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Abstract: GPR91 is an orphan G-protein-coupled receptor (GPCR) that has been characterized as a receptor for succinate, a citric acid cycle intermediate, in several tissues. In the heart, the role of succinate is unknown. We now report that rat ventricular cardiomyocytes express GPR91. We found that succinate, through GPR91, increases the amplitude and the rate of decline of global Ca2+ transient, by increasing the phosphorylation levels of ryanodine receptor and phospholamban, two well known Ca2+ handling proteins. The effects of succinate on Ca2+ transient were abolished by pre-treatment with adenylyl cyclase and cAMP-dependent protein kinase (PKA) inhibitors. Direct PKA activation by succinate was further confirmed using a FRET-based A-kinase activity reporter. Additionally, succinate decreases cardiomyocyte viability through a caspase-3 activation pathway, effect also prevented by PKA inhibition. Taken together, these observations show that succinate acts as a signaling molecule in cardiomyocytes, modulating global Ca2+ transient and cell viability through a PKA-dependent pathway. [Copyright &y& Elsevier]

Abnormal calcium influx and glutamatergic excitotoxicity have been extensively associated with neuronal death in Huntington's disease (HD), a genetic movement disorder. Currently, there is no effective treatment for this fatal condition. The neurotoxin Phα1β has demonstrated therapeutic effects as a calcium channel blocker, for example during pain control. However, little is known about its neuroprotective effect in HD. Herein, we investigated if Phα1β is effective in inhibiting neuronal cell death in the BACHD mouse model for HD. We performed intrastriatal injection of Phα1β in WT and BACHD mice. No side effects or unusual behaviors were observed upon Phα1β administration. Using three different motor behavior tests, we observed that injection of the toxin in BACHD mice greatly improved the animals' motor-force as seen in the Wire-hang test, and also the locomotor performance, according to the Open field test. NeuN labeling for mature neuron detection revealed that Phα1β toxin promoted neuronal preservation in the striatum and cortex, when injected locally. Intrastriatal injection of Phα1β was not able to preserve neurons from the spinal cord and also not revert muscle atrophy in BACHD mice. Finally, we observed that Phα1β might, at least in part, exert its protective effect by decreasing L-glutamate, measured in cerebrospinal fluid. Our data provide evidence of a novel neuroprotector effect of Phα1β, paving a path for the development of new approaches to treat HD motor symptoms. [ABSTRACT FROM AUTHOR]