NRF2 signalling in cancer-associated adipose tissue supports Warburg effect and early metabolic integration in breast cancer

Abstract

Objective: Metabolic crosstalk between breast cancer cells and cancer-associated adipose tissue (CAAT), the major component of their tumour microenvironment (TME), is prerequisite for malignant phenotype. Nuclear factor erythroid 2-related factor 2 (NRF2) is a key factor in redox–metabolic interplay; however, its role in TME during breast tumourigenesis, particularly regarding the Warburg effect, remains unexplored. Methods: Using an orthotopic breast cancer model in wild-type (WT) and Nrf2 knockout (Nrf2KO) mice, we examined how Nrf2^-/- CAAT as a major TME constituent influences tumour glycolysis and lactate-centred communication with CAAT during early breast tumour growth (∼10, 50, and 200 mg tumours). Results: Key glycolytic regulators, PFKFB3, PFK-1, HIF-1α, and pAMPKα, increased with tumour growth in breast tumours. However, 10 mg tumours from Nrf2KO mice exhibited reduced levels of these proteins and lower insulin levels compared to WT counterparts, indicating altered tumour glycolysis regulation in Nrf2KO mice. Whilst key mediators of lactate metabolism and pH homoeostasis, MCT4 and CAIX, showed tumour growth-dependent increases in WT mice, 10 mg tumours from Nrf2KO mice displayed increased LDHA, LDHB, and MCT4 protein levels. WT CAAT characterised declining glycolytic and lactate metabolic enzymes with tumour growth, exhibiting reverse Warburg effect. Strikingly, Nrf2KO CAAT displayed elevated PFKFB3, HIF-1α, LDHB, and MCT4 levels and reduced LDHA levels compared to WT CAAT in the 10 mg tumour growth phase. Conclusion: These findings identify NRF2 in CAAT as a critical regulator of early metabolic reprogramming in breast cancer; early targeting of tumour glucose and/or lactate metabolism through NRF2 signalling within TME may hold high therapeutic potential for breast cancer.