Okadaic acid: a tool to study regulatory mechanisms for neurodegeneration and regeneration in Alzheimer's disease

Okadaic acid： Okadaic acid （OKA）, a polyether （C38 fatty acid） toxin, is a potent and selective inhibitor of protein phosphatase, PP1 and protein phosphatase 2A （PP2A）. It is mainly extracted from a black sponge Hallichondria okadaii and has been suggested to play a potent probe for studying the various molecular, cellular, biochemical and mechanism of neurotoxicity. It is known as a selective and potent in- hibitor of serine/threonine phosphatases 1 and 2A induces hyperphosphorylation of tau in vitro and in vivo. It has been reported that Alzheimer＇s disease （AD） is a complex multi- factorial neurodegenerative disorder and hyperphosphor- ylated tau protein is a major pathological hallmark of AD. The reduced activity of phosphatases like, PP2A has been implicated in the brain of AD patients. OKA also induced inhibition of protein phosphatases cause neurofibrillary tangles （NFTs） like pathological changes and tau hyperphos- phorylation seen in AD pathology. Our and others reports inferred that OKA induces neurodegeneration along with tau hyperphosphorylation, GSK3β activation, oxidative stress, neuroinflammation and neurotoxicity which are char- acteristic of AD pathology （Figure 1）.

Transforming growth factor β1-mediated anti-inflammation slows progression of midbrain dopaminergic neurodegeneration in Parkinson's disease?

Parkinson’s disease（PD）is characterized by the progressive loss of midbrain dopaminergic（m DA）neurons and a subsequent decrease in striatal dopamine levels,which cause the typical clinical motor symptoms such as muscle rigidity,bradykinesia and tremor.

Modulation of microglial functions by methyl jasmonate

Neuroinflammation contributes to the neurodegenerative processes in Alzheimer＇s disease（AD）;therefore,characterization of novel drug candidates aimed at combatting inflammation in the central nervous system is one of the potential avenues for the development of effective AD treatment and prevention strategies.Non-neuronal microglial cells orchestrate neuroinflammatory reactions,and their adverse activation has been linked to AD pathogenesis.Methyl jasmonate（MJ） has anti-cancer properties and has also been shown to reduce peripheral inflammation in pre-clinical models.Recently,anti-neuroinflammatory activity of MJ was demonstrated in mice,but the exact cellular and molecular mechanisms responsible for this beneficial effect are unknown.We hypothesized that MJ can regulate select microglial functions,and used two different in vitro models of microglia to test this hypothesis.MJ inhibited the production of damaging reactive oxygen species by differentiated human HL-60 promyelocytic leukemia cells without reducing their viability.MJ also selectively upregulated phagocytic activity of murine BV-2 microglia,but had no effect on nitric oxide secretion by these cells.Since microglial phagocytosis can be beneficial for clearance of amyloid β aggregates in AD,the observed upregulation of phagocytic activity by MJ,combined with its inhibitory effect on reactive oxygen species production,supports continued studies of MJ as a candidate drug for managing adverse neuroinflammation in AD.

Protective effects of Bushen Tiansui decoction on hippocampal synapses in a rat model of Alzheimer's disease

Bushen Tiansui decoction is composed of six traditional Chinese medicines：Herba Epimedii,Radix Polygoni multiflori,Plastrum testudinis,Fossilia Ossis Mastodi,Radix Polygalae,and Rhizoma Acorus tatarinowii.Because Bushen Tiansui decoction is effective against amyloid beta（Aβ） toxicity,we hypothesized that it would reduce hippocampal synaptic damage and improve cognitive function in Alzheimer＇s disease.To test this hypothesis,we used a previously established animal model of Alzheimer＇s disease,that is,microinjection of aggregated Aβ25–35 into the bilateral brain ventricles of Sprague-Dawley rats.We found that long-term（28 days） oral administration of Bushen Tiansui decoction（0.563,1.688,and 3.375 g/m L;4 m L/day） prevented synaptic loss in the hippocampus and increased the expression levels of synaptic proteins,including postsynaptic density protein 95,the N-methyl-D-aspartate receptor 2 B subunit,and Shank1.These results suggested that Bushen Tiansui decoction can protect synapses by maintaining the expression of these synaptic proteins.Bushen Tiansui decoction also ameliorated measures reflecting spatial learning and memory deficits that were observed in the Morris water maze（i.e.,increased the number of platform crossings and the amount of time spent in the target quadrant and decreased escape latency） following intraventricular injections of aggregated Aβ25–35 compared with those measures in untreated Aβ_（25–35）-injected rats.Overall,these results provided evidence that further studies on the prevention and treatment of dementia with this traditional Chinese medicine are warranted.

Necrostatin-1 protection of dopaminergic neurons

Necroptosis is characterized by programmed necrotic cell death and autophagic activation and might be involved in the death process of dopaminergic neurons in Parkinson＇s disease. We hypothesized that necrostatin-1 could block necroptosis and give protection to dopaminergic neurons. There is likely to be crosstalk between necroptosis and other cell death pathways, such as apoptosis and autophagy. PC12 cells were pretreated with necroststin-1 1 hour before exposure to 6-hydroxydopamine. We examined cell viability, mitochondrial membrane potential and expression patterns of apoptotic and necroptotic death signaling proteins. The results showed that the autophagy/lysosomal pathway is involved in the 6-hydroxydopamine-induced death process of PC12 cells. Mitochondrial disability induced overactive autophagy, increased cathepsin B expression, and diminished Bcl-2 expression. Necrostatin-1 within a certain concentration range（5–30 μM） elevated the viability of PC12 cells, stabilized mitochondrial membrane potential, inhibited excessive autophagy, reduced the expression of LC3-II and cathepsin B, and increased Bcl-2 expression. These findings suggest that necrostatin-1 exerted a protective effect against injury on dopaminergic neurons. Necrostatin-1 interacts with the apoptosis signaling pathway during this process. This pathway could be a new neuroprotective and therapeutic target in Parkinson＇s disease.

The E3 ubiquitin ligase seven in absentia homolog 1 may be a potential new therapeutic target for Parkinson's disease

In this study, we investigated the effect of an antibody against E3 ubiquitin ligase seven in absentia homolog 1（SIAH-1） in PC12 cells. 1-Methyl-4-phenylpyridinium（MPP＋） treatment increased α-synuclein, E1 and SIAH-1 protein levels in PC12 cells, and it reduced cell viability; however, there was no significant change in light chain 3 expression. Treatment with an SIAH-1 antibody decreased m RNA expression levels of α-synuclein, light chain 3 and SIAH-1, but increased E1 m RNA expression. It also increased cell viability. Combined treatment with MPP＋ and rapamycin reduced SIAH-1 and α-synuclein levels. Treatment with SIAH-1 antibody alone diminished α-synuclein immunoreactivity in PC12 cells, and reduced the colocalization of α-synuclein and light chain 3. These findings suggest that the SIAH-1 antibody reduces the monoubiquitination and aggregation of α-synuclein, promoting its degradation by the ubiquitin-proteasome pathway. Consequently, SIAH-1 may be a potential new therapeutic target for Parkinson’s disease.

Chaperone-mediated autophagy: roles in neurodegeneration

Chaperone-mediated autophagy(CMA)selectively delivers cytosolic proteins with an exposed CMA-targeting motif to lysosomes for degradation and plays an important role in protein quality control and cellular homeostasis.A growing body of evidence supports the hypothesis that CMA dysfunction may be involved in the pathogenic process of neurodegenerative diseases.Both down-regulation and compensatory up-regulation in CMA activities have been observed in association with neurodegenerative conditions.Recent studies have revealed several new mechanisms by which CMA function may be involved in the regulation of factors critical for neuronal viability and homeostasis.Here,we summarize these recent advances in the understanding of the relationship between CMA dysfunction and neurodegeneration and discuss the therapeutic potential of targeting CMA in the treatment of neurodegenerative diseases.