Olfactory Dysfunction in Parkinson's Disease, Its Functional and Neuroanatomical Correlates

Robust In Vitro Models for Studying Parkinson's Disease? LUHMES Cells and SH-SH5Y Cells

As our population ages, there is an increased unmet clinical need surrounding neurodegenerative diseases such as Parkinson's disease (PD). To tackle this ever-increasing problem, we must ensure that the cell models that we use to develop therapeutics in vitro are robust, reliable, and replicable. In this study, we compared SH-SY5Y cells with LUHMES cells in response to 6-Hydroxydopamine (6OHDA) and 1-Methyl-4-phenylpyridinium (MPP+), two common Parkinson's insults used in in vitro analysis. Both these cell types have apparent dopaminergic phenotypes, which could aid us in understanding their potential in this race to novel therapies. The LUHMES cells showed consistent dopaminergic (DA) expression through tyrosine hydroxylase (TH) positivity, alongside depleted ATP levels and elevated reactive oxygen species (ROS) production, whereas the SH-SH5Y cells displayed resilience to both chemical insults, raising questions about their utility in accurately modelling PD pathology. Further electrophysiological analysis revealed comparable firing rates and ion channel signalling between both cell types; however, LUHMES cells demonstrated stronger calcium signalling responses, further supporting their use as a more robust PD model. While SH-SY5Y cells showed some adaptability in vitro, their inconsistent DA phenotype and limited response to chemical insults limit their suitability for advanced research, suggesting that LUHMES cells should and must take their place as a hallmark in Parkinson's disease research.

SARS-CoV-2 Infection and Alpha-Synucleinopathies: Potential Links and Underlying Mechanisms

Alpha-synuclein (α-syn) is a 140-amino-acid, intrinsically disordered, soluble protein that is abundantly present in the brain. It plays a crucial role in maintaining cellular structures and organelle functions, particularly in supporting synaptic plasticity and regulating neurotransmitter turnover. However, for reasons not yet fully understood, α-syn can lose its physiological role and begin to aggregate. This altered α-syn disrupts dopaminergic transmission and causes both presynaptic and postsynaptic dysfunction, ultimately leading to cell death. A group of neurodegenerative diseases known as α-synucleinopathies is characterized by the intracellular accumulation of α-syn deposits in specific neuronal and glial cells within certain brain regions. In addition to Parkinson's disease (PD), these conditions include dementia with Lewy bodies (DLBs), multiple system atrophy (MSA), pure autonomic failure (PAF), and REM sleep behavior disorder (RBD). Given that these disorders are associated with α-syn-related neuroinflammation-and considering that SARS-CoV-2 infection has been shown to affect the nervous system, with COVID-19 patients experiencing neurological symptoms-it has been proposed that COVID-19 may contribute to neurodegeneration in PD and other α-synucleinopathies by promoting α-syn misfolding and aggregation. In this review, we focus on whether SARS-CoV-2 could act as an environmental trigger that facilitates the onset or progression of α-synucleinopathies. Specifically, we present new evidence on the potential role of SARS-CoV-2 in modulating α-syn function and discuss the causal relationship between SARS-CoV-2 infection and the development of parkinsonism-like symptoms.

Hippocampus and olfactory impairment in Parkinson disease: a comparative exploratory combined volumetric/functional MRI study

INTRODUCTION

Patients with Parkinson's Disease (PD) commonly experience Olfactory Dysfunction (OD). Our exploratory study examined hippocampal volumetric and resting-state functional magnetic resonance imaging (rs-fMRI) variations in a Healthy Control (HC) group versus a cognitively normal PD group, further categorized into PD with No/Mild Hyposmia (PD-N/MH) and PD with Severe Hyposmia (PD-SH).

METHODS

We calculated participants' relative Total Hippocampal Volume (rTHV) and performed Spearman's partial correlations, controlled for age and gender, to examine the correlation between rTHV and olfactory performance assessed by the Odor Stick Identification Test for the Japanese (OSIT-J) score. Mann-Whitney U tests assessed rTHV differences across groups and subgroups, rejecting the null hypothesis for p < 0.05. Furthermore, a seed-based rs-fMRI analysis compared hippocampal connectivity differences using a one-way ANCOVA covariate model with controls for age and gender.

RESULTS

Spearman's partial correlations indicated a moderate positive correlation between rTHV and OSIT-J in the whole study population (ρ = 0.406; p = 0.007), PD group (ρ = 0.493; p = 0.008), and PD-N/MH subgroup (ρ = 0.617; p = 0.025). Mann-Whitney U tests demonstrated lower rTHV in PD-SH subgroup compared to both HC group (p = 0.013) and PD-N/MH subgroup (p = 0.029). Seed-to-voxel rsfMRI analysis revealed reduced hippocampal connectivity in PD-SH subjects compared to HC subjects with a single cluster of voxels.

CONCLUSIONS

Although the design of the study do not allow to make firm conclusions, it is reasonable to speculate that the progressive involvement of the hippocampus in PD patients is associated with the progression of OD.