Stochastic Optical Reconstruction Microscopy Imaging of Multiple System Atrophy Inclusions Suggests Stepwise α-Synuclein Aggregation

BACKGROUND

The architecture and composition of glial (GCI) and neuronal (NCI) α-synuclein inclusions observed in multiple system atrophy (MSA) remain to be precisely defined to better understand the disease.

METHODS

Here, we used stochastic optical reconstruction microscopy (STORM) to characterize the nanoscale organization of glial (GCI) and neuronal (NCI) α-synuclein inclusions in cryopreserved brain sections from MSA patients.

RESULTS

STORM revealed a dense cross-linked internal structure of α-synuclein in all GCI and NCI. The internal architecture of hyperphosphorylated α-synuclein (p-αSyn) inclusions was similar in glial and neuronal cells, suggesting a common aggregation mechanism. A similar sequence of p-αSyn stepwise intracellular aggregation was defined in oligodendrocytes and neurons, starting from the perinuclear area and growing inside the cells. Consistent with this hypothesis, we found a higher mitochondrial density in GCI and NCI compared to oligodendrocytes and neurons from unaffected donors (P < 0.01), suggesting an active recruitment of the organelles during the aggregation process.

CONCLUSIONS

These first STORM images of GCI and NCI suggest stepwise α-synuclein aggregation in MSA. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Are LRRK2 mysteries lurking in the gut?

Gut-brain axis and inflammation are two hot topics in Parkinson's disease (PD). In this setting, the leucine-rich repeat kinase 2 (LRRK2) gene, which encodes the eponym protein, has attracted much attention. LRRK2 is not only the gene most commonly associated with Parkinson's disease but also a susceptibility gene for Crohn's disease (CD), thereby suggesting that it may sit at the crossroads of gastrointestinal inflammation, Parkinson's, and Crohn's disease. In contrast to the accumulated data on LRRK2 in the central nervous system (CNS), research on LRRK2 in the digestive tract is still in its infancy, and the scope of the present review article is therefore to review existing studies on LRRK2 in the gastrointestinal tract in both physiological and pathological conditions. In light of current data on LRRK2 in the gastrointestinal tract, we discuss if LRRK2 could be or not regarded as a molecular link between gut inflammation, Parkinson's disease, and Crohn's disease, and we suggest directions for future research.

LRRK2 expression in normal and pathologic human gut and in rodent enteric neural cell lines

Leucine-rich repeat kinase 2 (LRRK2) gene, which is the gene most commonly associated with Parkinson's disease (PD), is also a susceptibility gene for Crohn's disease, thereby suggesting that LRRK2 may sit at the crossroads of gastrointestinal inflammation, Parkinson's, and Crohn's disease. LRRK2 protein has been studied intensely in both CNS neurons and in immune cells, but there are only few studies on LRRK2 in the enteric nervous system (ENS). LRRK2 is present in ENS ganglia and the existing studies on LRRK2 expression in colonic biopsies from PD subjects have yielded conflicting results. Herein, we propose to extend these findings by studying in more details LRRK2 expression in the ENS. LRRK2 expression was evaluated in full thickness segments of colon of 16 Lewy body, 12 non-Lewy body disorders cases, and 3 non-neurodegenerative controls and in various enteric neural cell lines. We showed that, in addition to enteric neurons, LRRK2 is constitutively expressed in enteric glial cells in both fetal and adult tissues. LRRK2 immunofluorescence intensity in the myenteric ganglia was not different between Lewy body and non-Lewy body disorders. Additionally, we identified the cAMP pathway as a key signaling pathway involved in the regulation of LRRK2 expression and phosphorylation in the enteric glial cells. Our study is the first detailed characterization of LRRK2 in the ENS and the first to show that enteric glial cells express LRRK2. Our findings provide a basis to unravel the functions of LRRK2 in the ENS and to further investigate the pathological changes in enteric synucleinopathies.

Idiopathic normal pressure hydrocephalus and frontotemporal dementia: an unexpected association

Idiopathic normal pressure hydrocephalus has a complex multifactorial pathogenesis and is associated with Alzheimer's disease in many patients. To date, it is not well known if a similar association exists with behavioural variant of frontotemporal lobar degeneration. In a first step, we compare the prevalence of idiopathic normal pressure hydrocephalus in two groups of patients, one with behavioural variant of frontotemporal lobar degeneration (n = 69) and the other with Alzheimer's disease (n = 178). In the second step, we describe more precisely the phenotype of patients with the association of idiopathic normal pressure hydrocephalus and behavioural variant of frontotemporal lobar degeneration. Firstly, we report that the prevalence of idiopathic normal pressure hydrocephalus was far higher in the group of patients with behavioural variant of frontotemporal lobar degeneration than in the group of patients with Alzheimer's disease (7.25% and 1.1%, respectively, P = 0.02). Secondly, we show that patients with the double diagnosis share common clinical and para-clinical features of both idiopathic normal pressure hydrocephalus and behavioural variant of frontotemporal lobar degeneration patients, including CSF shunting efficacy in real-life experience. Overall, our results suggest a link between these two conditions and should encourage neurologists to look for idiopathic normal pressure hydrocephalus in their behavioural variant of frontotemporal lobar degeneration patients in the event of gait disturbances; the benefit/risk balance could indeed be in favour of shunt surgery for selected patients with this newly described entity.

Comparison of commercially available antibodies for the detection of phosphorylated alpha-synuclein in primary culture of ENS

BACKGROUND

It is now well established that phosphorylated alpha-synuclein histopathology, the pathologic hallmark of Parkinson's disease (PD) is not limited to the brain but also extends to the enteric nervous system (ENS). This observation led to the hypothesis that the ENS could play a pivotal role in the development of PD. Research on the enteric synucleinopathy has, however, been hampered by difficulties in detecting phosphorylated alpha-synuclein in the ENS by Western blotting, even when the transferred membrane is fixed with an optimized protocol. This suggests that the available antibodies used in previous studies lacked of sensitivity for the detection of phosphorylated alpha-synuclein at Ser129 in enteric neurons. Here, we evaluated three recent commercially available phospho-alpha-synuclein antibodies and compared them to two antibodies used in previous research.

METHODS

The specificity and sensitivity of the 5 antibodies were evaluated by Western blot performed with recombinant alpha-synuclein and with protein lysates from rat primary cultures of ENS. In primary culture of ENS, additional experiments were performed with the most specific antibody in order to modulate alpha-synuclein phosphorylation and to validate its utilization in immunofluorescence experiments.

RESULTS

The rabbit monoclonal antibody D1R1R uniquely and robustly detected endogenous phosphorylated alpha-synuclein at Ser129 in rat primary culture of ENS without any non-specific bands, allowing for a reliable analysis of phosphorylated alpha-synuclein regulation by pharmacologic means.

CONCLUSIONS AND INFERENCES

Using D1R1R antibody together with the optimized protocol for membrane fixation may help deciphering the signaling pathways involved in enteric alpha-synuclein post-translational regulation in PD.

Gastrointestinal mucosal biopsies in Parkinson's disease: beyond alpha-synuclein detection

Alpha-synuclein deposits, the pathological hallmarks of Parkinson's disease, are consistently found in the gastrointestinal tract of parkinsonian subjects. These observations have raised the potential that endoscopically obtainable mucosal biopsies can aid to a molecular diagnosis of the disease. The possible usefulness of mucosal biopsies is, however, not limited to the detection of alpha-synuclein, but also extends to other essential aspects underlying pathophysiological mechanisms of gastrointestinal manifestations in Parkinson's disease. The aim of the current review is to provide an appraisal of the existing studies showing that gastrointestinal biopsies can be used for the analysis of enteric neuronal and glial cell morphology, intestinal epithelial barrier function, and gastrointestinal inflammation in Parkinson's disease. A perspective on the generation of organoids with GI biopsies and the potential use of single-cell and spatial transcriptomic technologies will be also addressed.

Enteric synucleinopathy: from trendy concept to real entity

An accumulating body of literature has emerged in the past 25 years to show that Parkinson's disease (PD) is not only a disorder of the brain but also of the gastrointestinal tract and more generally of the gut-brain axis. Gastrointestinal symptoms occur in almost every PD patient at some point and in nearly every case examined pathologically autopsy studies find alpha-synuclein deposits, the pathological hallmarks of PD, in the enteric nervous system. This concept of 'enteric synucleinopathy' led to the hypothesis that the enteric nervous system might play a pivotal role in the initiation and spreading of PD. Although this hypothesis opens up interesting perspectives on the pathogenesis of neurodegenerative disorders, some important questions are still pending. The present opinion paper describes and compares the physiological and pathophysiological properties of alpha-synuclein in the brain and the enteric nervous system. We conclude that the existing data supports the existence of pathological alpha-synuclein species in the gut in PD. We also discuss if gut-brain interactions are important in other neurodegenerative disorders.