Human red blood cells contain antifibrogenic factors that stimulate MMP-1 expression in dermal fibroblasts

The healing of a burn injury is a dynamic biological process, and there must be a set of factors that gradually slow down and/or terminate this healing process upon epithelialization. We have previously demonstrated that some members of the 14-3-3 protein family including stratifin, which is mainly released by differentiated keratinocytes, have a potent matrix metalloproteinase-1 (MMP-1), -3, -8, and -24 stimulatory effect for fibroblasts. During the course of our studies, we discovered that human red blood cells (RBCs) contain a high level of different 14-3-3 isoforms. In this study, we evaluated the presence of these proteins in RBC and examined the efficacy of RBC in stimulating the expression of MMP-1 in dermal fibroblasts using Western blot analysis. The findings revealed the presence of all seven isoforms of 14-3-3 (η, γ, ε, σ, β, ζ, and τ) in RBC lysate, though with different levels of expression. Interestingly, the levels of some of these proteins were higher in RBC from new born babies compared to those of adults. We also found that RBC lysate significantly increased the expression of MMP-1 in different strains of fibroblasts, and this effect has been abrogated by almost 20% when R18 was used to deplete the 14-3-3 proteins from lysate. However, when RBC lysate was passed through a 3-kDa filter, and then whole RBC lysate, retentate, and filtrate were used to treat three strains of fibroblasts, MMP-1 expression was increased significantly, indicating the presence of MMP-1-inducing factors smaller than 3kDa in RBC lysate as well. The MMP-1 stimulatory effect of RBC lysate for fibroblasts was stable at freeze/thawing as well as freezing for at least 1 year. In conclusion, the MMP-1 stimulatory effect of RBC lysates might play an important role in the regulation of extracellular matrix under physiological and pathological conditions. Because of its MMP-1 stimulating effect, the RBC lysate might be used as an antifibrogenic factor for the treatment of some fibroproliferative conditions such as hypertrophic scarring and keloid.