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

Abstract

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.

Correlates of polyneuropathy in Parkinson’s disease

“…Here, immunoreactivity of total aSyn and phosphorylated aSyn is seen as a putative in vivo biomarker of disease and was shown to very precisely discriminate alpha‐Synucleinopathies such as PD and MSA from other parkinsonian syndromes with high sensitivity and specificity 28 . In a very recent study, aSyn oligomers were also quantified in synaptic terminals of peripheral nerve autonomic fibers and were shown to be significantly increased in PD patients compared to healthy controls with a specificity of 82% 29 . As progression of PD is supposed to involve spreading of pathology from the periphery to the CNS, 30 the peripheral nerve involvement itself may also progress and aSyn pathology could increasingly compromise peripheral nerve function and lead to functional and morphologic alterations 31 …”

“…28 In a very recent study, aSyn oligomers were also quantified in synaptic terminals of peripheral nerve autonomic fibers and were shown to be significantly increased in PD patients compared to healthy controls with a specificity of 82%. 29 As progression of PD is supposed to involve spreading of pathology from the periphery to the CNS, 30 the peripheral nerve involvement itself may also progress and aSyn pathology could increasingly compromise peripheral nerve function and lead to functional and morphologic alterations. 31 Limitations of the presented study are the patient number and the monocentric, observational study design.…”

Tau-proximity ligation assay reveals extensive previously undetected pathology prior to neurofibrillary tangles in preclinical Alzheimer’s disease

“…Here, we describe tau-PLA, a technique that enables the specific histological visualization in situ of the tau–tau interactions, regardless of tau phosphorylation state and conformational changes, with preservation of the cellular and subcellular morphology. PLA has been used previously to detect both heterotypic [ 58 ] as well as homotypic protein interactions [ 33 , 42 , 53 , 56 ], which shows the reliability of the PLA approach. We analyzed the presence of tau–tau interactions in FFPE hippocampal and temporal isocortex sections from 67 post-mortem human brains from all Braak stages using tau-PLA and compared with the presence of phosphorylated and misfolded tau using immunohistochemistry.…”

Tau and Alpha Synuclein Synergistic Effect in Neurodegenerative Diseases: When the Periphery Is the Core

“…Indeed, phosphorylated αSyn has been found in skin small fibers nerves innervating autonomic structures [ 247 ] in PD, and of note also in RBD patients, suggesting the potential value of skin biopsy as an early biomarker of disease [ 248 , 249 ]. More recently, aggregated αSyn has been demonstrated in skin nerves by conformational antibodies, recognizing oligomeric forms of the protein [ 244 , 250 ] and by using proximity ligation assay technology in the skin [ 251 ]. In addition, skin biopsy offers the great advantages of being minimally invasive, compared to other biopsy sites like the gastro-enteric system; it can be repeated in time during follow-ups and offers the unique opportunity to access the sympathetic structures in the skin (sweat glands, small arterioles, muscle arrector pili), which animal models have demonstrated as possibly involved early [ 239 ].…”