lithium-chloride and Cardiomegaly

Glycogen synthase kinase 3beta (GSK-3beta) negatively regulates cardiac hypertrophy. A potential target mediating the antihypertrophic effect of GSK-3beta is eukaryotic translation initiation factor 2Bepsilon (eIF2Bepsilon). Overexpression of GSK-3beta increased the cellular kinase activity toward GST-eIF2Bepsilon in neonatal rat cardiac myocytes, whereas LiCl (10 mmol/L) or isoproterenol (ISO) (10 micromol/L), a treatment known to inhibit GSK-3beta, decreased it. Immunoblot analyses using anti-S535 phosphospecific eIF2Bepsilon antibody showed that S535 phosphorylation of endogenous eIF2Bepsilon was decreased by LiCl or ISO, suggesting that GSK-3beta is the predominant kinase regulating phosphorylation of eIF2Bepsilon-S535 in cardiac myocytes. Decreases in eIF2Bepsilon-S535 phosphorylation were also observed in a rat model of cardiac hypertrophy in vivo. Overexpression of wild-type eIF2Bepsilon alone moderately increased cell size (+31+/-11%; P<0.05 versus control), whereas treatment of eIF2Bepsilon-transduced myocytes with LiCl (+73+/-22% versus eIF2Bepsilon only; P<0.05) or ISO (+84+/-33% versus eIF2Bepsilon only; P<0.05) enhanced the effect of eIF2Bepsilon. Overexpression of eIF2Bepsilon-S535A, which is not phosphorylated by GSK-3beta, increased cell size (+107+/-35%) as strongly as ISO (+95+/-25%), and abolished antihypertrophic effects of GSK-3beta, indicating that S535 phosphorylation of eIF2Bepsilon critically mediates antihypertrophic effects of GSK-3beta. Furthermore, expression of eIF2Bepsilon-F259L, a dominant-negative mutant, inhibited ISO-induced hypertrophy, indicating that eIF2Bepsilon is required for beta-adrenergic hypertrophy. Interestingly, expression of eIF2Bepsilon-S535A partially increased cytoskeletal reorganization, whereas it did not increase expression of atrial natriuretic factor gene. These results suggest that GSK-3beta is the predominant kinase mediating phosphorylation of eIF2Bepsilon-S535 in cardiac myocytes, which in turn plays an important role in regulating cardiac hypertrophy primarily through protein synthesis.

Topics: Adenoviridae; Adrenergic beta-Agonists; Adrenergic beta-Antagonists; Animals; Animals, Newborn; Atrial Natriuretic Factor; Cardiomegaly; Cells, Cultured; Eukaryotic Initiation Factor-2B; Gene Expression Regulation; Genetic Vectors; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Heart Ventricles; Hypertrophy; Isoproterenol; Lithium Chloride; Male; Myocardial Infarction; Myocytes, Cardiac; Myosin Heavy Chains; Peptide Chain Initiation, Translational; Phosphoserine; Propranolol; Protein Processing, Post-Translational; Rats; Rats, Wistar; Recombinant Fusion Proteins; Transduction, Genetic; Ventricular Remodeling

Status epilepticus was induced in rats by sequential injections of lithium and pilocarpine. Seizure activity was aborted by a combination of MK-801 and diazepam, with status duration ranging from 3 to 180 min. When the hearts were examined 8-12 days later, rats that had experienced an episode of status epilepticus had significantly heavier hearts than did controls. The nature of the cardiac tissue changes was not examined, and deserves further study.

Topics: Animals; Body Weight; Cardiomegaly; Diazepam; Dizocilpine Maleate; Electroencephalography; Lithium Chloride; Male; Myocardium; Organ Size; Pilocarpine; Rats; Rats, Sprague-Dawley; Status Epilepticus