Endocrine Abstracts

The brain plays a crucial role in maintaining the body’s energy needs, a process involving the activity of a group of hypothalamic neurons that express the neuropeptidergic marker pro-opiomelanocortin (POMC). POMC neuronal dysfunction can cause obesity and its associated metabolic sequelae. However, this population of neurons is highly diverse at a molecular and functional level, and whether or not such heterogeneity is implicated in disease establishment or progression has yet to be elucidated. Here, using a lineage-tracing approach in combination with histological and electrophysiological tools, we have characterized POMC neuronal cells at a single-cell resolution in control of lean and diet-induced obese (DIO) mice. Thanks to this genetic strategy, we ‘traced’ with a reporter protein POMC neurons in adult mice, thus studying these neuronal cells independently from the expression of their main marker POMC. Different histological techniques, including immunohistochemistry, fluorescent in-situ hybridization, and RNAscope, have been used to cluster genetically ‘traced’ POMC neuronal cells based on their expression of the main marker POMC. These different approaches consistently allowed the identification of a previously uncharacterized sub-population that expresses negligible POMC mRNA and protein levels, which we named Ghost-POMC neurons. We also observed that Ghost-POMC neurons are insensitive to acute nutritional cues (fasting and refeeding) relative to ‘classic’ POMC positive neurons. Intriguingly, DIO mice presented an increased number of Ghost-POMC neurons relative to control animals. Furthermore, we developed an approach that combines whole-cell patch-clamp of traced POMC neurons with the subsequent molecular profiling of the patched cell by single-cell qPCR. Thanks to this approach, we observed that DIO leads to electrical alterations only in a fraction of POMC neurons expressing undetectable levels of POMC mRNA, which is reminiscent of the Ghost population previously identified by histological techniques. Thus, Ghost-POMC neurons might constitute a novel subpopulation of POMC neurons that undergo dysfunction in response to prolonged dietary cues, perhaps contributing to obesity establishment or progression.

Keywords: POMC neurons; heterogeneity; neuroanatomy; electrophysiology.