Marco Koch

Obesity resulting from chronic overnutrition and physical inactivity promotes the development of metabolic disorders by disrupting physiological processes in metabolically active organs, including skeletal muscles. To investigate whether skeletal muscle stem cells (satellite cells, SCs) are affected by systemic metabolic stress, we established primary SC cultures from male mice fed a high-fat diet (HFD) for 8 wk, and from control mice fed a standard chow (CTL). This model allowed us to assess diet-induced obesity (DIO)–related changes in SC-specific molecular and cellular signatures. Although body weight, body fat composition, and adipose tissue-associated macrophages differed significantly between DIO and CTL ex vivo, we observed no differences in the in vitro behaviour of primary SC-derived myoblasts from either group. Parameters such as proliferation and differentiation following serum deprivation were comparable. Expression levels and distribution patterns of myogenic regulatory factors (MRF), SC-specific markers (Pax7, CD56, Itga7), and hallmarks for senescence (GLB1), autophagy (p62, LC3B), and oxidative stress (ALDH1A1, ALDH1A3) remained unchanged. Thus, potential differences in the signatures of SC-derived myoblasts after 8 wk of a high-fat diet cannot be depicted in vitro. However, future experiments should address whether prolonged and metabolically more susceptible diets will exert long-term effects on myogenesis in vitro or not. Overall, we propose that primary SC cultures are better suited for acute in vitro testing regarding the molecular and cellular plasticity in metabolic shifts as induced by pharmacological treatments or genetical modifications, rather than for modeling long-term dietary effects.

The hypothalamic arcuate nucleus (Arc) is a central unit that controls the appetite through the integration of metabolic, hormonal, and neuronal afferent inputs. Agouti-related protein (AgRP), proopiomelanocortin (POMC), and dopaminergic neurons in the Arc differentially regulate feeding behaviors in response to hunger, satiety, and appetite, respectively. At the time of writing, the anatomical and electrophysiological characterization of these three neurons has not yet been intensively explored. Here, we interrogated the overall characterization of AgRP, POMC, and dopaminergic neurons using genetic mouse models, immunohistochemistry, and whole-cell patch recordings. We identified the distinct geographical location and intrinsic properties of each neuron in the Arc with the transgenic lines labelled with cell-specific reporter proteins. Moreover, AgRP, POMC, and dopaminergic neurons had different firing activities to ghrelin and leptin treatments. Ghrelin led to the increased firing rate of dopaminergic and AgRP neurons, and the decreased firing rate of POMC. In sharp contrast, leptin resulted in the decreased firing rate of AgRP neurons and the increased firing rate of POMC neurons, while it did not change the firing rate of dopaminergic neurons in Arc. These findings demonstrate the anatomical and physiological uniqueness of three hypothalamic Arc neurons to appetite control.

Cannabinoids are lipid messengers that modulate a variety of physiological processes and modify the generation of specific behaviors. In this regard, the cannabinoid receptor type 1 (CB1) represents the most relevant target molecule of cannabinoids so far. One main function of central CB1 signaling is to maintain whole body energy homeostasis. Thus, cannabinoids functionally interact with classical neurotransmitters in neural networks that control energy metabolism and feeding behavior. The promotion of CB1 signaling can increase appetite and stimulate feeding, while blockade of CB1 suppresses hunger and induces hypophagia. However, in order to treat overeating, pharmacological blockade of CB1 by the inverse agonist rimonabant not only suppressed feeding but also resulted in psychiatric side effects. Therefore, research within the last decade focused on deciphering the underlying cellular and molecular mechanisms of central cannabinoid signaling that control feeding and other behaviors, with the overall aim still being the identification of specific targets to develop safe pharmacological interventions for the treatment of obesity. Today, many studies unraveled the subcellular localization of CB1 and the function of cannabinoids in neurons and glial cells within circumscribed brain regions that represent integral parts of neural circuitries controlling feeding behavior. Here, these novel experimental findings will be summarized and recent advances in understanding the mechanisms of CB1-dependent cannabinoid signaling being relevant for central regulation of feeding behavior will be highlighted. Finally, presumed alternative pathways of cannabinoids that are not driven by CB1 activation but also contributing to control of feeding behavior will be introduced.