Huntington's disease (HD) is a neurodegenerative disease characterized by progressive motor, cognitive and psychiatric deficits, associated with predominant loss of striatal neurons and caused by a polyglutamine expansion in the huntingtin protein. There is so far neither cure nor approved disease-slowing therapy for HD, though recent clinical studies have shown a beneficial long-term effect of pridopidine in patients with HD. The nature of this effect, purely symptomatic or, in addition, neuroprotective, is difficult to elucidate in clinical trials. Pridopidine and (-)-OSU6162 are members of a new family of compounds referred to as dopaminergic stabilizers, which normalize abnormal dopamine neurotransmission. We investigated the effects of (-)-OSU6162 on huntingtin knocked-in striatal neurons in culture. Control neurons had normal full-length huntingtin with 7 glutamines while "mutant" neurons had large expansions (Q=111). We studied the dose-effect curves of (-)-OSU6162 on mitochondrial activity, LDH levels, necrosis and apoptosis in untreated Q7 and Q111 cells. In addition, we investigated the effects of (-)-OSU6162 on Q7 and Q111 neurons challenged with different neurotoxins such as sodium glutamate, H(2)O(2), rotenone and 3-nitropropionic acid (3NP). As we found prevention of toxicity of some of these neurotoxins, we investigated the putative neuroprotective mechanisms of action of (-)-OSU6162 measuring the effects of this dopaminergic stabilizer on expression and release of BDNF, the ratios of Bcl2/Bax proteins and of p-ERK/ERK, the levels of chaperones and GSH, and the effects of (-)-OSU6162 on dopamine uptake and release. We found that (-)-OSU6162, 3-150 μM, produces a dose dependent increase of mitochondrial activity and a reduction of cell death. (-)-OSU6162 does not change glutamate toxicity, but it partially prevents that of H(2)O(2), rotenone and 3-nitropropionic acid. (-)-OSU6162 increases the intracellular levels of BDNF and Bcl2/Bax and decreases those of p-ERK/ERK and CHIP in Q111 cells. (-)-OSU6162 increased (3)H-dopamine uptake and amphetamine-induced (3)H-dopamine release in E13 mouse mid brain neurons. Our studies demonstrate that (-)-OSU6162 improves survival and mitochondrial function in striatal Q111 neurons and the resistance of these cells to several striatal neurotoxins, suggesting that (-)-OSU6162 and related compounds should be tested for neuroprotection in animal models and, eventually, in patients with HD.
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