OXPHOS remodeling in high-grade prostate cancer involves mtDNA mutations and a prognostic gene expression signature

Rewiring of energy metabolism and adaptation of mitochondrial respiratory functions are considered to impact on prostate cancer development and progression. High-resolution respirometry of paired benign and malignant human prostate tissue samples revealed reduced respiratory capacities with NADH-pathway substrates glutamate and malate in malignant tissue and a significant metabolic shift towards respiratory capacity with succinate, particularly in high-grade tumors. The load of potentially deleterious mitochondrial-DNA mutations was higher in tumor tissue and associated with unfavorable risk factors. High levels of potentially deleterious mutations in mitochondrial Complex I-encoding genes were associated with a 70% reduction in NADH-pathway capacity and compensation by increased S-pathway capacity. Structural analyses of these mutations revealed amino acid alterations leading to potentially deleterious effects on Complex I, supporting a causal relationship. RNA-seq revealed a signature of metabolic enzymes corresponding to the altered mitochondrial respiratory pathways and enabled extraction of a metagene set for prediction of shorter disease-free survival. Fig. 1. Sample workflow and histological staining. A. From each of 50 radical prostatectomy specimens a tumor and a non-malignant benign tissue punch needle biopsy was extracted by an experienced uropathologist from contralateral sites of the specimens. While a small portion of the extracted tissue cores (blue area) was fixed and used for histological stainings (pink arrow) and confirmation of tissue identity, the rest was used immediately for high-resolution respirometry (HRR, blue arrow), subsequent NGS mtDNA profiling (orange arrow) and mtDNA copy number determination (grey arrow). From 16 cases of this cohort, frozen tissue samples directly adjacent to the biopsy cores (green area) were isolated by macrodissection followed by RNA extraction for gene expression profiling via total RNA-NGS (green arrow). B. Hematoxylin and eosin staining (H&E), p63 (non-malignant tissue marker, brown) and AMACR (malignant cell marker, red) double-immunostaining (p63/AMACR) of fixed and paraffin embedded benign and cancerous prostate tissue samples extracted for HRR.