Poly (ADP-ribose) polymerase 1 and Parkinson's disease: A study in post-mortem human brain

Poly (ADP-ribose) polymerase 1 (PARP1) is crucial in both maintenance of genome integrity and cell death. PARP1 activation has been very recently linked to Parkinson's disease (PD) and its role in inducing the pathologic accumulation of α-Synuclein demonstrated in a PD mouse model. The objective of this study was to investigate the presence and localization of PARP1 in PD brain. PARP1 localization was assessed by immunostaining and confocal microscopy in post-mortem human brains obtained from PD patients (Braak stage VI) compared to controls. PARP1 positive nuclei in substantia nigra, mainly in dopaminergic neurons but also in astrocytes and oligodendrocytes, were decreased in PD. The same alteration was observed in several areas that are affected in PD pathology, namely the dorsal motor nucleus of vagus, frontal and cingulate cortex, whereas no changes in PARP1 staining were detectable in the inferior olivary nucleus that is unaffected in PD. In addition, PARP1 co-localizes with α-Synuclein that is accumulated in the cytoplasm and in Lewy bodies of PD tissue sections. Our data reveal previously unknown changes of PARP1 localization in the brain of PD patients, in both neurons and glia, supporting its widespread involvement in this pathology and its potential use as a therapeutic target.

α-Synuclein oligomers in skin biopsy of idiopathic and monozygotic twin patients with Parkinson's disease

A variety of cellular processes, including vesicle clustering in the presynaptic compartment, are impaired in Parkinson’s disease and have been closely associated with α-synuclein oligomerization. Emerging evidence proves the existence of α-synuclein-related pathology in the peripheral nervous system, even though the presence of α-synuclein oligomers in situ in living patients remains poorly investigated. In this case-control study, we show previously undetected α-synuclein oligomers within synaptic terminals of autonomic fibres in skin biopsies by means of the proximity ligation assay and propose a procedure for their quantification (proximity ligation assay score). Our study revealed a significant increase in α-synuclein oligomers in consecutive patients with Parkinson’s disease compared to consecutive healthy controls (P < 0.001). Proximity ligation assay score (threshold value > 96 using receiver operating characteristic) was found to have good sensitivity, specificity and positive predictive value (82%, 86% and 89%, respectively). Furthermore, to disclose the role of putative genetic predisposition in Parkinson’s disease aetiology, we evaluated the differential accumulation of oligomers in a unique cohort of 19 monozygotic twins discordant for Parkinson’s disease. The significant difference between patients and healthy subjects was confirmed in twins. Intriguingly, although no difference in median values was detected between consecutive healthy controls and healthy twins, the prevalence of healthy subjects positive for proximity ligation assay score was significantly greater in twins than in the consecutive cohort (47% versus 14%, P = 0.019). This suggests that genetic predisposition is important, but not sufficient, in the aetiology of the disease and strengthens the contribution of environmental factors. In conclusion, our data provide evidence that α-synuclein oligomers accumulate within synaptic terminals of autonomic fibres of the skin in Parkinson’s disease for the first time. This finding endorses the hypothesis that α-synuclein oligomers could be used as a reliable diagnostic biomarker for Parkinson’s disease. It also offers novel insights into the physiological and pathological roles of α-synuclein in the peripheral nervous system.

Phospho-HDAC6 Gathers Into Protein Aggregates in Parkinson's Disease and Atypical Parkinsonisms

HDAC6 is a unique histone deacetylase that targets cytoplasmic non-histone proteins and has a specific ubiquitin-binding activity. Both of these activities are required for HDAC6-mediated formation of aggresomes, which contain misfolded proteins that will ultimately be degraded via autophagy. HDAC6 deacetylase activity is increased following phosphorylation on serine 22 (phospho-HDAC6). In human, HDAC6 localizes in neuronal Lewy bodies in Parkinson’s disease (PD) and in oligodendrocytic Papp–Lantos bodies in multiple system atrophy (MSA). However, the expression of phospho-HDAC6 in post-mortem human brains is currently unexplored. Here, we evaluate and compare the distribution of HDAC6 and its phosphorylated form in human brains obtained from patients affected by three forms of parkinsonism: two synucleinopathies (PD and MSA) and a tauopathy (progressive supranuclear palsy, PSP). We find that both HDAC6 and its phosphorylated form localize with pathological protein aggregates, including α-synuclein-positive Lewy bodies in PD and Papp–Lantos bodies in MSA, and phospho-tau-positive neurofibrillary tangles in PSP. We further find a direct interaction of HDAC6 with α-synuclein with proximity ligation assay (PLA) in neuronal cell of PD patients. Taken together, our findings suggest that both HDAC6 and phospho-HDAC6 regulate the homeostasis of intra-neuronal proteins in parkinsonism.