AHO is the most common cause of osteomyelitis in children [11]. If not treated promptly, it can progress to chronic osteomyelitis, severely impacting the quality of life of affected children [12]. Therefore, timely diagnosis of AHO is crucial for managing the disease's progression. However, an early diagnostic method is still lacking in clinical practice. In this study, we analyzed datasets from the GEO database and identified 125 genes that were upregulated in AHO. GO analysis indicated that these genes are primarily involved in positive regulation of locomotion, defense response to bacteria, wound healing, secretory granule lumen, extracellular matrix, glycosaminoglycan binding, and endopeptidase activity. KEGG pathway analysis revealed significant enrichment in pathways related to focal adhesion and proteoglycans in cancer. These findings suggest that these genes actively participate in the inflammatory process and may be critical to the development of AHO. Additionally, 154 genes were identified as downregulated in AHO. GO analysis indicated that these genes are mainly involved in neuron projection morphogenesis, behavior, cell-cell junctions, the perinuclear region of the cytoplasm, signaling receptor activator activity, and purinergic nucleotide receptor activity. KEGG pathway analysis revealed significant enrichment in the PI3K-Akt signaling pathway and Calcium signaling pathway. These findings suggest that these genes are inhibited during inflammation and may play a crucial role in mitigating the progression of AHO.
To identify potential diagnostic biomarkers for AHO, we analyzed the aforementioned 279 DEGs using three machine learning algorithms and ultimately identified five key genes: LOC401525, VARS, CTNND1, MPO, and PRTN3. Among these, LOC401525, VARS, and CTNND1 were downregulated, while MPO and PRTN3 were upregulated. Currently, there are no literature reports on the function of LOC401525. VARS is a valyl-tRNA synthetase, primarily responsible for attaching valine to tRNA during protein synthesis [13]. Current research suggests that VARS is mainly associated with hereditary neurological diseases [14]. The CTNND1 gene encodes a protein called p120-catenin, which is a key component of adherens junctions [15]. These structures play a crucial role in maintaining cell-cell adhesion and tissue structural integrity [16]. In this study, we hypothesize that Staphylococcus aureus infections typically invade and spread by disrupting the adhesive structures of host cells. In the context of osteomyelitis, CTNND1 may play a role in maintaining cellular structure and resisting the spread of infection. If CTNND1 function is impaired or its expression is reduced, it may lead to weakened cell-cell adhesion, thereby facilitating the propagation and spread of Staphylococcus aureus infection.
Using machine learning algorithms, we identified LOC401525, VARS, and CTNND1 as downregulated genes in AHO samples. However, cohort studies using sequencing data revealed that LOC401525 had a p-value greater than 0.05, indicating no statistically significant difference. ROC analysis of the data for VARS and CTNND1 showed AUC values of 0.7614 and 0.8106, respectively. Given the current literature on VARS and the observation that the AUC curve for VARS was significantly lower than that of the other three genes during ROC analysis, further testing of VARS was not pursued in subsequent human experiments. Based on related research and our experimental studies, we believe that CTNND1 is a potential diagnostic biomarker for AHO.
MPO is a heme-containing enzyme primarily produced by neutrophils and monocytes, playing a critical role in immune responses and inflammation [17]. It is predominantly located in the lysosomes of these cells. During an inflammatory response, neutrophils generate hydrogen peroxide through a respiratory burst, and MPO utilizes this hydrogen peroxide to react with chloride ions, producing hypochlorous acid. Hypochlorous acid is a potent oxidant capable of killing a wide range of pathogens, including bacteria, fungi, and viruses [17–18]. However, the hypochlorous acid and other oxidative products generated by MPO not only exert bactericidal effects but also have the potential to damage host cells and tissues [19]. Current research indicates that MPO contributes to the pathogenesis of osteomyelitis not only through its antimicrobial activity but also by exacerbating local inflammatory responses via the production of oxidative products. These oxidative products can induce oxidative stress, leading to tissue damage, further intensifying inflammation, and consequently delaying the healing of bone tissue [20–21]. In chronic osteomyelitis, sustained MPO activity may result in a prolonged inflammatory state, hindering bone tissue repair, and ultimately leading to persistent tissue destruction and functional loss. Additionally, elevated MPO levels in osteomyelitis patients have been found to correlate with disease severity [22]. PRTN3 is a serine protease primarily located in the granules of neutrophils. In the antibacterial defense mechanism of neutrophils, PRTN3 plays a crucial role by cleaving microbial proteins and directly killing pathogens [23]. Moreover, PRTN3 can activate other antimicrobial molecules, further enhancing the bactericidal capacity of neutrophils [24]. Additionally, PRTN3 is capable of cleaving and modulating various cytokines and chemokines, thus influencing the intensity and duration of the inflammatory response [24]. However, overexpression of PRTN3 may disrupt the bone matrix and soft tissues, impeding bone tissue repair and reconstruction, thereby delaying the recovery process [25]. In this study, we observed significant differences in the expression levels of PRTN3 and MPO between AHO samples and normal samples. ROC analysis further validated their robust ability to distinguish AHO samples from normal samples. Importantly, in our cohort, we confirmed that the expression levels of PRTN3 and MPO were significantly upregulated in AHO samples. Our study also reveals that MPO and PRTN3 are positively correlated with the severity of AHO, and their levels show a decreasing trend after treatment. This suggests that MPO and PRTN3 can serve as indicators for evaluating the effectiveness of AHO treatment. Additionally, current literature suggests that a sustained inflammatory response involving MPO and PRTN3 may contribute to the transition from acute to chronic osteomyelitis. Further experiments could be conducted to explore the mechanisms of chronic osteomyelitis formation by regulating MPO and PRTN3.
In conclusion, this study found that the expression levels of MPO, PRTN3, and CTNND1 play important roles in the serum of children with AHO. According to the Cierny-Mader staging system for osteomyelitis, PRTN3 and CTNND1 were positively correlated with the severity of the disease, while CTNND1 was negatively correlated. Therefore, MPO, PRTN3, and CTNND1 may serve as potential biomarkers for predicting S. aureus-induced acute osteomyelitis in children.