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 preliminary observations in a mouse model of appendage injury, this proposal will address the 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. Ear whole closure, as seen in rabbits and in the inbred MRL mouse strain is considered to be a mammalian example of regeneration similar to limb regeneration in amphibians. Ear holes close completely with the replacement of cartilage and without scarring. In this proposal, we present in-vitro and in-situ evidence that the wound site during this regenerative response is pro-inflammatory and that pharmacological up- regulators of inflammation induce regeneration in otherwise non-regeneration competent mice. Inflammation has been shown to be regulated by the transcription factor HIF1a and we will focus on HIF1a up-regulation in C57BL/6 mice to further explore its role in the regenerative response. Since HIF1a is modulated at the protein level and its degradation is initiated by hydroxylation accomplished by prolyl hydroxylases (PHDs), we will examine several inhibitors of HIF1a degradation including a PHD inhibitor, a direct HIF1a hydroxylation inhibitor and an inhibitor of ubiquination. These molecules will be screened for activity in HIF-luciferase reporter mice and their cells in-vitro as 1) topical agents or soluble injectants into the wound site or administered systemically and 2) coupled to a biomaterial. Given that HIF activity regulates as much as 10% of all cellular functions and especially the metabolic state and inflammation, it is important that HIF-activating drugs be present only at the wound site and in a controlled manner. Novel in- situ forming macromolecular biomaterials will be designed with the goal of fine control, both spatial and temporal, of HIF levels at the wound site. We envision that this approach of mimicking the complex tissue 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 that regulate metabolism and inflammation and are under biological control.
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