Inhibiting 5-lipoxygenase prevents skeletal muscle atrophy by targeting organogenesis signaling and insulin-like growth factor-1

Background Skeletal muscle atrophy can occur in response to numerous factors, such as aging and certain medications, and produces a major socioeconomic burden. At present, there are no approved drugs for treating skeletal muscle atrophy. Arachidonate 5-lipoxygenase (Aox5) is a drug target for a number of diseases. However, pharmacological targeting of Alox5, and its role in skeletal muscle atrophy, is unclear.

Methods The potential effects of gene knockdown and pharmacological targeting of Alox5 on skeletal muscle atrophy was investigated using cell-based models, animal models, and human skeletal muscle tissue cultures. Malotilate, a clinically safe drug developed for enhancing liver regeneration and Alox5 inhibitor, was investigated as a repurposing candidate. Mechanism(s) of action in skeletal muscle atrophy were assessed by measuring the expression level or activation status of key regulatory pathways, and validated using gene knockdown and RNA sequencing.

Results Myotubes treated with the atrophy-inducing glucocorticoid, dexamethasone, were protected from catabolic responses by treatment with malotilate (+41.29%, P < 0.01). Similar anti-atrophy effects were achieved by gene knockdown of Alox5 (+30.4%, P < 0.05). Malotilate produced anti-atrophy effects without affecting the myogenic differentiation program. In an in vivo model of skeletal muscle atrophy, malotilate treatment enhanced muscle performance (Grip strength: +35.72%, Latency to fall: +553.1%, P < 0.05), increased mass and fiber cross sectional area (Quadriceps: +23.72%, Soleus: +33.3%, P < 0.01), and down-regulated atrogene expression (Atrogin-1: -61.58%, Murf-1: -66.06%, P < 0.01). Similar, beneficial effects of malotilate treatment were observed in an aging muscle, which also showed the preservation of fast twitch fibers (Type 2a: +56.48%, Type 2b: +37.32%, P < 0.01). Leukotrine B4, a product of Alox5 activity with inflammatory and catabolic functions, was found to be elevated in skeletal muscle undergoing atrophy (Quadriceps: +224.4%, P < 0.001). Cellular transcriptome analysis showed that targeting Alox5 upregulated biological processes regulating organogenesis and increased the expression of insulin-like growth factor-1, a key anti-atrophy hormone (+226.5%, P < 0.05). Interestingly, these effects were restricted to the atrophy condition and not observed in normal skeletal muscle cultures with Alox5 inhibition. Human skeletal muscle tissue was also protected from atrophy by pharmacological targeting of Alox5 (+23.68%, P < 0.05).

Conclusion These results shed new light on novel drug targets and mechanisms underpinning skeletal muscle atrophy. Alox5 is a regulator and drug target for muscle atrophy, and malotilate is an attractive compound for repurposing studies to treat this disease.