- •Preface
- •Contents
- •1 Extracellular and Intracellular Signaling – a New Approach to Diseases and Treatments
- •1.1 Introduction
- •1.1.1 Linear Model of Drug Receptor Interactions
- •1.1.2 Matrix Model of Drug Receptor Interactions
- •1.2 Experimental Approaches to Disease Treatment
- •1.3 Adipokines and Disease Causation
- •1.4 Questions in Disease Treatment
- •1.5 Toxic Lifestyles and Disease Treatment
- •References
- •2.1 Introduction
- •2.2 Heterogeneity of Adipose Tissue Composition in Relation to Adipokine and Cytokine Secretion
- •2.3 Feedback between FA and the Adipocyte
- •2.6 Metabolic Programming of Autocrine Signaling in Adipose Tissue
- •2.8 Cell Heterogeneity in the Pancreatic Islet
- •2.16 Concluding Remarks
- •Acknowledgements
- •References
- •3 One Receptor for Multiple Pathways: Focus on Leptin Signaling
- •3.1 Leptin
- •3.2 Leptin Receptors
- •3.3 Leptin Receptor Signaling
- •3.3.4 AMPK
- •3.3.5 SOCS3
- •3.4 Leptin Receptor Interactions
- •3.4.1 Apolipoprotein D
- •3.4.2 Sorting Nexin Molecules
- •3.4.3 Diacylglycerol Kinase Zeta
- •3.4.4 Apolipoprotein J
- •References
- •4.1 Introduction
- •4.2 Leptin: A Brief Introduction
- •4.3 Expression of Leptin Receptors in Cardiovascular Tissues
- •4.6 Post Receptor Leptin Signaling
- •4.6.2 Mitogen Activated Protein Kinase Stimulation
- •4.7 Adiponectin
- •4.7.1 Adiponectin and Cardiovascular Disease
- •4.7.2 Adiponectin and Experimental Cardiac Hypertrophy
- •4.8 Resistin
- •4.8.1 Cardiac Actions of Resistin
- •4.8.1.1 Experimental Studies on the Cardiac Actions of Resistin
- •4.9 Apelin
- •4.9.1 Apelin and Heart Disease
- •4.10 Visfatin
- •4.11 Other Novel Adipokines
- •4.12 Summary, Conclusions and Future Directions
- •Acknowledgements
- •References
- •5 Regulation of Muscle Proteostasis via Extramuscular Signals
- •5.1 Basic Protein Synthesis
- •5.2.1 Hormones
- •5.2.1.1 Mechanisms of Action: Glucocorticoids
- •5.2.1.2 Mechanisms of Action: TH (T3)
- •5.2.1.3 Mechanisms of Action: Testosterone
- •5.2.1.4 Mechanisms of Action: Epinephrine
- •5.2.2 Local Factors (Autocrine/Paracrine)
- •5.2.2.1 Mechanisms of Action: Insulin/IGF Spliceoforms
- •5.2.2.2 Mechanisms of Action: Fibroblast Growth Factor (FGF)
- •5.2.2.3 Mechanisms of Action: Myostatin
- •5.2.2.4 Mechanisms of Action: Cytokines
- •5.2.2.5 Mechanisms of Action: Neurotrophins
- •5.2.2.7 Mechanisms of Action: Extracellular Matrix
- •5.2.2.8 Mechanisms of Action: Amino Acids (AA)
- •5.3 Regulation of Muscle Proteostasis in Humans
- •5.3.1 Nutrients as Regulators of Muscle Proteostasis in Man
- •5.3.2 Muscular Activity (i.e. Exercise) as a Regulator of Muscle Proteostasis
- •5.4 Conditions Associated with Alterations in Muscle Proteostasis in Humans
- •5.4.2 Disuse Atrophy
- •5.4.3 Sepsis
- •5.4.4 Burns
- •5.4.5 Cancer Cachexia
- •References
- •6 Contact Normalization: Mechanisms and Pathways to Biomarkers and Chemotherapeutic Targets
- •6.1 Introduction
- •6.2 Contact Normalization
- •6.3 Cadherins
- •6.4 Gap Junctions
- •6.5 Contact Normalization and Tumor Suppressors
- •6.6 Contact Normalization and Tumor Promoters
- •6.7 Conclusions
- •References
- •7.1 Introduction
- •7.2 Background on Migraine Headache
- •7.3 Migraine and Neuropathic Pain
- •7.4 Role of Astrocytes in Pain
- •7.5 Adipokines and Related Extracellular Signalling
- •7.6 The Future of Signaling Research to Migraine
- •Acknowledgements
- •References
- •8.1 Alzheimer’s Disease
- •8.1.2 Target for AD Therapy
- •8.2 AD and Metabolic Dysfunction
- •8.2.1 Impaired Glucose Metabolism
- •8.2.2 Lipid Disorders
- •8.2.3 Obesity
- •8.3 Adipokines
- •8.3.1 Leptin
- •8.3.2 Adiponectin
- •8.3.3 Resistin
- •8.3.4 Visfatin
- •8.3.5 Plasminogen Activator Inhibitor
- •8.3.6 Interleukin-6
- •8.4 Conclusions
- •References
- •9.1 Introduction
- •9.1.1 Structure and Function of Astrocytes
- •9.1.1.1 Morphology
- •9.1.1.2 Astrocyte Functions
- •9.1.2 Responses of Astrocytes to Injury
- •9.1.2.1 Reactive Astrocytosis
- •9.1.2.2 Cell Swelling
- •9.1.2.3 Alzheimer Type II Astrocytosis
- •9.2 Intracellular Signaling System in Reactive Astrocytes
- •9.2.1 Oxidative/Nitrosative Stress (ONS)
- •9.2.2 Protein Kinase C (PKC)
- •9.2.5 Signal Transducer and Activator of Transcription 3 (STAT3)
- •9.3 Signaling Systems in Astrocyte Swelling
- •9.3.1 Oxidative/Nitrosative Stress (ONS)
- •9.3.2 Cytokines
- •9.3.3 Protein Kinase C (PKC)
- •9.3.5 Protein Kinase G (PKG)
- •9.3.7 Signal Transducer and Activator of Transcription 3 (STAT3)
- •9.3.10 Ion Channels/Transporters/Exchangers
- •9.4 Conclusions and Perspectives
- •Acknowledgements
- •References
- •10.1 Adipokines, Toxic Lipids and the Aging Brain
- •10.1.1 Toxic Lifestyles, Adipokines and Toxic Lipids
- •10.1.2 Ceramide Toxicity in the Brain
- •10.3 Oxygen Radicals, Hydrogen Peroxide and Cell Death
- •10.4 Gene Transcription and DNA Damage
- •10.5 Conclusions
- •References
- •11.1 Introduction
- •11.2 Cellular Signaling
- •11.2.1 Types of Signaling
- •11.2.2 Membrane Proteins in Signaling
- •11.3 G Protein-Coupled Receptors
- •11.3.1 Structure of GPCRs
- •11.3.1.1 Structure Determination
- •11.3.1.2 Structural Diversity of Current GPCR Structures
- •11.3.1.3 Prediction of GPCR Structure and Ligand Binding
- •11.3.2 GPCR Activation: Conformation Driven Functional Selectivity
- •11.3.2.2 Ligand or Mutation Stabilized Ensemble of GPCR Conformations
- •11.3.2.4 GPCR Dimers and Interaction with Other Proteins
- •11.3.3 Functional Control of GPCRs by Ligands
- •11.3.3.1 Biased Agonism
- •11.3.3.2 Allosteric Ligands and Signal Modulation
- •11.3.4 Challenges in GPCR Targeted Drug Design
- •11.4 Summary and Looking Ahead
- •Acknowledgements
- •References
- •12.1 Introduction
- •12.5.1 Anthocyanins
- •12.5.2 Gallates
- •12.5.3 Quercetin
- •12.5.5 Piperine
- •12.5.6 Gingerol
- •12.5.7 Curcumin
- •12.5.8 Guggulsterone
- •12.6.1 Phytanic Acid
- •12.6.2 Dehydroabietic Acid
- •12.6.3 Geraniol
- •12.7 Agonists of LXR that Reciprocally Inhibit NF-jB
- •12.7.1 Stigmasterol
- •12.7.3 Ergosterol
- •12.8 Conclusion
- •References
- •13.1 Introduction
- •13.2 Selective Dopaminergic Neuronal Death
- •13.3 Signaling Pathways Involved in Selective Dopaminergic Neuronal Death
- •13.3.1 Initiators and Signaling Molecules
- •13.3.1.1 Response to Oxidative and Nitrosative Stress
- •13.3.1.2 Response to Altered Proteostasis
- •13.3.1.3 Response to Glutamate
- •13.3.1.4 Other Initiators
- •13.3.2 Signal Transducers, Intracellular Messengers and Upstream Elements
- •13.3.2.2 Small GTPases
- •13.3.3 Intracellular Signaling Cascades
- •13.3.3.1 Mitogen Activated Protein Kinases (MAPK) Pathway
- •13.3.3.2 PI3K/Akt Pathway
- •13.3.3.4 Unfolded Protein Response (UPR)
- •13.3.4 Potentially Involved Intracellular Signaling Components
- •13.3.4.3 PINK1
- •13.3.5.2 Dopamine Metabolism
- •13.3.5.3 Cell Cycle
- •13.3.5.4 Autophagy
- •13.3.5.5 Apoptosis
- •13.4 Conclusions
- •References
- •Subject Index
Cell Signaling Mechanisms Underlying the Cardiac Actions of Adipokines |
61 |
hypertrophic e ects of either endothelin-1 or angiotensin II were associated with increased OBR expression and release of leptin into the culture medium. Moreover, anti-OBR antibodies completely abrogated the hypertrophic responses to both endothelin-1 and angiotensin II.3 These results need to be confirmed in other models but if validated they suggest that leptin plays a critical paracrine or autocrine obligatory role in mediating the hypertrophic to both endothelin-1 and angiotensin II and possibly other pro-hypertrophic factors.
Leptin has been shown to increase hyperplasia of the murine atrial HL-1 cell line as well as pediatric cardiomyocytes.19 Activation of ERK and phosphatidylinositol 3-kinase was demonstrated and implicated in the increase in cell number. It should be noted that leptin-induced hypertrophy has also been shown in human pediatric ventricular myocytes, which was associated with increased ERK, p38 and JAK phosphorylation.20
As will be discussed later in this chapter, activation of the RhoA/ROCK pathway likely plays a unique and critical role in mediating the cardiomyocyte hypertrophic e ect of leptin.
4.6 Post Receptor Leptin Signaling
In general, the complexity and diversity of leptin’s e ects are exemplified by its ability to activate several signal transduction pathways. It is beyond the scope of this review to comprehensively discuss leptin-mediated signaling in all tissues or organ systems. Instead, the discussion below focuses on signaling pathways that have been elucidated in cardiovascular tissue or that appear to be particularly relevant for understanding leptin-mediated cardiac signaling and its possible relationship to pathology, particularly in view of harnessing these pathways for cardiac therapeutics. For a more general treatise of this subject interested readers can consult various recent publications.21–24 In terms of cardiac pathology it is important to consider that the status of the leptin cell signaling system is likely substantially altered in disease states. For example, the leptin system in the myocardium including leptin expression and expression of OBR is upregulated in heart failure.25 Accordingly, the cell-signaling processes described below are most likely in a state of enhanced activity under pathological conditions.
4.6.1JAK-STAT Pathway Activation
It is generally accepted that OBRb is the fully competent signal transduction isoform of the receptor, and that the short-form OBRs (a,c,d,f), while capable of signal transduction, do so to a lesser extent.26,27 The major signaling pathway activated by leptin binding to OBRb is the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway,26 although this pathway may also be stimulated secondary to activation of the short form of the OBR.28 Upon binding of leptin to its receptor JAK1 and JAK2 are both capable of associating with the cytoplasmic domain of OBRb; however,
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Chapter 4 |
recently it has been demonstrated that JAK2 activation likely represents the physiologically relevant activated JAK during OBR signaling.29 Activation of JAKs results in transphosphorylation of other JAK as well as phosphorylation of tyrosine residues of OBRb.30 Recently, protein tyrosine phosphatase 1B
(PTP1B) has been shown to be a negative regulator of JAK-STAT signaling.31,32 PTP1B dephosphorylates the consensus recognition motif on JAK2,
resulting in inactivation of downstream STAT proteins.33 PTP1B knockout mice exhibit increased leptin sensitivity, STAT3 activation and decreased leptin to body-weight ratios.33 Phosphorylation of the cytoplasmic domain of the receptor
results in a docking site for STAT protein binding. STAT1, STAT3, STAT5 and STAT 6 have all been associated with leptin signaling in vitro.34–36 Upon binding
the receptor complex, STAT is phosphorylated by JAK where it dissociates
from the receptor, forms a homoor heterodimer and then translocates to the nucleus to act as a transcription factor.34,35,37 STAT3 can be inhibited by PIAS3,
an endogenous protein inhibitor of this transcriptional factor.38
Evidence for JAK-STAT-dependent signaling in cardiac tissue in terms of physiological e ects is at present limited but recent evidence suggests that it may be involved in the negative inotropic e ect of leptin in cardiomyocytes based on the ability of the JAK2 inhibitor AG-490 to abrogate these e ects.8 Interestingly, however, the e ect of AG-490 was mimicked by the MAPkinase inhibitor SB203580 suggesting that leptin exerts its e ects via multiple, and likely independent, cell signaling pathways.8
4.6.2Mitogen Activated Protein Kinase Stimulation
Mitogen-activated protein kinase (MAPK) represents an additional target for leptin-mediated e ects. In fact, OBRa has signal transduction capabilities through
MAPK pathways both dependently and independently of JAK phosphorylation.12,26,30 JAK2 phosphorylation of OBR tyrosine residue-985 (Tyr985) results
in docking of an SH2-domain containing protein tyrosine phosphatase (SHP-2), which associates with an adaptor molecule, Grb-2, to activate extracellular regulated kinase (ERK) signaling.30 Although ERK activation is possible in the absence of Tyr985, it still requires SHP-2 phosphatase activity.30 SHP-2 activation by leptin-OBR interaction leads to ERK activation, possibly through MEK1, but this has not yet been confirmed.22 Activation of ERK results in alterations in gene expression patterns for several genes including c-fos.12 Another MAPK, p38, has not been studied as extensively as ERK, but has been shown to be activated by leptin in mononuclear cells.39 In contrast, leptin was shown to reduce insulininduced p38 activation, while having no e ect on p38 activation on its own.23 The role of leptin signaling through c-jun NH2-terminal protein kinase (JNK) has not been well characterized. However, there are two reports of leptin activating JNK in endothelial cells,40 and in prostate cancer cells.41
In the cardiovascular system, leptin has been demonstrated to activate components of the MAPK pathways. In cultured neonatal myocytes, ERK1/2 and p38, but not JNK, were activated by leptin; inhibiting ERK had no e ect, while inhibition of p38 completely inhibited leptin-induced cardiomyocyte