Neuregulin-1 suppresses muscarinic receptor expression and acetylcholine-activated muscarinic K+ channels in cardiac myocytes

Neuregulin-1/ErbB4 upregulates acetylcholine receptors via Akt/mTOR/p70S6K: a study in a rat model of obstetric brachial plexus palsy and in vitro

In obstetric brachial plexus palsy (OBPP), the operative time window for nerve reconstruction of the intrinsic muscles of the hand (IMH) is much shorter than that of biceps. The reason is that the atrophy of IMH becomes irreversible more quickly than that of biceps. A previous study confirmed that the motor endplates of denervated intrinsic muscles of the forepaw (IMF) were destabilized, while those of denervated biceps remained intact. However, the specific molecular mechanism of regulating the self-repair of motor endplates is still unknown. In this study, we use a rat model of OBPP with right C5-C6 rupture plus C7-C8-T1 avulsion and left side as a control. Bilateral IMF and biceps are harvested at 5 weeks postinjury to assess relative protein and mRNA expression. We also use L6 skeletal myoblasts to verify the effects of signaling pathways regulating acetylcholine receptor (AChR) protein synthesis in vitro. The results show that in the OBPP rat model, the protein and mRNA expression levels of NRG-1/ErbB4 and phosphorylation of Akt/mTOR/p70S6K are lower in denervated IMF than in denervated biceps. In L6 myoblasts stimulated with NRG-1, overexpression and knockdown of ErbB4 lead to upregulation and downregulation of AChR subunit protein synthesis and Akt/mTOR/p70S6K phosphorylation, respectively. Inhibition of mTOR abolishes protein synthesis of AChR subunits elevated by NRG-1/ErbB4. Our findings suggest that in the OBPP rat model, lower expression of AChR subunits in the motor endplates of denervated IMF is associated with downregulation of NRG-1/ErbB4 and phosphorylation of Akt/mTOR/p70S6K. NRG-1/ErbB4 can promote protein synthesis of the AChR subunits in L6 myoblasts via phosphorylation of Akt/mTOR/p70S6K.

Pretreatment with neuregulin-1 improves cardiac electrophysiological properties in a rat model of myocardial infarction

Neuregulin-1 (NRG-1) is considered to be a potential therapeutic agent for cardiovascular diseases due to its diverse protective effects. The aim of the present study was to investigate the effect of NRG-1 on cardiac electrophysiology in rats with myocardial infarction (MI). The rats were randomly divided into three groups: The sham operation group (SO; n=8); MI group (n=8); and the MI with recombinant human NRG (rhNRG)-1 administration group (NRG-1 group; 10 µg/kg; n=8). A rat MI model was established via ligation of the left anterior descending coronary artery. The rats in the NRG-1 group received a 10 µg/kg rhNRG-1 injection through the tail vein 30 min prior to ligation. Following 24 h of intervention, the field potential (FP) parameters, including the interspike interval (ISI), field potential duration (FPD), FPrise, FPmin, FPmax and conduction velocity (CV), were measured using microelectrode array technology. Subsequently, burst pacing was performed to assess ventricular arrhythmia (VA) susceptibility in the left ventricle. FP parameters in the MI group were significantly different when compared with those observed in the SO group. ISI, FPD, FPrise and FPmax in the infarct, peri-infarct and normal zones, as well as the CV of the infarct and peri-infarct zones, were all significantly decreased, and FPmin in the normal zone was increased (P<0.05). However, when compared with the MI group, NRG-1 prolonged the ISI and FPD in the 3 zones, and increased FPrise in the infarct zone, FPmax in the normal zone and CV in the peri-infarct zone; it also decreased FPmin in the normal zone (P<0.05). Furthermore, the incidence of VA was significantly reduced in the NRG-1 group when compared with the MI group (P<0.05). In conclusion, NRG-1 improved cardiac electrophysiological properties and reduced VA susceptibility in acute MI.

4-O-Methylhonokiol Influences Normal Cardiovascular Development in Medaka Embryo

Although 4-O-Methylhonokiol (MH) effects on neuronal and immune cells have been established, it is still unclear whether MH can cause a change in the structure and function of the cardiovascular system. The overarching goal of this study was to evaluate the effects of MH, isolated from Magnolia grandiflora, on the development of the heart and vasculature in a Japanese medaka model in vivo to predict human health risks. We analyzed the toxicity of MH in different life-stages of medaka embryos. MH uptake into medaka embryos was quantified. The LC₅₀ of two different exposure windows (stages 9–36 (0–6 days post fertilization (dpf)) and 25–36 (2–6 dpf)) were 5.3 ± 0.1 μM and 9.9 ± 0.2 μM. Survival, deformities, days to hatch, and larval locomotor response were quantified. Wnt 1 was overexpressed in MH-treated embryos indicating deregulation of the Wnt signaling pathway, which was associated with spinal and cardiac ventricle deformities. Overexpression of major proinflammatory mediators and biomarkers of the heart were detected. Our results indicated that the differential sensitivity of MH in the embryos was developmental stage-specific. Furthermore, this study demonstrated that certain molecules can serve as promising markers at the transcriptional and phenotypical levels, responding to absorption of MH in the developing embryo.

The effect of deficient muscarinic signaling on commonly reported biochemical effects in schizophrenia and convergence with genetic susceptibility loci in explaining symptom dimensions of psychosis

With the advent of DSM 5 criticism has generally centered on a lack of biological validity of the diagnostic criteria. Part of the problem in describing a nosology of psychosis is the tacit assumption of multiple genetic causes each with an incremental loading on the clinical picture that fails to differentiate a clear underlying pathophysiology of high impact. The aim of this paper is to consolidate a primary theory of deficient muscarinic signaling underlying key clinical features of schizophrenia and its regulation by several important genetic associations including neuregulin, DISC and dysbindin. Secondary reductions in markers for GABAergic function and changes in the levels of interneuron calcium binding proteins parvalbumin and calbindin can be attributed to dysfunctional muscarinic transduction. A parallel association exists for cytokine production. The convergent pathway hypothesis is likewise used to model dopaminergic and glutamatergic theories of schizophrenia. The negative symptom dimension is correlated with dysfunction of Akt and ERK transduction, a major point of convergence. The present paradigm predicts the importance of a recent finding of a deletion in a copy number variant of PLCB1 and its potential use if replicated, as one of the first testable biological markers differentiating schizophrenia from bipolar disorder and further subtyping of schizophrenia into deficit and non-deficit. Potential limitations of PLCB1 as a prospective marker are also discussed.

Association study of the KCNJ3 gene as a susceptibility candidate for schizophrenia in the Chinese population

We recently reported the results of a genome-wide association study (GWAS) of schizophrenia in the Japanese population. In that study, a single nucleotide polymorphism (SNP) (rs3106653) in the KCNJ3 (potassium inwardly rectifying channel, subfamily J, member 3) gene located at 2q24.1 showed association with schizophrenia in two independent sample sets. KCNJ3, also termed GIRK1 or Kir3.1, is a member of the G protein-activated inwardly rectifying K(+) channel (GIRK) group. GIRKs are widely distributed in the brain and play an important role in regulating neural excitability through the activation of various G protein-coupled receptors. In this study, we set out to examine this association using a different population. We first performed a gene-centric association study of the KCNJ3 gene, by genotyping 38 tagSNPs in the Chinese population. We detected nine SNPs that displayed significant association with schizophrenia (lowest P = 0.0016 for rs3106658, Global significance = 0.036). The initial marker SNP (rs3106653) examined in our prior GWAS in the Japanese population also showed nominally significant association in the Chinese population (P = 0.028). Next, we analyzed transcript levels in the dorsolateral prefrontal cortex of postmortem brains from patients with schizophrenia and bipolar disorder and from healthy controls, using real-time quantitative RT-PCR. We found significantly lower KCNJ3 expression in postmortem brains from schizophrenic and bipolar patients compared with controls. These data suggest that the KCNJ3 gene is genetically associated with schizophrenia in Asian populations and add further evidence to the "channelopathy theory of psychiatric illnesses".

Hawthorn (Crataegus monogyna Jacq.) extract exhibits atropine-sensitive activity in a cultured cardiomyocyte assay

Hawthorn (Crataegus spp.) plant extract is used as a herbal alternative medicine for the prevention and treatment of various cardiovascular diseases. Recently, it was shown that hawthorn extract preparations caused negative chronotropic effects in a cultured neonatal murine cardiomyocyte assay, independent of beta-adrenergic receptor blockade. The aim of this study was to further characterize the effect of hawthorn extract to decrease the contraction rate of cultured cardiomyocytes. To test the hypothesis that hawthorn is acting via muscarinic receptors, the effect of hawthorn extract on atrial versus ventricular cardiomyocytes in culture was evaluated. As would be expected for activation of muscarinic receptors, hawthorn extract had a greater effect in atrial cells. Atrial and/or ventricular cardiomyocytes were then treated with hawthorn extract in the presence of atropine or himbacine. Changes in the contraction rate of cultured cardiomyocytes revealed that both muscarinic antagonists significantly attenuated the negative chronotropic activity of hawthorn extract. Using quinuclidinyl benzilate, L-[benzylic-4,4'-(3)H] ([(3)H]-QNB) as a radioligand antagonist, the effect of a partially purified hawthorn extract fraction to inhibit muscarinic receptor binding was quantified. Hawthorn extract fraction 3 dose-dependently inhibited [(3)H]-QNB binding to mouse heart membranes. Taken together, these findings suggest that decreased contraction frequency by hawthorn extracts in neonatal murine cardiomyocytes may be mediated via muscarinic receptor activation.

Neuregulin effect on quantal content dissociated from effect on miniature endplate potential amplitude

Members of the neuregulin family of signaling proteins increase transcription of acetylcholine receptor (AChR) subunit genes in muscle fibers and the number of AChRs in the muscle membrane. In adult mice heterozygous for targeted deletion of type I neuregulins (Ig-NRG(+/-)), postsynaptic AChR density was decreased and transmitter release was increased. We examined the relationship between functional AChR density and ACh release in postnatal day 7 (P7), P14, and adult NRG-deficient mice. Here we report that changes in postsynaptic sensitivity and transmitter release are not temporally coupled during postnatal development in Ig-NRG-deficient mice. Although miniature endplate potential (MEPP) amplitude was decreased compared with control in P7 Ig-NRG(+/-) mice, quantum content was not increased. Quantum content was increased in adult heterozygotes despite normal MEPP amplitudes. Thus, during postnatal maturation, both quantal size and quantum content were influenced by decreased Ig-NRG expression, although the effects were dissociated in time.

Expressional reprogramming of survival pathways in rat cardiocytes by neuregulin-1beta

Neuregulin/ErbB2-induced kinase signaling provides essential survival and protection clues for functional integrity of the adult heart and skeletal muscle. To define the regulatory pathways involved in neuregulin-dependent muscle cell survival, we set out to map the largely unknown transcript targets of this growth/differentiation factor in cardiocytes. Freshly isolated adult primary rat cardiocytes were treated for 24 h with recombinant human neuregulin-1beta (NRG-1beta, 30 ng/ml). Transcript level alterations in NRG-1beta-treated and control cardiocytes (n = 6) were identified with Atlas Rat Toxicology 1.2 cDNA arrays (BD Clontech) and established permutation L1 regression analysis. Selected transcriptional adjustments were confirmed by RT-PCR and Western blotting. Involvement of MAPK pathways was verified with the inhibitor PD-98059. Application of the single dose of NRG-1beta to quiescent cardiocytes induced expressional reprogramming of distinct cellular processes. This response included a prominent 50-100% increase in transcripts of multiple redox systems. It also involved a comparable mRNA augmentation of protein synthetic and folding factors together with augmented message for the trigger of cardiac hypertrophy, cyclin D1 (CCND1). First evidence for a role of neuregulin in promotion of mitochondrial turnover, voltage-gated ion channel expression, and the suppression of fatty acid transporter mRNAs was revealed. Subsequent analysis confirmed a corresponding upregulation of redox factor proteins thioredoxin and the thioredoxin reductase 1, GSTP-1, and CCND1 and demonstrated downregulation of the related transcripts by PD-98059 in neuregulin-stimulated cultures. These MAPK-dependent expressional adjustments point to novel oxidative defense and hypertrophy pathways being involved in the longer lasting protective function of neuregulin in the heart.