The hypothalamic CREB transcription factor is regulated by palmitate and hyperlipidic diet

Whole-body energy homeostasis depends on the coordinated action of different hypothalamic neurons, such as POMC/CART and NPY/AgRP. The activation of POMC neurons inhibits food consumption and increases energy expenditure. The proper action of POMC depends on its processing, which is catalyzed by several convertases resulting in neuropeptide formation. POMC neurons are responsive to hormones and nutrients. Socioeconomic changes that occurred along the last century impacted on eating habits, increasing the consumption of processed foods, rich in sugars and saturated fats, such as palmitate. The deleterious effects of palmitate on POMC processing are yet to be fully elucidated, depending on several intracellular signaling pathways. Due to its essential role in the transcription of several genes, which are essential for neuronal survival and plasticity, the cAMP-responsive binding protein (CREB) pathway has emerged as a potential target for this fatty acid. CREB is a nuclear protein regulated by phosphorylations catalyzed by PKA and/or CaMKII. In this project, we investigated the transcription factor CREB could be modulated by palmitate and contribute to the anomalous processing of POMC. Through different experimental approaches (in vivo and ex vivo) we initially confirmed that PKA, CaMKII, and CREB are expressed by POMC neurons. Chronic consumption of a high-fat diet modified the anatomical distribution of pCaMKII and pCREB in the mediobasal hypothalamus. Mice fed a high-fat diet for only nine hours increased phosphorylation of CREB in the hypothalamus. To isolate the effects of palmitate from those of other components of the diet, C57BL/6J-Unib mice fed standard chow received an intracerebroventricular injection (ICV) of 30 µM palmitate; in addition, a POMC cell line was treated with 50 µM of palmitate. In mice, ICV palmitate, promoted a significant increase in phosphorylation of CaMKII, confirming the involvement of this pathway in the response to palmitate. Both, mice and cell culture, responded to palmitate by changing the expression of convertase proteins and increasing the expression of different inflammatory markers. To confirm CREB and CaMKII involvement on convertase proteins expression, we employed lentiviral particles to reduce the expression of either protein in the basal middle hypothalamus of mice, which were later fed on a high-fat diet or received an intracerebroventricular injection (ICV) of 30 µM of palmitate. The reduction in CREB and CaMKII expression was responsible for altering the expression of POMC, PC1/3 and PC2, after stimulation with palmitate and a high-fat diet, in addition to promoting an increase in adiposity and food intake. These results confirm that the high-fat diet, and particularly palmitate, act directly on the expression of hypothalamic CREB and CaMKII altering the expression of POMC and convertase proteins, which in turn are essential for the proper processing of this neuropeptide (AU)