The ral exchange factor rgl2 promotes cardiomyocyte survival and inhibits cardiac fibrosis.

Cardiomyocytes compensate to acute cardiac stress by increasing in size and contractile function. However, prolonged stress leads to a decompensated response characterized by cardiomyocyte death, tissue fibrosis and loss of cardiac function. Identifying approaches to inhibit this transition to a decompensated response may reveal important targets for treating heart failure. The Ral guanine nucleotide disassociation (RalGDS) proteins are Ras-interacting proteins that are upregulated by hypertrophic stimuli. The Ral guanine nucleotide dissociation stimulator-like 2 (Rgl2) is a member of the RalGDS family that modulates expression of hypertrophic genes in cardiomyocytes. However, the pathophysiologic consequence of increased Rgl2 expression in cardiomyoctyes remains unclear. To evaluate the effect of increasing Rgl2 activity in the heart, transgenic mice with cardiac-targeted over-expression of Rgl2 were generated. Although Ral activation was increased, there were no apparent morphologic or histological differences between the hearts of Rgl2 transgenic and nontransgenic mice indicating that increased Rgl2 expression had no effect on basal cardiac phenotype. To determine if Rgl2 modulates the cardiac response to stress, mice were infused with the ß-adrenergic receptor agonist, isoproterenol. Isoproterenol infusion increased heart mass in both Rgl2 transgenic and nontransgenic mice. However, unlike nontransgenic mice, Rgl2 transgenic mice showed no morphologic evidence of cardiomyocyte damage or increased cardiac fibrosis following isoproterenol infusion. Increased Rgl2 expression in cultured cardiomyocytes stimulated Ral activation and inhibited staurosporine-induced apoptosis via increased activation of PI3-kinase. Activation of the PI3-kinase signaling pathway was confirmed in hearts isolated from Rgl2 transgenic mice. Increased expression and function of Rgl2 in cardiomyocytes promotes activation of the PI3-kinase signaling cascade and protects from carciomyocyte death and pathologic cardiac fibrosis. Taken further, these results suggest that Rgl2 upregulation in hypertrophic hearts may be a protetive mechanism, and that Rgl2 may be a novel therapeutic target in treating heart disease.

The neurotoxicity induced by ethanol withdrawal in mature organotypic hippocampal slices might involve cross-talk between metabotropic glutamate type 5 receptors and N-methyl-D-aspartate receptors.

BACKGROUND: We recently reported that the sodium salt of acamprosate (Na-acamprosate) demonstrates the characteristics of an antagonist at metabotropic glutamate type 5 receptors (mGluR5s) rather than at N-methyl-d-aspartate receptors (NMDARs). Because mGluR5s are able to enhance the function of NMDARs, this interplay may be involved in the dysregulation of glutamatergic transmission during ethanol withdrawal. The following studies use organotypic hippocampal slice cultures at a mature age to investigate the potential for this interplay in the neurotoxicity associated with withdrawal from long-term ethanol exposure. METHODS: At 25 days in vitro, organotypic hippocampal slice cultures prepared from male and female 8-day-old rats were exposed to an initial concentration of 100 mM ethanol for 10 days before undergoing a 24-hr period of withdrawal. The effects of Na-acamprosate; 2-methyl-6-(2-phenylethenyl)pyridine (SIB-1893), a noncompetitive antagonist at mGluR5s; 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester, a noncompetitive antagonist at mGluR1s; dizocilpine (MK-801), a noncompetitive NMDAR antagonist; and staurosporine on the neurotoxicity induced by ethanol withdrawal were assessed by determining differences in propidium iodide uptake. Polypeptide levels of mGluR5s and the NR1 and NR2B subunits of NMDARs were also determined via Western blot analyses after 10 days of ethanol exposure. RESULTS: Significant neurotoxicity was always evident in the CA1 hippocampal region after a 24-hr withdrawal period. This spontaneous neurotoxicity resulted from intrinsic changes induced by the long-term presence of ethanol. Na-acamprosate (200-1000 microM), SIB-1893 (200-500 microM), MK-801 (20 microM), and staurosporine (200 nM) were all neuroprotective. The polypeptide levels of mGluR5s and NR1 and NR2B subunits of NMDARs were all increased after ethanol exposure; however, the increase in mGluR5s did not achieve statistical significance. CONCLUSIONS: From this model of long-term ethanol exposure and withdrawal, the functional interplay between mGluR5s and NMDARs might represent a novel target for the prevention of neurotoxicity associated with ethanol withdrawal.