Klaus Fechner

Cutaneous Expression of CRH and CRH-R: Is There a “Skin Stress Response System?”

ABSTRACT: The classical neuroendocrine pathway for response to systemic stress is by hypothalamic release of corticotropin releasing hormone (CRH), subsequent activation of pituitary CRH receptors (CRH‐R), and production and release of proopiomelanocortin (POMC) derived peptides. It has been proposed that an equivalent to the hypothalamic‐pituitary‐adrenal axis functions in mammalian skin, in response to local stress (see Reference 1 ). To further define such system we used immunocytochemistry, RP‐HPLC separation, and RIA techniques, in rodent and human skin, and in cultured normal and malignant melanocytes and keratinocytes. Production of mRNA for CRH‐R1 was documented in mouse and human skin using RT‐PCR and Northern blot techniques; CRH binding sites and CRH‐R1 protein were also identified. Addition of CRH to immortalized human keratinocytes, and to rodent and human melanoma cells induced rapid, specific, and dose‐dependent increases in intracellular Ca2+. The latter were inhibited by the CRH antagonist α‐helical‐CRH(9–41) and by the depletion of extracellular calcium with EGTA. CRH production was enhanced by ultraviolet light radiation and forskolin (a stimulator for intracellular cAMP production), and inhibited by dexamethasone. Thus, evidence that skin cells, both produce CRH and express functional CRH‐R1, supports the existence of a local CRH/CRH‐R neuroendocrine pathway that may be activated within the context of a skin stress response system.

CORTICOTROPIN RELEASING HORMONE AND RELATED PEPTIDES CAN ACT AS BIOREGULATORY FACTORS IN HUMAN KERATINOCYTES

SummaryFollowing previous findings in human skin of the functional expression of genes for the corticotropin releasing hormone (CHR) receptor type 1 (CRH-R1) and CRH itself, we searched for local phenotypic effects for peptides related to CRH. We now report that CRH, sauvagine, and urocortin inhibit proliferation of human HaCaT keratinocytes in a dose-dependent manner. The peptides produced variable cyclic adenosine 3′∶5′-monophosphate stimulation with CRH having the highest potency. Binding of iodine 125 CRH to intact keratinocytes was inhibited by increasing doses of CRH, sauvagine, or urocortin, all showing equal inhibitory potency. Immunocytochemistry identified CRH-R1 immunoreactivity in HaCaT keratinocytes. In conclusion, CRH (exogenous or produced locally) and the related urocortin and sauvagine peptides can modify human keratinocyte phenotype through a receptor-mediated pathway.

Intracellular calcium measurements of single human skin cells after stimulation with corticotropin-releasing factor and urocortin using confocal laser scanning microscopy

Using confocal laser scanning microscopy we investigated the Ca2+ distribution in single corticotropin releasing factor- and urocortin-stimulated human skin cells. The models tested included melanoma cells, neonatal melanocytes and keratinocytes, and immortalized HaCaT keratinocytes. The changes in intracellular Ca2+ signal intensities observed after stimulation of different cell types with corticotropin releasing factor and urocortin showed that: (1) the increase of intracellular Ca2+ concentration was caused by a Ca2+ influx (inhibition by EGTA); (2) this Ca2+ influx took place through voltage-activated Ca2+ ion channels (inhibition by d-cis-diltiazem, verapamil) and (3) cyclic nucleotide-gated ion channels were not involved in this process (no effect of Mg2+). The effects were also observed at very low peptide concentrations (10-13 M) with no apparent linear correlation between peptide dosage and increase of fluorescence intensity, which implied co-expression of different corticotropin releasing factor receptor forms in the same cell. Immortalized (HaCaT) keratinocytes exhibited the strongest differential increases of a Ca2+ fluorescence after peptide-stimulation. Corticotropin releasing factor induced Ca2+ flux into the cytoplasm, while urocortin Ca2+ flux into the nucleus with a remarkable oscillatory effect. The latter indicated the presence of an intracellular urocortin-induced signal transduction pathway that is unique to keratinocytes.

Substance P: in vitro inactivation by rat brain fractions and human plasma.

Abstract The in vitro degradation of substance P (SP) by rat brain fractions and human plasma was studied by means of polyacrylamide gel electrophoresis and 3 H-[Nle] 11 SP. Substance P was degraded by neutral metalloendopeptidase systems of the crude synaptosomal fraction and plasma with K m values of 3.6 × 10 −5 and 8 × 10 −6 M, respectively. The peptide was also degraded by other subcellular brain fractions. The degradation rates corresponded with the biological inactivation as assayed on guinea pig ileum. The basic N-terminal sequence of the peptide was found to be important for this inactivation. No specific uptake of the peptide in the synaptosomal brain fraction could be observed. It is concluded that in vivo substance P is degraded with first order dependence and that this proteolytic breakdown is responsible for the termination of the biological activity of substance P as a putative neurotransmitter or neuromodulator.

Corticotropin-releasing hormone (CRH) receptors in the mesenteric small arteries of rats resemble the (2)-subtype☆

The potencies of the corticotropin-releasing hormone (CRH) agonistic peptides oCRH, h/rCRH, frog sauvagine, and carp urotensin I and of the antagonistic peptide alpha-helical CRH9-41 were compared in 3 different in vitro assays: (a) receptor binding to rat brain membranes; (b) release of ACTH/beta-endorphin from rat pituitary cells; and (c) relaxation of rat mesenteric small arteries. From their potency profiles, especially from the high potency of sauvagine relative to CRH in the relaxation assay, it is concluded that the receptors mediating the hypotensive action of systemic CRH in vascular smooth muscle are different from those in the pituitary and brain, and may be identical or very similar to the recently cloned new CRH receptor type 2.

Hexa-histidin tag position influences disulfide structure but not binding behavior of in vitro folded N-terminal domain of rat corticotropin-releasing factor receptor type 2a

The oxidative folding, particularly the arrangement of disulfide bonds of recombinant extracellular N‐terminal domains of the corticotropin‐releasing factor receptor type 2a bearing five cysteines (C2 to C6), was investigated. Depending on the position of a His‐tag, two types of disulfide patterns were found. In the case of an N‐terminal His‐tag, the disulfide bonds C2–C3 and C4–C6 were found, leaving C5 free, whereas the C‐terminal position of the His‐tag led to the disulfide pattern C2–C5 and C4–C6, and leaving C3 free. The latter pattern is consistent with the disulfide arrangement of the extracellular N‐terminal domain of the corticotropin‐releasing factor (CRF) receptor type 1, which has six cysteines (C1 to C6) and in which C1 is paired with C3. However, binding data of the two differently disulfide‐bridged domains show no significant differences in binding affinities to selected ligands, indicating the importance of the C‐terminal portion of the N‐terminal receptor domains, particularly the disulfide bond C4–C6 for ligand binding.

Influence of Continuous Levels of Fentanyl in Rats on the μ-Opioid Receptor in the Central Nervous System

The highly potent and efficacious mu-opioid agonist fentanyl was SC infused into rats with submaximal analgesic doses (0-1.14 mumol/kg/day) continuously for 8 days, checked by the constant daily urinary recovery of intact drug (0.43 +/- 0.031% of the daily dose). Tail-flick latencies measured at 24 (day 1) and 48 h (day 2) after starting the infusion were increased in a dose-dependent fashion compared with those before the infusion (day 0). However, at day 8, the latencies were increased only weakly, not significantly, revealing tolerance to the antinociceptive activity of fentanyl. Fentanyl at all doses showed no significant effect on the capacity (Bmax) and affinity (Kd) of the mu-opioid receptor binding of DAMGO to whole brain (Bmax 126.2 +/- 3.00 fmol/mg protein, Kd 1.00 +/- 0.04 nM) and spinal cord (Bmax 48.24 +/- 2.71 fmol/mg protein, Kd 1.93 +/- 0.13 nM) membranes gained from the rats after killing them at day 8. Gpp(NH)p increased the Kd for brain and spinal cord sites by 3.09 and 2.65, respectively, independent of the fentanyl dose. The infusion with fentanyl did not after the basal and forskolin-stimulated adenylate cyclase activity in the whole brain membranes, nor did it change the inhibition of the forskolin-stimulated activity by DAMGO. It is concluded that, in rats, constant long-term body levels of highly potent mu-agonists result in a tolerant state that, however, does not produce overall changes in the parameters of their specific receptor sites in the CNS, i.e., receptor capacity and affinity, and in the events closely related to them, i.e., their regulation by GTP and of adenylate cyclase. This does not exclude such possible changes to be restricted to specific regions in the CNS.

In-vivo Release of a GnRH Agonist from a Slow-release Poly(lactide-glycolide) Copolymer Preparation: Comparison in Rat, Rabbit and Guinea-Pig

Abstract— Different batches of 50:50 poly((±)‐lactide‐glycolide) copolymer (PLG) were used as biodegradable carriers for D‐Phe6‐gonadotropin‐releasing hormone (GnRHa) in the form of injectable long‐acting implants loaded with 10% GnRHa and tracer amounts of [125I]GnRHa. After their injection subcutaneously into rats, rabbits, and guinea‐pigs, the release kinetics of the peptide were determined by counting the radioactivity remaining in the implants (i) after recovery from the rats after death or (ii) directly on the skin above the injection site of rabbits and guinea‐pigs in‐vivo. No significant differences in the release pattern of the peptide amongst the three species whether the release process was controlled by diffusion or by degradation of the polymeric matrix were found. It is concluded that the results of in‐vivo release tests using laboratory animals are valid for man and that enzymes are not involved in the degradation of the polymeric matrix. The results may be of general importance for the use of long‐term release PLG formulations of highly active drugs, especially peptides and proteins.

Effect of dextran on the release of gonadotropin-releasing hormone (GnRH) injected into rats: plasma GnRH and gonadotropin response.

Prolonged release of the peptide gonadotropin-releasing hormone (GnRH) from its aqueous solution was achieved by addition of the polymer dextran (Mw ∼ 500,000). This effect observed in an in vitro system was caused by a decrease of the diffusion coefficient of the peptide. When GnRH was intramuscularly injected into male rats, the addition of dextran to the injected peptide solution led to a prolongation of the GnRH plasma level at the expense of its peak value. This change can be explained by a decrease of the absorption rate of GnRH into blood, which parallels the in vitro observation. As a result, the gonadotropin response to GnRH was stronly increased.

Ago-antagonists for G protein-coupled peptide hormone receptor by modifying the agonist's signalling domain.

Introduction Most of the pharmaceuticals today target at G protein-coupled receptors (GPCRs) [1] that transmit extracellular signals into cells. GPCRs are promiscuous, that means a single receptor can activate different signalling events, presumably via different G protein subtypes. Functional selectivity of GPCR ligands has been observed and points at a new orientation in pharmaceutical research. However, the structural characteristics of ligands that produce this selectivity are far from known [2]. The polypeptide hormone urocortin I (Ucn) activates both Gs and Gi proteins via the corticotropin-releasing factor receptor type 1 (CRF1). We have recently developed an easy method for the separate measurement of Gs and Gi activation at HEK 293 cells stably transfected with cDNA coding for CRF1 [3,4]. The aim of this study was to search for structural determinants of the peptide agonist Ucn (DDPPLSIDLT FHLLRTLLEL ARTQSQRERA EQNRIIFDSV-NH2) that direct the signalling to Gs and Gi, respectively. For this purpose, the effect of single replacements by bulky amino acids, benzoyl-phenylalanine (Bpa) and naphthyl alanine (Nal), on Gs and Gi signalling pathways was measured in HEK-CRF1 cells, using receptor binding, [S]-GTPγS binding stimulation, and cAMP accumulation assays.