The Signaling Pathway Of Glucocorticoids On Its Rapid Regulation Of Vascular Smooth Muscle Cells Contraction Mediated By Norepinephrine

Glucocorticoids (GCs) are steroid hormones secreted by adrenal cortex zona fasciculate cells. They have a wide range of physiological and clinical significance. They play a pivotal role in stress and are successfully used in anti-allergic, anti-inflammatory and immunosuppressive.Over the passed decades, it was widely assumed that GCs work solely through regulating gene expression and synthesis of protein, which needs several hours or days to take its biological effect. Recent evidence, however, indicates that GCs can also exert rapid non-genomic effects on various tissues and cells. Non-genomic effects characterized as short latency and insensitive to inhibitors of DNA transcription or protein synthesis compared to genomic effects.The role of GCs on the circulatory system mainly show its permissive regulation of vascular smooth muscle cell (VSMC) contraction mediated by catecholamine (CA) and enhance the maintenance of vascular tone and blood pressure. In the clinic blood pressure in some patients, especially in the rescue therapy in shock, the pressor effect of norepinephrine (NE) alone is considered unsatisfactory. While a small amount of cortisol was given, the pressor effect of NE could be significantly enhanced.Our previous research used adrenalectomized rats for septic shock model induced by cecal ligation and puncture to observe the effect of GCs. GCs could rapidly reversed the hyporeactivities of vasocontraction to NE within 10 minutes. GCs could rapidly elevate contraction of single VSMC induced by NE. In addition, Dexamethasone (Dex) could also regulate actin filament rearrangement in VSMC administrated with NE. And Dex could increased the peak of [Ca²⁺]i elevation in VSMC induced by NE. However, the elevation occurred in the initial phase of contraction, and then returned to a normal level. These results have elucidated that there is non-genomic mechanism by which GCs enhanced the NE-mediated contraction of VSMC. And the [Ca²⁺]i elevation play a role in the effect. Besides, there may be an important mechanism for a long-term contraction.VSMC contraction and relaxation are largely mediated by the phosphorylation and dephosphorylation of the 20-kDa regulatory myosin light chain (MLC20) at threonine-18 and serine-19 by myosin light chain kinase (MLCK) and myosin light chain phosphase (MLCP). The initial phase of contraction is mediated by a rise in intracellular calcium and results in calmodulin-dependent activation of MLCK, The sustained phase of vascular contraction is thought to involve the Ca²⁺ sensitization mechanisms. RhoA/ROCK pathway has been proposed to play a role in Ca²⁺ sensitization. The activation of ERK and p38 are involved in agonist-induced smooth muscle stimulation.We used rat aortic smooth muscle cells to observe the effects of Dex for NE-mediated contraction. Therefore, the objective of our study was to characterize the rapid effect of the Dex on the NE-mediated phosphorylation of MLC20 in VSMC and to disclose the mechanism behind this clinically important interaction.Based on the above ideas, the subject took the following studies:1. The effects of Dex on the NE-mediated contraction in VSMC: Preincubation with LPS could simulate an acute septic shock model. The MLC20 phosphorylation of VSMC was detected by Western Blotting analysis.2. The mechanism of Dex enhances the NE-mediated contraction of VSMC:(1) The involvement of RhoA/ROCK signaling pathway: The activation of MYPT1, which was downstream target of ROCK, was examined by Western Blotting.(2) To further assess if involvement of ROCK in the rapid function of Dex for NE-mediated VSMC contraction, we examined the effects of selective inhibitor of Rho kinase, Y-27632.(3) The activation of p38 and ERK: the phosphorylation of p38 and ERK were detected by Western Blotting.The main results were as follows:1. Dex could rapidly enhance MLC20 phosphorylation of VSMC mediated by NE. And GCs nuclear receptor antagonist could not block the rapid action.2 Dex could enhance NE-mediated phosphorylation of MYPT1 which is activated by RhoA/ROCK pathway. Inhibition of Rho kinase activity reverses Dex for NE-mediated MLC20 phosphorylation3. Dex could increase NE-mediated activation of p38 and ERK. In conclusion, Dex could rapidly enhance the NE-mediated MLC phosphorylation and lead to increasing VSMC contraction. The [Ca²⁺]i elevation play a role in the initial phase of contraction. And in the sustained phase of vascular contraction it may via increasing activation of RhoA/ROCK signaling pathway. The selective ROCK inhibitor, Y-27632, could completely reverse the effect. Moreover, we also demonstrate that ERK and p38 pathway plays an important role in the effect of Dex on NE-mediated contraction of VSMC.These results have offered evidence to clinical therapy for the septic shock, and elucidated a new concept to the mechanism of Dex rapidly enhance NE-mediated VSMC contraction and provided a broader clinical use of the ideas and direction.