Periodic Reporting for period 2 - PROTEOFIT (Adapting protein fate for muscle function and fitness)
Période du rapport: 2021-06-01 au 2022-11-30
More than half of the European population is overweight. Obesity is a growing health problem, as it increases the risk for diabetes, cardiovascular disease, and cancer. Muscle function is essential for motion, exercise, and shivering, whereas physical inactivity is causally related to reduced metabolic fitness in animal models and humans. A critical requirement for muscle function is that proteins are properly produced and, if necessary, degraded to adapt the proteome to meet metabolic demands. However, there is a fundamental, open gap in understanding how challenges to muscle proteostasis are sensed and how protein fate is subsequently adapted to enhance muscle function in exercise or, conversely, how it is compromised in obesity. The hypothesis of this project is that protein fate is highly adaptive and can be fine-tuned to promote proteostasis, the integrity of muscle cells, and metabolic health. Identifying novel key regulators of these mechanisms in muscle may hold great therapeutic promise for targeting metabolic fitness to combat obesity and associated disorders. In this innovative project I want to define new mechanisms of muscle adaptation in humans and preclinical mouse models, with the ultimate goal of using this knowledge to improve muscle function and fitness in obesity. This novel work will provide a transformative molecular understanding of muscle adaption to metabolic challenges and provide insight into how this translates into metabolic fitness and the development of obesity and associated disorders in humans.
We set out to understand remodeling of the proteome in muscle by developing a mass spectromy-based approach to study ubiquitin-modified proteins. Ubiquitination of proteins either represents their targeting for degradation by the proteasome or signaling properties. As ubiquitin levels are a steady state measures, we also performed dynamic measurements of proteasome activity by state-of-art biochemical assays. We found that in obesity, proteins targeted for degradation accumulate and this is likely caused by increased protein damage, as proteasome function was enhanced concomitantly. Next, we studied the impact of the transcription factor Nfe2l1, which is a master transcription factor for the regulation of proteasome function. Interestingly, Nfe2l1 was required for proper regulation of ubiquitin levels, and this led to a resistance to high-fat diet-induced obesity and impaired aerobic exercise capacity. Loss of Nfe2l1 was associated with complex, hypoxia-induced immunometabolic activation of muscle.
It was unknown if the proteome in muscle can be adapted in a beneficial way to help skeletal myocytes withstand obesity-induced metabolic dysfunction. First, our work shows that there are specific alterations in ubiquitin profiles that may serve as novel biomarkers of obesity- or ageing induced muscle function. Second, we have established Nfe2l1 as a critical regulator of muscle function linked to obesity and exercise capacity. Our next steps include identify serum biomarkers, hormones and metabolites, that are linked to beneficial proteome remodeling and delineate specific ubiquitin sites that are critical for Nfe2l1-mediated action.