Thomas R. Howdieshell

Sex differences in susceptibility to ischemia/reperfusion injury have been documented in humans. Premenopausal women have a lower risk of ischemic heart disease than age‐matched men, whereas after menopause, the risk is similar or even higher in women. However, little is known about the effects of sex on myocutaneous ischemia/reperfusion. To explore sex differences in wound revascularization, we utilized a murine myocutaneous flap model of graded ischemia. A cranial‐based, peninsular‐shaped, myocutaneous flap was surgically created on the dorsum of male and female mice. Physiological, pathological, immunohistochemical, and molecular parameters were analyzed. Flaps created on female mice were re‐attached to the recipient site resulting in nearly complete viability at post‐operative day 10. In contrast, distal full‐thickness myocutaneous necrosis was evident at 10 days post‐surgery in male mice. Over the 10 day study interval, laser speckle imaging documented functional revascularization in all flap regions in female mice, but minimal distal flap reperfusion in male mice. Day 10 immunostained histologic sections confirmed significant increases in distal flap vessel count and vascular surface area in female compared to male mice. RT‐PCR demonstrated significant differences in growth factor and metabolic gene expression between female and male mice at day 10. In conclusion, in a graded‐ischemia wound healing model, flap revascularization was more effective in female mice. The recognition and identification of sex‐specific wound healing differences may lead to a better understanding of the underlying mechanisms of myocutaneous revascularization and drive novel discovery to improve soft tissue wound healing following tissue transfer for traumatic injury and cancer resection.

Background: Murine models of diabetes and obesity have provided insight into the pathogenesis of impaired epithelialization of excisional skin wounds. However, knowledge of postischemic myocutaneous revascularization in these models is limited. Materials and methods: A myocutaneous flap was created on the dorsum of wild type (C57BL/6), genetically obese and diabetic (ob/ob, db/db), complementary heterozygous (ob⁺/ob⁻ , db⁺/db⁻), and diet-induced obese (DIO) mice (n=48 total; five operative mice per strain and three unoperated mice per strain as controls). Flap perfusion was documented by laser speckle contrast imaging. Local gene expression in control and postoperative flap tissue specimens was determined by quantitative reverse transcription polymerase chain reaction (RT-PCR). Image analysis of immunochemically stained histologic sections confirmed microvascular density and macrophage presence. Results: Day 10 planimetric analysis revealed mean flap surface area necrosis values of 10.8%, 12.9%, 9.9%, 0.4%, 1.4%, and 23.0% for wild type, db⁺/db⁻, ob⁺/ob⁻, db/db, ob/ob, and DIO flaps, respectively. Over 10 days, laser speckle imaging documented increased perfusion at all time points with revascularization to supranormal perfusion in db/db and ob/ob flaps. In contrast, wild type, heterozygous, and DIO flaps displayed expected graded ischemia with failure of perfusion to return to baseline values. RT-PCR demonstrated statistically significant differences in angiogenic gene expression between lean and obese mice at baseline (unoperated) and at day 10. Conclusion: Unexpected increased baseline skin perfusion and augmented myocutaneous revascularization accompanied by a control proangiogenic transcriptional signature in genetically obese mice compared to DIO and lean mice are reported. In future research, laser speckle imaging has been planned to be utilized in order to correlate spatiotemporal wound reperfusion with changes in cell recruitment and gene expression to better understand the differences in wound microvascular biology in lean and obese states.

Background. Erythropoietin (Epo) and its cognate receptor (EpoR) have been recently identified in nonhematopoietic cells. Epo structural variants, which possess tissue protective effects while exhibiting no effect on erythropoiesis, appear to require a second distinct receptor component, the common receptor (beta cR) of IL-3, IL-5, and GM-CSF for ligand signal transduction. The goal of this work was to determine the temporal and spatial presence of Epo, EpoR, and beta cR in porcine wound fluid and granulation tissue. Methods. A ventral hernia, surgically created in the abdominal wall of female swine (n = 8), was repaired with silicone sheeting and skin closure. Over time, a fluid-filled wound compartment formed, bounded by subcutaneous and omental granulation tissue; its thickness was measured by ultrasonography. Serial wound fluid samples were obtained by percutaneous aspiration. On day 14, the animals were sacrificed. Protein isolated from skin, kidney, granulation tissue, and peritoneal and wound fluids was analyzed by Western blotting. Sections of formalin-fixed abdominal wall tissue were stained for immunoreactivity to Epo, EpoR, and beta cR. Results. A progressive increase in granulation tissue thickness was measured during the 14-day interval. Western blot analysis of serial wound fluid samples demonstrated an 8-fold increase in local wound fluid Epo concentration. Immunoblotting of day 0 skin and day 14 granulation tissue homogenates demonstrated presence of Epo, EpoR, and beta cR in wound granulation tissue but not in control skin. Immunostaining demonstrated localization of Epo and its receptors in granulation endothelial cells, fibroblasts, macrophages, and smooth muscle cells. Conclusion. Temporal expression of soluble Epo was associated with a progressive increase in porcine granulation tissue formation. Receptor expression, spatially localized to cellular constituents of granulation tissue, increased in the wound environment compared to control tissue. Epo variants, which signal via a heteroreceptor complex including both EpoR and beta cR, may be an effective therapeutic approach to improve wound healing.