A new model of regenerative healing via inflammation-modulating biomaterials

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Abstract The ability to regenerate tissue in mammals has remained elusive. While the use of stem cell populations in the context of bio-scaffolds has shown promise as a potential means of replacing lost, damaged, or diseased tissue, significant challenges remain. An alternative approach is to attempt to evoke a classical in situ regenerative response emulating that seen in lower species such as newts. While this trait was thought to be lost in evolution, our observation (Heber-Katz) that the MRL mouse and related strains have a significant spontaneous regenerative capability demonstrates that the trait is retained in mammals. Studies over the past almost 20 years have culminated in the identification of the HIF-1α (hypoxia inducible factor) pathway as the central actor regulating regeneration in mice. HIF-1α is significantly elevated during the early phases of wound healing in MRL mice and inhibiting HIF-1α with si-RNA blocks regeneration entirely. When we mimicked this HIF-1α response in otherwise non-regenerating Swiss Webster mice the regeneration trait was conferred with the faithful replacement of tissue architecture indistinguishable from normal tissue. This was achieved using the PHD inhibitor 1,4-DPCA in a novel biomaterial construct (Messersmith) leading to the stabilization of high levels of HIF-1α in vivo. In this current proposal, we provide preliminary results suggesting that impressive healing is also seen in a mouse model of periodontal disease, ligature-induced bacterial accumulation leading to an inflammatory host response with bone loss (Hajishengallis model). We show that bone recovers, the periodontal ligament (PDL) is restored, and an unusually robust stem cell response in the tooth pulp and in periodontal tissue is found. We will use advanced molecular design to produce a biomaterial capable of achieving single dose and local delivery vs. the current three-dose delivery system. In addition to yielding a novel soft and bone tissue regeneration therapy, we believe that this system provides an impressive landscape of phenomena that will yield important mechanistic information about in- situ regenerative responses in oral tissues. In Aim 1, we will create new biomaterials to yield extended drug release to provide a single-dose treatment with rapidly degradable gels; in Aim 2, we will examine the effect of drug preparations, both original and new, on bone and PDL loss and regrowth using microCT and molecular analysis; in Aim 3, we will further explore the metabolic response after modulating HIF levels; and in Aim 4, we will determine mechanistic factors involved in the inflammatory, overall immune, and stem cell responses. In conclusion, a successful in-situ drug-induced regenerative therapy would significantly advance the treatment of periodontal disease beyond current surgical procedures.