Alpha synuclein post translational modifications: potential targets for Parkinson’s disease therapy?

Parkinson’s disease (PD) is the most common neurodegenerative disorder with motor symptoms. The neuropathological alterations characterizing the brain of patients with PD include the loss of dopaminergic neurons of the nigrostriatal system and the presence of Lewy bodies (LB), intraneuronal inclusions that are mainly composed of alpha-synuclein (α-Syn) fibrils. The accumulation of α-Syn in insoluble aggregates is a main neuropathological feature in PD and in other neurodegenerative diseases, including LB dementia (LBD) and multiple system atrophy (MSA), which are therefore defined as synucleinopathies. Compelling evidence supports that α-Syn post translational modifications (PTMs) such as phosphorylation, nitration, acetylation, O-GlcNAcylation, glycation, SUMOylation, ubiquitination and C-terminal cleavage, play important roles in the modulation α-Syn aggregation, solubility, turnover and membrane binding. In particular, PTMs can impact on α-Syn conformational state, thus supporting that their modulation can in turn affect α-Syn aggregation and its ability to seed further soluble α-Syn fibrillation. This review focuses on the importance of α-Syn PTMs in PD pathophysiology but also aims at highlighting their general relevance as possible biomarkers and, more importantly, as innovative therapeutic targets for synucleinopathies. In addition, we call attention to the multiple challenges that we still need to face to enable the development of novel therapeutic approaches modulating α-Syn PTMs

Acetylated α-Tubulin and α-Synuclein: Physiological Interplay and Contribution to α-Synuclein Oligomerization

Emerging evidence supports that altered α-tubulin acetylation occurs in Parkinson’s disease (PD), a neurodegenerative disorder characterized by the deposition of α-synuclein fibrillary aggregates within Lewy bodies and nigrostriatal neuron degeneration. Nevertheless, studies addressing the interplay between α-tubulin acetylation and α-synuclein are lacking. Here, we investigated the relationship between α-synuclein and microtubules in primary midbrain murine neurons and the substantia nigra of post-mortem human brains. Taking advantage of immunofluorescence and Proximity Ligation Assay (PLA), a method allowing us to visualize protein–protein interactions in situ, combined with confocal and super-resolution microscopy, we found that α-synuclein and acetylated α-tubulin colocalized and were in close proximity. Next, we employed an α-synuclein overexpressing cellular model and tested the role of α-tubulin acetylation in α-synuclein oligomer formation. We used the α-tubulin deacetylase HDAC6 inhibitor Tubacin to modulate α-tubulin acetylation, and we evaluated the presence of α-synuclein oligomers by PLA. We found that the increase in acetylated α-tubulin significantly induced α-synuclein oligomerization. In conclusion, we unraveled the link between acetylated α-tubulin and α-synuclein and demonstrated that α-tubulin acetylation could trigger the early step of α-synuclein aggregation. These data suggest that the proper regulation of α-tubulin acetylation might be considered a therapeutic strategy to take on PD

Synapsin III Regulates Dopaminergic Neuron Development in Vertebrates

Attention deficit and hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by alterations in the mesocorticolimbic and nigrostriatal dopaminergic pathways. Polymorphisms in the Synapsin III (Syn III) gene can associate with ADHD onset and even affect the therapeutic response to the gold standard ADHD medication, methylphenidate (MPH), a monoamine transporter inhibitor whose efficacy appears related with the stimulation of brain-derived neurotrophic factor (BDNF). Interestingly, we previously showed that MPH can bind Syn III, which can regulate neuronal development. These observations suggest that Syn III polymorphism may impinge on ADHD onset and response to therapy by affecting BDNF-dependent dopaminergic neuron development. Here, by studying zebrafish embryos exposed to Syn III gene knock-down (KD), Syn III knock-out (ko) mice and human induced pluripotent stem cells (iPSCs)-derived neurons subjected to Syn III RNA interference, we found that Syn III governs the earliest stages of dopaminergic neurons development and that this function is conserved in vertebrates. We also observed that in mammals Syn III exerts this function acting upstream of brain-derived neurotrophic factor (BDNF)- and cAMP-dependent protein kinase 5 (Cdk5)-stimulated dendrite development. Collectively, these findings own significant implications for deciphering the biological basis of ADHD

Methylphenidate Analogues as a New Class of Potential Disease-Modifying Agents for Parkinson’s Disease: Evidence from Cell Models and Alpha-Synuclein Transgenic Mice

Parkinson’s disease (PD) is characterized by dopaminergic nigrostriatal neurons degeneration and Lewy body pathology, mainly composed of α-synuclein (αSyn) fibrillary aggregates. We recently described that the neuronal phosphoprotein Synapsin III (Syn III) participates in αSyn pathology in PD brains and is a permissive factor for αSyn aggregation. Moreover, we reported that the gene silencing of Syn III in a human αSyn transgenic (tg) mouse model of PD at a pathological stage, manifesting marked insoluble αSyn deposits and dopaminergic striatal synaptic dysfunction, could reduce αSyn aggregates, restore synaptic functions and motor activities and exert neuroprotective effects. Interestingly, we also described that the monoamine reuptake inhibitor methylphenidate (MPH) can recover the motor activity of human αSyn tg mice through a dopamine (DA) transporter-independent mechanism, which relies on the re-establishment of the functional interaction between Syn III and α-helical αSyn. These findings support that the pathological αSyn/Syn III interaction may constitute a therapeutic target for PD. Here, we studied MPH and some of its analogues as modulators of the pathological αSyn/Syn III interaction. We identified 4-methyl derivative I-threo as a lead candidate modulating αSyn/Syn III interaction and having the ability to reduce αSyn aggregation in vitro and to restore the motility of αSyn tg mice in vivo more efficiently than MPH. Our results support that MPH derivatives may represent a novel class of αSyn clearing agents for PD therapy

Alpha-synuclein/synapsin III pathological interplay boosts the motor response to methylphenidate

16siLoss of dopaminergic nigrostriatal neurons and fibrillary α-synuclein (α-syn) aggregation in Lewy bodies (LB) characterize Parkinson's disease (PD). We recently found that Synapsin III (Syn III), a phosphoprotein regulating dopamine (DA) release with α-syn, is another key component of LB fibrils in the brain of PD patients and acts as a crucial mediator of α-syn aggregation and toxicity. Methylphenidate (MPH), a monoamine reuptake inhibitor (MRI) efficiently counteracting freezing of gait in advanced PD patients, can bind α-syn and controls α-syn-mediated DA overflow and presynaptic compartmentalization. Interestingly, MPH results also efficient for the treatment of attention deficits and hyperactivity disorder (ADHD), a neurodevelopmental psychiatric syndrome associated with Syn III and α-syn polymorphisms and constituting a risk factor for the development of LB disorders. Here, we studied α-syn/Syn III co-deposition and longitudinal changes of α-syn, Syn III and DA transporter (DAT) striatal levels in nigrostriatal neurons of a PD model, the human C-terminally truncated (1−120) α-syn transgenic (SYN120 tg) mouse, in comparison with C57BL/6J wild type (wt) and C57BL/6JOlaHsd α-syn null littermates. Then, we analyzed the locomotor response of these animals to an acute administration of MPH (d-threo) and other MRIs: cocaine, that we previously found to stimulate Syn III-reliant DA release in the absence of α-syn, or the selective DAT blocker GBR-12935, along aging. Finally, we assessed whether these drugs modulate α-syn/Syn III interaction by fluorescence resonance energy transfer (FRET) and performed in silico studies engendering a heuristic model of the α-syn conformations stabilized upon MPH binding. We found that only MPH was able to over-stimulate a Syn III-dependent/DAT-independent locomotor activity in the aged SYN120 tg mice showing α-syn/Syn III co-aggregates. MPH enhanced full length (fl) α-syn/Syn III and even more (1–120) α-syn/Syn III interaction in cells exhibiting α-syn/Syn III inclusions. Moreover, in silico studies confirmed that MPH may reduce α-syn fibrillation by stabilizing a protein conformation with increased lipid binding predisposition. Our observations indicate that the motor-stimulating effect of MPH can be positively fostered in the presence of α-syn/Syn III co-aggregation. This evidence holds significant implications for PD and ADHD therapeutic management.openopenFaustini G.; Longhena F.; Bruno A.; Bono F.; Grigoletto J.; La Via L.; Barbon A.; Casiraghi A.; Straniero V.; Valoti E.; Costantino G.; Benfenati F.; Missale C.; Pizzi M.; Spillantini M.G.; Bellucci A.Faustini, G.; Longhena, F.; Bruno, A.; Bono, F.; Grigoletto, J.; La Via, L.; Barbon, A.; Casiraghi, A.; Straniero, V.; Valoti, E.; Costantino, G.; Benfenati, F.; Missale, C.; Pizzi, M.; Spillantini, M. G.; Bellucci, A

Kinetics of hepatitis B virus load during haemodialysis sessions and α-interferon: A prospective study

Background: It has been reported a slow progression of hepatitis B in patients undergoing maintenance dialysis, and a role of dialysis session per se has been suggested. The aim of the present study is to evaluate the kinetics of the hepatitis B viral load (HBV DNA) in serum during haemodialysis sessions using a highly sensitive technique; the role of interferon-\u3b1 in lowering HBV viral load in such patients was also investigated. Methods: HBV DNA was determined in 24 HBsAg positive patients on maintenance hemodialysis immediately before and after a 4-hour hemodialysis session, the same measurements were repeated 48 and 72 hours later. HBV DNA quantitation was performed by a novel RealTime PCR assay. Serum IFN-\u3b1 levels were tested in parallel in a subset of HD sessions (n=40) by ELISA. Results: 20 (83%) HBsAg positive patients had detectable HBV DNA in serum. Positive status for HBV DNA in serum was not predicted by demographic, clinical or biochemical parameters. HBV load decreased in many patients after hemodialysis sessions 5.92 log10IU/mL (95% CI, 5.34 to 6.28 log10IU/mL) vs. 4.79 log10IU/mL (95% CI, 4.23 to 6.15 log10IU/mL) (P=0.02). A significant relationship between mean HBV DNA levels before dialysis and percentage reduction of HBV DNA during HD sessions occurred [F-test=5.41, rho (least squares)=0.307]. Increase of serum IFN-\u3b1 levels was found in a minority (3/40=7%) of HD sessions. Conclusions: Hemodialysis procedure gives reduction of HBV load in HBsAg chronic carriers; no relationship with IFN-\u3b1 activity during HD sessions was found. The kinetics of HBV viremia in HD procedures could explain the low viral load which is typically observed in these patients. Further studies to identify the mechanisms responsible for reduction of HBV viremia during HD procedures are under way

Study of alpha-synuclein fibrillation: State of the art and expectations

Since the discovery of the presence of fibrillary forms of α-synuclein (α-syn) in Lewy bodies (LB) and Lewy neurites in the brain of patients affected by Parkinson’s disease (PD) and dementia with LB, great effort has been dedicated to study the features of α-syn fibrillation. In parallel, the pathological relevance of the different toxic forms of α-syn has been also matter of investigation. In the last twenty years, scientists have been able to single out that α-syn fibrillation initiates pathological mechanisms that by contributing to or triggering neurodegeneration/neuroinflammation, may lead to PD pathogenesis. This notwithstanding, we still ignore the reasons why α-syn shifts from its natively unfolded conformation to toxic oligomeric and fibrillary forms. The chameleonic nature of monomeric α-syn, and the extremely polymorphic characteristics of aggregated strains, renders it difficult to picture the real nature of α-syn fibrils, their exact composition and formation dynamics. Recently, sophisticated biophysical methods and microscopy techniques have been exploited to study α-syn fibrillation. Here, we provide an overview of the most relevant advancement in our understanding of α-syn fibrils formation and conformation. Nonetheless, numerous techniques and patient- derived experimental models still need to be optimized to actively disclose causes and characteristics of α-syn fibrillation in disease-specific cellular milieux

Nuclear Factor-κB Dysregulation and α-Synuclein Pathology: Critical Interplay in the Pathogenesis of Parkinson’s Disease

The loss of dopaminergic neurons of the nigrostriatal system underlies the onset of the typical motor symptoms of Parkinson’s disease (PD). Lewy bodies (LB) and Lewy neurites (LN), proteinaceous inclusions mainly composed of insoluble α-synuclein (α-syn) fibrils are key neuropathological hallmarks of the brain of affected patients. Compelling evidence supports that in the early prodromal phases of PD, synaptic terminal and axonal alterations initiate and drive a retrograde degeneration process culminating with the loss of nigral dopaminergic neurons. This notwithstanding, the molecular triggers remain to be fully elucidated. Although it has been shown that α-syn fibrillary aggregation can induce early synaptic and axonal impairment and cause nigrostriatal degeneration, we still ignore how and why α-syn fibrillation begins. Nuclear factor-κB (NF-κB) transcription factors, key regulators of inflammation and apoptosis, are involved in the brain programming of systemic aging as well as in the pathogenesis of several neurodegenerative diseases. The NF-κB family of factors consists of five different subunits (c-Rel, p65/RelA, p50, RelB, and p52), which combine to form transcriptionally active dimers. Different findings point out a role of RelA in PD. Interestingly, the nuclear content of RelA is abnormally increased in nigral dopamine (DA) neurons and glial cells of PD patients. Inhibition of RelA exert neuroprotection against (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) MPTP and 1-methyl-4-phenylpyridinium (MPP+) toxicity, suggesting that this factor decreases neuronal resilience. Conversely, the c-Rel subunit can exert neuroprotective actions. We recently described that mice deficient for c-Rel develop a PD-like motor and non-motor phenotype characterized by progressive brain α-syn accumulation and early synaptic changes preceding the frank loss of nigrostriatal neurons. This evidence supports that dysregulations in this transcription factors may be involved in the onset of PD. This review highlights observations supporting a possible interplay between NF-κB dysregulation and α-syn pathology in PD, with the aim to disclose novel potential mechanisms involved in the pathogenesis of this disorder

The good and bad of therapeutic strategies that directly target α-synuclein

Synucleinopathies are neurodegenerative diseases characterized by the accumulation of either neuronal/axonal or glial insoluble proteinaceous aggregates mainly composed of α‐synuclein (α‐syn). Among them, the most common disorders are Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, and some forms of familial parkinsonism. Both α‐syn fibrils and oligomers have been found to exert toxic effects on neurons or oligodendroglial cells, can activate neuroinflammatory responses, and mediate the spreading of α‐syn pathology. This poses the question of which is the most toxic α‐syn species. What is worst, α‐syn appears as a very peculiar protein, exerting multiple physiological functions in neurons, especially at synapses, but without acquiring a stable tertiary structure. Its conformation is particularly plastic, and the protein can exist in a natively unfolded state (mainly in solution), partially α‐helical folded state (when it interacts with biological membranes), or oligomeric state (tetramers or dimers with debated functional profile). The extent of α‐syn expression impinges on the resilience of neuronal cells, as multiplications of its gene locus, or overexpression, can cause neurodegeneration and onset of motor phenotype. For these reasons, one of the main challenges in the field of synucleinopathies, which still nowadays can only be managed by symptomatic therapies, has been the development of strategies aimed at reducing α‐syn levels, oligomer formation, fibrillation, or cell‐to‐cell transmission. This review resumes the therapeutic approaches that have been proposed or are under development to counteract α‐syn pathology by direct targeting of this protein and discuss their pros and cons in relation to the current state‐of‐the‐art α‐syn biology