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Biomedical subjects

M C Schaub

Publications and source records attributed to M C Schaub.

At least 19 recordsLinked to original sources
PubMed2005

Anaesthetic preconditioning but not postconditioning prevents early activation of the deleterious cardiac remodelling programme: evidence of opposing genomic responses in cardioprotection by pre- and postconditioning.

BACKGROUND: Anaesthetic preconditioning (A_PreC) and postconditioning (A_PostC) both provide protection against ischaemia-reperfusion in the heart. However, post-ischaemic gene responses may differ between the two therapeutic strategies. METHODS: Isolated perfused rat hearts were exposed to 40 min test ischaemia followed by 3 h reperfusion and used to determine transcriptional changes in response to A_PreC and A_PostC. A_PreC was induced by 15 min of isoflurane 2.1 vol% followed by 10 min of washout, and A_PostC was induced by 15 min of isoflurane 2.1 vol% administered at the onset of reperfusion. Untreated hearts served as ischaemic control (ISCH). Coupled-two way clustering (CTWC) and principal component analysis (PCA) were used to identify gene expression patterns. RESULTS: A_PreC (7[sd 1]%) and A_PostC (6[2]%) produced a similar decrease in infarct size (ISCH 36[1]%, P<0.05). However, post-ischaemic genomic reprogramming was completely different. Few genes were jointly regulated (2.1 per thousand of upregulated genes and 1.3% of downregulated genes). Eight stable gene clusters including three subclusters emerged from CTWC and were related to inflammation, signalling, ion channels, transcription factors, long interspersed repetitive DNA, heat shock response and remodelling. Two stable sample clusters were identified for postconditioned hearts (first cluster) and for all other protocols (second cluster), emphasizing the unique cardiac phenotype elicited by A_PostC. PCA revealed a close genomic relationship between A_PreC and non-ischaemic healthy myocardium. CONCLUSIONS: A_PreC, but not A_PostC, induces a post-ischaemic gene expression profile similar to virgin myocardium and prevents activation of the deleterious cardiac remodelling programme. Hence A_PreC and A_PostC are not interchangeable with respect to their molecular outcome in the heart.

Anesthetics↗
PubMed2005

[Strategies for perioperative sympatho-modulation].

Despite the growing evidence for the efficacy of different sympatho-modulatory therapies to lower perioperative cardiac morbidity and mortality, such therapeutic strategies are rather infrequently used in daily clinical practice. Most physicians involved in perioperative medicine are aware of the increasing literature related to this topic, but only few comply with current clinical practice guidelines even in the absence of contraindications. This review discusses possible explanations for this reluctance and again summarizes the basic and clinical principles of current sympatho-modulatory therapies including alpha(2)-agonism, beta-adrenergic antagonism, and regional anesthetic techniques in modern anesthetic practice. In addition, the emerging perioperative concept of a patient-tailored individualized pharmacotherapy based on "gene profiling", particularly the adrenergic polymorphisms, is discussed.

Adrenergic alpha-Agonists↗
PubMed2004

Cellular mechanisms in sympatho-modulation of the heart.

Cardiovascular function relies on complex servo-controlled regulation mechanisms that involve both fast-acting feedback responses and long-lasting adaptations affecting the gene expression. The adrenergic system, with its specific receptor subtypes and intracellular signalling cascades provides the major regulatory system, while the parasympathetic system plays a minor role. At the molecular level, Ca(2+) acts as the general signal trigger for the majority of cell activities including contraction, metabolism and growth. During recent years, important new results have emerged allowing an integrated view of how the multifarious Ca(2+)-signalling mechanisms transmit adrenergic impulses to intracellular target sites. These insights into cellular and molecular mechanisms are pivotal in improving pharmacological control of the sympathetic responses to surgical trauma and perioperative stress. They are examined in detail in this review, with particular emphasis being given to the differences in intracellular signalling between cardiomyocytes and vascular smooth muscle cells.

Calcium↗
PubMed2004

The role of utrophin and Dp71 for assembly of different dystrophin-associated protein complexes (DPCs) in the choroid plexus and microvasculature of the brain.

In the brain, utrophin is present in the choroid plexus epithelium and vascular endothelial cells, whereas the short C-terminal isoform of dystrophin (Dp71) is localized in the glial end-feet surrounding blood vessels. Both proteins serve as anchors for the so-called dystrophin-associated protein complex (DPC), composed of isoforms of syntrophin, dystroglycan and dystrobrevin. Numerous transporter proteins and channels have a polarized distribution in vascular endothelial cells and in glial end-feet, suggesting an association with the DPC. We investigated the composition and localization of the DPC in dependence on the anchoring proteins in mice lacking either utrophin (utrophin0/0) or dystrophin isoforms (mdx3Cv). Three distinct complexes were identified: (i) associated with utrophin in the basolateral membrane of the choroid plexus epithelium, (ii) associated with utrophin in vascular endothelial cells, and (iii) associated with Dp71 in the glial end-feet. Upon ablation of utrophin or Dp71, the corresponding DPCs were disrupted and no compensation of the missing protein by its homologue was observed. Association of the water channel aquaporin 4 with the glial DPC likewise was disrupted in mdx3Cv mice. These results demonstrate the essential role of utrophin and Dp71 for assembly of the DPC and suggest that these proteins contribute to the proper functioning of the cerebrospinal fluid and blood-brain barriers.

Animals↗
PubMed2003

Anaesthetics and cardiac preconditioning. Part I. Signalling and cytoprotective mechanisms.

Cardiac preconditioning represents the most potent and consistently reproducible method of rescuing heart tissue from undergoing irreversible ischaemic damage. Major milestones regarding the elucidation of this phenomenon have been passed in the last two decades. The signalling and amplification cascades from the preconditioning stimulus, be it ischaemic or pharmacological, to the putative end-effectors, including the mechanisms involved in cellular protection, are discussed in this review. Volatile anaesthetics and opioids effectively elicit pharmacological preconditioning. Anaesthetic-induced preconditioning and ischaemic preconditioning share many fundamental steps, including activation of G-protein-coupled receptors, multiple protein kinases and ATP-sensitive potassium channels (K(ATP) channels). Volatile anaesthetics prime the activation of the sarcolemmal and mitochondrial K(ATP) channels, the putative end-effectors of preconditioning, by stimulation of adenosine receptors and subsequent activation of protein kinase C (PKC) and by increased formation of nitric oxide and free oxygen radicals. In the case of desflurane, stimulation of alpha- and beta-adrenergic receptors may also be of importance. Similarly, opioids activate delta- and kappa-opioid receptors, and this also leads to PKC activation. Activated PKC acts as an amplifier of the preconditioning stimulus and stabilizes, by phosphorylation, the open state of the mitochondrial K(ATP) channel (the main end-effector in anaesthetic preconditioning) and the sarcolemmal K(ATP) channel. The opening of K(ATP) channels ultimately elicits cytoprotection by decreasing cytosolic and mitochondrial Ca(2+) overload.

Adaptation, Physiological↗
PubMed2003

Anaesthetics and cardiac preconditioning. Part II. Clinical implications.

There is compelling evidence that preconditioning occurs in humans. Experimental studies with potential clinical implications as well as clinical studies evaluating ischaemic, pharmacological and anaesthetic cardiac preconditioning in the perioperative setting are reviewed. These studies reveal promising results. However, there are conflicting reports on the efficacy of preconditioning in the diseased and aged myocardium. In addition, many anaesthetics and a significant number of perioperatively administered drugs affect the activity of cardiac sarcolemmal and mitochondrial K(ATP) channels, the end-effectors of cardiac preconditioning, and thereby markedly modulate preconditioning effects in myocardial tissue. Although these modulatory effects on K(ATP) channels have been investigated almost exclusively in laboratory investigations, they may have potential implications in clinical medicine. Important questions regarding the clinical utility and applicability of perioperative cardiac preconditioning remain unresolved and need more experimental work and randomized controlled clinical trials.

Adaptation, Physiological↗
PubMed2002

Modulation of beta-adrenergic receptor subtype activities in perioperative medicine: mechanisms and sites of action.

This review focuses on the mechanisms and sites of action underlying beta-adrenergic antagonism in perioperative medicine. A large body of knowledge has recently emerged from basic and clinical research concerning the mechanisms of the life-saving effects of beta-adrenergic antagonists (beta-AAs) in high-risk cardiac patients. This article re-emphasizes the mechanisms underlying beta-adrenergic antagonism and also illuminates novel rationales behind the use of perioperative beta-AAs from a biological point of view. Particularly, it delineates new concepts of beta-adrenergic signal transduction emerging from transgenic animal models. The role of the different characteristics of various beta-AAs is discussed, and evidence will be presented for the selection of one specific agent over another on the basis of individual drug profiles in defined clinical situations. The salutary effects of beta-AAs on the cardiovascular system will be described at the cellular and molecular levels. Beta-AAs exhibit many effects beyond a reduction in heart rate, which are less known by perioperative physicians but equally desirable in the perioperative care of high-risk cardiac patients. These include effects on core components of an anaesthetic regimen, such as analgesia, hypnosis, and memory function. Despite overwhelming evidence of benefit, beta-AAs are currently under-utilized in the perioperative period because of concerns of potential adverse effects and toxicity. The effects of acute administration of beta-AAs on cardiac function in the compromised patient and strategies to counteract potential adverse effects will be discussed in detail. This may help to overcome barriers to the initiation of perioperative treatment with beta-AAs in a larger number of high-risk cardiac patients undergoing surgery.

Adrenergic beta-Antagonists↗
PubMed2001

Alterations in dystrophin and utrophin expression parallel the reorganization of GABAergic synapses in a mouse model of temporal lobe epilepsy.

Dystrophin and its autosomal homologue utrophin are coexpressed in muscle cells, and utrophin is functionally able to replace dystrophin in models of Duchenne muscular dystrophy. In brain, the two proteins are expressed differentially, suggesting distinct functional roles. Dystrophin is associated with postsynaptic GABA(A) receptors in hippocampus, cortex and cerebellum, whereas utrophin is present extrasynaptically, notably in large brainstem neurons. Here, the regulation of dystrophin and utrophin was investigated in a model of temporal lobe epilepsy. Adult mice were injected unilaterally with kainic acid into the dorsal hippocampus to induce loss of pyramidal cells and hypertrophy of dentate gyrus (DG) granule cells, as described (Suzuki, F., Junier, M.P., Guilhem, D., Sorensen, J.C. & Onteniente, B. (1995) Neuroscience, 64, 665--674.). These morphological changes were associated with an increase in postsynaptic GABA(A)-receptors in the ipsilateral DG, as demonstrated by a parallel increase in punctate immunoreactivity to GABA(A)-receptor alpha 2 subunit, gephyrin and dystrophin in the molecular layer. Thus, both dystrophin and gephyrin were involved in postsynaptic clustering of GABA(A) receptors. A transient induction of utrophin was seen at the onset of degeneration in CA1 and CA3 pyramidal cells and in the hilus. Most strikingly, however, utrophin immunoreactivity appeared in the granule cell layer of the DG and became very strong in hypertrophic granule cells 1--2 months post-kainate treatment. These results suggest that utrophin provides structural support of neuronal membranes, whereas dystrophin is a component of GABAergic synapses.

Animals↗
PubMed2000

Differential expression of utrophin and dystrophin in CNS neurons: an in situ hybridization and immunohistochemical study.

The cellular distribution of utrophin, the autosomal homologue of dystrophin, was investigated in developing and adult rat and mouse brain by in situ hybridization and immunohistochemistry. Digoxigenin-labeled cRNA probes complementary to N-terminal, rod-domain, and C-terminal encoding sequences of utrophin were used to differentiate between full-length and short C-terminal isoforms. Largely overlapping distribution patterns were seen for the three probes in neurons of cerebral cortex, accessory olfactory bulb, and several sensory and motor brainstem nuclei as well as in blood vessels, pia mater, and choroid plexus. The C-terminal probe was detected in addition in the main olfactory bulb, striatum, thalamic reticular nucleus, and hypothalamus, suggesting a selective expression of G-utrophin in these neurons. Western blot analysis with isoform-specific antisera confirmed the expression of both full-length and G-utrophin in brain. Immunohistochemically, only full-length utrophin was detected in neurons, in close association with the plasma membrane. In addition, intense staining was seen in blood vessels, meninges, and choroid plexus, selectively localized in the basolateral membrane of immunopositive epithelial cells. The expression pattern of utrophin was already established at early postnatal stages and did not change thereafter. Double-labeling analysis revealed that utrophin and dystrophin are differentially expressed on the cellular and subcellular levels in juvenile and adult brain. Likewise, in mice lacking full-length dystrophin isoforms (mdx mice), no change in utrophin expression and distribution could be detected in brain, although utrophin was markedly up-regulated in muscle cells. These results suggest that utrophin and dystrophin are independently regulated and have distinct functional roles in CNS neurons.

Age Factors↗
PubMed2000

Identification and characterisation of transcript and protein of a new short N-terminal utrophin isoform.

Dystrophin and utrophin are known to link the intracellular cytoskeleton to the extracellular matrix via a transmembraneous glycoprotein complex. Four short C-terminal isoforms (Dp71, Dp116, Dp140, and Dp260) are described for dystrophin and three for utrophin (Up71, Up113, and Up140). We describe here for the first time the existence of a 3.7-kb transcript and a 62-kDa protein in C6 glioma cells representing a short N-terminal isoform unique for utrophin (N-utrophin). More than 20 clones covering the entire coding region of utrophin were isolated from a rat C6 glioma cell cDNA library. Two clones were found to code for a protein with 539 amino acids. Its sequence is identical to that of the full-length utrophin, except for the last residue where Cys is replaced by Val. This isoform contains the actin binding domain (consisting of two calponin homology subdomains), followed by two spectrin-like repeats. A recombinant fragment corresponding to N-utrophin binds to F-actin in vitro with an equilibrium constant (affinity) K of 4.5 x 10(5) M(-1) and a stoichiometry of one fragment per around five actin monomers. Immunocytochemical staining of C6 glioma cells with antisera specific for different utrophin regions localised full-length utrophin in the submembraneous cortical actin layer as revealed by confocal microscopy. A distinct staining pattern for the N-utrophin was not detectable, although it was expected to localise at the actin stress fibers. It is assumed that it co-localises via the two spectrin-like repeats with the full-length utrophin at the cell membrane.

Actins↗
PubMed2000

Dynamics of early contact formation in cultured adult rat cardiomyocytes studied by N-cadherin fused to green fluorescent protein.

We investigated dynamic events during the formation of intercalated disc-like structures of adult rat cardiomyocytes (ARC) in long-term culture. Given the complexity of ARC cytoIarchitecture after de- and re-differentiation, and the non-uniform morphological development of individual cells, green fluorescent protein (GFP) technology was used to track N-cadherin in living cells. Sorting and functionality of the GFP fusion protein was tested in ARC. Isolated ARC were micro-injected with the expression construct at the onset of spreading in culture, and the fluorescence signals were tracked during contact formation and in fully redifferentiated living cells. The first contact sites were found to be established by cellular protrusions, which were marked by an ultrastructure similar to microspikes and probably have a role as exploratory units in the spreading phase. Subsequently, initial contact sites served as anchorage for the most prominent stress fibre-like structures. The fusion protein appeared before connexin-43 at newly established cell-cell contacts. Membrane invaginations at the sarcolemma facing the substratum of cultured ARC may be responsible for the appearance of a striped pattern of N-cadherin and other adherens junction proteins away from intercalated disc-like structures. The stripes were immobile in redifferentiated cells, while the distinct small fluorescent particles in the cell body were found to move directionally at speeds around 10 micro m/min. These results contribute to the understanding of the mechanisms of cell-cell contact formation of adult cardiomyocytes, which is a prerequisite for any future implantation technology.

Animals↗
PubMed2000

Lack of nuclear apoptosis in cardiomyocytes and increased endothelin-1 levels in a rat heart model of myocardial stunning.

OBJECTIVE: Reperfusion injury may affect the cardiac NO and endothelin production. We investigated whether 20 min of total ischemia followed by 40 min of reperfusion can induce apoptosis in a Langendorff model of retrogradely perfused rat hearts (37 degrees C; paced at 300/'), and we attempted to correlate these findings with measured tissue NO and ET-1 levels. METHODS: An apoptosis detection system was utilized which catalytically incorporates fluorescein-12-dUTP at the 3'-OH DNA ends using the principle of the TUNEL assay, with direct visualization of the labeled DNA. ET-1 was measured by radioimmunoassay and NO3/NO2 by ion pairing HPLC on C18 reverse phase columns. RESULTS: None of the postischemic (n = 6) nor of the control perfused (90 min, n = 6) hearts showed signs of apoptosis, while those exposed to longer ischemia (40 min) and reperfusion (2 h) confirmed the presence of apoptotic cells. Myocardial ET-1 concentrations were 4.8 +/- 1.0 versus 8.3 +/- 2.5 pg/100 mg (control vs. ischemic hearts, respectively; mean +/- SD; p < 0.05). Myocardial NO contents showed no differences. CONCLUSION: These data suggest that the time window of apoptosis with detectable DNA fragmentation exceeds 20 min of global total ischemia and 40 min of reperfusion, a model frequently used for inducing myocardial stunning. While NO was not increased in postischemic hearts, increased ET-1 levels indirectly argue for a role of ET-1 as inducer of apoptosis, but only at a later stage of reperfusion.

Animals↗
PubMed1999

Short communication: altered synaptic clustering of GABAA receptors in mice lacking dystrophin (mdx mice).

Dystrophin is selectively localized in the postsynaptic density of neurons in cerebral cortex, hippocampus and cerebellum. Here, we show by double-immunofluorescence staining that dystrophin is extensively colocalized with GABAA receptor subunit clusters in these brain regions. To determine the relevance of this observation, we investigated in mdx mice, which provide a model of Duchenne muscular dystrophy, whether the absence of dystrophin affects the synaptic clustering of GABAA receptors. A marked reduction in the number of clusters immunoreactive for the alpha1 and alpha2 subunits was observed in, respectively, cerebellum and hippocampus of mdx mice, but not in striatum, which is normally devoid of dystrophin. Furthermore, these alterations were not accompanied by a change in gephyrin staining, although gephyrin is colocalized with the majority of GABAA receptor clusters in these regions. These results indicate that dystrophin may play an important role in the clustering or stabilization of GABAA receptors in a subset of central inhibitory synapses. These deficits may underlie the cognitive impairment seen in Duchenne patients.

Animals↗
PubMed1998

Differential protein localization in sarcomeric and nonsarcomeric contractile structures of cultured cardiomyocytes.

The use of cardiomyocyte cell culture models allows the identification of various cell mediators that bring about changes in subcellular structures and gene expression associated with hypertrophy. The effects of insulin-like growth factor-I (IGF-I), basic fibroblast growth factor (bFGF), and triiodothyronine (T3) on gene expression and on the structural organization of myofibrillar and cytoskeletal proteins were compared in adult atrial (aARC) and ventricular (vARC) as well as in neonatal ventricular rat cardiomyocytes (vNRC) in long-term culture. Structural changes were evaluated by confocal microscopy and correlated to biochemical alterations. In vARC, IGF-I enhanced myofibrillar growth, whereas bFGF or T3 restricted sarcomere assembly to the central cell area, forming a sharp boundary in more than 50% of the cells. However, myosin occurred both in the cross-striated myofibrillar structures and in patches running along the nonsarcomeric fibrillar structures (also called stress fiber-like structures) in the cell periphery. In cells treated with either bFGF or T3, the expression of alpha-smooth muscle actin (alpha-sm actin) was greatly increased. This actin isoform was incorporated mainly into the nonsarcomeric contractile structures outside the area where myofibrils ended abruptly. alpha-sm actin protein increased up to 14- to 17-fold while the mRNA showed a moderate increase of 2- to 4-fold. This suggests that alpha-sm actin is mainly regulated at the translational or posttranslational level. In contrast, the cytoskeletal proteins alpha-actinin and vinculin increased only moderately (less than 2-fold) but also showed a relocalization in cells with restricted myofibrils. In aARC and in vNRC, alpha-sm actin was only moderately upregulated by bFGF or T3 and no drastic morphological changes were observed. In conclusion, IGF-I, bFGF, and T3 induced characteristic structural phenotypes depending on the type of cardiomyocyte. Large amounts of alpha-sm actin as expressed in bFGF and T3 treated vARC seem to be incompatible with sarcomere assembly.

Actinin↗
PubMed1998

Triiodothyronine restricts myofibrillar growth and enhances beating frequency in cultured adult rat cardiomyocytes.

Adult rat cardiomyocytes (ARC) isolated from ventricles follow a defined sequence of structural remodeling during culturing for 2-3 weeks. Rod-shaped cells round up, attach to the substratum, and start growing out in all directions until they form contacts with one another and resume rhythmic contractile activity. In general, myofibrils redevelop along the actin scaffold into the periphery. IGF-I enhances this process while bFGF restricts the outgrowing of myofibrils to the central cell area. Presence of T3 in the culture medium also restricts myofibrillar growth like bFGF. At the same time, T3 increases spontaneous beating frequency in a dose-dependent manner. With 10 nM T3 beating frequency is increased three-fold versus control. Addition of isoproterenol or of epinephrine further increases the frequency at all T3 concentrations tested. Propranolol inhibits the fully stimulated beating frequency to about the same extent at all T3 concentrations. Therefore, T3 seems to determine the beating frequency of ARC in culture directly and not by changing the composition of the adrenoceptor population nor by changing their responsiveness.

Actins↗
PubMed1998

Modulation of contractility in human cardiac hypertrophy by myosin essential light chain isoforms.

Cardiac hypertrophy is an adaptive response that normalizes wall stress and compensates for increased workload. It is accompanied by distinct qualitative and quantitative changes in the expression of protein isoforms concerning contractility, intracellular Ca(2+)-homeostasis and metabolism. Changes in the myosin subunit isoform expression improves contractility by an increase in force generation at a given Ca(2+)-concentration (increased Ca(2+)-sensitivity) and by improving the economy of the chemo-mechanical transduction process per amount of utilised ATP (increased duty ratio). In the human atrium this is achieved by partial replacement of the endogenous fast myosin by the ventricular slow-type heavy and light chains. In the hypertrophic human ventricle the slow-type beta-myosin heavy chains remain unchanged, but the ectopic expression of the atrial myosin essential light chain (ALC1) partially replaces the endogenous ventricular isoform (VLC1). The ventricular contractile apparatus with myosin containing ALC1 is characterised by faster cross-bridge kinetics, a higher Ca(2+)-sensitivity of force generation and an increased duty ratio. The mechanism for cross-bridge modulation relies on the extended Ala-Pro-rich N-terminus of the essential light chains of which the first eleven residues interact with the C-terminus of actin. A change in charge in this region between ALC1 and VLC1 explains their functional difference. The intracellular Ca(2+)-handling may be impaired in heart failure, resulting in either higher or lower cytosolic Ca(2+)-levels. Thus the state of the cardiomyocyte determines whether this hypertrophic adaptation remains beneficial or becomes detrimental during failure. Also discussed are the effects on contractility of long-term changes in isoform expression of other sarcomeric proteins. Positive and negative modulation of contractility by short-term phosphorylation reactions at multiple sites in the myosin regulatory light chain, troponin-I, troponin-T, alpha-tropomyosin and myosin binding protein-C are considered in detail.

Animals↗