Achilleas Gravanis

Corticotropin-releasing hormone promotes blastocyst implantation and early maternal tolerance

The semi-allograft embryo in the blastocyst stage implants itself in the endometrium, yet no immune rejection processes are activated. Embryonic trophoblast and maternal decidua produce corticotropin-releasing hormone (CRH) and express Fas ligand (FasL), a proapoptotic cytokine. We found that antalarmin, a CRH receptor type 1 antagonist, decreased FasL expression and promoted apoptosis of activated T lymphocytes, an effect which was potentiated by CRH and inhibited by antalarmin. Female rats treated with antalarmin showed a marked decrease in implantation sites and live embryos and diminished endometrial FasL expression. Embryos from mothers that lacked T cells or from syngeneic matings were not rejected when the mothers were given antalarmin. These findings suggested that locally produced CRH promotes implantation and maintenance of early pregnancy primarily by killing activated T cells.

Neurosteroids as Endogenous Inhibitors of Neuronal Cell Apoptosis in Aging

Abstract:  The neuroactive steroids dehydroepiandrosterone (DHEA), its sulfate ester DHEAS, and allopregnanolone (Allo) are produced in the adrenals and the brain. Their production rate and levels in serum, brain, and adrenals decrease gradually with advancing age. The decline of their levels was associated with age‐related neuronal dysfunction and degeneration, most probably because these steroids protect central nervous system (CNS) neurons against noxious agents. Indeed, DHEA(S) protects rat hippocampal neurons against NMDA‐induced excitotoxicity, whereas Allo ameliorates NMDA‐induced excitotoxicity in human neurons. These steroids exert also a protective role on the sympathetic nervous system. Indeed, DHEA, DHEAS, and Allo protect chromaffin cells and the sympathoadrenal PC12 cells (an established model for the study of neuronal cell apoptosis and survival) against serum deprivation–induced apoptosis. Their effects are time‐ and dose‐dependent with EC50 1.8, 1.1, and 1.5 nM, respectively. The prosurvival effect of DHEA(S) appears to be NMDA‐, GABAA‐ sigma1‐, or estrogen receptor‐independent, and is mediated by G‐protein‐coupled‐specific membrane binding sites. It involves the antiapoptotic Bcl‐2 proteins, and the activation of prosurvival transcription factors CREB and NF‐κB, upstream effectors of the antiapoptotic Bcl‐2 protein expression, as well as prosurvival kinase PKCα/β, a posttranslational activator of Bcl‐2. Furthermore, they directly stimulate biosynthesis and release of neuroprotective catecholamines, exerting a direct transcriptional effect on tyrosine hydroxylase, and regulating actin depolymerization and submembrane actin filament disassembly, a fast‐response cellular system regulating trafficking of catecholamine vesicles. These findings suggest that neurosteroids may act as endogenous neuroprotective factors. The decline of neurosteroid levels during aging may leave the brain unprotected against neurotoxic challenges.

Neurosteroid Dehydroepiandrosterone Interacts with Nerve Growth Factor (NGF) Receptors, Preventing Neuronal Apoptosis

The neurosteroid dehydroepiandrosterone (DHEA), produced by neurons and glia, affects multiple processes in the brain, including neuronal survival and neurogenesis during development and in aging. We provide evidence that DHEA interacts with pro-survival TrkA and pro-death p75NTR membrane receptors of neurotrophin nerve growth factor (NGF), acting as a neurotrophic factor: (1) the anti-apoptotic effects of DHEA were reversed by siRNA against TrkA or by a specific TrkA inhibitor; (2) [3H]-DHEA binding assays showed that it bound to membranes isolated from HEK293 cells transfected with the cDNAs of TrkA and p75NTR receptors (KD: 7.4±1.75 nM and 5.6±0.55 nM, respectively); (3) immobilized DHEA pulled down recombinant and naturally expressed TrkA and p75NTR receptors; (4) DHEA induced TrkA phosphorylation and NGF receptor-mediated signaling; Shc, Akt, and ERK1/2 kinases down-stream to TrkA receptors and TRAF6, RIP2, and RhoGDI interactors of p75NTR receptors; and (5) DHEA rescued from apoptosis TrkA receptor positive sensory neurons of dorsal root ganglia in NGF null embryos and compensated NGF in rescuing from apoptosis NGF receptor positive sympathetic neurons of embryonic superior cervical ganglia. Phylogenetic findings on the evolution of neurotrophins, their receptors, and CYP17, the enzyme responsible for DHEA biosynthesis, combined with our data support the hypothesis that DHEA served as a phylogenetically ancient neurotrophic factor.

Membrane androgen receptor activation triggers down-regulation of PI-3K/Akt/NF-kappaB activity and induces apoptotic responses via Bad, FasL and caspase-3 in DU145 prostate cancer cells

BackgroundRecently we have reported membrane androgen receptors-induced apoptotic regression of prostate cancer cells regulated by Rho/ROCK/actin signaling. In the present study we explored the specificity of these receptors and we analyzed downstream effectors controlling survival and apoptosis in hormone refractory DU145-prostate cancer cells stimulated with membrane androgen receptor-selective agonists.ResultsUsing membrane impermeable conjugates of serum albumin covalently linked to testosterone, we show here down-regulation of the activity of pro-survival gene products, namely PI-3K/Akt and NF-κB, in DU145 cells. Testosterone-albumin conjugates further induced FasL expression. A FasL blocking peptide abrogated membrane androgen receptors-dependent apoptosis. In addition, testosterone-albumin conjugates increased caspase-3 and Bad protein activity. The actin cytoskeleton drug cytochalasin B and the ROCK inhibitor Y-27632 inhibited FasL induction and caspase-3 activation, indicating that the newly identified Rho/Rock/actin signaling may regulate the downstream pro-apoptotic effectors in DU145 cells. Finally, other steroids or steroid-albumin conjugates did not interfere with these receptors indicating testosterone specificity.ConclusionCollectively, our results provide novel mechanistic insights pointing to specific pro-apoptotic molecules controlling membrane androgen receptors-induced apoptotic regression of prostate cancer cells and corroborate previously published observations on the potential use of membrane androgen receptor-agonists as novel anti-tumor agents in prostate cancer.

Corticotropin-releasing hormone (CRH) and immunotolerance of the fetus

The hypothalamic neuropeptide corticotropin-releasing hormone (CRH) is produced by several tissues of the female reproductive system, including the endometrial glands and decidualized stroma, as well as the trophoblast, syncytiotrophoblast, and placental decidua. CRH is also secreted at inflammatory sites and possesses potent pro-inflammatory properties influencing both innate and acquired immune processes. Recent experimental findings show that uterine CRH participates in local immune phenomena associated with early pregnancy, such as differentiation of endometrial stroma to decidua and protection of the fetus from the maternal immune system. CRH induces the expression of apoptotic Fas ligand (FasL) on invasive extravillous trophoblast and maternal decidual cells at the fetal-maternal interface. Furthermore, CRH increases the apoptosis of activated T lymphocytes through FasL induction, participating in the processes of both implantation and early pregnancy tolerance.

Effects of novel synthetic microneurotrophins in diabetic retinopathy

Diabetic retinopathy (DR) is a neovascular, inflammatory and neurodegenerative disease. The neovascular component is treatable but no therapeutic agents are available for the other two components. Early changes in the diabetic retina include neuronal death of amacrine and retinal ganglion cells (RGC)(Barber et al., J Clin Invest,1998), and elevated levels of inflammatory mediators (Yoshimura et al., Plos One,2009). Nerve Growth factor (NGF) receptors, namely TrkA and p75NTR, are expressed in RGC. The TrkA receptor activates prosurvival, while p75NTR activates inflammatory and apoptotic pathways (Mysona et al., Expert Rev Ophthalmol,2014). Dehydroepiandrosterone (DHEA) binds to both receptors, mimicking NGF. It affords anti-apoptotic, neuroprotective and anti-inflammatory effects in the retina (Kokona et al., Neuro-pharmacol, 2012, Straub et al., J Clin Endocrinol, 1998). The therapeutic use of DHEA is restricted due to its metabolic products. The main objective of this study was to investigate and compare the neuroprotective and anti-inflammatory effects of DHEA and its spiro-epoxy derivatives BNN27 and BNN20(Calogeropoulou et al., J Med Chem,2009) (not metabolized to estrogens and androgens), in the rat streptozotocin model of DR. BNN27, via TrkA activation, protected in a dose-dependent manner (2, 10, 50mg/kg, ip) bNOS (brain nitric oxide synthetase) and TH (tyrosine hydroxylase) expressing amacrine cells and ganglion axons (NFL immunoreactivity) similar to DHEA’s actions, while BNN20 was less effective. BNN27 activated the TrkA prosurvival signaling pathway ERK1/2 kinase. It reduced the activation of SAPK/JNK kinase and the expression of p75NTR. BNN27 also increased the expression of anti-inflammatory cytokines (IL10). These results suggest that NGF TrkA receptor is involved in the neuroprotective and anti-inflammatory effects of BNN27 and is a valuable target via which BNN27 could afford efficacious therapeutics for the treatment of DR.

The PC12 rat pheochromocytoma cell line expresses the prodynorphin gene and secretes the 8 kDa dynorphin product

Most adrenal chromaffin cells synthesize opioids derived from proenkephalin but not from prodynorphin. However, human pheochromocytomas and the PC12 rat pheochromocytoma cell line synthesize dynorphins. The aim of this study was to confirm the presence of the authentic prodynorphin transcript and its dynorphin product in PC12 cells. We have found that the sequence of a 458 bp cDNA fragment derived from RT-PCR amplification of total PC12 RNA was in complete accordance with the published sequence of the equivalent region of the prodynorphin gene. It encodes the potent endogenous kappa opioid agonists alpha-neo-endorphin, dynorphin A and dynorphin B. Furthermore, immunoaffinity-purified PC12 cell extracts were subjected to RP-HPLC. Most of its IR-dynorphin eluted on a peak exhibiting the retention time of similarly treated rat anterior pituitary. The expression of the prodynorphin gene in pheochromocytomas can be explained as either the result of (a) the process of dedifferentiation of chromaffin cells to pheochromocytoma which may thus cause the expression of a previously unexpressed prodynorphin or that (b) those pheochromocytomas expressing the prodynorphin gene derive from the few, centrally located chromaffin cells, which express this gene even under normal conditions.

Uterine and Embryonic Trophoblast CRH Promotes Implantation and Maintenance of Early Pregnancy

Abstract: Epithelial cells of human endometrium and differentiated endometrial stromal cells express the corticotropin‐releasing hormone (CRH) gene. CRH is also produced by the human placental cytotrophoblast. Endometrial and placental CRH is under the endocrine control of gonadal steroids as well as under an autocrine/paracrine regulation by prostanoids and interleukins. Human endometrium, myometrium and placenta also express the relevant receptors. Invasive trophoblasts promote apoptosis of activated Fas‐expressing human T lymphocytes, an effect potentiated by CRH and inhibited by the CRH type 1 antagonist, antalarmin. Female rats treated with antalarmin during the first 6 days of gestation had a dose‐dependent decrease of implantation sites and live embryos, and significantly decreased endometrial FasL expression. Our data suggest important physiological roles of endometrial and placental CRH in the regulation of decidualization, blastocyst implantation, and early maternal tolerance.