Expression of urocortin 2 and its inhibitory effects on intracellular ca2+ via L-type voltage-gated calcium channels in rat pheochromocytoma (PC12) cells

The role of amphipathic and cationic helical peptides in Parkinson's disease

Peptides are attracting a growing interest for therapeutic applications in biomedicine. In Parkinson's disease (PD), different human endogenous peptides have been associated with beneficial effects, including protein aggregation inhibition, reduced inflammation, or the protection of dopaminergic neurons. Such effects seem to be connected to the spatial arrangement of peptide side chains, and many of these human molecules share common conformational traits, displaying a distinctive amphipathic and cationic helical structure, which is believed to be crucial for their activities. This review delves into the relationship between these structural properties and the current evidence connecting biogenic peptides to the amelioration of PD symptoms. We discuss their implications in the disease, the different mechanisms of action, their state of validation, and their therapeutic potential.

Stress hormones mediate developmental plasticity in vertebrates with complex life cycles

The environment experienced by developing organisms can shape the timing and character of developmental processes, generating different phenotypes from the same genotype, each with different probabilities of survival and performance as adults. Chordates have two basic modes of development, indirect and direct. Species with indirect development, which includes most fishes and amphibians, have a complex life cycle with a free-swimming larva that is typically a growth stage, followed by a metamorphosis into the adult form. Species with direct development, which is an evolutionarily derived developmental mode, develop directly from embryo to the juvenile without an intervening larval stage. Among the best studied species with complex life cycles are the amphibians, especially the anurans (frogs and toads). Amphibian tadpoles are exposed to diverse biotic and abiotic factors in their developmental habitat. They have extensive capacity for developmental plasticity, which can lead to the expression of different, adaptive morphologies as tadpoles (polyphenism), variation in the timing of and size at metamorphosis, and carry-over effects on the phenotype of the juvenile/adult. The neuroendocrine stress axis plays a pivotal role in mediating environmental effects on amphibian development. Before initiating metamorphosis, if tadpoles are exposed to predators they upregulate production of the stress hormone corticosterone (CORT), which acts directly on the tail to cause it to grow, thereby increasing escape performance. When tadpoles reach a minimum body size to initiate metamorphosis they can vary the timing of transformation in relation to growth opportunity or mortality risk in the larval habitat. They do this by modulating the production of thyroid hormone (TH), the primary inducer of metamorphosis, and CORT, which synergizes with TH to promote tissue transformation. Hypophysiotropic neurons that release the stress neurohormone corticotropin-releasing factor (CRF) are activated in response to environmental stress (e.g., pond drying, food restriction, etc.), and CRF accelerates metamorphosis by directly inducing secretion of pituitary thyrotropin and corticotropin, thereby increasing secretion of TH and CORT. Although activation of the neuroendocrine stress axis promotes immediate survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Small size at transformation can impair performance of the adult, reducing probability of survival in the terrestrial habitat, or fecundity. Furthermore, elevations in CORT in the tadpole caused by environmental stressors cause long term, stable changes in neuroendocrine function, behavior and physiology of the adult, which can affect fitness. Comparative studies show that the roles of stress hormones in developmental plasticity are conserved across vertebrate taxa including humans.

Diltiazem aggravates testicular function impairment induced by cyclosporine A or tacrolimus in unilateral nephrectomised rats

The aim of this study was to elucidate the reproductive toxicity of the coadministration of diltiazem and cyclosporine A or tacrolimus. Testicular development, semen quality, sex hormones and testicular tissues were assessed in unilateral nephrectomised (UN) rats, including the control group, UN group, UN+CsA group, UN+FK506 group, UN+Rapa group, UN+CsA+Dil group and UN+FK506+Dil group. The testicular coefficient, the sperm number and the sperm motility were lower in the treatment groups (except UN+FK506) than in the control and UN groups (all p < 0.05). The lowest sperm number and motility were identified in the UN+CsA+Dil group, followed by the UN+CsA group. The proportion of abnormal sperm was higher in the UN+CsA and UN+CsA+Dil groups than in the control and UN groups, respectively (p < 0.05). The plasma concentrations of sex hormones were changed in the treatment groups. Dil can increase the blood concentrations of CsA and FK506 (◇p < 0.05, ◆p < 0.05). Therapeutic doses of these agents induced morphological changes in the testicular tissue and ultrastructural changes in the testosterone, mesenchymal cells and supporting cells. Our present study suggests that Dil can increase the testicular toxicity of CNIs (calcineurin inhibitors, including CsA and FK506) by enhancing the plasma concentrations of CNIs.

Endocrinology and the brain: corticotropin-releasing hormone signaling

Corticotropin-releasing hormone (CRH) is a key player of basal and stress-activated responses in the hypothalamic-pituitary-adrenal axis (HPA) and in extrahypothalamic circuits, where it functions as a neuromodulator to orchestrate humoral and behavioral adaptive responses to stress. This review describes molecular components and cellular mechanisms involved in CRH signaling downstream of its G protein-coupled receptors (GPCRs) CRHR1 and CRHR2 and summarizes recent findings that challenge the classical view of GPCR signaling and impact on our understanding of CRHRs function. Special emphasis is placed on recent studies of CRH signaling that revealed new mechanistic aspects of cAMP generation and ERK1/2 activation in physiologically relevant contexts of the neurohormone action. In addition, we present an overview of the pathophysiological role of the CRH system, which highlights the need for a precise definition of CRHRs signaling at molecular level to identify novel targets for pharmacological intervention in neuroendocrine tissues and specific brain areas involved in CRH-related disorders.

P/Q-type voltage-gated calcium channels mediate the ethanol and CRF sensitivity of central amygdala GABAergic synapses

The central amygdala (CeA) GABAergic system is hypothesized to drive the development of alcohol dependence, due to its pivotal roles in the reinforcing actions of alcohol and the expression of negative emotion, anxiety and stress. Recent work has also identified an important role for the CeA corticotropin-releasing factor (CRF) system in the interaction between anxiety/stress and alcohol dependence. We have previously shown that acute alcohol and CRF each increase action potential-independent GABA release in the CeA via their actions at presynaptic CRF type 1 receptors (CRF₁s); however, the shared mechanism employed by these two compounds requires further investigation. Here we report that acute alcohol interacts with the CRF/CRF₁ system, such that CRF and alcohol act via presynaptic CRF₁s and P/Q-type voltage-gated calcium channels to promote vesicular GABA release and that both compounds occlude the effects of each other at these synapses. Chronic alcohol exposure does not alter P/Q-type voltage-gated calcium channel membrane abundance or this CRF₁/P/Q-type voltage-gated calcium channel mechanism of acute alcohol-induced GABA release, indicating that alcohol engages this molecular mechanism at CeA GABAergic synapses throughout the transition to dependence. Thus, P/Q-type voltage-gated calcium channels, like CRF₁s, are key regulators of the effects of alcohol on GABAergic signaling in the CeA.

Urocortin affects migration of hepatic cancer cell lines via differential regulation of cPLA2 and iPLA2

Urocortin (UCN) is a member of corticotrophin-releasing factor (CRF) family, which has been reported to play a role in many biological processes, including inflammation and cancer development. Growing evidence shows that PLA2 (phospholipase A2) enzymes also participate in inflammation and tumor development. The primary aim of the present study was to identify a novel signaling pathway of CRF receptor activation leading to migration of two kinds of hepatoma carcinoma cell lines, HepG2 and SMMC-7721, linking the stimulation of PLA2 expression by UCN to UCN-induced tumor cell migration. Pharmacological inhibitors and genetic approaches (such as stable transfection and siRNAs) were used in this study. Unlike HepG2 cells which express both CRF receptors themselves, SMMC-7721 cells which hardly express these two CRF receptors needed stable transfection with CRFR1 or CRFR2 to observe the effect of UCN. Two types of PLA2 enzymes, cPLA2 and iPLA2, were found to be regulated by UCN. Our data showed that UCN raised cPLA2 expression but lowered iPLA2 expression. Moreover, UCN was found to act on the certain region of iPLA2 promoter to reduce its transcription. UCN promoted tumor cell migration by up-regulating cPLA2 expression via CRFR1 whereas it suppressed tumor cell migration by down-regulating iPLA2 expression via CRFR2. These results indicate the dual roles for UCN in the hepatoma carcinoma cell migration, which involve the regulation of both cPLA2and iPLA2.

Urocortin is a novel regulator of osteoclast differentiation and function through inhibition of a canonical transient receptor potential 1-like cation channel

This study investigated the role of urocortin (UCN), a member of the corticotrophin-releasing factor (CRF) family of peptides, in osteoclast maturation and function. We found that 10(-7) M UCN significantly (P<0.05) suppressed osteoclast differentiation from bone marrow precursor cells in culture and reduced the expression of several osteoclastic markers. Furthermore, UCN potently suppressed osteoclast bone resorption, by significantly inhibiting both the plan area of bone resorbed by osteoclasts and actin ring formation within osteoclasts at 10(-9) M (P<0.05), with complete inhibition at 10(-7) M (P<0.001). UCN also inhibited osteoclast motility (10(-7) M) but had no effect on osteoclast survival. Osteoclasts expressed mRNA encoding both UCN and the CRF receptor 2β subtype. Pre-osteoclasts however, expressed CRF receptor 2β alone. Unstimulated osteoclasts contained constitutively active cation channel currents with a unitary conductance of 3-4 pS, which were inhibited by over 70% with UCN (10(-7) M). Compounds that regulate calcium signalling and energy status of the cell, both crucial for osteoclast activity were investigated. The non-selective cation channel blockers, lanthanum (La(3)(+)) and gadolinium (Gd(3)(+)), inhibited actin ring formation in osteoclasts, whereas modulators of voltage-dependent Ca(2)(+) channels and K(ATP) channels had no effect. These findings show for the first time that UCN is a novel anti-resorptive molecule that acts through a direct effect on osteoclasts and their precursor cells.

Stress hormones mediate environment-genotype interactions during amphibian development

Environments experienced by organisms during early development shape the character and timing of developmental processes, leading to different probabilities of survival in the developmental habitat, and often profound effects on phenotypic expression later in life. Amphibian larvae have immense capacity for plasticity in behavior, morphology, growth and development rate. This creates the potential for extreme variation in the timing of, and size at metamorphosis, and subsequent phenotype in the juvenile and adult stage. Hormones of the neuroendocrine stress axis play pivotal roles in mediating environmental effects on animal development. Corticotropin-releasing factor, whose secretion by hypothalamic neurons is induced by environmental stress, influences the timing of amphibian metamorphosis by controlling the activity of the thyroid and interrenal (adrenal; corticosteroids) glands. At target tissues, corticosteroids synergize with thyroid hormone to promote metamorphosis. Thus, environmental stress acts centrally to increase the activity of the two principle endocrine axes controlling metamorphosis, and the effectors of these axes synergize at the level of target tissues to promote morphogenesis. While stress hormones can promote survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Furthermore, exposure to elevated corticosteroids early in life can cause permanent changes in the expression of genes of the neuroendocrine stress axis, leading to altered physiology and behavior in the juvenile/adult stage. Persistent effects of stress hormone actions early in life may have important fitness consequences.

Involvement of extracellular signal-regulated protein kinase in acute cocaine-induced c-fos in nucleus accumbens

It is well known that acute cocaine administration increases c-Fos expression that is involved in cocaine-induced persistent changes in the central nervous system. In the present study, we investigated a possible involvement of extracellular signal-regulated protein kinase (ERK) in induction of c-fos expression in response to acute cocaine treatment in nucleus accumbens (NAc). We found that inhibition of ERK activation significantly attenuated cocaine-induced c-fos expression at both protein and mRNA levels in the NAc. Furthermore, using an immunofluorescent staining approach, we found that inhibition of ERK activation completely abolished cocaine-induced increase in number of c-Fos-positive cells in the core region of NAc, whereas, in shell region of NAc, inhibition of ERK activation partially attenuated cocaine-induced c-Fos expression. Our findings suggest that ERK might participate in cocaine-induced c-fos expression in the NAc, particularly in the core region of NAc.

CRF facilitates calcium release from intracellular stores in midbrain dopamine neurons

Changes in cytosolic calcium are crucial for numerous processes including neuronal plasticity. This study investigates the regulation of cytosolic calcium by corticotropin-releasing factor (CRF) in midbrain dopamine neurons. The results demonstrate that CRF stimulates the release of intracellular calcium from stores through activation of adenylyl cyclase and PKA. Imaging and photolysis experiments showed that the calcium originated from dendrites and required both functional IP3 and ryanodine receptor channels. The elevation in cytosolic calcium potentiated calcium-sensitive potassium channels (sK) activated by action potentials and metabotropic Gq-coupled receptors for glutamate and acetylcholine. This increase in cytosolic calcium activated by postsynaptic Gs-coupled CRF receptors may represent a fundamental mechanism by which stress peptides and hormones can shape Gq-coupled receptor-mediated regulation of neuronal excitability and synaptic plasticity in dopamine neurons.

The corticotrophin-releasing factor-like peptide urocortin reverses key deficits in two rodent models of Parkinson's disease

The potential neuroprotective action of the corticotrophin-releasing factor-related peptide urocortin (UCN) was investigated in the rat 6-hydroxydopamine (6-OHDA) and lipopolysaccharide (LPS) paradigms of Parkinson's disease. UCN (20 fmol) was either given at the same time as (T = 0) or 7 days after (T = +7) intracerebral 6-OHDA or LPS injection. At 14 days after 6-OHDA or LPS injection, circling behaviour was measured following apomorphine challenge. Circling was significantly lower in rats given UCN at either T = 0 or T = +7 compared with animals given 6-OHDA or LPS and vehicle. Sham-treated rats showed no circling. Consistent with these observations, striatal dopamine concentrations were markedly higher in 6-OHDA/LPS + UCN rats vs. 6-OHDA/LPS + vehicle groups. Additionally, L-dihydroxyphenylalanine production by tyrosine hydroxylase was greatly reduced in the striata of 6-OHDA/LPS + vehicle rats, whereas this was not the case in rats coadministered UCN. Finally, the numbers of tyrosine hydroxylase-positive cells recorded in the substantia nigra of 6-OHDA/LPS + vehicle-treated animals were markedly lower than those of sham-operated or 6-OHDA/LPS + UCN rats. Critically, UCN was effective in reversing lesion-induced deficits when given either at the same time as or 7 days after the neurotoxic insult. To our knowledge, this is the first time that such an effect has been demonstrated in vivo. The apparent ability of UCN to arrest the progression of or even reverse nigral lesions once established suggests that pharmacological manipulation of this system could have substantial therapeutic utility.

Effects of celecoxib on voltage-gated calcium channel currents in rat pheochromocytoma (PC12) cells

Cyclooxygenase-2 (COX-2) plays crucial roles in the development and invasion of tumors. Celecoxib, a selective COX-2 inhibitor, has been shown to be chemopreventive against cancer. However, to date, the mechanisms of these effects remain unclear. In this study, we investigate the effects of celecoxib on voltage-gated calcium channel (VGCC) currents in undifferentiated pheochromocytoma (PC12) cells using whole-cell patch clamp. Our results showed that celecoxib, instead of rofecoxib or NS-398, another selective COX-2 inhibitor, reversibly inhibited the current density of VGCC in a concentration-dependent manner, but had no apparent effects on the cells treated with nifedipine (1 microM), an L-type calcium channel blocker. Upon pre-incubation of PC12 cells with omega-conotoxia GVIA (1 microM), an N-type calcium channel blocker, omega-agatoxin IVA (1microM), a P/Q-type calcium channel blocker, or SNX-482 (1microM), a R-type calcium channel blocker, celecoxib (1microM) inhibited the currents by 36%, 28%, and 25%, respectively. Celecoxib up-shifted the current-voltage (I-V), and hyperpolarizedly shifted the inactivation curve, but did not markedly affect the activation curve. Intracellular application of H89, a protein kinase A inhibitor, failed to affect the celecoxib's VGCC currents inhibition. Taken together, our present results suggested that celecoxib inhibited L-type calcium channels in PC12 cells via a COX-2 independent pathway, which might be responsible for its clinical effects including anti-tumor.

Modulation of T-type Ca2+ channels by corticotropin-releasing factor through protein kinase C pathway in MN9D dopaminergic cells

Corticotrophin-releasing factor (CRF) is the main regulator of the body's stress axis and its signal is translated through G-protein-coupled CRF receptors (CRF-R1, CRF-R2). Even though CRF receptors are present in the midbrain dopamine neurons, the cellular mechanism of CRF action is not clear yet. Since voltage-dependent Ca(2+) channels are highly expressed and important in dopamine neuronal functions, we tested the effect of CRF on voltage-dependent Ca(2+) channels in MN9D cells, a model of dopamine neurons. The application of CRF-related peptide, urocortin 1, reversibly inhibited T-type Ca(2+) currents, which was a major Ca(2+) channel in the cells. The effect of urocortin was abolished by specific CRF-R1 antagonist and was mimicked by protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate. PKC inhibitors abolished the effect of urocortin. These results suggest that urocortin modulates T-type Ca(2+) channel by interacting with CRF-R1 via the activation of PKC signal pathway in MN9D cells.