Purpose: Proliferative vitreoretinopathy (PVR) is an inflammatory fibrotic disease resulting from the inflammatory milieu after retinal detachment, which can prevent retinal healing. This study aimed to elucidate the effect of substance P (SP) on retinal degeneration caused by retinal detachment in vivo and to examine the role of SP in the tumor necrosis factor-alpha (TNF-α)-induced epithelial-mesenchymal transition (EMT) of human RPE cells in vitro.
Methods: PVR-like retinal damage was induced by intravitreally injecting dispase into mice, and SP was systemically injected twice a week for 3 weeks. Histological analysis and cytokine profile with enzyme-linked immunosorbent assay (ELISA) were performed. The direct effect of SP on induction of EMT in vitro was studied by adding SP to TNF-α-treated ARPE-19 cells and then evaluating the change in the characteristics of the epithelial and mesenchymal cells.
Results: Dispase injection led to a PVR-like retinal condition, demonstrating an inflammatory response with disruption of RPE interaction within 1 week and severe destruction with enfolding within 3 weeks after the dispase injection. The inflammatory environment promoted apoptosis and migration of fibroblast-like cells in the retinal layer, which can cause fibrotic disease, such as PVR. However, SP treatment suppressed early inflammatory responses by reducing TNF-α and elevating interleukin-10 (IL-10), with cell death and the appearance of fibroblastic cells inhibited and the progression of retinal degeneration obviously delayed. Moreover, SP ameliorated TNF-α-induced EMT of the RPE and directly prevented fibrotic change in the RPE.
Conclusions: This study revealed that SP can block apoptosis and EMT due to retinal inflammation and inhibit the development of PVR. This effect most likely occurred by modulating the secretion and action of TNF-α..