Browsing by Subject "cAMP"

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    The cAMP transduction cascade mediates the prostaglandin E2 enhancement of the capsaicin-elicited current in rat sensory neurons: whole-cell and single-channel studies
    (Society for Neuroscience, 1998-08-15) Lopshire, John C.; Nicol, Grant D.; Pharmacology and Toxicology, School of Medicine
    Treatment with proinflammatory prostaglandin E2 (PGE2) produced a transient sensitization of whole-cell currents elicited by the vanilloid capsaicin. The intracellular signaling pathways that mediate the initiation of this PGE2-induced sensitization of the capsaicin-elicited current in rat sensory neurons are not well established. Treatment with either forskolin (100 nM to 10 microM) or membrane-permeant analogs of cAMP, 8-bromo-cAMP (8-Br-cAMP) and chlorphenylthio-cAMP (10 microM to 1 mM), transiently sensitized neuronal responses elicited by capsaicin in a manner analogous to that produced by PGE2. The duration of sensitization was lengthened with increasing concentrations of forskolin; however, higher concentrations of 8-Br-cAMP or chlorphenylthio-cAMP led to a shortening of sensitization. The inactive analog of forskolin, dideoxy-forskolin, had no effect on capsaicin responses. Inclusion of the inhibitor of protein kinase A in the recording pipette completely suppressed the sensitization produced by PGE2 or forskolin. In recordings from membrane patches in the cell-attached configuration, the bath application of capsaicin evoked single-channel currents in which the level of channel activity was concentration-dependent and had an EC50 of 1.4 microM. These single-channel currents evoked by capsaicin exhibited an apparent reversal potential of +4 mV and were blocked by the capsaicin antagonist capsazepine. Exposure of the sensory neuron to either PGE2 or forskolin produced a large and transient increase in the mean channel activity (NPo) elicited by capsaicin, although the unitary conductance remained unaltered. Taken together, these observations suggest that modulation of the capsaicin-gated channel by the cAMP-protein kinase A signaling pathway enhanced the gating of these channels and consequently resulted in the sensitization of the whole-cell currents.
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    The Effects of Taurocholic Acid on Biliary Damage and Liver Fibrosis Are Mediated by Calcitonin-Gene-Related Peptide Signaling
    (MDPI, 2022-05-09) Mancinelli, Romina; Ceci, Ludovica; Kennedy, Lindsey; Francis, Heather; Meadows, Vik; Chen, Lixian; Carpino, Guido; Kyritsi, Konstantina; Wu, Nan; Zhou, Tianhao; Sato, Keisaku; Pannarale, Luigi; Glaser, Shannon; Chakraborty, Sanjukta; Alpini, Gianfranco; Gaudio, Eugenio; Onori, Paolo; Franchitto, Antonio; Medicine, School of Medicine
    Background & aims: Cholangiocytes are the target cells of liver diseases that are characterized by biliary senescence (evidenced by enhanced levels of senescence-associated secretory phenotype, SASP, e.g., TGF-β1), and liver inflammation and fibrosis accompanied by altered bile acid (BA) homeostasis. Taurocholic acid (TC) stimulates biliary hyperplasia by activation of 3',5'-cyclic cyclic adenosine monophosphate (cAMP) signaling, thereby preventing biliary damage (caused by cholinergic/adrenergic denervation) through enhanced liver angiogenesis. Also: (i) α-calcitonin gene-related peptide (α-CGRP, which activates the calcitonin receptor-like receptor, CRLR), stimulates biliary proliferation/senescence and liver fibrosis by enhanced biliary secretion of SASPs; and (ii) knock-out of α-CGRP reduces these phenotypes by decreased cAMP levels in cholestatic models. We aimed to demonstrate that TC effects on liver phenotypes are dependent on changes in the α-CGRP/CALCRL/cAMP/PKA/ERK1/2/TGF-β1/VEGF axis. Methods: Wild-type and α-CGRP-/- mice were fed with a control (BAC) or TC diet for 1 or 2 wk. We measured: (i) CGRP levels by both ELISA kits in serum and by qPCR in isolated cholangiocytes (CALCA gene for α-CGRP); (ii) CALCRL immunoreactivity by immunohistochemistry (IHC) in liver sections; (iii) liver histology, intrahepatic biliary mass, biliary senescence (by β-GAL staining and double immunofluorescence (IF) for p16/CK19), and liver fibrosis (by Red Sirius staining and double IF for collagen/CK19 in liver sections), as well as by qPCR for senescence markers in isolated cholangiocytes; and (iv) phosphorylation of PKA/ERK1/2, immunoreactivity of TGF-β1/TGF- βRI and angiogenic factors by IHC/immunofluorescence in liver sections and qPCR in isolated cholangiocytes. We measured changes in BA composition in total liver by liquid chromatography/mass spectrometry. Results: TC feeding increased CALCA expression, biliary damage, and liver inflammation and fibrosis, as well as phenotypes that were associated with enhanced immunoreactivity of the PKA/ERK1/2/TGF-β1/TGF-βRI/VEGF axis compared to BAC-fed mice and phenotypes that were reversed in α-CGRP-/- mice fed TC coupled with changes in hepatic BA composition. Conclusion: Modulation of the TC/ α-CGRP/CALCRL/PKA/ERK1/2/TGF-β1/VEGF axis may be important in the management of cholangiopathies characterized by BA accumulation.
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    The PDE4 Inhibitors Roflumilast and Rolipram Rescue ADO2 Osteoclast Resorption Dysfunction
    (Springer, 2024-03-14) Hong, Jung Min; Gerard-O’Riley, Rita L.; Acton, Dena; Alam, Imranul; Econs, Michael J.; Bruzzaniti, Angela; Biomedical Sciences and Comprehensive Care, School of Dentistry
    Autosomal Dominant Osteopetrosis type II (ADO2) is a rare bone disease of impaired osteoclastic bone resorption caused by heterozygous missense mutations in the chloride channel 7 (CLCN7). Adenylate cyclase, which catalyzes the formation of cAMP, is critical for lysosomal acidification in osteoclasts. We found reduced cAMP levels in ADO2 osteoclasts compared to wild-type (WT) osteoclasts, leading us to examine whether regulating cAMP would improve ADO2 osteoclast activity. Although forskolin, a known activator of adenylate cyclase and cAMP levels, negatively affected osteoclast number, it led to an overall increase in ADO2 and WT osteoclast resorption activity in vitro. Next, we examined cAMP hydrolysis by the phosphodiesterase 4 (PDE4) proteins in ADO2 versus WT osteoclasts. QPCR analysis revealed higher expression of the three major PDE4 subtypes (4a, 4b, 4d) in ADO2 osteoclasts compared in WT, consistent with reduced cAMP levels in ADO2 osteoclasts. In addition, we found that the PDE4 antagonists, rolipram and roflumilast, stimulated ADO2 and WT osteoclast formation in a dose-dependent manner. Importantly, roflumilast and rolipram displayed a concentration-dependent increase in osteoclast resorption activity which was greater in ADO2 than WT osteoclasts. Moreover, treatment with roflumilast rescued cAMP levels in ADO2 OCLs. The key findings from our studies demonstrate that osteoclasts from ADO2 mice exhibit reduced cAMP levels and PDE4 inhibition rescues cAMP levels and ADO2 osteoclast activity dysfunction in vitro. The mechanism of action of PDE4 inhibitors and their ability to reduce the high bone mass of ADO2 mice in vivo are currently under investigation. Importantly, these studies advance the understanding of the mechanisms underlying the ADO2 osteoclast dysfunction which is critical for the development of therapeutic approaches to treat clinically affected ADO2 patients.