Arachidonic acid triggers spermidine synthase secretion from primary tumor to induce skeletal muscle weakness upon irradiation

Radiotherapy (RT) reduces the risk of cancer recurrence and death, while accompanied by multiple side effects including muscle weakness, seriously affects the life quality of patients. However, the underlying mechanism is not well defined. Here, we identify cancer cells secrete more spermidine synthase (SRM) protein through small extracellular vesicles (sEVs) to trigger skeletal muscle weakness upon RT. Mechanistically, RT-triggered arachidonic acid (ArA) accumulation elevates the ISGylation of SRM protein, facilitating SRM package into EVs from primary tumor. Circulating SRM proteins enhance spermidine accumulation in skeletal muscle and type I collagen fibers biosynthesis in an eIF5A-dependent manner. Deposition of randomly aligned collogen fibers induced by SRM+ EVs results in skeletal muscle fibrosis and weakness, as well as bone matrix loss. However, losartan treatment blocks the ISGylation of SRM and its subsequent secretion. Collectively, our findings determine that ArA functions in concert for circulating SRM secretion upon RT, which aggravates skeletal muscle fibrosis through rewiring polyamine metabolism, shedding light on the alleviation of RT-mediated muscle weakness when combined with losartan treatment. Comparative gene expression profiling analysis of RNA-seq data for ArA-treated and non-treated MDA-MB-231 cells