[Dapagliflozin, a Sodium-Glucose Co-transporter-2 Inhibitor, Acutely Reduces Energy Expenditure in Brown Adipose Tissue via Neural Signals in Mice].

　Selective sodium glucose transporter-2 inhibitor (SGLT2i) treatment promotes urinary glucose excretion, thereby reducing blood glucose as well as body weight. However, only limited body weight reductions are achieved with SGLT2i administration. Hyperphagia is reportedly one of the causes of this limited weight loss. However, the effects of SGLT2i on systemic energy expenditure have not been fully elucidated. We investigated the acute effects of dapagliflozin, an SGLT2i, on systemic energy expenditure in mice. Eighteen hours after dapagliflozin administration, oxygen consumption and brown adipose tissue (BAT) expression of ucp1, a thermogenesis-related gene, were significantly decreased as compared with those after vehicle administration. In addition, dapagliflozin significantly suppressed norepinephrine (NE) turnover in BAT and c-fos expression in the rostral raphe pallidus nucleus (rRPa), which contains the sympathetic premotor neurons responsible for thermogenesis. These findings indicate that the dapagliflozin-mediated acute decrease in energy expenditure involves a reduction in BAT thermogenesis via decreased sympathetic nerve activity from the rRPa. Furthermore, common hepatic branch vagotomy abolished the reductions in ucp1 expression, NE contents in BAT, and c-fos expression in the rRPa. In addition, alterations in hepatic carbohydrate metabolism, such as decreases in glycogen contents and upregulation of phosphoenolpyruvate carboxykinase, occurred prior to the suppression of BAT thermogenesis, e.g., 6 h after dapagliflozin treatment. Collectively, these results suggest that SGLT2i acutely suppresses energy expenditure in BAT via regulation of an interorgan neural network consisting of the common hepatic vagal branch and sympathetic nerves.

Reduced Serotonin Transporter Levels and Inflammation in the Midbrain Raphe of 12 Month Old APPswe/PSEN1dE9 Mice.

BACKGROUND: Although mood and sleep disturbances are nearly universal among patients with Alzheimer's disease (AD), brain structures involved in non-cognitive processing remain under characterized in terms of AD pathology. OBJECTIVES: This study was designed to evaluate hallmarks of AD pathology in the brainstem of the APPswe/PS1dE9 mouse model of familial AD. METHODS: Fresh-frozen sections from female, 12 month old, transgenic and control B6C3 mice (n=6/genotype) were examined for amyloid burden and neurofibrillary alterations, by using 6E10 immunohistochemistry and the Gallyas silver stain, respectively. Serotonin transporter (SERT) densities in the dorsal and the median raphe were quantified by [3H]DASB autoradiography. SERT mRNA expression was measured by RT-PCR and visualized by in situ hybridization. Neuroinflammation was evaluated by immunohistochemical staining for microglia and astrocytes, and by measuring mRNA levels of the proinflammatory cytokines TNF-α, IL-1ß and IL-6. RESULTS: No amyloid- and tau-associated lesions were observed in the midbrain raphe of 12 month old APPswe/PS1dE9 mice. SERT binding levels were reduced in transgenic animals compared to age-matched controls, and SERT mRNA levels were decreased by at least 50% from control values. Intense microglial, but not astrocytic immunoreactivity was observed in APPswe/PS1dE9 vs. wild-type mice. Levels of TNF-α mRNA were two-fold higher than control and correlated positively with SERT mRNA expression levels in transgenic animals. CONCLUSIONS: There was no amyloid accumulation and tau-associated pathology in the midbrain raphe of 12 month old APPswe/PS1dE9 mice. However, there was a local neuroinflammatory response with loss of serotonergic markers, which may partially account for some of the behavioral symptoms of AD.

Dapagliflozin, a Sodium-Glucose Co-Transporter 2 Inhibitor, Acutely Reduces Energy Expenditure in BAT via Neural Signals in Mice.

Selective sodium glucose cotransporter-2 inhibitor (SGLT2i) treatment promotes urinary glucose excretion, thereby reducing blood glucose as well as body weight. However, only limited body weight reductions are achieved with SGLT2i treatment. Hyperphagia is reportedly one of the causes of this limited weight loss. However, the effects of SGLT2i treatment on systemic energy expenditure have not been fully elucidated. Herein, we investigated the acute effects of dapagliflozin, a SGLT2i, on systemic energy expenditure in mice. Eighteen hours after dapagliflozin treatment oxygen consumption and brown adipose tissue (BAT) expression of ucp1, a thermogenesis-related gene, were significantly decreased as compared to those after vehicle treatment. In addition, dapagliflozin significantly suppressed norepinephrine (NE) turnover in BAT and c-fos expression in the rostral raphe pallidus nucleus (rRPa) which contains the sympathetic premotor neurons responsible for thermogenesis. These findings indicate that the dapagliflozin-mediated acute decrease in energy expenditure involves a reduction in BAT thermogenesis via decreased sympathetic nerve activity from the rRPa. Furthermore, common hepatic branch vagotomy abolished the reductions in ucp1 expression and NE contents in BAT and c-fos expression in the rRPa. In addition, alterations in hepatic carbohydrate metabolism, such as decreases in glycogen contents and upregulation of phosphoenolpyruvate carboxykinase, manifested prior to the suppression of BAT thermogenesis, e.g. 6 hours after dapagliflozin treatment. Collectively, these results suggest that SGLT2i treatment acutely suppresses energy expenditure in BAT via regulation of an inter-organ neural network consisting of the common hepatic vagal branch and sympathetic nerves.

Conditional anterograde tracing reveals distinct targeting of individual serotonin cell groups (B5-B9) to the forebrain and brainstem.

Serotoninergic innervation of the central nervous system is provided by hindbrain raphe nuclei (B1-B9). The extent to which each raphe subdivision has distinct topographic organization of their projections is still unclear. We provide a comprehensive description of the main targets of the rostral serotonin (5-HT) raphe subgroups (B5-B9) in the mouse brain. Adeno-associated viruses that conditionally express GFP under the control of the 5-HT transporter promoter were used to label small groups of 5-HT neurons in the dorsal (B7d), ventral (B7v), lateral (B7l), and caudal (B6) subcomponents of the dorsal raphe (DR) nucleus as well as in the rostral and caudal parts of the median raphe (MR) nucleus (B8 and B5, respectively), and in the supralemniscal (B9) cell group. We illustrate the distinctive and largely non-overlapping projection areas of these cell groups: for instance, DR (B7) projects to basal parts of the forebrain, such as the amygdala, whereas MR (B8) is the main 5-HT source to the hippocampus, septum, and mesopontine tegmental nuclei. Distinct subsets of B7 have preferential brain targets: B7v is the main source of 5-HT for the cortex and amygdala while B7d innervates the hypothalamus. We reveal for the first time the target areas of the B9 cell group, demonstrating projections to the caudate, prefrontal cortex, substantia nigra, locus coeruleus and to the raphe cell groups. The broad topographic organization of the different raphe subnuclei is likely to underlie the different functional roles in which 5-HT has been implicated in the brain. The present mapping study could serve as the basis for genetically driven specific targeting of the different subcomponents of the mouse raphe system.

Evidence for the existence of FGFR1-5-HT1A heteroreceptor complexes in the midbrain raphe 5-HT system.

The ascending midbrain 5-HT neurons known to contain 5-HT1A autoreceptors may be dysregulated in depression due to a reduced trophic support. With in situ proximity ligation assay (PLA) and supported by co-location of the FGFR1 and 5-HT1A immunoreactivities in midbrain raphe 5-HT cells, evidence for the existence of FGFR1-5-HT1A heteroreceptor complexes were obtained in the dorsal and median raphe nuclei of the Sprague-Dawley rat. Their existence in the rat medullary raphe RN33B cell cultures was also established. After combined FGF-2 and 8-OH-DPAT treatment, a marked and significant increase in PLA positive clusters was found in the RN33B cells. Similar results were reached upon coactivation by agonists in HEK293T cells using the Fluorescent Resonance Energy Transfer (FRET) technique resulting in increased FRETmax and reduced FRET50 values. The heteroreceptor complex formation was dependent on TMV of the 5-HT1A receptor since it was blocked by incubation with TMV but not with TMII. Taken together, the 5-HT1A autoreceptors by being recruited into a FGFR1-5-HT1A heteroreceptor complex in the midbrain raphe 5-HT nerve cells may develop a novel function, namely a trophic role in many midbrain 5-HT neuron systems originating from the dorsal and medianus raphe nuclei.