Hybrid nutraceutical of 2-ketoglutaric acid in improving inflammatory bowel disease: Role of prebiotics and TAK1 inhibitor

The main cause of inflammatory bowel disease (IBD) is abnormal intestinal permeability due to the disruption of the tight junction of the intestinal barrier through a pathogen-mediated inflammatory mechanism and an imbalance of the gut microbiota. This study aimed to evaluate whether 2-ketoglutaric acid alleviated permeability dysfunction with tight junction localization, activated the transforming growth factor beta-activated kinase 1 (TAK1) inflammation pathway, and regulated the homeostasis of the intestinal microbiome in vitro and in vivo IBD model. Our findings revealed that 2-ketoglutaric acid significantly suppressed abnormal intestinal permeability, delocalization of tight junction proteins from the intestinal cell, expression of inflammatory cytokines, such as TNF-α, both in vitro and in vivo. 2-Ketoglutaric acid was found to directly bind to TAK1 and inhibit the TNF receptor-associated factor 6 (TRAF6)-TAK1 interaction, which is related to the activation of nuclear factor kappa B (NF-κB) pathways, thereby regulating the expression of mitogen-activated protein kinase. Dietary 2-ketoglutaric acid also alleviated gut microbiota dysbiosis and IBD symptoms, as demonstrated by improvements in the intestine length and the abundance of Ligilactobacillus, Coriobacteriaceae_UCG_002, and Ruminococcaceae_unclassified in mice with colitis. This study indicated that 2-ketoglutaric acid binds to TAK1 for activity inhibition which is related to the NF-κB pathway and alleviates abnormal permeability by regulating tight junction localization and gut microbiome homeostasis. Therefore, 2-ketoglutaric acid is an effective nutraceutical agent and prebiotic for the treatment of IBD.

Fluoride disrupts intestinal epithelial tight junction integrity through intracellular calcium-mediated RhoA/ROCK signaling and myosin light chain kinase

Fluoride is a common contaminant of groundwater and agricultural commodity, which poses challenges to animal and human health. A wealth of research has demonstrated its detrimental effects on intestinal mucosal integrity; however, the underlying mechanisms remain obscure. This study aimed to investigate the role of the cytoskeleton in fluoride-induced barrier dysfunction. After sodium fluoride (NaF) treatment of the cultured Caco-2 cells, both cytotoxicity and cytomorphological changes (internal vacuoles or massive ablation) were observed. NaF lowered transepithelial electrical resistance (TEER) and enhanced paracellular permeation of fluorescein isothiocyanate dextran 4 (FD-4), indicating Caco-2 monolayers hyperpermeability. In the meantime, NaF treatment altered both the expression and distribution of the tight junction protein ZO-1. Fluoride exposure increased myosin light chain II (MLC2) phosphorylation and triggered actin filament (F-actin) remodeling. While inhibition of myosin II by Blebbistatin blocked NaF-induced barrier failure and ZO-1 discontinuity, the corresponding agonist Ionomycin had effects comparable to those of fluoride, suggesting that MLC2 serves as an effector. Given the mechanisms upstream of p-MLC2 regulation, further studies demonstrated that NaF activated RhoA/ROCK signaling pathway and myosin light chain kinase (MLCK), strikingly increasing the expression of both. Pharmacological inhibitors (Rhosin, Y-27632 and ML-7) reversed NaF-induced barrier breakdown and stress fiber formation. The role of intracellular calcium ions ([Ca²⁺]_i) in NaF effects on Rho/ROCK pathway and MLCK was investigated. We found that NaF elevated [Ca²⁺]_i, whereas chelator BAPTA-AM attenuated increased RhoA and MLCK expression as well as ZO-1 rupture, thus, restoring barrier function. Collectively, abovementioned results suggest that NaF induces barrier impairment via Ca²⁺-dependent RhoA/ROCK pathway and MLCK, which in turn triggers MLC2 phosphorylation and rearrangement of ZO-1 and F-actin. These results provide potential therapeutic targets for fluoride-induced intestinal injury.

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.

Dexmedetomidine protects against burn-induced intestinal barrier injury via the MLCK/p-MLC signalling pathway

BACKGROUND

Evidence suggests that sedative dexmedetomidine can prevent intestinal dysfunction. However, the specific mechanisms of its protective effects against burn-induced intestinal barrier injury remain unclear. We aimed to explore the possible positive effects of dexmedetomidine on burn-induced intestinal barrier injury and the effects the myosin light chain kinase (MLCK)/phosphorylated myosin light chain (p-MLC) signalling pathway in an experimental model of burn injury.

METHODS

In this study, the plasma concentration of fluorescein isothiocyanate-labelled dextran (FITC-dextran) was measured. Histological changes were evaluated using haematoxylin and eosin (HE) staining. Tight junction proteins were evaluated by western blot and immunofluorescence analyses to assess the structural integrity of intestinal tight junctions. The level of inflammation was detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The results shows that the increase in intestinal permeability caused by burn injury is accompanied by histological damage to the intestine, decreases in the expression of the tight junction proteins Zonula Occludens-1 (ZO-1) and Occludin, increases in inflammatory cytokine levels and elevation of both MLCK protein expression and MLC phosphorylation. After dexmedetomidine treatment, the burn-induced changes were ameliorated.

CONCLUSIONS

In conclusion, dexmedetomidine exerted an anti-inflammatory effect and protected tight junction complexes against burn‑induced intestinal barrier damage by inhibiting the MLCK/p-MLC signalling pathways.

Imidacloprid increases intestinal permeability by disrupting tight junctions

The neonicotinoid pesticide, imidacloprid (IMI), is frequently detected in the environment and in foods. It is absorbed and metabolized by the intestine; however, its effects on intestinal barrier integrity are not well studied. We investigated whether IMI disrupts the permeability of the intestinal epithelial barrier via in vivo tests on male Wistar rats, in vitro assays using the human intestinal epithelial cell line, Caco-2, and in silico analyses. A repeated oral dose 90-day toxicity study was performed (0.06 mg/kg body weight/day). IMI exposure significantly increased intestinal permeability, which led to significantly elevated serum levels of endotoxin and inflammatory biomarkers (tumor necrosis factor-alpha and interleukin-1 beta) without any variation in body weight. Decreased transepithelial electrical resistance with increased permeability was also observed in 100 nM and 100 μM IMI-treated Caco-2 cell monolayers. Amounts of tight junction proteins in IMI-treated colon tissues and between IMI-treated Caco-2 cells were significantly lower than those of controls. Increased levels of myosin light chain phosphorylation, myosin light chain kinase (MLCK), and p65 subunit of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB p65) phosphorylation were found in IMI-exposed cells compared with control cells. Furthermore, the barrier loss caused by IMI was rescued by the MLCK inhibitor, ML-7, and cycloheximide. Pregnane X receptor (PXR, NR1I2) was inhibited by low-dose IMI treatment. In silico analysis indicated potent binding sites between PXR and IMI. Together, these data illustrate that IMI induces intestinal epithelial barrier disruption and produces an inflammatory response, involving the down-regulation of tight junctions and disturbance of the PXR-NF-κB p65-MLCK signaling pathway. The intestinal barrier disruption caused by IMI deserves attention in assessing the safety of this neonicotinoid pesticide.

Recombinant angiopoietin-like protein 4 attenuates intestinal barrier structure and function injury after ischemia/reperfusion

BACKGROUND

Intestinal barrier breakdown, a frequent complication of intestinal ischemia-reperfusion (I/R) including dysfunction and the structure changes of the intestine, is characterized by a loss of tight junction and enhanced permeability of the intestinal barrier and increased mortality. To develop effective and novel therapeutics is important for the improvement of outcome of patients with intestinal barrier deterioration. Recombinant human angiopoietin-like protein 4 (rhANGPTL4) is reported to protect the blood-brain barrier when administered exogenously, and endogenous ANGPTL4 deficiency deteriorates radiation-induced intestinal injury.

AIM

To identify whether rhANGPTL4 may protect intestinal barrier breakdown induced by I/R.

METHODS

Intestinal I/R injury was elicited through clamping the superior mesenteric artery for 60 min followed by 240 min reperfusion. Intestinal epithelial (Caco-2) cells and human umbilical vein endothelial cells were challenged by hypoxia/ reoxygenation to mimic I/R in vitro.

RESULTS

Indicators including fluorescein isothiocyanate-conjugated dextran (4 kilodaltons; FD-4) clearance, ratio of phosphorylated myosin light chain/total myosin light chain, myosin light chain kinase and loss of zonula occludens-1, claudin-2 and VE-cadherin were significantly increased after intestinal I/R or cell hypoxia/reoxygenation. rhANGPTL4 treatment significantly reversed these indicators, which were associated with inhibiting the inflammatory and oxidative cascade, excessive activation of cellular autophagy and apoptosis and improvement of survival rate. Similar results were observed in vitro when cells were challenged by hypoxia/reoxygenation, whereas rhANGPTL4 reversed the indicators close to normal level in Caco-2 cells and human umbilical vein endothelial cells significantly.

CONCLUSION

rhANGPTL4 can function as a protective agent against intestinal injury induced by intestinal I/R and improve survival via maintenance of intestinal barrier structure and functions.

Phosphorylation-dependent subcellular redistribution of small myosin light chain kinase

BACKGROUND

Myosin light chain kinase (MLCK) is a Ca²⁺-calmodulin-dependent enzyme dedicated to phosphorylate and activate myosin II to provide force for various motile processes. In smooth muscle cells and many other cells, small MLCK (S-MLCK) is a major isoform. S-MLCK is an actomyosin-binding protein firmly attached to contractile machinery in smooth muscle cells. Still, it can leave this location and contribute to other cellular processes. However, molecular mechanisms for switching the S-MLCK subcellular localization have not been described.

METHODS

Site-directed mutagenesis and in vitro protein phosphorylation were used to study functional roles of discrete in-vivo phosphorylated residues within the S-MLCK actin-binding domain. In vitro co-sedimentation analysis was applied to study the interaction of recombinant S-MLCK actin-binding fragment with filamentous actin. Subcellular distribution of phosphomimicking S-MLCK mutants was studied by fluorescent microscopy and differential cell extraction.

RESULTS

Phosphorylation of S-MLCK actin-binding domain at Ser25 and/or Thr56 by proline-directed protein kinases or phosphomimicking these posttranslational modifications alters S-MLCK binding to actin filaments both in vitro and in cells, and induces S-MLCK subcellular translocation with no effect on the enzyme catalytic properties.

CONCLUSIONS

Phosphorylation of the amino terminal actin-binding domain of S-MLCK renders differential subcellular targeting of the enzyme and may, thereby, contribute to a variety of context-dependent responses of S-MLCK to cellular and tissue stimuli.

GENERAL SIGNIFICANCE

S-MLCK physiological function can potentially be modulated via phosphorylation of its actin recognition domain, a regulation distinct from the catalytic and calmodulin regulatory domains.

via inhibition of myosin light chain kinase activity in the porcine coronary artery

ETHNOPHARMACOLOGICAL RELEVANCE

Asphodelus tenuifolius Cav. (Asphodelaceae), a wild, terrestrial, annual stemless herb, is widely used in traditional medicine for the treatment of hypertension, diabetes, atherosclerosis and circulatory problems. A previous research study from our laboratory revealed that A. tenuifolius has beneficial effects in reducing blood pressure and improves aortic endothelial dysfunction in chronically glucose fed rats. Despite the fact that A. tenuifolius reduces blood pressure and improves endothelial function in vivo, there are no detailed studies about its possible mechanism of action.

AIM OF THE STUDY

This study was designed to provide pharmacological basis and mechanism of action for the traditional use of A. tenuifolius in hypertension and circulatory problems. We explored the vasorelaxant effect of A. tenuifolius and its underlying vasorelaxation mechanism in porcine coronary artery rings.

MATERIALS AND METHODS

Aqueous methanolic crude extract of A. tenuifolius was prepared by maceration process and then activity guided fractionation was carried out by using different polarity based solvents. Phytochemical studies were carried out using LC-DAD-MS. Segments of porcine distal coronary artery were set up in a wire myograph for isometric force measurements. Extract/fractions of A. tenuifolius seeds were tested for vasodilator activity by measurement of changes in tone after pre-contraction with the thromboxane mimetic U46619 in the presence or absence of inhibitors of intracellular signaling cascades.

RESULTS

Crude extract/fractions of A. tenuifolius produced dose dependent endothelium independent vasorelaxant response in coronary rings, whereas, the butanol fraction of A. tenuifolius (BS-AT) produced the largest relaxation response with 100% relaxation at 1 mg/ml, therefore the mechanism of relaxation of this fraction was determined. The relaxation to BS-AT was unaffected by removal of the endothelium, pre-contraction with KCl, or the presence of the non-selective potassium channel blocker tetraethylammonium, indicating that the relaxation was endothelium-independent, and does not involve activation of potassium channels. BS-AT (1 mg/ml) inhibited the contractile response to calcium,the L-type calcium channel activator BAY K8664,and ionomycin, indicating that it inhibits calcium-induced contractions. The relaxation response to BS-AT was attenuated in the absence of extracellular calcium. However, relaxations to BS-AT were also reduced after deletion of calcium from intracellular stores with cyclopiazonic acid. Incubation with 1 mg/ml BS-AT also inhibited phosphorylation of myosin light chains in homogenates of coronary artery.

CONCLUSION

The butanol extract of Asphodelus tenuifolius produces a large endothelium-independent relaxation of the porcine coronary artery through inhibition of calcium-induced contractions. The effect appears to be downstream of calcium influx, possibly through inhibition of myosin light chain kinase. This study supports previous studies demonstrating that A. tenuifolius reduces blood pressure. Future studies will aim to determine the active compounds underlying this response.

Myosin light chain kinase mediates intestinal barrier dysfunction following simulated microgravity based on proteomic strategy

Microgravity induces injury of intestinal barrier. However, the underlying mechanism remains unclear. The present study aimed to investigate the pathological change of intestinal mucosa induced by long term simulated microgravity and to explore its etiological mechanism using a proteomic approach. The well accepted tail-suspended rat model was used to simulate microgravity. The damage of rat small intestine was evaluated via histological and molecular test, and a label-free comparative proteomic strategy was used to determine the molecular mechanism. Simulated microgravity for 21 days damaged intestine barrier with decreased numbers of the goblet cells, large intercellular space, and down-regulated adhesion molecules, accompanied by increased intestinal permeability. Proteomic analysis identified 416 differentially expressed proteins and showed simulated microgravity dramatically down-regulated the adhesion molecules and deteriorated several pathways for metabolism, focal adhesion, and regulation of actin cytoskeleton. Western-blot analysis confirmed that myosin regulatory light chain (MLC) 12B was significantly down-regulated, while rho-associated protein kinase, myosin light chain kinase (MLCK), and phosphorylated MLC were dramatically up-regulated. Taken together, these data reveal that down-regulation of adhesion molecules and MLCK dependent up-regulation MLC phosphorylation mediate intestinal barrier dysfunction during simulated microgravity injury. Our results also indicate that regulation of epithelial MLCK is a potential target for the therapeutic treatment of microgravity injury.

β-adrenergic activation may promote myosin light chain kinase degradation through calpain in pressure overload-induced cardiac hypertrophy: β-adrenergic activation results in MLCK degradation

BACKGROUND

β-adrenergic activation is able to exacerbate cardiac hypertrophy. Myosin light chain kinase (MLCK) and its phosphorylated substrate, phospho-myosin light chain 2 (p-MLC2), play vital roles in regulating cardiac hypertrophy. However, it is not yet clear whether there is a relationship between β-adrenergic activation and MLCK in the progression of cardiac hypertrophy. Therefore, we explored this relationship and the underlying mechanisms in this work.

METHODS

Cardiac hypertrophy and cardiomyocyte hypertrophy were induced by pressure overload and isoproterenol (ISO) stimulation, respectively. Echocardiography, histological analysis, immunofluorescence and qRT-PCR were used to confirm the successful establishment of the models. A β-blocker (metoprolol) and a calpain inhibitor (calpeptin) were administered to inhibit β-adrenergic activity in rats and calpain in cardiomyocytes, respectively. The protein expression levels of MLCK, myosin light chain 2 (MLC2), p-MLC2, myosin phosphatase 2 (MYPT2), calmodulin (CaM) and calpain were measured using western blotting. A cleavage assay was performed to assess the degradation of recombinant human MLCK by recombinant human calpain.

RESULTS

The β-blocker alleviated cardiac hypertrophy and dysfunction, increased MLCK and MLC2 phosphorylation and decreased calpain expression in pressure overload-induced cardiac hypertrophy. Additionally, the calpain inhibitor calpeptin attenuated cardiomyocyte hypertrophy, upregulated MLCK and p-MLC2 and reduced MLCK degradation in ISO-induced cardiomyocyte hypertrophy. Recombinant human calpain degraded recombinant human MLCK in vitro in concentration- and time-dependent manners, and this degradation was inhibited by the calpain inhibitor calpeptin.

CONCLUSION

Our study suggested that β-adrenergic activation may promote the degradation of MLCK through calpain in pressure overload-induced cardiac hypertrophy.

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.

Myosin light chain kinase inhibitor ML7 improves vascular endothelial dysfunction and permeability via the mitogen-activated protein kinase pathway in a rabbit model of atherosclerosis

Endothelial dysfunction (ED) and hyperpermeability are considered as the initiating steps in early atherosclerosis. Phosphorylation of myosin light chain (MLC) is key to cause vascular hyperpermeability via endothelial cell contraction. However, it is unclear whether MLC phosphorylation can also regulate the balance between contraction and relaxation of endothelial cells, thereby affecting endothelium-dependent diastolic function and leading to ED. The present study investigated relationships between ED and MLC phosphorylation and underlying mechanisms. Twenty-four male New Zealand white rabbits were randomly divided into three groups: control, AS, and ML7 (MLCK inhibitor) groups, and fed with normal diet, high-fat diet (HFD), and HFD plus oral ML7 (1 mg/kg daily) respectively. HFD-fed rabbits showed typical atheromatous lesions and endothelial hyperpermeability, and these lesions could be partly reversed following ML7 therapy. Western blotting revealed significant increased expression of myosin light chain kinase (MLCK) and phosphorylation of MLC, JNK, and ERK in the arterial wall of rabbits in the AS group compared with those of the control group (p < 0.05), whereas the ML7 group showed markedly decreased levels of these proteins compared with the AS group (p <  0.05). The endothelium-dependent relaxation rate was significantly reduced both in vitro and in vivo in AS group, and was improved using ML7 therapy. Taken together, these results indicate that MLCK expression and subsequent MLC phosphorylation increase vascular endothelial permeability and endothelium-dependent diastolic dysfunction by promoting endothelial cell contraction, which may be initiated by the activation of the MAP/ERK (MEK) and MAP/JNK (MEK) pathways.

Collagen fiber structure guides 3D motility of cytotoxic T lymphocytes

Lymphocyte motility is governed by a complex array of mechanisms, and highly dependent on external microenvironmental cues. Tertiary lymphoid sites in particular have unique physical structure such as collagen fiber alignment, due to matrix deposition and remodeling. Three dimensional studies of human lymphocytes in such environments are lacking. We hypothesized that aligned collagenous environment modulates CD8+ T cells motility. We encapsulated activated CD8+ T cells in collagen hydrogels of distinct fiber alignment, a characteristic of tumor microenvironments. We found that human CD8+ T cells move faster and more persistently in aligned collagen fibers compared with nonaligned collagen fibers. Moreover, CD8+ T cells move along the axis of collagen alignment. We showed that myosin light chain kinase (MLCK) inhibition could nullify the effect of aligned collagen on CD8+ T cell motility patterns by decreasing T cell turning in unaligned collagen fiber gels. Finally, as an example of a tertiary lymphoid site, we found that xenograft prostate tumors exhibit highly aligned collagen fibers. We observed CD8+ T cells alongside aligned collagen fibers, and found that they are mostly concentrated in the periphery of tumors. Overall, using an in vitro controlled hydrogel system, we show that collagen fiber organization modulates CD8+ T cells movement via MLCK activation thus providing basis for future studies into relevant therapeutics.

Effects of hypoxia inducible factor-1α on expression levels of MLCK, p-MLC and ZO-1 of rat endothelial cells

OBJECTIVE

To examine the aberrant expression of endothelial permeability associated proteins including MLCK, p-MLC and ZO-1 in presence of different levels of hypoxia-inducible factor 1 alpha (HIF-1α).

METHODS

We established monolayer vascular endothelial cell model with the primary rat endothelial cells. Over-expressed or under-expressed HIF-1α cell lines were made by endothelial cells transfected with plasmid vector constructed with HIF-1α gene or HIF-1α-specific short hairpin RNA (shRNA). Levels of mRNA and protein of MLCK, p-MLC and ZO-1 were determined using Real-Time PCR and Western blot. All data were analyzed using by One-Way ANOVA method and LSD.

RESULTS

We successfully cultured the rat endothelial primary cells for four days. The mRNA and protein levels of MLCK and p-MLC were significantly increased in the HIF-1α over-expression group than that in the blank control group and the empty plasmid GV230 group (P＜0.05). ZO-1 was significantly lower in the HIF-1α over-expression group than that in the blank control group and the GV230 group. On the contrary, the mRNA and protein levels of MLCK and p-MLC were significantly lower in the HIF-1α under-expression group than that in the blank control group and the shRNA-NC group (P＜0.05). ZO-1 was significantly higher in the HIF-1α low-expression group than that in the blank control group and the shRNA-NC group.

CONCLUSION

HIF-1α positively regulates the expression of MLCK and p-MLC and negatively regulates the expression of ZO-1 in rat monolayer endothelial cells.

Intestinal barrier dysfunction in severe burn injury

Severe burn injury is often accompanied by intestinal barrier dysfunction, which is closely associated with post-burn shock, bacterial translocation, systemic inflammatory response syndrome, hypercatabolism, sepsis, multiple organ dysfunction syndrome, and other complications. The intestinal epithelium forms a physical barrier that separates the intestinal lumen from the internal milieu, in which the tight junction plays a principal role. It has been well documented that after severe burn injury, many factors such as stress, ischemia/hypoxia, proinflammatory cytokines, and endotoxins can induce intestinal barrier dysfunction via multiple signaling pathways. Recent advances have provided new insights into the mechanisms and the therapeutic strategies of intestinal epithelial barrier dysfunction associated with severe burn injury. In this review, we will describe the current knowledge of the mechanisms involved in intestinal barrier dysfunction in response to severe burn injury and the emerging therapies for treating intestinal barrier dysfunction following severe burn injury.

Genetic knockout of myosin light chain kinase (MLCK210) prevents cerebral microhemorrhages and attenuates neuroinflammation in a mouse model of vascular cognitive impairment and dementia

The blood-brain barrier (BBB) is critical in maintenance of brain homeostasis, and loss of its functional integrity is a key feature across a broad range of neurological insults. This includes both acute injuries such as traumatic brain injury and stroke, as well as more chronic pathologies associated with aging, such as vascular cognitive impairment and dementia (VCID). A specific form of myosin light chain kinase (MLCK210) is a major regulator of barrier integrity in general, including the BBB. Studies have demonstrated the potential of MLCK210 as a therapeutic target for peripheral disorders involving tissue barrier dysfunction, but less is known about its potential as a target for chronic neurologic disorders. We report here that genetic knockout (KO) of MLCK210 protects against cerebral microhemorrhages and neuroinflammation induced by chronic dietary hyperhomocysteinemia. Overall, the results are consistent with an accumulating body of evidence supporting MLCK210 as a potential therapeutic target for tissue barrier dysfunction and specifically implicate it in BBB dysfunction and neuroinflammation in a model of VCID.

Pharmacological restoration of gut barrier function in stressed neonates partially reverses long-term alterations associated with maternal separation

RATIONALE

Intestinal permeability plays an important role in gut-brain axis communication. Recent studies indicate that intestinal permeability increases in neonate pups during maternal separation (MS).

OBJECTIVES

The present study aims to determine whether pharmacological inhibition of myosin light chain kinase (MLCK), which regulates tight junction contraction and controls intestinal permeability, in stressed neonates, protects against the long-term effects of MS.

METHODS

Male Wistar rats were exposed to MS (3 h per day from post-natal day (PND)2 to PND14) or left undisturbed and received daily intraperitoneal injection of a MLCK inhibitor (ML-7, 5 mg/kg) or vehicle during the same period. At adulthood, emotional behaviors, corticosterone response to stress, and gut microbiota composition were analyzed.

RESULTS

ML-7 restored gut barrier function in MS rats specifically during the neonatal period. Remarkably, ML-7 prevented MS-induced sexual reward-seeking impairment and reversed the alteration of corticosterone response to stress at adulthood. The effects of ML-7 were accompanied by the normalization of the abundance of members of Lachnospiraceae, Clostridiales, Desulfovibrio, Bacteroidales, Enterorhabdus, and Bifidobacterium in the feces of MS rats at adulthood.

CONCLUSIONS

Altogether, our work suggests that improvement of intestinal barrier defects during development may alleviate some of the long-term effects of early-life stress and provides new insight on brain-gut axis communication in a context of stress.

[Regulation of hypoxia inducible factor-1α on permeability of vascular endothelial cells and the mechanism]

Objective: To investigate the regulation of hypoxia-inducible factor-1α (HIF-1α) on permeability of rat vascular endothelial cells and the mechanism. Methods: Twelve male Sprague-Dawley rats aged 35 to 38 days were collected and vascular endothelial cells were separated and cultured. The morphology of cells was observed after 4 days of culture, and the following experiments were performed on the 2nd or 3rd passage of cells. (1) Rat vascular endothelial cells were collected and divided into blank control group, negative control group, HIF-1α interference sequence 1 group, HIF-1α interference sequence 2 group, and HIF-1α interference sequence 3 group according to the random number table (the same grouping method below), with 3 wells in each group. Cells in negative control group, HIF-1α interference sequence 1 group, HIF-1α interference sequence 2 group, and HIF-1α interference sequence 3 group were transfected with GV248 empty plasmid, recombinant plasmid respectively containing HIF-1α interference sequence 1, interference sequence 2, and interference sequence 3 with liposome 2000. Cells in blank control group were only transfected with liposome 2000. After transfection of 24 h, expression levels of HIF-1α mRNA and protein of cells in each group were respectively detected by reverse transcription real-time fluorescent quantitative polymerase chain reaction and Western blotting (the same detecting methods below) . The sequence with the highest interference efficiency was selected. (2) Another batch of rat vascular endothelial cells were collected and divided into blank control group, negative control group, and HIF-1α low expression group, with 3 wells in each group. Cells in blank control group were only transfected with liposome 2000, and cells in negative control group and HIF-1α low expression group were respectively transfected with GV248 empty plasmid and low expression HIF-1α recombinant plasmid selected in experiment (1) with liposome 2000. After 14 days of culture, the mRNA and protein expressions of HIF-1α in each group were detected. (3) Another batch of rat vascular endothelial cells were collected and divided into blank control group, negative control group, and HIF-1α high expression group, with 3 wells in each group. Cells in blank control group were transfected with liposome 2000, and cells in negative control group and HIF-1α high expression group were respectively transfected with GV230 empty plasmid and HIF-1α high expression recombinant plasmid with liposome 2000. After 14 days of culture, the mRNA and protein expressions of HIF-1α of cells in each group were detected. (4) After transfection of 24 h, cells of three groups in experiment (1) and three groups in experiment (2) were collected, and mRNA and protein expressions of myosin light chain kinase (MLCK), phosphorylated myosin light chain (p-MLC), and zonula occludens 1 (ZO-1) of cells were detected. Data were processed with one-way analysis of variance and t test. Results: After 4 days of culture, the cells were spindle-shaped, and rat vascular endothelial cells were successfully cultured. (1) The interference efficiencies of HIF-1α of cells in HIF-1α interference sequence 1 group, HIF-1α interference sequence 2 group, and HIF-1α interference sequence 3 group were 47.66%, 45.79%, and 62.62%, respectively, and the interference sequence 3 group had the highest interference efficiency. After transfection of 24 h, the mRNA and protein expression levels of HIF-1α of cells in interference sequence 3 group were significantly lower than those in blank control group (t=18.404, 9.140, P<0.01) and negative control group (t=15.099, 7.096, P<0.01). (2) After cultured for 14 days, the mRNA and protein expression levels of HIF-1α of cells in HIF-1α low expression group were significantly lower than those in blank control group (t=21.140, 5.440, P<0.01) and negative control group (t= 14.310, 5.210, P<0.01). (3) After cultured for 14 days, the mRNA and protein expression levels of HIF-1α of cells in HIF-1α high expression group were significantly higher than those in blank control group (t=19.160, 7.710, P<0.01) and negative control group (t= 19.890, 7.500, P<0.01). (4) After transfection of 24 h, the mRNA expression levels of MLCK and p-MLC of cells in HIF-1α low expression group were significantly lower than those in blank control group (t=2.709, 4.011, P<0.05 or P<0.01) and negative control group (t=2.373, 3.744, P<0.05 or P<0.01). The mRNA expression level of ZO-1 of cells in HIF-1α low expression group was significantly higher than that in blank control group and negative control group (t=4.285, 5.050, P<0.01). The mRNA expression levels of MLCK and p-MLC of cells in HIF-1α high expression group were significantly higher than those in blank control group (t=9.118, 11.313, P<0.01) and negative control group (t=9.073, 11.280, P<0.01). The mRNA expression level of ZO-1 of cells in HIF-1α high expression group was significantly lower than that in blank control group and negative control group (t=2.889, 2.640, P<0.05). (5) After transfection of 24 h, the protein expression levels of MLCK and p-MLC of cells in HIF-1α low expression group were significantly lower than those in blank control group (t=2.652, 3.983, P<0.05 or P<0.01) and negative control group (t=2.792, 4.065, P<0.05 or P<0.01). The protein expression of ZO-1 of cells in HIF-1α low expression group was significantly higher than that in blank control group and negative control group (t=3.881, 3.570, P<0.01). The protein expression levels of MLCK and p-MLC of cells in HIF-1α high expression group were 1.18±0.24 and 0.68±0.22, which were significantly higher than 0.41±0.21 and 0.35±0.14 in blank control group (t=5.011, 3.982, P<0.05 or P<0.01) and 0.43±0.20 and 0.36±0.12 in negative control group (t= 4.880, 3.862, P<0.05 or P<0.01). The protein expression level of ZO-1 of cells in HIF-1α high expression group was 0.08±0.06, which was significantly lower than 0.20±0.09 in blank control group and 0.19±0.09 in negative control group (t=4.178, 3.830, P<0.05 or P<0.01). Conclusions: HIF-1α up-regulates expressions of MLCK and p-MLC and down-regulates expression of ZO-1, thereby increasing the permeability of rat vascular endothelial cells.

OTA induces intestinal epithelial barrier dysfunction and tight junction disruption in IPEC-J2 cells through ROS/Ca2+-mediated MLCK activation

Ochratoxin A (OTA) is a frequent contaminant of feed and food worldwide. The toxicity of OTA on intestinal barrier was investigated in porcine intestinal epithelial cells (IPEC-J2). We observed that OTA induced intestinal barrier dysfunction as indicated by the reduction in transepithelial electrical resistance (TEER) and elevation in paracellular permeability to 4 kDa dextran. The barrier dysfunction was accompanied with tight junction disruption including a down-regulation in ZO-1 expression and redistribution of Occludin and ZO-1. Moreover, OTA exposure increased reactive oxygen species (ROS) generation, elevated the intracellular calcium level ([Ca²⁺]_c) and activated myosin light chain kinase (MLCK). Simultaneously, NAC, a ROS scavenger, blocked OTA-induced ROS generation, [Ca²⁺]_c elevation, barrier dysfunction and tight junction disruption, suggesting that OTA-induced ROS generation may act as a trigger. Next, we found that OTA-induced MLCK activation was inhibited by BAPTA-AM, the cytosolic Ca²⁺ chelator, demonstrating that OTA-induced MLCK activation is dependent on [Ca²⁺]_c elevation. Furthermore, inhibition of MLCK with ML-7 or inhibition of [Ca²⁺]_c elevation with BAPTA-AM markedly prevented OTA-induced barrier dysfunction and tight junction disruption. Taken together, our results indicated that OTA induces ROS generation, and then elevates the [Ca²⁺]_c and MLCK activity in turn, which finally induces barrier dysfunction and disrupts tight junction in IPEC-J2 cell monolayers.

MYLK promotes hepatocellular carcinoma progression through regulating cytoskeleton to enhance epithelial-mesenchymal transition

Myosin light chain kinase (MYLK) is found to catalyze the phosphorylation of myosin light chains (MLC) and regulate invasion and metastasis in some malignancies. However, there is little knowledge on the role of MYLK in hepatocellular carcinoma (HCC), and no studies have been conducted to investigate the mechanisms underlying MYLK-mediated promotion of HCC invasion and metastasis until now. In this study, we investigated the expression of MYLK in 50 pairs of human HCC and adjacent liver specimens. High MYLK expression was significantly correlated with aggressive clinicopathological features including tumor encapsulation, microvascular invasion and metastasis. In vitro assays showed that shRNA-induced MYLK knockdown significantly inhibited the wound-healing ability of HCC cells and the ability to migrate and invade through Matrigel. We next uncovered that MYLK knockdown resulted in a reduction in the number of F-actin stress fibers, disorganization of F-actin architectures and morphological alterations of HCC cells. Phosphorylated MLC, rather than total MLC, was found to be markedly reduced in response to downregulation of MYLK expression, and MYLK-regulated actin cytoskeleton through phosphorylating MLC in HCC cells. In addition, Western blotting assay revealed downregulation of the epithelial marker E-cadherin and upregulation of mesenchymal markers Vimentin, N-cadherin and Snail. Taken together, our findings indicate that MYLK promotes HCC progression by altering cytoskeleton to enhance epithelial-mesenchymal transition (EMT).

Myosin phosphorylation improves contractile economy of mouse fast skeletal muscle during staircase potentiation

Phosphorylation of the myosin regulatory light chain (RLC) by skeletal myosin light chain kinase (skMLCK) potentiates rodent fast twitch muscle but is an ATP-requiring process. Our objective was to investigate the effect of skMLCK-catalyzed RLC phosphorylation on the energetic cost of contraction and the contractile economy (ratio of mechanical output to metabolic input) of mouse fast twitch muscle in vitro (25°C). To this end, extensor digitorum longus (EDL) muscles from wild-type (WT) and from skMLCK-devoid (skMLCK^-/-) mice were subjected to repetitive low-frequency stimulation (10 Hz for 15 s) to produce staircase potentiation of isometric twitch force, after which muscles were quick frozen for determination of high-energy phosphate consumption (HEPC). During stimulation, WT muscles displayed significant potentiation of isometric twitch force while skMLCK^-/- muscles did not (i.e. 23% versus 5% change, respectively). Consistent with this, RLC phosphorylation was increased ∼3.5-fold from the unstimulated control value in WT but not in skMLCK^-/- muscles. Despite these differences, the HEPC of WT muscles was not greater than that of skMLCK^-/- muscles. As a result of the increased contractile output relative to HEPC, the calculated contractile economy of WT muscles was greater than that of skMLCK^-/- muscles. Thus, our results suggest that skMLCK-catalyzed phosphorylation of the myosin RLC increases the contractile economy of WT mouse EDL muscle compared with skMLCK^-/- muscles without RLC phosphorylation.

Angiotensin II Facilitates Matrix Metalloproteinase-9-Mediated Myosin Light Chain Kinase Degradation in Pressure Overload-Induced Cardiac Hypertrophy

BACKGROUND/AIMS

Angiotensin II (Ang II) has been shown to promote cardiac remodeling during the process of hypertrophy. Myosin light chain kinase (MLCK), a specific kinase for the phosphorylation of myosin light chain 2 (MLC2), plays an important role in regulating cardiac muscle contraction and hypertrophy. However, whether Ang II could facilitate cardiac hypertrophy by altering the expression of MLCK remains unclear. This study aimed to investigate this effect and the underlying mechanisms.

METHODS

Cardiac hypertrophy was induced via pressure overload in rats, which were then evaluated via histological and biochemical measurements and echocardiography. Angiotensin-converting enzyme inhibitor (ACEI) was used to inhibit Ang II. Neonatal rat cardiomyocytes were stimulated with Ang II to induce hypertrophy and were treated with a matrix metalloproteinase 9 (MMP9) inhibitor. Myocyte hypertrophy was evaluated using immunofluorescence and qRT-PCR. Degradation of recombinant human MLCK by recombinant human MMP9 was tested using a cleavage assay. The expression levels of MLCK, MLC2, phospho-myosin light chain 2 (p-MLC2), myosin phosphatase 2 (MYPT2), and calmodulin (CaM) were measured using western blotting.

RESULTS

ACEI improved cardiac function and remodeling and increased the levels of MLCK and p-MLC2 as well as reduced the expression of MMP9 in pressure overload-induced cardiac hypertrophy. Moreover, the MMP9 inhibitor alleviated myocyte hypertrophy and upregulated the levels of MLCK and p-MLC2 in Ang II-induced cardiomyocyte hypertrophy. Recombinant human MLCK was concentration- and time-dependently degraded by recombinant human MMP9 in vitro, and this process was prevented by the MMP9 inhibitor.

CONCLUSION

Our results suggest that Ang II is involved in the degradation of MLCK in pressure overload-induced cardiac hypertrophy and that this process was mediated by MMP9.

Ardipusilloside-I stimulates gastrointestinal motility and phosphorylation of smooth muscle myosin by myosin light chain kinase

Ardipusilloside-I is a natural triterpenoid saponin, which was isolated from Ardisia pusilla A. DC. The aim of the study was to evaluate the stimulation of ardipusilloside-I on gastrointestinal motility in vitro and in vivo. The experiment of smooth muscle contraction directly monitored the contractions of the isolated jejunal segment (IJS) in different contractile states, and the effects of ardipusilloside-I on myosin were measured in the presence of Ca²⁺-calmodulin using the activities of 20 kDa myosin light chain (MLC₂₀) phosphorylation and myosin Mg²⁺-ATPase. The effects of ardipusilloside-I on gastro emptying and intestinal transit in constipation-predominant rats were observed, and the MLCK expression in jejuna of constipated rats was determined by western blot. The results showed that, ardipusilloside-I increased the contractility of IJS in a dose-dependent manner and reversed the low contractile state (LCS) of IJS induced by low Ca²⁺, adrenaline, and atropine respectively. There were synergistic effects on contractivity of IJS between ardipusilloside-I and ACh, high Ca²⁺, and histamine, respectively. Ardipusilloside-I could stimulate the phosphorylation of MLC₂₀ and Mg²⁺-ATPase activities of Ca²⁺- dependent phosphorylated myosin. Ardipusilloside-I also stimulated the gastric emptying and intestinal transit in normal and constipated rats in vivo, respectively, and increased the MLCK expression in the jejuna of constipation-predominant rats. Briefly, the findings demonstrated that ardipusilloside-I could effectively excite gastrointestinal motility in vitro and in vivo.

Myosin regulatory light chain phosphorylation is associated with leiomyosarcoma development

Leiomyosarcoma is a rare malignant smooth muscle tumor which can be very unpredictable. Myosin II is involved in many functions, including cell contraction, migration, and adhesion. The phosphorylation of myosin regulatory light chain (MLC) by myosin light chain kinase (MLCK) determines the activity of Myosin II. However, it is still unclear whether MLC phosphorylation is involved in cell proliferation in leiomyosarcoma. In this study, we aimed to explore the role of MLCK-dependent MLC phosphorylation in leiomyosarcoma development. We found that the expression of MLCK, phosphorylated MLC, and Ki67 in leiomyosarcoma was significantly higher than in leiomyoma and adjacent normal smooth muscle cells. MLCK expression was significantly correlated with phosphorylated MLC level. Kaplan-Meier survival analysis revealed that patients with high expression of MLCK or phosphorylated MLC had shorter overall survival times compared with the patients with low expression of MLCK or phosphorylated MLC. In vitro studies revealed a causative link between MLC phosphorylation and cellular proliferation as expression of phosphomimetic MLC (T19D, S20D) increased cellular proliferation as assessed by Ki67 staining. In contrast, MLCK specific inhibitor reduced cellular proliferation. We concluded that MLCK, phosphorylated MLC and Ki67 were overexpressed in leiomyosarcoma. MLCK dependent MLC phosphorylation might be responsible for the high proliferative state in leiomyosarcoma. MLCK and phosphorylated MLC are potential prognostic indicators of leiomyosarcoma.

Rebeccamycin Attenuates TNF-α-Induced Intestinal Epithelial Barrier Dysfunction by Inhibiting Myosin Light Chain Kinase Production

BACKGROUND/AIMS

Although proinflammatory cytokine-induced disruption of intestinal epithelial barrier integrity is associated with intestinal inflammatory disease, effective treatment for barrier dysfunction is lacking. Previously, we demonstrated that rebeccamycin alleviates epithelial barrier dysfunction induced by inflammatory cytokines in Caco-2 cell monolayers; however, the underlying mechanism remained unclear. Here, we investigated the mechanism by which rebeccamycin protects the epithelial barrier function of Caco-2 cells exposed to TNF-α.

METHODS

To confirm the epithelial barrier function of Caco-2 cell monolayers, transepithelial electrical resistance (TER) and paracellular permeability were measured. Production levels and localization of tight junction (TJ) proteins were analyzed by immunoblot and immunofluorescence, respectively. Phosphorylated myosin light chain (pMLC) and MLC kinase (MLCK) mRNA expression levels were determined by immunoblot and quantitative RT-PCR, respectively.

RESULTS

Rebeccamycin attenuated the TNF-α-induced reduction in TER and increase in paracellular permeability. Rebeccamycin increased claudin-5 expression, but not claudin-1, -2, -4, occludin or ZO-1 expression, and prevented the TNF-α-induced changes in ZO-1 and occludin localization. Rebeccamycin suppressed the TNF-α-induced increase in MLCK mRNA expression, thus suppressing MLC phosphorylation. The rebeccamycin-mediated reduction in MLCK production and protection of epithelial barrier function were alleviated by Chk1 inhibition.

CONCLUSION

Rebeccamycin attenuates TNF-α-induced disruption of intestinal epithelial barrier integrity by inducing claudin-5 expression and suppressing MLCK production via Chk1 activation.

Acanthopanax senticosus polysaccharides-induced intestinal tight junction injury alleviation via inhibition of NF-κB/MLCK pathway in a mouse endotoxemia model

AIM

To examine the effects of Acanthopanax senticosus polysaccharides (ASPS) on intestinal tight junction (TJ) disruption and nuclear factor-kappa B (NF-κB)/myosin light chain kinase (MLCK) activation in endotoxemia.

METHODS

BALB/C mice (6-8-weeks-old) received continuous intragastric gavage of ASPS for 7 d before injection of lipopolysaccharide (LPS), or received ASPS once after LPS injection. Blood and intestinal mucosal samples were collected 6 h after LPS challenge. Clinical symptoms, histological injury, intestinal permeability, TJ ultrastructure, and TJ protein expression were determined.

RESULTS

Compared with mice in the LPS group, pretreatment with ASPS improved clinical and histological scores by 390.9% (P < 0.05) and 57.89% (P < 0.05), respectively, and gut permeability change in endotoxemic mice was shown by a 61.93% reduction in reduced leakage of fluorescein isothiocyanate-dextran 6 h after LPS injection (P < 0.05). ASPS pretreatment also prevented LPS-induced TJ ultrastructure breakdown supported by increased electron dense materials between adjoining cells, sustained redistribution and expression of occludin (0.597 ± 0.027 vs 0.103 ± 0.009, P < 0.05) and zonula occludens-1 (0.507 ± 0.032 vs 0.125 ± 0.019, P < 0.05), and suppressed activation of the NF-κB/MLCK pathway indicated by reduced expression of NF-κB, phospho-inhibitor kappa B-alpha, MLCK and phospho-myosin light-chain-2 by 16.06% (P < 0.05), 54.31% (P < 0.05), 66.10% (P < 0.05) and 64.82% (P < 0.05), respectively.

CONCLUSION

ASPS pretreatment may be associated with inhibition of the NF-κB/MLCK pathway and concomitant amelioration of LPS-induced TJ dysfunction of intestinal epithelium in endotoxemia.

Shortening speed dependent force potentiation is attenuated but not eliminated in skeletal muscles without myosin phosphorylation

We investigated the influence of shortening speed on concentric force potentiation at different frequencies in muscles devoid of skeletal myosin light chain kinase (skMLCK^-/-) and unable to phosphorylate myosin. EDL muscles from skMLCK^-/- mice were activated in vitro (25 °C) across a range of stimulation frequencies (10-100 Hz) during shortening ramps at 0.10, 0.30, or 0.50 of maximum shortening velocity (V_max) before and after a potentiating stimulus (PS). When collapsed across all frequencies, the PS increased relative (post/pre) concentric force to 1.27 ± 0.02 and 1.17 ± 0.02 of pre-PS values at 0.50 and 0.30 V_max, respectively (n = 4, P < 0.05 for all speeds). In addition, potentiation was significantly greater at low and intermediate-than at high stimulus frequencies at both speeds. In contrast, during shortening at 0.10 V_max, a posttetanic depression was observed as mean concentric forces were reduced to 0.85 ± 0.02 of pre-PS values. Thus, although reduced compared to published values for wildtype muscles (Gittings et al., J Muscle Res Cell Motil 33:359-368, 2012), skMLCK^-/- muscles displayed a speed dependent potentiation of concentric force during moderate and fast shortening speed at all frequencies tested. Our data support the presence of a myosin phosphorylation-independent mechanism(s) for concentric force potentiation at moderate speeds of shortening, and also suggests that myosin phosphorylation may be necessary to prevent the concentric force depression that may be present at slow speeds of shortening. Although additive in nature, further work is needed to parse out the relative influence of myosin phosphorylation-independent and dependent potentiation mechanisms on wildtype contractile function during dynamic conditions.

Heart Failure Induced by Perinatal Ablation of Cardiac Myosin Light Chain Kinase

Background: Germline knockout mice are invaluable in understanding the function of the targeted genes. Sometimes, however, unexpected phenotypes are encountered, due in part to the activation of compensatory mechanisms. Germline ablation of cardiac myosin light chain kinase (cMLCK) causes mild cardiac dysfunction with cardiomyocyte hypertrophy, whereas ablation in adult hearts results in acute heart failure with cardiomyocyte atrophy. We hypothesized that compensation after ablation of cMLCK is dependent on developmental staging and perinatal-onset of cMLCK ablation will result in more evident heart failure than germline ablation, but less profound when compared to adult-onset ablation.

Methods and Results: The floxed-Mylk3 gene was ablated at the beginning of the perinatal stage using a single intra-peritoneal tamoxifen injection of 50 mg/kg into pregnant mice on the 19th day of gestation, this being the final day of gestation. The level of cMLCK protein level could no longer be detected 3 days after the injection, with these mice hereafter denoted as the perinatal Mylk3-KO. At postnatal day 19, shortly before weaning age, these mice showed reduced cardiac contractility with a fractional shortening 22.8 ± 1.0% (n = 7) as opposed to 31.4 ± 1.0% (n = 11) in controls. The ratio of the heart weight relative to body weight was significantly increased at 6.68 ± 0.28 mg/g (n = 12) relative to the two control groups, 5.90 ± 0.16 (flox/flox, n = 11) and 5.81 ± 0.33 (wild/wild/Cre, n = 5), accompanied by reduced body weight. Furthermore, their cardiomyocytes were elongated without thickening, with a long-axis of 101.8 ± 2.4 μm (n = 320) as opposed to 87.1 ± 1.6 μm (n = 360) in the controls.

Conclusion: Perinatal ablation of cMLCK produces an increase of heart weight/body weight ratio, a reduction of contractility, and an increase in the expression of fetal genes. The perinatal Mylk3-KO cardiomyocytes were elongated in the absence of thickening, differing from the compensatory hypertrophy shown in the germline knockout, and the cardomyocyte thinning shown in adult-inducible knockout.

Role of myosin light chain phosphatase in cardiac physiology and pathophysiology

Maintenance of contractile performance of the heart is achieved in part by the constitutive 40% phosphorylation of myosin regulatory light chain (RLC) in sarcomeres. The importance of this extent of RLC phosphorylation for optimal cardiac performance becomes apparent when various mouse models and resultant phenotypes are compared. The absence or attenuation of RLC phosphorylation results in poor performance leading to heart failure, whereas increased RLC phosphorylation is associated with cardiac protection from stresses. Although information is limited, RLC phosphorylation appears compromised in human heart failure which is consistent with data from mouse studies. The extent of cardiac RLC phosphorylation is determined by the balanced activities of cardiac myosin light chain kinases and phosphatases, the regulatory mechanisms of which are now emerging. This review thusly focuses on kinases that may participate in phosphorylating RLC to make the substrate for cardiac myosin light chain phosphatases, in addition to providing perspectives on the family of myosin light chain phosphatases and involved signaling mechanisms. Because biochemical and physiological information about cardiac myosin light chain phosphatase is sparse, such studies represent an emerging area of investigation in health and disease.

CaMKII and at least two unidentified kinases phosphorylate regulatory light chain in non-contracting cardiomyocytes

In cardiac tissue, regulatory light chain (RLC, myosin light chain 2) phosphorylation (Ser(15)) leads to modulation of muscle contraction through Ca(2+)-sensitization. To elucidate which kinases that are involved in the basal (diastolic phase) RLC phosphorylation, we studied non-contracting adult rat cardiomyocytes. RLC kinase activities in situ were unmasked by maximally inhibiting myosin light chain phosphatase (MLCP) by calyculin A in the absence and presence of various protein kinase inhibitors. Surprisingly MLCK did not contribute to the phosphorylation of RLC in the non-contracting cardiomyocytes. Two kinase activity groups were revealed by different sensitivities to staurosporine. The fraction with the highest sensitivity to staurosporine was inhibited by KN-93, a selective CaMKII inhibitor, producing a 23% ± 7% reduction in RLC phosphorylation. Calmodulin antagonism (W7) and reduction in Ca(2+) (EGTA) combined with low concentration of staurosporine caused a larger decrease in RLC phosphorylation than staurosporine alone. These data strongly suggest that in addition to CaMKII, there is another Ca(2+)/calmodulin-dependent kinase and a Ca(2+)/calmodulin-independent kinase phosphorylating RLC. Thus the RLC phosphorylation seems to be ensured by redundant kinase activities.

Nestin regulates neural stem cell migration via controlling the cell contractility

Neural stem cells (NSCs) migration is essential for neurogenesis and neuroregeneration after brain injury. Nestin, a widely used marker of NSCs, is expressed abundantly in several cancers, where it may correlate with tumor migration and invasion. However, it is not yet known whether nestin participates in NSC migration. Here, we show that nestin down-regulation significantly inhibits the migration and contraction of murine neural stem cells, but does not obviously influence the proliferation, filamentous actin (F-actin) content, distribution or focal adhesion assembly of these cells. Mechanistically, nestin knockdown was found to affect the phosphorylation state of myosin regulatory light chain (MRLC) and regulate the activity of myosin light chain kinase (MLCK). Co-immunoprecipitation experiments showed that it interacts with MLCK and MRLC. Together, our results indicate that nestin may increase NSC motility via elevating MLCK activity through direct binding and provide new insight into the roles of nestin in NSC migration and repair.

Olanzapine May Inhibit Colonic Motility Associated with the 5-HT Receptor and Myosin Light Chain Kinase

OBJECTIVE

To study whether the effects of olanzapine on gastrointestinal motility is related to the serotonin antagonism and myosin light chain kinase.

METHODS

Male Sprague-Dawley rats were randomly divided into four groups. Olanzapine gavage was performed for each treatment group during the course of 30 continuous days, while the same volume of saline was given to the rats in the control group. Defecation of the rats was observed on days 7 and 30 after olanzapine gavage. The effects of olanzapine on contraction of colonic smooth muscles were observed in ex vivo experiments. A Western blot was used to evaluate expression levels of the serotonin transporter (SERT) and MLCK in colon segments of the rats.

RESULTS

ResultsaaCompared to the control group, 5-160 µ M of olanzapine could inhibit dose-dependently the contraction of colonic smooth muscle ex vivo experiments. The maximum smooth muscle contraction effects of 5-HT and acetylcholine significantly decreased after treatment with 40-160 µ M of olanzapine. Constipation was found in the olanzapine-treated rats on day 7 and have sustained day 30 after gavage. Expression of MLCK in olanzapine-treated rats was significantly decreased, whereas the expression of SERT significantly increased on the day 7, then significantly decreased on the day 30 after olanzapine gavage.

CONCLUSION

SERT and MLCK may involve in the inhibition of colonic contraction induced by olanzapine.

G protein coupled signal transduction mechanisms in malfunction of smooth muscle relaxation and contraction in functional dyspepsia

Functional dyspepsia (FD) is a heterogeneous disease associated with gastrointestinal dysmotility, and it relates to malfunction of smooth muscle relaxation and contraction that is mainly mediated by G protein coupled signal transduction mechanisms involving phosphatidyl inositol (PI) signal transduction pathway, cyclic nucleus signal transduction pathway and small G protein signal transduction pathway. By discussing different components and signal pathways of G protein coupled signal transduction system and their associations with malfunction of smooth muscle relaxation and contraction in FD, this review aims to provide a new thought about the treatment of FD through the regulation of gastrointestinal motility from a microcosmic perspective.

Role of myosin light chain kinase in hypertriglyceridemia-associated acute pancreatitis in rats

AIM: To investigate the role of myosin light chain kinase (MLCK) in hypertriglyceridemia-associated acute pancreatitis (HTGP).

METHODS: Forty-eight male SD rats were randomly divided into two groups to be fed either a high-fat diet (group A) or a normal diet (group B). After being raised for 4 weeks, blood was harvested from the retroorbital venous plexus to measure serum triglyceride (TG) levels. After that, group A was randomly divided into three subgroups: HTG, HTG + AP, and HTG + AP + ML-7; group B were also randomly divided into three subgroups: C, AP, and AP + ML-7. All rats were sacrificed 24 h after the last injection of cerulein. The pancreases were carefully removed for HE staining and transmission electron microscopy to observe the morphological changes, ultrastructure and tight junction (TJ). Blood was obtained from the heart to measure serum amylase levels. The expression and localization of MLCK and p-JNK in the pancreas were assayed by immunohistochemistry.

RESULTS: Compared with group B, serum TG level was significantly increased in group A after being fed a high fat diet (P < 0.01). The pathologic score of the pancreas and serum amylase (AMY) activity were significantly elevated in the HTG + AP group, compared with the AP group (P < 0.05). The ultrastructure of the pancreas in the HTG + AP and AP groups was damaged and the TJ was broadened (most significant in the HTG + AP group). Besides, MLCK and p-JNK were significantly up-regulated in the HTG + AP group compared with those in the AP group (P < 0.05), and there was a positive correlation between the expression of MLCK and p-JNK in the pancreas and the pathologic score of the pancreas (r₁ = 0.795, r₂ = 0.789, P < 0.01). ML-7, an inhibitor of MLCK, significantly ameliorated the pathologic signs of the pancreas, down-regulated AMY level (P < 0.01), improved the TJ and decreased the expression of p-JNK (P < 0.05).

CONCLUSION: MLCK may be associated with the severity of HTGP, and involved in the formation of HTGP by broadening cell-cell TJ and activation of the JNK pathway.

Matrine inhibits diethylnitrosamine-induced HCC proliferation in rats through inducing apoptosis via p53, Bax-dependent caspase-3 activation pathway and down-regulating MLCK overexpression

The proliferation of hepatocellular carcinoma (HCC) cells is one of the leading causes of liver cancer mortality in humans. The inhibiting effects of matrine on HCC cell proliferation have been studied, but the mechanism of that inhibition has not been fully elucidated. Since, apoptosis plays an important role in HCC cell proliferation. We examined the apoptosis-inducing effect of matrine on tumor cells. Western blot analysis of p53, Bax, cleaved caspase-3 and myosin light chain kinase (MLCK) revealed that matrine induced tumor cell apoptosis by controlling anoikis. It activated p53, Bax-dependent caspase-3 and blocked the ECM-integrin mediated cell survival pathway through down-regulating MLCK over-expression in the liver of rats with diethyl nitrosamine (DENA)-induced HCC. Our results suggest that matrine can inhibit the proliferation of HCC cells through inducing tumor cell apoptosis via activation of the p53 pathway and inhibition of MLCK overexpression. Matrine may thus be used as a potentially promising reagent to inhibit HCC cell proliferation and MLCK may be a novel target for the treatment of HCC.

Regulation of calcium channels in smooth muscle: new insights into the role of myosin light chain kinase

Smooth muscle myosin light chain kinase (MLCK) plays a crucial role in artery contraction, which regulates blood pressure and blood flow distribution. In addition to this role, MLCK contributes to Ca(2+) flux regulation in vascular smooth muscle (VSM) and in non-muscle cells, where cytoskeleton has been suggested to help Ca(2+) channels trafficking. This conclusion is based on the use of pharmacological inhibitors of MLCK and molecular and cellular techniques developed to down-regulate the enzyme. Dissimilarities have been observed between cells and whole tissues, as well as between large conductance and small resistance arteries. A differential expression in MLCK and ion channels (either voltage-dependent Ca(2+) channels or non-selective cationic channels) could account for these observations, and is in line with the functional properties of the arteries. A potential involvement of MLCK in the pathways modulating Ca(2+) entry in VSM is described in the present review.

Functions of myosin light chain-2 (MYL2) in cardiac muscle and disease

Myosin light chain-2 (MYL2, also called MLC-2) is an ~19kDa sarcomeric protein that belongs to the EF-hand calcium binding protein superfamily and exists as three major isoforms encoded by three distinct genes in mammalian striated muscle. Each of the three different MLC-2 genes (MLC-2f; fast twitch skeletal isoform, MLC-2v; cardiac ventricular and slow twitch skeletal isoform, MLC-2a; cardiac atrial isoform) has a distinct developmental expression pattern in mammals. Genetic loss-of-function studies in mice demonstrated an essential role for cardiac isoforms of MLC-2, MLC-2v and MLC-2a, in cardiac contractile function during early embryogenesis. In the adult heart, MLC-2v function is regulated by phosphorylation, which displays a specific 1`expression pattern (high in epicardium and low in endocardium) across the heart. These data along with new data from computational models, genetic mouse models, and human studies have revealed a direct role for MLC-2v phosphorylation in cross-bridge cycling kinetics, calcium-dependent cardiac muscle contraction, cardiac torsion, cardiac function and various cardiac diseases. This review focuses on the regulatory functions of MLC-2 in the embryonic and adult heart, with an emphasis on phosphorylation-driven actions of MLC-2v in adult cardiac muscle, which provide new insights into mechanisms regulating myosin cycling kinetics and human cardiac diseases.

Neurotensinergic augmentation of glutamate release at the perforant path-granule cell synapse in rat dentate gyrus: Roles of L-Type Ca²⁺ channels, calmodulin and myosin light-chain kinase

Neurotensin (NT) serves as a neuromodulator in the brain where it is involved in modulating a variety of physiological functions including nociception, temperature, blood pressure and cognition, and many neurological diseases such as Alzheimer's disease, schizophrenia and Parkinson's disease. Whereas there is compelling evidence demonstrating that NT facilitates cognitive processes, the underlying cellular and molecular mechanisms have not been fully determined. Because the dentate gyrus expresses high densities of NT and NT receptors, we examined the effects of NT on the synaptic transmission at the synapse formed between the perforant path (PP) and granule cells (GC) in the rats. Our results demonstrate that NT persistently increased the amplitude of the AMPA receptor-mediated EPSCs at the PP-GC synapse. NT-induced increases in AMPA EPSCs were mediated by presynaptic NTS1 receptors. NT reduced the coefficient of variation and paired-pulse ratio of AMPA EPSCs suggesting that NT facilitates presynaptic glutamate release. NT increased the release probability and the number of readily releasable vesicles with no effects on the rate of recovery from vesicle depletion. NT-mediated augmentation of glutamate release required the influx of Ca(2+) via L-type Ca(2+) channels and the functions of calmodulin and myosin light chain kinase. Our results provide a cellular and molecular mechanism to explain the roles of NT in the hippocampus.

Electron microscopic examination of podosomes induced by phorbol 12, 13 dibutyrate on the surface of A7r5 cells

The role of myosin light chain kinase (MLCK) in inducing podosomes was examined by confocal and electron microscopy. Removal of myosin from the actin core of podosomes using blebbistatin, a myosin inhibitor, resulted in the formation of smaller podosomes. Downregulation of MLCK by the transfection of MLCK small interfering RNA (siRNA) led to the failure of podosome formation. However, ML-7, an inhibitor of the kinase activity of MLCK, failed to inhibit podosome formation. Based on our previous report (Thatcher et al. J.Pharm.Sci. 116 116-127, 2011), we outlined the important role of the actin-binding activity of MLCK in producing smaller podosomes.

Pharmacokinetic difference of berberine between normal and chronic visceral hypersensitivity irritable bowel syndrome rats and its mechanism

Berberine is one of active alkaloids from Rhizoma coptidis in traditional Chinese medicine. The pharmacokinetics of berberine in rat plasma were compared between normal and chronic visceral hypersensitivity irritable bowel syndrome rats (CVH-IBS) established by mechanical colon irritation using angioplasty balloons for 2 weeks after oral administration of berberine hydrochloride (25 mg/kg) with the equivalent dose of 22 mg/kg for berberine according to body weight. Immunohistochemical analysis of c-fos and myosin light chain kinase (MLCK) and immunofluorescence analysis of MLCK in rat colon were conducted. Quantification of berberine in rat plasma was achieved by using a sensitive and rapid UPLC-MS/MS method. Plasma samples were collected at 15 different points in time and the pharmacokinetic parameters were analyzed by WinNonlin software. The great different pharmacokinetic behavior of berberine was observed between normal and CVH-IBS model rats. Compared with normal group, T1/2 and AUC(0-t) of berberine in the model group were significantly increased, respectively (573.21 ± 127.53 vs 948.22 ± 388.57 min; 8,657.19 ± 1,562.54 vs 11,415.12 ± 1,670.72 min.ng/ml). Cl/F of berberine in the model group significantly decreased, respectively (13.89 ± 1.69 vs 9.19 ± 2.91 L/h/kg). Additionally, the expressions of c-fos and MLCK in model group were higher than those in normal group. The pharmacokinetic behavior of berberine was significantly altered in CVH-IBS pathological conditions, which indicated the dosage modification of berberine hydrochloride in CVH-IBS were necessary. Especially, improved exposure to berberine in rat plasma in CVH-IBS model rats was attributed to increased the expression of MLCK.

Role of myosin light chain kinase in inflammatory bowel disease

Myosin light chain kinase (MLCK) dependent myosin light chain (MLC) phosphorylation plays an important role in the pathogenesis of inflammatory bowel disease (IBD). Cytoskeletal contraction induced by the phosphorylation of MLC is essential for the destruction of the intestinal epithelial barrier, and increased expression of MLCK can mediate epithelial barrier dysfunction. Currently studies focused mainly on the mechanism of MLCK in the intestinal epithelial barrier. This review discusses the role of MLCK in IBD.

The role of molecular remodeling in differential regulation of tight junction permeability. Semin Cell Dev Biol. 2014;36:204-212. [PMID: 25263012 DOI: 10.1016/j.semcdb.2014.09.022]

Tight junctions create a paracellular barrier that is essential for survival of complex organisms. In many cases tight junctions define separate, generally sterile, tissue compartments. In the skin and gut, tight junctions must also seal the paracellular space to prevent microbiota from accessing the internal milieu. This is a relatively simple task in the integument, where an absolute barrier is effective. However, intestinal epithelial tight junctions are charged with the far more complex task of supporting paracellular transport of water, ions, and nutrients while providing a barrier to microbial translocation. The delicate nature of this balance, which is disrupted in disease, makes the intestine a unique organ in which to explore the complexities of tight junction permeability and barrier regulation. Here we review recent progress in understanding the molecular determinants of barrier function and events responsible for regulation, and dysregulation, of tight junction permeability.

Effect of advanced glycation end products on myosin light chain kinase expression in smooth muscle cells and colonic motility dysfunction in diabetic rats

AIM: To investigate whether advanced glycation end products (AGEs) affect colonic motility and the expression of myosin light chain kinase in diabetic rats.

METHODS: Forty-eight SD rats were evenly and randomly divided into four groups: normal controls, normal rats treated with aminoguanidine (AG, an inhibitor of AGEs), diabetic rats, and diabetic rats treated with AG. Diabetes mellitus (DM) was induced by a single intraperitoneal injection of streptozotocin (STZ) (60 mg/kg). AG was given in drinking water at a dose of 1 g/L after DM was induced. ELISA and Western blot were used to measure levels of AGEs in serum and the colonic muscle layer, respectively. Colon transit time was measured by glass bead expulsion test, and the contractility of circular smooth muscle strips was tested using the MPA analysis system. The protein expression level of myosin light chain kinase (MLCK) was determined by Western blot.

RESULTS: Compared with the normal control group, the expression levels of AGEs in the colonic muscle layer and serum (3.00 μg/mL ± 0.34 μg/mL vs 4.31 μg/mL ± 0.73 μg/mL, P < 0.01) were increased, colon transit time was delayed (209.50 min ± 48.88 min vs 297.00 min ± 35.71 min, P < 0.01), the contractility of circular smooth muscle strips was weakened (2.17 g ± 0.57 g vs 0.80 g ± 0.34 g, P < 0.01), and the expression of MLCK in the colonic muscle layer was lower (1.46 ± 0.11 vs 1.01 ± 0.08, P < 0.01) in the diabetic group. There was no significant change in blood glucose levels in rats treated with AG. Compared with the diabetic group, DM rats treated with AG showed decreased levels of AGEs in the colon muscle layer and serum (4.31 μg/mL ± 0.73 μg/mL vs 3.35 μg/mL ± 0.58 μg/mL, P < 0.05), shortened colon transit time (297.00 min ± 35.71 min vs 212.13 min ± 42.95 min, P < 0.01), enhanced contractility of circular smooth muscle strips (0.80 g ± 0.34 g vs 1.49 g ± 0.44 g, P < 0.01), and higher expression of MLCK in the colonic muscle layer (1.01 ± 0.08 vs 1.40 ± 0.09, P < 0.01).

CONCLUSION: AGEs might be involved in the pathogenesis of colonic motility dysfunction in diabetic rats via decreasing the expression of MLCK.

Molecular and cellular basis of the regulation of lymphatic contractility and lymphatic absorption

Lymphatic absorption is a highly regulated process driven by both an extrinsic mechanism (external force) and an intrinsic mechanism (lymphatic vessel contractility). The lymphatic muscle is a specialized smooth muscle with unique mechanical properties. To understand the molecular mechanism and relative contribution of smooth muscle contraction in lymphatic absorption, we analyzed mice with a smooth muscle-specific deletion of Mylk, a critical gene for smooth muscle contraction. Interestingly, the knockout mice were significantly resistant to anesthesia reagents. Upon injection in the feet with FITC-dextran, the mutant mice displayed a 2-fold delay of the absorption peak in the peripheral circulation. Examining the ear lymphatic vessels of the mutant mice revealed a reduction in the amount of fluid in the lumens of the lymphangions, suggesting an impairment of lymph formation. The Mylk-deficient lymphatic muscle exhibited a significant reduction of peristalsis and of myosin light chain phosphorylation in response to depolarization. We thus concluded that MLCK and myosin light chain phosphorylation are required for lymphatic vessel contraction. Lymphatic contractility is not an exclusive requirement for lymphatic absorption, and external force appears to be necessary for absorption.

Screening of protein kinase inhibitors and knockdown experiments identified four kinases that affect mitochondrial ATP synthesis activity

Mitochondrial ATP synthase, a major ATP supplier in respiring cells, should be regulated in amount and in activity to respond to the varying demands of cells for ATP. We screened 80 protein kinase inhibitors and found that HeLa cells treated with four inhibitors exhibited reduced mitochondrial ATP synthesis activity. Consistently, knockdown of their target kinases (PKA, PKCδ, CaMKII and smMLCK) resulted in a decrease in mitochondrial ATP synthesis activity. Among them, mitochondria of smMLCK-knockdown cells contained only a small amount of ATP synthase, while the α- and β-subunits of ATP synthase were produced normally, suggesting that smMLCK affects assembly (or decay) of ATP synthase.