Metabolic alteration in the tumor microenvironment played a vital role in carcinogenesis, progression, and therapeutic resistance of many cancers, especially BC. Previous studies had demonstrated that the alteration of glutamine and glycolytic levels in BC cells could promote the progression of BC [6, 13]. Considering the importance of the metabolic environment in cancer development, it is crucial to identify metabolic-related prognostic biomarkers for BC. In the present study, we identify 23 MAGs, which were differentially expressed in both mRNA and protein levels. GO and KEGG analyses showed that these MAGs were associated with multiple metabolic pathways. In addition, five differentially expressed MAGs (PLOD1, CKB, PYGB, AKR1B1, PDE5A) were finally used to construct a prognostic signature and survival analysis indicated that high MAGs risk scores were significantly related to the poor OS, DSS, and PFI of BC patients. Subsequently, Cox regression analyses indicated that the MAGs signature was an independent prognostic factor for BC patients and closely related to stage, grade, T, and M. Nomograms have been used to predict the prognosis of patients by incorporating a variety of significant prognostic factors. We established a prognostic nomogram with clinical factors and the MAGs based signature risk score, which can superiorly predict the OS of BC patients. RT-PCR showed that the expression of four MAGs was elevated in T24 cells and M2 TAMs can promote the expression of PLOD1, CKB, and PYGB in T24 cells by secreting TGF-β1. M2 TAM was associated with the progression of tumors and TGF-β1 was closely related to the proliferation, invasion and metastasis of tumors. Therefore, M2 TAMs may influence the metabolic reprogramming in BC by secreting TGF-β1 to promote the recurrence and progression of BC.
Among these MAGs, PLOD1 encodes lysyl hydroxylases, which are crucial for collagen biosynthesis, cross-linking, and deposition and can promote cancer progression and metastasis . Yamada Y et al. revealed that overexpression of PLOD1 was closely related to poor survival and downregulation of PLOD1 can decrease the progression of BC . CKB was participated in metabolic processes involving glycolysis and could serve as a biomarker for predicting tumor progression . However, the precise role of CKB in the occurrence and progression of BC has not been well studied. PYGB is an enzyme that metabolizes glycogen and can influence the growth and apoptosis of the cancer cell by regulating the NF‑κB/Nrf2 signaling pathway . In addition, PYGB was associated with the poor prognosis of cancer and can promote the proliferation and invasion of cancer cells by activating Wnt/β-catenin signaling [18–19]. AKR1B1, a member of the aldo/keto reductase superfamily, was associated with the poor survival outcomes of cancer and can promote the occurrence and metastasis of cancer by activating epithelial-mesenchymal transition . PDE5A was overexpressed in various tumors and inhibition of PDE5A can induce apoptosis and attenuate β-catenin-mediated transcription in breast cancer cells [21–23].
Although some of these MAGs have previously been confirmed as prognostic markers for BC, in this study five MAGs, which were identified closely associated with the survival outcomes of BC by bioinformatics methods, were integrated into a MAGs based signature. All these MAGs have participated in the process of metabolic signaling pathways, such as amino acid metabolism, glucose metabolism, and lipid metabolism. Therefore, we suggested that the MAGs based signature can also reflect the metabolic status of patients with BC. However, several limitations should be considered in our research. Firstly, this is a retrospective study. Therefore, we could not obtain complete information, which may lead to bias. Secondly, more samples need to be further confirmed before clinical application and further experimental studies are needed to investigate the potential molecular mechanisms of these MAGs in BC.
In conclusion, our study identified 23 differentially expressed MAGs and established a MAGs based signature, which can be used as an independent signature in evaluating the prognosis of patients with BC. Furthermore, M2 TAMs may promote the expression of PLOD1, CKB, and PYGB via the TGF-β1 signaling pathway. Further clinical trials and experimental exploration are needed to validate our observations in BC.