P094 Lack of DNA methyltransferase DNMT3A in fibroblasts impairs cell growth and wound healing

Abstract

Abstract Background Fibrotic scarring is an untreatable pathological wound-healing complication that invalidates correct organ function. However, pathomechanisms leading to intestinal fibrosis during inflammatory bowel disease (IBD) are not fully understood. Since the de novo DNA methyltransferase DNMT3A has been associated with increased risk for IBD and alters epithelial homeostasis, we sought to characterize how DNMT3A loss might affect fibroblasts, the key mesenchymal cells involved in wound healing. Methods We stably depleted Dnmt3a in 3T3 fibroblast cell line using CRISPR-Cas9 technology and subsequently selected GFP-positive clones using FACS sorting. Cell cultures were performed in vessels with or without 0.2% gelatin coat. Reverse transcription quantitative PCR, western blot, and immunofluorescence were used to confirm Dnmt3a gene deletion and characterize wild-type (WT) and knockout cells (KO). Wound healing assays in the presence or absence of tissue repair cytokine TGF-β served to quantify and assess cell capacity of wound closure. Results 3T3 fibroblasts lacking Dnmt3a acquire an activated myofibroblast phenotype (characterized by increased α-SMA expression) that also overexpress tissue remodelling matrix metalloproteinase Mmp3, and the inflammation-induced necroptosis marker RIPK3 when compared to their WT counterparts. In addition, Dnmt3a-depleted 3T3 cells grow overlapped in tightly aggregated foci (fig. 1), and when seeded in vessels without the gelatin coat, they form spheroids. To assess healing properties, the closure of a wound (gap) in a cell monolayer was monitored. While WT 3T3 fibroblasts closed the gap within 48h, Dnmt3a KO 3T3 cells were unable to refill the empty space and formed aggregated foci in the vicinity of the wound (fig. 1). When the wound healing assay was repeated in the presence of TGF-β, WT cells nearly closed the gap within 24h whereas Dnmt3a KO 3T3 still failed to grow. Conclusion We conclude that Dnmt3a is crucial for fibroblast homeostasis and correct wound healing. Furthermore, TGF-β signalling is impaired when Dnmt3a is lacking. Thus, additional characterization of Dnmt3a depletion in fibroblasts will deepen the understanding of fibrosis and point towards new therapeutic approaches for this untreatable complication.