Scott L. Hansen

HOXA3 induces cell migration in endothelial and epithelial cells promoting angiogenesis and wound repair

Wound repair requires both the recruitment and coordination of numerous cell types including inflammatory cells, fibroblasts, endothelial and epithelial cells. Each cell type has a distinct set of cell behavior such as formation of granulation tissue and basement membrane, migration, proliferation and redifferentiation. These processes are dependent on cell-cell and cell-ECM signaling, intracellular signal transduction cascades, and ultimately, changes in gene transcription. We have investigated the role of the transcription factor HOXA3 in wound repair and angiogenesis. Here we show that HOXA3 increases endothelial cell migration, induces angiogenesis in vivo, and leads to increased expression of the matrix metalloproteinase-14 (MMP-14) and urokinase-type plasminogen activator receptor (uPAR) genes in endothelial cells in culture and in vivo in response to injury. We find that HOXA3 gene expression is upregulated during wound healing in angiogenic endothelial cells and keratinocytes, and that HOXA3 is not induced in genetically diabetic mice that have impaired angiogenesis and wound repair. We demonstrate that gene transfer of HOXA3 into diabetic mouse wounds leads to dramatic improvements in both angiogenesis and wound closure. In addition, we show that HOXA3 promotes migration of endothelial cells and keratinocytes in a uPAR-dependent manner. Together these findings illustrate how the morphoregulatory protein, HOXA3 can facilitate tissue remodeling via coordinated changes in both epithelial and endothelial cell gene expression and behavior in adult tissues during wound repair.

HoxD3 Accelerates Wound Healing in Diabetic Mice

Poorly healing diabetic wounds are characterized by diminished collagen production and impaired angiogenesis. HoxD3, a homeobox transcription factor that promotes angiogenesis and collagen synthesis, is up-regulated during normal wound repair whereas its expression is diminished in poorly healing wounds of the genetically diabetic (db/db) mouse. To determine whether restoring expression of HoxD3 would accelerate diabetic wound healing, we devised a novel method of gene transfer, which incorporates HoxD3 plasmid DNA into a methylcellulose film that is placed on wounds created on db/db mice. The HoxD3 transgene was expressed in endothelial cells, fibroblasts, and keratinocytes of the wounds for up to 10 days. More importantly, a single application of HoxD3 to db/db mice resulted in a statistically significant acceleration of wound closure compared to control-treated wounds. Furthermore, we also observed that the HoxD3-mediated improvement in diabetic wound repair was accompanied by increases in mRNA expression of the HoxD3 target genes, Col1A1 and beta 3-integrin leading to enhanced angiogenesis and collagen deposition in the wounds. Although HoxD3-treated wounds also show improved re-epithelialization as compared to control db/db wounds, this effect was not due to direct stimulation of keratinocyte migration by HoxD3. Finally, we show that despite the dramatic increase in collagen synthesis and deposition in HoxD3-treated wounds, these wounds showed normal remodeling and we found no evidence of abnormal wound healing. These results indicate that HoxD3 may provide a means to directly improve collagen deposition, angiogenesis and closure in poorly healing diabetic wounds.

Implantable Venous Doppler Monitoring in Head and Neck Free Flap Reconstruction Increases the Salvage Rate

BACKGROUND Free flap success depends on rapid identification and subsequent salvage of failing flaps. Conventional free flap monitoring techniques require an external component, whereas an implantable monitor readily indicates changes in free flap perfusion, especially in buried flaps used in head and neck reconstruction. METHODS This is a retrospective review of 169 consecutive head and neck free flaps reconstructed mostly for oncologic surgical defects in 155 patients from April of 2000 to December of 2006, all of which were monitored by an implantable venous Doppler device. RESULTS There were 25 buried flaps, representing 14.8 percent of 169 flaps. Flap ischemia caused by thrombosis (n = 16), hematoma (n = 2), or tight closure (n = 1) occurred in 11.2 percent of the cases. The Doppler probe detected all of the failing free flaps, and we were able to salvage 18 of 19 ischemic flaps (94.7 percent). All Doppler-detected ischemic nonburied flaps (100 percent) and three of the four buried free flaps were salvaged (75 percent). There were 33 total complications (19.5 percent), with thrombosis occurring in 9.5 percent of the flaps, whereas 12 flaps required reoperation for vascular revision (7.1 percent). The mortality rate was less than 1 percent (0.6 percent). The overall success rate using the implantable Doppler probe was 98.2 percent, which was similar to that of the most recent reported cases of all free flaps in the literature, with significant improvement in the salvage rate for both buried and nonburied head and neck free flaps. CONCLUSION The implantable Doppler probe is a useful monitoring device in buried free flaps and should be considered for use in head and neck reconstruction.

Human Satellite Cell Transplantation and Regeneration from Diverse Skeletal Muscles

Summary Identification of human satellite cells that fulfill muscle stem cell criteria is an unmet need in regenerative medicine. This hurdle limits understanding how closely muscle stem cell properties are conserved among mice and humans and hampers translational efforts in muscle regeneration. Here, we report that PAX7 satellite cells exist at a consistent frequency of 2–4 cells/mm of fiber in muscles of the human trunk, limbs, and head. Xenotransplantation into mice of 50–70 fiber-associated, or 1,000–5,000 FACS-enriched CD56+/CD29+ human satellite cells led to stable engraftment and formation of human-derived myofibers. Human cells with characteristic PAX7, CD56, and CD29 expression patterns populated the satellite cell niche beneath the basal lamina on the periphery of regenerated fibers. After additional injury, transplanted satellite cells robustly regenerated to form hundreds of human-derived fibers. Together, these findings conclusively delineate a source of bona-fide endogenous human muscle stem cells that will aid development of clinical applications.

HoxD3 expression and collagen synthesis in diabetic fibroblasts

Diabetic wound healing is characterized by deficiencies in both growth factor and collagen production. We have observed that expression of homeobox D3 (HoxD3), a collagen‐inducing transcription factor, and expression of collagen are reduced in an established animal model of diabetic wound repair, the leptin‐deficient diabetic (db/db) mouse. We sought to evaluate whether the diminished expression of collagen and HoxD3 would be maintained once fibroblasts were removed from the diabetic wound environment. Fibroblasts were isolated from both wild‐type and diabetic animals and expression of HoxD3 and collagen assessed. We found that when removed from the diabetic wound environment, HoxD3 and type I collagen expression are increased in diabetic fibroblasts when compared to wild‐type fibroblasts. The increase in type I collagen is not related to increased production or activation of transforming growth factor‐β1. However, when the diabetic fibroblasts are cultured in a 3D collagen matrix, expression of type I collagen and HoxD3 is markedly reduced and reflects the pattern of gene expression observed in the in vivo diabetic wound environment. Thus, although diabetic fibroblasts can regain the capacity to express high levels of collagen and HoxD3 once removed from the diabetic wound environment, culturing cells in the presence of a 3D collagen matrix is sufficient to revert these fibroblasts to their previous nonsynthetic state. (WOUND REP REG 2003;11:474–480)

Superficial temporal artery and vein as recipient vessels for facial and scalp microsurgical reconstruction.

Background: Although free flap transfer is commonly performed to reconstruct defects of the upper two-thirds of the face and scalp, the superficial temporal artery and vein have historically not been considered adequate for microsurgical reconstruction and have rarely been described as recipient vessels. The purpose of this study was to determine the indications for and effectiveness of using the superficial temporal vessels for scalp and face reconstruction. Methods: Retrospective chart review on all patients undergoing microsurgical reconstruction for defects of the upper two-thirds of the face between 1996 and 2003 revealed 45 free tissue transfers in which the superficial temporal artery and vein were considered for use as recipient vessels. Flap success rates and postoperative course were evaluated. Results: Forty-three patients underwent 45 free flap transfers. The superficial temporal artery was used as the recipient artery in every case. In three cases, the superficial temporal vein was not suitable as the recipient vein and required use of a vein in the neck. The median length of follow-up was 4 years. Flap survival was 96 percent. Five patients required reoperation for vascular compromise. One of these patients ultimately had flap failure. In that patient, a subsequent attempt at microvascular flap reconstruction was successful using the same superficial temporal artery and vein as recipient vessels. Conclusions: Use of the superficial temporal artery and vein for scalp and face reconstruction is reliable and safe. The superficial temporal artery and vein should be considered as primary recipient vessels in microsurgical reconstruction of the upper two-thirds of the face and/or scalp.

Effects of decreased insulin-like growth factor-1 stimulation on hypoxia inducible factor 1-α protein synthesis and function during cutaneous repair in diabetic mice

Insulin‐like growth factor‐1 (Igf‐1), a critical mediator of tissue repair, is significantly decreased in diabetic wounds. Furthermore, decreased levels of hypoxia‐inducible factor 1‐α (Hif‐1α) and its target genes are also associated with impaired wound healing in diabetic mice. The aim of our study was to examine whether the reduced levels of Igf‐1 are responsible for the reduction in Hif‐1α protein synthesis and activity in diabetic wounds. We provide evidence that Igf‐1 regulates Hif‐1α protein synthesis and activity during wound repair. In addition, Igf‐1 stimulated phosphytidylinositol 3‐kinase activity in diabetic fibroblasts, which, in turn, increased activation of the translational regulatory protein, p70 S6 kinase. Moreover, improved healing of diabetic wounds by addition of recombinant IGF‐1 protein was associated with an increase in Hif‐1α protein synthesis and function in vivo.

Outcomes Analysis of Biologic Mesh Use for Abdominal Wall Reconstruction in Clean-Contaminated and Contaminated Ventral Hernia Repair.

BackgroundRepair of grade 3 and grade 4 ventral hernias is a distinct challenge, given the potential for infection, and the comorbid nature of the patient population. This study evaluates our institutional outcomes when performing single-stage repair of these hernias, with biologic mesh for abdominal wall reinforcement. MethodsA prospectively maintained database was reviewed for all patients undergoing repair of grade 3 (potentially contaminated) or grade 4 (infected) hernias, as classified by the Ventral Hernia Working Group. All those patients undergoing repair with component separation techniques and biologic mesh reinforcement were included. Patient demographics, comorbidities, and postoperative complications were analyzed. Univariate analysis was performed to define factors predictive of hernia recurrence and wound complications. ResultsA total of 41 patients underwent single-stage repair of grade 3 and grade 4 hernias during a 4-year period. The overall postoperative wound infection rate was 15%, and hernia recurrence rate was 12%. Almost all recurrences were seen in grade 4 hernia repairs, and in those patients undergoing bridging repair of the hernia. One patient required removal of the biologic mesh. Those factors predicting hernia recurrence were smoking (P = 0.023), increasing body mass index (P = 0.012), increasing defect size (P = 0.010), and bridging repair (P = 0.042). No mesh was removed due to perioperative infection. Mean follow-up time for this patient population was 25 months. ConclusionsSingle-stage repair of grade 3 hernias performed with component separation and biologic mesh reinforcement is effective and offers a low recurrence rate. Furthermore, the use of biologic mesh allows for avoidance of mesh explantation in instances of wound breakdown or infection. Bridging repairs are associated with a high recurrence rate, as is single-stage repair of grade 4 hernias.

Management of Acute Wounds

The acute wound presents a spectrum of issues that prevent its ultimate closure. These issues include host factors, etiology, anatomic location, timing, and surgical techniques to achieve successful wound closure. Basic surgical principles need to be followed to obtain stable, long-term coverage, ultimately restoring form and function. Recent advances in dressings, debridement techniques, and surgical repertoire allow the modern plastic surgeon to address any wound of any complexity. This article discusses these principles that can be applied to any wound.

Reconstruction of congenital differences of the hand.

Summary: Congenital differences of the upper limb occur in approximately 0.16 to 0.18 percent of live births. These patients provide a unique challenge for the reconstructive hand surgeon. The correct and timely diagnosis of hand and upper limb congenital differences will lead to appropriate care and rehabilitation. The International Federation of Societies for Surgery of the Hand has classified congenital upper limb differences based on abnormalities of embryogenesis: failure of formation of parts, failure of differentiation of parts, duplication, overgrowth, undergrowth, constriction ring syndrome, and general skeletal abnormalities. This classification scheme is used as a basis for discussion of the most common upper limb anomalies. Both surgical and nonsurgical treatments are discussed, as is appropriate timing of intervention.