Erythropoietin-induced upregulation of endothelial nitric oxide synthase but not vascular endothelial growth factor prevents musculocutaneous tissue from ischemic damage

Paeoniflorin Suppresses TBHP-Induced Oxidative Stress and Apoptosis in Human Umbilical Vein Endothelial Cells via the Nrf2/HO-1 Signaling Pathway and Improves Skin Flap Survival

Random-pattern skin flap is a vital technique frequently applied in reconstruction surgeries for its convenience and effectiveness in solving skin defects. However, ischemic necrosis, especially in the distal areas of the flap, still needs extra attention after surgery. Earlier evidence has suggested that paeoniflorin (PF) could stimulate angiogenesis and suppress ischemic cardiovascular disease. However, few studies have focused on the role of PF in flap survival. In this study, we have demonstrated that the human umbilical vein endothelial cells (HUVECs) treated with PF can alleviate tert-butyl hydroperoxide (TBHP)-stimulated cellular dysfunction and apoptosis. To better evaluate, HUVECs' physiology, cell tube formation, migration, and adhesion were assessed. Mechanistically, PF protects HUVECs against apoptosis via stimulating the nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/heme oxygenase 1 (HO-1) pathway. PF also downregulates mitochondrial ROS production to reduce excessive intracellular ROS production induced by TBHP and restore TBHP-induced mitochondrial depolarization. As a result, silencing Nrf2 partially abolishes the protective effect of PF exposure on HUVECs. In in vivo experiments, the oral administration of PF was shown to have enhanced the vascularization of regenerated tissues and promote flap survival. However, the PF-mediated protection was partially lost after co-treatment with ML385, a selective Nrf2 inhibitor, suggesting that PF is a crucial modulator regulating the Nrf2/HO-1 signaling pathway. In summary, our data have provided a new insight into PF as a potential therapy for enhancing random-pattern flap viability.

Vascularization Strategies in the Prevention of Nonunion Formation

Delayed healing and nonunion formation are major challenges in orthopedic surgery, which require the development of novel treatment strategies. Vascularization is considered one of the major prerequisites for successful bone healing, providing an adequate nutrient supply and allowing the infiltration of progenitor cells to the fracture site. Hence, during the last decade, a considerable number of studies have focused on the evaluation of vascularization strategies to prevent or to treat nonunion formation. These involve (1) biophysical applications, (2) systemic pharmacological interventions, and (3) tissue engineering, including sophisticated scaffold materials, local growth factor delivery systems, cell-based techniques, and surgical vascularization approaches. Accumulating evidence indicates that in nonunions, these strategies are indeed capable of improving the process of bone healing. The major challenge for the future will now be the translation of these strategies into clinical practice to make them accessible for the majority of patients. If this succeeds, these vascularization strategies may markedly reduce the incidence of nonunion formation. Impact statement Delayed healing and nonunion formation are a major clinical problem in orthopedic surgery. This review provides an overview of vascularization strategies for the prevention and treatment of nonunions. The successful translation of these strategies in clinical practice is of major importance to achieve adequate bone healing.

Erythropoietin accelerates the revascularization of transplanted pancreatic islets

BACKGROUND AND PURPOSE

Pancreatic islet transplantation is a promising therapeutic approach for Type 1 diabetes. A major prerequisite for the survival of grafted islets is a rapid revascularization after transplantation. Erythropoietin (EPO), the primary regulator of erythropoiesis, has been shown to promote angiogenesis. Therefore, we investigated in this study whether EPO improves the revascularization of transplanted islets.

EXPERIMENTAL APPROACH

Islets from FVB/N mice were transplanted into dorsal skinfold chambers of recipient animals, which were daily treated with an intraperitoneal injection of EPO (500 IU·kg^-1 ) or vehicle (control) throughout an observation period of 14 days. In a second set of experiments, animals were only pretreated with EPO over a 6-day period prior to islet transplantation. The revascularization of the grafts was assessed by repetitive intravital fluorescence microscopy and immunohistochemistry. In addition, a streptozotocin-induced diabetic mouse model was used to study the effect of EPO-pretreatment on the endocrine function of the grafts.

KEY RESULTS

EPO treatment slightly accelerated the revascularization of the islet grafts. This effect was markedly more pronounced in EPO-pretreated animals, resulting in significantly higher numbers of engrafted islets and an improved perfusion of endocrine tissue without affecting systemic haematocrit levels when compared with controls. Moreover, EPO-pretreatment significantly accelerated the recovery of normoglycaemia in diabetic mice after islet transplantation.

CONCLUSION AND IMPLICATIONS

These findings demonstrate that, particularly, short-term EPO-pretreatment represents a promising therapeutic approach to improve the outcome of islet transplantation, without an increased risk of thromboembolic events.

Ischemic tissue injury in the dorsal skinfold chamber of the mouse: a skin flap model to investigate acute persistent ischemia

Despite profound expertise and advanced surgical techniques, ischemia-induced complications ranging from wound breakdown to extensive tissue necrosis are still occurring, particularly in reconstructive flap surgery. Multiple experimental flap models have been developed to analyze underlying causes and mechanisms and to investigate treatment strategies to prevent ischemic complications. The limiting factor of most models is the lacking possibility to directly and repetitively visualize microvascular architecture and hemodynamics. The goal of the protocol was to present a well-established mouse model affiliating these before mentioned lacking elements. Harder et al. have developed a model of a musculocutaneous flap with a random perfusion pattern that undergoes acute persistent ischemia and results in ~50% necrosis after 10 days if kept untreated. With the aid of intravital epi-fluorescence microscopy, this chamber model allows repetitive visualization of morphology and hemodynamics in different regions of interest over time. Associated processes such as apoptosis, inflammation, microvascular leakage and angiogenesis can be investigated and correlated to immunohistochemical and molecular protein assays. To date, the model has proven feasibility and reproducibility in several published experimental studies investigating the effect of pre-, peri- and postconditioning of ischemically challenged tissue.

Endothelial nitric oxide synthase mediates the cerebrovascular effects of erythropoietin in traumatic brain injury

Background: Erythropoietin (Epo) improves post-traumatic cerebral blood flow (CBF), pressure autoregulation, and vascular reactivity to l-arginine. This study examines the dependence of these cerebral hemodynamic effects of Epo on nitric oxide generated by endothelial nitric oxide synthase (eNOS).

Methods: Using laser Doppler flow imaging, CBF was monitored in wild-type (WT) and eNOS-deficient mice undergoing controlled cortical impact followed by administration of Epo (5000 U/kg) or normal saline.

Results: Cerebral blood flow decreased in all groups post-injury with the greatest reductions occurring at the impact site. Epo administration resulted in significantly higher CBF in the peri-contusional sites in the WT mice [70.2 ± 3.35% in Epo-treated compared to 53 ± 3.3% of baseline in saline-treated mice (p < 0.0001)], but no effect was seen in the eNOS-deficient mice. No CBF differences were found at the core impact site where CBF dropped to 20–25% of baseline in all groups.

Conclusion: These differences between eNOS-deficient and WT mice indicate that the Epo mediated improvement in CBF in traumatic brain injury is eNOS dependent.

Erythropoietin promotes retinal angiogenesis in a mouse model

This study aimed to investigate the effect and potential mechanisms of exogenous administration of recombinant human erythropoietin (rhEPO) on retinal angiogenesis in a mouse model of oxygen-induced retinopathy (OIR). Postnatal day 7 (P7) mice (n=132) were randomly assigned to one of six groups: Control group (n=22), OIR group (n=22), OIR + vehicle control group (n=22), OIR + rhEPO 10 IU group (n=22), OIR + rhEPO 50 IU group (n=22), and OIR + rhEPO 100 IU group (n=22). OIR was induced by exposing mice to 75±2% O2 for five days, followed by exposure to room air for a further five days. Animals in groups 3-6 (the OIR + vehicle control group and OIR + rhEPO 10 IU, 50 IU, and 100 IU groups) received an intraperitoneal injection of saline, or rhEPO 10 IU, 50 IU and 100 IU, respectively, which were administered daily from P7-P12. Immunofluorescent and hematoxylin-eosin staining were used to detect retinal neovascularization (RNV) in retinal whole mounts. Quantitative polymerase chain reaction and western blot analysis were used to detect the expression levels of vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), and neuronal nitric oxide synthase (nNOS). RNV occurred in the OIR groups and was accompanied by dilated, twisted and occluded blood vessels. rhEPO treatment resulted in an increase in the number of newly formed and severely dilated vessels. rhEPO increased RNV in a dose-dependent manner, which was accompanied by an increase in the messenger RNA and protein expression of VEGF, eNOS and nNOS. Thus, exogenous use of rhEPO promotes the RNV in a mouse model of OIR and is accompanied by increased expression levels of VEGF, eNOS and nNOS.

Systemic treatment with erythropoietin protects the neurovascular unit in a rat model of retinal neurodegeneration

Rats expressing a transgenic polycystic kidney disease (PKD) gene develop photoreceptor degeneration and subsequent vasoregression, as well as activation of retinal microglia and macroglia. To target the whole neuroglialvascular unit, neuro- and vasoprotective Erythropoietin (EPO) was intraperitoneally injected into four –week old male heterozygous PKD rats three times a week at a dose of 256 IU/kg body weight. For comparison EPO-like peptide, lacking unwanted side effects of EPO treatment, was given five times a week at a dose of 10 µg/kg body weight. Matched EPO treated Sprague Dawley and water-injected PKD rats were held as controls. After four weeks of treatment the animals were sacrificed and analysis of the neurovascular morphology, glial cell activity and pAkt localization was performed. The number of endothelial cells and pericytes did not change after treatment with EPO or EPO-like peptide. There was a nonsignificant reduction of migrating pericytes by 23% and 49%, respectively. Formation of acellular capillaries was significantly reduced by 49% (p<0.001) or 40% (p<0.05). EPO-treatment protected against thinning of the central retina by 10% (p<0.05), a composite of an increase of the outer nuclear layer by 12% (p<0.01) and in the outer segments of photoreceptors by 26% (p<0.001). Quantification of cell nuclei revealed no difference. Microglial activity, shown by gene expression of CD74, decreased by 67% (p<0.01) after EPO and 36% (n.s.) after EPO-like peptide treatment. In conclusion, EPO safeguards the neuroglialvascular unit in a model of retinal neurodegeneration and secondary vasoregression. This finding strengthens EPO in its protective capability for the whole neuroglialvascular unit.

Erythropoietin action in stress response, tissue maintenance and metabolism

Erythropoietin (EPO) regulation of red blood cell production and its induction at reduced oxygen tension provides for the important erythropoietic response to ischemic stress. The cloning and production of recombinant human EPO has led to its clinical use in patients with anemia for two and half decades and has facilitated studies of EPO action. Reports of animal and cell models of ischemic stress in vitro and injury suggest potential EPO benefit beyond red blood cell production including vascular endothelial response to increase nitric oxide production, which facilitates oxygen delivery to brain, heart and other non-hematopoietic tissues. This review discusses these and other reports of EPO action beyond red blood cell production, including EPO response affecting metabolism and obesity in animal models. Observations of EPO activity in cell and animal model systems, including mice with tissue specific deletion of EPO receptor (EpoR), suggest the potential for EPO response in metabolism and disease.

Secondary burn progression decreased by erythropoietin

OBJECTIVE

To investigate whether systemic erythropoietin administration can prevent secondary burn progression in an experimental model and to elucidate the underlying mechanisms.

DESIGN

Prospective study.

SETTING

University-based laboratory research.

SUBJECTS

Twenty-one male Wistar rats.

INTERVENTIONS

The burn comb model creates four rectangular burned surfaces that are intercalated by three unburned zones (interspaces) prone to secondary necrosis. Twenty-one animals were randomized to three experimental groups: 1) Local cooling with water for 20 minutes (control, 17°C); 2) and 3) local cooling with water and intraperitoneal erythropoietin once a day for five days starting 45 minutes after burn injury (500 IU/kg body weight: EPO 500 or 2500 IU/kg body weight: EPO 2500).

MEASUREMENTS AND MAIN RESULTS

Secondary burn progression-both in depth (histology) and in surface (planimetry)-as well as interspace perfusion (laser Doppler flowmetry) and hematocrit were analyzed. Further, dilatory response (inducible nitric oxide synthase expression), inflammation (leukocyte count), and angiogenesis (CD31 expression) were assessed. Finally, wound healing time and contracture rate were reported. Burn progression resulted in complete dermal destruction as well as in important interspace necrosis in control animals, whereas burn progression was significantly reduced in a dose-dependent manner in animals treated with erythropoietin. Tissue protection was associated with an increased interspace perfusion with EPO 500, but not with EPO 2500, and was paralleled by a significant increase in inducible nitric oxide synthase expression and decreased inflammation, independent of the erythropoietin dosage. EPO 2500 led to a significant increase of hematocrit at day 4. Finally, faster wound healing and less contracture were observed in animals treated with EPO 500 only.

CONCLUSIONS

Erythropoietin represents an easy-to-use therapeutic approach to prevent secondary burn progression, i.e., to control damage after burn injury. It preserves microcirculatory perfusion within the endangered areas in a dose-dependent manner.

A multi-center study on the regenerative effects of erythropoietin in burn and scalding injuries: study protocol for a randomized controlled trial

Background

Although it was initially assumed that erythropoietin (EPO) was a hormone that only affected erythropoiesis, it has now been proposed that EPO plays an additional key role in the regulation of acute and chronic tissue damage.

Via the inhibition of inflammatory reactions and of apoptosis, stem cell recruitment, advancement of angiogenesis and growth factor release, EPO enhances healing and thus restitutio ad integrum after trauma. Human skin contains EPO receptors and is able to synthesize EPO. We therefore hypothesize that EPO is able to optimize wound healing in thermally injured patients.

Methods/Design

This is a large, prospective, randomized, double-blind, multi-center study, funded by the German Federal Ministry of Education and Research, and fully approved by the designated ethics committee. The trial, which is to investigate the effects of EPO in severely burned patients, is in its recruitment phase and is being carried out in 13 German burn care centers. A total of 150 patients are to be enrolled to receive study medication every other day for 21 days (EPO 150 IU/kg body weight or placebo). A follow-up of one year is planned. The primary endpoint of this study is the time until complete re-epithelialization of a defined skin graft donor site is reached. Furthermore, clinical parameters such as wound healing, scar formation (using the Vancouver scar scale), laboratory values, quality of life (SF-36), angiogenic effects, and gene- and protein-expression patterns are to be determined. The results will be carefully evaluated for gender differences.

Discussion

We are seeking new insights into the mechanisms of wound healing in thermally injured patients and more detailed information about the role EPO plays, specifically in these complex interactions. We additionally expect that the biomimetic effects of EPO will be useful in the treatment of acute thermal dermal injuries.

Trial registration

EudraCT Number: 2006-002886-38, Protocol Number: 0506, ISRCT Number: http://controlled-trials.com/ISRCTN95777824/ISRCTN95777824.

Bevacizumab diminishes experimental autoimmune encephalomyelitis by inhibiting spinal cord angiogenesis and reducing peripheral T-cell responses

Angiogenesis in the animal model of multiple sclerosis experimental autoimmune encephalomyelitis (EAE) is regulated by vascular endothelial growth factor (VEGF) and angiopoietin-2. We determined whether VEGF blockade with the anti-VEGF monoclonal antibody bevacizumab could inhibit angiogenesis and affect peripheral pathogenic immune responses in EAE. Mice treated with bevacizumab from the time of onset of clinical signs showed reduced clinical and pathologic scores. Bevacizumab suppressed angiogenesis and reduced angiopoietin-2 expression at Day 21 but had no effect on VEGF upregulation at Day 14. Messenger RNA levels for the angiogenesis-related protein CD105 were increased at Day 14. Bevacizumab reduced vascular permeability in the spinal cord at Day 14 and Day 21. In peripheral lymph nodes, it induced retention of CD4-positive T cells and inhibited T-cell proliferation. It also reduced mononuclear cell infiltration into spinal cord and the relative proportion of T cells. Isolated lymphoid cells showed reduced secretion of the T-helper 17 (Th-17) cell cytokine interleukin 17 and the Th-1 cytokine interferon-γ. When bevacizumab was added to naive T cells or to antigen-stimulated T cells from mice with untreated EAE in vitro, it had no effect on proliferation or the secretion of interleukin 17 or interferon-γ. These data indicate that bevacizumab ameliorates vascular and T-cell responses during EAE, but its effects on T cells may be indirect, possibly by suppressing angiogenesis.

Prevention of arthrofibrosis by monoclonal antibody against vascular endothelial growth factor: a novel use of bevacizumab in rabbits

BACKGROUND

Prevention of arthrofibrosis by different drugs and surgical techniques is an essential issue in modern orthopedics.

HYPOTHESIS

Intra-articular injection of bevacizumab can reduce arthrofibrosis on the rabbit's stifle joint model.

MATERIALS AND METHODS

Arthrofibrosis was induced in the right stifle joint of thirty male New Zealand white rabbits by removing the cortical bone of the medial femoral condyle under general anesthesia. The rabbits were randomly divided into three equal groups. The control group received intra-articular injection of saline; the one-injection group received a single dose of bevacizumab (2.5mg/kg), and the two-injection group received two intra-articular injections; the operation day and 14 days later. Forty-five days after surgery, animals were sacrificed. The severity of fibrosis was assessed based on the range of motion of the joint, a macroscopic adhesion score, and histopathologic variables such as the number of fibroblasts and of inflammatory cells, collagenous matrix deposition, synovial hyperplasia, granulation tissue formation, vascular proliferation, and presence of giant cells.

RESULTS

Although no statistically significant differences were found between the range of motion (P=0.222) and the macroscopic evaluation (P=0.067) of the control group and the one-injection group, all microscopic variables regarding the prevention of arthrofibrosis were significantly superior in the one-injection group except granulation tissue (P=0.347). Compared to the one-injection group, the two-injection group had better results not only in terms of macroscopic evaluation (P=0.001 for range of motion and 0.012 for visual adhesion score) but also in most of the histopathologic variables especially the number of fibroblasts (P=0.002), vascularity (P=0.028) and collagenous matrix deposition (P=0.039).

CONCLUSION

A single intra-articular injection of bevacizumab was effective for prevention of microscopically detected arthrofibrosis in the rabbit. Compared to single injection, two injections of bevacizumab improved the clinical outcome.

LEVEL OF EVIDENCE

Level II.

Erythropoietin in the prevention of experimental burn progression

Background

Damage control is essential in first aid of burn lesions. The aim of the present study was to investigate whether systemic erythropoietin (EPO) administration could prevent secondary burn progression in an experimental model.

Methods

The burn comb model creates four rectangular burn surfaces intercalated by three unburned zones prone to progression. Twenty-one Wistar rats were randomized to a control group or to receive intraperitoneal EPO (500 units per kg) once a day for 5 days starting 45 min (EPO45min) or 6 h (EPO6h) after burn injury. Histological analyses assessing burn depth, inflammation and neoangiogenesis, planimetric evaluation of burn progression, and laser Doppler flowmetry to assess perfusion were performed after 1, 4 and 7 days. Final scarring time and contracture rate were assessed once a week.

Results

Burn progression was decreased significantly with EPO45min but not EPO6h; progression of burn depth stopped in the intermediate dermis (mean(s.e.m.) burn depth score 3·3(0·6) for EPO45min versus 4·7(0·3) and 5·0(0·0) for EPO6h and control respectively on day 7; P = 0·026) and the surface extension was significantly reduced (45(8), 65(4) and 78(4) respectively on day 7; P = 0·017). This was paralleled by faster re-establishment of perfusion with EPO45min (114(5) per cent on day 4 versus 85(6) and 91(3) per cent for EPO6h and control respectively; P = 0·096). The reduction in progression resulted in a decreased healing time (7·3(0·7) weeks for EPO45min versus 11·5(1·0) and 10·8(0·5) weeks for EPO6h and control; P = 0·020) and contracture rate (P = 0·024).

Conclusion

Early EPO prevented burn progression, mainly by improved vascular perfusion.

The nonhematopoietic effects of erythropoietin in skin regeneration and repair: from basic research to clinical use

Erythropoietin (EPO) is the main regulator of red blood cell production but there exists also a variety of nonhematopoietic properties. More recent data show that EPO is also associated with the protection of tissues suffering from ischemia and reperfusion injury as well as with improved regeneration in various organ systems, in particular the skin. This review highlights the mechanisms of EPO in the different stages of wound healing and the reparative processes in the skin emphasizing pathophysiological mechanisms and potential clinical applications. There is clear evidence that EPO effectively influences all wound-healing phases in a dose-dependent manner. This includes inflammation, tissue, and blood vessel formation as well as the remodeling of the wound. The molecular mechanism is predominantly based on an increased expression of the endothelial and inducible nitric oxide (NO) synthase with a consecutive rapid supply of NO as well as an increased content of vascular endothelial growth factor (VEGF) in the wound. The improved understanding of the functions and regulatory mechanisms of EPO in the context of wound-healing problems and ischemia/reperfusion injury, especially during flap surgery, may lead to new considerations of this growth hormone for its regular clinical application in patients.

Ghrelin protects musculocutaneous tissue from ischemic necrosis by improving microvascular perfusion

Persistent ischemia in musculocutaneous tissue may lead to wound breakdown and necrosis. The objective of this experimental study was to analyze, whether the gastric peptide ghrelin prevents musculocutaneous tissue from necrosis and to elucidate underlying mechanisms. Thirty-two C57BL/6 mice equipped with a dorsal skinfold chamber containing ischemic musculocutaneous tissue were allocated to four groups: 1) ghrelin; 2) Nω-nitro-l-arginine methyl ester (l-NAME); 3) ghrelin and l-NAME; and 4) control. Microcirculation, inflammation, angiogenesis, and tissue survival were assessed by fluorescence microscopy. Inducible and endothelial nitric oxide synthase (iNOS I and eNOS), vascular endothelial growth factor (VEGF), as well as nuclear factor κB (NF-κB) were assessed by Western blot analysis. Ghrelin-treated animals showed an increased expression of iNOS and eNOS in critically perfused tissue compared with controls. This was associated with arteriolar dilation, increased arteriolar perfusion, and a sustained functional capillary density. Ghrelin further upregulated NF-κB and VEGF and induced angiogenesis. Finally, ghrelin reduced microvascular leukocyte-endothelial cell interactions, apoptosis, and overall tissue necrosis ( P < 0.05 vs. control). Inhibition of nitric oxide by l-NAME did not affect the anti-inflammatory and angiogenic action of ghrelin but completely blunted the ghrelin-induced tissue protection by abrogating the arteriolar dilation, the improved capillary perfusion, and the increased tissue survival. Ghrelin prevents critically perfused tissue from ischemic necrosis. Tissue protection is the result of a nitric oxide synthase-mediated improvement of the microcirculation but not due to induction of angiogenesis or attenuation of inflammation. This might represent a promising, noninvasive, and clinically applicable approach to protect musculocutaneous tissue from ischemia.

Darbepoetin enhances endothelium-dependent vasomotor function in patients with stable coronary artery disease only after preceding ischaemia/reperfusion

Vasoprotective effects of erythropoietin in animal models are mediated by endothelium-derived NO and/or mobilization of EPCs (endothelial progenitor cells) and may be enhanced by ischaemia: whether they are present in humans is unknown. We examined whether the erythropoietin analogue darbepoetin improves FMD (flow-mediated dilatation), a measure of endothelium-derived NO, and whether this is influenced by preceding I/R (ischaemia/reperfusion). A total of 36 patients (50–75 years) with stable coronary artery disease were randomized to receive a single dose of darbepoetin (300 μg) or saline placebo. FMD was measured at the brachial artery using high-resolution ultrasound. CD133+/CD34+/VEGFR2+ (vascular endothelial growth factor receptor 2) circulating EPCs were enumerated by flow cytometry. Measurements were made immediately before darbepoetin/placebo and at 24 h, 72 h and 7 days. At 24 h, FMD was repeated after 20 min of I/R of the upper limb. A further group of 11 patients was studied according to the same protocol, all receiving darbepoetin, with omission of forearm I/R at 24 h. Immunoreactive erythropoietin peaked at 24 h and remained elevated at approximately 50-fold of baseline at 72 h. FMD did not differ significantly between groups at 24 h (before I/R). At 72 h (48 h after I/R), FMD was greater (by 2.3±0.5% in the darbepoetin compared with the placebo group, a 66% increase over baseline; P<0.001) and greater than FMD at the same time point without preceding I/R (P<0.01). Increases in CD133+/CD34+/VEGFR2+ cells after darbepoetin did not differ according to the presence or absence of preceding I/R. Preceding I/R is required for darbepoetin to enhance endothelial function, possibly by increasing expression of the erythropoietin receptor and by a mechanism likely to involve Akt/NO rather than circulating EPCs.

Epo is relevant neither for microvascular formation nor for the new formation and maintenance of mice skeletal muscle fibres in both normoxia and hypoxia

Erythropoietin (Epo) and vascular growth factor (VEGF) are known to be involved in the regulation of cellular activity when oxygen transport is reduced as in anaemia or hypoxic conditions. Because it has been suggested that Epo could play a role in skeletal muscle development, regeneration, and angiogenesis, we aimed to assess Epo deficiency in both normoxia and hypoxia by using an Epo-deficient transgenic mouse model (Epo-TAg^h). Histoimmunology, ELISA and real time RT-PCR did not show any muscle fiber atrophy or accumulation of active HIF-1α but an improvement of microvessel network and an upregulation of VEGFR2 mRNA in Epo-deficient gastrocnemius compared with Wild-Type one. In hypoxia, both models exhibit an upregulation of VEGF120 and VEGFR2 mRNA but no accumulation of Epo protein. EpoR mRNA is not up-regulated in both Epo-deficient and hypoxic gastrocnemius. These results suggest that muscle deconditioning observed in patients suffering from renal failure is not due to Epo deficiency.