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Parkinson's disease (PD), the second most common neurodegenerative disease in the elderly, is characterized by selective loss of dopaminergic neurons and accumulation of α-synuclein (α-syn), mitochondrial dysfunction, Ca 2+ dyshomeostasis, and neuroinflammation. Since current treatments for PD merely address symptoms, there is an urgent need to identify the PD pathophysiological mechanisms to develop better therapies. Increasing evidence has identified K V 3.4, a ROS-sensitive K V channel carrying fast-inactivating currents, as a potential therapeutic target against neurodegeneration. In fact, it has been hypothesized that K V 3.4 channels could play a role in PD etiopathogenesis, controlling astrocytic activation and detrimental pathways in A53T mice, a well-known model of familial PD. Here, we showed that the A53T midbrain, primarily involved in the initial phase of PD pathogenesis, displayed an early upregulation of the K V 3.4 channel at 4 months, followed by its reduction at 12 months, compared with age-matched WT. On the other hand, in the A53T striatum, the expression of K V 3.4 remained high at 12 months, decreasing thereafter, in 16-month-old mice. The proteomic profile highlighted a different detrimental phenotype in A53T brain areas. In fact, the A53T striatum and midbrain differently expressed neuroprotective/detrimental pathways, with the variation of astrocytic p27 kip1 , XIAP, and Smac/DIABLO expression. Of note, a switch from protective to detrimental phenotype was characterized by the upregulation of Smac/DIABLO and downregulation of p27 kip1 and XIAP. This occurred earlier in the A53T midbrain, at 12 months, compared with the striatum proteomic profile. In accordance, an upregulation of Smac/DIABLO and a downregulation of p27 kip1 occurred in the A53T striatum only at 16 months, showing the slowest involvement of this brain area. Of interest, HIF-1α overexpression was associated with the detrimental profile in midbrain and its major vulnerability. At the cellular level, patch-clamp recordings revealed that primary A53T striatum astrocytes showed hyperpolarized resting membrane potentials and lower firing frequency associated with K V 3.4 ROS-dependent hyperactivity, whereas primary A53T midbrain astrocytes displayed a depolarized resting membrane potential accompanied by a slight increase of K V 3.4 currents. Accordingly, intracellular Ca 2+ homeostasis was significantly altered in A53T midbrain astrocytes, in which the ER Ca 2+ level was lower than in A53T striatum astrocytes and the respective littermate controls. Collectively, these results suggest that the early K V 3.4 overexpression and ROS-dependent hyperactivation in astrocytes could take part in the different vulnerabilities of midbrain and striatum, highlighting astrocytic K V 3.4 as a possible new therapeutic target in PD.

Many natural-derived compounds, including the essential oils from plants, are investigated to find new potential protective agents in several neurodegenerative disorders such as Alzheimer's disease (AD). In the present study, we tested the neuroprotective effect of limonene, one of the main components of the genus Citrus , against the neurotoxicity elicited by Aβ 1-42 oligomers, currently considered a triggering factor in AD. To this aim, we assessed the acetylcholinesterase activity by Ellman's colorimetric method, the mitochondrial dehydrogenase activity by MTT assay, the nuclear morphology by Hoechst 33258, the generation of reactive oxygen species (ROS) by DCFH-DA fluorescent dye, and the electrophysiological activity of K V 3.4 potassium channel subunits by patch-clamp electrophysiology. Interestingly, the monoterpene limonene showed a specific activity against acetylcholinesterase with an IC 50 almost comparable to that of galantamine, used as positive control. Moreover, at the concentration of 10 µg/mL, limonene counteracted the increase of ROS production triggered by Aβ 1-42 oligomers, thus preventing the upregulation of K V 3.4 activity. This, in turn, prevented cell death in primary cortical neurons, showing an interesting neuroprotective profile against Aβ 1-42 -induced toxicity. Collectively, the present results showed that the antioxidant properties of the main component of the genus Citrus , limonene, may be useful to prevent neuronal suffering induced by Aβ 1-42 oligomers preventing the hyperactivity of K V 3.4.