Divergent role of calcium on Aβ- and MPTP-induced cell death in SK-N-SH neuroblastoma

Phosphodiesterase in heart and vessels: from physiology to diseases

Phosphodiesterases (PDEs) are a superfamily of enzymes that hydrolyze cyclic nucleotides, including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both cyclic nucleotides are critical secondary messengers in the neurohormonal regulation in the cardiovascular system. PDEs precisely control spatiotemporal subcellular distribution of cyclic nucleotides in a cell- and tissue-specific manner, playing critical roles in physiological responses to hormone stimulation in the heart and vessels. Dysregulation of PDEs has been linked to the development of several cardiovascular diseases, such as hypertension, aneurysm, atherosclerosis, arrhythmia, and heart failure. Targeting these enzymes has been proven effective in treating cardiovascular diseases and is an attractive and promising strategy for the development of new drugs. In this review, we discuss the current understanding of the complex regulation of PDE isoforms in cardiovascular function, highlighting the divergent and even opposing roles of PDE isoforms in different pathogenesis.

Proanthocyanidins exert a neuroprotective effect via ROS/JNK signaling in MPTP‑induced Parkinson's disease models in vitro and in vivo

The pathological alterations of Parkinson's disease (PD) predominantly manifest as a loss of dopaminergic neurons in the substantia nigra, which may be caused by oxidative stress damage. Proanthocyanidins (PCs) are a class of compounds found in various plants, which have significant antioxidant and free radical-scavenging activity. The present study investigated the protective effects and underlying mechanisms of PCs in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD model in vitro and in vivo. MTT assays were used to detect cell viability, and flow cytometry and TUNEL assays were used to detect cell apoptosis. Mitochondrial membrane potential (MMP) alterations were investigated using a JC-1 MMP Assay kit. The pole test was used to measure motor behavior in a mouse model of PD. Levels of reactive oxygen species (ROS) were measured using the fluorescent probe, 2′,7′-dichlorodihydrofluorescein diacetate. Immunohistochemistry and western blotting were performed to detect the expression levels of proteins associated with PD. In vitro, it was demonstrated that in MPTP-treated PC12 cells, PCs increased cell viability and reduced cell apoptosis in a dose-dependent manner. In vivo, it was revealed that PC treatment inhibited striatal dopamine depletion, which resulted in significant improvements in PD-like movement impairment. Reactive oxygen species (ROS) production and MPTP-induced apoptosis were also inhibited. Furthermore, the results demonstrated that the neuroprotective activity of PCs may be mediated via the inhibition of ROS generation, as well as modulation of c-Jun N-terminal kinase activation. Taken together, these data revealed that PCs may exert neuroprotective effects in in vivo and in vitro PD models, and may have potential in the prevention or treatment of PD.

The role of inflammatory and oxidative stress mechanisms in the pathogenesis of Parkinson's disease: focus on astrocytes

Neuroinflammation plays a key role in the pathogenesis of Parkinson's disease (PD). Epidemiologic, animal, human, and therapeutic studies support the role of oxidative stress and inflammatory cascade in initiation and progression of PD. In Parkinson's disease pathophysiology, activated glia affects neuronal injury and death through production of neurotoxic factors like glutamate, S100B, tumor necrosis factor alpha (TNF-α), prostaglandins, and reactive oxygen and nitrogen species. As disease progresses, inflammatory secretions engage neighboring cells, including astrocytes and endothelial cells, resulting in a vicious cycle of autocrine and paracrine amplification of inflammation leading to neurodegeneration. The exact mechanism of these inflammatory mediators in the disease progression is still poorly understood. In this review, we highlight and discuss the mechanisms of oxidative stress and inflammatory mediators by which they contribute to the disease progression. Particularly, we focus on the altered role of astroglial cells that presumably initiate and execute dopaminergic neurodegeneration in PD. In conclusion, we focus on the molecular mechanism of neurodegeneration, which contributes to the basic understanding of the role of neuroinflammation in PD pathophysiology.

Splice isoform-specific suppression of the Cav2.1 variant underlying spinocerebellar ataxia type 6

Spinocerebellar ataxia type 6 (SCA6) is an inherited neurodegenerative disease caused by a polyglutamine (polyQ) expansion in the Ca(V)2.1 voltage-gated calcium channel subunit (CACNA1A). There is currently no treatment for this debilitating disorder and thus a pressing need to develop preventative therapies. RNA interference (RNAi) has proven effective at halting disease progression in several models of spinocerebellar ataxia (SCA), including SCA types 1 and 3. However, in SCA6 and other dominantly inherited neurodegenerative disorders, RNAi-based strategies that selectively suppress expression of mutant alleles may be required. Using a Ca(V)2.1 mini-gene reporter system, we found that pathogenic CAG expansions in Ca(V)2.1 enhance splicing activity at the 3'end of the transcript, leading to a CAG repeat length-dependent increase in the levels of a polyQ-encoding Ca(V)2.1 mRNA splice isoform and the resultant disease protein. Taking advantage of this molecular phenomenon, we developed a novel splice isoform-specific (SIS)-RNAi strategy that selectively targets the polyQ-encoding Ca(V)2.1 splice variant. Selective suppression of transiently expressed and endogenous polyQ-encoding Ca(V)2.1 splice variants was achieved in a variety of cell-based models including a human neuronal cell line, using a new artificial miRNA-like delivery system. Moreover, the efficacy of gene silencing correlated with effective intracellular recognition and processing of SIS-RNAi miRNA mimics. These results lend support to the preclinical development of SIS-RNAi as a potential therapy for SCA6 and other dominantly inherited diseases.

Inhibition of platelet aggregation by 1-methyl-4-phenyl pyridinium ion (MPP+) through ATP depletion: Evidence for the reduced platelet activities in Parkinson's disease

Neuronal accumulation of 1-methyl-4-phenylpyridinium ion (MPP(+)), the metabolite of neural toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahyropyridine (MPTP), induces a rapid depletion of cellular ATP level and loss of neuronal cell viability which simulates human Parkinson's disease (PD). Since ATP plays an important role in the physiology and function of platelets, which share many biochemical and physiological features with neuronal cells, we examined the effect of MPP(+) on platelet aggregation and viability using freshly isolated rat platelets. While the treatment of MPP(+) to platelets did not induce cytotoxicity, it significantly attenuated agonist-induced platelet aggregation in a concentration dependent manner. The inhibition of aggregation by MPP(+) was mediated by the depletion of the cytoplasmic ATP pool and resultant decreased ATP secretion. Different from the previous reports in neuronal cells, MPP(+) did not affect intracellular levels of glutathione and cytoplasmic Ca(2+) in platelets. The combined treatment with MPP(+) and 2-deoxyglucose, a glycolysis inhibitor, showed the additive effect in the decrease of ATP secretion and intracellular content. Consistent with these findings, inhibitory effects of MPP(+) on platelet aggregation was significantly enhanced by the treatment with 2-deoxyglucose. In conclusion, these results suggested that MPP(+) can induce ATP depletion in platelets and attenuate platelet aggregation providing a new theory on the reduced platelet activities in PD patients.

Glioblastoma cell death induced by asiatic acid

Asiatic acid (AA), a triterpene, is known to be cytotoxic to several tumor cell lines. AA induces dose- and time-dependent cell death in U-87 MG human glioblastoma. This cell death occurs via both apoptosis and necrosis. The effect of AA may be cell type-specific as AA-induced cell death was mainly apoptotic in colon cancer RKO cells. AA-induced glioblastoma cell death is associated with decreased mitochondrial membrane potential, activation of caspase-9 and -3, and increased intracellular free Ca2+. Although treatment of glioblastoma cells with the caspase inhibitor zVAD-fmk completely abolished AA-induced caspase activation, it did not significantly block AA-induced cell death. AA-induced cell death was significantly prevented by an intracellular Ca2+ inhibitor, BAPTA/AM. Taken together, these results indicate that AA induces cell death by both apoptosis and necrosis, with Ca2+-mediated necrotic cell death predominating.