ABSTRACT
The neurotrophic effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on rat sensory neuronal cell line ND7/23 cells were investigated. PACAP caused a concentration-dependent increase in the number of neurite-bearing cells and the expression of the substance P precursor (PPT) mRNA in 24 h. The effects of PACAP were mimicked by vasoactive intestinal polypeptide with lower potency and dibutyryl-cyclic AMP, and inhibited by inhibitors of protein kinase A, ERK kinase or p38 kinase, KT5720, U0126, or SB203580, respectively. In a PPT promoter luciferase reporter assay, the increase of PPT mRNA was the result of an increase in PPT gene transcriptional activity by PACAP. The increasing effects of PACAP on PPT mRNA were similarly observed in primary cultured rat dorsal root ganglion cells. Thus, PACAP could induce differentiation-like phenomena in sensory neurons in a cAMP-, protein kinase A-, ERK kinase-, and p38 kinase-dependent manner. These results provide evidence of the neurotrophic action of PACAP, which may function to rescue damaged neurons or to switch the neuronal phenotype in injured or inflamed sensory neurons.
Subject(s)
Cyclic AMP-Dependent Protein Kinases/physiology , Pituitary Adenylate Cyclase-Activating Polypeptide/pharmacology , Sensory Receptor Cells/drug effects , Signal Transduction/drug effects , Substance P/biosynthesis , Animals , Cell Differentiation/drug effects , Cells, Cultured/drug effects , Cells, Cultured/metabolism , Cyclic AMP-Dependent Protein Kinases/antagonists & inhibitors , Extracellular Signal-Regulated MAP Kinases/antagonists & inhibitors , Extracellular Signal-Regulated MAP Kinases/physiology , Ganglia, Spinal/cytology , Gene Expression Regulation/drug effects , Genes, Reporter , Hybrid Cells/drug effects , Hybrid Cells/metabolism , Male , Neurites/drug effects , Neurites/ultrastructure , Phenotype , Protein Kinase Inhibitors/pharmacology , Protein Precursors/biosynthesis , Protein Precursors/genetics , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , Rats , Rats, Wistar , Recombinant Fusion Proteins/biosynthesis , Recombinant Fusion Proteins/genetics , Reverse Transcriptase Polymerase Chain Reaction , Sensory Receptor Cells/metabolism , Sensory Receptor Cells/ultrastructure , Substance P/genetics , Tachykinins/biosynthesis , Tachykinins/genetics , Transcription, Genetic/drug effects , p38 Mitogen-Activated Protein Kinases/antagonists & inhibitors , p38 Mitogen-Activated Protein Kinases/physiologyABSTRACT
Thrombin activates immunocompetent microglia and increases release of inflammatory cytokines under intracerebral hemorrhage (ICH) insults. Also, thrombin injection into the striatum evokes acute necrosis and delayed apoptosis of neurons. A nucleoprotein high-mobility group box 1 (HMGB1) that is released from necrotic cells has been suggested to behave like a cytokine and cause over-facilitation of immune functions. Here we examined the effect of glycyrrhizin, known as an inhibitor of HMGB1, on thrombin-induced injury in rat cortico-striatal slice cultures and in vivo rat ICH model. In slice cultures, thrombin-induced a drastic increase in propidium iodide fluorescence indicating necrotic cell death in the cortical region, and robust shrinkage of the striatal tissue. Glycyrrhizin (10-100 µM) attenuated thrombin-induced cortical injury in a concentration-dependent manner. The protective effect of glycyrrhizin was not mediated by glucocorticoid receptors or modulation of nitric oxide production, but was reversed by exogenous HMGB1 application. The injury induced by a high concentration of HMGB1 was suppressed by glycyrrhizin. In vivo, unilateral injection of type IV collagenase into rat striatum induced ICH associated with brain edema formation, contralateral paralysis and neuron death. Once daily intraperitoneal administration of glycyrrhizin attenuated ICH-induced edema in both the cortex and the basal ganglia, and improved behavioral performance of rats in forelimb placing. Moreover, glycyrrhizin partially but significantly ameliorated ICH-induced neuron loss inside hematoma. These findings suggest that an HMGB1 inhibitor glycyrrhizin is a potential candidate for a remedy for ICH.