Objective: Chronic wounds represent a considerable burden for the affected patients and the health care system. To overcome this problem, effective treatment strategies are urgently required. In this study, we tested a novel approach by combining platelet-rich plasma (PRP) and microvascular fragments (MVF) to create a prevascularized gel dressing. Approach: MVF were enzymatically isolated from the epididymal fat pads of transgenic green fluorescent protein (GFP) ⁺ C57BL/6J donor mice. Subsequently, 5,000 MVF were suspended in 10 μL murine PRP as carrier and transferred into full-thickness skin wounds within dorsal skinfold chambers of C57BL/6J wild-type mice (PRP+MVF). Wound healing in comparison to empty wounds (control) and wounds filled with PRP alone was repeatedly analyzed throughout 14 days by means of stereomicroscopy, histology, and immunohistochemistry. Results: Planimetric assessment of the wound size over time revealed a significantly accelerated and improved healing of PRP+MVF-treated wounds when compared with PRP-treated and empty control wounds. These wounds also exhibited a significantly higher density of blood and lymph vessels, which originated from the GFP ⁺ MVF isolates and effectively promoted granulation tissue formation inside the skin defects. Innovation: This study is the first to combine PRP and MVF for the improvement of wound healing. Conclusion: The combination of PRP and MVF represents a promising approach for the future treatment of wounds that do not heal spontaneously due to poor wound-healing conditions.

Heat preconditioning has been shown to promote nutritive perfusion and tissue survival in autologous fat grafting as well as in flap and breast surgery. However, its impact on the vascularization properties of nanofat has not been investigated so far. Therefore, we exposed nanofat from donor mice to a temperature of 43 °C for 1 h and assessed the effects of this heat stress on cell viability and the expression of heat shock proteins (HSPs) and angiogenesis-related factors. Moreover, dermal substitutes seeded with heat-preconditioned and non-preconditioned control nanofat were implanted into dorsal skinfold chambers of recipient mice to study their vascularization and tissue integration in vivo by means of repeated intravital fluorescence microscopy, histology and immunohistochemistry. Heat preconditioning upregulated the expression of HSPs in nanofat without affecting cell viability. Moreover, it resulted in the downregulation of many pro-angiogenic factors and the increased expression of anti-angiogenic factors, indicating a shift towards an anti-angiogenic phenotype. Accordingly, implanted dermal substitutes seeded with heat-preconditioned nanofat exhibited a reduced vascularization and were not better integrated into the host tissue when compared to controls. These findings indicate that heat preconditioning cannot be recommended for enhancing the vascularization capacity of nanofat.

Islet transplantation can improve glycemic control in a subset of patients with type 1 diabetes mellitus (T1DM). This therapeutic approach is often limited by scarcity of adequate donor islets and an insufficient revascularization capacity of grafted islets. Recent findings reveal that sex is an important determinant for the outcome of islet transplantation. However, it is still unknown how the biological sex of islet donors and recipients affects the revascularization of the grafts during the initial ischemic post-transplantation phase. In this study, we observed in a mouse dorsal skinfold chamber model a higher revascularization capacity of female islets transplanted in female or male recipient mice when compared to male islets transplanted in female or male recipients. To mimic the ischemic in vivo conditions ex vivo, we subjected isolated female and male islets to oxygen-glucose deprivation. Under these conditions female islets expressed and secreted significantly more glucagon (GCG). By a panel of functional angiogenesis assays, we could further demonstrate that GCG exhibits a strong pro-angiogenic function. This effect was pronounced in blood vessels as well as endothelial cells and pericytes of female origin due to a higher expression of GCG receptor. Taken together, these results not only confirm the clinical observation that transplantation of female islets improves the outcome of islet transplantation but also indicate that this is mediated by an accelerated GCG-driven islet engraftment.

Clinical islet transplantation is limited by ischemia-induced islet cell death. Recently, it has been reported that the absent in melanoma (AIM)2 inflammasome is upregulated by ischemic cell death due to recognition of aberrant cytoplasmic self-dsDNA. However, it is unknown whether AIM2 determines the outcome of islet transplantation. To investigate this, isolated wild type (WT) and AIM2-deficient (AIM2^−/−) islets were exposed to oxygen-glucose deprivation to mimic ischemia, and their viability, endocrine function, and interferon (IFN) signaling were assessed. Moreover, the revascularization and endocrine function of grafted WT and AIM2^−/− islets were analyzed in the mouse dorsal skinfold chamber model and the diabetic kidney capsule model. Ischemic WT and AIM2^−/− islets did not differ in their viability. However, AIM2^−/− islets exhibited a higher protein level of p202, a transcriptional regulator of IFN-β and IFN-γ gene expression. Accordingly, these cytokines were upregulated in AIM2^−/− islets, resulting in a suppressed gene expression and secretion of insulin. Moreover, the revascularization of AIM2^−/− islet grafts was deteriorated when compared to WT controls. Furthermore, transplantation of AIM2^−/− islets in diabetic mice failed to restore physiological blood glucose levels. These findings indicate that AIM2 crucially determines the engraftment and endocrine function of transplanted islets by repressing IFN signaling.

Surgical sutures are widely used biomaterials in clinical practice. Like all other biomaterials, they induce a foreign body response after implantation that involves inflammation and angiogenesis. Although it is well known that these processes differ in males and females, sex-specific differences in the tissue response to sutures have not been investigated so far. To do this in the present study, polypropylene sutures were implanted into the dorsal skinfold chamber and subcutaneous flank tissue of male and female mice to assess their acute and chronic effects on the local tissue microenvironment using intravital fluorescence microscopy and immunohistochemistry over 14 and 28 days, respectively. Microhemodynamic parameters and the numbers of rolling and adherent leukocytes in venules next to the implants were comparable in male and female mice. Immunohistochemical analyses on day 14 revealed a stronger neutrophilic (myeloperoxidase (MPO)⁺ cells: 526 ± 29 mm⁻²) and macrophage (CD86⁺ cells: 188 ± 21 mm⁻²; CD163⁺ cells: 269 ± 25 mm⁻²) response, as well as reduced T-cell activation (CD3⁺ cells: 31 ± 4 mm⁻²) in females when compared to males (MPO⁺ cells: 221 ± 25 mm⁻²; CD86⁺ cells: 120 ± 15 mm⁻²; CD163⁺ cells: 101 ± 19 mm⁻²; CD3⁺ cells: 62 ± 13 mm⁻²), while microvessel density and collagen deposition in the forming granulation tissue around the implants did not differ between sexes. In the flank model, there were no detectable sex-specific differences in the chronic foreign body response. These findings demonstrate that polypropylene sutures provoke a stronger early activation of the innate immune system in females, whereas the chronic foreign body response to the implants is comparable in both sexes.

Hypoxic preconditioning is increasingly explored to enhance the survival and vascularization of fat grafts. In this study, nanofat from donor mice was exposed to hypoxia (1% O₂) for 24 h to investigate the effects of this preconditioning protocol on the viability, gene expression and vascularization capacity of this mechanically processed fat derivative. Ex vivo analyses revealed that hypoxic preconditioning does neither affect apoptotic nor necrotic cell death within nanofat but significantly upregulates the expression of hypoxia-inducible factor (HIF)-1α and stromal cell-derived factor (SDF)-1 compared to non-preconditioned nanofat. Moreover, preconditioned nanofat exhibited a pro-angiogenic protein expression profile. For in vivo analyses, dermal substitutes were either seeded with preconditioned or non-preconditioned nanofat and transferred into dorsal skinfold chambers of mice to assess their vascularization by intravital fluorescence microscopy. Unexpectedly, implants seeded with preconditioned nanofat exhibited a significantly reduced functional microvessel density when compared to non-preconditioned controls. Immunohistochemical analyses also confirmed a lower microvessel density within the implants of the preconditioned group. These findings suggest that hypoxic preconditioning at 1% O₂ for 24 h cannot be recommended for enhancing the regenerative in vivo vascularization capacity of nanofat. Therefore, milder preconditioning protocols with shorter periods of hypoxia or higher oxygen levels should be alternatively tested in future studies.