It is well known that prolonged inflammation hinders the optimal goal of wound repair, namely prompt closure of the wound with minimal scarring. However, the objective of tissue regeneration (as opposed to wound repair) is to reconstitute and replace damaged tissue with a functional biological replica of the lost tissue without scarring. In this latter case, the role of inflammation is not well established for the simple reason that most mammals including humans have rarely demonstrated any capacity for regeneration (with the exception of the liver) precluding experimental approaches. Based upon our observations in a mouse model of appendage injury (ear hole closure in the MRL mouse), this proposal will address the counter-intuitive possibility that enhancing at least some aspects of inflammation will re-direct wound healing towards regeneration. We will also examine the use of novel biomaterials to locally harness key aspects of the inflammatory response and facilitate tissue regeneration. MRL mice have been shown to be robust regenerators of multiple tissue types and we have consistently noted that regeneration is accompanied by intense and prolonged inflammation at the injury site. Administration of the anti-inflammatory COX2 inhibitor meloxicam inhibits MRL ear hole closure suggesting that inflammation may be functionally involved in appendage regeneration. We directly tested this possibility in non-regenerating C57BL/6 mice by topically applying the pro-inflammatory drug imiquimod, a toll-like receptor (TLR) ligand, to injury sites in two wound models: ear hole healing and digit amputation. In both cases, a positive regenerative result ensued. In this proposal, we will 1) examine the TLRs involved in the MRL regenerative response and 2) attempt to stimulate those predominant TLRs using select TLR ligands applied topically to elicit a regenerative response in the non-regenerating C57BL/6 mouse. The level of inflammation and regenerative response will be determined at the transcript, protein, cellular and tissue levels. 3) We will apply those TLR ligands not only topically but will generate chemically conjugated compounds to a biomaterial. The latter will provide us with a novel injectable in-situ forming macromolecular biomaterial (NCL hydrogel) that can be used for injuries that are not only surface injuries but deep injuries as well. We envision that this approach of mimicking the inflammatory microenvironment of a healing wound will allow for biomaterial degradation accompanied by tissue regeneration, leading in the future to new clinical modalities for tissue regeneration.
Achieving predictable regeneration of damaged tissues and organs is a major goal of medicine. By studying the remarkable ability of the MRL mouse to heal injuries and the role of inflammation in this process, we will gain insight into methods to help translate this knowledge into patient care. In particular, we will examine the role of implantable "smart" biomaterials that release regeneration-specific drugs under biological control.
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