Work performed and Overview of the Results
In order to understand the role of VMH neurons in acute and chronic energy balance, we have performed a series of cell type specific neuronal activity manipulation e experiments while closely monitoring appetite and body weight phenotypes. To achieve this, we utilized state of the art chemogenetic actuators, DREADDs, to increase or decrease VMH neuronal activity.
Acute chemogenetic inhibition of VMH neurons: We have used a transgenic mouse line, sf1-cre, and a set of Cre-dependent viral tools, to selectively target chemogenetic activity manipulation tools to VMH neurons. Using stereotaxic delivery method, we expressed chemogenetic silencer DREADD, hM4D, in VMH-SF1 neurons. With the help of hM4D, we can acutely silence VMH neurons within minutes upon intraperitoneal injection its ligand, CNO. Our results suggest that acute chemogenetic silencing of VMH neurons does not increase food intake. This is in contrast to expectations from the literature that VMH lesions drive hyperphagia and obesity. We suggest that VMH lesions, which are chronic manipulations by nature, may have additional long lasting effects on appetite, which is not recapitulated in acute silencing experiments.
Chronic inhibition of VMH neurons: Classical lesion experiments have suffered from a setback of being nonspecific in the area of lesion as well as disruption of the fibers of passage through the periphery of VMH area. To resolve whether chronic loss of function of VMH neurons actually drive overeating, we used ablated VMH-SF1 neurons using virally targeted Cre-dependent caspase virus. Our cell type specific ablation experiment results confirmed that, as observed in classical lesioning studies, SF1 ablated animals are hyperphagic. Together with the acute chemogenetic silencing results, these experiments establish that reduced activity in SF1 neurons fails to drive veracious eating and appetite in short time scales but increases overall food intake in the longer terms.
Acute and chronic activation of VMH neurons: Silencing results established that VMH inhibition is not sufficient to drive acute food consumption. We next investigated whether VMH silencing is necessary for appetite. We used chemogenetic activator hM3D to selectively and acutely increase SF1 neuronal activity. Our results suggest that, both dark onset as well as food deprivation induced feeding can be strongly suppressed by increasing VMH-SF1 neuronal activity. Collectively these results suggest that VMH neuronal activity have permissive role in feeding in the short term but sufficient to cause positive energy balance in the longer terms.
Exploitation and dissemination of results: Our results implicate VMH as a novel target for appetite reduction. Understanding how SF1 activation suppresses food intake may provide novel targets for satiety circuits. To disseminate our findings, we are currently preparing our results as a manuscript for publication. In addition, these results will be orally presented in the international congress of Turkish Molecular Biology Organisation in September 2017.
