Abstract
BACKGROUND: Keloids are a common form of pathologic wound healing characterized by excessive production of extracellular matrix. The unfolded protein response (UPR) is a cellular response to hypoxia, a component of the wound microenvironment, capable of protecting cells from the effects of over-accumulation of misfolded proteins. Since keloids have hypersecretion of extracellular matrix, we hypothesized that keloid fibroblasts (KFs) may have enhanced activation of the UPR compared with normal fibroblasts (NFs). METHODS: KFs and NFs were placed in a hypoxia chamber for 0, 24, and 48h. We also used tunicamycin to specifically up-regulate the UPR. UPR activation was assayed by PCR for xbp-1 splicing and by immunoblotting with specific antibodies for the three UPR transducers. Nuclear localization of XBP-1 protein in KFs was confirmed by immunofluorescence. RESULTS: There is increased activation of XBP-1 protein in KFs compared with NFs following exposure to hypoxia. Pancreatic ER kinase (PERK) and ATF-6, two other pathways activated by the UPR, show comparable activation between KFs and NFs. We confirmed that there is enhanced activation of XBP-1 by demonstrating increased nuclear localization of XBP-1 using immunofluorescence. CONCLUSION: In contrast to our initial hypothesis that keloids would have broad activation of the UPR, we demonstrate here that there is a specific up-regulation of one facet of the UPR response. This may represent a specific molecular defect in KFs compared with NFs, and also suggests modulation of the UPR can be used in wound healing therapy.