Protein Nutrition in Experimental Uremia

Project Abstract Protein-Energy Wasting (PEW) is a prevalent complication in chronic kidney disease (CKD), leading to muscle wasting and significantly contributing to morbidity and mortality. Maintaining skeletal muscle homeostasis and function is essential for CKD patient care. However, the precise mechanisms causing muscle wasting and the development of effective therapeutic strategies remain under investigation. We aim to pinpoint the CRL4ACRBN ubiquitin E3 ligase as a novel catabolic mediator responsible for muscle protein loss in CKD. Our initial findings indicate that the CRL4ACRBN E3 ligase is activated in CKD mouse muscles. Targeted disruption of this ligase in muscles effectively counters CKD-induced muscle wasting. Using tandem-affinity purification of ubiquitinated proteins combined with quantitative mass spectrometry, we identified two potential CRL4ACRBN E3 ligase targets: ovarian tumor deubiquitinase 7B (OTUD7B) and peroxiredoxin-5 (PRDX5). OTUD7B is an enzyme that inhibits TRAF7-induced NF-kB signaling, while PRDX5 is recognized for its protective role against mitochondrial-associated oxidative stress. In human skeletal muscle cell cultures, we noted that pomalidomide, a CRL4ACRBN E3 ligase inhibitor, counters cytokine-induced reductions in OTUD7B and PRDX5. This intervention results in the suppression of atrogene expression, proteolysis, and oxidative stress. From these observations, we hypothesize that activating CRL4ACRBN E3 ligase hastens the degradation of OTUD7B and PRDX5, amplifying atrogene expression and oxidative stress. Conversely, inhibiting this E3 ligase should deter catabolic signaling and combat oxidative stress, thereby curbing the onset of muscle wasting in CKD. In this proposal, we plan to employ multi- omics methods, transgenic models, and a humanized mouse model to address three pivotal questions: How does CKD activate the CRL4ACRBN E3 ligase in muscles? Through what mechanisms does it exacerbate muscle wasting? Can the FDA-approved drug, pomalidomide, reverse CKD-induced muscle wasting? Our research could unveil novel pathways implicated in muscle wasting and showcase the promise of drug repurposing as a cost-effective and efficient means for devising viable therapeutic strategies.