Abstract

Introduction-Hypothalamic tanycytes are localized in the lower lateral wall of the third ventricle. They are in contact with cerebrospinal fluid and have extended cell processes that contact the neurons in the arcuate nucleus (AN) that regulates food intake, in particular neuropeptide Y (NPY)- and pro-opiomelanocortin (POMC)-expressing neurons. Previously, we demonstrated that tanycytes in culture release lactate in response to high glucose, which reach hypothalamic neurons through MCTs transporters. Our hypothesis is that tanycytes communicates with the AN-neurons not only through lactate but also by ketone bodies, in particular in fasting condition. Aim-In this work we study the ketogenic potential of tanycytes and the POMC-neurons activity in response to lactate and β-HB. Methods- We made colorimetric assays to measure the tanycyte release of β-HB. Trough whole cell-patch clamp we evaluate changes in action potential frequency (APF) of POMC-EGFP neurons in response to lactate and β-HB. Furthermore, we made qPCR in hypothalamic neurons to evaluate POMC and NPY expression in response to lactate and β-HB. Results- Primary cultures of tanycytes release up 20 µM of β-HB which is enhanced by AMPK activation. 100% of POMC-EGFP neurons respond to glucose and lactate, increasing the APF. In contrast, these neurons decrease their activity in the presence of β-HB. Interestingly, by incubating the slices with 4-cinnamate, a blocker of MCT1 and MCT4, the neurons stop responding to glucose. In agreement with the above, in these neurons lactate and β-HB have opposite effects in POMC and NPY expression. Discussion- These results agree with the hypothesis that in POMC neurons, an indirect mechanism of glucodetection operates. Thus, lactate activates POMC-Neuorns and β-HB inhibit it, presumably through HCA2.