Osteosarcoma (OS) is the most common type of bone malignancy, originating from mesenchymal cells and characterized by the production of bone-like tissue or bone tissue by the tumor cells. And osteosarcoma is commonly found in the long bones of the limbs, particularly the epiphysis, and is characterized by strong localized aggressiveness and early haematogenous metastasis. In recent years, significant advances have been made in the diagnosis and treatment of osteosarcoma, including neoadjuvant chemotherapy and improvements in surgical techniques. Although early detection and timely treatment have largely improved the survival rate of the disease, osteosarcoma currently remains a high mortality rate among malignancies in children and adolescents. Therefore, it is necessary to search for markers with high predictive value for patient prognosis during OS development, so that more precise treatment can be implemented. There is no doubt that this has important implications for patients and clinicians alike.
With advances in computer technology and molecular biology, a new interdisciplinary discipline, bioinformatics, has emerged. The analytical tools of bioinformatics can identify those that are meaningful from the vast amount of biological data. The advent of bioinformatics has transformed disease research, with advanced methods and tools used to explore the mechanisms involved in the onset and progression of disease, which also includes various tumors. At the same time, the application of high-throughput sequencing technologies has enabled a comprehensive molecular characterization of tumors, both temporally and spatially. In 2019, Yizhe Xi et al. conducted a study in which they analyzed several hundred circ RNAs that were differentially expressed between osteosarcoma and paraneoplastic tissues and analyzed their potential functions[18]. Kun-Peng Zhu et al.'s study combined bioinformatics analysis and experimentation to construct an RNA regulatory network and explore the underlying mechanisms of OS chemoresistance[19]。In addition to this, there is a large body of literature that has examined OS using bioinformatics and has found valuable information. However, there is no literature that correlates the possible reasons for the poor prognosis of OS patients. Therefore, in the present study, the potential causes of low survival in OS patients were focused on. We grouped patients according to their survival status and conducted a series of studies.
In our study, we identified several hundred genes that were differentially expressed between the survival and death groups and defined these genes as death-related genes (DRGs). Then a functional analysis of these genes was performed. KEGG enrichment analysis revealed a pathway related to intercellular signaling. We therefore hypothesize that the OS cell-to-cell signaling was more active in the dead group, and that the OS tissue was more "active" and more prone to metastasis and invasion, resulting in a lower survival rate.
Our main concern was how to predict the prognosis of patients more accurately. The fourteen-DGRs signature obtained after a series of analyses helped us to solve this problem to some extent, and both the KM survival curve and the ROC curve showed the high value of the signature. We have analyzed the two key genes obtained and established a regulatory network. Both CSAG1 and MAGEA12 are related to cancer/testis antigen family. There are several studies have been reported on the role of two key genes in a variety of human tumors. MAGEA12 has been shown to act as a prognostic-related gene in gastric cancer[20]. In addition, overexpression of MAGEA12 is involved in the pathogenesis of human cutaneous squamous cell carcinoma and can also promote invasion of breast cancer cells[21, 22]. The study by Chuzhao Lin et al. reported that cancer/testis antigen CSAGE was concurrently expressed with MAGE in chondrosarcoma[23]. In our study, both CSAG1 and MAGEA12 were positively associated with T cells CD8 (Fig. 6E, H). And the percentage of T cells CD8 was higher in the death group than in the survival group (P < 0.05). These results suggest that MAGEA12 and CSAG1 may act through some mechanism on T cell CD8 to promote the progression of osteosarcoma, which is the direction of our future research.
In addition, we also noted that of the fourteen DGRs that comprised the signature, only TAC4 expression was relatively low in the death group (log2FC = -1.629). This gene is a member of the tachykinin family of neurotransmitter-encoding genes. And the products of this gene preferentially activate tachykinin receptor 1, and are thought to regulate peripheral endocrine and paracrine functions including blood pressure, the immune system, and endocrine gland secretion[24–26]. Unfortunately, no studies have reported a relationship between TAC4 and human tumors. We believe that the relationship between TAC4 and tumors is of interest to explore.
The interaction between immune function and tumor has received increasing attention in recent years and a large number of studies have been reported in the literature. Immunotherapy has a long history in osteosarcoma, with inactivated bacteria being used to treat osteosarcoma for over 100 years, but with controversial results[27]. Mifamurtide, as an immune adjuvant, has been at the forefront of osteosarcoma treatment, but there is a lack of large-scale clinical trials to demonstrate its efficacy and safety, so Maya Kansara et al. suggest that the understanding of the relationship between bone tumors and immune function is still in its infancy[1]. Our GO enrichment data show that DRGs are focused on a number of immune-related pathways. Our analysis of the immune cell composition of OS revealed that Macrophanges M0, Macrophanges M2, and T cells CD4 memory resting were the three most predominant. When comparing the two groups of OS samples, the proportion of T cells CD8 was significantly higher in the death group than in the survival group (P < 0.05). There is no doubt that CD8+ T cells are important for their protective immune role against pathogens and tumors. In the case of chronic infections or tumors, the "load" on the immune system is significantly increased. Excessive antigenic and/or inflammatory signals continue to act on CD8+ T cells and this leads to a progressive deterioration of T cell function, T cell depletion in RE and ultimately to hypo- and even loss of immune function. Therefore, we believe that the reason for the low survival rate in OS patients is most likely related to the reduced function of the immune system.
As with the immune system, the tumor microenvironment has been one of the focal points of research in recent years. Osteosarcoma grows in a complex and specific bone microenvironment composed of a wide range of cells. Of these cells that make up the microenvironment, stromal cells and immune cells have received the most attention. Notably, the "Mr. Tumor" will adapt the local microenvironment to its own heterogeneity in a way that suits it. We therefore scored stromal cells and immune cells separately and derived an estimatescore based on these two scores. As shown in the figure, patients with higher scores had significantly higher overall survival (P < 0.05). We believe that the scores we obtained are useful as a guide to clinical decision-making, although the process of performing the scoring is more complex.
However, there are some limitations to this study. Firstly, the number of cases we obtained was not sufficiently large and a larger sample is needed to validate the efficacy of the fourteen-DGR signature. In addition, the mechanism by which key genes affect patient’s survival needs to be further explored.