Skeletal muscle atrophy is a debilitating response to systemic diseases, including diabetes, cancer, and chronic kidney disease (CKD). Under these conditions, muscle protein loss occurs, which contributes substantially to morbidity and mortality. Therefore, maintenance of skeletal muscle function is one of the top health priorities reported by patients living with catabolic diseases. Although significant progress has been made in this area during recent decades, the signaling pathways that regulate muscle proteolysis and the development of therapeutic strategies treating muscle atrophy are still being investigated. We plan to identify the CRL4ACRBN ubiquitin E3 ligase as a novel catabolic mediator promoting muscle protein degradation. Our Preliminary Results demonstrate that the CRL4ACRBN E3 ligase was activated in muscle of CKD mice. Disruption of CRL4ACRBN specifically in muscle significantly inhibits CKD-induced muscle atrophy. This beneficial response was associated with suppressed atrogenes expression and reduced oxidative stress. Using the tandem-affinity purification of ubiquitinated proteins following quantitative mass spectrometry analysis, we identified two proteins, ovarian tumor (OTU) deubiquitinase 7B (OTUD7B) and peroxiredoxin-5 (PRDX5), that represent potential targets of the CRL4ACRBN E3 ligase. OTUD7B is a deubiquitinating enzyme that is involved in the regulation of mechanistic target of rapamycin complex 2 (mTORC2) and PRDX5 reportedly suppresses mitochondrial-associated oxidative stress. In cultured human skeletal muscle cells, pomalidomide, a CRL4ACRBN inhibitor, blocked cytokines-induced decline in OTUD7B and PRDX5 and this response was associated with impeded atrogenes expression and proteolysis. Thus, we hypothesize that the activation of CRL4ACRBN accelerates the degradation of OTUD7B and PRDX5, resulting in suppression of anabolic signaling and enhanced oxidative stress. Conversely, the genomic or pharmacological inhibition of CRL4ACRBN should improve anabolic signaling and prevent oxidative stress, consequently, limiting the development of muscle atrophy under catabolic conditions. To test our hypothesis, we plan to use human skeletal muscle cells and a humanized mouse model to pursue three Specific Aims:
Specific Aim 1 : To identify how the CRL4ACRBN E3 ligase is activated during catabolic states.
Specific Aim 2 : To identify the mechanisms by which the disruption of CRL4ACRBN E3 ligase can prevent muscle atrophy.
Specific Aim 3 : To determine whether the pharmacologic inhibition of CRL4ACRBN E3 ligase can reverse muscle atrophy under catabolic conditions. The results of these studies could identify novel pathways involved in the pathogenesis of muscle atrophy and provide a feasible therapeutic strategy to combat muscle atrophy.
Skeletal muscle atrophy is a dread complication of chronic diseases because it increases morbidity and mortality. We have preliminary evidence that CRL4ACRBN E3 ubiquitin ligase promotes muscle atrophy. Genetic or pharmacologic inhibition of this E3 ligase could prevent muscle atrophy in chronic diseases.
