Increase in membrane surface expression and phosphorylation of TRPC3 related to olfactory dysfunction in α-synuclein transgenic mice.

Olfactory impairment is an initial non-motor symptom of Parkinson's disease that causes the deposition of aggregated α-synuclein (α-syn) in olfactory neurons. Transient receptor potential canonical (TRPC) channels are a diverse group of non-selective Ca2+ entry channels involved in the progression or pathogenesis of PD via Ca2+ homeostatic regulation. However, the relationship between TRPC and α-syn pathology in an olfactory system remains unclear. To address this issue, we assessed the olfactory function in α-syn transgenic mice. In contrast with control mice, the transgenic mice exhibited impaired olfaction, TRPC3 activation and apoptotic neuronal cell death in the olfactory system. Similar results were observed in primary cultures of olfactory neurons, that is TRPC3 activation, increasing intracellular Ca2+ concentration and apoptotic cell death in the α-syn-overexpressed neurons. These changes were significantly attenuated by TRPC3 knockdown. Therefore, our findings suggest that TRPC3 activation and calcium dyshomeostasis play a key role in α-syn-induced olfactory dysfunction in mice.

Galectin-1 attenuates neurodegeneration in Parkinson's disease model by modulating microglial MAPK/IκB/NFκB axis through its carbohydrate-recognition domain.

The vicious cycle between the chronicactivationofmicroglia and dopamine neurons degeneration is linked with the progression of Parkinson's disease (PD). Targeting microglialactivationhas proven to be a viable option to develop a disease-modified therapy for PD. Galectin-1, which has been reported to have an anti-neuroinflammation effect was used in the present study to evaluate its therapeutic effects on microglia activation and neuronal degeneration in Parkinson's disease model. It was found that galectin-1 attenuated the inflammatory insult and the apoptosis of SK-N-SH human neuroblastoma cells from conditioned medium of activated microglia induced by Lipopolysaccharides (LPS). Nonetheless, galectin-1 administration (0.5 mg/kg) inhibited the microglia activation, improved the motor deficits in PD mice model induced by MPTP (25 mg/kg weight of mouse, i.p.) and prevented the degeneration of dopaminergic neurons in the substantia nigra. Administration of galectin-1 resulted in p38 and ERK1/2 dephosphorylation followed by IκB/NFκB signaling pathway inhibition. Galectin-1 significantly decreased the secretion of pro-inflammatory cytokines, including interleukin (IL)-1ß, tumor necrosis factor-α (TNF-α), and protein levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). The protective effects and modulation of the MAPK/IκB/NFκB signaling pathway were abolished with ß-D-galactose which blocked the carbohydrate-recognition domain of galectin-1. The present study demonstrated that galectin-1 inhibited microglia activation and ameliorated neurodegenerative process in PD model by modulating MAPK/IκB/NFκB axis through its carbohydrate-recognition domain.

New insight into Alzheimer's disease: Light reverses Aß-obstructed interstitial fluid flow and ameliorates memory decline in APP/PS1 mice.

INTRODUCTION: Pharmacological therapies to treat Alzheimer's disease (AD) targeting "Aß" have failed for over 100 years. Low levels of laser light can disassemble Aß. In this study, we investigated the mechanisms that Aß-blocked extracellular space (ECS) induces memory disorders in APP/PS1 transgenic mice and addressed whether red light (RL) at 630 nm rescues cognitive decline by reducing Aß-disturbed flow of interstitial fluid (ISF). METHODS: We compared the heating effects on the brains of rats illuminated with laser light at 630, 680, and 810 nm for 40 minutes, respectively. Then, a light-emitting diode with red light at 630 nm (LED-RL) was selected to illuminate AD mice. The changes in the structure of ECS in the cortex were examined by fluorescent double labeling. The volumes of ECS and flow speed of ISF were quantified by magnetic resonance imaging. Spatial memory behaviors in mice were evaluated by the Morris water maze. Then, the brains were sampled for biochemical analysis. RESULTS: RL at 630 nm had the least heating effects than other wavelengths associated with ~49% penetration ratio into the brains. For the molecular mechanisms, Aß could induce formaldehyde (FA) accumulation by inactivating FA dehydrogenase. Unexpectedly, in turn, FA accelerated Aß deposition in the ECS. However, LED-RL treatment not only directly destroyed Aß assembly in vitro and in vivo but also activated FA dehydrogenase to degrade FA and attenuated FA-facilitated Aß aggregation. Subsequently, LED-RL markedly smashed Aß deposition in the ECS, recovered the flow of ISF, and rescued cognitive functions in AD mice. DISCUSSION: Aß-obstructed ISF flow is the direct reason for the failure of the developed medicine delivery from superficial into the deep brain in the treatment of AD. The phototherapy of LED-RL improves memory by reducing Aß-blocked ECS and suggests that it is a promising noninvasive approach to treat AD.

Constitutive expression of GmF6'H1 from soybean improves salt tolerance in transgenic Arabidopsis.

Coumarin plays a pivotal role in plant response to biotic stress, as well as in the mediation of nutrient acquisition. However, its functions in response to abiotic stresses are largely unknown. In this work, a homologous gene, GmF6'H1, of AtF6'H1, which encodes the enzyme catalyzing the final rate-limiting step in the biosynthesis pathway of coumarin, was isolated from soybean. GmF6'H1 protein shares very high amino acid identity with AtF6'H1, and expression of GmF6'H1 in atf6'h1 can successfully restore the decreased coumarin production in the T-DNA insertion mutant. Further study revealed that the expression of GmF6'H1 in soybean was remarkably induced by salt stress. Constitutive expression of GmF6'H1 in Arabidopsis, driven by 35S promoter, significantly enhanced the resistance to salt of transgenic Arabidopsis. All these results suggest that GmF6'H1 can be used as a potential candidate gene for the engineering of plants with improved resistance to both biotic and abiotic stresses.

Progress of immunotherapy of anti-α-synuclein in Parkinson's disease.

Many neurodegenerative diseases are characterized by progressive loss of neurons and abnormal protein accumulation, including amyloid (A)ß and tau in Alzheimer's disease and Lewy bodies and α-synuclein (α-syn) in Parkinson's disease (PD). Recent evidence suggests that adaptive immunity plays an important role in PD, and that anti-α-syn antibodies can be used as therapy in neurodegenerative diseases; monoclonal antibodies were shown to inhibit α-syn propagation and aggregation in PD models and patients. In this review, we summarize the different pathological states of α-syn, including gene mutations, truncation, phosphorylation, and the high molecular weight form, and describe the specific antibodies that recognize the α-syn monomer or oligomer, some of which have been tested in clinic trials. We also discuss future research directions and potential targets in PD therapy.

Leucine Carboxyl Methyltransferase Downregulation and Protein Phosphatase Methylesterase Upregulation Contribute Toward the Inhibition of Protein Phosphatase 2A by α-Synuclein.

The pathology of Parkinson's disease (PD) is characterized by intracellular neurofibrillary tangles of phosphorylated α-synuclein (α-syn). Protein phosphatase 2A (PP2A) is responsible for α-syn dephosphorylation. Previous work has demonstrated that α-syn can regulate PP2A activity. However, the mechanisms underlying α-syn regulation of PP2A activity are not well understood. In this study, we found that α-syn overexpression induced increased α-syn phosphorylation at serine 129 (Ser129), and PP2A inhibition, in vitro and in vivo. α-syn overexpression resulted in PP2A demethylation. This demethylation was mediated via downregulated leucine carboxyl methyltransferase (LCMT-1) expression, and upregulated protein phosphatase methylesterase (PME-1) expression. Furthermore, LCMT-1 overexpression, or PME-1 inhibition, reversed α-syn-induced increases in α-syn phosphorylation and apoptosis. In addition to post-translational modifications of the catalytic subunit, regulatory subunits are involved in the regulation of PP2A activity. We found that the levels of regulatory subunits which belong to the PPP2R2 subfamily, not the PPP2R5 subfamily, were downregulated in the examined brain regions of transgenic mice. Our work identifies a novel mechanism to explain how α-syn regulates PP2A activity, and provides the optimization of PP2A methylation as a new target for PD treatment.

Pink1 Regulates Tyrosine Hydroxylase Expression and Dopamine Synthesis.

PTEN induced putative kinase 1 (PINK1), also known as PARK6, is causally linked to familial Parkinsonism, and heterozygous loss of PINK1 is a risk factor for sporadic Parkinson's disease. However, little is known about its physiological function. Its deficiency was shown to decrease dopamine without significant loss of dopaminergic neurons. We investigated the mechanistic basis for this observation in the present study using dopaminergic MN9D cells. We found that PINK1 knockdown resulted in dopamine content to decrease with suppressed tyrosine hydroxylase expression in cells. Conversely, PINK1 overexpression increased tyrosine hydroxylase protein level. We also found that PINK1 deficiency blocked the nuclear translocation and activity of nuclear receptor-related 1, a transcription factor regulating tyrosine hydroxylase gene expression. These data suggest that PINK1 regulates tyrosine hydroxylase gene expression and dopamine content by modulating the transcriptional activity of nuclear receptor-related 1. Taken together, our results reveal a novel function of PINK1 in dopamine homeostasis.

Piperlongumine restores the balance of autophagy and apoptosis by increasing BCL2 phosphorylation in rotenone-induced Parkinson disease models.

Parkinson disease (PD) is the second most common neurodegenerative disorder after Alzheimer disease and is caused by genetics, environmental factors and aging, with few treatments currently available. Apoptosis and macroautophagy/autophagy play critical roles in PD pathogenesis; as such, modulating their balance is a potential treatment strategy. BCL2 (B cell leukemia/lymphoma 2) is a key molecule regulating this balance. Piperlongumine (PLG) is an alkaloid extracted from Piper longum L. that has antiinflammatory and anticancer effects. The present study investigated the protective effects of PLG in rotenone-induced PD cell and mouse models. We found that PLG administration (2 and 4 mg/kg) for 4 wk attenuated motor deficits in mice and prevented the loss of dopaminergic neurons in the substantia nigra induced by oral administration of rotenone (10 mg/kg) for 6 wk. PLG improved cell viability and enhanced mitochondrial function in primary neurons and SK-N-SH cells. These protective effects were exerted via inhibition of apoptosis and induction of autophagy through enhancement of BCL2 phosphorylation at Ser70. These results demonstrate that PLG exerts therapeutic effects in a rotenone-induced PD models by restoring the balance between apoptosis and autophagy. ABBREVIATIONS: 6-OHDA, 6-hydroxydopamine; ACTB, actin, beta; BafA1, bafilomycin A1; BAK1, BCL2-antagonist/killer 1; BAX, BCL2-associated X protein; BCL2, B cell leukemia/lymphoma2; BECN1, Beclin 1, autophagy related; CoQ10, coenzyme Q10; COX4I1/COX IV, cytochrome c oxidase subunit 4I1; CsA, cyclosporine A; ED50, 50% effective dose; FITC, fluorescein isothiocyanate; GFP, green fluorescent protein; HPLC, high-performance liquid chromatography; JC-1, tetraethylbenz-imidazolylcarbocyanine iodide; LC3, microtubule-associated protein 1 light chain3; LC-MS/MS, liquid chromatography-tandem mass spectrometry; LDH, lactate dehydrogenase; l-dopa, 3, 4-dihydroxyphenyl-l-alanine; MAPK8/JNK1, mitogen-activated protein kinase 8; MMP, mitochondrial membrane potential; mPTP, mitochondrial permeability transition pore; mRFP, monomeric red fluorescent protein; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NFE2L2/NRF2, nuclear factor, erythroid derived 2, like 2; PD, Parkinson disease; PLG, piperlongumine; pNA, p-nitroanilide; PI, propidium iodide; PtdIns3K, phosphatidylinositol 3-kinase; PtdIns3P, phosphatidylinositol-3-phosphate; PTX, paclitaxel; Rap, rapamycin; SQSTM1/p62, sequestosome 1; TH, tyrosine hydroxylase; TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labeling; WIPI2, WD repeat domain, phosphoinositide interacting 2; ZFYVE1/DFCP1, zinc finger, FYVE domain containing 1.

PINK1 suppresses alpha-synuclein-induced neuronal injury: a novel mechanism in protein phosphatase 2A activation.

Alpha-synuclein (α-Syn) and phosphatase and tensin homolog deleted on chromosome ten (PTEN)-induced putative kinase (PINK) 1 are proteins found in Lewy bodies, which are a pathological hallmark of Parkinson's disease (PD). PINK1 overexpression suppresses α-Syn-induced phenotypes and increases lifespan and health in an animal model of PD. It has been suggested that the two proteins regulate protein phosphatase (PP) 2A activity, but the underlying mechanisms and neuroprotective action of PP2A against PD-associated pathology are unknown. We found that α-Syn overexpression in SK-N-SH neuroblastoma cells and primary cortical neurons caused mitochondrial dysfunction and cell injury via phosphorylation of PP2A at Tyr307 and inhibition of its activity. Concomitant overexpression of PINK1 reversed this effect and restored the activity. The level of phospho-activated Src was increased in cells overexpressing α-Syn, which was reversed by co-expressing PINK1, suggesting that the latter suppressed α-Syn-induced PP2A inactivation by inhibiting Src activity. Calmodulin/Src complex formation was also enhanced in α-Syn-overexpressing cells, which was reversed by co-expression of PINK1 as a result of reduced mitochondrial Ca2+ releasing. Interestingly, the protective effects of PINK1 in α-Syn induced models were abolished by treatment with the PP2A inhibitor okadaic acid, indicating that PP2A is a target of PINK1. These findings indicate that PINK1 protects against α-Syn-induced neurodegeneration by promoting the dissociation of the calmodulin/Src complex and inhibiting Src, thereby enhancing PP2A activity. This was supported by the observation that PP2A activity was decreased in PD patients, which was negatively correlated with Hoehn and Yahr scores. Our results provide novel insight into the mechanisms underlying neurodegeneration in PD as well as possible avenues for therapeutic intervention in the treatment of this disease.

Morphological analysis of mitochondria for evaluating the toxicity of α-synuclein in transgenic mice and isolated preparations by atomic force microscopy.

A key molecular event in the pathogenesis of Parkinson's disease is mitochondrial damage caused by α-synuclein (α-syn). Mitochondria mediates both necrosis and apoptosis, which are associated with morphological changes. However, the mechanism by which α-syn alters mitochondrial morphology remains unclear. To address this issue, we investigated mitochondrial permeability transition pore (mPTP) opening and changes in cardiolipin (CL) levels in mitochondria isolated from the brain of Thy1α-syn mice. Cytoplasmic cytochrome C and cleaved caspase-3 protein levels were upregulated in the brain of transgenic mice. Morphological analysis by atomic force microscopy (AFM) suggested a correlation between mitochondrial morphology and function in these animals. Incubation of isolated mitochondria with recombinant human α-synuclein N terminus (α-syn/N) decreased mitochondrial CL content. An AFM analysis showed that α-syn/N induced mitochondrial swelling and the formation of pore-like structures, which was associated with decreased mitochondrial transmembrane potential and complex I activity. The observed mitochondrial dysfunction was abrogated by treatment with the mPTP inhibitor cyclosporin A, although there was no recovery of CL content. These results provide insight into the mechanism by which α-syn/N directly undermines mitochondrial structure and function via modulation of mPTP opening and CL levels, and suggests that morphological analysis of isolated mitochondria by AFM is a useful approach for evaluating mitochondrial injury.

Pink1 interacts with α-synuclein and abrogates α-synuclein-induced neurotoxicity by activating autophagy.

Parkinson's disease (PD) is one of the most common neurodegenerative diseases, characterized by degeneration of dopaminergic neurons in the substantia nigra. α-synuclein (α-syn) and PTEN-induced putative kinase (PINK)1 are two critical proteins associated with the pathogenesis of PD. α-syn induces mitochondrial deficits and apoptosis, PINK1 was found to alleviate α-syn-induced toxicity, but the mechanistic details remain obscure. Here, we show that PINK1 interacts with α-syn mainly in the cytoplasm, where it initiates autophagy. This interaction was dependent on the kinase activity of PINK1 and was abolished by deletion of the kinase domain or a G309D point mutation, an inactivating mutation in the kinase domain. Interaction between PINK1 and α-syn stimulated the removal of excess α-syn, which prevented mitochondrial deficits and apoptosis. Our findings provide evidence for a novel mechanism underlying the protective effects of PINK1 against α-syn-induced neurodegeneration and highlight a novel therapeutic target for PD treatment.

Age-dependent alpha-synuclein accumulation is correlated with elevation of mitochondrial TRPC3 in the brains of monkeys and mice.

Aberrant α-synuclein (α-syn) accumulation has been shown to impair mitochondrial function by reducing mitochondrial membrane potential (MMP). However, the underlying mechanisms remain elusive. Transient receptor potential canonical (TRPC) channels are a diverse group of non-selective Ca2+ channels, among which TRPC3 is the only one that is localized in mitochondria and plays a role in maintaining the normal MMP. This raises a possibility that altered TRPC3 expression may play a role in the mitochondrial dysfunction induced by α-syn accumulation. To demonstrate this possibility, we first examined the expressions of mitochondrial TRPC3 in the brains of aging monkeys and α-syn transgenic and wild-type mice. We showed that α-syn levels increased in mitochondria in an age-dependent manner that was positively correlated to an elevation of mitochondrial TRPC3. This correlation was more prominent in the striatum than in the cerebellum, possibly due to the greater age-dependent α-syn accumulation in the striatum than in the cerebellum. We then used primary neurons overexpressing α-syn to investigate the effect of the α-syn-induced elevation of mitochondrial TRPC3 on the MMP and apoptotic cell death. We found that neurons with overexpressed α-syn had increased mitochondrial TRPC3 and decreased MMP, which were accompanied by increased number of apoptotic neurons. Suppressing TRPC3 expression partially reversed the reduction of MMP and alleviated the apoptotic cell death, indicating that the mitochondrial TRPC3 may play a role in the mitochondrial dysfunction in neurons with α-syn accumulation that may occur in not only the aged brain but also the brain with PD.

Piperine induces autophagy by enhancing protein phosphotase 2A activity in a rotenone-induced Parkinson's disease model.

Parkinson's disease (PD) is the second most common neurodegenerative disorder, but there are few treatments currently available. The autophagy pathway plays an important role in the pathogenesis of PD; modulating this pathway is considered to be a promising treatment strategy. Piperine (PIP) is a Chinese medicine with anti-inflammatory and antioxidant effects. The present study investigated the neuroprotective effects of PIP on rotenone-induced neurotoxicity in SK-N-SH cells, primary rat cortical neurons, and in a mouse model. Mice were administered rotenone (10mg/kg) for 6 weeks; PIP (25mg/kg, 50mg/kg) was subsequently administered for 4 weeks. We found that PIP treatment attenuated rotenone-induced motor deficits, and rescued the loss of dopaminergic neurons in the substantia nigra. PIP increased cell viability and restored mitochondrial functioning in SK-N-SH cells and primary neurons. In addition, PIP induced autophagy by inhibiting mammalian target of rapamycin complex 1(mTORC1) via activation of protein phosphotase 2A (PP2A). However, inhibiting PP2A activity with okadaic acid reduced these protective effects, suggesting that PP2A is a target of PIP. These findings demonstrate that PIP exerts neuroprotective effects in PD models via induction of autophagy, and may be an effective agent for PD treatment.

V63 and N65 of overexpressed α-synuclein are involved in mitochondrial dysfunction.

Parkinson's Disease (PD) is one of the most common neurodegenerative diseases. α-Synuclein (α-Syn)-encoded by SNCA, the first-identified PD-related gene-is the main component of Lewy bodies, which are a pathological hallmark of PD. We previously reported that α-Syn accumulates in mitochondria in PD, causing mitochondrial abnormalities and disrupting mitochondrial membrane potential (Δψm) and mitochondrial potential transition pore (mPTP) opening by interacting with the voltage-dependent anion channel (VDAC) and adenine nucleotide translocator. However, the mechanistic basis of mitochondrial impairment caused by α-Syn has yet to be elucidated. It has been suggested that the amino acid residues Q62, V63, and N65 of α-Syn are important for the interaction of the protein with membranes. To investigate whether this underlies the mitochondrial dysfunction induced by α-Syn overexpression, we mutated these residues to alanine and transfected HEK293T and MN9D cells with the mutated forms of α-Syn protein. The V63A and N65A mutations prevented mitochondrial Ca(2+) overload and Δψm dysregulation as well as complex I inactivation and reactive oxygen species production while blocking mPTP opening and caspase 9 activation, possibly by reducing α-Syn accumulation in mitochondria. These results indicate that V63 and N65 are critical residues mediating mitochondrial inactivation. These findings provide novel insight into the molecular events contributing to PD pathogenesis.

The novel mechanism of rotenone-induced α-synuclein phosphorylation via reduced protein phosphatase 2A activity.

Rotenone has been shown to induce many parkinsonian features and has been widely used in chemical models of Parkinson's disease (PD). Its use is closely associated with α-synuclein (α-syn) phosphorylation both in vivo and in vitro. However, the mechanisms whereby rotenone regulates α-syn phosphorylation remain unknown. Protein phosphatase 2A (PP2A) has been shown to play an important role in α-syn dephosphorylation. We therefore investigated if rotenone caused α-syn phosphorylation by down-regulation of PP2A activity in mice. Rotenone increased the phosphorylation of α-syn at Ser129, consistent with the inhibition of PP2A activity by increased phosphorylation of tyrosine 307 at the catalytic subunit of PP2A (pTyr307 PP2Ac). We further explored the interactions among rotenone, PP2A, and α-syn in SK-N-SH cells and primary rat cortical neurons. Rotenone inhibited PP2A activity via phosphorylation of PP2Ac at Tyr307. The reduction in PP2A activity and rotenone cytotoxicity were reversed by treatment with the PP2A agonist, C2 ceramide, and the Src kinase inhibitor, SKI606. Immunoprecipitation experiments showed that rotenone induced an increase in calmodulin-Src complex in SK-N-SH cells, thus activating Src kinase, which in turn phosphorylated PP2A at Tyr307 and inhibited its activity. C2 ceramide and SKI606 significantly reversed the rotenone-induced phosphorylation and aggregation of α-syn by increasing PP2A activity. These results demonstrate that rotenone-reduced PP2A activity via Src kinase is involved in the phosphorylation of α-syn. These findings clarify the novel mechanisms whereby rotenone can induce PD.

Reduction of Endogenous Melatonin Accelerates Cognitive Decline in Mice in a Simulated Occupational Formaldehyde Exposure Environment.

Individuals afflicted with occupational formaldehyde (FA) exposure often suffer from abnormal behaviors such as aggression, depression, anxiety, sleep disorders, and in particular, cognitive impairments. Coincidentally, clinical patients with melatonin (MT) deficiency also complain of cognitive problems associated with the above mental disorders. Whether and how FA affects endogenous MT metabolism and induces cognitive decline need to be elucidated. To mimic occupational FA exposure environment, 16 healthy adult male mice were exposed to gaseous FA (3 mg/m³) for 7 consecutive days. Results showed that FA exposure impaired spatial memory associated with hippocampal neuronal death. Biochemical analysis revealed that FA exposure elicited an intensive oxidative stress by reducing systemic glutathione levels, in particular, decreasing brain MT concentrations. Inversely, intraperitoneal injection of MT markedly attenuated FA-induced hippocampal neuronal death, restored brain MT levels, and reversed memory decline. At tissue levels, injection of FA into the hippocampus distinctly reduced brain MT concentrations. Furthermore, at cellular and molecular levels, we found that FA directly inactivated MT in vitro and in vivo. These findings suggest that MT supplementation contributes to the rescue of cognitive decline, and may alleviate mental disorders in the occupational FA-exposed human populations.

[Research Progress of Pathogenesis and Treatment of Parkinsons Disease].

Parkinson's disease (PD) is the second most common neurodegenerative disease. The most prominent pathological features are the loss of dopaminergic neurons in the substantia nigra pars compacta and the deposition of intraneuronal inclusions named Lewy bodies in most cases. The most prominent symptom of PD is the impairment of motor behavior due to the loss of dopaminergic neurons and the consequent loss of the dopamine signaling in the basal ganglia. So DA replacement (including L-dopa, the gold standard treatment) still remains to be the best treatment for the disease due to its ability of relieving most of the motor symptoms. Growing evidence suggests that a combination of environmental, genetic factors and aging may contribute to PD. Mitochondrial dysfunction, oxidative stress, neuroinflammation, and excitability toxicity contribute to the pathogensis of PD. Currently available treatments for PD, including drug therapy, surgical treatment, cell and tissue transplantation and gene therapy, but their efficacy was unsatisfactory. Here we review the most recent findings and developments about pathogenesis and treatment of PD, and hope to offer some clues for clinical drug development and novel alternative therapies.

GBA deficiency promotes SNCA/α-synuclein accumulation through autophagic inhibition by inactivated PPP2A.

Loss-of-function mutations in the gene encoding GBA (glucocerebrosidase, ß, acid), the enzyme deficient in the lysosomal storage disorder Gaucher disease, elevate the risk of Parkinson disease (PD), which is characterized by the misprocessing of SNCA/α-synuclein. However, the mechanistic link between GBA deficiency and SNCA accumulation remains poorly understood. In this study, we found that loss of GBA function resulted in increased levels of SNCA via inhibition of the autophagic pathway in SK-N-SH neuroblastoma cells, primary rat cortical neurons, or the rat striatum. Furthermore, expression of the autophagy pathway component BECN1 was downregulated as a result of the GBA knockdown-induced decrease in glucocerebrosidase activity. Most importantly, inhibition of autophagy by loss of GBA function was associated with PPP2A (protein phosphatase 2A) inactivation via Tyr307 phosphorylation. C2-ceramide (C2), a PPP2A agonist, activated autophagy in GBA-silenced cells, while GBA knockdown-induced SNCA accumulation was reversed by C2 or rapamycin (an autophagy inducer), suggesting that PPP2A plays an important role in the GBA knockdown-mediated inhibition of autophagy. These findings demonstrate that loss of GBA function may contribute to SNCA accumulation through inhibition of autophagy via PPP2A inactivation, thereby providing a mechanistic basis for the increased PD risk associated with GBA deficiency.

Alpha-synuclein overexpression negatively regulates insulin receptor substrate 1 by activating mTORC1/S6K1 signaling.

Alpha-synuclein (α-Syn) is a major component of Lewy bodies, a pathological feature of Parkinson's and other neurodegenerative diseases collectively known as synucleinopathies. Among the possible mechanisms of α-Syn-mediated neurotoxicity is interference with cytoprotective pathways such as insulin signaling. Insulin receptor substrate (IRS)-1 is a docking protein linking IRs to downstream signaling pathways such as phosphatidylinositol 3-kinase/Akt and mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase (S6K)1; the latter exerts negative feedback control on insulin signaling, which is impaired in Alzheimer's disease. Our previous study found that α-Syn overexpression can inhibit protein phosphatase (PP)2A activity, which is involved in the protective mechanism of insulin signaling. In this study, we found an increase in IRS-1 phosphorylation at Ser636 and decrease in tyrosine phosphorylation, which accelerated IRS-1 turnover and reduced insulin-Akt signaling in α-Syn-overexpressing SK-N-SH cells and transgenic mice. The mTOR complex (C)1/S6K1 blocker rapamycin inhibited the phosphorylation of IRS-1 at Ser636 in cells overexpressing α-Syn, suggesting that mTORC1/S6K1 activation by α-Syn causes feedback inhibition of insulin signaling via suppression of IRS-1 function. α-Syn overexpression also inhibited PP2A activity, while the PP2A agonist C2 ceramide suppressed both S6K1 activation and IRS-1 Ser636 phosphorylation upon α-Syn overexpression. Thus, α-Syn overexpression negatively regulated IRS-1 via mTORC1/S6K1 signaling while activation of PP2A reverses this process. These results provide evidence for a link between α-Syn and IRS-1 that may represent a novel mechanism for α-Syn-associated pathogenesis.