Neuromedin B receptor disruption impairs adipogenesis in mice and 3T3-L1 cells

Neuromedin B, a bombesin-like peptide, and its receptor, are expressed in white adipose tissue with undefined roles. Female mice with disruption of neuromedin B receptor (NB-R) exhibited partial resistance to diet-induced obesity leading to our hypothesis that NB-R is involved in adipogenesis. Here, we showed that adipose stem/stromal cells (ASC) from perigonadal fat of female NB-R-knockout mice, exposed to a differentiation protocol in vitro, accumulated less lipid (45%) than wild type, suggesting reduced capacity to differentiate under adipogenic input. To further explore mechanisms, preadipocytes 3T3-L1 cells were incubated in the presence of NB-R antagonist (PD168368) during the first 3 days in culture. Cells were analyzed in the end of the treatment (Day 3) and later when fully differentiated (Day 21). NB-R antagonist induced lower number of cells at day 3 and 21 (33-39%), reduced cell proliferation at day 3 (-53%) and reduced lipid accumulation at day 21 (-86%). The mRNA expressions of several adipocyte differentiation markers were importantly reduced at both days: Cebpb and Pparg and Fabp4, Plin-1 and Adipoq, and additionally Lep mRNA at day 21. The antagonist had no effect when incubated with mature 3T3-L1 adipocytes. Therefore, genetically disruption of NB-R in mice ASC or pharmacological antagonism of NB-R in 3T3-L1 cells impairs adipogenesis. The mechanisms suggested by results in 3T3-L1 cells involve reduction of cell proliferation and of early gene expressions, leading to decreased number of mature adipocytes. We speculate that NB-R antagonism may be useful to limit the increase in adiposity due to pre-adipocyte differentiation.

Differential Regulation of Thyroid Hormone Metabolism Target Genes during Non-thyroidal [corrected] Illness Syndrome Triggered by Fasting or Sepsis in Adult Mice

Fasting and sepsis induce profound changes in thyroid hormone (TH) central and peripheral metabolism. These changes affect TH action and are called the non-thyroidal illness syndrome (NTIS). To date, it is still debated whether NTIS represents an adaptive response or a real hypothyroid state at the tissue level. Moreover, even though it has been considered the same syndrome, we hypothesized that fasting and sepsis induce a distinct set of changes in thyroid hormone metabolism. Herein, we aimed to evaluate the central and peripheral expression of genes involved in the transport (MCT8/Slc16a2 and MCT10/Slc16a10), metabolism (Dio1, Dio2, and Dio3) and action (Thra and Thrb) of TH during NTIS induced by fasting or sepsis. Male mice were subjected to a 48 h period of fasting or cecal ligation and puncture (CLP)-induced sepsis. At the peripheral level, fasting led to: (1) reduced serum thyroxine (T₄) and triiodothyronine (T₃), expression of Dio1, Thra, Slc16a2, and MCT8 protein in liver; (2) increased hepatic Slc16a10 and Dio3 expression; and (3) decreased Slc16a2 and Slc16a10 expressions in the thyroid gland. Fasting resulted in reduction of Tshb expression in the pituitary and increased expression of Dio2 in total hypothalamus, arcuate (ARC) and paraventricular (PVN) nucleus. CLP induced sepsis resulted in reduced: (1) T₄ serum levels; (2) Dio1, Slc16a2, Slc16a10, Thra, and Thrb expression in liver as well as Slc16a2 expression in the thyroid gland (3) Thrb and Tshb mRNA expression in the pituitary; (4) total leukocyte counts in the bone marrow while increased its number in peritoneal and pleural fluids. In summary, fasting- or sepsis-driven NTIS promotes changes in the set point of hypothalamus-pituitary-thyroid axis through different mechanisms. Reduced hepatic THRs expression in conjunction with reduced TH transporters expression in the thyroid gland may indicate, respectively, reduction in the peripheral action and in the secretion of TH, which may contribute to the low TH serum levels observed in both models.

Mice with Deletion of Neuromedin B Receptor Exhibit Decreased Oral Glucose-Stimulated Insulin Release

Neuromedin B (NB) and gastrin-releasing peptide (GRP) are bombesin-like peptides, found in the gastrointestinal tube and pancreas, among other tissues. Consistent data proposed that GRP stimulates insulin secretion, acting directly in pancreatic cells or in the release of gastrointestinal hormones that are incretins. However, the role of NB remains unclear. We examined the glucose homeostasis in mice with deletion of NB receptor (NBR-KO). Female NBR-KO exhibited similar fasting basal glucose with lower insulinemia (48.4%) and lower homeostasis model assessment of insulin resistance index (50.5%) than wild type (WT). Additionally, they were more tolerant to oral glucose, demonstrated by a decrease in the area under the glucose curve (18%). In addition, 15 min after an oral glucose load, female and male NBR-KO showed lower insulin serum levels (45.6 and 26.8%, respectively) than WT, even though blood glucose rose to similar levels in both groups. Single injection of NB, one hour before the oral glucose administration, tended to induce higher serum insulin in WT (28.9%, p=0.3), however the same did not occur in NBR-KO. They showed no changes in fasting insulin content in pancreatic islets by immunohistochemistry, however, the fasting serum levels of glucagon-like peptide, a potent incretin, exhibited a strong trend to reduction (40%, p=0.07). Collectively, mice with deletion of NB receptor have lower insulinemia, especially in response to oral glucose, and females also exhibited a better glucose tolerance, suggesting the involvement of NB and its receptor in regulation of insulin secretion induced by incretins, and also, in insulin sensitivity.

Hypothyroidism Induces Hypophagia Associated with Alterations in Protein Expression of Neuropeptide Y and Proopiomelanocortin in the Arcuate Nucleus, Independently of Hypothalamic Nuclei-Specific Changes in Leptin Signaling

BACKGROUND

Thyroid hormone and leptin are essential regulators of energy homeostasis. Both hormones stimulate energy expenditure but have opposite effects on appetite. The mechanisms behind food intake regulation in thyroid dysfunctions are poorly understood. It has been shown that hypothyroid rats exhibited impaired leptin anorexigenic effect and signaling in total hypothalamus, even though they were hypophagic. It was hypothesized that hypothyroidism modulates the expression of neuropeptides: orexigenic neuropeptide Y (NPY) and anorexigenic proopiomelanocortin (POMC), independently of inducing nuclei-specific changes in hypothalamic leptin signaling.

METHODS

Adult male rats were rendered hypothyroid by administration of 0.03% methimazole in the drinking water for 21 days. Protein content of NPY, POMC, and leptin signaling (the signal transducer and activator of transcription 3 [STAT3] pathway) were evaluated by Western blot, and mRNA levels by real time reverse transcription polymerase chain reaction in arcuate (ARC), ventromedial (VMN), and paraventricular (PVN) hypothalamic nuclei isolated from euthyroid (eu) and hypothyroid (hypo) rats. Leptin anorexigenic effect was tested by recording food intake for two hours after intracerebroventricular (i.c.v.) administration of leptin. Statistical differences were considered significant at p ≤ 0.05.

RESULTS

Hypothyroidism was confirmed by decreased serum triiodothyronine, thyroxine, and increased thyrotropin, in addition to increased levels of pro-TRH mRNA in PVN and Dio2 mRNA in the ARC of hypo rats. Hypothyroidism decreased body weight and food intake associated with decreased protein content of NPY and increased content of POMC in the ARC. Conversely, hypothyroidism induced central resistance to the acute anorexigenic effect of leptin, since while euthyroid rats displayed reduced food intake after leptin i.c.v. injection, hypothyroid rats showed no response. Hypothyroid rats exhibited decreased leptin receptor (ObRb) protein content in ARC and VMN but not in PVN nucleus. ObRb protein changes were concomitant with decreased phosphorylated STAT3 in the ARC, and decreased total STAT3 in VMN and PVN. However, hypothyroidism did not affect mRNA levels of Lepr or Stat3 in the hypothalamic nuclei.

CONCLUSIONS

Experimental hypothyroidism induced a negative energy balance accompanied by decreased NPY and increased POMC protein content in the ARC, resulting in predominance of anorexigenic pathways, despite central leptin resistance and impairment of the leptin signaling cascade in a nuclei-specific manner.