MLCK and PKC Involvements via Gi and Rho A Protein in Contraction by the Electrical Field Stimulation in Feline Esophageal Smooth Muscle

Action and therapeutic targets of myosin light chain kinase, an important cardiovascular signaling mechanism

The global incidence of cardiac diseases is increasing, imposing a substantial socioeconomic burden on healthcare systems. The pathogenesis of cardiovascular disease is complex and not fully understood, and the physiological function of the heart is inextricably linked to well-regulated cardiac muscle movement. Myosin light chain kinase (MLCK) is essential for myocardial contraction and diastole, cardiac electrophysiological homeostasis, vasoconstriction of vascular nerves and blood pressure regulation. In this sense, MLCK appears to be an attractive therapeutic target for cardiac diseases. MLCK participates in myocardial cell movement and migration through diverse pathways, including regulation of calcium homeostasis, activation of myosin light chain phosphorylation, and stimulation of vascular smooth muscle cell contraction or relaxation. Recently, phosphorylation of myosin light chains has been shown to be closely associated with the activation of myocardial exercise signaling, and MLCK mediates systolic and diastolic functions of the heart through the interaction of myosin thick filaments and actin thin filaments. It works by upholding the integrity of the cytoskeleton, modifying the conformation of the myosin head, and modulating innervation. MLCK governs vasoconstriction and diastolic function and is associated with the activation of adrenergic and sympathetic nervous systems, extracellular transport, endothelial permeability, and the regulation of nitric oxide and angiotensin II. Additionally, MLCK plays a crucial role in the process of cardiac aging. Multiple natural products/phytochemicals and chemical compounds, such as quercetin, cyclosporin, and ML-7 hydrochloride, have been shown to regulate cardiomyocyte MLCK. The MLCK-modifying capacity of these compounds should be considered in designing novel therapeutic agents. This review summarizes the mechanism of action of MLCK in the cardiovascular system and the therapeutic potential of reported chemical compounds in cardiac diseases by modifying MLCK processes.

Intracellular signaling pathways of muscarinic acetylcholine receptor-mediated detrusor muscle contractions

Acetylcholine plays an essential role in the regulation of detrusor muscle contractions, and antimuscarinics are widely used in the management of overactive bladder syndrome. However, several adverse effects limit their application and patients' compliance. Thus, this study aimed to further analyze the signal transduction of M2 and M3 receptors in the murine urinary bladder to eventually find more specific therapeutic targets. Experiments were performed on adult male wild-type, M2, M3, M2/M3, or Gαq/11 knockout (KO), and pertussis toxin (PTX)-treated mice. Contraction force and RhoA activity were measured in the urinary bladder smooth muscle (UBSM). Our results indicate that carbamoylcholine (CCh)-induced contractions were associated with increased activity of RhoA and were reduced in the presence of the Rho-associated kinase (ROCK) inhibitor Y-27632 in UBSM. CCh-evoked contractile responses and RhoA activation were markedly reduced in detrusor strips lacking either M2 or M3 receptors and abolished in M2/M3 KO mice. Inhibition of Gαi-coupled signaling by PTX treatment shifted the concentration-response curve of CCh to the right and diminished RhoA activation. CCh-induced contractile responses were markedly decreased in Gαq/11 KO mice; however, RhoA activation was unaffected. In conclusion, cholinergic detrusor contraction and RhoA activation are mediated by both M2 and M3 receptors. Furthermore, whereas both Gαi and Gαq/11 proteins mediate UBSM contraction, the activation at the RhoA-ROCK pathway appears to be linked specifically to Gαi. These findings may aid the identification of more specific therapeutic targets for bladder dysfunctions.NEW & NOTEWORTHY Muscarinic acetylcholine receptors are of utmost importance in physiological regulation of micturition and also in the development of voiding disorders. We demonstrate that the RhoA-Rho-associated kinase (ROCK) pathway plays a crucial role in contractions induced by cholinergic stimulation in detrusor muscle. Activation of RhoA is mediated by both M2 and M3 receptors as well as by Gi but not Gq/11 proteins. The Gi-RhoA-ROCK pathway may provide a novel therapeutic target for overactive voiding disorders.

Effects of Microbeam Irradiation on Rodent Esophageal Smooth Muscle Contraction

BACKGROUND

High-dose-rate radiotherapy has shown promising results with respect to normal tissue preservation. We developed an ex vivo model to study the physiological effects of experimental radiotherapy in the rodent esophageal smooth muscle.

METHODS

We assessed the physiological parameters of the esophageal function in ex vivo preparations of the proximal, middle, and distal segments in the organ bath. High-dose-rate synchrotron irradiation was conducted using both the microbeam irradiation (MBI) technique with peak doses greater than 200 Gy and broadbeam irradiation (BBI) with doses ranging between 3.5-4 Gy.

RESULTS

Neither MBI nor BBI affected the function of the contractile apparatus. While peak latency and maximal force change were not affected in the BBI group, and no changes were seen in the proximal esophagus segments after MBI, a significant increase in peak latency and a decrease in maximal force change was observed in the middle and distal esophageal segments.

CONCLUSION

No severe changes in physiological parameters of esophageal contraction were determined after high-dose-rate radiotherapy in our model, but our results indicate a delayed esophageal function. From the clinical perspective, the observed increase in peak latency and decreased maximal force change may indicate delayed esophageal transit.

Stage-dependent sequential organization of nascent smooth muscle cells and its implications for the gut coiling morphogenesis in Xenopus larva

In vertebrates, gut coiling proceeds left-right asymmetrically during expansion of the gastrointestinal tract with highly organized muscular structures facilitating peristalsis. In this report, we explored the mechanisms of larval gut coiling morphogenesis relevant to its nascent smooth muscle cells using highly transparent Xenopus early larvae. First, to visualize the dynamics of intestinal smooth muscle cells, whole-mount specimens were immunostained with anti-smooth muscle-specific actin (SM-actin) antibody. We found that the nascent gut of Xenopus early larvae gradually expands the SM-actin-positive region in a stage-dependent manner. Transverse orientation of smooth muscle cells was first established, and next, the cellular longitudinal orientation along the gut axis was followed to make a meshwork of the contractile cells. Finally, anisotropic torsion by the smooth muscle cells was generated in the center of gut coiling, suggesting that twisting force might be involved in the late phase of coiling morphogenesis of the gut. Administration of S-(-)-Blebbistatin to attenuate the actomyosin contraction in vivo resulted in cancellation of coiling of the gut. Development of decapitation embryos, trunk 'torso' explants, and gut-only explants revealed that initial coiling of the gut proceeds without interactions with the other parts of the body including the central nervous system. We newly developed an in vitro model to assess the gut coiling morphogenesis, indicating that coiling pattern of the nascent Xenopus gut is partially gut-autonomous. Using this gut explant culture technique, inhibition of actomyosin contraction was performed by administrating either actin polymerization inhibitor, myosin light chain kinase inhibitor, or calmodulin antagonist. All of these reagents decreased the extent of gut coiling morphogenesis in vitro. Taken together, these results suggest that the contraction force generated by actomyosin-rich intestinal smooth muscle cells during larval stages is essential for the normal coiling morphogenesis of this muscular tubular organ.

Alternating Electric Fields (TTFields) Activate Cav1.2 Channels in Human Glioblastoma Cells

Tumor treating fields (TTFields) represent a novel FDA-approved treatment modality for patients with newly diagnosed or recurrent glioblastoma multiforme. This therapy applies intermediate frequency alternating electric fields with low intensity to the tumor volume by the use of non-invasive transducer electrode arrays. Mechanistically, TTFields have been proposed to impair formation of the mitotic spindle apparatus and cytokinesis. In order to identify further potential molecular targets, here the effects of TTFields on Ca²⁺-signaling, ion channel activity in the plasma membrane, cell cycle, cell death, and clonogenic survival were tested in two human glioblastoma cell lines in vitro by fura-2 Ca²⁺ imaging, patch-clamp cell-attached recordings, flow cytometry and pre-plated colony formation assay. In addition, the expression of voltage-gated Ca²⁺ (Ca_v) channels was determined by real-time RT-PCR and their significance for the cellular TTFields response defined by knock-down and pharmacological blockade. As a result, TTFields stimulated in a cell line-dependent manner a Ca_v1.2-mediated Ca²⁺ entry, G₁ or S phase cell cycle arrest, breakdown of the inner mitochondrial membrane potential and DNA degradation, and/or decline of clonogenic survival suggesting a tumoricidal action of TTFields. Moreover, inhibition of Ca_v1.2 by benidipine aggravated in one glioblastoma line the TTFields effects suggesting that Ca_v1.2-triggered signaling contributes to cellular TTFields stress response. In conclusion, the present study identified Ca_v1.2 channels as TTFields target in the plasma membrane and provides the rationale to combine TTFields therapy with Ca²⁺ antagonists that are already in clinical use.

Identification of Potential Key Genes and Pathways in Early-Onset Colorectal Cancer Through Bioinformatics Analysis

This study was designed to identify the potential key protein interaction networks, genes, and correlated pathways in early-onset colorectal cancer (CRC) via bioinformatics methods. We selected microarray data GSE4107 consisting 12 patient's colonic mucosa and 10 healthy control mucosa; initially, the GSE4107 were downloaded and analyzed using limma package to identify differentially expressed genes (DEGs). A total of 131 DEGs consisting of 108 upregulated genes and 23 downregulated genes of patients in early-onset CRC were selected by the criteria of adjusted P values <.01 and |log2 fold change (FC)| ≥ 2. The gene ontology functional enrichment analysis and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were accomplished to view the biological process, cellular components, molecular function, and the KEGG pathways of DEGs. Finally, protein-protein interactions (PPIs) were constructed, and the hub protein module was identified. Genes such as ACTA2, ACTG2, MYH11, CALD1, MYL9, TPM2, and LMOD1 were strongly implicated in CRC. In summary, in this study, we indicated that molecular mechanisms were involved in muscle contraction and vascular smooth muscle contraction signaling pathway, which improve our understanding of CRC and could be used as new therapeutic targets for CRC.

Role of PKC and RhoA/ROCK pathways in the spontaneous phasic activity in the rectal smooth muscle

The role of PKC and RhoA/ROCK pathways in the phasic activities in the rectal smooth muscles (RSM) in the basal state is not known. We examined this issue by determining the effects of PKC inhibitors (calphostin C and Gö-6850) and a ROCK inhibitor (Y-27632) on the slow-rate (~3/min) and fast-rate (~25/min) phasic activities. We also examined the corresponding signal transduction cascades and the PKC and ROCK enzymatic activities in the RSM in the basal state. PKC inhibition with calphostin C and Gö-6850 (10(-5) M) caused a significant decrease (~25%) in slow-rate (but not fast-rate) phasic activity (monitored by frequency and amplitude of contractions) of the RSM. Conversely, ROCK inhibition with Y-27632 (10(-5) M) caused a significant decrease not only in slow-rate, but also fast-rate, phasic activity caused by ROCK inhibition in the RSM. Western blot analysis revealed that the PKC inhibition-induced decrease in RSM phasic activity was associated with decreases in PKCα translocation, phosphorylated (Thr(38)) PKC-potentiated inhibitor (CPI-17), and phosphorylated (Thr(18)/Ser(19)) 20-kDa myosin regulatory light chain. Conversely, decreases in the phasic activity in the RSM by ROCK inhibition were accompanied by the additional decrease in phosphorylated (Thr(696)) myosin phosphatase target subunit 1. Data show that while PKC and RhoA/ROCK pathways play a significant role in slow-rate high-amplitude spontaneous phasic activity, only the RhoA/ROCK pathway primarily mediates fast-rate low-amplitude phasic activity, in the RSM. Such knowledge is important in the understanding of the pathophysiology of large intestinal motility disorders. Relative contributions of the PKC vs. the RhoA/ROCK pathway in the phasic activity remain to be determined.

Characteristics of 5-hydroxytryptamine receptors involved in contraction of feline ileal longitudinal smooth muscle

A number of studies have demonstrated that 5-hydroxytryptamine (5-HT) can induce muscle contraction or relaxation response and enhance secretion in the gastrointestinal tract via a multiplicity of 5-HT receptor subtypes. In the present study, we investigated the pharmacological characterization of the 5-HT-induced contractile response in longitudinal smooth muscle isolated from the feline ileum. Addition of 5-HT into muscle chambers enhanced the basal tone and spontaneous activity in a concentration-dependent manner. The neurotoxin tetrodotoxin did not alter the 5-HT-induced contraction of the longitudinal muscles. Neither atropine nor guanethidine affected the contraction. The 5-HT agonists, 5-methylserotonin hydrochloride and mosapride, also evoked concentration-dependent contractions. The 5-HT-induced contraction was enhanced by the 5HT(2) receptor antagonist ketanserin and the 5-HT(3) receptor antagonist ondansetron but was inhibited by the 5-HT(1) receptor antagonist methysergide and 5-HT(4) receptor antagonist GR113808. These results indicate that 5-HT(1) and 5-HT(4) receptors may mediate the contraction of the 5-HT-induced response and 5-HT(2) and 5-HT(3) receptors may mediate 5-HT-induced relaxation in feline ileal longitudinal smooth muscles.

Albumin causes increased myosin light chain kinase expression in astrocytes via p38 mitogen-activated protein kinase

Myosin light chain kinase (MLCK) plays an important role in the reorganization of the cytoskeleton, leading to disruption of vascular barrier integrity in multiple organs, including the blood-brain barrier (BBB), after traumatic brain injury (TBI). MLCK has been linked to transforming growth factor (TGF) and rho kinase signaling pathways, but the mechanisms regulating MLCK expression following TBI are not well understood. Albumin leaks into the brain parenchyma following TBI, activates glia, and has been linked to TGF-β receptor signaling. We investigated the role of albumin in the increase of MLCK in astrocytes and the signaling pathways involved in this increase. After midline closed-skull TBI in mice, there was a significant increase in MLCK-immunoreactive (IR) cells and albumin extravasation, which was prevented by treatment with the MLCK inhibitor ML-7. Using immunohistochemical methods, we identified the MLCK-IR cells as astrocytes. In primary astrocytes, exposure to albumin increased both isoforms of MLCK, 130 and 210. Inhibition of the TGF-β receptor partially prevented the albumin-induced increase in both isoforms, which was not prevented by inhibition of smad3. Inhibition of p38 MAPK, but not ERK, JNK, or rho kinase, also prevented this increase. These results are further evidence of a role of MLCK in the mechanisms of BBB compromise following TBI and identify astrocytes as a cell type, in addition to endothelium in the BBB, that expresses MLCK. These findings implicate albumin, acting through p38 MAPK, in a novel mechanism by which activation of MLCK following TBI may lead to compromise of the BBB.

P2X and P2Y Receptors Mediate Contraction Induced by Electrical Field Stimulation in Feline Esophageal Smooth Muscle

It is well-known that electrical field stimulation (EFS)-induced contraction is mediated by a cholinergic mechanism and other neurotransmitters. NO, ATP, calcitonin gene-related peptide (CGRP), and substance P are released by EFS. To investigate the purinergic mechanism involved in the EFS-induced contraction, purinegic receptors antagonists were used. Suramine, a non-selective P2 receptor antagonist, reduced the contraction induced by EFS. NF023 (10(-7)~10(-4) M), a selective P2X antagonist, inhibited the contraction evoked by EFS. Reactive blue (10(-6)~10(-4) M), selective P2Y antagonist, also blocked the contraction in a dose-dependent manner. In addition, P2X agonist α,β-methylene 5'-adenosine triphosphate (αβMeATP, 10(-7)~10(-5) M) potentiated EFS-induced contraction in a dose-dependent manner. P2Y agonist adenosine 5'-[β-thio]diphosphate trilithium salt (ADPβS, 10(-7)~10(-5) M) also potentiated EFS-induced contractions in a dose-dependent manner. Ecto-ATPase activator apyrase (5 and 10 U/ml) reduced EFS-induced contractions. Inversely, 6-N,N-diethyl-D-β,γ-dibromomethylene 5'-triphosphate triammonium (ARL 67156, 10(-4) M) increased EFS-induced contraction. These data suggest that endogenous ATP plays a role in EFS-induced contractions which are mediated through both P2X-receptors and P2Y-receptors stimulation in cat esophageal smooth muscle.