Erythropoietin modulates the neural control of hypoxic ventilation

Numerous factors involved in general homeostasis are able to modulate ventilation. Classically, this comprises several kind of molecules, including neurotransmitters and steroids that are necessary for fine tuning ventilation under different conditions such as sleep, exercise, and acclimatization to high altitude. Recently, however, we have found that erythropoietin (Epo), the main regulator of red blood cell production, influences both central (brainstem) and peripheral (carotid bodies) respiratory centers when the organism is exposed to hypoxic conditions. Here, we summarize the effect of Epo on the respiratory control in mammals and highlight the potential implication of Epo in the ventilatory acclimatization to high altitude, as well as in the several respiratory sickness and syndromes occurring at low and high altitude. (Part of a multi-author review.

Erythropoietin but not VEGF has a protective effect on auditory hair cells in the inner ear

It has recently been shown that the oxygen-regulated factors erythropoietin (Epo) and vascular endothelial growth factor (VEGF) confer protection on different cells, including neuronal-derived ones. The receptors for Epo and VEGF are widely expressed in different organs. Since mammalian auditory hair cells can irreversibly be damaged by different agents, we aimed to identify otoprotective compounds. We focused on the role of Epo and VEGF in the inner ear and review the recent studies. Epo and its receptor are expressed in the inner ear. In vitro experiments on auditory hair cells showed a protective effect of Epo in ischemia- and gentamicin-induced hair cell damage. In contrast, an in vivo study using an animal model of noise-induced hearing loss showed a negative effect of Epo. Also VEGF and its receptors are expressed in the inner ear. Changes in the expression of VEGF or its receptors have been found in the cochlea after noise exposure, transcranial vibration and diabetic or aged animals. Until now, there are no studies about a direct effect of VEGF on auditory hair cells in vitro or in vivo. We could exclude a protective effect of VEGF on gentamicin-induced auditory hair cell damage in vitro. Thus, we conclude that Epo but not VEGF has a protective effect on auditory hair cell damage at least in vitro. (Part of a multi-author review.

Regular endurance training reduces the exercise induced HIF-1α and HIF-2α mRNA expression in human skeletal muscle in normoxic conditions

Regular exercise induces a variety of adaptive responses that enhance the oxidative and metabolic capacity of human skeletal muscle. Although the physiological adjustments of regular exercise have been known for decades, the underlying mechanisms are still unclear. The hypoxia inducible factors 1 and 2 (HIFs) are clearly related heterodimeric transcription factors that consist of an oxygen-depended α-subunit and a constitutive β-subunit. With hypoxic exposure, HIF-1α and HIF-2α protein are stabilized. Upon heterodimerization, HIFs induce the transcription of a variety of genes including erythropoietin (EPO), transferrin and its receptor, as well as vascular endothelial growth factor (VEGF) and its receptor. Considering that several of these genes are also induced with exercise, we tested the hypothesis that the mRNA level of HIF-1α and HIF-2α subunits increases with a single exercise bout, and that this response is blunted with training. We obtained muscle biopsies from a trained (5days/week during 4weeks) and untrained leg from the same human subject before, immediately after, and during the recovery from a 3h two-legged knee extensor exercise bout, where the two legs exercised at the same absolute workload. In the untrained leg, the exercise bout induced an increase (P<0.05) in HIF-1α fold and HIF-2α fold mRNA at 6h of recovery. In contrast, HIF-1α and HIF-2α mRNA levels were not altered at any time point in the trained leg. Obviously, HIF-1α and HIF-2α mRNA levels are transiently increased in untrained human skeletal muscle in response to an acute exercise bout, but this response is blunted after exercise training. We propose that HIFs expression is upregulated with exercise and that it may be an important transcription factor that regulates adaptive gene responses to exercis

Regulating cellular oxygen sensing by hydroxylation

Oxygen homeostasis under conditions of limited O2 supply requires hypoxia-dependent gene regulation. The transcription factor complex hypoxia-inducible factor 1 (HIF-1) has been recognized as the master regulator that mediates the adaptational genetic response to ensure restoration of energy supply. This review will focus on the recent advances in understanding the hypoxia-induced cellular response with particular respect to cellular O2 sensing for adequate control of HIF-1 activatio

P-274: Activated endothelin system in polyglobulia

The role of the endothelin system, the functional counterpart of NO, in the pathophysiology of polyglobulia remains still elusive. Therefore a novel erythropoietin overexpressing mouse was generated, with hematocrit levels of about 80%. Hence, we analyzed vascular contractions to ET-1 and big endothelin-1 (big ET-1), endothelin-1 (ET-1) promoter activity, ET-1 immunochemistry, endothelin-1 (ET-1)-protein tissue levels, ETA/B-receptor mRNA expression in this novel transgenic model of severe polyglobulia. For analysis of ET-1 promotor activity, EPO transgenic mice were mated with homozygous transgenic mice expressing the lacZ gene under control of the human ET-1 promoter and immunochistochemistry for gal blue was performed in lacZ transgenic animals. Notwithstanding markedly increased eNOS expression, NO-mediated endothelium-dependent relaxation and circulating and vascular tissue NO levels indicating enhanced bioavailability of NO, ET-1 tissue levels were also augmented in heart, kidney, liver and aorta (2.2±0.3 vs. 0.5±0.1 pg/mg tissue; P<0.01) of transgenic polyglobulic animals. Accordingly, immunohistochemistry demonstrated enhanced expression of ET-1 protein in the vascular wall of polyglobulic animals as compared to controls (p< 0.05), while increase of ET-1 promoter activity was confined to the perivascular tissue (P<0.05). NOS inhibition with L-NAME unmasked increased vascular reactivity to ET-1 and bigET-1 and aortic ETA/B receptor mRNA gene expression was enhanced (p<0.05 vs. controls). Administration of the NOS inhibitor L-NAME led to acute vasoconstriction of peripheral resistance vessels, hypertension and death of transgenic mice within 2 days, while wildtypes did not show increased mortality. Treatment with the ETA antagonist darusentan doubled survival time of transgenic polyglobulic mice after NO synthase inhibition (p<0.01 vs placebo). In conclusion, in this study we provide first evidence that the tissue endothelin system is activated by polyglobulia. Together with a stimulated NO system it contributes to cardiovascular regulation in pathophysiological conditions associated with increased hematocri

Tissue-specific expression of a FMR1/β-galactosidase fusion gene in transgenic mice

Fragile X syndrome is one of the most common genetic causes of mental retardation, yet the mechanisms controlling expression of the fragile X mental retardation gene FMR1 are poorly understood. To identify sequences regulating FMR1 transcription, transgenic mouse lines were established using a fusion gene consisting of an E.coli β-galactosidase reporter gene (lacZ) linked to a 2.8 kb fragment spanning the 5′-region of FMR1. Five transgenic mouse lines showed lacZ expression in brain, in particular in neurons of the hippocampus and the granular layer of the cerebellum. Expression of the reporter gene was also detected in Leydig cells and spermatogonia in the testis, in many epithelia of adult mice, and in the two other steroidogenic cell types, adrenal cortex cells and ovarian follicle cells. Embryonic tissues which showed strong activity of the reporter gene included the telencephalon, the genital ridge, and the notochord. This expression pattern closely resembles the endogenous one, indicating that the 5′ FMR1 gene promoter region used in this study contains most cis-acting elements regulating FMR1 transcriptio

Erythropoietin protects from reperfusion-induced myocardial injury by enhancing coronary endothelial nitric oxide production

Objective: Cardioprotective properties of recombinant human Erythropoietin (rhEpo) have been shown in in vivo regional or ex vivo global models of ischemia-reperfusion (I/R) injury. The aim of this study was to characterize the cardioprotective potential of rhEPO in an in vivo experimental model of global I/R approximating the clinical cardiac surgical setting and to gain insights into the myocardial binding sites of rhEpo and the mechanism involved in its cardioprotective effect. Methods: Hearts of donor Lewis rats were arrested with cold crystalloid cardioplegia and after 45 min of cold global ischemia grafted heterotopically into the abdomen of recipient Lewis rats. Recipients were randomly assigned to control non-treated or Epo-treated group receiving 5000 U/kg of rhEpo intravenously 20 min prior to reperfusion. At 5 time points 5-1440 min after reperfusion, the recipients (n = 6-8 at each point) were sacrificed, blood and native and grafted hearts harvested for subsequent analysis. Results: Treatment with rhEpo resulted in a significant reduction in myocardial I/R injury (plasma troponin T) in correlation with preservation of the myocardial redox state (reduced glutathione). The extent of apoptosis (activity of caspase 3 and caspase 9, TUNEL test) in our model was very modest and not significantly affected by rhEpo. Immunostaining of the heart tissue with anti-Epo antibodies showed an exclusive binding of rhEpo to the coronary endothelium with no binding of rhEpo to cardiomyocytes. Administration of rhEpo resulted in a significant increase in nitric oxide (NO) production assessed by plasma nitrite levels. Immunostaining of heart tissue with anti-phospho-eNOS antibodies showed that after binding to the coronary endothelium, rhEpo increased the phosphorylation and thus activation of endothelial nitric oxide synthase (eNOS) in coronary vessels. There was no activation of eNOS in cardiomyocytes. Conclusions: Intravenous administration of rhEpo protects the heart against cold global I/R. Apoptosis does not seem to play a major role in the process of tissue injury in this model. After binding to the coronary endothelium, rhEpo enhances NO production by phosphorylation and thus activation of eNOS in coronary vessels. Our results suggest that cardioprotective properties of rhEpo are at least partially mediated by NO released by the coronary endotheliu

Fast-Twitch Glycolytic Skeletal Muscle Is Predisposed to Age-Induced Impairments in Mitochondrial Function

The etiology of mammalian senescence is suggested to involve the progressive impairment of mitochondrial function; however, direct observations of age-induced alterations in actual respiratory chain function are lacking. Accordingly, we assessed mitochondrial function via high-resolution respirometry and mitochondrial protein expression in soleus, quadricep, and lateral gastrocnemius skeletal muscles, which represent type 1 slow-twitch oxidative muscle (soleus) and type 2 fast-twitch glycolytic muscle (quadricep and gastrocnemius), respectively, in young (10-12 weeks) and mature (74-76 weeks) mice. Electron transport through mitochondrial complexes I and III increases with age in quadricep and gastrocnemius, which is not observed in soleus. Mitochondrial coupling efficiency during respiration through complex I also deteriorates with age in gastrocnemius and shows a tendency (p = .085) to worsen in quadricep. These data demonstrate actual alterations in electron transport function that occurs with age and are dependent on skeletal muscle typ