The pre-synaptic protein alpha-synuclein is the main component of Lewy bodies and Lewy neurites, the defining neuropathological characteristics of Parkinson's disease and dementia with Lewy bodies. Mutations in the alpha-synuclein gene cause familial forms of Parkinson's disease and dementia with Lewy bodies. We previously described a transgenic mouse line expressing truncated human alpha-synuclein(1-120) that develops alpha-synuclein aggregates, striatal dopamine deficiency and reduced locomotion, similar to Parkinson's disease. We now show that in the striatum of these mice, as in Parkinson's disease, synaptic accumulation of alpha-synuclein is accompanied by an age-dependent redistribution of the synaptic SNARE proteins SNAP-25, syntaxin-1 and synaptobrevin-2, as well as by an age-dependent reduction in dopamine release. Furthermore, the release of FM1-43 dye from PC12 cells expressing either human full-length alpha-synuclein(1-140) or truncated alpha-synuclein(1-120) was reduced. These findings reveal a novel gain of toxic function of alpha-synuclein at the synapse, which may be an early event in the pathogenesis of Parkinson's disease.

Parkinson's disease (PD) is a common neurodegenerative disorder with prominent loss of nigro-striatal dopaminergic neurons. The resultant dopamine (DA) deficiency underlies the onset of typical motor symptoms (MS). Nonetheless, individuals affected by PD usually show a plethora of nonmotor symptoms (NMS), part of which may precede the onset of motor signs. Besides DA neuron degeneration, a key neuropathological alteration in the PD brain is Lewy pathology. This is characterized by abnormal intraneuronal (Lewy bodies) and intraneuritic (Lewy neurites) deposits of fibrillary aggregates mainly composed of α-synuclein. Lewy pathology has been hypothesized to progress in a stereotypical pattern over the course of PD and α-synuclein mutations and multiplications have been found to cause monogenic forms of the disease, thus raising the question as to whether this protein is pathogenic in this disorder. Findings showing that the majority of α-synuclein aggregates in PD are located at presynapses and this underlies the onset of synaptic and axonal degeneration, coupled to the fact that functional connectivity changes correlate with disease progression, strengthen this idea. Indeed, by altering the proper action of key molecules involved in the control of neurotransmitter release and re-cycling as well as synaptic and structural plasticity, α-synuclein deposition may crucially impair axonal trafficking, resulting in a series of noxious events, whose pressure may inevitably degenerate into neuronal damage and death. Here, we provide a timely overview of the molecular features of synaptic loss in PD and disclose their possible translation into clinical symptoms through functional disconnection.

J. Neurochem. (2011) 116, 588–605. Abstract Accumulation of misfolded proteins in the endoplasmic reticulum (ER) is the main event leading to the induction of the ER stress‐related unfolded protein response (UPR). Recent postmortem evaluation, showing that the UPR pathway is activated in nigral dopaminergic neurons bearing α‐synuclein inclusions in the brain of Parkinson’s disease (PD) patients, suggests that the activation of the UPR may be induced by the accumulation of α‐synuclein. In this study, we show that the misfolded protein‐sensor/UPR activator glucose‐regulated protein 78/immunoglobulin heavy chain‐binding protein was bound to α‐synuclein and was increased in ‘in vitro’ and ‘in vivo’ models showing aggregated α‐synuclein accumulation. Moreover, α‐synuclein accumulation induced the expression of the UPR‐related activating transcription factor 4/cAMP‐responsive element‐2. These findings indicate that activation of the UPR pathway in the PD brain is associated with α‐synuclein accumulation occurring in part within the ER.

Mice transgenic for human P301S tau protein exhibit many characteristics of the human tauopathies, including the formation of abundant filaments made of hyperphosphorylated tau protein and neurodegeneration leading to nerve cell loss. At 5 months of age, the pathological changes are most marked in brainstem and spinal cord. Here we show that these changes are accompanied by marked neuroinflammation. Many tau-positive nerve cells in brainstem and spinal cord were strongly immunoreactive for interleukin-1beta and cyclooxygenase-2, indicating induction and overproduction of proinflammatory cytokines and enzymes. In parallel, numerous activated microglial cells were present throughout brain and spinal cord of transgenic mice, where they concentrated around tau-positive nerve cells. These findings suggest that inflammation may play a significant role in the events leading to neurodegeneration in the tauopathies and that anti-inflammatory compounds may have therapeutic potential.