Periodic Reporting for period 2 - Yoyo-LepReSens (Weight Maintenance by AgRP neurons)
Reporting period: 2023-03-01 to 2024-08-31
Obesity and its comorbid sequelae are major health burdens across European nations. Many citizens would greatly benefit from permanent weight loss, but only a few succeed. They rather suffer from weight regain after dieting, often referred to as Yoyo dieting effect. This effect is largely driven by specific areas in our brain that developed over millions of years when food scarcity was a major threat to life. Today, in our highly obesogenic environment with a sedentary lifestyle and overabundance of high calorie food, these brain areas are programmed to drive obesity and/or weight regain in individuals with a history of obesity, and are thus at the centre of my grant proposal.
In the past, my lab explored the potential for therapeutic anti-obesity strategies built upon leptin action in the brain. Leptin is a satiety hormone produced by our fat tissue. The more fat we accumulate, the more leptin is secreted into circulation. Leptin then enters the brain and activates satiety in specific subpopulations of neurons that decrease our food intake and ultimately fat storage and body weight. In lean individuals, leptin is thereby a major contributor to appetite control and weight maintenance. In overweight and obese individuals, that weight regulatory function of leptin is lost due to a phenomenon called leptin resistance. In the grant proposal, we aim to delineate the molecular basis for that failure of leptin to decrease food intake and body weight. Specifically, we employ mouse models of obesity and weight loss and modern techniques to isolate specific subpopulations of neurons, and characterize how leptin, and small plant-derived molecules such as the leptin sensitizer celastrol, affect signalling pathways and transcriptional programs in these major areas of weight control. In the same brain areas and their respective neuronal subpopulations, we moreover aim to explore whether an epigenetic memory for obesity exists. Specifically, we aim to test whether diet induced obesity in mice can encode an epigenetic program in neurons that ultimately drives weight regain after dieting to reach the weight and fat mass the mouse once had. In sum, delineating the largely unexplored, brain-driven molecular events that impede sustainable weight loss and drive the Yoyo effect is a prerequisite for future therapies, and a major goal of my proposal.
In the past, my lab explored the potential for therapeutic anti-obesity strategies built upon leptin action in the brain. Leptin is a satiety hormone produced by our fat tissue. The more fat we accumulate, the more leptin is secreted into circulation. Leptin then enters the brain and activates satiety in specific subpopulations of neurons that decrease our food intake and ultimately fat storage and body weight. In lean individuals, leptin is thereby a major contributor to appetite control and weight maintenance. In overweight and obese individuals, that weight regulatory function of leptin is lost due to a phenomenon called leptin resistance. In the grant proposal, we aim to delineate the molecular basis for that failure of leptin to decrease food intake and body weight. Specifically, we employ mouse models of obesity and weight loss and modern techniques to isolate specific subpopulations of neurons, and characterize how leptin, and small plant-derived molecules such as the leptin sensitizer celastrol, affect signalling pathways and transcriptional programs in these major areas of weight control. In the same brain areas and their respective neuronal subpopulations, we moreover aim to explore whether an epigenetic memory for obesity exists. Specifically, we aim to test whether diet induced obesity in mice can encode an epigenetic program in neurons that ultimately drives weight regain after dieting to reach the weight and fat mass the mouse once had. In sum, delineating the largely unexplored, brain-driven molecular events that impede sustainable weight loss and drive the Yoyo effect is a prerequisite for future therapies, and a major goal of my proposal.
After installation and training of a competent team of scientists to our established methods, protocols and (murine) models, we were able to approach the two major objectives of our project on multiple levels and in parallel. We conducted several crucial animal experiments and first ex vivo as well as in vitro tests. Murine studies and the subsequent RNA sequencing have been performed for several subaims. First results of our single nucleus sequencing on leptin and celastrol action in hypothalamic subpopulations of leptin receptor harboring cells were presented, e.g. at the ECE congress 2023 in Istanbul or the FENS meeting in Vienna, 2024. Likewise, we identified first gene targets that were subjected to Crispr-Cas9 gene editing of murine hypothalamic cells, folloed by extensive screening of protein and gene expression signatures. Last, we have performed first RNAseq analyses of post-mortem human infundibular nuclus samples of lean, obese and type 2 diabetic subjects to assess the clinical relevance of our murine studies. At current, implementation of all objectives and tasks appears feasible and not in danger, profound roadblocks and obstacles have so far not been identified.
In the course of period 1, we have conducted several experiments in mice chronically exposed to chow or high-fat diet, subjected to leptin or leptin sensitizers, or to weight loss paradigms such as calorie restriction or vertical sleeve gastrectomy surgery. RNAseq analyses have been employed for most studies, focusing on AgRP neurons as sole neuronal subpopulation. In parallel, we conducted single nucleus sequencing to widen our approach to additional subpopulations of cells for our leptin and celastrol treatment experiments. snRNAseq analyses were superior in terms of data tightness and richness over our “bulk” RNAseq analyses. This led us to solely employ single nucleus sequencing to allow a broader view on cellular events. In that context, we could identify new subpopulations of neurons that communicate with AgRP neurons. These hitherto unknown interactions with novel subpopulations of hypothalamic leptin-responsive cells, plus the identification of new, potentially targetable genes regulated by leptin and celastrol, will propel our understanding of leptin resistance, and may be the basis for new therapeutic intervention strategies built upon leptin resensitization.