Whole-brain mapping of amylin-induced neuronal activity in receptor activity-modifying protein 1/3 knockout mice.

The pancreatic hormone amylin plays a central role in regulating energy homeostasis and glycaemic control by stimulating satiation and reducing food reward, making amylin receptor agonists attractive for the treatment of metabolic diseases. Amylin receptors consist of heterodimerized complexes of the calcitonin receptor and receptor-activity modifying proteins subtype 1-3 (RAMP1-3). Neuronal activation in response to amylin dosing has been well characterized, but only in selected regions expressing high levels of RAMPs. The current study identifies global brain-wide changes in response to amylin and by comparing wild type and RAMP1/3 knockout mice reveals the importance of RAMP1/3 in mediating this response. Amylin dosing resulted in neuronal activation as measured by an increase in c-Fos labelled cells in 20 brain regions, altogether making up the circuitry of neuronal appetite regulation (e.g., area postrema (AP), nucleus of the solitary tract (NTS), parabrachial nucleus (PB), and central amygdala (CEA)). c-Fos response was also detected in distinct nuclei across the brain that typically have not been linked with amylin signalling. In RAMP1/3 knockout amylin induced low-level neuronal activation in seven regions, including the AP, NTS and PB, indicating the existence of RAMP1/3-independent mechanisms of amylin response. Under basal conditions RAMP1/3 knockout mice show reduced neuronal activity in the hippocampal formation as well as reduced hippocampal volume, suggesting a role for RAMP1/3 in hippocampal physiology and maintenance. Altogether these data provide a global map of amylin response in the mouse brain and establishes the significance of RAMP1/3 receptors in relaying this response.

Protection against overfeeding-induced weight gain is preserved in obesity but does not require FGF21 or MC4R.

Overfeeding triggers homeostatic compensatory mechanisms that counteract weight gain. Here, we show that both lean and diet-induced obese (DIO) male mice exhibit a potent and prolonged inhibition of voluntary food intake following overfeeding-induced weight gain. We reveal that FGF21 is dispensable for this defense against weight gain. Targeted proteomics unveiled novel circulating factors linked to overfeeding, including the protease  legumain (LGMN). Administration of recombinant LGMN lowers body weight and food intake in DIO mice. The protection against weight gain is also associated with reduced vascularization in the hypothalamus and sustained reductions in the expression of the orexigenic neuropeptide genes, Npy and Agrp, suggesting a role for hypothalamic signaling in this homeostatic recovery from overfeeding. Overfeeding of melanocortin 4 receptor (MC4R) KO mice shows that these mice can suppress voluntary food intake and counteract the enforced weight gain, although their rate of weight recovery is impaired. Collectively, these findings demonstrate that the defense against overfeeding-induced weight gain remains intact in obesity and involves mechanisms independent of both FGF21 and MC4R.

Insulin and leptin oscillations license food-entrained browning and metabolic flexibility.

Timed feeding drives adipose browning, although the integrative mechanisms for the same remain unclear. Here, we show that twice-a-night (TAN) feeding generates biphasic oscillations of circulating insulin and leptin, representing their entrainment by timed feeding. Insulin and leptin surges lead to marked cellular, functional, and metabolic remodeling of subcutaneous white adipose tissue (sWAT), resulting in increased energy expenditure. Single-cell RNA-sequencing (scRNA-seq) analyses and flow cytometry demonstrate a role for insulin and leptin surges in innate lymphoid type 2 (ILC2) cell recruitment and sWAT browning, since sWAT depot denervation or loss of leptin or insulin receptor signaling or ILC2 recruitment each dampens TAN feeding-induced sWAT remodeling and energy expenditure. Consistently, recreating insulin and leptin oscillations via once-a-day timed co-injections is sufficient to favorably remodel innervated sWAT. Innervation is necessary for sWAT remodeling, since denervation of sWAT, but not brown adipose tissue (BAT), blocks TAN-induced sWAT remodeling and resolution of inflammation. In sum, reorganization of nutrient-sensitive pathways remodels sWAT and drives the metabolic benefits of timed feeding.

Atlas of exercise-induced brain activation in mice.

OBJECTIVES: There is significant interest in uncovering the mechanisms through which exercise enhances cognition, memory, and mood, and lowers the risk of neurodegenerative diseases. In this study, we utilize forced treadmill running and distance-matched voluntary wheel running, coupled with light sheet 3D brain imaging and c-Fos immunohistochemistry, to generate a comprehensive atlas of exercise-induced brain activation in mice. METHODS: To investigate the effects of exercise on brain activity, we compared whole-brain activation profiles of mice subjected to treadmill running with mice subjected to distance-matched wheel running. Male mice were assigned to one of four groups: a) an acute bout of voluntary wheel running, b) confinement to a cage with a locked running wheel, c) forced treadmill running, or d) placement on an inactive treadmill. Immediately following each exercise or control intervention, blood samples were collected for plasma analysis, and brains were collected for whole-brain c-Fos quantification. RESULTS: Our dataset reveals 255 brain regions activated by acute exercise in mice, the majority of which have not previously been linked to exercise. We find a broad response of 140 regulated brain regions that are shared between voluntary wheel running and treadmill running, while 32 brain regions are uniquely regulated by wheel running and 83 brain regions uniquely regulated by treadmill running. In contrast to voluntary wheel running, forced treadmill running triggers activity in brain regions associated with stress, fear, and pain. CONCLUSIONS: Our findings demonstrate a significant overlap in neuronal activation signatures between voluntary wheel running and distance-matched forced treadmill running. However, our analysis also reveals notable differences and subtle nuances between these two widely used paradigms. The comprehensive dataset is accessible online at www.neuropedia.dk, with the aim of enabling future research directed towards unraveling the neurobiological response to exercise.

Targeting postsynaptic glutamate receptor scaffolding proteins PSD-95 and PICK1 for obesity treatment.

Human genome-wide association studies (GWAS) suggest a functional role for central glutamate receptor signaling and plasticity in body weight regulation. Here, we use UK Biobank GWAS summary statistics of body mass index (BMI) and body fat percentage (BF%) to identify genes encoding proteins known to interact with postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartate (NMDA) receptors. Loci in/near discs large homolog 4 (DLG4) and protein interacting with C kinase 1 (PICK1) reached genome-wide significance (P < 5 × 10-8) for BF% and/or BMI. To further evaluate the functional role of postsynaptic density protein-95 (PSD-95; gene name: DLG4) and PICK1 in energy homeostasis, we used dimeric PSD-95/disc large/ZO-1 (PDZ) domain-targeting peptides of PSD-95 and PICK1 to demonstrate that pharmacological inhibition of PSD-95 and PICK1 induces prolonged weight-lowering effects in obese mice. Collectively, these data demonstrate that the glutamate receptor scaffolding proteins, PICK1 and PSD-95, are genetically linked to obesity and that pharmacological targeting of their PDZ domains represents a promising therapeutic avenue for sustained weight loss.

Uncovering CNS access of lipidated exendin-4 analogues by quantitative whole-brain 3D light sheet imaging.

Peptide-based drug development for CNS disorders is challenged by poor blood-brain barrier (BBB) penetrability of peptides. While acylation protractions (lipidation) have been successfully applied to increase circulating half-life of therapeutic peptides, little is known about the CNS accessibility of lipidated peptide drugs. Light-sheet fluorescence microscopy (LSFM) has emerged as a powerful method to visualize whole-brain 3D distribution of fluorescently labelled therapeutic peptides at single-cell resolution. Here, we applied LSFM to map CNS distribution of the clinically relevant GLP-1 receptor agonist (GLP-1RA) exendin-4 (Ex4) and lipidated analogues following peripheral administration. Mice received an intravenous dose (100 nmol/kg) of IR800 fluorophore-labelled Ex4 (Ex4), Ex4 acylated with a C16-monoacid (Ex4_C16MA) or C18-diacid (Ex4_C18DA). Other mice were administered C16MA-acylated exendin 9-39 (Ex9-39_C16MA), a selective GLP-1R antagonist, serving as negative control for GLP-1R mediated agonist internalization. Two hours post-dosing, brain distribution of Ex4 and analogues was predominantly restricted to the circumventricular organs, notably area postrema and nucleus of the solitary tract. However, Ex4_C16MA and Ex9-39_C16MA also distributed to the paraventricular hypothalamic nucleus and medial habenula. Notably, Ex4_C18DA was detected in deeper-lying brain structures such as dorsomedial/ventromedial hypothalamic nuclei and the dentate gyrus. Similar CNS distribution maps of Ex4_C16MA and Ex9-39_C16MA suggest that brain access of lipidated Ex4 analogues is independent on GLP-1 receptor internalization. The cerebrovasculature was devoid of specific labelling, hence not supporting a direct role of GLP-1 RAs in BBB function. In conclusion, peptide lipidation increases CNS accessibility of Ex4. Our fully automated LSFM pipeline is suitable for mapping whole-brain distribution of fluorescently labelled drugs.

GLP-1 and nicotine combination therapy engages hypothalamic and mesolimbic pathways to reverse obesity.

Glucagon-like peptide-1 receptor (GLP-1R) agonists promote nicotine avoidance. Here, we show that the crosstalk between GLP-1 and nicotine extends beyond effects on nicotine self-administration and can be exploited pharmacologically to amplify the anti-obesity effects of both signals. Accordingly, combined treatment with nicotine and the GLP-1R agonist, liraglutide, inhibits food intake and increases energy expenditure to lower body weight in obese mice. Co-treatment with nicotine and liraglutide gives rise to neuronal activity in multiple brain regions, and we demonstrate that GLP-1R agonism increases excitability of hypothalamic proopiomelanocortin (POMC) neurons and dopaminergic neurons in the ventral tegmental area (VTA). Further, using a genetically encoded dopamine sensor, we reveal that liraglutide suppresses nicotine-induced dopamine release in the nucleus accumbens in freely behaving mice. These data support the pursuit of GLP-1R-based therapies for nicotine dependence and encourage further evaluation of combined treatment with GLP-1R agonists and nicotinic receptor agonists for weight loss.

Deep learning reveals 3D atherosclerotic plaque distribution and composition.

Complications of atherosclerosis are the leading cause of morbidity and mortality worldwide. Various genetically modified mouse models are used to investigate disease trajectory with classical histology, currently the preferred methodology to elucidate plaque composition. Here, we show the strength of light-sheet fluorescence microscopy combined with deep learning image analysis for characterising and quantifying plaque burden and composition in whole aorta specimens. 3D imaging is a non-destructive method that requires minimal ex vivo handling and can be up-scaled to large sample sizes. Combined with deep learning, atherosclerotic plaque in mice can be identified without any ex vivo staining due to the autofluorescent nature of the tissue. The aorta and its branches can subsequently be segmented to determine how anatomical position affects plaque composition and progression. Here, we find the highest plaque accumulation in the aortic arch and brachiocephalic artery. Simultaneously, aortas can be stained for markers of interest (for example the pan immune cell marker CD45) and quantified. In ApoE-/- mice we observe that levels of CD45 reach a plateau after which increases in plaque volume no longer correlate to immune cell infiltration. All underlying code is made publicly available to ease adaption of the method.