Dysfunctional iron metabolism in pressure injuries is related to aberrant CD163 and Homx-1 signal transduction

Dysregulation of iron metabolism has been associated with impaired chronic wound healing. However, changes in iron metabolism have yet to be reported in pressure injuries, a type of chronic wound. In this study, we aimed to investigate changes in iron metabolism and associated regulatory mechanisms in pressure injuries. We collected tissue biopsies and data from 20 consenting stage IV-pressure injuries patients and 5 non-pressure injuries patients hospitalised at the Affiliated Hospital of Qingdao University between March 2021 and June 2021. In addition, we measured the iron content by inductively coupled plasma mass spectrometry and Prussian blue staining in deep tissue pressure injury mouse models. An Enzyme-linked immune sorbent assay measured the expression of ferritin, ferroportin-1 and transferrin. Immunofluorescence staining, high-throughput transcriptome sequencing, Western blot and RT-qPCR further analysed the fundamental mechanisms regulating iron metabolism. In this study, we observed numerous inflammatory cells infiltrating the marginal tissues of stage IV pressure injury patients and in deep tissue pressure injury models. The expression levels of pro-inflammatory factors, such as inducible nitric oxide synthase and interleukin-6, were significantly increased (p < 0.05). The iron level was proportional to the degree of progression, with the most significant change appearing on the third day in deep tissue pressure injury models (p < 0.05). Enzyme-linked immune sorbent assay results suggested abnormal gene expression was related to iron metabolism, including a substantial increase in ferritin and a significant decrease in the expression of ferroportin-1 (p < 0.05). In addition, immunofluorescence staining and Western blot showed that the expression of macrophage membrane receptor CD163 was abnormally elevated (p < 0.05). Both high-throughput transcriptome sequencing and qRT-PCR results suggested aberrant expression of the CD163/Homx-1-mediated signalling pathway. Dysfunctional iron metabolism was suggested to be related to the aberrant CD163/Homx-1 signalling pathway in deep tissue pressure injury models.