Faculty Bibliography

The trafficking of circulating stem and progenitor cells to areas of tissue damage is poorly understood. The chemokine stromal cell-derived factor-1 (SDF-1 or CXCL12) mediates homing of stem cells to bone marrow by binding to CXCR4 on circulating cells. SDF-1 and CXCR4 are expressed in complementary patterns during embryonic organogenesis and guide primordial stem cells to sites of rapid vascular expansion. However, the regulation of SDF-1 and its physiological role in peripheral tissue repair remain incompletely understood. Here we show that SDF-1 gene expression is regulated by the transcription factor hypoxia-inducible factor-1 (HIF-1) in endothelial cells, resulting in selective in vivo expression of SDF-1 in ischemic tissue in direct proportion to reduced oxygen tension. HIF-1-induced SDF-1 expression increases the adhesion, migration and homing of circulating CXCR4-positive progenitor cells to ischemic tissue. Blockade of SDF-1 in ischemic tissue or CXCR4 on circulating cells prevents progenitor cell recruitment to sites of injury. Discrete regions of hypoxia in the bone marrow compartment also show increased SDF-1 expression and progenitor cell tropism. These data show that the recruitment of CXCR4-positive progenitor cells to regenerating tissues is mediated by hypoxic gradients via HIF-1-induced expression of SDF-1

Chronic hyperglycemia impairs intracellular redox homeostasis and contributes to impaired diabetic tissue regeneration. The Keap1/Nrf2 pathway is a critical regulator of the endogenous antioxidant response system and its dysfunction has been implicated in numerous pathologies. Here, we characterize the effect of chronic hyperglycemia on Nrf2 signaling within a diabetic cutaneous regeneration model. We characterized the effects of chronic hyperglycemia on the Keap1/Nrf2 pathway within models of diabetic cutaneous wound regeneration. We assessed reactive oxygen species (ROS) production and antioxidant gene expression following alterations in the Nrf2 suppressor, Keap1, and the subsequent changes in Nrf2 signaling. We also developed a topical siRNA-based therapy to restore redox homeostasis within diabetic wounds. Western blot demonstrated that chronic hyperglycemia-associated oxidative stress inhibits nuclear translocation of Nrf2 and impairs activation of antioxidant genes, thus contributing to ROS accumulation. Keap1 inhibition increased Nrf2 nuclear translocation, increased antioxidant gene expression, and reduced ROS production to normoglycemic levels, both in vitro and in vivo. Topical siKeap1 therapy resulted in improved regenerative capacity of diabetic wounds and accelerated closure. We report that chronic hyperglycemia weakens the endogenous antioxidant response and the consequences of this defect are manifested by intracellular redox dysregulation, which can be restored by Keap1 inhibition. Targeted siRNA-based therapy represents a novel, efficacious strategy to reestablish redox homeostasis and accelerate diabetic cutaneous tissue regeneration.

Therapeutics utilizing siRNA are currently limited by the availability of safe and effective delivery systems. Cutaneous diseases, specifically ones with significant genetic components are ideal candidates for topical siRNA based therapy but the anatomical structure of skin presents a considerable hurdle. Here, we optimized a novel liposome and protein hybrid nanoparticle delivery system for the topical treatment of diabetic wounds with severe oxidative stress. We utilized a cationic lipid nanoparticle (CLN) composed of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and the edge activator sodium cholate (NaChol), in a 6:1 ratio of DOTAP:NaChol (DNC). Addition of a cationic engineered supercharged coiled-coil protein (CSP) in a 10:1:1 ratio of DNC:CSP:siRNA produced a stable lipoproteoplex (LPP) nanoparticle, with optimal siRNA complexation, minimal cytotoxicity, and increased transfection efficacy. In a humanized murine diabetic wound healing model, our optimized LPP formulation successfully delivered siRNA targeted against Keap1, key repressor of Nrf2 which is a central regulator of redox mechanisms. Application of LPP complexing siKeap1 restored Nrf2 antioxidant function, accelerated diabetic tissue regeneration, and augmented reduction-oxidation homeostasis in the wound environment. Our topical LPP delivery system can readily be translated into clinical use for the treatment of diabetic wounds and can be extended to other cutaneous diseases with genetic components.

IMPORTANCE/UNASSIGNED:Catastrophic facial injury with globe loss remains a formidable clinical problem with no previous reports of reconstruction by whole eye or combined whole eye and facial transplant. OBJECTIVE/UNASSIGNED:To develop a microsurgical strategy for combined whole eye and facial transplant and describe the clinical findings during the first year following transplant. DESIGN, SETTING, AND PARTICIPANT/UNASSIGNED:A 46-year-old man who sustained a high-voltage electrical injury with catastrophic tissue loss to his face and left globe underwent combined whole eye and face transplant using personalized surgical devices and a novel microsurgical strategy at a specialized center for vascularized composite allotransplantation. MAIN OUTCOMES AND MEASURES/UNASSIGNED:Reperfusion and viability of the whole eye and facial allografts, retinal function, and incidence of acute rejection. RESULTS/UNASSIGNED:The patient underwent a combined whole eye and face transplant from an immunologically compatible donor with primary optic nerve coaptation and conventional postoperative immunosuppression. Globe and retinal perfusion were maintained throughout the immediate postoperative period, evidenced by fluorescein angiography. Optical coherence tomography demonstrated atrophy of inner retinal layers and attenuation and disruption of the ellipsoid zone. Serial electroretinography confirmed retinal responses to light in the transplanted eye. Using structural and functional magnetic resonance imaging, the integrity of the transplanted visual pathways and potential occipital cortical response to light stimulation of the transplanted eye was demonstrated. At 1 year post transplant (postoperative day 366), there was no perception of light in the transplanted eye. CONCLUSIONS AND RELEVANCE/UNASSIGNED:This is the first report of whole eye transplant combined with facial transplant, demonstrating allograft survival including rejection-free graft survival and electroretinographic measurements indicating retinal response to light stimuli. These data highlight the potential for clinical allotransplantation for globe loss.

Background: Vascularized composite allotransplantation (VCA) has become a viable option for restoration of devastating injuries that are not amenable to conventional reconstructive techniques. However, the relative scarcity of procedures performed worldwide, as well as the potential for iatrogenic injury with biopsies, makes studying the immunopathogenesis of acute rejection challenging. Translational VCA research focuses on developing strategies to overcome these barriers with the use of animal models can be technically challenging and difficult to replicate without highly trained microsurgeons. Methods: We describe a modified model of a femur-based composite tissue allograft using an adapted vascular cuff anastomotic technique with a tunneled skin flap in a rodent model. Results: The use of a heterotopic osteomyocutaneous flap with a subcutaneously tunneled-skin paddle to the posterolateral aspect of the recipient rodent allows for ease of flap monitoring and reduces the risk of self-mutilation. A total of six transplantations were conducted with no signs of self-mutilation. Operative time decreased as our surgical technique improved, and long-term graft tolerance was possible under our immunosuppressive regimen. Additionally, we demonstrate cases of successful transplantation in both an allogeneic and syngeneic rodent model. Conclusion: Animal models, although technically challenging, are a reliable and reproducible modality that has been used to investigate various aspects of VCA immunology. We describe the success of an osteomyocutaneous flap with a modified vascular cuff anastomosis that can be used by investigators with less experience in microsurgical techniques to further our understanding of VCA physiology. Furthermore, tunneling of the skin paddle reduces the risk of self-mutilation and other external factors affecting the graft.

OBJECTIVE:Rejection is common and pernicious following Vascularized Composite Allotransplantation (VCA). Current monitoring and diagnostic modalities include the clinical exam which is subjective and biopsy with dermatohistopathologic Banff grading, which is subjective and invasive. We reviewed literature exploring non- and minimally invasive modalities for diagnosing and monitoring rejection (NIMMs) in VCA. METHODS:PubMed, Cochrane, and Embase databases were queried, 3125 unique articles were reviewed, yielding 26 included studies exploring 17 distinct NIMMs. Broadly, NIMMs involved Imaging, Liquid Biomarkers, Epidermal Sampling, Clinical Grading Scales, and Introduction of Additional Donor Tissue. RESULTS:Serum biomarkers including MMP3 and donor-derived microparticles rose with rejection onset. Epidermal sampling non-invasively enabled measurement of cytokine & gene expression profiles implicated in rejection. Both hold promise for monitoring. Clinical grading scales were useful diagnostically as was reflection confocal microscopy. Introducing additional donor tissue showed promise for preemptively identifying rejection but requires additional allograft tissue burden for the recipient. CONCLUSION/CONCLUSIONS:NIMMs have the potential to dramatically improve monitoring and diagnosis in VCA. Many modalities show promise however, additional research is needed and a multimodal algorithmic approach should be explored.

Background: In properly selected patients, combined face and whole eye transplantation (FWET) may offer a more optimal aesthetic and potentially functional outcome while avoiding the complications and stigma of enucleation and prosthetics. This study presents the most comprehensive cadaveric assessment for FWET to date, including rehearsal allograft procurement on a brain-dead donor. Methods: Over a 2-year period, 15 rehearsal dissections were performed on 21 cadavers and one brain-dead donor. After identification of a potential recipient, rehearsals assessed clinical feasibility and enabled operative planning, technical practice, refinement of personalized equipment, and improved communication among team members. Operative techniques are described. Results: Facial allograft procurement closely followed previously described face transplant techniques. Ophthalmic to superficial temporal (O-ST) vessel anastomosis for globe survival was assessed. Craniectomy allowed for maximal optic nerve and ophthalmic vessel pedicle length. Appropriate pedicle length and vessel caliber for O-ST anastomosis was seen. Research procurement demonstrated collateral blood flow to the orbit and surrounding structures from the external carotid system as well as confirmed the feasibility of timely O-ST anastomosis. Personalized cutting guides enabled highly accurate bony inset. Conclusions: This study formalizes an approach to FWET, which is feasible for clinical translation in judiciously selected patients. O-ST anastomosis seems to minimize retinal ischemia time and allow perfusion of the combined allograft on a single external carotid pedicle. Although restoration of vision likely remains out of reach, globe survival is possible.

BACKGROUND:An update on the epidemiology of distal radius fractures in the United States is necessary, particularly as the elderly population grows. Additionally, age and frailty have been associated with complications following surgical fixation of DRFs. Herein, we utilize the National Trauma Data Bank, a robust nationwide resource, to investigate the relationship between demographics, comorbidities, injury and fracture characteristics, and admission details. METHODS:Patients with isolated distal radius fractures were identified from the National Trauma Data Bank (2016-2019) according to ICD-10 codes. Univariate and multivariate regressions were conducted to determine independent risk factors for bilateral fractures, displaced fractures, open fractures, as well as length of hospital stay and adverse discharge disposition for patients undergoing inpatient surgical fixation. RESULTS:The incidence of DRFs was 3.6/1,000 trauma-related emergency department visits and 10.8/1,000 upper extremity traumas. Trauma mechanism was significantly associated with displaced and open fractures. Age (OR 1.01, 95% CI 1.01-1.01), BMI (OR 1.02, 95% CI 1.01-1.02), smoking (OR 1.34, 95% CI 1.15-1.57), and alcohol level (trace: OR 2.18, 95% CI 1.41-3.29; intoxicated: OR 2.20, 95% CI 1.63-2.95) were significantly associated with open fractures. Machinery (β=2.04, 95% CI 1.00-3.08) and MVT (β=0.39, 95% CI 0.08-0.69) mechanisms were independent risk factors for longer length of stay. mFI-5 was an independent risk factor, in a stepwise fashion, for both length of stay and adverse discharge disposition. CONCLUSIONS:High-energy mechanisms and risk factors for poor skin quality were significantly associated with open fractures. mFI-5 was an independent risk factor for longer length of stay and non-routine discharges in patients of all ages, despite controlling for other comorbidities, unrelated complications, and mechanism of injury. Trauma mechanism was an independent risk factor for prolonged length of stay only, particularly in patients younger than 65 years of age.

BACKGROUND/UNASSIGNED:In properly selected patients, combined face and whole eye transplantation (FWET) may offer a more optimal aesthetic and potentially functional outcome while avoiding the complications and stigma of enucleation and prosthetics. This study presents the most comprehensive cadaveric assessment for FWET to date, including rehearsal allograft procurement on a brain-dead donor. METHODS/UNASSIGNED:Over a 2-year period, 15 rehearsal dissections were performed on 21 cadavers and one brain-dead donor. After identification of a potential recipient, rehearsals assessed clinical feasibility and enabled operative planning, technical practice, refinement of personalized equipment, and improved communication among team members. Operative techniques are described. RESULTS/UNASSIGNED:Facial allograft procurement closely followed previously described face transplant techniques. Ophthalmic to superficial temporal (O-ST) vessel anastomosis for globe survival was assessed. Craniectomy allowed for maximal optic nerve and ophthalmic vessel pedicle length. Appropriate pedicle length and vessel caliber for O-ST anastomosis was seen. Research procurement demonstrated collateral blood flow to the orbit and surrounding structures from the external carotid system as well as confirmed the feasibility of timely O-ST anastomosis. Personalized cutting guides enabled highly accurate bony inset. CONCLUSIONS/UNASSIGNED:This study formalizes an approach to FWET, which is feasible for clinical translation in judiciously selected patients. O-ST anastomosis seems to minimize retinal ischemia time and allow perfusion of the combined allograft on a single external carotid pedicle. Although restoration of vision likely remains out of reach, globe survival is possible.