Dedicated myosin light chain kinases with diverse cellular functions

Presynaptic structural and functional plasticity are coupled by convergent Rap1 signaling

Dynamic presynaptic actin remodeling drives structural and functional plasticity at synapses, but the underlying mechanisms remain largely unknown. Previous work has shown that actin regulation via Rac1 guanine exchange factor (GEF) Vav signaling restrains synaptic growth via bone morphogenetic protein (BMP)-induced receptor macropinocytosis and mediates synaptic potentiation via mobilization of reserve pool vesicles in presynaptic boutons. Here, we find that Gef26/PDZ-GEF and small GTPase Rap1 signaling couples the BMP-induced activation of Abelson kinase to this Vav-mediated macropinocytosis. Moreover, we find that adenylate cyclase Rutabaga (Rut) signaling via exchange protein activated by cAMP (Epac) drives the mobilization of reserve pool vesicles during post-tetanic potentiation (PTP). We discover that Rap1 couples activation of Rut-cAMP-Epac signaling to Vav-mediated synaptic potentiation. These findings indicate that Rap1 acts as an essential, convergent node for Abelson kinase and cAMP signaling to mediate BMP-induced structural plasticity and activity-induced functional plasticity via Vav-dependent regulation of the presynaptic actin cytoskeleton.

Molecular mechanism of MLCK1 inducing 5-Fu resistance in colorectal cancer cells through activation of TNFR2/NF-κB pathway

BACKGROUND AND AIMS

Chemotherapy resistance in colorectal cancer have been faced with significant challenges in recent years. Particular interest is directed to tumor microenvironment function. Recent work has, identified a small molecule named Divertin that prevents myosin light chain kinase 1(MLCK1) recruitment to the perijunctional actomyosin ring(PAMR), restores barrier function after tumor necrosis factor(TNF)-induced barrier loss and prevents disease progression in experimental inflammatory bowel disease. Studies have shown that MLCK is a potential target for affecting intestinal barrier function, as well as for tumor therapy. However, the relative contributions of MLCK expression and chemotherapy resistance in colorectal cancers have not been defined.

METHODS

Statistical analysis of MYLK gene expression differences in colorectal cancer patients and normal population and prognosis results from The Cancer Genome Atlas(TCGA) data. Cell activity was detected by Cell counting Kit-8. Cell proliferation was detected by monoclonal plate. The apoptosis was detected by flow cytometry and western blot. Determine the role of MLCK1 in inducing 5-Fluorouracil(5-Fu) resistance in colorectal cancer cells was detected by overexpression of MLCK1 and knock-down expression of MLCK1.

RESULTS

MLCK1 is expressed at different levels in different colorectal cancer cells, high MLCK1 expressing cell lines are less sensitive to 5-Fu, and low MLCK1 expressing cell lines are more sensitive to 5-Fu. MLCK1 high expression enhances resistance to 5-Fu in colorectal cancer cells and the sensitivity to 5-Fu was increased after knocking down the expression of MLCK1, that might be closely correlated to TNFR2/NF-κB pathway.

CONCLUSIONS

MLCK1 high expression can enhance resistance to 5-Fu in colorectal cancer cells and the sensitivity to 5-Fu was increased after knocking down the expression of MLCK1, that might be closely correlated to TNFR2/NF-κB pathway, which will provide a new method for the treatment of colorectal cancer patients who are resistant to 5-Fu chemotherapy.

The activation of INF2 by Piezo1/Ca2+ is required for mesenchymal to amoeboid transition in confined environments

To invade heterogenous tissues, transformed cells may undergo a mesenchymal to amoeboid transition (MAT). However, the molecular mechanisms regulating this transition are poorly defined. In invasive melanoma cells, we demonstrate that intracellular [Ca2+] increases with the degree of confinement in a Piezo1 dependent fashion. Moreover, Piezo1/Ca2+ is found to drive amoeboid and not mesenchymal migration in confined environments. Consistent with a model in which Piezo1 senses tension at the plasma membrane, the percentage of cells using amoeboid migration is further increased in undulating microchannels. Surprisingly, amoeboid migration was not promoted by myosin light chain kinase (MLCK), which is sensitive to intracellular [Ca2+]. Instead, we report that Piezo1/Ca2+ activates inverted formin-2 (INF2) to induce widespread actin cytoskeletal remodeling. Strikingly, the activation of INF2 is found to promote de-adhesion, which in turn facilitates MAT. Using micropatterned surfaces, we demonstrate that cells require INF2 to effectively migrate in environments with challenging mechanochemical properties.

A harmful MYH11 variant detected in a family with thoracic aortic dissection and patent ductus arteriosus

Thoracic aortic dissection (TAD) is an important cause of sudden cardiac death and is characterized by high morbidity, mortality, and a poor prognosis. Patent ductus arteriosus (PDA) is a common congenital heart disease. The pathogenesis of both TAD and PDA has been reported to be related to genetic factors. The MYH11 gene, which encodes myosin heavy chain 11, has been reported in individuals with both TAD and PDA. Herein, we first detected a harmful MYH11 missense variant (c. T3728C, p. L1243P) in a TAD and PDA family. This missense variant co-segregated with the TAD/PDA phenotype in this family of four individuals, providing evidence of its harmfulness. Histopathological examinations revealed the presence of fragmented, broken, and lessened elastic fibers and the deposition of proteoglycans in the median of aortic dissection. Moreover, the immunofluorescence results showed that the labeled MYH11 protein in the tissue of the aortic dissection was weaker than that in the normal aorta. We present this familial case to stress the necessity of postmortem genetic testing in such cases among forensic practices. Identifying those culprit gene variants can direct effective genetic counseling and personalized health management in family members (especially first-degree relatives) with high-risk genotypes.

Mechanisms underlying distinct subcellular localization and regulation of epithelial long myosin light-chain kinase splice variants

Intestinal epithelia express two long myosin light-chain kinase (MLCK) splice variants, MLCK1 and MLCK2, which differ by the absence of a complete immunoglobulin (Ig)-like domain 3 within MLCK2. MLCK1 is preferentially associated with the perijunctional actomyosin ring at steady state, and this localization is enhanced by inflammatory stimuli including tumor necrosis factor (TNF). Here, we sought to identify MLCK1 domains that direct perijunctional MLCK1 localization and their relevance to disease. Ileal biopsies from Crohn's disease patients demonstrated preferential increases in MLCK1 expression and perijunctional localization relative to healthy controls. In contrast to MLCK1, MLCK2 expressed in intestinal epithelia is predominantly associated with basal stress fibers, and the two isoforms have distinct effects on epithelial migration and barrier regulation. MLCK1(Ig1-4) and MLCK1(Ig1-3), but not MLCK2(Ig1-4) or MLCK1(Ig3), directly bind to F-actin in vitro and direct perijunctional recruitment in intestinal epithelial cells. Further study showed that Ig1 is unnecessary, but that, like Ig3, the unstructured linker between Ig1 and Ig2 (Ig1/2us) is essential for recruitment. Despite being unable to bind F-actin or direct recruitment independently, Ig3 does have dominant negative functions that allow it to displace perijunctional MLCK1, increase steady-state barrier function, prevent TNF-induced MLCK1 recruitment, and attenuate TNF-induced barrier loss. These data define the minimal domain required for MLCK1 localization and provide mechanistic insight into the MLCK1 recruitment process. Overall, the results create a foundation for development of molecularly targeted therapies that target key domains to prevent MLCK1 recruitment, restore barrier function, and limit inflammatory bowel disease progression.

Transcriptome analysis reveals tissue-specific responses of Mytilus unguiculatus to Vibrio alginolyticus infection

Mytilus unguiculatus is an important economic bivalve species with wide consumption and aquaculture value. Disease is one of the primary limiting factors in mussel aquaculture, thus understanding the response of different tissues of M. unguiculatus to pathogens is crucial for disease prevention and control. In this study, we investigated the physiological and transcriptomic responses of the gills, adductor muscle, and mantle of M. unguiculatus infected with Vibrio alginolyticus. The results showed that V. alginolyticus infection caused inflammation and tissue structure changes in the gill, adductor muscle and mantle of M. unguiculatus. Meanwhile, the activities of superoxide dismutase and catalase in the three tissues increased, while the total antioxidant capacity decreased, suggesting that M. unguiculatus have an activated defense mechanism against infection-induced oxidative stress, despite a compromised total antioxidant capacity. Transcriptomic studies reveal that infected M. unguiculatus exhibits upregulation of endocytosis, lysosome activity, cellular apoptosis, and immune-related signaling pathways, indicating that M. unguiculatus responds to pathogen invasion by upregulating efferocytosis. Compared with the gill and adductor muscle, the mantle had a higher level of mytimycin, mytilin and myticin, and the three tissues also increased the expression of mytimycin to cope with the invasion of pathogens. In addition, the analysis of genes related to taste transduction pathways and muscle contraction and relaxation found that after infection with V. alginolyticus, M. unguiculatus may reduce appetite by inhibiting taste transduction in the gill, while improving muscle contraction of the adductor muscle and keeping the shell closed, to resist further invasion of pathogens and reduce the risk of pathogen transmission in the population.

p90RSK2, a new MLCK mediates contractility in myosin light chain kinase null smooth muscle

Introduction: Phosphorylation of smooth muscle (SM) myosin regulatory light chain (RLC20) is a critical switch leading to SM contraction. The canonical view held that only the short isoform of myosin light chain kinase (MLCK1) catalyzed this reaction. It is now accepted that auxiliary kinases may contribute to vascular SM tone and contractility. We have previously reported that p90 ribosomal S6 kinase (RSK2) functions as such a kinase, in parallel with MLCK1, contributing ∼25% of the maximal myogenic force in resistance arteries. Thus, RSK2 may be instrumental in the regulation of basal vascular tone and blood pressure. Here, we take advantage of a MLCK1 null mouse (mylk1 -/-) to further test our hypothesis that RSK2 can function as an MLCK, playing a significant physiological role in SM contractility. Methods: Using fetal (E14.5-18.5) SM tissues, as embryos die at birth, we investigated the necessity of MLCK for contractility and fetal development and determined the ability of RSK2 kinase to compensate for the lack of MLCK and characterized its signaling pathway in SM. Results and Discussion: Agonists induced contraction and RLC20 phosphorylation in mylk1 -/- SM was attenuated by RSK2 inhibition. The pCa-tension relationships in permeabilized strips of bladder showed no difference in Ca2+ sensitivity in WT vs mylk1 -/- muscles, although the magnitude of force responses was considerably smaller in the absence of MLCK. The magnitude of contractile responses was similar upon addition of GTPγS to activate the RhoA/ROCK pathway or calyculinA to inhibit the myosin phosphatase. The Ca2+-dependent tyrosine kinase, Pyk2, contributed to RSK2-mediated contractility and RLC20 phosphorylation. Proximity-ligation and immunoprecipitation assays demonstrated an association of RSK2, PDK1 and ERK1/2 with MLCK and actin. RSK2, PDK1, ERK1/2 and MLCK formed a signaling complex on the actin filament, positioning them for interaction with adjacent myosin heads. The Ca2+-dependent component reflected the agonist mediated increases in Ca2+, which activated the Pyk2/PDK1/RSK2 signaling cascade. The Ca2+-independent component was through activation of Erk1/2/PDK1/RSK2 leading to direct phosphorylation of RLC20, to increase contraction. Overall, RSK2 signaling constitutes a new third signaling pathway, in addition to the established Ca2+/CaM/MLCK and RhoA/ROCK pathways to regulate SM contractility.

Delineating Zinc Influx Mechanisms during Platelet Activation

Zinc (Zn2+) is released by platelets during a hemostatic response to injury. Extracellular zinc ([Zn2+]o) initiates platelet activation following influx into the platelet cytosol. However, the mechanisms that permit Zn2+ influx are unknown. Fluctuations in intracellular zinc ([Zn2+]i) were measured in fluozin-3-loaded platelets using fluorometry and flow cytometry. Platelet activation was assessed using light transmission aggregometry. The detection of phosphoproteins was performed by Western blotting. [Zn2+]o influx and subsequent platelet activation were abrogated by blocking the sodium/calcium exchanged, TRP channels, and ZIP7. Cation store depletion regulated Zn2+ influx. [Zn2+]o stimulation resulted in the phosphorylation of PKC substates, MLC, and β3 integrin. Platelet activation via GPVI or Zn2+ resulted in ZIP7 phosphorylation in a casein kinase 2-dependent manner and initiated elevations of [Zn2+]i that were sensitive to the inhibition of Orai1, ZIP7, or IP3R-mediated pathways. These data indicate that platelets detect and respond to changes in [Zn2+]o via influx into the cytosol through TRP channels and the NCX exchanger. Platelet activation results in the externalization of ZIP7, which further regulates Zn2+ influx. Increases in [Zn2+]i contribute to the activation of cation-dependent enzymes. Sensitivity of Zn2+ influx to thapsigargin indicates a store-operated pathway that we term store-operated Zn2+ entry (SOZE). These mechanisms may affect platelet behavior during thrombosis and hemostasis.

Migration speed of captured breast cancer subpopulations correlates with metastatic fitness

The genetic alterations contributing to migration proficiency, a phenotypic hallmark of metastatic cells required for colonizing distant organs, remain poorly defined. Here, we used single-cell magneto-optical capture (scMOCa) to isolate fast cells from heterogeneous human breast cancer cell populations, based on their migratory ability alone. We show that captured fast cell subpopulations retain higher migration speed and focal adhesion dynamics over many generations as a result of a motility-related transcriptomic profile. Upregulated genes in isolated fast cells encoded integrin subunits, proto-cadherins and numerous other genes associated with cell migration. Dysregulation of several of these genes correlates with poor survival outcomes in people with breast cancer, and primary tumors established from fast cells generated a higher number of circulating tumor cells and soft tissue metastases in pre-clinical mouse models. Subpopulations of cells selected for a highly migratory phenotype demonstrated an increased fitness for metastasis.

Myosin Light-Chain Kinase Inhibition Potentiates the Antitumor Effects of Avapritinib in PDGFRA D842V-Mutant Gastrointestinal Stromal Tumor

PURPOSE

To create an in vivo model of PDGFRA D842V-mutant gastrointestinal stromal tumor (GIST) and identify the mechanism of tumor persistence following avapritinib therapy.

EXPERIMENTAL DESIGN

We created a patient-derived xenograft (PDX) of PDGFRA D842V-mutant GIST and tested the effects of imatinib, avapritinib, and ML-7, an inhibitor of myosin light-chain kinase (MYLK). Bulk tumor RNA sequencing and oncogenic signaling were evaluated. Apoptosis, survival, and actin cytoskeleton were evaluated in GIST T1 cells and isolated PDX cells in vitro. Human GIST specimens were analyzed for MYLK expression.

RESULTS

The PDX was minimally responsive to imatinib but sensitive to avapritinib. Avapritinib therapy increased tumor expression of genes related to the actin cytoskeleton, including MYLK. ML-7 induced apoptosis and disrupted actin filaments in short-term cultures of PDX cells and decreased survival in GIST T1 cells in combination with imatinib or avapritinib. Combined therapy with ML-7 improved the antitumor effects of low-dose avapritinib in vivo. Furthermore, MYLK was expressed in human GIST specimens.

CONCLUSIONS

MYLK upregulation is a novel mechanism of tumor persistence after tyrosine kinase inhibition. Concomitant MYLK inhibition may enable the use of a lower dose of avapritinib, which is associated with dose-dependent cognitive side effects.

p90RSK2, a new MLCK, rescues contractility in myosin light chain kinase null smooth muscle

Background

Phosphorylation of smooth muscle (SM) myosin regulatory light chain (RLC 20 ) is a critical switch leading to contraction or cell migration. The canonical view held that the only kinase catalyzing this reaction is the short isoform of myosin light chain kinase (MLCK1). Auxiliary kinases may be involved and play a vital role in blood pressure homeostasis. We have previously reported that p90 ribosomal S6 kinase (RSK2) functions as such a kinase, in parallel with the classical MLCK1, contributing ∼25% of the maximal myogenic force in resistance arteries and regulating blood pressure. Here, we take advantage of a MLCK1 null mouse to further test our hypothesis that RSK2 can function as an MLCK, playing a significant physiological role in SM contractility.

Methods

Fetal (E14.5-18.5) SM tissues were used as embryos die at birth. We investigated the necessity of MLCK for contractility, cell migration and fetal development and determined the ability of RSK2 kinase to compensate for the lack of MLCK and characterized it's signaling pathway in SM.

Results

Agonists induced contraction and RLC 20 phosphorylation in mylk1 -/- SM, that was inhibited by RSK2 inhibitors. Embryos developed and cells migrated in the absence of MLCK. The pCa-tension relationships in WT vs mylk1 -/- muscles demonstrated a Ca 2+ -dependency due to the Ca 2+ -dependent tyrosine kinase Pyk2, known to activate PDK1 that phosphorylates and fully activates RSK2. The magnitude of contractile responses was similar upon addition of GTPγS to activate the RhoA/ROCK pathway. The Ca 2+ -independent component was through activation of Erk1/2/PDK1/RSK2 leading to direct phosphorylation of RLC 20 , to increase contraction. RSK2, PDK1, Erk1/2 and MLCK formed a signaling complex on the actin filament, optimally positioning them for interaction with adjacent myosin heads.

Conclusions

RSK2 signaling constitutes a new third signaling pathway, in addition to the established Ca 2+ /CAM/MLCK and RhoA/ROCK pathways to regulate SM contractility and cell migration.

Elevation of HO-1 expression protects the intestinal mucosal barrier in severe acute pancreatitis via inhibition of the MLCK/p-MLC signaling pathway

In severe acute pancreatitis (SAP), intestinal mucosal barrier damage can cause intestinal bacterial translocation and induce or aggravate systemic infections. Heme oxygenase-1 (HO-1) is a validated antioxidant and cytoprotective agent. This research aimed to investigate the effect and mechanism of HO-1 on SAP-induced intestinal barrier damage in SAP rats. Healthy adult male Sprague-Dawley rats were randomly separated into the sham-operated group, SAP group, SAP + Hemin group, and SAP + Znpp group. The rat model of SAP was established by retrograde injection of sodium taurocholate (5%) into the biliopancreatic duct. Hemin (a potent HO-1 activator) and Znpp (a competitive inhibitor of HO-1) were injected intraperitoneally in the selected groups 24 h before SAP. Serum and intestinal tissue samples were collected for analysis after 24 h in each group. Hemin pretreatment significantly reduced systemic inflammation, intestinal oxidative stress, and intestinal epithelial apoptosis in SAP by increasing HO-1 expression. Meanwhile, pretreatment with Hemin abolished the inhibitory effect on the expression of the tight junction proteins and significantly inhibited the activation of the MLCK/P-MLC signaling pathway. Conversely, ZnPP completely reversed these effects. Our study indicates that upregulation of HO-1 expression attenuates the intestinal mucosal barrier damage in SAP. The protective effect of HO-1 on the intestine is attributed to MLCK/p-MLC signaling pathway inhibition.

Tight junctions: from molecules to gastrointestinal diseases

Intestinal epithelium functions as a tissue barrier to prevent interaction between the internal compartment and the external milieu. Intestinal barrier function also determines epithelial polarity for the absorption of nutrients and the secretion of waste products. These vital functions require strong integrity of tight junction proteins. In fact, intestinal tight junctions that seal the paracellular space can restrict mucosal-to-serosal transport of hostile luminal contents. Tight junctions can form both an absolute barrier and a paracellular ion channel. Although defective tight junctions potentially lead to compromised intestinal barrier and the development and progression of gastrointestinal (GI) diseases, no FDA-approved therapies that recover the epithelial tight junction barrier are currently available in clinical practice. Here, we discuss the impacts and regulatory mechanisms of tight junction disruption in the gut and related diseases. We also provide an overview of potential therapeutic targets to restore the epithelial tight junction barrier in the GI tract.

Piezo1 activation attenuates thrombin-induced blebbing in breast cancer cells

Cancer cells exploit a variety of migration modes to leave primary tumors and establish metastases, including amoeboid cell migration, which is typically reliant on bleb formation. Here we demonstrate that thrombin induces dynamic blebbing in the MDA-MB-231 breast cancer cell line and confirm that protease-activated receptor 1 (PAR1) activation is sufficient to induce this effect. Cell confinement has been implicated as a driving force in bleb-based migration. Unexpectedly, we found that gentle contact compression, exerted using a custom built ‘cell press’ to mechanically stimulate cells, reduced thrombin-induced blebbing. Thrombin-induced blebbing was similarly attenuated using the small molecule Yoda1, an agonist of the mechanosensitive Ca²⁺ channel Piezo1, and this attenuation was impaired in Piezo1-depleted cells. Additionally, Piezo1 activation suppressed thrombin-induced phosphorylation of ezrin, radixin and moesin (ERM) proteins, which are implicated in the blebbing process. Our results provide mechanistic insights into Piezo1 activation as a suppressor of dynamic blebbing, specifically that which is induced by thrombin.

Summary: Thrombin and protease-activated receptor agonists induce dynamic blebbing in breast cancer cells, which can be attenuated by contact-mediated compression, and activation of the mechanosensitive ion channel Piezo1.

Endothelial Cell Plasma Membrane Biomechanics Mediates Effects of Pro-Inflammatory Factors on Endothelial Mechanosensors: Vicious Circle Formation in Atherogenic Inflammation

Chronic low-grade vascular inflammation and endothelial dysfunction significantly contribute to the pathogenesis of cardiovascular diseases. In endothelial cells (ECs), anti-inflammatory or pro-inflammatory signaling can be induced by different patterns of the fluid shear stress (SS) exerted by blood flow on ECs. Laminar blood flow with high magnitude is anti-inflammatory, while disturbed flow and laminar flow with low magnitude is pro-inflammatory. Endothelial mechanosensors are the key upstream signaling proteins in SS-induced pro- and anti-inflammatory responses. Being transmembrane proteins, mechanosensors, not only experience fluid SS but also become regulated by the biomechanical properties of the lipid bilayer and the cytoskeleton. We review the apparent effects of pro-inflammatory factors (hypoxia, oxidative stress, hypercholesterolemia, and cytokines) on the biomechanics of the lipid bilayer and the cytoskeleton. An analysis of the available data suggests that the formation of a vicious circle may occur, in which pro-inflammatory cytokines enhance and attenuate SS-induced pro-inflammatory and anti-inflammatory signaling, respectively.

Regulation of β1-integrin in autophagy and apoptosis of gastric epithelial cells infected with Helicobacter pylori

Helicobacter pylori infection is an essential factor in the development of human gastric diseases, but its pathogenic mechanism is still unclear. In this work we have showed that, the LC3II levels were increased and β1-integrin levels were decreased in H. pylori-positive human gastric tissue samples and H. pylori co-cultured GES-1 cells. There was significant upregulation of LC3II levels and downregulation of P62 levels in GES-1 cells after β1-integrin knockdown co-cultured with H. pylori. This indicated that β1-integrin downregulation promoted autophagy in GES-1 cells after H. pylori infection. The cell apoptosis rate and poly ADP-ribose polymerase (PARP) and caspase-3 activities were increased in GES-1 cells pretreated with 3-methyladenine (3-MA ) after H. pylori infection. Furthermore, there was a significant decrease in apoptosis of β1-integrin knockdown GES-1 cells co-cultured with H. pylori; apoptosis was also downregulated in β1-integrin knockdown- and 3-MA-treated GES-1 cells co-cultured with H. pylori. Correspondingly, PARP and caspase-3 activities were decreased in β1-integrin knockdown cells co-cultured with H. pylori and β1-integrin knockdown-3-MA-treated-1 cells with H. pylori infection. Thus, β1-integrin is a novel autophagy and apoptosis regulator during H. pylori infection. However, inhibition of autophagy did not reverse the decrease in apoptosis caused by downregulation of β1-integrin.

Thyroxine Induces Acute Relaxation of Rat Skeletal Muscle Arteries via Integrin αvβ3, ERK1/2 and Integrin-Linked Kinase

Aim: Hyperthyroidism is associated with a decreased peripheral vascular resistance, which could be caused by the vasodilator genomic or non-genomic effects of thyroid hormones (TH). Non-genomic, or acute, effects develop within several minutes and involve a wide tissue-specific spectrum of molecular pathways poorly studied in vasculature. We aimed to investigate the mechanisms of acute effects of TH on rat skeletal muscle arteries.

Methods: Sural arteries from male Wistar rats were used for isometric force recording (wire myography) and phosphorylated protein content measurement (Western blotting).

Results: Both triiodothyronine (T3) and thyroxine (T4) reduced contractile response of sural arteries to α₁-adrenoceptor agonist methoxamine. The effect of T4 was more prominent than T3 and not affected by iopanoic acid, an inhibitor of deiodinase 2. Endothelium denudation abolished the effect of T3, but not T4. Integrin αvβ3 inhibitor tetrac abolished the effect of T4 in endothelium-denuded arteries. T4 weakened methoxamine-induced elevation of phospho-MLC2 (Ser19) content in arterial samples. The effect of T4 in endothelium-denuded arteries was abolished by inhibiting ERK1/2 activation with U0126 as well as by ILK inhibitor Cpd22 but persisted in the presence of Src- or Rho-kinase inhibitors (PP2 and Y27632, respectively).

Conclusion: Acute non-genomic relaxation of sural arteries induced by T3 is endothelium-dependent and that induced by T4 is endothelium-independent. The effect of T4 on α₁-adrenergic contraction is stronger compared to T3 and involves the suppression of extracellular matrix signaling via integrin αvβ3, ERK1/2 and ILK with subsequent decrease of MLC2 (Ser19) phosphorylation.

Are Osteoclasts Mechanosensitive Cells?

Skeleton metabolism is a process in which osteoclasts constantly remove old bone and osteoblasts form new osteoid and induce mineralization; disruption of this balance may cause diseases. Osteoclasts play a key role in bone metabolism, as osteoclastogenesis marks the beginning of each bone remodeling cycle. As the only cell capable of bone resorption, osteoclasts are derived from the monocyte/macrophage hematopoietic precursors that terminally adhere to mineralized extracellular matrix, and they subsequently break down the extracellular compartment. Bone is generally considered the load-burdening tissue, bone homeostasis is critically affected by mechanical conductions, and the bone cells are mechanosensitive. The functions of various bone cells under mechanical forces such as chondrocytes and osteoblasts have been reported; however, the unique bone-resorbing osteoclasts are less studied. The oversuppression of osteoclasts in mechanical studies may be because of its complicated differentiation progress and flexible structure, which increases difficulty in targeting mechanical structures. This paper will focus on recent findings regarding osteoclasts and attempt to uncover proposed candidate mechanosensing structures in osteoclasts including podosome-associated complexes, gap junctions and transient receptor potential family (ion channels). We will additionally describe possible mechanotransduction signaling pathways including GTPase ras homologue family member A (RhoA), Yes-associated protein/transcriptional co-activator with PDZ-binding motif (TAZ), Ca²⁺ signaling and non-canonical Wnt signaling. According to numerous studies, evaluating the possible influence of various physical environments on osteoclastogenesis is conducive to the study of bone homeostasis.

CHD1L prevents lipopolysaccharide-induced hepatocellular carcinomar cell death by activating hnRNP A2/B1-nmMYLK axis

Chromodomain helicase/ATPase DNA-binding protein 1-like gene (CHD1L) has been characterized to be a driver gene in hepatocellular carcinoma (HCC). However, the intrinsic connections between CHD1L and intestinal dysbacteriosis-related inflammation reaction in HCC progression remain incompletely understood. In this study, a specific correlation between CHD1L and nonmuscle isoform of myosin light chain kinase (nmMLCK/nmMYLK), a newly identified molecule associated NF-κB signaling transduction, was disclosed in HCC. CHD1L promotes nmMYLK expression and prevents lipopolysaccharide (LPS) induced tumor cell death. In vitro experiment demonstrated that overexpressed nmMYLK is essential for CHD1L to maintain HCC cell alive, while knocking down nmMYLK significantly attenuate the oncogenic roles of CHD1L. Mechanism analysis revealed that nmMYLK can prevent Caspase-8 from combining with MyD88, an important linker of TLRs signaling pathway, while, knocking down nmMYLK facilitate the MyD88 combines with Caspase-8 and lead to the proteolytic cascade of Caspase as well as the consequent cell apoptosis. Mechanism analysis showed that CHD1L promotes the nmMYLK expression potentially through upregulating the heterogeneous nuclear ribonucleoproteins A2/B1 (hnRNP A2/B1) expression, which can bind to myosin light chain kinase (MYLK) pre-mRNA and lead to the regnant translation of nmMYLK. In summary, this work characterizes a previously unknown role of CHD1L in preventing LPS-induced tumor cell death through activating hnRNP A2/B1-nmMYLK axis. Further inhibition of CHD1L and its downstream signaling could be a novel promising strategy in HCC treatment.

Inhibition of Peripheral ERK Signaling Ameliorates Persistent Muscle Pain Around Trigger Points in Rats

The purpose of this study was to investigate whether the ERK signaling pathway was involved in ameliorating chronic myofascial hyperalgesia from contused gastrocnemius muscle in rats. We established an animal model associated with myofascial pain syndrome and described the mechanism of muscle pain in an animal model. Changes in the mechanical pain threshold were observed 0.5, 1, 2, 3, 4, 5, 8, 12, 18, and 24 h after ERK inhibitor injection around myofascial trigger points (MTrPs) of the gastrocnemius muscle in rats. Morphological changes in gastrocnemius muscle cells were observed by hematoxylin and eosin (H&E) staining. ERK signaling pathway activation was detected through immunohistochemistry and Western blotting. The main morphological characteristics of injured muscle fibers around MTrPs include gathered circular or elliptical shapes of different sizes in the cross-section and continuous inflated and tapering fibers in the longitudinal section. After intramuscular injection of U0126 (ERK inhibitor), the mechanical pain threshold significantly increased. The reduction in mechanical hyperalgesia was accompanied by reduced ERK protein phosphorylation, myosin light chain kinase (MLCK) protein, p-MLC protein expression, and the cross-sectional area of skeletal muscle cells around MTrPs. An ERK inhibitor contributed to the attenuation of mechanical hyperalgesia in the rat myofascial pain model, and the increase in pain threshold may be related to MLCK downregulation and other related contraction-associated proteins by ERK.

Postnatal development alters functional compartmentalization of myosin light chain kinase in ovine carotid arteries

The rate-limiting enzyme for vascular contraction, myosin light chain kinase (MLCK), phosphorylates regulatory myosin light chain (MLC₂₀) at rates that appear faster despite lower MLCK abundance in fetal compared with adult arteries. This study explores the hypothesis that greater apparent tissue activity of MLCK in fetal arteries is due to age-dependent differences in intracellular distribution of MLCK in relation to MLC₂₀. Under optimal conditions, common carotid artery homogenates from nonpregnant adult female sheep and near-term fetuses exhibited similar values of V_max and K_m for MLCK. A custom-designed, computer-controlled apparatus enabled electrical stimulation and high-speed freezing of arterial segments at exactly 0, 1, 2, and 3 s, calculation of in situ rates of MLC₂₀ phosphorylation, and measurement of time-dependent colocalization between MLCK and MLC₂₀. The in situ rate of MLC₂₀ phosphorylation divided by total MLCK abundance averaged to values 147% greater in fetal (1.06 ± 0.28) than adult (0.43 ± 0.08) arteries, which corresponded, respectively, to 43 ± 10% and 31 ± 3% of the V_max values measured in homogenates. Confocal colocalization analysis revealed in fetal and adult arteries that 33 ± 6% and 20 ± 5% of total MLCK colocalized with pMLC₂₀, and that MLCK activation was greater in periluminal than periadventitial regions over the time course of electrical stimulation in both age groups. Together, these results demonstrate that the catalytic activity of MLCK is similar in fetal and adult arteries, but that the fraction of total MLCK in the functional compartment involved in contraction is significantly greater in fetal than adult arteries.

Two Motors and One Spring: Hypothetic Roles of Non-Muscle Myosin II and Submembrane Actin-Based Cytoskeleton in Cell Volume Sensing

Changes in plasma membrane curvature and intracellular ionic strength are two key features of cell volume perturbations. In this hypothesis we present a model of the responsible molecular apparatus which is assembled of two molecular motors [non-muscle myosin II (NMMII) and protrusive actin polymerization], a spring [a complex between the plasma membrane (PM) and the submembrane actin-based cytoskeleton (smACSK) which behaves like a viscoelastic solid] and the associated signaling proteins. We hypothesize that this apparatus senses changes in both the plasma membrane curvature and the ionic strength and in turn activates signaling pathways responsible for regulatory volume increase (RVI) and regulatory volume decrease (RVD). During cell volume changes hydrostatic pressure (HP) changes drive alterations in the cell membrane curvature. HP difference has opposite directions in swelling versus shrinkage, thus allowing distinction between them. By analogy with actomyosin contractility that appears to sense stiffness of the extracellular matrix we propose that NMMII and actin polymerization can actively probe the transmembrane gradient in HP. Furthermore, NMMII and protein-protein interactions in the actin cortex are sensitive to ionic strength. Emerging data on direct binding to and regulating activities of transmembrane mechanosensors by NMMII and actin cortex provide routes for signal transduction from transmembrane mechanosensors to cell volume regulatory mechanisms.

Metabolomics in asthma: A platform for discovery

Asthma, characterized by airway hyperresponsiveness, inflammation and remodeling, is a chronic airway disease with complex etiology. Severe asthma is characterized by frequent exacerbations and poor therapeutic response to conventional asthma therapy. A clear understanding of cellular and molecular mechanisms of asthma is critical for the discovery of novel targets for optimal therapeutic control of asthma. Metabolomics is emerging as a powerful tool to elucidate novel disease mechanisms in a variety of diseases. In this review, we summarize the current status of knowledge in asthma metabolomics at systemic and cellular levels. The findings demonstrate that various metabolic pathways, related to energy metabolism, macromolecular biosynthesis and redox signaling, are differentially modulated in asthma. Airway smooth muscle cell plays pivotal roles in asthma by contributing to airway hyperreactivity, inflammatory mediator release and remodeling. We posit that metabolomic profiling of airway structural cells, including airway smooth muscle cells, will shed light on molecular mechanisms of asthma and airway hyperresponsiveness and help identify novel therapeutic targets.

Phosphorylation of MYL12 by Myosin Light Chain Kinase Regulates Cellular Shape Changes in Cochlear Hair Cells

The organ of Corti is an auditory organ located in the cochlea, comprising hair cells (HCs) and other supporting cells. Cellular shape changes of HCs are important for the development of auditory epithelia and hearing function. It was previously observed that HCs and inner sulcus cells (ISCs) demonstrate cellular shape changes similar to the apical constriction of the neural epithelia. Apical constriction is induced via actomyosin cable contraction in the apical junctional complex and necessary for the physiological function of the epithelium. Actomyosin cable contraction is mainly regulated by myosin regulatory light chain (MRLC) phosphorylation by myosin light chain kinase (MLCK). However, MRLC and MLCK isoforms expressed in HCs and ISCs are unknown. Hence, we investigated the expression patterns and roles of MRLCs and MLCKs in HCs. Droplet digital PCR revealed that HCs expressed MYL12A/B and MYL9, which are non-muscle MRLC and smooth muscle MLCK (smMLCK), respectively. Immunofluorescence staining throughout the organ of Corti demonstrated that only MYL12 was expressed in the apical portion of HCs, whereas MYL12 and MYL9 were expressed on ISCs. In addition, purified MYL12B was phosphorylated by smMLCK in vitro, and the harvested HCs contained phosphorylated MYL12. Furthermore, accompanied by the expansion of the cell area of outer HCs, MYL12 phosphorylation was reduced by ML-7, which is an inhibitor of smMLCK. In conclusion, MYL12 phosphorylation by smMLCK contributed to the apical constriction-like cellular shape change of HCs possibly relating to the development of auditory epithelia and hearing function.

Helicobacter pylori regulates ILK to influence autophagy through Rac1 and RhoA signaling pathways in gastric epithelial cells

The ability of Helicobacter pylori to manipulate host autophagy is an important pathogenic mechanism. We found an inverse correlation between the expression of ILK and the autophagy marker protein LC3B in H. pylori-positive human samples, H. pylori-infected mice models and H. pylori-infected GES-1 cell lines. When the ILK-knockdown GES-1 cells were infected by H. pylori, CagA were significantly degraded, autophagosomes accumulation and autolysosomes formation were significantly increased, and LC3B protein levels and ratio of LC3BII to LC3BI were also remarkably upregulated. And chloroquine treatment increased LC3B levels in ILK-knockdown GES-1 cells. The expression levels of both Rac1 and RhoA were downregulated in GES-1 cells after H. pylori infection and were decreased in ILK-knockdown GES-1 cells. The mRNA and protein levels of PAK1, MLC, and LIMK were significantly decreased and cofilin mRNA and protein levels were significantly increased in GES-1 cells treated with the Rac1 inhibitor NSC 23766. The mRNA and protein levels of ROCK1, ROCK2, MLC, and LIMK1 were significantly reduced and cofilin mRNA and protein levels were significantly increased in GES-1 cells treated with the RhoA inhibitor CCG-1423. F-actin was significantly reduced in Rac1- or RhoA-inhibited GES-1 cells. F-actin depolymerization induced autophagosomes accumulation, autolysosomes formation, and the increase of LC3B levels in GES-1 cells. Therefore, these findings revealed that ILK could serve as a novel regulator to affect Rac1/PAK1 and RhoA/ROCKs signaling pathways, thereby influencing H. pylori-induced autophagy.

Striated Preferentially Expressed Protein Kinase (SPEG) in Muscle Development, Function, and Disease

Mutations in striated preferentially expressed protein kinase (SPEG), a member of the myosin light chain kinase protein family, are associated with centronuclear myopathy (CNM), cardiomyopathy, or a combination of both. Burgeoning evidence suggests that SPEG plays critical roles in the development, maintenance, and function of skeletal and cardiac muscles. Here we review the genotype-phenotype relationships and the molecular mechanisms of SPEG-related diseases. This review will focus on the progress made toward characterizing SPEG and its interacting partners, and its multifaceted functions in muscle regeneration, triad development and maintenance, and excitation-contraction coupling. We will also discuss future directions that are yet to be investigated including understanding of its tissue-specific roles, finding additional interacting proteins and their relationships. Understanding the basic mechanisms by which SPEG regulates muscle development and function will provide critical insights into these essential processes and help identify therapeutic targets in SPEG-related disorders.

Can High-Intensity Interval Training Promote Skeletal Muscle Anabolism?

Exercise training in combination with optimal nutritional support is an effective strategy to maintain or increase skeletal muscle mass. A single bout of resistance exercise undertaken with adequate protein availability increases rates of muscle protein synthesis and, when repeated over weeks and months, leads to increased muscle fiber size. While resistance-based training is considered the 'gold standard' for promoting muscle hypertrophy, other modes of exercise may be able to promote gains in muscle mass. High-intensity interval training (HIIT) comprises short bouts of exercise at or above the power output/speed that elicits individual maximal aerobic capacity, placing high tensile stress on skeletal muscle, and somewhat resembling the demands of resistance exercise. While HIIT induces rapid increases in skeletal muscle oxidative capacity, the anabolic potential of HIIT for promoting concurrent gains in muscle mass and cardiorespiratory fitness has received less scientific inquiry. In this review, we discuss studies that have determined muscle growth responses after HIIT, with a focus on molecular responses, that provide a rationale for HIIT to be implemented among populations who are susceptible to muscle loss (e.g. middle-aged or older adults) and/or in clinical settings (e.g. pre- or post-surgery).

Regulatory Light Chains in Cardiac Development and Disease

The role of regulatory light chains (RLCs) in cardiac muscle function has been elucidated progressively over the past decade. The RLCs are among the earliest expressed markers during cardiogenesis and persist through adulthood. Failing hearts have shown reduced RLC phosphorylation levels and that restoring baseline levels of RLC phosphorylation is necessary for generating optimal force of muscle contraction. The signalling mechanisms triggering changes in RLC phosphorylation levels during disease progression remain elusive. Uncovering this information may provide insights for better management of heart failure patients. Given the cardiac chamber-specific expression of RLC isoforms, ventricular RLCs have facilitated the identification of mature ventricular cardiomyocytes, opening up possibilities of regenerative medicine. This review consolidates the standing of RLCs in cardiac development and disease and highlights knowledge gaps and potential therapeutic advancements in targeting RLCs.

An overview of pharmacotherapy for cerebral vasospasm and delayed cerebral ischemia after subarachnoid hemorrhage

Introduction: Survival from aneurysmal subarachnoid hemorrhage has increased in the past few decades. However, functional outcome after subarachnoid hemorrhage is still suboptimal. Delayed cerebral ischemia (DCI) is one of the major causes of morbidity.Areas covered: Mechanisms underlying vasospasm and DCI after aneurysmal subarachnoid hemorrhage and pharmacological treatment are summarized in this review.Expert opinion: Oral nimodine, an L-type dihydropyridine calcium channel blocker, is the only FDA-approved drug for the prevention and treatment of neurological deficits after aneurysmal subarachnoid hemorrhage. Fasudil, a potent Rho-kinase inhibitor, has also been shown to improve the clinical outcome and has been approved in some countries for use in patients with aneurysmal subarachnoid hemorrhage. Although other drugs, including nicardipine, cilostazol, statins, clazosentan, magnesium and heparin, have been expected to have beneficial effects on DCI, there has been no convincing evidence supporting the routine use of those drugs in patients with aneurysmal subarachnoid hemorrhage in clinical practice. Further elucidation of the mechanisms underlying DCI and the development of effective therapeutic strategies for DCI, including combination therapy, are necessary to further improve the functional outcome and mortality after subarachnoid hemorrhage.

The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells

The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca²⁺ signals and Ca²⁺ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca²⁺ signal on arterial contractility depends on the type of Ca²⁺ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca²⁺ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca²⁺ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca²⁺ signals have already been confirmed, while further investigation is needed for other Ca²⁺ signals. This article focuses on endothelial and smooth muscle Ca²⁺ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca²⁺ entry pathways at the plasma membrane, Ca²⁺ release signals from the intracellular stores, the functional and physiological relevance of Ca²⁺ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca²⁺ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.

Skeletal Muscle Transcriptome Analysis of Hanzhong Ma Duck at Different Growth Stages Using RNA-Seq

As one of the most important poultry worldwide, ducks (Anas platyrhynchos) are raised mainly for meat and egg products, and muscle development in ducks is important for meat production. Therefore, an investigation of gene expression in duck skeletal muscle would significantly contribute to our understanding of muscle development. In this study, twenty-four cDNA libraries were constructed from breast and leg muscles of Hanzhong Ma ducks at day 17, 21, 27 of the embryo and postnatal at 6-month-old. High-throughput sequencing and bioinformatics were used to determine the abundances and characteristics of transcripts. A total of 632,172,628 (average 52,681,052) and 637,213,938 (average 53,101,162) reads were obtained from the sequencing data of breast and leg muscles, respectively. Over 71.63% and 77.36% of the reads could be mapped to the Anas platyrhynchos genome. In the skeletal muscle of Hanzhong duck, intron variant (INTRON), synonymous variant (SYNONYMOUS_CODING), and prime 3' UTR variant (UTR_3_PRIME) were the main single nucleotide polymorphisms (SNP) annotation information, and "INTRON", "UTR_3_PRIME", and downstream-gene variant (DOWNSTREAM) were the main insertion-deletion (InDel) annotation information. The predicted number of alternative splicing (AS) in all samples were mainly alternative 5' first exon (transcription start site)-the first exon splicing (TSS) and alternative 3' last exon (transcription terminal site)-the last exon splicing (TTS). Besides, there were 292 to 2801 annotated differentially expressed genes (DEGs) in breast muscle and 304 to 1950 annotated DEGs in leg muscle from different databases. It is worth noting that 75 DEGs in breast muscle and 49 DEGs in leg muscle were co-expressed at all developmental points of comparison, respectively. The RNA-Seq data were confirmed to be reliable by qPCR. The identified DEGs, such as CREBL2, RHEB, GDF6, SHISA2, MYLK2, ACTN3, RYR3, and STMN1, were specially highlighted, indicating their strong associations with muscle development in the Hanzhong Ma duck. KEGG pathway analysis suggested that regulation of actin cytoskeleton, oxidative phosphorylation, and focal adhesion were involved in the development of skeletal muscle. The findings from this study can contribute to future investigations of the growth and development mechanism in duck skeletal muscle.

Intrinsic Mechanisms Regulating Neuronal Migration in the Postnatal Brain

Neuronal migration is a fundamental brain development process that allows cells to move from their birthplaces to their sites of integration. Although neuronal migration largely ceases during embryonic and early postnatal development, neuroblasts continue to be produced and to migrate to a few regions of the adult brain such as the dentate gyrus and the subventricular zone (SVZ). In the SVZ, a large number of neuroblasts migrate into the olfactory bulb (OB) along the rostral migratory stream (RMS). Neuroblasts migrate in chains in a tightly organized micro-environment composed of astrocytes that ensheath the chains of neuroblasts and regulate their migration; the blood vessels that are used by neuroblasts as a physical scaffold and a source of molecular factors; and axons that modulate neuronal migration. In addition to diverse sets of extrinsic micro-environmental cues, long-distance neuronal migration involves a number of intrinsic mechanisms, including membrane and cytoskeleton remodeling, Ca²⁺ signaling, mitochondria dynamics, energy consumption, and autophagy. All these mechanisms are required to cope with the different micro-environment signals and maintain cellular homeostasis in order to sustain the proper dynamics of migrating neuroblasts and their faithful arrival in the target regions. Neuroblasts in the postnatal brain not only migrate into the OB but may also deviate from their normal path to migrate to a site of injury induced by a stroke or by certain neurodegenerative disorders. In this review, we will focus on the intrinsic mechanisms that regulate long-distance neuroblast migration in the adult brain and on how these pathways may be modulated to control the recruitment of neuroblasts to damaged/diseased brain areas.

Distinct Roles of Smooth Muscle and Non-muscle Myosin Light Chain-Mediated Smooth Muscle Contraction

Both smooth muscle (SM) and non-muscle (NM) myosin II are expressed in hollow organs such as the bladder and uterus, but their respective roles in contraction and corresponding physiological functions remain to be determined. In this report, we assessed their roles by analyzing mice deficient of Myl9, a gene encoding the SM myosin regulatory light chain (SM RLC). We find that global Myl9-deficient bladders contracted with an apparent sustained phase, despite no initial phase. This sustained contraction was mediated by NM myosin RLC (NM RLC) phosphorylation by myosin light chain kinase (MLCK). NM myosin II was expressed abundantly in the uterus and young mice bladders, of which the force was accordingly sensitive to NM myosin inhibition. Our findings reveal distinct roles of SM RLC and NM RLC in SM contraction.

Myosin light chain kinase regulates intestinal permeability of mucosal homeostasis in Crohn's disease

Introduction: Researchers have investigated the potential role of intestinal permeability in Crohn's disease pathogenesis. Intestinal permeability is usually mediated by cytoskeleton and intercellular junctions. The myosin light chain kinase (MLCK) is an enzyme that activates the myosin light chain to exert its function related to cytoskeleton contraction and tight junction regulation. The correlation between MLCK and Crohn's disease pathogenesis has been consistently proven. Areas covered: This study aims to expand the understanding of the regulation and function of MLCK in Crohn's disease. An extensive literature search in the MEDLINE database (via PubMed) has been performed up to Oct. 2020. The roles of MLCK in tight junction activation, intestinal permeability enhancement, and cell signal regulation are comprehensively discussed. Expert opinion: Targeting the MLCK-related pathways such as TNF-α in CD treatment has been put into clinical use. More accurate targeting such as MLCK and TNFR2 has been proposed to reduce side effects. MLCK may also have the potential to become biomarkers in fields like CD activity. With the application of cutting age research methods and tools, the MLCK research could be accelerated.

Expression of smooth muscle-like effectors and core cardiomyocyte regulators in the contractile papillae of Ciona

BACKGROUND

The evolution of vertebrate smooth muscles is obscured by lack of identifiable smooth muscle-like cells in tunicates, the invertebrates most closely related to vertebrates. A recent evolutionary model was proposed in which smooth muscles arose before the last bilaterian common ancestor, and were later diversified, secondarily lost or modified in the branches leading to extant animal taxa. However, there is currently no data from tunicates to support this scenario.

METHODS AND RESULTS

Here, we show that the axial columnar cells, a unique cell type in the adhesive larval papillae of the tunicate Ciona, are enriched for orthologs of vertebrate smooth/non-muscle-specific effectors of contractility, in addition to developing from progenitors that express conserved cardiomyocyte regulatory factors. We show that these cells contract during the retraction of the Ciona papillae during larval settlement and metamorphosis.

CONCLUSIONS

We propose that the axial columnar cells of Ciona are a myoepithelial cell type required for transducing external stimuli into mechanical forces that aid in the attachment of the motile larva to its final substrate. Furthermore, they share developmental and functional features with vertebrate myoepithelial cells, vascular smooth muscle cells, and cardiomyocytes. We discuss these findings in the context of the proposed models of vertebrate smooth muscle and cardiomyocyte evolution.

Double the trouble: giant proteins with dual kinase activity in the heart

Obscurin and its homolog, striated muscle preferentially expressed gene (SPEG), constitute a unique group of proteins abundantly expressed in striated muscles that contain two tandemly arranged MLCK-like kinases. The physiological significance of the dual kinase motifs is largely understudied; however, a collection of recent studies characterizing their binding interactions, putative targets, and disease-linked mutations have begun to shed light on their potential roles in muscle pathophysiology. Specifically, obscurin kinase 1 is proposed to regulate cardiomyocyte adhesion via phosphorylating N-cadherin, whereas SPEG kinases 1 and 2 regulate Ca²⁺ cycling by phosphorylating junctophilin-2 and the sarcoendoplasmic Ca²⁺ ATPase 2 (SERCA2). Herein, we review what is currently known regarding the potential substrates, physiological roles, and disease associations of obscurin and SPEG tandem kinase domains and provide future directions that have yet to be investigated.

Signaling pathways underlying changes in the contractility of the stomach fundus smooth muscle in diabetic rats

Dysfunction of gastrointestinal (GI) motility is a common complication in patients with diabetes mellitus (DM). Studies related to changes in fundus contraction induced by inhibitors in DM are not well known. Therefore, this study aimed to investigate the signaling pathways involved in the changes in the contraction of fundus smooth muscle obtained from control and DM rats. DM was induced by injecting streptozotocin (65 mg/kg) into Sprague-Dawley rats. The rats were sacrificed after 14 days. Fundus smooth muscle contraction was stimulated using electrical field stimulation (amplitude, 50 V; duration, 1 min; frequency, 2-20 Hz) and acetylcholine (0.1 mM). The inhibitor-mediated cell membrane was pre-treated with atropine, verapamil, methysergide, ketanserin, ondansetron, and GR 113808. Inhibitors related to intracellular signaling, such as U73122, chelerythrine, L-NNA, were also used. ML-9 and Y-27632 were identified as inhibitors of factors of myosin light chain (MLC). The contractility was observed to be lower in the DM group than in the control group. Further, the activities of phospholipase C (PLC), protein kinase C (PKC), and myosin light chain kinase (MLCK) were decreased in the DM group. DM reduced the activity of PLC, PKC, and MLCK, which resulted in a decrease in the contractility of the fundus smooth muscle. Therefore, our results present the mechanism of this DM-mediated GI disorder.

The Altered Signaling on EFS-Induced Colon Contractility in Diabetic Rats

Diabetes mellitus affects the colonic motility developing gastrointestinal symptoms, such as constipation. The aim of the study was to examine the role of intracellular signaling pathways contributing to colonic dysmotility in diabetes mellitus. To generate diabetes mellitus, the rats were injected by a single high dose of streptozotocin (65 mg/kg) intraperitoneally. The proximal colons from both normal and diabetic rats were contracted by applying an electrical field stimulation with pulse voltage of 40 V in amplitude and pulse duration of 1 ms at frequencies of 1, 2, 4, and 6 Hz. The muscle strips from both normal rats and rats with diabetes mellitus were pretreated with different antagonists and inhibitors. Rats with diabetes mellitus had lower motility than the control group. There were significant differences in the percentage of inhibition of contraction between normal rats and rats with diabetes mellitus after the incubation of tetrodotoxin (neuronal blocker), atropine (muscarinic receptor antagonist), prazosin (α₁ adrenergic receptor antagonist), DPCPX (adenosine A1 receptor antagonist), verapamil (L-type Ca²⁺ channel blocker), U73122 (PLC inhibitor), ML-9 (MLCK inhibitor), udenafil (PDE₅ inhibitor), and methylene blue (guanylate cyclase inhibitor). The protein expression of p-MLC and PDE₅ were decreased in the diabetic group compared to the normal group. These results showed that the reduced colonic contractility resulted from the impaired neuronal conduction and decreased muscarinic receptor sensitivity, which resulted in decreased phosphorylation of MLC via MLCK, and cGMP activity through PDE₅.

Muscle Cell Morphogenesis, Structure, Development and Differentiation Processes Are Significantly Regulated during Human Ovarian Granulosa Cells In Vitro Cultivation

Granulosa cells (GCs) have many functions and are fundamental for both folliculogenesis and oogenesis, releasing hormones and communicating directly with the oocyte. Long-term in vitro cultures of GCs show significant stem-like characteristics. In the current study, RNA of human ovarian granulosa cells was collected at 1, 7, 15 and 30 days of long-term in vitro culture. Understanding the process of differentiation of GCs towards different cell lineages, as well as the molecular pathways underlying these mechanisms, is fundamental to revealing other possible stemness markers of this type of cell. Identifying new markers of GC plasticity may help to understand the aetiology and recurrence of a wide variety of diseases and health conditions and reveal possible clinical applications of the ovarian tissue cells, affecting not only the reproductive ability but also sex hormone production. Granulosa cells were the subject of this study, as they are readily available as remnant material leftover after in vitro fertilisation procedures and exhibit significant stem-like characteristics in culture. The change in gene expression was investigated through a range of molecular and bioinformatic analyses. Expression microarrays were used, allowing the identification of groups of genes typical of specific cellular pathways. This candidate gene study focused on ontological groups associated with muscle cell morphogenesis, structure, development and differentiation, namely, “muscle cell development”, “muscle cell differentiation”, “muscle contraction”, “muscle organ development”, “muscle organ morphogenesis”, “muscle structure development”, “muscle system process” and “muscle tissue development”. The results showed that the 10 most upregulated genes were keratin 19, oxytocin receptor, connective tissue growth factor, nexilin, myosin light chain kinase, cysteine and glycine-rich protein 3, caveolin 1, actin, activating transcription factor 3 and tropomyosin, while the 10 most downregulated consisted of epiregulin, prostaglandin-endoperoxide synthase 2, transforming growth factor, interleukin, collagen, 5-hydroxytryptmine, interleukin 4, phosphodiesterase, wingless-type MMTV integration site family and SRY-box 9. Moreover, ultrastructural observations showing heterogeneity of granulosa cell population are presented in the study. At least two morphologically different subpopulations were identified: large, light coloured and small, darker cells. The expression of genes belonging to the mentioned ontological groups suggest the potential ability of GCs to differentiate and proliferate toward muscle lineage, showing possible application in muscle regeneration and the treatment of different diseases.

The Regulation of Intestinal Mucosal Barrier by Myosin Light Chain Kinase/Rho Kinases

The intestinal epithelial apical junctional complex, which includes tight and adherens junctions, contributes to the intestinal barrier function via their role in regulating paracellular permeability. Myosin light chain II (MLC-2), has been shown to be a critical regulatory protein in altering paracellular permeability during gastrointestinal disorders. Previous studies have demonstrated that phosphorylation of MLC-2 is a biochemical marker for perijunctional actomyosin ring contraction, which increases paracellular permeability by regulating the apical junctional complex. The phosphorylation of MLC-2 is dominantly regulated by myosin light chain kinase- (MLCK-) and Rho-associated coiled-coil containing protein kinase- (ROCK-) mediated pathways. In this review, we aim to summarize the current state of knowledge regarding the role of MLCK- and ROCK-mediated pathways in the regulation of the intestinal barrier during normal homeostasis and digestive diseases. Additionally, we will also suggest potential therapeutic targeting of MLCK- and ROCK-associated pathways in gastrointestinal disorders that compromise the intestinal barrier.

Kindlin-2 deficiency induces fatal intestinal obstruction in mice

Rationale: Smooth muscle-motility disorders are mainly characterized by impaired contractility and functional intestinal obstruction. Some of these cases are caused by genetic mutations of smooth muscle genes ACTA2, ACTG2, MYH11, MYLK and LMOD1. Still the etiology is complex and multifactorial and the underlying pathology is poorly understood. Integrin interaction protein Kindlin-2 is widely expressed in striated and smooth muscle cells (SMC). However, the function of Kindlin-2 in the smooth muscle remains elusive.

Methods: We generated two mouse models using different cre promoter transgenic mice, Kindlin-2^fl/fl SM22α-cre+ (cKO mice) and Kindlin-2^fl/fl; MYH-cre+ (iKO mice). Embryos and adult tissues were prepared for hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) apoptosis assay. We investigated ultrastructure changes of mouse smooth muscle using transmission electron microscopy (TEM) and measured smooth muscle contractile force in mounting aortic and intestinal rings using the multiwire myograph system (DMT 620M). In addition, cell traction force microscopy (CTFM) was applied to observe the functional change of primary SMC after Kindlin-2 depletion by RNAi.

Results: Depletion of Kindlin-2 encoding gene Fermt2 in embryonic smooth muscles leads to apoptosis, downregulates the key components of SMC, impairs smooth muscle development, and finally causes embryonic death at E14.5. Tamoxifen-induced Kindlin-2-specific knockout in adult mouse smooth muscle showed decreased blood pressure, intestinal hypoperistalsis, and eventually died of intestinal obstruction. Kindlin-2 depletion also leads to downregulated Myh11, α-SMA, and CNN, shortened myofilament, broken myofibrils, and impaired contractility of the smooth muscles in iKO mice. Mechanistically, loss of Kindlin-2 decreases Ca2⁺ influx in primary vascular smooth muscle cells (PVSMC) by downregulating the expression of calcium-binding protein S100A14 and STIM1.

Conclusion: We demonstrated that Kindlin-2 is essential for maintaining the normal structure and function of smooth muscles. Loss of Kindlin-2 impairs smooth muscle formation during embryonic development by inducing apoptosis and jeopardizes the contraction of adult smooth muscle by blocking Ca²⁺ influx that leads to intestinal obstruction. Mice with Kindlin-2 depletion in adult smooth muscle could be a potent animal model of intestinal obstruction for disease research, drug treatment and prognosis.

P2Y6 receptor inhibition aggravates ischemic brain injury by reducing microglial phagocytosis

Introduction

Clearance of damaged cells and debris is beneficial for the functional recovery after ischemic brain injury. However, the specific phagocytic receptor that mediates microglial phagocytosis after ischemic stroke is unknown.

Aim

To investigate whether P2Y6 receptor‐mediated microglial phagocytosis is beneficial for the debris clearance and functional recovery after ischemic stroke.

Results

The expression of the P2Y6 receptor in microglia increased within 3 days after transient middle cerebral artery occlusion. Inhibition of microglial phagocytosis by the selective inhibitor MRS2578 enlarged the brain atrophy and edema volume after ischemic stroke, subsequently aggravated neurological function as measured by modified neurological severity scores and Grid walking test. MRS2578 treatment had no effect on the expression of IL‐1α, IL‐1β, IL‐6, IL‐10, TNF‐α, TGF‐β, and MPO after ischemic stroke. Finally, we found that the expression of myosin light chain kinase decreased after microglial phagocytosis inhibition in the ischemic mouse brain, which suggested that myosin light chain kinase was involved in P2Y6 receptor‐mediated phagocytosis.

Conclusion

Our results indicate that P2Y6 receptor‐mediated microglial phagocytosis plays a beneficial role during the acute stage of ischemic stroke, which can be a therapeutic target for ischemic stroke.

Cardiac myosin regulatory light chain kinase modulates cardiac contractility by phosphorylating both myosin regulatory light chain and troponin I

Heart muscle contractility and performance are controlled by posttranslational modifications of sarcomeric proteins. Although myosin regulatory light chain (RLC) phosphorylation has been studied extensively in vitro and in vivo, the precise role of cardiac myosin light chain kinase (cMLCK), the primary kinase acting upon RLC, in the regulation of cardiomyocyte contractility remains poorly understood. In this study, using recombinantly expressed and purified proteins, various analytical methods, in vitro and in situ kinase assays, and mechanical measurements in isolated ventricular trabeculae, we demonstrate that human cMLCK is not a dedicated kinase for RLC but can phosphorylate other sarcomeric proteins with well-characterized regulatory functions. We show that cMLCK specifically monophosphorylates Ser²³ of human cardiac troponin I (cTnI) in isolation and in the trimeric troponin complex in vitro and in situ in the native environment of the muscle myofilament lattice. Moreover, we observed that human cMLCK phosphorylates rodent cTnI to a much smaller extent in vitro and in situ, suggesting species-specific adaptation of cMLCK. Although cMLCK treatment of ventricular trabeculae exchanged with rat or human troponin increased their cross-bridge kinetics, the increase in sensitivity of myofilaments to calcium was significantly blunted by human TnI, suggesting that human cTnI phosphorylation by cMLCK modifies the functional consequences of RLC phosphorylation. We propose that cMLCK-mediated phosphorylation of TnI is functionally significant and represents a critical signaling pathway that coordinates the regulatory states of thick and thin filaments in both physiological and potentially pathophysiological conditions of the heart.

Contributions of Myosin Light Chain Kinase to Regulation of Epithelial Paracellular Permeability and Mucosal Homeostasis

Intestinal barrier function is required for the maintenance of mucosal homeostasis. Barrier dysfunction is thought to promote progression of both intestinal and systemic diseases. In many cases, this barrier loss reflects increased permeability of the paracellular tight junction as a consequence of myosin light chain kinase (MLCK) activation and myosin II regulatory light chain (MLC) phosphorylation. Although some details about MLCK activation remain to be defined, it is clear that this triggers perijunctional actomyosin ring (PAMR) contraction that leads to molecular reorganization of tight junction structure and composition, including occludin endocytosis. In disease states, this process can be triggered by pro-inflammatory cytokines including tumor necrosis factor-α (TNF), interleukin-1β (IL-1β), and several related molecules. Of these, TNF has been studied in the greatest detail and is known to activate long MLCK transcription, expression, enzymatic activity, and recruitment to the PAMR. Unfortunately, toxicities associated with inhibition of MLCK expression or enzymatic activity make these unsuitable as therapeutic targets. Recent work has, however, identified a small molecule that prevents MLCK1 recruitment to the PAMR without inhibiting enzymatic function. This small molecule, termed Divertin, restores barrier function after TNF-induced barrier loss and prevents disease progression in experimental chronic inflammatory bowel disease.

CRISPR-Cas9/phosphoproteomics identifies multiple noncanonical targets of myosin light chain kinase

Prior studies have implicated myosin light chain kinase (MLCK) in the regulation of aquaporin-2 (AQP2) in the renal collecting duct. To discover signaling targets of MLCK, we used CRISPR-Cas9 to delete the MLCK gene (Mylk) to obtain MLCK-null mpkCCD cells and carried out comprehensive phosphoproteomics using stable isotope labeling with amino acids in cell culture for quantification. Immunocytochemistry and electron microscopy demonstrated a defect in the processing of AQP2-containing early endosomes to late endosomes. The phosphoproteomics experiments revealed that, of the 1,743 phosphopeptides quantified over multiple replicates, 107 were changed in abundance by MLCK deletion (29 decreased and 78 increased). One of the decreased phosphopeptides corresponded to the canonical target site in myosin regulatory light chain. Network analysis indicated that targeted phosphoproteins clustered into distinct structural/functional groups: actomyosin, signaling, nuclear envelope, gene transcription, mRNA processing, energy metabolism, intermediate filaments, adherens junctions, and tight junctions. There was significant overlap between the derived MLCK signaling network and a previously determined PKA signaling network. The presence of multiple proteins in the actomyosin category prompted experiments showing that MLCK deletion inhibits the normal effect of vasopressin to depolymerize F-actin, providing a potential explanation for the AQP2 trafficking defect. Changes in phosphorylation of multiple proteins in the nuclear envelope prompted measurement of nuclear size, showing a significant increase in average nuclear volume. We conclude that MLCK is part of a multicomponent signaling pathway in both the cytoplasm and nucleus that includes much more than simple regulation of conventional nonmuscle myosins through myosin regulatory light chain phosphorylation.

Increased expression of desmin and vimentin reduces bladder smooth muscle contractility via JNK2

Bladder dysfunction is associated with the overexpression of the intermediate filament (IF) proteins desmin and vimentin in obstructed bladder smooth muscle (BSM). However, the mechanisms by which these proteins contribute to BSM dysfunction are not known. Previous studies have shown that desmin and vimentin directly participate in signal transduction. In this study, we hypothesized that BSM dysfunction associated with overexpression of desmin or vimentin is mediated via c-Jun N-terminal kinase (JNK). We employed a model of murine BSM tissue in which increased expression of desmin or vimentin was induced by adenoviral transduction to examine the sufficiency of increased IF protein expression to reduce BSM contraction. Murine BSM strips overexpressing desmin or vimentin generated less force in response to KCl and carbachol relative to the levels in control murine BSM strips, an effect associated with increased JNK2 phosphorylation and reduced myosin light chain (MLC₂₀ ) phosphorylation. Furthermore, desmin and vimentin overexpressions did not alter BSM contractility and MLC₂₀ phosphorylation in strips isolated from JNK2 knockout mice. Pharmacological JNK2 inhibition produced results qualitatively similar to those caused by JNK2 knockout. These findings suggest that inhibition of JNK2 may improve diminished BSM contractility associated with obstructive bladder disease.

Rho-associated kinase and zipper-interacting protein kinase, but not myosin light chain kinase, are involved in the regulation of myosin phosphorylation in serum-stimulated human arterial smooth muscle cells

Myosin regulatory light chain (LC₂₀) phosphorylation plays an important role in vascular smooth muscle contraction and cell migration. Ca²⁺/calmodulin-dependent myosin light chain kinase (MLCK) phosphorylates LC₂₀ (its only known substrate) exclusively at S19. Rho-associated kinase (ROCK) and zipper-interacting protein kinase (ZIPK) have been implicated in the regulation of LC₂₀ phosphorylation via direct phosphorylation of LC₂₀ at T18 and S19 and indirectly via phosphorylation of MYPT1 (the myosin targeting subunit of myosin light chain phosphatase, MLCP) and Par-4 (prostate-apoptosis response-4). Phosphorylation of MYPT1 at T696 and T853 inhibits MLCP activity whereas phosphorylation of Par-4 at T163 disrupts its interaction with MYPT1, exposing the sites of phosphorylation in MYPT1 and leading to MLCP inhibition. To evaluate the roles of MLCK, ROCK and ZIPK in these phosphorylation events, we investigated the time courses of phosphorylation of LC₂₀, MYPT1 and Par-4 in serum-stimulated human vascular smooth muscle cells (from coronary and umbilical arteries), and examined the effects of siRNA-mediated MLCK, ROCK and ZIPK knockdown and pharmacological inhibition on these phosphorylation events. Serum stimulation induced rapid phosphorylation of LC₂₀ at T18 and S19, MYPT1 at T696 and T853, and Par-4 at T163, peaking within 30–120 s. MLCK knockdown or inhibition, or Ca²⁺ chelation with EGTA, had no effect on serum-induced LC₂₀ phosphorylation. ROCK knockdown decreased the levels of phosphorylation of LC₂₀ at T18 and S19, of MYPT1 at T696 and T853, and of Par-4 at T163, whereas ZIPK knockdown decreased LC₂₀ diphosphorylation, but increased phosphorylation of MYPT1 at T696 and T853 and of Par-4 at T163. ROCK inhibition with GSK429286A reduced serum-induced phosphorylation of LC₂₀ at T18 and S19, MYPT1 at T853 and Par-4 at T163, while ZIPK inhibition by HS38 reduced only LC₂₀ diphosphorylation. We also demonstrated that serum stimulation induced phosphorylation (activation) of ZIPK, which was inhibited by ROCK and ZIPK down-regulation and inhibition. Finally, basal phosphorylation of LC₂₀ in the absence of serum stimulation was unaffected by MLCK, ROCK or ZIPK knockdown or inhibition. We conclude that: (i) serum stimulation of cultured human arterial smooth muscle cells results in rapid phosphorylation of LC₂₀, MYPT1, Par-4 and ZIPK, in contrast to the slower phosphorylation of kinases and other proteins involved in other signaling pathways (Akt, ERK1/2, p38 MAPK and HSP27), (ii) ROCK and ZIPK, but not MLCK, are involved in serum-induced phosphorylation of LC₂₀, (iii) ROCK, but not ZIPK, directly phosphorylates MYPT1 at T853 and Par-4 at T163 in response to serum stimulation, (iv) ZIPK phosphorylation is enhanced by serum stimulation and involves phosphorylation by ROCK and autophosphorylation, and (v) basal phosphorylation of LC₂₀ under serum-free conditions is not attributable to MLCK, ROCK or ZIPK.

High-fat diet promotes experimental colitis by inducing oxidative stress in the colon

Diets high in animal fats are associated with increased risks of inflammatory bowel disease, but the mechanism remains unclear. In this study, we investigated the effect of high-fat diet (HFD) on the development of experimental colitis in mice. Relative to mice fed low-fat diet (LFD), HFD feeding for 4 wk increased the levels of triglyceride, cholesterol, and free fatty acids in the plasma as well as within the colonic mucosa. In an experimental colitis model induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS), mice on 4-wk HFD exhibited more severe colonic inflammation and developed more severe colitis compared with the LFD counterparts. HFD feeding resulted in higher production of mucosal pro-inflammatory cytokines, greater activation of the myosin light chain kinase (MLCK) tight junction regulatory pathway, and greater increases in mucosal barrier permeability in mice following TNBS induction. HFD feeding also induced gp91, an NADPH oxidase subunit, and promoted reactive oxygen species (ROS) production in both colonic epithelial cells and lamina propria cells. In HCT116 cell culture, palmitic acid or palmitic acid and TNF-α combination markedly increased ROS production and induced the MLCK pathway, and these effects were markedly diminished in the presence of a ROS scavenger. Taken together, these data suggest that HFD promotes colitis by aggravating mucosal oxidative stress, which rapidly drives mucosal inflammation and increases intestinal mucosal barrier permeability.NEW & NOTEWORTHY This study demonstrates high-fat diet feeding promotes colitis in a 2,4,6-trinitrobenzenesulfonic acid-induced experimental colitis model in mice. The underlying mechanism is that high-fat diet induces oxidative stress in the colonic mucosa, which increases colonic epithelial barrier permeability and drives colonic mucosal inflammation. These observations provide molecular evidence that diets high in saturated fats are detrimental to patients with inflammatory bowel diseases.

ZIPK mediates endothelial cell contraction through myosin light chain phosphorylation and is required for ischemic-reperfusion injury

The paracellular gap formed by endothelial cell (EC) contraction is fundamental for endothelium permeability, but the mechanism underlying EC contraction has yet to be determined. Here, we identified the zipper-interacting protein kinase (ZIPK) as the kinase for EC contraction and myosin light chain (MLC) phosphorylation. Inhibition of ZIPK activity by pharmacological inhibitors and small interfering RNAs led to a significant decrease in the mono- and diphosphorylation of MLCs along with a contractile response to thrombin, suggesting an essential role of ZIPK in EC paracellular permeability. To assess the role of ZIPK in vivo, we established mouse lines with conditional deletion of Zipk gene. The endothelium-specific deletion of Zipk led to embryonic lethality, whereas the UBC-Cre^ERT2-mediated deletion of Zipk by tamoxifen induction at adulthood caused no apparent phenotype. The induced deletion of Zipk significantly inhibited ischemia-reperfusion-induced blood-brain barrier dysfunction and neuronal injuries from middle cerebral artery occlusion and reperfusion, as evidenced by reduced infarct and edema volume, attenuated Evans blue dye leakage, and improved neuronal behavior. We thus concluded that ZIPK and its phosphorylation of MLC were required for EC contraction and ischemic neuronal injuries. ZIPK may be a prospective therapeutic target for stroke.-Zhang, Y., Zhang, C., Zhang, H., Zeng, W., Li, S., Chen, C., Song, X., Sun, J., Sun, Z., Cui, C., Cao, X., Zheng, L., Wang, P., Zhao, W., Zhang, Z., Xu, Y., Zhu, M., Chen, H. ZIPK mediates endothelial cell contraction through myosin light chain phosphorylation and is required for ischemic-reperfusion injury.