DFU is one of the most serious complications of diabetes. Up to a quarter of diabetic patients will develop DFU, and approximately 25% of the hospitalization time of diabetic patients is due to infection or ischemic DFU (17). At present, it is known that DFU is closely related to microvascular lesions, and type 2 diabetes can induce microvascular disease, resulting in endothelial cells that exhibit an imbalance between vasoconstrictor and dilator (18). However, there are few studies on the involvement of lymphatic vessels in diabetic skin changes. We compared the gene expression profiles of DLECs of type 2 diabetes patients to non-diabetic patients in this study, in order to reveal the gene expression differences of DLECs in diabetic skin. We considered EGFR as a potential biomarker which plays a key role in the development of DFU based on multiple database data and LASSO prediction model, and constructed a ceRNA network around EGFR. Furthermore, enrichment analysis implies that the HIF-1 signaling pathway probably plays a role in the pathogenesis of DFU.
Hypoxia is defined as the presence of a small amount of oxygen at the tissue level. Hypoxia is a characteristic condition during wound healing that is established immediately after skin injury due to vascular injury or collapse (19). Hypoxia-inducible factor-1 (HIF-1) is a protein that contains the HIF-1 and HIF-1 subunits and has been shown to have a function in controlling angiogenesis as well as wound healing after vascular damage (20). HIF-1 is a hypoxia-resistant transcription factor. HIF-1 is stable and accumulates in the nucleus under hypoxia conditions, where it binds to hypoxia response elements to trigger the activation of target genes (21). However, studies have shown that in the diabetic wound environment, the stability of HIF-1α under hypoxia will be seriously damaged, and the instability of HIF-1α is considered to be the main factor of diabetic wound nonunion (22). In this study, KEGG enrichment analysis showed that HIF-1 signaling pathway enrichment was the most significant. However, due to the low expression of genes involved in the regulatory pathway, including EGFR, ENO2, SLC2A1, IL6R and TFRC, in diabetic DLECs, the function of the HIF-1 signaling pathway was inhibited, resulting in delayed wound healing, which is consistent with the appeal conclusion. As a result, there are strong reasons to expect that understanding the molecular mechanism of HIF-1 signal down-regulation and the related low-expression genes would help to clarify novel predication and therapy options for DFU wound healing.
The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein that belongs to the ErbB tyrosine kinase receptor family, which has four members (23). EGFR is made up of three domains: (1) extracellular domain, which binds to the ligand that activates the receptor; (2) hydrophobic transmembrane region, which is involved in receptor dimerization; and (3) intracellular tyrosine kinase domain, which binds to a tyrosine residue on the phosphorylated substrate protein (24). EGFR plays a key role in cell growth, cell differentiation, tissue development, and function. It is an integration of extracellular growth and survival signals that converge and transform into intracellular output (25). Its function is related to a series of neurological metabolic disorders, including diabetes, Alzheimer 's disease and aging (25). The binding of EGFR to polypeptide growth factors can induce the interaction of homologous and heterologous dimers between family members (26). This initiates a series of downstream signaling pathways leading to cell growth, differentiation, adhesion, migration, cell survival (anti-apoptosis), drug and radiation sensitivity (26). In addition, enrichment analysis showed that EGFR has the function of binding to exogenous proteins. It is well known that proteins show excellent biological activity in promoting diabetic wound healing and skin regeneration (27). However, the results of this study showed low expression of EGFR in the DLECs of DFU. We considered that EGFR function cannot be fully manifested in patients with diabetes, which leads to the difficulty of healing ulcer wounds. In addition, we constructed a ceRNA network of lncRNAs. The results revealed that OLMALINC, KCNQ1OT1, HELLPAR, OIP5-AS1, and SNHG16 are likely to act as EGFR upstream regulators affecting the development of DFU. As a driver of ferroptosis, EGFR has been employed as a target for treatment in a variety of diseases(28, 29). The present study demonstrated that EGFR expression was lower in DFU patients than in healthy subjects, but this does not indicate that ferroptosis is inhibited in DFU, as disease development is caused by multifactorial and multifactorial regulation. Therefore, the specific mechanism of action played by EGFR as a target of ferroptosis in DFU needs to be further analyzed and explored.
However, there are limitations to this study. Firstly, the machine learning prediction model of LASSO in the external validation cohort affects the accuracy due to the small sample size, leading to misdiagnosis and missed diagnoses. Thus, the larger DFU sample size can improve the prediction accuracy. Secondly, EGFR as a ferroptosis-related biomarker for DLECs of DFU identified in this study that require further literature support and basic experimental validation.