Abstract:

Abstract:
OBJECTIVE: Steroidogenic factor-1 (SF1) neurons of the ventromedial hypothalamus play key roles in the regulation of food intake, body weight and glucose metabolism. The bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) is expressed in the hypothalamus, where it determines some of the actions of bile acids on food intake and body weight through still poorly defined neuronal mechanisms. Here, we examined the role of TGR5 in SF1 neurons in the regulation of energy balance and glucose metabolism. METHODS: We used a genetic approach combined with metabolic phenotyping and molecular analyses to establish the effect of TGR5 deletion in SF1 neurons on meal pattern, body weight, body composition, energy expenditure and use of energy substrates as well as on possible changes in glucose handling and insulin sensitivity. RESULTS: Our findings reveal that TGR5 in SF1 neurons does not play a major role in the regulation of food intake or body weight under standard chow, but it is involved in the adaptive feeding response to the acute exposure to cold or to a hypercaloric, high-fat diet, without changes in energy expenditure. Notably, TGR5 in SF1 neurons hinder glucose metabolism, since deletion of the receptor improves whole-body glucose uptake through heightened insulin signaling in the hypothalamus and in the brown adipose tissue. CONCLUSIONS: TGR5 in SF1 neurons favours satiety by differently modifying the meal pattern in response to specific metabolic cues. These studies also reveal a novel key function for TGR5 in SF1 neurons in the regulation of whole-body insulin sensitivity, providing new insight into the role played by neuronal TGR5 in the regulation of metabolism.

Abstract:
The hypothalamus contains a remarkable diversity of neurons that orchestrate behavioural and metabolic outputs in a highly plastic manner. Neuronal diversity is key to enabling hypothalamic functions and, according to the neuroscience dogma, it is predetermined during embryonic life. Here, by combining lineage tracing of hypothalamic pro-opiomelanocortin (Pomc) neurons with single-cell profiling approaches in adult male mice, we uncovered subpopulations of 'Ghost' neurons endowed with atypical molecular and functional identity. Compared to 'classical' Pomc neurons, Ghost neurons exhibit negligible Pomc expression and are 'invisible' to available neuroanatomical approaches and promoter-based reporter mice for studying Pomc biology. Ghost neuron numbers augment in diet-induced obese mice, independent of neurogenesis or cell death, but weight loss can reverse this shift. Our work challenges the notion of fixed, developmentally programmed neuronal identities in the mature hypothalamus and highlight the ability of specialised neurons to reversibly adapt their functional identity to adult-onset obesogenic stimuli.

Abstract:
Down syndrome (DS) or Trisomy 21 is the most common genetic cause of mental retardation with severe learning and memory deficits. DS is due to the complete or partial triplication of human chromosome 21 (HSA21) triggering gene overexpression and protein synthesis alterations responsible for a plethora of mental and physical phenotypes. Among the diverse brain target systems that affect hippocampal-dependent learning and memory deficit impairments in DS, the upregulation of the endocannabinoid system (ECS), and notably the overexpression of the cannabinoid type-1 receptor (CB1), seems to play a major role. Combining various protein and gene expression targeted approaches using western blot, qRT-PCR and FISH techniques, we investigated the expression pattern of ECS components in the hippocampus (HPC) of male Ts65Dn mice. Among all the molecules that constitute the ECS, we found that the expression of the CB1 is altered in the HPC of Ts65Dn mice. CB1 distribution is differentially segregated between the dorsal and ventral part of the HPC and within the different cell populations that compose the HPC. CB1 expression is upregulated in GABAergic neurons of Ts65Dn mice whereas it is downregulated in glutamatergic neurons. These results highlight a complex regulation of the CB1 encoding gene (Cnr1) in Ts65Dn mice that could open new therapeutic solutions for this syndrome.

Abstract:
Hypothalamic pro-opiomelanocortin (POMC) neurons are known to trigger satiety. However, these neuronal cells encompass heterogeneous subpopulations that release γ-aminobutyric acid (GABA), glutamate, or both neurotransmitters, whose functions are poorly defined. Using conditional mutagenesis and chemogenetics, we show that blockade of the energy sensor mechanistic target of rapamycin complex 1 (mTORC1) in POMC neurons causes hyperphagia by mimicking a cellular negative energy state. This is associated with decreased POMC-derived anorexigenic α-melanocyte-stimulating hormone and recruitment of POMC/GABAergic neurotransmission, which is restrained by cannabinoid type 1 receptor signaling. Electrophysiology and optogenetic studies further reveal that pharmacological blockade of mTORC1 simultaneously activates POMC/GABAergic neurons and inhibits POMC/glutamatergic ones, implying that the functional specificity of these subpopulations relies on mTORC1 activity. Finally, POMC neurons with different neurotransmitter profiles possess specific molecular signatures and spatial distribution. Altogether, these findings suggest that mTORC1 orchestrates the activity of distinct POMC neurons subpopulations to regulate feeding behavior.

Abstract:
Despite the central role of Rho GTPases in neuronal development, their functions in adult hippocampal neurogenesis remain poorly explored. Here, by using a retrovirus-based loss-of-function approach in vivo, we show that the atypical Rho GTPase Rnd2 is crucial for survival, positioning, somatodendritic morphogenesis, and functional maturation of adult-born dentate granule neurons. Interestingly, most of these functions are specific to granule neurons generated during adulthood since the deletion of Rnd2 in neonatally-born granule neurons only affects dendritogenesis. In addition, suppression of Rnd2 in adult-born dentate granule neurons increases anxiety-like behavior whereas its deletion in pups has no such effect, a finding supporting the adult neurogenesis hypothesis of anxiety disorders. Thus, our results are in line with the view that adult neurogenesis is not a simple continuation of earlier processes from development, and establish a causal relationship between Rnd2 expression and anxiety.

Abstract:
Bile acids (BAs) improve metabolism and exert anti-obesity effects through the activation of the Takeda G protein-coupled receptor 5 (TGR5) in peripheral tissues. TGR5 is also found in the brain hypothalamus, but whether hypothalamic BA signaling is implicated in body weight control and obesity pathophysiology remains unknown. Here we show that hypothalamic BA content is reduced in diet-induced obese mice. Central administration of BAs or a specific TGR5 agonist in these animals decreases body weight and fat mass by activating the sympathetic nervous system, thereby promoting negative energy balance. Conversely, genetic downregulation of hypothalamic TGR5 expression in the mediobasal hypothalamus favors the development of obesity and worsens established obesity by blunting sympathetic activity. Lastly, hypothalamic TGR5 signaling is required for the anti-obesity action of dietary BA supplementation. Together, these findings identify hypothalamic TGR5 signaling as a key mediator of a top-down neural mechanism that counteracts diet-induced obesity.

Abstract:
Until recently, 10% of hepatocellular adenomas (HCAs) remained unclassified (UHCA). Among the UHCAs, the sonic hedgehog HCA (shHCA) was defined by focal deletions that fuse the promoter of Inhibin beta E chain with GLI1. Prostaglandin D2 synthase was proposed as immunomarker. In parallel, our previous work using proteomic analysis showed that most UHCAs constitute a homogeneous subtype associated with overexpression of argininosuccinate synthase (ASS1). To clarify the use of ASS1 in the HCA classification and avoid misinterpretations of the immunohistochemical staining, the aims of this work were to study (1) the link between shHCA and ASS1 overexpression and (2) the clinical relevance of ASS1 overexpression for diagnosis. Molecular, proteomic, and immunohistochemical analyses were performed in UHCA cases of the Bordeaux series. The clinico-pathological features, including ASS1 immunohistochemical labeling, were analyzed on a large international series of 67 cases. ASS1 overexpression and the shHCA subgroup were superimposed in 15 cases studied by molecular analysis, establishing ASS1 overexpression as a hallmark of shHCA. Moreover, the ASS1 immunomarker was better than prostaglandin D2 synthase and only found positive in 7 of 22 shHCAs. Of the 67 UHCA cases, 58 (85.3%) overexpressed ASS1, four cases were ASS1 negative, and in five cases ASS1 was noncontributory. Proteomic analysis performed in the case of doubtful interpretation of ASS1 overexpression, especially on biopsies, can be a support to interpret such cases. ASS1 overexpression is a specific hallmark of shHCA known to be at high risk of bleeding. Therefore, ASS1 is an additional tool for HCA classification and clinical diagnosis.

Abstract:
Ciliary neurotrophic factor (CNTF) potently decreases food intake and body weight in diet-induced obese mice by acting through neuronal circuits and pathways located in the arcuate nucleus (ARC) of the hypothalamus. CNTF also exerts pro-inflammatory actions within the brain. Here we tested whether CNTF modifies energy balance by inducing inflammatory responses in the ARC and whether these effects depend upon the mechanistic target of rapamycin complex 1 (mTORC1) pathway, which regulates both energy metabolism and inflammation. To this purpose, chow- and high fat diet (HFD)- fed mice lacking the S6 kinase 1 (S6K1(-/-)), a downstream target of mTORC1, and their wild-type (WT) littermates received 12 days continuous intracerebroventricular (icv) infusion of the CNTF analogue axokine (CNTFAx15). Behavioral, metabolic and molecular effects were evaluated. Central chronic administration of CNTFAx15 decreased body weight and feed efficiency in WT mice only, when fed HFD, but not chow. These metabolic effects correlated with increased number of iba-1 positive microglia specifically in the ARC and were accompanied by significant increases of IL-1beta and TNF-alpha mRNA expression in the hypothalamus. Hypothalamic iNOS and SOCS3 mRNA, molecular markers of pro-inflammatory response, were also increased by CNTFAx15. All these changes were absent in S6K1(-/-) mice. This study reveals that CNTFAx15 requires a functional S6K1 to modulate energy balance and hypothalamic inflammation in a diet-dependent fashion. Further investigations should determine whether S6K1 is a suitable target for the treatment of pathologies characterized by a high neuroinflammatory state.

Abstract:
The paraventricular nucleus of the hypothalamus (PVN) regulates energy balance by modulating not only food intake, but also energy expenditure and brown adipose tissue (BAT) thermogenesis. To test the hypothesis that cannabinoid type 1 (CB1) receptor in PVN neurons might control these processes, we used the Cre/loxP system to delete CB1 from Single minded 1 (Sim1) neurons, which account for the majority of PVN neurons. On standard chow, mice lacking CB1 receptor in Sim1 neurons (Sim1-CB1-KO) had food intake, body weight, adiposity, glucose metabolism and energy expenditure comparable to wild-type (Sim1-CB1-WT) littermates. However, maintenance on a high-fat diet (HFD) revealed a gene-by-diet interaction whereby Sim1-CB1-KO mice had decreased adiposity, improved insulin sensitivity and increased energy expenditure, while feeding behavior was similar to Sim1-CB1-WT mice. Additionally, HFD-fed Sim1-CB1-KO mice had increased mRNA expression of the beta3-adrenergic receptor, as well as of UCP-1, Cox-IV and Tfam in the BAT, all molecular changes suggestive of increased thermogenesis. Pharmacological studies using beta-blockers suggested that modulation of beta-adrenergic transmission play an important role in determining energy expenditure changes observed in Sim1-CB1-KO. Finally, chemical sympathectomy abolished the obesity-resistant phenotype of Sim1-CB1-KO mice. Altogether, these findings reveal a diet-dependent dissociation in the CB1 receptor control of food intake and energy expenditure, likely mediated by the PVN, where CB1 receptors on Sim1-positive neurons do not impact food intake, but hinder energy expenditure during dietary environmental challenges that promote body weight gain.