Pressure sores are a common debilitating complication of spinal cord injury (SCI) and tend to occur in soft tissues located around bony prominences where body weight is concentrated while the patient is sitting or lying. Among the many metabolic and physiological changes reported in tissues innervated below the level of SCI, compromised blood flow regulation is a major contributor to the impaired wound healing; however, there have been no studies in controlled experimental settings due to the lack of suitable animal models. We have recently developed a mouse model where the wound healing process of experimentally induced pressure wounds (PWs) and excisional wounds (EWs) was characterized in SCI. Our results to date clearly show that wound healing is significantly delayed in SCI mouse. Furthermore, using state-of-the-art multiphoton microscopy methods, we confirmed that the tissue was oxygen-starved at the wound edge in the SCI mouse, while oxygen delivery was increased in normal controls, as expected in a normal wound healing process.Hypothesis or Objective: The mouse model described above is well suited to understand the role of impaired blood flow in skin wound healing below the level of SCI and to test new therapeutic strategies that locally enhance blood flow in an attempt to overcome impaired wound healing in SCI. More specifically, we will test two hypotheses: (a) SCI impairs blood flow regulation in skin wounds, thus resulting in impaired healing below the level of SCI and (b) topical angiogenic peptides consisting of VEGF and/or PDGF fused to elastin-like peptides (ELPs) to render them more resistant to degradation by wound proteases can restore blood flow regulation, thus resulting in improved wound healing.Specific Aims: This study is divided into the three specific aims, as described below.Specific Aim 1: To characterize the effect of SCI on blood flow regulation in experimental skin wounds below and above the level of SCI in mice.Specific Aim 2: To develop protease-resistant angiogenic fusion proteins and test their biological activity in vitro.Specific Aim 3: To test the effect of angiogenic fusion proteins on blood flow and healing of experimental wounds in SCI animals.Study Design: We will induce SCI either via complete transection or contusion of spinal cord (T9-T10) to characterize the impact of SCI on wound healing. Immediately after SCI, mice will receive a clinically relevant PW by applying two magnets (5×12 mm diameter, 3800 G magnetic field) on either side of a dorsal skin fold for 12 hours, or experimentally relevant EW by removing the full skin thickness (1x1 cm2) on the dorsum below and above the SCI site. First, ELP fusion proteins will be tested for their angiogenic properties in vitro and for their stability in human wound fluid (provided by our physician-scientist collaborator Henry Hsia at Yale University). Then, the same fusion proteins will be applied locally onto PWs and EWs to assess whether they speed up wound closure and reverse the impaired blood flow in the wound as a result of SCI. Macroscopic images of the wounds will be taken as a function of time and wound closure dynamics and compared with their respective controls as well as below and above the level of SCI groups. At selected times, we will harvest, section, and stain wounds for morphology, cell proliferation (Ki67), angiogenesis (CD31), and myofibroblast formation (alpha-smooth muscle actin). In addition, we will characterize blood flow dynamics within and around the wounds by ultrasound, and to confirm that decreased blood flow causes hypoxia down at the cellular level, tissue sections will be visualized by multiphoton microscopy by our collaborator Kyle Quinn at the University of Arkansas to map out the mitochondrial redox distribution over the wound area.Impact: There are ~17,000 new cases of SCI reported each year, and >250,000 individuals living with SCI in the United States. Approximately 30%-40% of SCI patients develop PW with a re-occurrence chance of 60%-85%. Overall, PWs negatively impact the daily lives of SCI patients and their family members. Successful completion of this study will lead to a better understanding of the impact of SCI on blood flow regulation in wounds and the resulting effect on wound healing. Furthermore, the fusion protein technology described herein may provide a new therapeutic strategy to heal such wounds and improve the health and quality of life of SCI patients.Military Relevance: Veterans of the US Armed Forces account for ~12% of SCI individuals. PWs are the second most common etiology for re-hospitalization in SCI patients and pose a significant financial burden to the healthcare system; for example, treating a pressure sore can increase the cost of treatment of an SCI patient by up to 80%. This project addresses the ongoing “Getting to Zero” initiative at the Veterans Administration to develop new methods to prevent and treat pressure ulcers.
|Effective start/end date||8/1/17 → 7/31/20|
- Congressionally Directed Medical Research Programs (CDMRP)
Spinal Cord Injuries
Wounds and Injuries