Molecular subtypes of human skeletal muscle in cancer cachexia

Cancer-associated muscle wasting is associated with poor clinical outcomes¹, but its underlying biology is largely uncharted in humans². Unbiased analysis of the RNAome (coding and non-coding RNAs) with unsupervised clustering using integrative non-negative matrix factorization³ provides a means of identifying distinct molecular subtypes and was applied here to muscle of patients with colorectal or pancreatic cancer. Rectus abdominis biopsies from 84 patients were profiled using high-throughput next-generation sequencing. Integrative non-negative matrix factorization with stringent quality metrics for clustering identified two highly coherent molecular subtypes within muscle of patients with cancer. Patients with subtype 1 (versus subtype 2) showed clinical manifestations of cachexia: high-grade weight loss, low muscle mass, atrophy of type IIA and type IIX muscle fibres, and reduced survival. On the basis of differential expression between the subtypes, we identified biological processes that may contribute to cancer-associated loss of muscle mass and function, including altered posttranscriptional regulation and perturbation of neuronal systems; cytokine storm and cellular immune response; pathways related to extracellular matrix; and metabolic abnormalities spanning xenobiotic metabolism, haemostasis, signal transduction, embryonic and/or pluripotent stem cells, and amino acid metabolism. Differential expression between subtypes indicated the involvement of multiple intertwined higher-order gene regulatory networks, suggesting that network interactions of (hub) long non-coding RNAs, microRNAs and mRNAs could represent targets for future research.