Acute changes in serum and skeletal muscle steroids in resistance-trained men

INTRODUCTION

Resistance exercise can significantly increase serum steroid concentrations after an exercise bout. Steroid hormones are involved in the regulation of several important bodily functions (e.g., muscle growth) through both systemic delivery and local production. Thus, we aimed to determine whether resistance exercise-induced increases in serum steroid hormone concentrations are accompanied by enhanced skeletal muscle steroid concentrations, or whether muscle contractions per se induced by resistance exercise can increase intramuscular steroid concentrations.

METHODS

A counterbalanced, within-subject, crossover design was applied. Six resistance-trained men (26 ± 5 years; 79 ± 8 kg; 179 ± 10 cm) performed a single-arm lateral raise exercise (10 sets of 8 to 12 RM - 3 min rest between sets) targeting the deltoid muscle followed by either squat exercise (10 sets of 8 to 12 RM - 1 min rest) to induce a hormonal response (high hormone [HH] condition) or rest (low hormone [LH] condition). Blood samples were obtained pre-exercise and 15 min and 30 min post-exercise; muscle specimens were harvested pre-exercise and 45 min post-exercise. Immunoassays were used to measure serum and muscle steroids (total and free testosterone, dehydroepiandrosterone sulfate, dihydrotestosterone, and cortisol; free testosterone measured only in serum and dehydroepiandrosterone only in muscle) at these time points.

RESULTS

In the serum, only cortisol significantly increased after the HH protocol. There were no significant changes in muscle steroid concentrations after the protocols.

DISCUSSION

Our study provides evidence that serum steroid concentration increases (cortisol only) seem not to be aligned with muscle steroid concentrations. The lack of change in muscle steroid after protocols suggests that resistance-trained individuals were desensitized to the exercise stimuli. It is also possible that the single postexercise timepoint investigated in this study might be too early or too late to observe changes. Thus, additional timepoints should be examined to determine if RE can indeed change muscle steroid concentrations either by skeletal muscle uptake of these hormones or the intramuscular steroidogenesis process.

Exploring the Intracrine Functions of VEGF-A

Vascular endothelial growth factor A (VEGF-A or VEGF) is a highly conserved secreted signalling protein best known for its roles in vascular development and angiogenesis. Many non-endothelial roles for VEGF are now established, with the discovery that VEGF and its receptors VEGFR1 and VEGFR2 are expressed in many non-vascular cell-types, as well as various cancers. In addition to secreted VEGF binding to its receptors in the extracellular space at the cell membrane (i.e., in a paracrine or autocrine mode), intracellularly localised VEGF is emerging as an important signalling molecule regulating cell growth, survival, and metabolism. This intracellular mode of signalling has been termed “intracrine”, and refers to the direct action of a signalling molecule within the cell without being secreted. In this review, we describe examples of intracrine VEGF signalling in regulating cell growth, differentiation and survival, both in normal cell homeostasis and development, as well as in cancer. We further discuss emerging evidence for the molecular mechanisms underpinning VEGF intracrine function, as well as the implications this intracellular mode of VEGF signalling may have for use and design of anti-VEGF cancer therapeutics.

Intracrine Endorphinergic Systems in Modulation of Myocardial Differentiation

A wide variety of peptides not only interact with the cell surface, but govern complex signaling from inside the cell. This has been referred to as an "intracrine" action, and the orchestrating molecules as "intracrines". Here, we review the intracrine action of dynorphin B, a bioactive end-product of the prodynorphin gene, on nuclear opioid receptors and nuclear protein kinase C signaling to stimulate the transcription of a gene program of cardiogenesis. The ability of intracrine dynorphin B to prime the transcription of its own coding gene in isolated nuclei is discussed as a feed-forward loop of gene expression amplification and synchronization. We describe the role of hyaluronan mixed esters of butyric and retinoic acids as synthetic intracrines, controlling prodynorphin gene expression, cardiogenesis, and cardiac repair. We also discuss the increase in prodynorphin gene transcription and intracellular dynorphin B afforded by electromagnetic fields in stem cells, as a mechanism of cardiogenic signaling and enhancement in the yield of stem cell-derived cardiomyocytes. We underline the possibility of using the diffusive features of physical energies to modulate intracrinergic systems without the needs of viral vector-mediated gene transfer technologies, and prompt the exploration of this hypothesis in the near future.

A proposed mechanism for the Berecek phenomenon with implications for cardiovascular reprogramming

Berecek et al reported in the 1990s that when spontaneously hypertensive rat (SHR) mating pairs were treated with captopril and the resulting pups were continued on the drug for 2 months followed by drug discontinuation, the pups did not develop full blown hypertension, and the cardiovascular structural changes associated with hypertension in SHR were mitigated. The offspring of the pups also displayed diminished hypertension and structural changes, suggesting that the drug therapy produced a heritable amelioration of the SHR phenotype. This observation is reviewed. The link between cellular renin angiotensin systems and epigenetic histone modification is explored, and a mechanism responsible for the observation is proposed. In any case, the observations of Berecek are sufficiently intriguing and biologically important to merit re-exploration and definitive explanation. Equally important is determining the role of renin angiotensin systems in epigenetic modification.

Role of intracellular angiotensin II

It has become clear that the vasoactive peptide angiotensin II, like other so-called intracrines, can act in the intracellular space. Evidence has accumulated indicating that such angiotensin II activity can be upregulated in disease states and cause pathology. Indeed, other intracrines appear to be involved in disease pathogenesis as well. At the same time, nitric oxide, potentially a cell protective factor, has been shown to be upregulated by intracellular angiotensin II. Recently data have been developed indicating that other potentially protective factors are directly upregulated at neuronal nuclei by angiotensin II. This led to the suggestion that intracellular angiotensin II is cell protective and not pathological. Here, the data on both sides of this issue and a possible resolution are discussed. In summary, there is evidence for both protective and pathological actions of intracellular angiotensin, just as there is abundant evidence derived from whole animal physiology to indicate that angiotensin-driven signaling cascades, including angiotensin II type 2 receptor- and Mas receptor-mediated events, can mitigate the effects of the angiotensin II/angiotensin II type 1 receptor axis (25). This mitigation does not negate the physiological and pathological importance of angiotensin II/angiotensin II type 1 receptor action but does expand our understanding of the workings of both intracellular and extracellular angiotensin II.

Blunting of estrogen modulation of cardiac cellular chymase/RAS activity and function in SHR

The relatively low efficacy of ACE-inhibitors in the treatment of heart failure in women after estrogen loss may be due to their inability to reach the intracellular sites at which angiotensin (Ang) II is generated and/or the existence of cell-specific mechanisms in which ACE is not the essential processing pathway for Ang II formation. We compared the metabolic pathway for Ang II formation in freshly isolated myocytes (CMs) and non-myocytes (NCMs) in cardiac membranes extracted from hearts of gonadal-intact and ovariectomized (OVX) adult WKY and SHR rats. Plasma Ang II levels were higher in WKY vs. SHR (strain effect: WKY: 62 ± 6 pg/ml vs. SHR: 42 ± 9 pg/ml; p < 0.01), independent of OVX. The enzymatic activities of chymase, ACE, and ACE2 were higher in NCMs versus CMs, irrespective of whether assays were performed in cardiac membranes from WKY or SHR or in the presence or absence of OVX. E2 depletion increased chymase activity, but not ACE activity, in both CMs and NCMs. Moreover, cardiac myocyte chymase activity associated with diastolic function in WKYs and cardiac structure in SHRs while no relevant functional and structural relationships between the classic enzymatic pathway of Ang II formation by ACE or the counter-regulatory Ang-(1-7) forming path from Ang II via ACE2 were apparent. The significance of these novel findings is that targeted cell-specific chymase rather than ACE inhibition may have a greater benefit in the management of HF in women after menopause.

Regulation of androgen action during establishment of pregnancy

During the establishment of pregnancy, the ovarian-derived hormones progesterone and oestradiol regulate remodelling of the endometrium to promote an environment that is able to support and maintain a successful pregnancy. Decidualisation is characterised by differentiation of endometrial stromal cells that secrete growth factors and cytokines that regulate vascular remodelling and immune cell influx. This differentiation process is critical for reproduction, and inadequate decidualisation is implicated in the aetiology of pregnancy disorders such as foetal growth restriction and preeclampsia. In contrast to progesterone and oestradiol, the role of androgens in regulating endometrial function is poorly understood. Androgen receptors are expressed in the endometrium, and androgens are reported to regulate both the transcriptome and the secretome of endometrial stromal cells. In androgen-target tissues, circulating precursors are activated to mediate local effects, and recent studies report that steroid concentrations detected in endometrial tissue are distinct to those detected in the peripheral circulation. New evidence suggests that decidualisation results in dynamic changes in the expression of androgen biosynthetic enzymes, highlighting a role for pre-receptor regulation of androgen action during the establishment of pregnancy. These results suggest that such enzymes could be future therapeutic targets for the treatment of infertility associated with endometrial dysfunction. In conclusion, these data support the hypothesis that androgens play a beneficial role in regulating the establishment and maintenance of pregnancy. Future studies should be focussed on investigating the safety and efficacy of androgen supplementation with the potential for utilisation of novel therapeutics, such as selective androgen receptor modulators, to improve reproductive outcomes in women.

Additional clues for a protective role of vitamin D in neurodegenerative diseases: 1,25-dihydroxyvitamin D3 triggers an anti-inflammatory response in brain pericytes

Epidemiological and experimental studies suggest that 1,25-dihydroxyvitamin D3 (1,25D) plays a neuroprotective role in neurodegenerative diseases including Alzheimer's disease. Most of the experimental data regarding the genes regulated by this hormone in brain cells have been obtained with neuron and glial cells. Pericytes play a critical role in brain function that encompasses their classical function in blood-brain barrier control and maintenance. However, the gene response of brain pericyte to 1,25D remains to be investigated. Analyses of the transcriptomic response of human brain pericytes to 1,25D demonstrate that human brain pericytes in culture respond to 1,25D by regulating genes involved in the control of neuroinflammation. In addition, pericytes respond to the pro-inflammatory cytokines tumor necrosis factor-α and Interferon-γ by inducing the expression of the CYP27B1 gene which is involved in 1,25D synthesis. Taken together, these results suggest that neuroinflammation could trigger the synthesis of 1,25D by brain pericytes, which in turn respond to the hormone by a global anti-inflammatory response. These findings identify brain pericytes as a novel 1,25D-responsive cell type and provide additional evidence for the potential value of vitamin D in the prevention or therapy of Alzheimer's disease and other neurodegenerative/neuropsychiatric diseases associated with an inflammatory component.

Impact of vitamin D on immune function: lessons learned from genome-wide analysis

Immunomodulatory responses to the active form of vitamin D (1,25-dihydroxyvitamin D, 1,25D) have been recognized for many years, but it is only in the last 5 years that the potential role of this in normal human immune function has been recognized. Genome-wide analyses have played a pivotal role in redefining our perspective on vitamin D and immunity. The description of increased vitamin D receptor (VDR) and 1α-hydroxylase (CYP27B1) expression in macrophages following a pathogen challenge, has underlined the importance of intracrine vitamin D as key mediator of innate immune function. It is now clear that both macrophages and dendritic cells (DCs) are able to respond to 25-hydroxyvitamin D (25D), the major circulating vitamin D metabolite, thereby providing a link between the function of these cells and the variations in vitamin D status common to many humans. The identification of hundreds of primary 1,25D target genes in immune cells has also provided new insight into the role of vitamin D in the adaptive immune system, such as the modulation of antigen-presentation and T cells proliferation and phenotype, with the over-arching effects being to suppress inflammation and promote immune tolerance. In macrophages 1,25D promotes antimicrobial responses through the induction of antibacterial proteins, and stimulation of autophagy and autophagosome activity. In this way variations in 25D levels have the potential to influence both innate and adaptive immune responses. More recent genome-wide analyses have highlighted how cytokine signaling pathways can influence the intracrine vitamin D system and either enhance or abrogate responses to 25D. The current review will discuss the impact of intracrine vitamin D metabolism on both innate and adaptive immunity, whilst introducing the concept of disease-specific corruption of vitamin D metabolism and how this may alter the requirements for vitamin D in maintaining a healthy immune system in humans.

Abiraterone in the treatment of metastatic castration-resistant prostate cancer

Androgen deprivation therapy remains the single most effective treatment for the initial therapy of advanced prostate cancer, but is uniformly marked by progression to castration-resistant prostate cancer (CRPC). Residual tumor androgens and androgen axis activation are now recognized to play a prominent role in mediating CRPC progression. Despite suppression of circulating testosterone to castrate levels, castration does not eliminate androgens from the prostate tumor microenvironment and residual androgen levels are well within the range capable of activating the androgen receptor (AR) and AR-mediated gene expression. Accordingly, therapeutic strategies that more effectively target production of intratumoral androgens are necessary. The introduction of abiraterone, a potent suppressor of cytochrome P450 17 α-hydroxysteroid dehydrogenase-mediated androgen production, has heralded a new era in the hormonal treatment of men with metastatic CRPC. Herein, the androgen and AR-mediated mechanisms that contribute to CRPC progression and establish cytochrome P450 17 α-hydroxysteroid dehydrogenase as a critical therapeutic target are briefly reviewed. The mechanism of action and pharmacokinetics of abiraterone are reviewed and its recently described activity against AR and 3-β-hydroxysteroid dehydrogenase is discussed. The Phase I and II data initially demonstrating the efficacy of abiraterone and Phase III data supporting its approval for patients with metastatic CRPC are reviewed. The safety and tolerability of abiraterone, including the incidence and management of side effects and potential drug interactions, are discussed. The current place of abiraterone in CRPC therapy is reviewed and early evidence regarding cross-resistance of abiraterone with taxane therapy, mechanisms of resistance to abiraterone, and observations of an abiraterone withdrawal response are presented. Future directions in the use of abiraterone, including optimal dosing strategies, the role of abiraterone in earlier disease settings, including castration sensitive, biochemically recurrent, or localized disease, and the rationale for combinatorial treatment strategies of abiraterone with enzalutamide and other targeted agents are also discussed.

Thirty years of intracrinology

BACKGROUND

Intracrinology is the study of the intracellular actions, regulation, trafficking, and interactions of extracellular signaling peptides/proteins.

METHODS

We describe the development of intracrine biology since the term was defined in 1984.

RESULTS

Intracrine biology plays a role in many normal and pathological processes and represents a fertile field for the development of novel therapeutics.

CONCLUSION

Although 30 years old, the field of intracrinology is only now becoming widely accepted. Intracrine principles can be applied to the investigation of physiological processes and to the development of new therapies.

Androgen action and metabolism in prostate cancer

The transcriptional programs regulated through the activity of the androgen receptor (AR) modulate normal prostate development and the maintenance of prostatic functions at maturity. AR signaling also controls key survival and growth functions operative in prostate cancer. Inhibiting the AR program remains the key target in the treatment of advanced prostate cancer, and suppressing AR also holds great potential for preventing the development or progression of early stage prostate cancer. In this review, we detail molecular mechanisms of AR activity, cellular components contributing to the maintenance of AR signaling despite AR-ligand suppression, and discuss treatment strategies designed to target components of resistance to AR-directed therapeutics.

Transgenic mice expressing an intracellular fluorescent fusion of angiotensin II demonstrate renal thrombotic microangiopathy and elevated blood pressure

We have generated transgenic mice that express angiotensin II (ANG II) fused downstream of enhanced cyan fluorescent protein, expression of which is regulated by the mouse metallothionein promoter. The fusion protein, which lacks a secretory signal, is retained intracellularly. In the present study, RT-PCR, immunoblot analyses, whole-animal fluorescent imaging, and fluorescent microscopy of murine embryonic fibroblasts confirm expression of the fusion protein in vivo and in vitro. The transgene is expressed in all tissues tested (including brain, heart, kidney, liver, lung, and testes), and radioimmunoassay of plasma samples obtained from transgenic mice indicate no increase in circulating ANG II over wild-type levels, consistent with intracellular retention of the transgene product. Kidneys from transgenic and corresponding wild-type littermates were histologically evaluated, and abnormalities in transgenic mice consistent with thrombotic microangiopathy were observed; microthrombosis was frequently observed within the glomerular capillaries and small vessels. In addition, systolic and diastolic blood pressures, measured by telemetry (n = 8 for each group), were significantly higher in transgenic mice compared with wild-type littermates. Blood pressure of line A male transgenic mice was 125 + or - 1.7 over 97 + or - 1.6 compared with 109 + or - 1.7 over 83 + or - 1.4 mmHg in wild-type littermates (systolic over diastolic). In summary, overexpression of an intracellular fluorescent fusion protein of ANG II correlates with elevated blood pressure and kidney pathology. This transgenic model may be useful to further explore the intracellular renin-angiotensin system and its implication in abnormal kidney function and hypertension.

Aggressive interactions rapidly increase androgen synthesis in the brain during the non-breeding season

In male song sparrows (Melospiza melodia), territorial challenges during the breeding season can rapidly increase circulating levels of testosterone (T). During the non-breeding season, male song sparrows are highly aggressive, but the gonads are regressed and plasma T levels are non-detectable and unaffected by territorial challenges. The pro-hormone dehydroepiandrosterone (DHEA) is elevated in song sparrow plasma and brain during the non-breeding season and may be locally converted to sex steroids in the brain to regulate aggression. The enzyme 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (3beta-HSD) converts DHEA to androstenedione (AE) using the cofactor NAD(+), and this is a critical rate-limiting step. We predicted that brain 3beta-HSD activity varies seasonally and is rapidly modulated by aggressive challenges. In the first study, brain 3beta-HSD activity was highest in the non-breeding season in specific regions. In the second study, a simulated territorial challenge rapidly increased aggressive behavior in non-breeding song sparrows. Brain 3beta-HSD activity, when measured without exogenous NAD(+), increased by approximately 250 to 500% in telencephalic regions of challenged subjects. When brain 3beta-HSD activity was measured with exogenous NAD(+), these effects of territorial challenges were not observed. These data suggest that territorial challenges rapidly increase endogenous NAD(+) levels or increase 3beta-HSD activity specifically within a NAD-rich subcellular compartment. Together, these two studies suggest a shift from systemic to local sex steroid signaling in the non-breeding season. Local steroid signaling produces high spatial and temporal specificity of steroid signals and avoids the costs of high systemic T levels during the non-breeding season.

Removal of the membrane-anchoring domain of epidermal growth factor leads to intracrine signaling and disruption of mammary epithelial cell organization

Autocrine EGF-receptor (EGFR) ligands are normally made as membrane-anchored precursors that are proteolytically processed to yield mature, soluble peptides. To explore the function of the membrane-anchoring domain of EGF, we expressed artificial EGF genes either with or without this structure in human mammary epithelial cells (HMEC). These cells require activation of the EGFR for cell proliferation. We found that HMEC expressing high levels of membrane- anchored EGF grew at a maximal rate that was not increased by exogenous EGF, but could be inhibited by anti-EGFR antibodies. In contrast, when cells expressed EGF lacking the membrane-anchoring domain (sEGF), their proliferation rate, growth at clonal densities, and receptor substrate phosphorylation were not affected by anti-EGFR antibodies. The sEGF was found to be colocalized with the EGFR within small cytoplasmic vesicles. It thus appears that removal of the membrane-anchoring domain converts autocrine to intracrine signaling. Significantly, sEGF inhibited the organization of HMEC on Matrigel, suggesting that spatial restriction of EGF access to its receptor is necessary for organization. Our results indicate that an important role of the membrane-anchoring domain of EGFR ligands is to restrict the cellular compartments in which the receptor is activated.