ABSTRACT
Excessive mechanical forces, particularly skin stretch, have been implicated in pathological cutaneous scarring. We hypothesize that this reflects, in part, stretch-induced vessel leakage that provokes prolonged wound/scar inflammation. However, this has never been observed directly. Here, a mouse model was used to examine the effect of skin flap stretching on vascular permeability. An in vitro model with pseudocapillaries grown in a stretchable chamber was also used to determine the effect of stretching on endothelial cell morphology and ion channel activity. METHODS: Murine skin flaps were stretched with a biaxial stretching device, after which FITC-conjugated-dextran was injected and imaged with fluorescence stereomicroscopy. Endothelial cells were induced to form pseudocapillary networks in an elastic chamber. The chamber was stretched and differential interference contrast microscopy was used to assess cell morphology. In other experiments, markers for Ca2+ influx and K+ efflux were added before a single stretch was conducted. Histamine served as a positive-control in all experiments. RESULTS: Cyclic stretching (20%) increased the vascular permeability of skin flaps almost as strongly as histamine. Both stimuli also partially disrupted the pseudocapillary networks, induced cell contraction, and created gaps between the cells. Both stimuli caused sustained K+ efflux; stretching had a milder effect on Ca2+ influx. CONCLUSIONS: Excessive cyclical stretching strongly increased the vascular permeability of skin vessels and in vitro pseudocapillaries. This effect associated with increased K+ efflux and some Ca2+ influx. Inhibiting such early stretch-induced signaling events may be an effective strategy for treating and preventing hypertrophic scars and keloids.
ABSTRACT
UNLABELLED: Pheochromocytomas and paragangliomas (PPGLs) can be localized by (18)F-FDG PET. The uptake is particularly high in tumors with an underlying succinate dehydrogenase (SDH) mutation. SDHx-related PPGLs are characterized by compromised oxidative phosphorylation and a pseudohypoxic response, which mediates an increase in aerobic glycolysis, also known as the Warburg effect. The aim of this study was to explore the hypothesis that increased uptake of (18)F-FDG in SDHx-related PPGLs is reflective of increased glycolytic activity and is correlated with expression of different proteins involved in glucose uptake and metabolism through the glycolytic pathway. METHODS: Twenty-seven PPGLs collected from patients with hereditary mutations in SDHB (n = 2), SDHD (n = 3), RET (n = 5), neurofibromatosis 1 (n = 1), and myc-associated factor X (n = 1) and sporadic patients (n = 15) were investigated. Preoperative (18)F-FDG PET/CT studies were analyzed; mean and maximum standardized uptake values (SUVs) in manually drawn regions of interest were calculated. The expression of proteins involved in glucose uptake (glucose transporters types 1 and 3 [GLUT-1 and -3, respectively]), phosphorylation (hexokinases 1, 2, and 3 [HK-1, -2, and -3, respectively]), glycolysis (monocarboxylate transporter type 4 [MCT-4]), and angiogenesis (vascular endothelial growth factor [VEGF], CD34) were examined in paraffin-embedded tumor tissues using immunohistochemical staining with peroxidase-catalyzed polymerization of diaminobenzidine as a read-out. The expression was correlated with corresponding SUVs. RESULTS: Both maximum and mean SUVs for SDHx-related tumors were significantly higher than those for sporadic and other hereditary tumors (P < 0.01). The expression of HK-2 and HK-3 was significantly higher in SDHx-related PPGLs than in sporadic PPGLs (P = 0.022 and 0.025, respectively). The expression of HK-2 and VEGF was significantly higher in SDHx-related PPGLs than in other hereditary PPGLs (P = 0.039 and 0.008, respectively). No statistical differences in the expression were observed for GLUT-1, GLUT-3, and MCT-4. The percentage anti-CD 34 staining and mean vessel perimeter were significantly higher in SDHx-related PPGLs than in sporadic tumors (P = 0.050 and 0.010, respectively). Mean SUVs significantly correlated with the expression of HK-2 (P = 0.027), HK-3 (P = 0.013), VEGF (P = 0.049), and MCT-4 (P = 0.020). CONCLUSION: The activation of aerobic glycolysis in SDHx-related PPGLs is associated with increased (18)F-FDG accumulation due to accelerated glucose phosphorylation by hexokinases rather than increased expression of glucose transporters.
