Understanding the role of macrophages in collagen-mimetic peptide (CMP)-mediated gene delivery

Sullivan, MillicentKiick, Kristi L.Chronic wounds are notoriously hard-to-heal wounds that typically afflict patients in the form of ulcers (i.e. diabetic foot ulcers). The pathophysiology of these wounds is directly linked to protracted inflammation, which prevents closure via normal cellular processes and poses major challenges for treatment (i.e. cellular senescence, proteolytic degradation). Due to the limited efficacy of existing treatments, gene delivery has garnered interest as an alternative strategy to circumvent roadblocks characteristic of the chronic wound by facilitating cellmediated healing through in situ production of critical healing factors. ☐ Previous work in our group demonstrated that collagen-mimetic peptide (CMP)-modified polyplexes encoding platelet-derived growth factor (PDGF) have the capacity to transfect fibroblasts with high efficiency when delivered from collagen scaffolds. However, the impact of the system on other cell types had not been explored. This work sought to augment the impact of the CMP-gene delivery system by incorporating gene delivery to macrophages, which directly cause chronic inflammation. Studies were conducted to elucidate (i) the capability of the existing system to transfect macrophages directly and (ii) the effect of PDGF secretion by transfected fibroblasts on macrophage behavior. ☐ A series of studies were completed to optimize bolus transfection of macrophages by polyplexes, varying the composition of the polyplexes and pDNA dosage. Optimal composition and pDNA dosage were found to be the same for both fibroblasts and macrophages, suggesting that the current system can successfully transfect macrophages. Additionally, transgene expression by macrophages was compared against fibroblasts, using a substrate-mediated transfection. Preliminary results indicated that fibroblasts were transfected at about 2-3x the rate of macrophages. To probe the involvement of macrophages in the CMP-mediated gene delivery system, we studied the effect of PDGF stimulation on macrophage transfection, proliferation, and migration. The results suggest that PDGF secretion by fibroblasts may enhance macrophage transfection by increasing their migration. PDGF was not found to induce macrophage proliferation, in contrast to its mitogenic effects on fibroblasts. ☐ Taken together, these results suggest that macrophages likely are transfected in the existing system (albeit to a lesser degree than fibroblasts). Furthermore, the CMP-polyplex gene delivery system could be applied to polarize macrophages to a pro-healing phenotype and enhance neovascularization in chronic wounds. Future work will be focused on (i) identifying the timing and phenotype of macrophage involvement for in vivo wound models and (ii) developing gene co-delivery systems to alter the behavior and phenotype of macrophages in an effort to resolve inflammation earlier.University of Delaware, Department of Chemical and Biomolecular EngineeringM.Ch.E