Glial fibrillary acidic protein vs. S100B to identify astrocytes impacted by sex and high fat diet.

The brain modulates energy balance by coordinating energy intake and energy expenditure to prevent metabolic diseases. Most research has focused on the role of neurons in this process, but recent work also implicates roles for astrocytes in energy balance. For example, astrocytes in the arcuate nucleus of the hypothalamus become reactive after mice are fed high fat diet (HFD) and their altered function is thought to contribute to obesity. However, limitations in labeling astrocytes in other brain areas has hindered determination of their roles in normal and altered energy balance. Reactive astrocytes increase expression of glial fibrillary acidic protein (GFAP), hence, GFAP has been commonly used as an astrocyte marker. Yet, there is scant immunolabeling of GFAP in brains of chow-fed mice, despite the presence of abundant astrocytes. These findings underscore the need for a marker to visualize astrocytes throughout the brain during normal physiology and exposure to diet-induced obesity, to permit study of how and where they contribute to energy balance. Here we compared immunofluorescence labeling of GFAP and another protein expressed in astrocytes, the S100 calcium binding protein beta (S100B), in brain sections from chow- and HFD-fed female and male mice. We compared the number of labeled cells in areas pertinent to control of ingestive behavior including the arcuate nucleus, lateral hypothalamic area, paraventricular nucleus, lateral preoptic area, and the periaqueductal gray. There was low GFAP expression throughout these brain regions that increased in some brain areas from HFD-fed mice, but intriguingly this only occurred in males. In contrast, S100B labeled more cells than GFAP in each of these areas but its expression was not altered by HFD or sex in most cases. Overall, these data suggest that S100B is superior to GFAP for visualizing astrocytes throughout the brain in both sexes regardless of diet exposure. This study will be a useful resource for researchers who want to identify and study astrocytes in response to diet and in other physiological contexts.