Regulation of myosin light-chain phosphorylation and its roles in cardiovascular physiology and pathophysiology

Central nervous system mechanisms of salt-sensitive hypertension

Salt-sensitive and salt-induced hypertension (SHTN) is a multifaceted and heterogeneous condition influenced by various factors, including lifestyle, genetics, sex, age, and dietary salt intake. Despite its prevalence, affecting about 50% of hypertensive and 25% of normotensive individuals, the precise mechanisms driving salt sensitivity remain incompletely understood. The central nervous system (CNS) plays a pivotal role in SHTN, as it detects changes in plasma and cerebrospinal fluid sodium (Na+) concentrations and integrates sensory signals from peripheral organs. These inputs, in turn, regulate the autonomic nervous system, leading to an increase in sympathetic nerve activity that contributes to the onset of SHTN. This review examines the CNS mechanisms involved in SHTN, focusing on the key afferent and efferent pathways in its pathogenesis. We summarize recent findings on critical neural circuits activated by dietary salt and examine several key signaling pathways, including the brain's renin-angiotensin system, aldosterone-"ouabain," and salt-sensitive G proteins. Additionally, we discuss the clinical relevance of targeting the CNS for SHTN treatment and review current therapeutic approaches.

Antithrombotic Effect of a Bivalent DNA Aptamer of Thrombin

Thrombin plays a critical role in both coagulation and platelet activation, and its interaction with thrombin-protease-activated receptor 1 (PAR1) on platelets and vascular smooth muscle cells (VSMCs) leads to a series of pathological processes such as thrombosis, restenosis, and atherosclerosis. This study investigated the antithrombotic properties of a bivalent DNA aptamer (bApt) with phosphorothioate backbone modification designed to inhibit thrombin, with a specific focus on its ability to regulate the thrombin-PAR1 signaling pathway. The results showed that bApt modulated the thrombin-PAR1 pathway, effectively reduced thrombus formation, platelet aggregation, and VSMC proliferation. Key findings from the study highlight that bApt successfully prolonged coagulation reaction time (R value), coagulation time (K value), maximum amplitude (MA) and reduced coagulation angle (α value), and also prolonged thrombin time (TT) and activated partial thromboplastin time (APTT), in a dose-dependent manner. Moreover, in an arterial injury model, bApt reduced thrombus formation significantly, supporting its potential as a therapeutic agent for thrombotic diseases.

Cyclic nucleotide phosphodiesterases as drug targets

Cyclic nucleotides are synthesized by adenylyl and/or guanylyl cyclase, and downstream of this synthesis, the cyclic nucleotide phosphodiesterase families (PDEs) specifically hydrolyze cyclic nucleotides. PDEs control cyclic adenosine-3',5'monophosphate (cAMP) and cyclic guanosine-3',5'-monophosphate (cGMP) intracellular levels by mediating their quick return to the basal steady state levels. This often takes place in subcellular nanodomains. Thus, PDEs govern short-term protein phosphorylation, long-term protein expression, and even epigenetic mechanisms by modulating cyclic nucleotide levels. Consequently, their involvement in both health and disease is extensively investigated. PDE inhibition has emerged as a promising clinical intervention method, with ongoing developments aiming to enhance its efficacy and applicability. In this comprehensive review, we extensively look into the intricate landscape of PDEs biochemistry, exploring their diverse roles in various tissues. Furthermore, we outline the underlying mechanisms of PDEs in different pathophysiological conditions. Additionally, we review the application of PDE inhibition in related diseases, shedding light on current advancements and future prospects for clinical intervention. SIGNIFICANCE STATEMENT: Regulating PDEs is a critical checkpoint for numerous (patho)physiological conditions. However, despite the development of several PDE inhibitors aimed at controlling overactivated PDEs, their applicability in clinical settings poses challenges. In this context, our focus is on pharmacodynamics and the structure activity of PDEs, aiming to illustrate how selectivity and efficacy can be optimized. Additionally, this review points to current preclinical and clinical evidence that depicts various optimization efforts and indications.

Vasorelaxant effects and its mechanisms of the rhizome of Acorus gramineus on isolated rat thoracic aorta

In conventional medicine, the rhizome of Acorus gramineus Solander (AGR) is used to treat cardiovascular and cerebrovascular diseases. Decoctions containing AGR exert vasorelaxant effects. Therefore, this research aimed to delve deeper into the vasorelaxant effects and underlying mechanisms of AGR and its constituents (α-asarone and β-asarone). We assessed the vasorelaxant effect of a 50% ethanol extract of AGR (AGRE) using aortic rings from Sprague-Dawley rats pre-constricted with phenylephrine (PE) and potassium chloride (KCl). The findings suggested that the mechanism of this effect was independent of endothelial cells and was associated with vascular smooth muscle cells (VSMC). Since vasodilatory mechanisms associated with VSMC are predominantly influenced by K+ and Ca2+ channels, we explored various channels, including calcium-activated K+, voltage-dependent (delayed rectifier) K+, ATP-sensitive K+, inwardly rectifying K+, receptor-operated Ca2+ (ROCC), and voltage-dependent Ca2+ channels (VDCC). Selective blockers were used to examine K+ channels, which inhibited vasorelaxant effect of AGRE. These findings suggest that AGRE-induced vasorelaxation is facilitated through K+ channels. In addition, the blockage of Ca2+ influx was observed in both groups treated with PE and KCl. Therefore, AGR appears to block Ca2+ influx through ROCC and VDCC. In conclusion, AGR demonstrates vasorelaxant effects by acting on VSMC.

Coordination among cytoskeletal organization, cell contraction, and extracellular matrix development is dependent on LOX for aneurysm prevention

Distinct and seemingly independent cellular pathways affecting intracellular machinery or extracellular matrix (ECM) deposition and organization have been implicated in aneurysm formation. One of the key genes associated with this pathology in both humans and mice is lysyl oxidase (LOX), a secreted ECM-modifying enzyme, highly expressed in medial vascular smooth muscle cells. To dissect the mechanisms leading to aneurysm development, we conditionally deleted Lox in smooth muscle cells. We find that cytoskeletal organization is lost following Lox deletion. Cell culture assays and in vivo analyses demonstrate a cell-autonomous role for LOX affecting myosin light-chain phosphorylation and cytoskeletal assembly resulting in irregular smooth muscle contraction. These results not only highlight new intracellular roles for LOX, but notably, they provide a link between multiple processes leading to aneurysm formation, suggesting LOX coordinates ECM development, cytoskeletal organization, and cell contraction required for media development and function.

Targeting cytoskeletal biomechanics to modulate airway smooth muscle contraction in asthma

To contract, to deform, and remodel, the airway smooth muscle cell relies on dynamic changes in the structure of its mechanical force-bearing cytoskeleton. These alternate between a "fluid-like" (relaxed) state characterized by weak contractile protein-protein interactions within the cytoskeletal apparatus and a "solid-like" (contractile) state promoted by strong and highly organized molecular interactions. In this review, we discuss the roles for actin, myosin, factors promoting actin polymerization and depolymerization, adhesome complexes, and cell-cell junctions in these dynamic processes. We describe the relationship between these cytoskeletal factors, extracellular matrix components of bronchial tissue, and mechanical stretch and other changes within the airway wall in the context of the physical mechanisms of cytoskeletal fluidization-resolidification. We also highlight studies that emphasize the distinct processes of cell shortening and force transmission in airway smooth muscle and previously unrecognized roles for actin in cytoskeletal dynamics. Finally, we discuss the implications of these discoveries for understanding and treating airway obstruction in asthma.

Regulation of Vascular Injury and Repair by P21-Activated Kinase 1 and P21-Activated Kinase 2: Therapeutic Potential and Challenges

The PAK (p21-activated kinases) family is a class of intracellular signal transduction protein kinases that regulate various cellular functions, mainly through their interactions with small GTP enzymes. PAK1 and PAK2 in the PAK kinase family are key signal transduction molecules that play important roles in various biological processes, including morphological changes, migration, proliferation, and apoptosis, and are involved in the progression of many diseases. Abnormal expression or dysregulation of PAK1 and PAK2 may be associated with several diseases, including cancer, neurological diseases, etc. The current research mainly focuses on studying the role of PAK and PAK inhibitors in the regulation of cancer progression, but relatively few reports are available that explore their potential role in cardiovascular diseases. Vascular injury and repair are complex processes involved in many cardiovascular conditions, including atherosclerosis, restenosis, and hypertension. Emerging research suggests that PAK1 and PAK2 have pivotal roles in vascular endothelial cell functions, including migration, proliferation, and angiogenesis. These kinases also modulate vascular smooth muscle relaxation, vascular permeability, and structural alterations, which are critical in the development of atherosclerosis and vascular inflammation. By targeting these activities, PAK proteins are essential for both normal vascular physiology and the pathogenesis of vascular diseases, highlighting their potential as therapeutic targets for vascular health. This review focuses on recent studies that offer experimental insights into the mechanisms by which PAK1 and PAK2 regulate the biological processes of vascular injury and repair and the therapeutic potential of the current existing PAK inhibitors in vascular-related diseases. The limitations of treatment with some PAK inhibitors and the ways that future development can overcome these challenges are also discussed.

Luteinizing hormone-induced changes in the structure of mammalian preovulatory follicles

Ovulation of a mammalian oocyte from its follicle, which occurs in response to luteinizing hormone (LH), requires complex restructuring of the ∼20 layers of surrounding somatic cells. This chapter describes the cellular architecture of preovulatory follicles, the localization of the receptors for LH, and the LH-induced changes in follicular structure, focusing on mice and other small mammals. The multiple interrelated processes that result in ovulation include breakdown of existing extracellular matrix, generation of new extracellular matrix, thinning of the follicular apex where the oocyte will be released, invagination of the follicular surface, and responses of the vascular system to support these dynamic changes. However, much remains unknown about how these events function together to release a fertilizable egg.

Toll-like receptor 3 involvement in vascular function

Maintaining endothelial cell (EC) and vascular smooth muscle cell (VSMC) integrity is an important component of human health and disease because both EC and VSMC regulate various functions, including vascular tone control, cellular adhesion, homeostasis and thrombosis regulation, proliferation, and vascular inflammation. Diverse stressors affect functions in both ECs and VSMCs and abnormalities of functions in these cells play a crucial role in cardiovascular disease initiation and progression. Toll-like receptors (TLRs) are important detectors of pathogen-associated molecular patterns derived from various microbes and viruses as well as damage-associated molecular patterns derived from damaged cells and perform innate immune responses. Among TLRs, several studies reveal that TLR3 plays a key role in initiation, development and/or protection of diseases, and an emerging body of evidence indicates that TLR3 presents components of the vasculature, including ECs and VSMCs, and plays a functional role. An agonist of TLR3, polyinosinic-polycytidylic acid [poly (I:C)], affects ECs, including cell death, inflammation, chemoattractant, adhesion, permeability, and hemostasis. Poly (I:C) also affects VSMCs including inflammation, proliferation, and modulation of vascular tone. Moreover, alterations of vascular function induced by certain molecules and/or interventions are exerted through TLR3 signaling. Hence, we present the association between TLR3 and vascular function according to the latest studies.

Proteomic and Phosphoproteomic analysis of thyroid papillary carcinoma: Identification of potential biomarkers for metastasis

Thyroid cancer has emerged as the most rapidly proliferating solid neoplasm. In this study, we included a cohort of patients who underwent sonographic assessment and surgical intervention at the Sir Run Run Shaw Hospital, associated with the School of Medicine at Zhejiang University, spanning from January 2019 to June 2020. Stratification of cases was based on a combination of preoperative ultrasonographic evaluations and postoperative histopathological diagnoses, resulting in three distinct groups: high-risk papillary thyroid carcinoma (PTC) labeled as C1, low-risk PTC designated as C2, and a control group (N) composed of benign thyroid tissue adjacent to the carcinoma. Proteomic and phosphoproteomic analyses were conducted on PTC specimens. The comparative assessment revealed that proteins up-regulated in the C1/N and C2/N groups were predominantly involved in functions such as amino acid binding, binding of phosphorylated compounds, and serine protease activity. Notably, proteins like NADH dehydrogenase, ATP synthase, oxidoreductases, and iron ion channels were significantly elevated in the C1 versus C2 comparative group. Through meticulous analysis of differential expression multiples, statistical significance, and involvement in metabolic pathways, this study identified eight potential biomarkers pertinent to PTC metastasis diagnostics, encompassing phosphorylated myosin 10, phosphorylated proline-directed protein kinase, leucine tRNA synthetase, 2-oxo-isovalerate dehydrogenase, succinic semialdehyde dehydrogenase, ADP/ATPtranslocase, pyruvate carboxylase, and fibrinogen. Therapeutic assays employing metformin, an AMP-activated protein kinase (AMPK) activator, alongside the phosphorylation-specific inhibitor ML-7 targeting Myosin10, demonstrated attenuated cellular proliferation, migration, and invasion capabilities in thyroid cancer cells, accompanied by a reduction in amino acid pools. Cellular colocalization and interaction studies elucidated that AMPK activation imposes an inhibitory influence on Myosin10 levels. The findings of this research corroborate the utility of proteomic and phosphoproteomic platforms in the identification of metastatic markers for PTC and suggest that modulation of AMPK activity, coupled with the inhibition of Myosin10 phosphorylation, may forge novel therapeutic avenues in the management of thyroid carcinoma. SIGNIFICANCE: The significance of our research lies in its potential to transform the current understanding and management of thyroid papillary carcinoma (PTC), particularly in its metastatic form. By integrating both proteomic and phosphoproteomic analyses, our study not only sheds light on the molecular alterations associated with PTC but also identifies eight novel biomarkers that could serve as indicators of metastatic potential.

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

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

Yiqi Kaimi prescription regulates protein phosphorylation to promote intestinal motility in slow transit constipation

ETHNOPHARMACOLOGICAL RELEVANCE

The clinical efficacy of the Yiqi Kaimi prescription has been confirmed in slow transit constipation. However, the effects and biological mechanism of Yiqi Kaimi prescription are still unclear.

AIMS OF THE STUDY

To identify the effects of Yiqi Kaimi prescription on intestinal motility; To reveal the potential key targets and pathways of Yiqi Kaimi prescription for the treatment of slow transit constipation.

MATERIALS AND METHODS

The effects of Yiqi Kaimi prescription on slow transit constipation were investigated in a mouse model. The terminal ink propulsion experiment and fecal indocyanine green imaging was used to measure the intestinal transit time. Protein phosphorylation changes in colon tissues treated with Yiqi Kaimi prescription were detected using a Phospho Explorer antibody microarray. Bioinformatic analyses were performed using the Database for Annotation Visualization and Integrated Discovery (DAVID) and the Search Tool for the Retrieval of Interacting Genes (STRING). Western blot analysis and immunohistochemistry confirmed the observed changes in phosphorylation.

RESULT

s: Yiqi Kaimi prescription significantly increased the intestinal transit rate (P < 0.05 vs. model) and reduced the time to first discharge of feces containing fecal indocyanine green imaging in mice (P < 0.05 vs. model). The administration of Yiqi Kaimi prescription induced phosphorylation changes in 41 proteins, with 9 upregulated proteins and 32 downregulated proteins. Functional classification of the phosphorylated proteins with DAVID revealed that the critical biological processes included tyrosine protein kinases, positive regulation of calcium-mediated signaling and response to muscle stretch. The phosphorylation of the spleen tyrosine kinase (SYK) at Tyr348 increased 2.19-fold, which was the most significant change. The phosphorylation level of the transcription factor p65 (RELA) at Thr505 was decreased 0.57-fold. SYK was a hub protein in the protein-protein interaction network and SYK and RELA formed the core of the secondary subnetwork. The key protein phosphorylation after treatment with Yiqi Kaimi prescription were verified by Western blot analysis and immunohistochemistry.

CONCLUSION

Yiqi Kaimi prescription significantly enhanced intestinal motility. This effect was attributed to alterations in the phosphorylation levels of various target proteins. The observed changes in protein phosphorylation, including SYK and RELA, may serve as crucial factors in the treatment of slow transit constipation.

Myosin Light Chain Phosphatase Plays an Important Role in Cardiac Fibrosis in a Model of Mineralocorticoid Receptor-Associated Hypertension

BACKGROUND

Myosin phosphatase targeting subunit 2 (MYPT2) is an important subunit of cardiac MLC (myosin light chain) phosphatase, which plays a crucial role in regulating the phosphorylation of MLC to phospho-MLC (p-MLC). A recent study demonstrated mineralocorticoid receptor-related hypertension is associated with RhoA/Rho-associated kinase/MYPT1 signaling upregulation in smooth muscle cells. Our purpose is to investigate the effect of MYPT2 on cardiac function and fibrosis in mineralocorticoid receptor-related hypertension.

METHODS AND RESULTS

HL-1 murine cardiomyocytes were incubated with different concentrations or durations of aldosterone. After 24-hour stimulation, aldosterone increased CTGF (connective tissue growth factor) and MYPT2 and decreased p-MLC in a dose-dependent manner. MYPT2 knockdown decreased CTGF. Cardiac-specific MYPT2-knockout (c-MYPT2-/-) mice exhibited decreased type 1 phosphatase catalytic subunit β and increased p-MLC. A disease model of mouse was induced by subcutaneous aldosterone and 8% NaCl food for 4 weeks after uninephrectomy. Blood pressure elevation and left ventricular hypertrophy were observed in both c-MYPT2-/- and MYPT2+/+ mice, with no difference in heart weights or nuclear localization of mineralocorticoid receptor in cardiomyocytes. However, c-MYPT2-/- mice had higher ejection fraction and fractional shortening on echocardiography after aldosterone treatment. Histopathology revealed less fibrosis, reduced CTGF, and increased p-MLC in c-MYPT2-/- mice. Basal global radial strain and global longitudinal strain were higher in c-MYPT2-/- than in MYPT2+/+ mice. After aldosterone treatment, both global radial strain and global longitudinal strain remained higher in c-MYPT2-/- mice compared with MYPT2+/+ mice.

CONCLUSIONS

Cardiac-specific MYPT2 knockout leads to decreased myosin light chain phosphatase and increased p-MLC. MYPT2 deletion prevented cardiac fibrosis and dysfunction in a model of mineralocorticoid receptor-associated hypertension.

Coordination between cytoskeletal organization, cell contraction and extracellular matrix development, is depended on LOX for aneurysm prevention

Distinct, seemingly independent, cellular pathways affecting intracellular machineries or extracellular matrix (ECM) deposition and organization, have been implicated in aneurysm formation. One of the key genes associated with the pathology in both humans and mice is Lysyl oxidase (LOX), a secreted ECM-modifying enzyme, highly expressed in medial vascular smooth muscle cells. To dissect the mechanisms leading to aneurysm development, we conditionally deleted Lox in smooth muscle cells. We find that cytoskeletal organization is lost following Lox deletion. Cell culture assays and in vivo analyses demonstrate a cell-autonomous role for LOX affecting myosin light chain phosphorylation and cytoskeletal assembly resulting in irregular smooth muscle contraction. These results not only highlight new intracellular roles for LOX, but notably they link between multiple processes leading to aneurysm formation suggesting LOX coordinates ECM development, cytoskeletal organization and cell contraction required for media development and function.

Phosphatases modified by LH signaling in ovarian follicles: testing their role in regulating the NPR2 guanylyl cyclase†

In response to luteinizing hormone (LH), multiple proteins in rat and mouse granulosa cells are rapidly dephosphorylated, but the responsible phosphatases remain to be identified. Because the phosphorylation state of phosphatases can regulate their interaction with substrates, we searched for phosphatases that might function in LH signaling by using quantitative mass spectrometry. We identified all proteins in rat ovarian follicles whose phosphorylation state changed detectably in response to a 30-min exposure to LH, and within this list, identified protein phosphatases or phosphatase regulatory subunits that showed changes in phosphorylation. Phosphatases in the phosphoprotein phosphatase (PPP) family were of particular interest because of their requirement for dephosphorylating the natriuretic peptide receptor 2 (NPR2) guanylyl cyclase in the granulosa cells, which triggers oocyte meiotic resumption. Among the PPP family regulatory subunits, PPP1R12A and PPP2R5D showed the largest increases in phosphorylation, with 4-10 fold increases in signal intensity on several sites. Although follicles from mice in which these phosphorylations were prevented by serine-to-alanine mutations in either Ppp1r12a or Ppp2r5d showed normal LH-induced NPR2 dephosphorylation, these regulatory subunits and others could act redundantly to dephosphorylate NPR2. Our identification of phosphatases and other proteins whose phosphorylation state is rapidly modified by LH provides clues about multiple signaling pathways in ovarian follicles.

Top-down proteomics of myosin light chain isoforms define chamber-specific expression in the human heart

Myosin functions as the "molecular motor" of the sarcomere and generates the contractile force necessary for cardiac muscle contraction. Myosin light chains 1 and 2 (MLC-1 and -2) play important functional roles in regulating the structure of the hexameric myosin molecule. Each of these light chains has an 'atrial' and 'ventricular' isoform, so called because they are believed to exhibit chamber-restricted expression in the heart. However, recently the chamber-specific expression of MLC isoforms in the human heart has been questioned. Herein, we analyzed the expression of MLC-1 and -2 atrial and ventricular isoforms in each of the four cardiac chambers in adult non-failing donor hearts using top-down mass spectrometry (MS)-based proteomics. Strikingly, we detected an isoform thought to be ventricular, MLC-2v (gene: MYL2), in the atria and confirmed the protein sequence using tandem MS (MS/MS). For the first time, a putative deamidation post-translation modification (PTM) located on MLC-2v in atrial tissue was localized to amino acid N13. MLC-1v (MYL3) and MLC-2a (MYL7) were the only MLC isoforms exhibiting chamber-restricted expression patterns across all donor hearts. Importantly, our results unambiguously show that MLC-1v, not MLC-2v, is ventricle-specific in adult human hearts. Moreover, we found elevated MLC-2 phosphorylation in male hearts compared to female hearts across each cardiac chamber. Overall, top-down proteomics allowed an unbiased analysis of MLC isoform expression throughout the human heart, uncovering previously unexpected isoform expression patterns and PTMs.

Metabolites of Life: Phosphate

The process of aging and escalating the failure of all body organs has become the center of interest in contemporary science and medicine. The leading role of phosphate-calcium tandem deficiency as a pacemaker of metabolic senescence has emerged recently. Most of the phosphates in the human body are stored in the bones, which seem to play a pivotal role in all metabolic and energetic processes. Bone metabolism combines physical activity with adaptive changes in the internal environment of the body, which is necessary for its survival. Phosphate-calcium signaling is the primary mechanism for controlling homeostasis and its recovery after exercise-induced disorders. Phosphates play an important role in the regulation of energy metabolism both by regulating postprandial glucose storage in the muscles and in the liver, as well as the distribution and adaptation of energy metabolites to the needs of the brain and skeletal muscles. The bone-driven energy metabolism is of decisive importance for maintaining all vital functions of the body organs, including their proper functioning and integrated interplay. The phosphate-calcium tandem contributes to the development and proper functioning of the organism, whereas energy dysmetabolism is the main cause of aging and the final termination of life.

Noradrenaline released from locus coeruleus axons contracts cerebral capillary pericytes via 2 adrenergic receptors

Noradrenaline (NA) release from locus coeruleus axons generates vascular contractile tone in arteriolar smooth muscle and contractile capillary pericytes. This tone allows neuronal activity to evoke vasodilation that increases local cerebral blood flow (CBF). Much of the vascular resistance within the brain is located in capillaries and locus coeruleus axons have NA release sites closer to pericytes than to arterioles. In acute brain slices, NA contracted pericytes but did not raise the pericyte cytoplasmic Ca2+ concentration, while the α1 agonist phenylephrine did not evoke contraction. Blocking α2 adrenergic receptors (α2Rs, which induce contraction by inhibiting cAMP production), greatly reduced the NA-evoked pericyte contraction, whereas stimulating α2Rs using xylazine (a sedative) or clonidine (an anti-hypertensive drug) evoked pericyte contraction. Noradrenaline-evoked pericyte contraction and capillary constriction are thus mediated via α2Rs. Consequently, α2Rs may not only modulate CBF in health and pathological conditions, but also contribute to CBF changes evoked by α2R ligands administered in research, veterinary and clinical settings.

A simple and accurate method to quantify real-time contraction of vascular smooth muscle cell in vitro

Vascular smooth muscle cells (VSMCs) constitute the medial layer of the blood vessel wall. Their contractile state regulates blood flow in physiological and pathological conditions. Current methods for assessing the contractility of VSMCs are not amenable to the high-throughput screening of pharmaceutical compounds. This study aimed to develop a method to address this shortcoming in the field. Real-time contraction was visualized in living VSMCs using the exogenous expression of green fluorescent protein (GFP). Image-Pro Plus software (IPPS) was used to measure various morphological cell indices. In phenylephrine-treated VSMCs, GFP fluorescence imaging was more accurate than brightfield imaging or phalloidin staining in representing VSMC morphology, as measured using IPPS. Among the multiple indices of VSMC shape, area and mean-diameter were more sensitive than length in reflecting the morphological changes in VSMC. We developed a new index, compound length, by combining the mean-diameter and length to differentiate contracted and uncontracted VSMCs. Based on the compound length, we further generated a contraction index to define a single-VSMC contractile status as single-VSMC contraction-index (SVCI). Finally, compound length and SVCI were validated to effectively assess cell contraction in VSMCs challenged with U46619 and KCl. In conclusion, GFP-based indices of compound length and SVCI can accurately quantify the real-time contraction of VSMCs. In future, the new method will be applied to high-throughput drug screening or basic cardiovascular research.