Hypothalamic pCREB control POMC processing and α-MSH production in response to dietary fat

RESUMO

INTRODUÇÃO: Hypothalamic POMC neurons act as first-order sensors of systemic energy stores, through α-MSH production, and this production is mediated by POMC processing enzymes (PCs). The cAMP response element-binding protein (CREB) is one of the transcription factors that control neuronal survival, plasticity, and the expression of POMC endopeptidases. It is well known that a high-fat diet (HFD), rich in saturated fatty acids, such as sodium palmitate (SP), triggers hypothalamic inflammation and eventually the damage of POMC neurons, which can result in abnormalities in α-MSH production and action. Together, these homeostatic changes result in hypothalamic-mediated metabolic dysfunction, characterized by impairment of energy homeostasis and food intake regulation.

OBJETIVOS: This study aimed at evaluating whether pCREB signaling is involved in the impaired POMC processing and α-MSH production upon HFD-induced hypothalamic inflammation and sodium palmitate actions.

MÉTODOS: In all experiments, we used C57BL/6J and POMC-GFP reporter mice with the approval of the Animal Use Ethics Committee of UNICAMP (CEUA: 5591-1/2020). Using immunostaining, we investigated phosphorylated CREB distribution and expression in the mediobasal hypothalamus of mice fed on HFD. To isolate the effects of fatty acids (FAs) from the diet in POMC neurons, we analyzed C57BL/6J and POMC-GFP reporter mice upon intracerebroventricular injection of SP (30 µM). To identify CREB signaling in PCs and α-MSH production, we downregulated CREB expression in the arcuate nucleus (ARC) through a target-specific lentiviral infection in mice fed on HFD or treated with SP. After the end of all experimental protocols, we harvested the hypothalamus and employed Western Blotting and quantitative PCR assays for protein and gene expression analysis, respectively, and stereology of coronal brain slices for quantification of double-labeling cells.

RESULTADOS: Our data show that phosphorylated CREB is widely expressed in the MBH and overlaps with POMC neurons in the ARC. CREB expression in POMC neurons increased after SP stimuli. After CREB downregulation, we identify an anomalous expression of PCs upon HFD feeding or SP stimuli, that results in a dysregulation of a-MSH, a subproduct of POMC.

CONCLUSÃO: In conclusion, we identified CREB as a transducer of signals that control the activity of hypothalamic neurons involved in the regulation of whole-body energy stores. Hypothalamic CREB downregulation result in abnormal regulation of POMC enzymatic cleavage system, leading to the impaired a-MSH response to a HFD and a reduction in energy expenditure. This study provides the first evidence for the involvement of CREB in the abnormal regulation of the hypothalamic POMC endopeptidase system in experimental obesity.

BIBLIOGRAFIA: Razolli, D. S., De Araújo, T. M., Sant’Ana, M. R., Kirwan, P., Cintra, D. E., Merkle, F. T., et al. (2020). Proopiomelanocortin Processing in the Hypothalamus Is Directly Regulated by Saturated Fat: Implications for the Development of Obesity. Neuroendocrinology 110, 92–104. doi:10.1159/000501023. Souza, G. F. P., Solon, C., Nascimento, L. F., De-Lima-Junior, J. C., Nogueira, G., Moura, R., et al. (2016). Defective regulation of POMC precedes hypothalamic inflammation in diet-induced obesity. Sci. Rep. 6, 1–9. doi:10.1038/srep29290. Velloso, L. A., and Schwartz, M. W. (2011). Altered hypothalamic function in diet-induced obesity. Int. J. Obes. 35, 1455–1465. doi:10.1038/ijo.2011.56.

PALAVRA-CHAVE: Proopiomelanocortin, obesity, diet, saturated fatty acid, CREB