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theses

Wound healing is a hierarchical process of intracellular and intercellular signaling. Insulin is a potent chemoattractant and mitogen for cells involved in wound healing. Insulin’s potential to promote keratinocyte growth and stimulate collagen synthesis in fibroblasts is well described. However, there currently lacks an appropriate delivery mechanism capable of continuously supplying a wound environment with insulin; current approaches require repeated applications of insulin, which increase the chances of infecting the wound. In addition to insulin, exogenous mesenchymal stromal cell or mesenchymal stem cell (MSC) application is a promising treatment strategy for chronic wounds, yet MSC therapies are still far from a clinical reality. MSCs have been shown to improve islet viability and function, regulate inflammation and secrete pro-wound healing factors. MSC-assisted wound healing is elicited through distinct pathways from insulin-assisted wound healing. In this dissertation, a potential synergistic effect of these two differing modes of wound healing was investigated. Since topical insulin creams preclude using MSCs, here insulin-producing cells (IPCs) and MSCs were combined in a dual-cell therapy approach for wound healing. Polyethylene glycol diacrylate (PEGDA) was used to encapsulate IPCs and/or MSCs and results showed that the encapsulation did not alter insulin or MSC secretion profiles. It was hypothesized that MSCs would improve IPC viability and insulin secretion and that the combination of encapsulated IPCs and MSCs would release factors that synergistically accelerate wound repair at greater rates than either cell used alone. The resulting coencapsulated IPC-MSC hydrogel system was applied to a diabetic mouse model of chronic wounds and provided prolonged release of insulin and soluble MSC factors without the need for reapplication. The results showed that IPCs encapsulated within PEGDA hydrogels improved wound healing by 1.6 times, and remarkably IPC and MSC coencapsulation further accelerated wound closure 2.5 times faster, thus supporting the hypothesis. Results further showed increased release of insulin, vascular endothelial growth factor (VEGF), and transforming growth factor β1 (TGF-β1) when IPCs and MSCs were combined than when they were encapsulated singly. Since each of these factors support wound healing, it is unsurprising that wound healing proceeded faster in these groups. In addition, coencapsulated IPCs and MSCs stimulated Akt phosphorylation in myoblasts more than any other treatment group. The phosphatidylinositol 3-kinase (PI3K)-Akt pathway stimulates growth, proliferation, migration and secretion by keratinocytes, endothelial cells and fibroblasts and induces angiogenesis by promoting VEGF secretion. Thus, the PI3-AkT pathway was another pro-wound healing mechanism recruited by the IPC-MSC system. Wounds healed without intermediate scab or scar formation and histology showed mature skin features in IPC-MSC treated wounds. The system’s ability to accelerate healing in chronic wounds with a single application has broad clinical and research implications.

ETD_7987

Ph.D.

Includes bibliographical references

by Ayesha Aijaz

doi:10.7282/T3N58Q5P

ETD doctoral

The author owns the copyright to this work.