Role of Discoidin Domain Receptor 1 in Collagen Fiber Reorganization

Background: Gingival overgrowth is a common adverse outcome of cyclosporine A (CsA) treatment. In this disorder, collagen remodeling is disrupted but the fibroblast receptors that mediate remodeling and that are dysregulated by CsA are not defined.  We hypothesized that the discoidin domain receptor 1 (DDR1) expressed by fibroblasts is important for collagen remodeling and that DDR1 function is affected by CsA, thereby disrupting collagen homeostasis.  

Objectives: 1) Determine whether DDR1 mediates collagen remodeling by fibroblasts; 2) Assess the effect of CsA on DDR1-mediated collagen remodeling.  

Methods: Mouse 3T3 fibroblastic cells that expressed DDR1 or were null for DDR1 were treated with vehicle (dimethyl sulfoxide-DMSO) or with CsA (10 µM in DMSO).  Cells were inoculated into floating or attached collagen gels to study the impact of DDR1 on collagen remodeling by fibrillar reorganization or cell-mediated traction, respectively. Cell migration was analyzed with in vitro scratch wound assays. 

Results: DDR1-expressing cells contracted floating collagen gels more rapidly than DDR1 null cells (mean slope±S.E.M.: DDR1=75.4±12.2 µm/hr; DDR1 null cells=18.9±4.8 µm/hr; p<0.001). DDR1-expressing cells treated with CsA exhibited a 2.2-fold reduction of gel contraction (34.4±2.3 µm/hr; p<0.01). CSA had no effect on DDR1 null cells (p>0.05).  In attached collagen gel contraction assays, DDR1-expressing cells contracted gels more rapidly than DDR1 null cells (877±63 µm/hr vs. 247±87 µm/hr; p<0.001). CsA did not affect attached gel contraction. DDR1 expression and CsA treatment also did not affect cell migration in scratch wound assays (p>0.05). 

Conclusions: DDR1 is important for collagen remodeling by fibrillar reorganization and by contraction in vitro but CsA only affects fibrillar reorganization. Accordingly, CsA perturbation of DDR1-mediated fibrillar reorganization may contribute to gingival overgrowth.