Enhanced Expression of the Sweet Taste Receptors and Alpha-gustducin in Reactive Astrocytes of the Rat Hippocampus Following Ischemic Injury

Abstract

The heterodimeric sweet taste receptors, T1R2 and T1R3, have recently been proposed to be associated with the brain glucose sensor. To identify whether sweet taste signaling is regulated in response to an ischemic injury inducing acute impairment of glucose metabolism, we investigated the spatiotemporal expression of the sweet taste receptors and their associated taste-specific G-protein α-gustducin in the rat hippocampus after ischemia. The expression profiles of both receptor subunits and α-gustducin shared overlapping expression patterns in sham-operated and ischemic hippocampi. Constitutive expression of both receptors and α-gustducin was localized in neurons of the pyramidal cell and granule cell layers, but their upregulation was detected in reactive astrocytes in ischemic hippocampi. Immunoblot analysis confirmed the immmunohistochemically determined temporal patterns of sweet-taste signaling proteins. These results suggest that the expression of sweet taste signaling proteins in astrocytes might be regulated in response to altered extracellular levels of glucose following an ischemic insult.

In vitro evidence supports the presence of glucokinase-independent glucosensing mechanisms in hypothalamus and hindbrain of rainbow trout

“…In the hypothalamus, exposure to enhanced glucose resulted in a decrease in the mRNA abundance of T1R3, a response similar than that observed in vivo (Otero-Rodiño et al, 2015). The response of the other markers assessed, T1R2 and Gnat3, to low glucose concentration in the medium was also similar to that previously observed under in vivo conditions, and is in agreement with the increase observed in mammalian brain under low glucose levels (Shin et al, 2010). These changes further support the differential response of these parameters compared with the mammalian model, where in the hypothalamus the increase in glucose concentration elicits a decrease in the mRNA abundance of T1R2 but not of T1R3 and Gnat3 (Ren et al, 2009).…”

Non-specific Immunostaining by a Rabbit Antibody against Gustducin α Subunit in Mouse Brain

“…It is worth emphasizing that we could not find positive staining in neuronal somata or astrocytes. However, previous studies using frozen sections (Shin et al 2010;Dehkodi et al 2012) claimed positive staining in neuronal somata and astrocytes. This discrepancy may be attributed to the differences in tissue processing.…”

“…Without proper controls, the previous reports of taste receptors and/or gustducin in the brain (Ren et al 2009;Shin et al 2010;Singh et al 2011;Dehkordi et al 2012) and retina (Son et al 2011) might be artificial. Rather than the conventional negative controls of pre-incubation with immune peptides or omission of primary antibodies, a better negative control may be necessary, especially when a new immunostaining pattern is to be verified.…”

“…However, many previous immunohistochemical studies solely adopt the conventional "negative control" by either omitting or blocking the primary antibody prior to staining (Ruiz-Avila et al 1995;Haga and Yoshie 2010;Shin et al 2010;Singh et al 2011;Son et al 2011;Dehkordi et al 2012). Peptide blocking might just confirm that the primary antibody is specific for the target peptide sequence (not the entire protein), which is competing against the immune peptide for binding to the primary antibody.…”

Expression of α-gustducin in mammalian retinas

“…G a -gust, along with T1R2/T1R3, was recently found within neurons in various regions of the mouse brain, including the hypothalamus, hippocampus, and cerebral cortex, leading to the proposal that hypothalamic G a -gust is involved in brain glucose sensing by the T1R2/T1R3 receptor [10]. Very recently, Shin et al [11] reported that G a -gust is expressed in reactive astrocytes of the rat hippocampus in response to ischemia/reperfusion injury, suggesting that G a -gust can be induced and regulated by ischemic damage and may be involved in pathophysiology in some of the neuronal diseases.…”