor-dependent patterns of inflammation. H2052/484 cells conserved their mesothelioma phenotype and most characteristics from the parental NCI-H2052 cells. After intra-thoracic injection of H2052/484 cells, thoracic tumors developed in nearly all mice (86%) within 14 days, faster than from parental NCI-H2052 cells. When the mice were euthanized, the pleural lavage fluid was examined for immune cell profiles. The pleural immune cell population increased with tumor development. Interestingly, the proportion of myeloid-derived suppressor cell and macrophage (especially CD206+ M2 macrophages) populations increased in the pleural fluid of mice with large mesothelioma development, as previously observed in immunocompetent mice. This reliable orthotopic model recapitulates human mesothelioma and may be used for the study of new treatment strategies.

Additional file 1: Table S1. of Preclinical validations of [18F]FPyPEGCBT-c(RGDfK): a 18F-labelled RGD peptide prepared by ligation of 2-cyanobenzothiazole and 1,2-aminothiol to image angiogenesis

Statistical analyses of the biodistribution data of [18F]FPyPEGCBT-c(RGDfK) in nude mice bearing U-87 MG or SKOV-3 subcutaneous tumours a . Figure S1. siRNA-mediated integrin depletions analysis by densitometry. αV, β1, β3 or β5 integrin subunits and indicated combinations were knocked-down by siRNA in U-87 MG and SKOV-3 and protein extracts were submitted to immunoblotting using specific antibodies. Expression levels of each integrin were then quantified with a Chemidoc MP. Data are mean fold expression changes in indicated samples as compared to untransfected cells (Unt) ± SD (n = 3). Figure S2. Uptake of [125I]echistatin in cells with selective siRNA-mediated integrin knocked down. U-87 MG and SKOV-3 cells knocked down for αV, β1, β3 or β5 integrin subunits and indicated combinations were incubated with 100 kBq/mL [18F]FPyPEGCBT-c(RGDfK) for 15 to 120 min at 37 °C. Depletions were verified by immunoblotting using specific antibodies as compared to untransfected cells (Unt) and to an irrelevant depletion of luciferase (si Luc). After incubation, cells were lysed and the cell-associated radioactivity was measured in a γ-counter. Data are means ± SD of at least three independent experiments performed in quadruplicate well. Statistical differences were analysed with the one-way ANOVA test followed by Dunnett’s post hoc test as compared to si Luc controls; #p

Study of rat skeletal muscle activation by PET/CT and [ 11 C]acetate

Purpose: The purpose of the present study is to apply kinetic analysis to investigate exercise-related changes in the skeletal muscle of the rat hind limb by [¹¹C]acetate PET/CT. Methods: One-leg contractions were induced in Wistar rats by electrostimulation of the VL muscle motor point. After 15 minutes of muscle contractions [¹¹C]acetate was injected and PET/CT of the rat hind limbs was acquired. The resting leg was used as a control reference. The perfusion index F was calculated for the target muscles (exercised and control) and correlated to the corresponding SUVs. For both F and the SUV, the ratio of the value extracted for the active muscle to the one derived for the muscle at rest was computed (respectively, F_E/F_R and SUV_E/SUV_R). Results: For the experimental dataset, a strong correlation (R² = 0.97, P = 0.01) between F_E/F_R and SUV_E/SUV_R was observed. The ratio F_E/F_R resulted to be higher than the ratio SUV_E/SUV_R (average values: 2.1 ± 0.7 and 1.19 ± 0.08, respectively). Conclusion: Preliminary results indicate that both kinetic modeling and the SUV can detect changes in muscles between rest and exercise conditions, when associated to [¹¹C]acetate PET/CT.