Browsing by Author "Domingos, Ana I."
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- A brain-sparing diphtheria toxin for chemical genetic ablation of peripheral cell lineagesPublication . Pereira, Mafalda M. A.; Mahú, Inês; Seixas, Elsa; Martinéz-Sánchez, Noelia; Kubasova, Nadiya; Pirzgalska, Roksana M; Cohen, Paul; Dietrich, Marcelo O; López, Miguel; Bernardes, Gonçalo J. L.; Domingos, Ana I.Conditional expression of diphtheria toxin receptor (DTR) is widely used for tissue-specific ablation of cells. However, diphtheria toxin (DT) crosses the blood-brain barrier, which limits its utility for ablating peripheral cells using Cre drivers that are also expressed in the central nervous system (CNS). Here we report the development of a brain-sparing DT, termed BRAINSPAReDT, for tissue-specific genetic ablation of cells outside the CNS. We prevent blood-brain barrier passage of DT through PEGylation, which polarizes the molecule and increases its size. We validate BRAINSPAReDT with regional genetic sympathectomy: BRAINSPAReDT ablates peripheral but not central catecholaminergic neurons, thus avoiding the Parkinson-like phenotype associated with full dopaminergic depletion. Regional sympathectomy compromises adipose tissue thermogenesis, and renders mice susceptible to obesity. We provide a proof of principle that BRAINSPAReDT can be used for Cre/DTR tissue-specific ablation outside the brain using CNS drivers, while consolidating the link between adiposity and the sympathetic nervous system.
- Leptin Resistance and the Neuro-Adipose ConnectionPublication . Barateiro, Andreia; Mahú, Ines; Domingos, Ana I.Obesity is a public health concern affecting both genders at all ages around the world. The worldwide prevalence of obesity is rapidly increasing and has nearly doubled between 1980 and 2016. Consequently, it places a large financial burden on the economy due to the increased morbidity and mortality, as well as the reduced quality of life and development of chronic diseases. Obesity is typically characterized by excessive amounts of the hormone leptin, a cytokine-like molecule produced in white adipose tissue (WAT) that is secreted into the systemic circulation. The circulating levels of leptin are proportional to the amount of fat and function as the afferent signal in a negative feedback loop that seeks to maintain body fat in a very narrow range of variation. Leptin has a central role in body weight homeostasis due to its inhibition of food intake inhibition and stimulation of energy expenditure. The effect of leptin on body weight is attributed to its action in a specific brain region, the hypothalamus. Hence, leptin is released by adipocytes in proportion to the size of fat depots, enters the circulation, and reaches the central nervous system by crossing the blood-brain barrier (BBB) through receptor-mediated endocytosis in which it acts mainly through the arcuate nucleus of the hypothalamus to mediate most of its actions. Specifically, leptin modulates the activity of two types of neurons to inhibit appetite, through production of anorexigenic peptides by the pro-opiomelanocortin (POMC) neurons and suppression of the orexigenic agouti-related protein (AgRP) neurons. Besides acting on the hypothalamus to suppress appetite, leptin also induces lipolysis in WAT and thermogenesis in brown adipose tissue (BAT) and browning of WAT, via the activation of the sympathetic nervous system (SNS). However, in most obese subjects, despite its high serum levels, leptin fails to perform its physiological functions and consequently fails to reduce weight. This effect has been coined as leptin resistance.
- The reward value of sucrose in leptin-deficient obese micePublication . Domingos, Ana I.; Vaynshteyn, Jake; Sordillo, Aylesse; Friedman, Jeffrey M.Leptin-deficient patients report higher "liking" ratings for food, and leptin replacement therapy normalizes these ratings even before weight loss is achieved. Since animals cannot report their ratings, we studied the relationship between leptin and food reward in leptin-deficient ob/ob mice using a optogenetic assay that quantifies the reward value of sucrose. In this assay, mice chose between one sipper dispensing the artificial sweetener sucralose coupled to optogenetic activation of dopaminergic (DA) neurons, and another sipper dispensing sucrose. We found that the reward value of sucrose was high under a state of leptin deficiency, as well as at a dose of leptin that does not suppress food intake (12.5 ng/h). Treatment with higher doses of leptin decreased the reward value of sucrose before weight loss was achieved (100 ng/h), as seen in leptin-deficient patients. These results phenocopy in mice the behavior of leptin-deficient patients.