Sato K, Iemitsu M, Aizawa K, Ajisaka R. Testosterone and DHEA activate the glucose metabolism-related signaling pathway in skeletal muscle. Am J Physiol Endocrinol Metab 294: E961-E968, 2008. First published March 18, 2008 doi:10.1152/ajpendo.00678.2007.-Circulating dehydroepiandrosterone (DHEA) is converted to testosterone or estrogen in the target tissues. Recently, we demonstrated that skeletal muscles are capable of locally synthesizing circulating DHEA to testosterone and estrogen. Furthermore, testosterone is converted to 5␣-dihydrotestosterone (DHT) by 5␣-reductase and exerts biophysiological actions through binding to androgen receptors. However, it remains unclear whether skeletal muscle can synthesize DHT from testosterone and/or DHEA and whether these hormones affect glucose metabolism-related signaling pathway in skeletal muscles. We hypothesized that locally synthesized DHT from testosterone and/or DHEA activates glucose transporter-4 (GLUT-4)-regulating pathway in skeletal muscles. The aim of the present study was to clarify whether DHT is synthesized from testosterone and/or DHEA in cultured skeletal muscle cells and whether these hormones affect the GLUT-4-related signaling pathway in skeletal muscles. In the present study, the expression of 5␣-reductase mRNA was detected in rat cultured skeletal muscle cells, and the addition of testosterone or DHEA increased intramuscular DHT concentrations. Addition of testosterone or DHEA increased GLUT-4 protein expression and its translocation. Furthermore, Akt and protein kinase C-/ (PKC-/) phosphorylations, which are critical in GLUT-4-regulated signaling pathways, were enhanced by testosterone or DHEA addition. Testosterone-and DHEA-induced increases in both GLUT-4 expression and Akt and PKC-/ phosphorylations were blocked by a DHT inhibitor. Finally, the activities of phosphofructokinase and hexokinase, main glycolytic enzymes, were enhanced by testosterone or DHEA addition. These findings suggest that skeletal muscle is capable of synthesizing DHT from testosterone, and that DHT activates the glucose metabolism-related signaling pathway in skeletal muscle cells. 5␣-dihydrotestosterone; dehydroepiandrosterone; glucose transporter-4; Akt; protein kinase C-/ SEX STEROID HORMONES ARE MAINLY produced and secreted by the ovary, testis, and adrenal cortex and affect diverse physiological processes of target organs or tissues, such as reproductive organs, bones, liver, heart, vasculature, brain, and skeletal muscles (22). Synthesis of testosterone is regulated by P-450 side-chain cleavage, 17␣-hydroxylase cytochrome P-450, 17␤-hydroxysteroid dehydrogenase (HSD), and 3␤-HSD enzymes. Dehydroepiandrosterone (DHEA) is a presubstance of sex steroid hormones, and DHEA is converted to testosterone by 17␤-HSD and 3␤-HSD enzymes (23). Recently, our laboratory found that 3␤-HSD, 17␤-HSD, and aromatase cytochrome P-450 existed in cultured skeletal muscle and steroid hormones, including testosterone, and were locally synthesized from DHEA (1). In a skeletal muscle specim...

No abstract

Hypoxia-inducible factors (HIFs) are crucial for oxygen homeostasis during both embryonic development and postnatal life. Here we show that a novel HIF family basic helix-loop-helix (bHLH) PAS (Per-Arnt-Sim) protein, which is expressed predominantly during embryonic and neonatal stages and thereby designated NEPAS (neonatal and embryonic PAS), acts as a negative regulator of HIF-mediated gene expression. NEPAS mRNA is derived from the HIF-3␣ gene by alternative splicing, replacing the first exon of HIF-3␣ with that of inhibitory PAS. NEPAS can dimerize with Arnt and exhibits only low levels of transcriptional activity, similar to that of HIF-3␣. NEPAS suppressed reporter gene expression driven by HIF-1␣ and HIF-2␣. By generating mice with a targeted disruption of the NEPAS/HIF-3␣ locus, we found that homozygous mutant mice (NEPAS/ HIF-3␣ ؊/؊ ) were viable but displayed enlargement of the right ventricle and impaired lung remodeling. The expression of endothelin 1 and platelet-derived growth factor ␤ was increased in the lung endothelial cells of NEPAS/HIF-3␣-null mice. These results demonstrate a novel regulatory mechanism in which the activities of HIF-1␣ and HIF-2␣ are negatively regulated by NEPAS in endothelial cells, which is pertinent to lung and heart development during the embryonic and neonatal stages.Hypoxia-inducible factors (HIFs) are crucial for oxygen homeostasis during both embryonic development and postnatal life. HIFs are heterodimeric transcription factors consisting of ␣ and ␤ subunits. To date, three ␣ subunits (HIF-1␣, HIF-2␣, and HIF-3␣) and one ␤ subunit (HIF-1␤, also called Arnt [aryl hydrocarbon receptor nuclear translocator]) have been identified (10, 34, 37). Oxygen-dependent activity of HIFs is mainly regulated through the stability of their ␣ subunits. Under the normoxic condition, HIF-␣ protein is rapidly degraded through the ubiquitin-proteasomal pathway. During this process, HIF-␣ is hydroxylated by proline hydroxylases and specifically interacts with the von Hippel-Lindau (VHL) tumor suppressor protein (8, 21), which acts as a component of E3 ubiquitin ligase and targets HIF-␣ molecules for ubiquitination and subsequent degradation (12). Under low oxygen tension, hydroxylation of HIF-␣ is significantly reduced because the activity of proline hydroxylases is repressed by hypoxia. Since VHL can recognize exclusively the hydroxylated HIF-␣ molecules, in the hypoxic condition HIF-␣ is stabilized and activates transcription of target genes with Arnt in the nucleus.Although it is indisputable that this ubiquitin-proteasomal pathway plays a central role in determining HIF activity, an additional regulatory mechanism should be considered under certain conditions. For instance, the availability of oxygen is limited in utero and embryos are continuously exposed to hypoxia (17). Under such conditions, it is likely that HIF-␣ proteins are no longer degraded and accumulate into the nucleus. Given the fact that both HIF-1␣ and HIF-2␣ are required for early embryonic development (13,25,33), HIF...

Aims: The Modelflow method can estimate cardiac output from arterial blood pressure waveforms using a three-element model of aortic input impedance (aortic characteristic impedance, arterial compliance, and systemic vascular resistance). We tested the reliability of a non-invasive cardiac output estimation during submaximal exercise using the Modelflow method from finger arterial pressure waveforms collected by Portapres in healthy young humans. Methods: The Doppler echocardiography method was used as a reference method. Sixteen healthy young subjects (nine males and seven females) performed a multi-stage cycle ergometer exercise at an intensity corresponding to 70, 90, 110 and 130% of their individual ventilatory threshold for 2 min each. The simultaneous estimation of cardiac output (15 s averaged data) using the Modelflow and Doppler echocardiography methods was performed at rest and during exercise. Results and Conclusion: The Modelflow-estimated cardiac output correlated significantly with the simultaneous estimates by the Doppler method in all subjects (r ¼ 0.87, P < 0.0001) and the SE of estimation was 1.93 L min )1 . Correlation coefficients in each subject ranged from 0.91 to 0.98. Although the Modelflow method overestimated cardiac output, the errors between two estimates were not significantly different among the exercise levels. These results suggest that the Modelflow method using Portapres could provide a reliable estimation of the relative change in cardiac output non-invasively and continuously during submaximal exercise in healthy young humans, at least in terms of the relative changes in cardiac output. Keywords cardiac output, Doppler echocardiography, finger arterial pressure waveform.Cardiac output (CO) is one indicator of cardiac function. A non-invasive estimation of CO with high time resonance is favourable in exercise physiological research. The Modelflow method involves the measurement of beat-by-beat aortic flow volume from arterial pressure waveforms (Wesseling et al.

Endothelial function deteriorates with aging. On the other hand, exercise training improves the function of vascular endothelial cells. Endothelin-1 (ET-1), which is produced by vascular endothelial cells, has potent constrictor and proliferative activity in vascular smooth muscle cells and, therefore, has been implicated in regulation of vascular tonus and progression of atherosclerosis. We previously reported significantly higher plasma ET-1 concentration in middle-aged than in young humans, and recently we showed that plasma ET-1 concentration was significantly decreased by aerobic exercise training in healthy young humans. We hypothesized that plasma ET-1 concentration increases with age, even in healthy adults, and that lifestyle modification (i.e., exercise) can reduce plasma ET-1 concentration in previously sedentary older adults. We measured plasma ET-1 concentration in healthy young women (21-28 yr old), healthy middle-aged women (31-47 yr old), and healthy older women (61-69 yr old). The plasma level of ET-1 significantly increased with aging (1.02 +/- 0.08, 1.33 +/- 0.11, and 2.90 +/- 0.20 pg/ml in young, middle-aged, and older women, respectively). Thus plasma ET-1 concentration was markedly higher in healthy older women than in healthy young or middle-aged women (by approximately 3- and 2-fold, respectively). In healthy older women, we also measured plasma ET-1 concentration after 3 mo of aerobic exercise (cycling on a leg ergometer at 80% of ventilatory threshold for 30 min, 5 days/wk). Regular exercise significantly decreased plasma ET-1 concentration in the healthy older women (2.22 +/- 0.16 pg/ml, P < 0.01) and also significantly reduced their blood pressure. The present study suggests that regular aerobic-endurance exercise reduces plasma ET-1 concentration in older humans, and this reduction in plasma ET-1 concentration may have beneficial effects on the cardiovascular system (i.e., prevention of progression of hypertension and/or atherosclerosis by endogenous ET-1).