Butyrate regulates leptin expression through different signaling pathways in adipocytes

Leptin is an adipocytokine that regulates body weight, and maintains energy homeostasis by promoting reduced food intake and increasing energy expenditure. Leptin expression and secretion is regulated by various factors including hormones and fatty acids. Butyrate is a short-chain fatty acid that acts as source of energy in humans. We determined whether this fatty acid can play a role in leptin expression in fully differentiated human adipocytes. Mature differentiated adipocytes were incubated with or without increasing concentrations of butyrate. RNA was extracted and leptin mRNA expression was examined by Northern blot analysis. Moreover, the cells were incubated with regulators that may affect signals which may alter leptin expression and analyzed with Northern blotting. Butyrate stimulated leptin expression, and stimulated mitogen activated protein kinase (MAPK) and phospho-CREB signaling in a time-dependent manner. Prior treatment of the cells with signal transduction inhibitors as pertusis toxin, Gi protein antagonist, PD98059 (a MAPK inhibitor), and wortmannin (a PI3K inhibitor) abolished leptin mRNA expression. These results suggest that butyrate can regulate leptin expression in humans at the transcriptional level. This is accomplished by: 1) Gi protein-coupled receptors specific for short-chain fatty acids, and 2) MAPK and phosphatidylinositol-3-kinase (PI3K) signaling pathways.

Evaluation of the immune humoral response of Brazilian patients with Rubinstein-Taybi syndrome

Rubinstein-Taybi syndrome (RTS) is a rare developmental disorder characterized by craniofacial dysmorphisms, broad thumbs and toes, mental and growth deficiency, and recurrent respiratory infections. RTS has been associated with CREBBP gene mutations, but EP300 gene mutations have recently been reported in 6 individuals. In the present study, the humoral immune response in 16 RTS patients with recurrent respiratory infections of possible bacterial etiology was evaluated. No significant differences between patients and 16 healthy controls were detected to explain the high susceptibility to respiratory infections: normal or elevated serum immunoglobulin levels, normal salivary IgA levels, and a good antibody response to both polysaccharide and protein antigens were observed. However, most patients presented high serum IgM levels, a high number of total B cell and B subsets, and also high percentiles of apoptosis, suggesting that they could present B dysregulation. The CREBBP/p300 family gene is extremely important for B-cell regulation, and RTS may represent an interesting human model for studying the molecular mechanisms involved in B-cell development.

VP16CREB-induced differentiation of neuroblastoma.

OBJECTIVE: Drug-induced differentiation is commonly used as a therapeutic modality for the treatment of neuroblastoma tumors. Increased level of cyclic adenosine 3', 5'-monophosphate (cAMP) mediates terminal differentiation in some neuroblastoma cell lines through activation of several signaling networks, including cAMP response element binding protein (CREB). Objective was to test whether cAMP-induced differentiation in a murine neuroblastoma cell line (NBP2) is partly mediated by CREB. METHODS: Fluorescent microscopy was used to document neuron-like morphological changes imparted by a constitutively active CREB (VP16CREB). Real time PCR (RT-PCR) was performed to verify changes in the expression of cAMP/CREB responsive genes. RESULTS: It was found that transient expression of VP16CREB into NBP2 cells resulted in morphological changes that were characteristics of terminally differentiated neurons. Furthermore, increased expression of cAMP responsive genes was compromised in cells resisting VP16CREB-mediated differentiation. CONCLUSION: A constitutively active CREB induces terminal differentiation in a subset of NBP2 cell population. Altered expression of cAMP responsive genes may account for differentiation resistant phenotype in NBP2 cells.