Dynamic cell-adhesive microenvironments and their effect on myogenic differentiation

Integrin-mediated cell adhesion plays a central role in cell behavior on biomaterial surfaces and influences various cell functions. Photoactivatable RGD adhesive peptides were used to investigate the effect of the density and time point of bioadhesive ligand presentation on cell adhesion, proliferation and differentiation. PEGylated self-assembled monolayers were functionalized with RGD and caged RGD ligands and seeded with C2C12 myoblasts. The cultures were irradiated at various time points between 1 and 48 h after cell seeding in order to increase RGD surface concentration at defined time points. Attachment, spreading and myogenic differentiation of C2C12 myoblasts strongly varied with the density of RGD at the surface. Proliferation and myogenesis were further regulated by the time point at which RGD was presented to the cell, reaching highest levels when RGD exposure occurred≤6 h after cell seeding. These results provide fundamental insights in cell-biomaterial interactions of C2C12 myoblasts in terms of temporal integrin-mediated cell responses.

Aerobic interval training partly reverse contractile dysfunction and impaired Ca2+ handling in atrial myocytes from rats with post infarction heart failure

BACKGROUND

There is limited knowledge about atrial myocyte Ca(2+) handling in the failing hearts. The aim of this study was to examine atrial myocyte contractile function and Ca(2+) handling in rats with post-infarction heart failure (HF) and to examine whether aerobic interval training could reverse a potential dysfunction.

METHODS AND RESULTS

Post-infarction HF was induced in Sprague Dawley rats by ligation of the left descending coronary artery. Atrial myocyte shortening was depressed (p<0.01) and time to relaxation was prolonged (p<0.01) in sedentary HF-rats compared to healthy controls. This was associated with decreased Ca(2+) amplitude, decreased SR Ca(2+) content, and slower Ca(2+) transient decay. Atrial myocytes from HF-rats had reduced sarcoplasmic reticulum Ca(2+) ATPase activity, increased Na(+)/Ca(2+)-exchanger activity and increased diastolic Ca(2+) leak through ryanodine receptors. High intensity aerobic interval training in HF-rats restored atrial myocyte contractile function and reversed changes in atrial Ca(2+) handling in HF.

CONCLUSION

Post infarction HF in rats causes profound impairment in atrial myocyte contractile function and Ca(2+) handling. The observed dysfunction in atrial myocytes was partly reversed after aerobic interval training.

Whole-cell patch-clamp recording of nicotinic acetylcholine receptors in adult Brugia malayi muscle

Lymphatic filariasis is a debilitating disease caused by clade III parasites like Brugia malayi and Wuchereria bancrofti. Current recommended treatment regimen for this disease relies on albendazole, ivermectin and diethylcarbamazine, none of which targets the nicotinic acetylcholine receptors in these parasitic nematodes. Our aim therefore has been to develop adult B. malayi for electrophysiological recordings to aid in characterizing the ion channels in this parasite as anthelmintic target sites. In that regard, we recently demonstrated the amenability of adult B. malayi to patch-clamp recordings and presented results on the single-channel properties of nAChR in this nematode. We have built on this by recording whole-cell nAChR currents from adult B. malayi muscle. Acetylcholine, levamisole, pyrantel, bephenium and tribendimidine activated the receptors on B. malayi muscle, producing robust currents ranging from >200 pA to ~1.5 nA. Levamisole completely inhibited motility of the adult B. malayi within 10 min and after 60 min, motility had recovered back to control values.

The archipelago ubiquitin ligase subunit acts in target tissue to restrict tracheal terminal cell branching and hypoxic-induced gene expression

The Drosophila melanogaster gene archipelago (ago) encodes the F-box/WD-repeat protein substrate specificity factor for an SCF (Skp/Cullin/F-box)-type polyubiquitin ligase that inhibits tumor-like growth by targeting proteins for degradation by the proteasome. The Ago protein is expressed widely in the fly embryo and larva and promotes degradation of pro-proliferative proteins in mitotically active cells. However the requirement for Ago in post-mitotic developmental processes remains largely unexplored. Here we show that Ago is an antagonist of the physiologic response to low oxygen (hypoxia). Reducing Ago activity in larval muscle cells elicits enhanced branching of nearby tracheal terminal cells in normoxia. This tracheogenic phenotype shows a genetic dependence on sima, which encodes the HIF-1α subunit of the hypoxia-inducible transcription factor dHIF and its target the FGF ligand branchless (bnl), and is enhanced by depletion of the Drosophila Von Hippel Lindau (dVHL) factor, which is a subunit of an oxygen-dependent ubiquitin ligase that degrades Sima/HIF-1α protein in metazoan cells. Genetic reduction of ago results in constitutive expression of some hypoxia-inducible genes in normoxia, increases the sensitivity of others to mild hypoxic stimulus, and enhances the ability of adult flies to recover from hypoxic stupor. As a molecular correlate to these genetic data, we find that Ago physically associates with Sima and restricts Sima levels in vivo. Collectively, these findings identify Ago as a required element of a circuit that suppresses the tracheogenic activity of larval muscle cells by antagonizing the Sima-mediated transcriptional response to hypoxia.

Development of polydimethylsiloxane substrates with tunable elastic modulus to study cell mechanobiology in muscle and nerve

Mechanics is an important component in the regulation of cell shape, proliferation, migration and differentiation during normal homeostasis and disease states. Biomaterials that match the elastic modulus of soft tissues have been effective for studying this cell mechanobiology, but improvements are needed in order to investigate a wider range of physicochemical properties in a controlled manner. We hypothesized that polydimethylsiloxane (PDMS) blends could be used as the basis of a tunable system where the elastic modulus could be adjusted to match most types of soft tissue. To test this we formulated blends of two commercially available PDMS types, Sylgard 527 and Sylgard 184, which enabled us to fabricate substrates with an elastic modulus anywhere from 5 kPa up to 1.72 MPa. This is a three order-of-magnitude range of tunability, exceeding what is possible with other hydrogel and PDMS systems. Uniquely, the elastic modulus can be controlled independently of other materials properties including surface roughness, surface energy and the ability to functionalize the surface by protein adsorption and microcontact printing. For biological validation, PC12 (neuronal inducible-pheochromocytoma cell line) and C2C12 (muscle cell line) were used to demonstrate that these PDMS formulations support cell attachment and growth and that these substrates can be used to probe the mechanosensitivity of various cellular processes including neurite extension and muscle differentiation.

[Oxidative power and intracellular distribution of mitochondria control cell oxygen regime when arterial hypoxemia occurs]

The regulatory impact of the mitochondria spatial distribution and enlargement in their oxidative power qO2 on the tissue oxygenation of skeletal muscle during hypoxia were studied. Investigations were performed by the mathematical modeling of 3D O2 diffusion-reaction in muscle fiber. The oxygen consumption rate VO2 and tissue pO2 were analyzed in response to a decrease in arterial blood oxygen concentration from 19.5 to 10 vol. % at a moderate load (3.5 ml/min per 100 g). The cells with evenly (case 1) and unevenly (case 2) distributed mitochondria were considered. According to calculations due to a rise in mitochondria oxidative power from 3.5 to 6.5 ml/min. per 100 g of tissue it is possible to maintain muscle oxygen V(O2) at constant level of 3.5 ml/min per 100 g despite a decrease in O2 delivery. Minimum value of tissue pO2 was about 0 and an area of hypoxia appeared inside the cell in case 1. But hypoxia disappeared and minimum value of pO2 increased from 0 to 4 mm Hg if mitochondria were distributed unevenly (case 2). It is shown that the possibilities of such regulation were limited and depended on the ratio of "the degree of hypoxemia--the level of oxygen delivery." It was assumed that an increase in mitochondria enzyme activity and mitochondria migration to the places of the greatest oxygen consumption rate can improve oxygen regime in the cells in terms of their adaptation to hypoxia. It is possible that changes in mitochondrial oxidative power and their intracellular redistribution may be considered as a new dimension in regulation of cell oxygen regime.

Microbial light-activatable proton pumps as neuronal inhibitors to functionally dissect neuronal networks in C. elegans

Essentially any behavior in simple and complex animals depends on neuronal network function. Currently, the best-defined system to study neuronal circuits is the nematode Caenorhabditis elegans, as the connectivity of its 302 neurons is exactly known. Individual neurons can be activated by photostimulation of Channelrhodopsin-2 (ChR2) using blue light, allowing to directly probe the importance of a particular neuron for the respective behavioral output of the network under study. In analogy, other excitable cells can be inhibited by expressing Halorhodopsin from Natronomonas pharaonis (NpHR) and subsequent illumination with yellow light. However, inhibiting C. elegans neurons using NpHR is difficult. Recently, proton pumps from various sources were established as valuable alternative hyperpolarizers. Here we show that archaerhodopsin-3 (Arch) from Halorubrum sodomense and a proton pump from the fungus Leptosphaeria maculans (Mac) can be utilized to effectively inhibit excitable cells in C. elegans. Arch is the most powerful hyperpolarizer when illuminated with yellow or green light while the action spectrum of Mac is more blue-shifted, as analyzed by light-evoked behaviors and electrophysiology. This allows these tools to be combined in various ways with ChR2 to analyze different subsets of neurons within a circuit. We exemplify this by means of the polymodal aversive sensory ASH neurons, and the downstream command interneurons to which ASH neurons signal to trigger a reversal followed by a directional turn. Photostimulating ASH and subsequently inhibiting command interneurons using two-color illumination of different body segments, allows investigating temporal aspects of signaling downstream of ASH.

Desmoplakin is important for proper cardiac cell-cell interactions

Normal cardiac function is maintained through dynamic interactions of cardiac cells with each other and with the extracellular matrix. These interactions are important for remodeling during cardiac growth and pathophysiological conditions. However, the precise mechanisms of these interactions remain unclear. In this study we examined the importance of desmoplakin (DSP) in cardiac cell-cell interactions. Cell-cell communication in the heart requires the formation and preservation of cell contacts by cell adhesion junctions called desmosome-like structures. A major protein component of this complex is DSP, which plays a role in linking the cytoskeletal network to the plasma membrane. Our laboratory previously generated a polyclonal antibody (1611) against the detergent soluble fraction of cardiac fibroblast plasma membrane. In attempting to define which proteins 1611 recognizes, we performed two-dimensional electrophoresis and identified DSP as one of the major proteins recognized by 1611. Immunoprecipitation studies demonstrated that 1611 was able to directly pulldown DSP. We also demonstrate that 1611 and anti-DSP antibodies co-localize in whole heart sections. Finally, using a three-dimensional in vitro cell-cell interaction assay, we demonstrate that 1611 can inhibit cell-cell interactions. These data indicate that DSP is an important protein for cell-cell interactions and affects a variety of cellular functions, including cytokine secretion.

[Diastolic dysfunction in the elderly]

Diastolic heart failure, or preserved systolic function, represents around half of all cases of heart failure. It is important to be aware of the mechanisms involved in order to be able to treat it correctly, in an ageing population which sees a higher incidence of this pathology.

Effects of rosiglitazone on the configuration of action potentials and ion currents in canine ventricular cells

BACKGROUND AND PURPOSE

In spite of its widespread clinical application, there is little information on the cellular cardiac effects of the antidiabetic drug rosiglitazone in larger experimental animals. In the present study therefore concentration-dependent effects of rosiglitazone on action potential morphology and the underlying ion currents were studied in dog hearts.

EXPERIMENTAL APPROACH

Standard microelectrode techniques, conventional whole cell patch clamp and action potential voltage clamp techniques were applied in enzymatically dispersed ventricular cells from dog hearts.

KEY RESULTS

At concentrations ≥10 µM rosiglitazone decreased the amplitude of phase-1 repolarization, reduced the maximum velocity of depolarization and caused depression of the plateau potential. These effects developed rapidly and were readily reversible upon washout. Rosiglitazone suppressed several transmembrane ion currents, concentration-dependently, under conventional voltage clamp conditions and altered their kinetic properties. The EC(50) value for this inhibition was 25.2 ± 2.7 µM for the transient outward K(+) current (I(to)), 72.3 ± 9.3 µM for the rapid delayed rectifier K(+) current (I(Kr)) and 82.5 ± 9.4 µM for the L-type Ca(2+) current (I(Ca) ) with Hill coefficients close to unity. The inward rectifier K(+) current (I(K1)) was not affected by rosiglitazone up to concentrations of 100 µM. Suppression of I(to), I(Kr), and I(Ca) was confirmed also under action potential voltage clamp conditions.

CONCLUSIONS AND IMPLICATIONS

Alterations in the densities and kinetic properties of ion currents may carry serious pro-arrhythmic risk in case of overdose with rosiglitazone, especially in patients having multiple cardiovascular risk factors, like elderly diabetic patients.

Cellular and muscular growth patterns during sipunculan development

Sipuncula is a lophotrochozoan taxon with annelid affinities, albeit lacking segmentation of the adult body. Here, we present data on cell proliferation and myogenesis during development of three sipunculan species, Phascolosoma agassizii, Thysanocardia nigra, and Themiste pyroides. The first anlagen of the circular body wall muscles appear simultaneously and not subsequently as in the annelids. At the same time, the rudiments of four longitudinal retractor muscles appear. This supports the notion that four introvert retractors were part of the ancestral sipunculan bodyplan. The longitudinal muscle fibers form a pattern of densely arranged fibers around the retractor muscles, indicating that the latter evolved from modified longitudinal body wall muscles. For a short time interval, the distribution of S-phase mitotic cells shows a metameric pattern in the developing ventral nerve cord during the pelagosphera stage. This pattern disappears close to metamorphic competence. Our findings are congruent with data on sipunculan neurogenesis, as well as with recent molecular analyses that place Sipuncula within Annelida, and thus strongly support a segmental ancestry of Sipuncula.

Distinct endothelium-derived hyperpolarizing factors emerge in vitro and in vivo and are mediated in part via connexin 40-dependent myoendothelial coupling

The endothelium-derived hyperpolarizing factor (EDHF) contributes critically to the regulation of vascular tone. Its dependency on direct signaling through myoendothelial gap junctions composed of connexins (Cx) is controversially discussed. We studied the impact of Cx40 in EDHF-type dilations in vivo and in vitro (wire and pressure myography) in small arteries (A. gracilis) using different Cx40-deficient mouse models. Acetylcholine induced prominent EDHF-type dilations (inhibition of NO synthase and cyclooxygenase) of ≈90% (maximum effect) in wild-type and Cx40-deficient vessels (Cx40-/-) in vitro under isobaric conditions. In contrast, under isometric conditions, EDHF-type relaxations were nearly abrogated in Cx40-/- (9±3%) but only slightly reduced in wild-type vessels (45±4%; P<0.05). Vessels expressing Cx45 instead of Cx40 exhibited similarly reduced relaxations (13±1%), demonstrating that Cx45 cannot replace Cx40 functionally. The necessity of Cx40 in EDHF-type dilations under isometric conditions was verified by the attenuation in vessels being specifically deficient for Cx40 in endothelial cells (Cx40fl:TIE2-Cre: 17±3%; Cx40-floxed controls: 67±6%; P<0.05). Nevertheless, EDHF-type dilations were Cx40 independent when studied isobarically. The EDHF-type dilation in vivo resembled the isobaric situation, being virtually Cx40 independent and similar powerful. Distinct EDHF mechanisms can be distinguished by their Cx40 dependency. A powerful EDHF is present in vivo and in vitro under isobaric conditions but is lacking in wire myography (isometric conditions). Herein, a less potent EDHF depends on Cx40 and may represent signaling through myoendothelial gap junctions. We suggest that distinct EDHFs (even in the same artery) explain partially the controversy on the role of myoendothelial gap junctions in EDHF signaling.

[Prevention of atherosclerosis. Excess of palmitic acid in food--a cause of hypercholesterolemia, inflammatory syndrome, insulin resistance in myocytes, and apoptosis]

Unity of the pathogenesis of atherosclerosis, type 2 diabetes mellitus, and metabolic syndrome gives rise to impaired biological function of adaptation, altered biological function of exotrophy (external feeding) and endoecology ("purity" of the intercellular medium). Biological reactions of inflammation and hydrodynamic pressure, or blood pressure, are in vivo activated to compensate for intercellular debris accumulation by endogenous phlogogens--ligand-free low density lipoproteins (LDL). The biological reactions jointly remove LDL from blood to the intima of elastic type arteries, to interstitial tissue for the local pool of the intravascular medium. The causes of formation of aphysiological LDLs are a preponderance of palmitate-oleate-palmitate triglycerides in the latter and impaired hydrolysis upon exposure to post-heparin lipase to give rise to small, dense LDLs; intimal macrophages utilize the debris only partially and develop atheromatosis from polyenic fatty acids (FA) etherified by cholesterol alcohol. Excess of palmitic saturated fatty acid (sFA) is responsible for the lowered permeability of the plasma membrane, cell death via the mechanism similar to apoptosis. Aphysiological protein palmitoylation (covalent interaction with palmitic sFA) increased the debris accumulation of the intercellular medium and the activity of both biological reactions. Elevated plasma palmitic sFA and its enhanced passive absorption in the form of unetherified FA, as well as high C-reactive protein levels are a cause of insulin resistance. The only way to prevent atherosclerosis in the population is to normalize the biological function of exotrophy when the energy value ratio of FA, proteins and carbohydrates is 1:1:1 and that of sFA, monoenic, and polyenic FA is also 1:1:1. The lower amount of palmitic sFA and the higher concentration of essential polyenic FA, the lower blood levels of cholesterol alcohol and triglycerides are. At the same time, simultaneously activations and the biological function of locomotion are a level of physical activity.

Biological and morphological characterization of in vitro expanded human muscle-derived stem cells

Stem cells are generally characterised as clonogenic and undifferentiated cells with the capacity of self-renewal and plasticity. Over the past few years, the adult stem cells have been derived from various types of tissues including the skeletal muscle. The main goal of the present study was the isolation, in vitro expansion and characterisation of muscle-derived stem cells (MDSCs). Thereby obtained results showed that MDSCs have a fibroblast-like shape with a large nucleus having one to four nucleoli. The cytoplasm was transparent without any signs of vacuolisation. TEM analysis showed an ultrastructure of cells with high proteosynthetic activity. MDSCs had a large and irregular nucleus with variable number of nucleoli. The cytoplasm contained a richly developed and rough endoplasmic reticulum, prominent Golgi apparatus cisterns as well as transport vesicles containing glycogen granules and variable microvilli and filopodia. They expressed alpha-actin and desmin. Results of the phenotypic characterization showed that the analyzed cells were positive for CD29, CD34, CD44, CD90, CD105 and HLA Class I. They did not express CD14, CD45, CD235a, HLA Class II and human fibroblast surface protein. According to these results it should be emphasised that MDSCs after performing the detailed studies focused on their immunological properties and differentiation potential may be used in the cell therapy of many degenerative diseases.

Impact of ageing on muscle cell regeneration

Skeletal muscle regeneration is a coordinate process in which several factors are sequentially activated to maintain and preserve muscle structure and function. The major role in the growth, remodeling and regeneration is played by satellite cells, a quiescent population of myogenic cells that reside between the basal lamina and plasmalemma and are rapidly activated in response to appropriate stimuli. However, in several muscle conditions, including aging, the capacity of skeletal muscle to sustain an efficient regenerative pathway is severely compromised. Nevertheless, if skeletal muscle possesses a stem cell compartment it is not clear why the muscle fails to regenerate under pathological conditions. Either the resident muscle stem cells are too rare or intrinsically incapable of repairing major damage, or perhaps the injured/pathological muscle is a prohibitive environment for stem cell activation and function. Although we lack definitive answers, recent experimental evidences suggest that the mere presence of endogenous stem cells may not be sufficient to guarantee muscle regeneration, and that the presence of appropriate stimuli and factors are necessary to provide a permissive environment that permits stem cell mediated muscle regeneration and repair. In this review we discuss the molecular basis of muscle regeneration and how aging impacts stem cell mediated muscle regeneration and repair.

Transcriptional networks that regulate muscle stem cell function

Muscle stem cells comprise different populations of stem and progenitor cells found in embryonic and adult tissues. A number of signaling and transcriptional networks are responsible for specification and survival of these cell populations and regulation of their behavior during growth and regeneration. Muscle progenitor cells are mostly derived from the somites of developing embryos, while satellite cells are the progenitor cells responsible for the majority of postnatal growth and adult muscle regeneration. In resting muscle, these stem cells are quiescent, but reenter the cell cycle during their activation, whereby they undergo decisions to self-renew, proliferate, or differentiate and fuse into multinucleated myofibers to repair damaged muscle. Regulation of muscle stem cell activity is under the precise control of a number of extrinsic signaling pathways and active transcriptional networks that dictate their behavior, fate, and regenerative potential. Here, we review the networks responsible for these different aspects of muscle stem cell biology and discuss prevalent parallels between mechanisms regulating the activity of embryonic muscle progenitor cells and adult satellite cells.

Depolarization-induced Ca2+ entry preferentially evokes release of large quanta in the developing Xenopus neuromuscular junction

The amplitude histogram of spontaneously occurring miniature synaptic currents (mSCs) is skewed positively at developing Xenopus neuromuscular synapses formed in culture. To test whether the quantal size of nerve-evoked quanta (eSCs) distributes similarly, we compared the amplitude histogram of single quantum eSCs in low external Ca(2+) with that of mSCs and found that nerve stimulation preferentially released large quanta. Depolarization of presynaptic terminals by elevating [K(+)] in the external solution or by direct injection of current through a patch pipette increased the mSC frequency and preferentially, but not exclusively, evoked the release of large quanta, resulting in a second broad peak in the amplitude histogram. Formation of the second peak under these conditions was blocked by the N-type Ca(2+) channel blocker, ω-conotoxin GVIA. In contrast, when the mSC frequency was elevated by thapsigargin- or caffeine-induced mobilization of internal Ca(2+), formation of the second peak did not occur. We conclude that the second peak in the amplitude histogram is generated by Ca(2+) influx through N-type Ca(2+) channels, causing a local elevation of internal Ca(2+). The mSC amplitude in the positively skewed portion of the histogram varied over a wide range. A competitive blocker of acetylcholine (ACh) receptors, d-tubocurarine, reduced the amplitude of smaller mSCs in this range relatively more than that of larger mSCs, suggesting that this variation in the mSC amplitude is due to variable amounts of ACh released from synaptic vesicles. We suggest that Ca(2+) influx through N-type Ca(2+) channels preferentially induces release of vesicles with large ACh content.

[Vitamin D deficiency, left ventricular dysfunction and heart failure]

Epidemiologic data indicate that about one million people worldwide suffer from and should be treated for vitamin D deficiency. The clinical impact of vitamin D deficiency is very high if we consider the pivotal role that this condition plays in determining osteoporosis, fractures, cancers, diabetes, vascular inflammation, which can severely reduce functional capacity, quality of life and may often lead to disability. Vitamin D deficiency is a widely underdiagnosed pathological condition. Although many cardiovascular diseases such as arterial hypertension, myocardial ischemia, diabetic cardiomyopathy and heart failure, may arise from a low vitamin D status, cardiologists do not routinely search for this disease in clinical practice. Vitamin D, indeed, stimulates the synthesis of various contractile proteins and activates crucial intracellular mechanisms that manage calcium metabolism and energy production. These functions can be altered once vitamin D deficiency develops. This review focuses on the relationship between vitamin D deficiency, asymptomatic changes in left ventricular geometry and function, and heart failure syndrome through a recall of the myocardial metabolic processes regulated by vitamin D. The analysis of the available data from the literature leads to raise some questions that, at present, have no answer. Future prospective studies are needed to assess the effect of treatment of vitamin D deficiency on cardiac function.

Computational modelling of the initiation and development of spontaneous intracellular Ca2+ waves in ventricular myocytes

Intracellular Ca(2+) dynamics provides excitation-contraction coupling in cardiac myocytes. Under pathological conditions, spontaneous Ca(2+) release events can lead to intracellular Ca(2+) travelling waves, which can break, giving transitory or persistent intracellular re-entrant Ca(2+) scroll waves. Intracellular Ca(2+) waves can trigger cellular delayed after-depolarizations of membrane potential, which if they occur in a cluster of a few hundred neighbouring myocytes may lead to cardiac arrhythmia. Quantitative prediction of the initiation and propagation of intracellular Ca(2+) waves requires the dynamics of Ca(2+)-induced Ca(2+) release, and the intracellular spatial distribution of Ca(2+) release units (CRUs). The spatial distribution of ryanodine receptor clusters within a few sarcomeres was reconstructed directly from confocal imaging measurements. It was then embedded into a three-dimensional ventricular cell model, with a resting membrane potential and simple stochastic Ca(2+)-induced Ca(2+) release dynamics. Isotropic global Ca(2+) wave propagation can be produced within the anisotropic intracellular architecture, by isotropic local Ca(2+) diffusion, and the branching Z-disc structure providing inter Z-disc pathways for Ca(2+) propagation. The branching Z-disc provides a broader spatial distribution of ryanodine receptor clusters across Z-discs, which reduces the likelihood of wave initiation by spontaneous Ca(2+) releases. Intracellular Ca(2+) dynamics during catecholaminergic polymorphic ventricular tachycardia (CPVT) was simulated phenomenologically by increasing the Ca(2+) sensitivity factor of the CRU, which results in an increased rate of Ca(2+) release events. Flecainide has been shown to prevent arrhythmias in a murine model of CPVT and in patients. The modelled actions of flecainide on the time course of Ca(2+) release events prevented the initiation of Ca(2+) waves.

Subtype identification and functional characterization of ryanodine receptors in rat cerebral artery myocytes

Ryanodine receptors (RyRs) regulate contractility in resistance-size cerebral artery smooth muscle, yet their molecular identity, subcellular location, and phenotype in this tissue remain unknown. Following rat resistance-size cerebral artery myocyte sarcoplasmic reticulum (SR) purification and incorporation into POPE-POPS-POPC (5:3:2; wt/wt) bilayers, unitary conductances of 110 +/- 8, 334 +/- 15, and 441 +/- 27 pS in symmetric 300 mM Cs(+) were usually detected. The most frequent (34/40 bilayers) conductance (334 pS) decreased to Collapse

Key Words

• calcium-release channels
• vascular smooth muscle

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MESH Headings

• Animals
• Cells, Cultured
• Cerebral Arteries/chemistry
• Cerebral Arteries/cytology
• Cerebral Arteries/physiology
• Female
• Male
• Muscle Cells/chemistry
• Muscle Cells/physiology
• Protein Subunits/analysis
• Protein Subunits/physiology
• Rats
• Rats, Sprague-Dawley
• Ryanodine Receptor Calcium Release Channel/analysis
• Ryanodine Receptor Calcium Release Channel/physiology

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Grants

• AA11560 NIAAA NIH HHS
• R01 HL094378 NHLBI NIH HHS
• HL77424 NHLBI NIH HHS
• HL67061 NHLBI NIH HHS
• HL94378 NHLBI NIH HHS

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Affiliation(s)

Thirumalini Vaithianathan Department Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
Damodaran Narayanan
Maria T Asuncion-Chin
Loice H Jeyakumar
Jianxi Liu
Sidney Fleischer
Jonathan H Jaggar
Alejandro M Dopico

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Pathogenesis of sialadenosis: possible role of functionally deficient myoepithelial cells

OBJECTIVES

The pathogenesis of acinar enlargement in sialadenosis is obscure. As myoepithelial cells had been reported to show degenerative changes, we decided to investigate the possible role of functionally deficient myoepithelial cells in the development of sialadenosis.

STUDY DESIGN

This study was a morphometric analysis of glands immunohistochemically stained for CK14, alpha-actin, and Ki67 in 10 cases of sialadenosis and 11 normal parotids.

RESULTS

In sialadenosis, acini were much larger; there was a minor decrease in the density of the distribution of myoepithelial cells stained for CK14 and a major decrease in the density of the distribution and thickness of the myofilament component of myoepithelial cells stained for alpha-actin; and the proliferation of acinar and myoepithelial cells was reduced.

CONCLUSIONS

Our results demonstrate a major loss and thinning of the myofilament component of the myoepithelial cells and thereby a loss of mechanical support for the acini in sialadenosis. This possibly allows acinar cells to expand as secretory granules accumulate intracellularly to produce the great acinar enlargement. This functional myoepithelial insufficiency is possibly a consequence of an autonomic neuropathy secondary to severe metabolic or hormonal disorders.

PTEN inhibition improves muscle regeneration in mice fed a high-fat diet

OBJECTIVE

Mechanisms impairing wound healing in diabetes are poorly understood. To identify mechanisms, we induced insulin resistance by chronically feeding mice a high-fat diet (HFD). We also examined the regulation of phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) during muscle regeneration because augmented IGF-1 signaling can improve muscle regeneration.

RESEARCH DESIGN AND METHODS

Muscle regeneration was induced by cardiotoxin injury, and we evaluated satellite cell activation and muscle maturation in HFD-fed mice. We also measured PIP(3) and the enzymes regulating its level, IRS-1-associated phosphatidylinositol 3-kinase (PI3K) and PTEN. Using primary cultures of muscle, we examined how fatty acids affect PTEN expression and how PTEN knockout influences muscle growth. Mice with muscle-specific PTEN knockout were used to examine how the HFD changes muscle regeneration.

RESULTS

The HFD raised circulating fatty acids and impaired the growth of regenerating myofibers while delaying myofiber maturation and increasing collagen deposition. These changes were independent of impaired proliferation of muscle progenitor or satellite cells but were principally related to increased expression of PTEN, which reduced PIP(3) in muscle. In cultured muscle cells, palmitate directly stimulated PTEN expression and reduced cell growth. Knocking out PTEN restored cell growth. In mice, muscle-specific PTEN knockout improved the defects in muscle repair induced by HFD.

CONCLUSIONS

Insulin resistance impairs muscle regeneration by preventing myofiber maturation. The mechanism involves fatty acid-stimulated PTEN expression, which lowers muscle PIP(3). If similar pathways occur in diabetic patients, therapeutic strategies directed at improving the repair of damaged muscle could include suppression of PTEN activity.

Enhanced invasion of stromal cells from adenomyosis in a three-dimensional coculture model is augmented by the presence of myocytes from affected uteri

OBJECTIVE

To compare endometrial stromal cell invasion from women with and without adenomyosis and the effect of myometrial cells using a three-dimensional coculture.

DESIGN

Case-controlled blinded comparison.

SETTING

University department.

PATIENT(S)

Premenopausal women with and without uterine adenomyosis.

INTERVENTION(S)

Human endometrial stromal and myometrial cells were grown in a three-dimensional coculture with crossover between cells from uteri with and without adenomyosis. Surface-enhanced laser desorption/ionization-time of flight-mass spectrometry proteomic analysis was performed on culture supernatants.

MAIN OUTCOME MEASURE(S)

Depth of stromal cell invasion into collagen matrix and protein expression profiles.

RESULT(S)

The depth of invasion for adenomyosis stromal cells (AS) was statistically significantly higher than controls (CS) whether grown on plain collagen, control muscle (CM), or adenomyosis muscle (AM). Coculture with AM enhanced invasion of both CS and AS. Enhanced invasion by AS was more marked in cocultures with AM than CM. Proteomic analysis identified differences that may account for the invasiveness and also many similarities between secretory products related to the disease status.

CONCLUSION(S)

Enhanced stromal invasion in adenomyosis is influenced by the myometrium in the in vitro coculture model. This suggests that adenomyosis may be a disease of both the endometrial stroma and myometrium.

Endothelium-derived hyperpolarising factors and associated pathways: a synopsis

The term endothelium-derived hyperpolarising factor (EDHF) was introduced in 1987 to describe the hypothetical factor responsible for myocyte hyperpolarisations not associated with nitric oxide (EDRF) or prostacyclin. Two broad categories of EDHF response exist. The classical EDHF pathway is blocked by apamin plus TRAM-34 but not by apamin plus iberiotoxin and is associated with endothelial cell hyperpolarisation. This follows an increase in intracellular [Ca(2+)] and the opening of endothelial SK(Ca) and IK(Ca) channels preferentially located in caveolae and in endothelial cell projections through the internal elastic lamina, respectively. In some vessels, endothelial hyperpolarisations are transmitted to myocytes through myoendothelial gap junctions without involving any EDHF. In others, the K(+) that effluxes through SK(Ca) activates myocytic and endothelial Ba(2+)-sensitive K(IR) channels leading to myocyte hyperpolarisation. K(+) effluxing through IK(Ca) activates ouabain-sensitive Na(+)/K(+)-ATPases generating further myocyte hyperpolarisation. For the classical pathway, the hyperpolarising "factor" involved is the K(+) that effluxes through endothelial K(Ca) channels. During vessel contraction, K(+) efflux through activated myocyte BK(Ca) channels generates intravascular K(+) clouds. These compromise activation of Na(+)/K(+)-ATPases and K(IR) channels by endothelium-derived K(+) and increase the importance of gap junctional electrical coupling in myocyte hyperpolarisations. The second category of EDHF pathway does not require endothelial hyperpolarisation. It involves the endothelial release of factors that include NO, HNO, H(2)O(2) and vasoactive peptides as well as prostacyclin and epoxyeicosatrienoic acids. These hyperpolarise myocytes by opening various populations of myocyte potassium channels, but predominantly BK(Ca) and/or K(ATP), which are sensitive to blockade by iberiotoxin or glibenclamide, respectively.

Application of the principles of systems biology and Wiener's cybernetics for analysis of regulation of energy fluxes in muscle cells in vivo

The mechanisms of regulation of respiration and energy fluxes in the cells are analyzed based on the concepts of systems biology, non-equilibrium steady state kinetics and applications of Wiener’s cybernetic principles of feedback regulation. Under physiological conditions cardiac function is governed by the Frank-Starling law and the main metabolic characteristic of cardiac muscle cells is metabolic homeostasis, when both workload and respiration rate can be changed manifold at constant intracellular level of phosphocreatine and ATP in the cells. This is not observed in skeletal muscles. Controversies in theoretical explanations of these observations are analyzed. Experimental studies of permeabilized fibers from human skeletal muscle vastus lateralis and adult rat cardiomyocytes showed that the respiration rate is always an apparent hyperbolic but not a sigmoid function of ADP concentration. It is our conclusion that realistic explanations of regulation of energy fluxes in muscle cells require systemic approaches including application of the feedback theory of Wiener’s cybernetics in combination with detailed experimental research. Such an analysis reveals the importance of limited permeability of mitochondrial outer membrane for ADP due to interactions of mitochondria with cytoskeleton resulting in quasi-linear dependence of respiration rate on amplitude of cyclic changes in cytoplasmic ADP concentrations. The system of compartmentalized creatine kinase (CK) isoenzymes functionally coupled to ANT and ATPases, and mitochondrial-cytoskeletal interactions separate energy fluxes (mass and energy transfer) from signalling (information transfer) within dissipative metabolic structures – intracellular energetic units (ICEU). Due to the non-equilibrium state of CK reactions, intracellular ATP utilization and mitochondrial ATP regeneration are interconnected by the PCr flux from mitochondria. The feedback regulation of respiration occurring via cyclic fluctuations of cytosolic ADP, Pi and Cr/PCr ensures metabolic stability necessary for normal function of cardiac cells.

Bistable dynamics of cardiac cell models coupled by dynamic gap junctions linked to cardiac memory

In an earlier study, we suggested that adaptive gap junctions (GJs) might be a basis of cardiac memory, a phenomenon which refers to persistent electrophysiological response of the heart to external pacing. Later, it was also shown that the proposed mechanism of adaptation of GJs is consistent with known electrophysiology of GJs. In the present article, we show that a pair of cardiac cell models coupled by dynamic, voltage-sensitive GJs exhibits bistable behavior under certain conditions. Three kinds of cell pairs are considered: (1) a Noble-Noble cell pair that represents adjacent cells in Purkinje network, (2) a pair of DiFranceso-Noble cells that represents adjacent SA nodal cells, and (3) a model of Noble cell coupled to Luo-Rudy cell model, which represents an interacting pair of a Purkinje fiber and a ventricular myocyte. Bistability is demonstrated in all the three cases. We suggest that this bistability might be an underlying factor behind cardiac memory. Focused analysis of a pair of Noble cell models showed that bistability is obtained only when the properties of GJs "match" with the properties of the pair of cells that is coupled by the GJs. This novel notion of match between GJs and cardiac cell types might give an insight into specialized distributions of various connexin proteins in cardiac tissue.

Insulin resistance is associated with higher intramyocellular triglycerides in type I but not type II myocytes concomitant with higher ceramide content

OBJECTIVE

We tested the primary hypotheses that sphingolipid and diacylglycerol (DAG) content is higher within insulin-resistant muscle and that the association between intramyocellular triglycerides (IMTG) and insulin resistance is muscle fiber type specific.

RESEARCH DESIGN AND METHODS

A nested case-control analysis was conducted in 22 obese (BMI >30 kg/m(2)) women who were classified as insulin-resistant (IR; n = 12) or insulin-sensitive (IS; n = 10), determined by hyperinsulinemic-euglycemic clamp (>30% greater in IS compared with IR, P < 0.01). Sphingolipid and DAG content was determined by high-performance liquid chromatography-tandem mass spectrometry. Fiber type-specific IMTG content was histologically determined. Gene expression was determined by quantitative PCR.

RESULTS

Total (555 +/- 53 vs. 293 +/- 54 pmol/mg protein, P = 0.004), saturated (361 +/- 29 vs. 179 +/- 34 pmol/mg protein, P = 0.001), and unsaturated (198 +/- 29 vs. 114 +/- 21 pmol/mg protein, P = 0.034) ceramides were higher in IR compared with IS. DAG concentrations, however, were similar. IMTG content within type I myocytes, but not type II myocytes, was higher in IR compared with IS subjects (P = 0.005). Insulin sensitivity was negatively correlated with IMTG within type I myocytes (R = -0.51, P = 0.026), but not with IMTG within type II myocytes. The proportion of type I myocytes was lower (41 vs. 59%, P < 0.01) in IR subjects. Several genes involved in lipid droplet and fatty acid metabolism were differentially expressed in IR compared with IS subjects.

CONCLUSIONS

Human skeletal muscle insulin resistance is related to greater IMTG content in type I but not type II myocytes, to greater ceramide content, and to alterations in gene expression associated with lipid metabolism.

Specificities of atrial electrophysiology: Clues to a better understanding of cardiac function and the mechanisms of arrhythmias

The electrical properties of the atria and ventricles differ in several aspects reflecting the distinct role of the atria in cardiac physiology. The study of atrial electrophysiology had greatly contributed to the understanding of the mechanisms of atrial fibrillation (AF). Only the atrial L-type calcium current is regulated by serotonine or, under basal condition, by phosphodiesterases. These distinct regulations can contribute to I(Ca) down-regulation observed during AF, which is an important determinant of action potential refractory period shortening. The voltage-gated potassium current, I(Kur), has a prominent role in the repolarization of the atrial but not ventricular AP. In many species, this current is based on the functional expression of K(V)1.5 channels, which might represent a specific therapeutic target for AF. Mechanisms regulating the trafficking of K(V)1.5 channels to the plasma membrane are being actively investigated. The resting potential of atrial myocytes is maintained by various inward rectifier currents which differ with ventricle currents by a reduced density of I(K1), the presence of a constitutively active I(KACh) and distinct regulation of I(KATP). Stretch-sensitive or mechanosensitive ion channels are particularly active in atrial myocytes and are involved in the secretion of the natriuretic peptide. Integration of knowledge on electrical properties of atrial myocytes in comprehensive schemas is now necessary for a better understanding of the physiology of atria and the mechanisms of AF.

The BK channel accessory beta1 subunit determines alcohol-induced cerebrovascular constriction

Ethanol-induced inhibition of myocyte large conductance, calcium- and voltage-gated potassium (BK) current causes cerebrovascular constriction, yet the molecular targets mediating EtOH action remain unknown. Using BK channel-forming (cbv1) subunits from cerebral artery myocytes, we demonstrate that EtOH potentiates and inhibits current at Ca(i)(2+) lower and higher than approximately 15 microM, respectively. By increasing cbv1's apparent Ca(i)(2+)-sensitivity, accessory BK beta(1) subunits shift the activation-to-inhibition crossover of EtOH action to <3 microM Ca(i)(2+), with consequent inhibition of current under conditions found during myocyte contraction. Knocking-down KCNMB1 suppresses EtOH-reduction of arterial myocyte BK current and vessel diameter. Therefore, BK beta(1) is the molecular effector of alcohol-induced BK current inhibition and cerebrovascular constriction.

Dual role of interleukin-6 in regulating insulin sensitivity in murine skeletal muscle

OBJECTIVE

Cytokines are elevated in various insulin-resistant states, including type 2 diabetes and obesity, although the contribution of interleukin-6 (IL-6) in the induction of these diseases is controversial.

RESEARCH DESIGN AND METHODS

We analyzed the impact of IL-6 on insulin action in murine primary myocytes, skeletal muscle cell lines, and mice (wild type and protein-tyrosine phosphatase 1B [PTP1B] deficient).

RESULTS

IL-6 per se increased glucose uptake by activating serine/threonine protein kinase 11 (LKB1)/AMP-activated protein kinase/protein kinase B substrate of 160 kDa (AS160) pathway. A dual effect on insulin action was observed when myotubes and mice were exposed to this cytokine: additive with short-term insulin (increased glucose uptake and systemic insulin sensitivity) but chronic exposure produced insulin resistance (impaired GLUT4 translocation to plasma membrane and defects in insulin signaling at the insulin receptor substrate 1 [IRS-1] level). Three mechanisms seem to operate in IL-6-induced insulin resistance: activation of c-Jun NH(2)-terminal kinase 1/2 (JNK1/2), accumulation of suppressor of cytokine signaling 3 (socs3) mRNA, and an increase in PTP1B activity. Accordingly, silencing JNK1/2 with either small interfering RNA or chemical inhibitors impaired phosphorylation of IRS-1 (Ser307), restored insulin signaling, and normalized insulin-induced glucose uptake in myotubes. When using a pharmacological approach, liver X receptor agonists overcome IL-6-induced insulin resistance by producing downregulation of socs3 and ptp1b gene expression. Finally, the lack of PTP1B confers protection against IL-6-induced insulin resistance in skeletal muscle in vitro and in vivo, in agreement with the protection against the IL-6 hyperglycemic effect observed on glucose and insulin tolerance tests in adult male mice.

CONCLUSIONS

These findings indicate the important role of IL-6 in the pathogenesis of insulin resistance and further implicate PTP1B as a potential therapeutic target in the treatment of type 2 diabetes.

Ion channel regulation of intracellular calcium and airway smooth muscle function

Airway hyper-responsiveness associated with asthma is mediated by airway smooth muscle cells (SMCs) and has a complicated etiology involving increases in cell contraction and proliferation and the secretion of inflammatory mediators. Although these pathological changes are diverse, a common feature associated with their regulation is a change in intracellular Ca(2+) concentration ([Ca(2+)](i)). Because the [Ca(2+)](i) itself is a function of the activity and expression of a variety of ion channels, in both the plasma membrane and sarcoplasmic reticulum of the SMC, the modification of this ion channel activity may predispose airway SMCs to hyper-responsiveness. Our objective is to review how ion channels determine the [Ca(2+)](i) and influence the function of airway SMCs and emphasize the potential of ion channels as sites for therapeutic approaches to asthma.

Mesencephalic astrocyte-derived neurotrophic factor is an ischemia-inducible secreted endoplasmic reticulum stress response protein in the heart

The endoplasmic reticulum (ER) stress response (ERSR) is activated when folding of nascent proteins in the ER lumen is impeded. Myocardial ischemia was recently shown to activate the ERSR; however, the role of this complex signaling system in the heart is not well understood. ER stress activates the transcription factor ATF6, which induces expression of proteins targeted to the ER, where they restore protein folding, thus fostering cytoprotection. We previously developed a transgenic mouse line that expresses a conditionally activated form of ATF6 in the heart. In this mouse line, ATF6 activation decreased ischemic damage in an ex vivo model of myocardial ischemia/reperfusion and induced numerous genes, including mesencephalic astrocyte-derived neurotrophic factor (MANF). In the present study, MANF expression was shown to be induced in cardiac myocytes and in other cell types in the hearts of mice subjected to in vivo myocardial infarction. Additionally, simulated ischemia induced MANF in an ATF6-dependent manner in neonatal rat ventricular myocyte cultures. In contrast to many other ER-resident ERSR proteins, MANF lacks a canonical ER-retention sequence, consistent with our finding that MANF was readily secreted from cultured cardiac myocytes. Knockdown of endogenous MANF with micro-RNA increased cell death upon simulated ischemia/reperfusion, whereas addition of recombinant MANF to media protected cultured cardiac myocytes from simulated ischemia/reperfusion-mediated death. Thus, a possible function of the ERSR in the heart is the ischemia-mediated induction of secreted proteins, such as MANF, that can function in an autocrine/paracrine manner to modulate myocardial damage from ER stresses, including ischemia.

Characteristics of signalling properties mediated by long-acting insulin analogue glargine and detemir in target cells of insulin

Glargine and detemir are long-acting human insulin analogues with a smooth peakless profile of action. Although their binding affinities to the insulin receptor have been studied, little is known about the subsequent signalling properties activated after the binding. We directly compared intracellular signalling properties of them in various cultured cells. Regarding the metabolic signalling, glargine and insulin-induced comparable dose-dependent phosphorylation of insulin receptor, IRS-1, Akt, and GSK3, whereas detemir-induced kinetics were markedly lower in 3T3-L1 adipocytes and L6 myocytes. A similar pattern of phosphorylation induction was observed in primary hepatocytes and vascular smooth muscle cells (VSMCs). Because of the binding of detemir to albumin with high affinity, the phosphorylation kinetics and glucose uptake of detemir, but not glargine, decreased with increasing concentrations of BSA. Concerning the mitogenic properties, glargine and insulin-induced comparable dose-dependent phosphorylation of MAP kinase (MAPK) and 5-bromo-2'-deoxyuridine (BrdU) incorporation. Detemir-induced phosphorylation of MAPK was apparently reduced, whereas it stimulated BrdU incorporation with relatively similar dose-dependent manner in VSMCs. These results indicate that glargine has comparable properties to human insulin in metabolic and mitogenic signalling and action. In contrast, detemir-induced metabolic signaling is less potent in all cell types studied, and is reduced further by increasing concentrations of albumin.

Intrauterine cardiomyopathy and cardiac mitochondrial proliferation in mitochondrial trifunctional protein (TFP) deficiency

Because of a switch in energy-producing substrate utilization from glucose in the fetal period to fatty acids postnatally, intrauterine morbidity of fatty acid oxidation defects has widely been denied. We report the intrauterine development of severe cardiomyopathy in a child with mitochondrial trifunctional protein deficiency after 27 weeks of gestation. The child was born at 31 weeks of gestation and died on day 3 of life. Severe cardiac mitochondrial proliferation was observed. Molecular analysis of both TFP genes was performed and confirmed a homozygous mutation in the TFP alpha-subunit introducing a stop codon at amino acid position 256 (g.871C>T, p.R256X). Despite severe intrauterine decompensation in our patient, no HELLP-syndrome or acute fatty liver of pregnancy was observed in the mother. In the pathogenesis of maternal HELLP-syndrome, toxic effects of accumulating long-chain hydroxy-acyl-CoAs or long-chain hydroxy-acylcarnitines are suspected. In our patient, acylcarnitine analysis on day 2 of life during severest metabolic decompensation did not reveal massive accumulation of long-chain hydroxy-acylcarnitines in blood, suggesting other pathogenic factors than toxic effects. The most important pathogenic mechanism for the development of intrauterine cardiomyopathy appears to be significant cardiac energy deficiency. In conclusion, our report implicates that fatty acid oxidation does play a significant role during intrauterine development with special regard to the heart. Severe cardiac mitochondrial proliferation in TFP deficiency suggests pathophysiologically relevant energy deficiency in this condition.

[Molecular effects of new calcium antagonists: is the principle of parcimony out of place?]

The calcium (Ca2+) channel antagonists (CCA) are used successfully in the treatment of hypertension and angina pectoris. Their mode of action is to decrease Ca2+ entry in the vascular smooth muscle cells. Their molecular targets are voltage activated Ca2+ channels (VACC), especially the L-type (VACC-L). This review examines the role of the VACC-L and of the T-type (VACC-T) in vascular physiology and hypertension. The molecular mechanisms at the base of the vascular selectivity of CCA are presented with, in filigree, the concern of trying to understand the effect of recently developed molecules. In particular, we will examine the ideas having recently emerged concerning the mode of action of last generation dihydropyridines (DHPs) stripped of some of the undesirable effects of prototypes AC considered as highly specific of the VACC-L. These properties could result, in particular, from their effects on the VACC-T, which could occur in addition to those classically observed on the VACC-L.

Progestin-regulated luminal cell and myoepithelial cell-specific responses in mammary organoid culture

Normal mammary gland development requires the coordinated proliferation and morphogenesis of both mammary luminal epithelial cells (LECs) and myoepithelial cells (MECs). Cell proliferation in cultured mammary organoids containing both LECs and MECs is not increased by progestin (R5020) or 17beta-estradiol (E2) alone or R5020+E2 but is increased by E2-regulated, mammary stroma-derived Hepatocyte growth factor (HGF) and further increased by HGF+R5020. We investigated the effects of HGF and/or R5020 on morphology and LEC- and MEC-specific in vitro proliferation in organoids. HGF-induced tubulogenesis was initiated and carried out by LECs starting with cellular extensions, followed by the formation of chains and cords, and culminating in tubule formation. MECs did not appear to have an active role in this process. Whereas HGF by itself caused maximal proliferation of LECs, HGF+R5020 produced a synergistic and specific increase in MEC proliferation. Because only LECs expressed progesterone receptors (PRs), we investigated the role of receptor activator of nuclear factor-kappaB ligand (RANKL), a progestin-induced paracrine factor, in mediating increased MEC proliferation. Quantitative RT-PCR showed that RANKL mRNA was induced by R5020 or HGF+R5020 and RANKL protein colocalized with PRs in LECs. The increased proliferation of MECs in response to HGF+R5020 could be blocked by neutralizing antibody to RANKL and reproduced by treatment with HGF plus exogenous RANKL in place of R5020. Neither R5020, nor exogenously administered RANKL increased proliferation of LECs. These results led us to conclude that RANKL, induced by progestin in PR-positive cells, is secreted and interacts with HGF to specifically increase proliferation of PR-negative MECs.

Inhibition of non-Ras protein farnesylation reduces in-stent restenosis

Ras has a key role in relation to cell proliferation, survival and migration and requires farnesylation for full activity. The effects of a Ras farnesyl transferase inhibitor, FPT III on human atherosclerotic vascular smooth muscle (VSM) cells proliferation and p42/p44 mitogen-activated protein kinase (p42/p44 MAPK) activity was measured. In addition the ability of FPT III to modify the development of neointimal growth was tested in cultured human arteries and in a rabbit model of in-stent restenosis. In human VSM cells FPT III (25 microM) inhibited FCS-stimulated cell proliferation through a ras-dependent mechanism (after 18 h exposure) and also a novel ras-independent mechanism (following 15 min exposure). FPT III incubation (18 h) inhibited platelet-derived growth factor (PDGF)-stimulated p42/p44 MAPK activation and p21 Ras membrane localization, whereas 15 min incubation had no effect on the activation of p42/p44 MAPK in response to PDGF (added at 18 h) or on membrane p21 Ras localization (measured at 18 h). In cultured human atherosclerotic arteries, the presence of 25 microM FPT III significantly reduced neointimal growth. In vivo, 15 min local infusion of 25 microM FPT III significantly reduced in-stent restenosis 28 days later without affecting vascular function in normal rabbit artery. This study demonstrates that brief administration of a farnesyl transferase inhibitor reduced in-stent restenosis in a rabbit model without deleterious effects on vascular function or endothelial regrowth. Acute application of FPT III was found to act through a novel mechanism to inhibit smooth muscle cell proliferation via a non-ras pathway, which may contribute to the prevention of in-stent restenosis.

Porcine peroxisome proliferator-activated receptor gamma induces transdifferentiation of myocytes into adipocytes

Peroxisome proliferator-activated receptor gamma2 (PPARgamma) is a nuclear transcription factor that regulates adipocyte differentiation and lipogenic genes during adipogenesis. The activity of rodent PPARgamma is regulated by phosphorylation of serine 112. The current experiment was designed to study the ability of porcine PPARgamma to stimulate transdifferentiation of myoblasts to adipocytes by overexpressing wild-type PPARgamma or mutated PPARgamma (serine 112 was mutated to alanine) in mouse myoblast cells. The expression of adipogenic marker genes (adipocyte fatty acid binding protein, lipoprotein lipase, and glycerol-3 phosphate dehydrogenase) in cells stably expressing mutated porcine PPARgamma was greater than in cells with wild-type PPARgamma, indicating that the mutated PPARgamma has greater adipogenic capability than the wild-type PPARgamma. Under treatment with a ligand, both wild-type and mutant porcine PPARgamma-expressing C2C12 myoblasts differentiated into adipocytes in 10 d. The expression of myogenic marker genes (myogenin, myogenic regulatory factor-4) was suppressed in cells transfected with the mutated PPARgamma or wild-type PPARgamma. Moreover, wild-type and mutant PPARgamma were able to inhibit myogenesis without addition of a ligand. Our results suggest that porcine wild-type PPARgamma and mutated PPARgamma can both convert myoblast cells into adipocytes, and also that the ability to transdifferentiate was greater in cells containing the mutated PPARgamma than in cells containing the wild-type PPARgamma. Therefore, the existence of serine 112 in PPARgamma may have a role in regulating adipocyte differentiation.

Changes in T-type calcium channel and its subtypes in overactive detrusor of the rats with partial bladder outflow obstruction

AIMS

To investigate the activity of the T-type calcium channel (TCC) and the expression of its subtypes in overactive detrusor (OD) myocytes in rats after partial bladder outflow obstruction (PBOO).

METHODS

Thirteen male Wistar rats with OD after PBOO (OD group) and eight sham-operated rats (control group) were studied. The two groups were compared regarding the expression of TCC subtype genes by reverse transcription-polymerase chain reaction (RT-PCR) and the TCC kinetics and cell action potential by whole-cell patch-clamp.

RESULTS

The time course and density of the current were significantly higher in the OD cells than those in the control detrusor. Whole-cell patch-clamp analysis showed that the activation of TCCs in detrusor myocytes in the OD group was faster than the control group, but inactivation was almost the same in both groups, suggesting a significant enhancement of the Ca(2+) "window" current in the OD group. Patch-clamp recording of action potentials in the OD cells indicated an increase in excitability and a decrease in the repolarization interval. RT-PCR assay showed an abnormal expression of alpha1G subtype in the OD cells.

CONCLUSIONS

TCCs could be one of the crucial factors for the abnormal excitation in OD cells. The development of OD after PBOO presumably relates to the increase in TCC current in the bladder cells, the enhancement of the Ca(2+) "window" current for Ca(2+) inflow, the prolongation of the intracellular calcium oscillations, and the acceleration of the cell depolarization.

Imaging of tissue structures and mechanical analysis

The anatomical structure of biological tissues and their mechanical function are closely related. Forces have a decisive influence on growth and remodeling of tissues; furthermore, intra- and extravascular transport processes are mostly controlled mechanically and the metabolism of many cells is influenced by flow-induced shear stresses. In order to facilitate a mechanical analysis of biological systems, the anatomical tissue structure has to be determined with the aid of 3D imaging methods. In particular, the anisotropic fibrous architecture of the organs involved along with appropriate constitutive relations have to be considered. Examples of structure-(mechanical) function relationships are discussed in an exemplary fashion for bone, the heart and the uterus. The behavior of biological structures under unphysiological loading situations, such as they may occur in accidents, is addressed.

Inward rectifier K(+) currents and Kir2.1 expression in renal afferent and efferent arterioles

The afferent and efferent arterioles regulate the inflow and outflow resistance of the glomerulus, acting in concert to control the glomerular capillary pressure and glomerular filtration rate. The myocytes of these two vessels are remarkably different, especially regarding electromechanical coupling. This study investigated the expression and function of inward rectifier K(+) channels in these two vessels using perfused hydronephrotic rat kidneys and arterioles and myocytes isolated from normal rat kidneys. In afferent arterioles pre-constricted with angiotensin II, elevating [K(+)](0) from 5 to 15 mmol/L induced hyperpolarization (-27 +/- 2 to 41 +/- 3 mV) and vasodilation (6.6 +/- 0.9 to 13.1 +/- 0.6 microm). This manipulation also attenuated angiotensin II-induced Ca(2+) signaling, an effect blocked by 100 micromol/LBa(2+). By contrast, elevating [K(+)](o) did not alter angiotensin II-induced Ca2(+) signaling or vasoconstriction in efferent arterioles, even though a significant hyperpolarization was observed (from -30 +/- 1 to 37 +/- 3 mV, P = 0.003). Both vessels expressed mRNA for Kir2.1 and exhibited anti-Kir2.1 antibody labeling.Patch-clamp measurements revealed prominent inwardly rectifying and Ba(2+)-sensitive currents in afferent and efferent arteriolar myocytes. Our findings indicate that both arterioles express an inward rectifier K(+) current, but that modulation of this current alters responsiveness of only the a different arteriole. The expression of Kir in the efferent arteriole, a resistance vessel whose tone is not affected by membrane potential, is intriguing and may suggest a novel function of this channel in the renal microcirculation.

Adipogenesis of bovine perimuscular preadipocytes

In this study, non-transformed progeny adipofibroblasts, derived from mature adipocyte dedifferentiation, was used as a novel in vitro model to study adipogenic gene expression in cattle. Adipofibroblasts from dedifferentiated mature perimuscular fat (PMF) tissue were cultured with differentiation stimulants until the cells exhibited morphological differentiation. Treated cells were harvested from day 2 to 16 for RNA extraction, whereas control cells were cultured without addition of stimulants. Results from time course gene expression assays by quantitative real-time PCR revealed that peroxisome proliferator-activated receptor gamma (PPAR-gamma), sterol regulatory element binding protein 1 (SREBP-1) and their six down-stream genes were co-expressed at day 2 post-differentiation induction. When compared to other adipogenesis culture systems, the adipogenic gene expression of bovine PMF adipofibroblasts culture was different, especially to the rodent model. Collectively, these results demonstrated PPAR-gamma and SREBP-1 cooperatively play a key role to regulate the re-differentiation of bovine adipofibroblasts, during early conversion stages in vitro.

Expression profiles of the genes associated with the myocyte differentiation during rat liver regeneration

Myocytes are important parts of tissues and organs. To study the effects of myocyte differentiation-related genes on rat liver regeneration (LR) at transcriptional level, we obtained these genes through collecting the database data and retrieving the pertinent thesis, and detected the expression profiles of above-mentioned genes during LR using the Rat Genome 230 2.0 array. LR-associated genes were identified by comparing the discrepancy in gene expression changes between partial hepatectomy (PH) group and sham-operation (SO) group, by which 52 LR-associated genes were confirmed. They were classified into 5 groups based on time relevance, including 0.5-1h; 2-12h; 16h, 30h, 42h, 96h; 18-24h, 36h, 48-60h; 66-72h,120-168h, in which the numbers of up-regulation and down-regulation genes were 8 and 10, 24 and 8, 21 and 24, 53 and 64, 28 and 36, respectively. Among these genes, the total 143 times of up-regulation and 136 times of down-regulation, as well as their 8 expression patterns displayed diversity and complexity of the genes associated with the myocyte differentiation. It was inferred that the differentiation of myoblasts and smooth muscle cells were enhanced during LR and the genes associated with the differentiation of skeletal muscle cells and cardiac muscle cells participated in the cellular physiological and biochemical activities of LR.