The hedgehog signaling pathway is expressed in the adult mouse hypothalamus and modulated by fasting

Abstract

The importance of the primary cilium was initially highlighted by the class of human genetic disorders known as ciliopathies. Patients with ciliopathies such as Bardet-Biedl and Alstrom syndrome exhibit hyperphagia-associated obesity as a core clinical phenotype. How primary cilia contribute to energy homeostasis and feeding behavior is complex and unclear, but cilia appear important in both developmental and homeostatic processes. Primary cilia are important signaling centers, required for hedgehog signaling and localization of specific G protein-coupled receptors (GPCRs) with known roles in feeding behavior in mammals. The hedgehog pathway is best known for its role in developmental patterning, but now has recognized roles in adult tissues as well. In the postnatal brain, cilia and hedgehog signaling are important for growth and maintenance of neural progenitors, however, the role of hedgehog signaling in the differentiated adult brain is less clear. Here, we provide a detailed analysis of the expression of core components of the hedgehog signaling pathway in the adult mouse hypothalamus with an emphasis on feeding centers. We show that hedgehog pathway genes continue to be expressed in differentiated neurons important for regulation of feeding behavior. Furthermore, we demonstrate for the first time that pathway activity is regulated at the transcriptional level by fasting. These data suggest that hedgehog signaling is involved in the proper functioning of brain regions which regulate feeding behavior and that hedgehog pathway dysfunction may play a role in the obesity observed in certain ciliopathies. Significance StatementHere we investigate the expression of hedgehog pathway components in the adult mouse hypothalamus. Using dual labeling in situ hybridization we show that core components of the signaling pathway are expressed in multiple neuronal cell types within the hypothalamic feeding centers. Our findings also support previous findings that astrocytes are responsive to hedgehog signaling, as determined by Gli1 and Ptch1 expression. Using qPCR analysis, we show that hypothalamic hedgehog pathway activity is upregulated in response to fasting and this response is nuclei specific. These data not only provide a more detailed understanding of hedgehog pathway expression in the adult mouse hypothalamus but also provide direct evidence of a novel role for hedgehog signaling in the physiological response to fasting.