Francisco S. Cayabyab

Differential inhibition of T-type calcium channels by neuroleptics.

T-type calcium channels play critical roles in cellular excitability and have been implicated in the pathogenesis of a variety of neurological disorders including epilepsy. Although there have been reports that certain neuroleptics that primarily target D2dopamine receptors and are used to treat psychoses may also interact with T-type Ca channels, there has been no systematic examination of this phenomenon. In the present paper we provide a detailed analysis of the effects of several widely used neuroleptic agents on a family of exogenously expressed neuronal T-type Ca channels (α1G, α1H, and α1Isubtypes). Among the neuroleptics tested, the diphenylbutylpiperidines pimozide and penfluridol were the most potent T-type channel blockers with Kd values (∼30–50 nm and ∼70–100 nm, respectively), in the range of their antagonism of the D2 dopamine receptor. In contrast, the butyrophenone haloperidol was ∼12- to 20-fold less potent at blocking the various T-type Ca channels. The diphenyldiperazine flunarizine was also less potent compared with the diphenylbutylpiperadines and preferentially blocked α1G and α1I T-type channels compared with α1H. The various neuroleptics did not significantly affect T-type channel activation or kinetic properties, although they shifted steady-state inactivation profiles to more negative values, indicating that these agents preferentially bind to channel inactivated states. Overall, our findings indicate that T-type Ca channels are potently blocked by a subset of neuroleptic agents and suggest that the action of these drugs on T-type Ca channels may significantly contribute to their therapeutic efficacy.

ABCG5/ABCG8 in cholesterol excretion and atherosclerosis.

Cholesterol is essential for the growth and function of all mammalian cells, but abnormally increased blood cholesterol is a major risk factor for atherosclerotic cardiovascular disease. ATP-binding cassette (ABC) transporters G5 (ABCG5) and G8 (ABCG8) form an obligate heterodimer that limits intestinal absorption and facilitates biliary secretion of cholesterol and phytosterols. Consistent with their function, ABCG5 and ABCG8 are located on the apical membrane of enterocytes and hepatocytes. Liver X receptor is the major positive regulator of ABCG5 and ABCG8 expression. Mutations in either of the two genes cause sitosterolemia, a condition in which cholesterol and plant sterols accumulate in the circulation leading to premature cardiovascular disease. Overexpression of ABCG5 and ABCG8 in mice retards diet-induced atherosclerosis because of reduced circulating and hepatic cholesterol. In the current review, we summarize recent developments and propose a future framework that provides new perspectives on the regulation of cholesterol metabolism and treatment of atherosclerotic cardiovascular disease.

p38 Mitogen-Activated Protein Kinase Contributes to Adenosine A1 Receptor-Mediated Synaptic Depression in Area CA1 of the Rat Hippocampus

Adenosine is arguably the most potent and widespread presynaptic modulator in the CNS, yet adenosine receptor signal transduction pathways remain unresolved. Here, we demonstrate a novel mechanism in which adenosine A1 receptor stimulation leads to p38 mitogen-activated protein kinase (MAPK) activation and contributes to the inhibition of synaptic transmission. Western blot analysis indicated that selective A1 receptor activation [with N6-cyclopentyladenosine (CPA)] resulted in rapid increases in phosphorylated p38 (phospho-p38) MAPK immunoreactivity in membrane fractions, and decreases in phospho-p38 MAPK in cytosolic fractions. Immunoprecipitation with a phospho-p38 MAPK antibody revealed constitutive association of this phosphoprotein with adenosine A1 receptors. Phospho-p38 MAPK activation by A1 receptor stimulation induced translocation of PP2a (protein phosphatase 2a) to the membrane. We then examined the actions of p38 MAPK activation in A1 receptor-mediated synaptic inhibition. Excitatory postsynaptic field potentials evoked in area CA1 of the rat hippocampus markedly decreased in response to adenosine (10 μm), the A1 receptor agonist CPA (40 nm), or a 5 min exposure to hypoxia. These inhibitory responses were mediated by A1 receptor activation because the selective antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine) (100 nm) prevented them. In agreement with the biochemical analysis, the selective p38 MAPK inhibitor SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole] (25 μm) blocked the inhibitory actions of A1 receptor activation, whereas both the inactive analog SB202474 [4-ethyl-2-(p-methoxyphenyl)-5-(4′-pyridyl)-1H-imidazole] (25 μm) and the ERK 1/2 (extracellular signal-regulated kinase 1/2) MAPK inhibitor PD98059 [2′-amino-3′-methoxyflavone] (50 μm) were ineffective. In contrast, the p38 MAPK inhibitors did not inhibit GABAB-mediated synaptic depression. These data suggest A1 receptor-mediated p38 MAPK activation is a crucial step underlying the presynaptic inhibitory effect of adenosine on CA3–CA1 synaptic transmission.

NPC1, intracellular cholesterol trafficking and atherosclerosis

Post-lysosomal cholesterol trafficking is an important, but poorly understood process that is essential to maintain lipid homeostasis. Niemann-Pick type C1 (NPC1), an integral membrane protein on the limiting membrane of late endosome/lysosome (LE/LY), is known to accept cholesterol from NPC2 and then mediate cholesterol transport from LE/LY to endoplasmic reticulum (ER) and plasma membrane in a vesicle- or oxysterol-binding protein (OSBP)-related protein 5 (ORP5)-dependent manner. Mutations in the NPC1 gene can be found in the majority of NPC patients, who accumulate massive amounts of cholesterol and other lipids in the LE/LY due to a defect in intracellular lipid trafficking. Liver X receptor (LXR) is the major positive regulator of NPC1 expression. Atherosclerosis is the pathological basis of coronary heart disease, one of the major causes of death worldwide. NPC1 has been shown to play a critical role in the atherosclerotic progression. In this review, we have summarized the role of NPC1 in regulating intracellular cholesterol trafficking and atherosclerosis.

NF-κB suppresses the expression of ATP-binding cassette transporter A1/G1 by regulating SREBP-2 and miR-33a in mice.

a Institute of Cardiovascular Research, Key Laboratory for Atherosclerology of Hunan Province, Life Science Research Center, University of South China, Hengyang, Hunan 421001, China b Department of Histology and Embryology, Guilin Medical University, Guilin, Guangxi 541004, China c Fourth year student in department of biochemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada d Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada e Department of Cardiovascular Medicine, Second Affiliated Hospital of University of South China, Hengyang 421001, Hunan, China

Hydrogen sulfide as a potent cardiovascular protective agent

Hydrogen sulfide (H2S) is a well-known toxic gas with the characteristic smell of rotten eggs. It is synthesized endogenously in mammals from the sulfur-containing amino acid l-cysteine by the action of several distinct enzymes: cystathionine-γ-lyase (CSE), cystathionine-ß-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3-MST) along with cysteine aminotransferase (CAT). In particular, CSE is considered to be the major H2S-producing enzyme in the cardiovascular system. As the third gasotransmitter next to nitric oxide (NO) and carbon monoxide (CO), H2S plays an important role in the regulation of vasodilation, angiogenesis, inflammation, oxidative stress and apoptosis. Growing evidence has demonstrated that this gas exerts a significant protective effect against the progression of cardiovascular diseases by a number of mechanisms such as vasorelaxation, inhibition of cardiovascular remodeling and resistance to form foam cells. The aim of this review is to provide an overview of the physiological functions of H2S and its protection against several major cardiovascular diseases, and to explore its potential health and therapeutic benefits. A better understanding will help develop novel H2S-based therapeutic interventions for these diseases.

Prolonged Adenosine A1 Receptor Activation in Hypoxia and Pial Vessel Disruption Focal Cortical Ischemia Facilitates Clathrin-Mediated AMPA Receptor Endocytosis and Long-Lasting Synaptic Inhibition in Rat Hippocampal CA3-CA1 Synapses: Differential Regulation of GluA2 and GluA1 Subunits by p38 MAPK and JNK

Activation of presynaptic adenosine A1 receptors (A1Rs) causes substantial synaptic depression during hypoxia/cerebral ischemia, but postsynaptic actions of A1Rs are less clear. We found that A1Rs and GluA2-containing AMPA receptors (AMPARs) form stable protein complexes from hippocampal brain homogenates and cultured hippocampal neurons from Sprague Dawley rats. In contrast, adenosine A2A receptors (A2ARs) did not coprecipitate or colocalize with GluA2-containing AMPARs. Prolonged stimulation of A1Rs with the agonist N6-cyclopentyladenosine (CPA) caused adenosine-induced persistent synaptic depression (APSD) in hippocampal brain slices, and APSD levels were blunted by inhibiting clathrin-mediated endocytosis of GluA2 subunits with the Tat-GluA2–3Y peptide. Using biotinylation and membrane fractionation assays, prolonged CPA incubation showed significant depletion of GluA2/GluA1 surface expression from hippocampal brain slices and cultured neurons. Tat-GluA2–3Y peptide or dynamin inhibitor Dynasore prevented CPA-induced GluA2/GluA1 internalization. Confocal imaging analysis confirmed that functional A1Rs, but not A2ARs, are required for clathrin-mediated AMPAR endocytosis in hippocampal neurons. Pharmacological inhibitors or shRNA knockdown of p38 MAPK and JNK prevented A1R-mediated internalization of GluA2 but not GluA1 subunits. Tat-GluA2–3Y peptide or A1R antagonist 8-cyclopentyl-1,3-dipropylxanthine also prevented hypoxia-mediated GluA2/GluA1 internalization. Finally, in a pial vessel disruption cortical stroke model, a unilateral cortical lesion compared with sham surgery reduced hippocampal GluA2, GluA1, and A1R surface expression and also caused synaptic depression in hippocampal slices that was consistent with AMPAR downregulation and decreased probability of transmitter release. Together, these results indicate a previously unknown mechanism for A1R-induced persistent synaptic depression involving clathrin-mediated GluA2 and GluA1 internalization that leads to hippocampal neurodegeneration after hypoxia/cerebral ischemia.

The effects of miR-467b on lipoprotein lipase (LPL) expression, pro-inflammatory cytokine, lipid levels and atherosclerotic lesions in apolipoprotein E knockout mice.

Atherosclerosis is a lipid disorder disease characterized by chronic blood vessel wall inflammation driven by the subendothelial accumulation of macrophages. Studies have shown that lipoprotein lipase (LPL) participates in lipid metabolism, but it is not yet known whether post-transcriptional regulation of LPL gene expression by microRNAs (miRNAs) occurs in vivo. Here, we tested that miR-467b provides protection against atherosclerosis by regulating the target gene LPL which leads to reductions in LPL expression, lipid accumulation, progression of atherosclerosis and production of inflammatory cytokines in apolipoprotein E knockout (apoE(-/-)) mice. Treatment of apoE(-/-) mice with intra-peritoneal injection of miR-467b agomir led to decreased blood plasma levels of total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), IL-1β and monocyte chemotactic protein-1 (MCP-1). Using Western blots and real time PCR, we determined that LPL expression in aorta and abdominal cavity macrophages were significantly down-regulated in the miR-467b agomir group. Furthermore, systemic treatment with miR-467b antagomir accelerated the progression of atherosclerosis in the aorta of apoE(-/-) mice. The present study showed that miR-467b protects apoE(-/-) mice from atherosclerosis by reducing lipid accumulation and inflammatory cytokine secretion via downregulation of LPL expression. Therefore, targeting miR-467b may offer a promising strategy to treat atherosclerotic vascular disease.

Interleukin-17A in lipid metabolism and atherosclerosis.

Interleukin-17 (IL-17) A, the most important cytokine of the IL-17 family predominantly secreted by T helper 17 (Th17) cells, plays a critical role in the development of inflammatory diseases. Its receptor is an obligate heterodimer composed of IL-17 receptor (IL-17R) A and C, the main members of the IL-17R family. Binding of IL-17A to the IL-17RA/C complex can activate a variety of downstream signaling pathways such as nuclear factor kappa-B (NF-κB), activator protein 1 (AP1) and CCAAT/enhancer-binding protein (C/EBP) to induce the expression of proinflammatory cytokines and chemokines. IL-17A also promotes mRNA stability. Growing evidence shows that IL-17A is involved in lipid metabolism and the pathogenesis of atherosclerosis, a chronic inflammatory arterial disease driven by both innate and adaptive immune responses to modified lipoproteins. In the current review, we describe recent progress on regulation and signaling of IL-17A, and highlight its impacts on lipid metabolism and atherosclerosis.

Adenosine A1 and A2A Receptors in the Brain: Current Research and Their Role in Neurodegeneration

The inhibitory adenosine A1 receptor (A1R) and excitatory A2A receptor (A2AR) are predominantly expressed in the brain. Whereas the A2AR has been implicated in normal aging and enhancing neurotoxicity in multiple neurodegenerative diseases, the inhibitory A1R has traditionally been ascribed to have a neuroprotective function in various brain insults. This review provides a summary of the emerging role of prolonged A1R signaling and its potential cross-talk with A2AR in the cellular basis for increased neurotoxicity in neurodegenerative disorders. This A1R signaling enhances A2AR-mediated neurodegeneration, and provides a platform for future development of neuroprotective agents in stroke, Parkinson’s disease and epilepsy.