In 2010, more than 875,000 Americans with diabetes were diagnosed with a lower extremity ulcer. Failed closure of these wounds results in more than 73,500 lower extremity amputations annually. One common feature to these wounds is inadequate vascularization of the wound bed, leading to ischemia, infection, and necrosis. In addition to diabetic ulcers, limited vascularization during regeneration of coronary, orthopaedic, dental and muscle tissues are frequent diabetic complications. Several growth factors, including Sonic hedgehog (Shh), can enhance wound healing by promoting neovascularization in the wound, but they are rapidly cleared from the wound environment and subject to proteolytic digestion. Thus, the translation of growth factors as clinical therapies has been limited by their short duration of site-specific bioactivity in vivo. We have developed multivalent growth factor conjugates that are designed to enhance the bioactivity and tissue-level stability of growth factors to facilitate their clinical translation as biological therapeutics. Using this approach, w have conjugated Shh to linear chains of hyaluronic acid (HyA), and by varying the ratio of Shh:HyA, we can modulate its ability to activate the Shh pathway. Conjugating Shh to a large macromolecule may also prevent its deactivation by proteolytic enzymes and enhance its molecular stability in the target tissues. Our overall hypothesis is that multivalent conjugates of Shh (mvShh) will enhance and sustain Shh-induced gene expression that promotes neovascularization during diabetic wound healing.
In Specific Aim 1, we will identify the mvShh formulations that yield maximal pathway activation in vitro using dermal fibroblasts harvested from db/db mice, a diabetic model animal that exhibits impaired wound healing and diminished angiogenic gene expression.
In Specific Aim 2 we will correlate the bioactivity of mvShh conjugates to their ability to accelerate healing of full-thickness excisional wounds in db/db mice. Finally, in Specific Aim 3 we will use the same db/db wound healing model to investigate how multivalent presentation of Shh can enhance Shh-induced expression of angiogenic genes and blood vessel formation in vivo. By testing our hypothesis, we will evaluate mvShh conjugates as a treatment for diabetic ulcers. The general mechanism of multivalent conjugation of Shh in angiogenic signaling may also be extended to a variety of other microvascular disorders. Likewise, this study will build a rationale for multivalent conjugation as an enabling strategy for protein-based therapies that require local delivery and sustained bioactivity.

Public Health Relevance

In 2010, more than 875,000 Americans with diabetes were diagnosed with a chronic lower extremity ulcer, this diabetic complication generates over $30 billion per year in related health care costs. We are developing an advanced therapeutic to accelerate healing in diabetic wounds by encouraging neovascularization and improving blood supply to the site of injury. The overall goal of our project is to evaluate how our treatment strategy can enhance the cellular mechanisms of blood vessel formation, and thus initiating its translation to a clinical therapy.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Exploratory/Developmental Grants (R21)
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Biomaterials and Biointerfaces Study Section (BMBI)
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Tseng, Hung H
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University of California Berkeley
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United States
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