Pathogenic roles of alpha-synuclein in Parkinson’s disease and multiple system atrophy

Alpha-synucleinopathies(α-synucleinopathies)are a diverse group of neurodegenerative diseases comprising Parkinson’s disease(PD),dementia with Lewy bodies(DLB),and multiple system atrophy(MSA).Although in all these diseases there exist abnormal accumulation of alpha-synuclein(α-syn)aggregates in nerve tissues,the pathological lesions formed byα-syn aggregates and their cellular locations are quite different.In PD and DLB,the hallmark pathological lesions are Lewy bodies(LBs)and Lewy neurites(LNs),which are localized in the neuronal somata and processes.In MSA,the characteristic pathologic structures are glial cytoplasmic inclusions,which are deposited in the cytoplasm of oligodendrocytes.The fact that PD and MSA have distinct pathologicalα-syn lesions suggest that different mechanisms play a role in the pathogenesis of the two diseases.In this review article,we compare the clinical manifestations and pathological features of PD and MSA,the two common synucleinopathies,and discuss the potential mechanisms for the formation ofα-syn aggregates and their pathologic roles in PD and MSA.

Subcellular localization of alpha-synuclein aggregates and their interaction with membranes

For more than a decade numerous evidence has been reported on the mechanisms of toxicity of α-synuclein（αS） oligomers and aggregates in α-synucleinopathies.These species were thought to form freely in the cytoplasm but recent reports of αS multimer conformations when bound to synaptic vesicles in physiological conditions,have raised the question about where αS aggregation initiates.In this review we focus on recent literature regarding the impact on membrane binding and subcellular localization of αS toxic species to understand how regular cellular function of αS contributes to pathology.Notably αS has been reported to mainly associate with specific membranes in neurons such as those of synaptic vesicles,ER/Golgi and the mitochondria,while toxic species of αS have been shown to inhibit,among others,neurotransmission,protein trafficking and mitochondrial function.Strategies interfering with αS membrane binding have shown to improve αS-driven toxicity in worms and in mice.Thus,a selective membrane binding that would result in a specific subcellular localization could be the key to understand how aggregation and pathology evolves,pointing out to αS functions that are primarily affected before onset of irreversible damage.

Constipation,deficit in colon contractions and alpha-synuclein inclusions within the colon precede motor abnormalities and neurodegeneration in the central nervous system in a mouse model of alphasynucleinopathy

Background:Gastrointestinal dysfunction can affect Parkinson’s disease(PD)patients long before the onset of motor symptoms.However,little is known about the relationship between gastrointestinal abnormalities and the development of PD.Contrary to other animal models,the human A53T alpha-synuclein(αS)transgenic mice,Line G2–3,developsαS-driven neurological and motor impairments after 9 months of age,displaying a long presymptomatic phase free of central nervous system(CNS)dysfunction.Methods:To determine whether this line can be suitable to study constipation as it occurs in prodromal PD,gastrointestinal functionality was assessed in young mice through a multidisciplinary approach,based on behavioral and biochemical analysis combined with electrophysiological recordings of mouse intestinal preparations.Results:We found that the A53TαS mice display remarkable signs of gastrointestinal dysfunction that precede motor abnormalities andαS pathology in the CNS by at least 6 months.YoungαS mice show a drastic delay in food transit along the gastrointestinal tract,of almost 2 h in 3 months old mice that increased to more than 3 h at 6 months.Such impairment was associated with abnormal formation of stools that resulted in less abundant but longer pellets excreted,suggesting a deficit in the intestinal peristalsis.In agreement with this,electrically evoked contractions of the colon,but not of the ileum,showed a reduced motor response in both longitudinal and circular muscle layers inαS mice already at 3 months of age,that was mainly due to an impaired cholinergic transmission of the underlying enteric nervous system.Interestingly,the presence of insoluble and aggregatedαS was found in enteric neurons in both myenteric and submucosal plexi only in the colon of 3 months oldαS mice,but not in the small intestine,and exacerbated with age,mimicking the increase in transit delay and the contraction deficit showed by behavioral and electrical recordings data.Conclusions:Gastrointestinal dysfunction in A53TαS mice represents an early sign ofαS-driven pathology without concomitant CNS involvement.We believe that this model can be very useful to study disease-modifying strategies that could extend the prodromal phase of PD and haltαS pathology from reaching the brain.

Adenosine A1 receptor ligands bind toα-synuclein:implications forα-synuclein misfolding andα-synucleinopathy in Parkinson’s disease

Background:Accumulatingα-synuclein(α-syn)aggregates in neurons and glial cells are the staples of many synucleinopathy disorders,such as Parkinson’s disease(PD).Since brain adenosine becomes greatly elevated in ageing brains and chronic adenosine A1 receptor(A1R)stimulation leads to neurodegeneration,we determined whether adenosine or A1R receptor ligands mimic the action of known compounds that promoteα-syn aggregation(e.g.,the amphetamine analogue 2-aminoindan)or inhibitα-syn aggregation(e.g.,Rasagiline metabolite 1-aminoindan).In the present study,we determined whether adenosine,A1R receptor agonist N^(6)-Cyclopentyladenosine(CPA)and antago-nist 8-cyclopentyl-1,3-dipropylxanthine(DPCPX)could directly interact withα-syn to modulateα-syn aggregation and neurodegeneration of dopaminergic neurons in the substantia nigra(SN).Methods:Nanopore analysis and molecular docking were used to test the binding properties of CPA and DPCPX withα-syn in vitro.Sprague-Dawley rats were administered with 7-day intraperitoneal injections of the A1R ligands and 1-and 2-aminoindan,and levels ofα-syn aggregation and neurodegeneration were examined in the SN pars compacta and hippocampal regions using confocal imaging and Western blotting.Results:Using nanopore analysis,we showed that the A1R agonists(CPA and adenosine)interacted with the N-terminus ofα-syn,similar to 2-aminoindan,which is expected to promote a“knot”conformation andα-syn misfolding.In contrast,the A1R antagonist DPCPX interacted with the N-and C-termini ofα-syn,similar to 1-aminoindan,which is expected to promote a“loop”conformation that preventsα-syn misfolding.Molecular docking studies revealed that adenosine,CPA and 2-aminoindan interacted with the hydrophobic core ofα-syn N-terminus,whereas DPCPX and 1-aminoindan showed direct binding to the N-and C-terminal hydrophobic pockets.Confocal imaging and Western blot analyses revealed that chronic treatments with CPA alone or in combination with 2-aminoindan increasedα-syn expression/aggregation and neurodegeneration in both SN pars compacta and hippocampus.In contrast,DPCPX and 1-aminoindan attenuated the CPA-inducedα-syn expression/aggregation and neurodegeneration in SN and hippocampus.Conclusions:The results indicate that A1R agonists and drugs promoting a“knot”conformation ofα-syn can causeα-synucleinopathy and increase neuronal degeneration,whereas A1R antagonists and drugs promoting a“loop”con-formation ofα-syn can be harnessed for possible neuroprotective therapies to decreaseα-synucleinopathy in PD.