Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the loss of dopaminergic neurons of the substantia nigra pars compacta and the brain accumulation of alpha-synuclein-positive Lewy bodies. The olfactory neuroepithelium, situated in the upper crypt of the nasal cavity, could be considered a "window to the brain". By a non-invasive nasal-brushing procedure, it is possible to collect it gently and painlessly from a broad surface area of olfactory mucosa. Therefore, the olfactory bulb represents one of the first alpha-synuclein-positive structures in the brain affected in the pre-symptomatic phase of PD, indicating this structure as one possible entry point of alpha-synuclein pathology originating in the periphery. In this area, the most vulnerable neurons seem to be the Substance P (SP) -containing neurons, which could represent an important factor involved in smell deficits observed in PD. It emerges that the SP/NK1 system could represent a target in the physiopathology and diagnosis of PD. This project aims to study olfactory sensory neurons (ONs) as potential biomarkers in PD, helping in predicting the patients with higher risk monitor the development of the disease and the effect of the antiparkinsonian therapies. We will study the expression of SP and its preferred NK1 receptor in the olfactory neuroepithelium collected by nasal brushing in control subjects, correlating their expressions to them observed in ONs acquired by PD patients of the regional Centre of PD. Since ONs contain SP, and neurotrophic factors are demonstrated to up-regulate the mRNA and secretion levels of SP in sensory neurons, a specific aim will be to characterize the expression level of SP and eventually NK1, comparing them to the levels obtained from PD corresponding control. Furthermore, to confirm the clinical data on ONs, we will perform pre-clinical experiments on an animal model of PD, obtained by intranigral injection of 6-hydroxydopamine.
This project aims to obtain scientific evidence that ONs could be useful to characterize potential biomarkers in PD, helping in predicting the patients with higher risk and offering the possibility to monitor the development of the disease over time and the effect of the common antiparkinsonian therapies.
Interestingly, the nasal brushing is an innovative, non-invasive technic which consents to easily collect the samples, bypassing the potential complications of a biopsy procedure, and allowing repeated withdrawals to monitor the pathology over time.
The working plan is to investigate, first of all, the expression pattern of proteins involved in neurodegeneration, as neurofilament light chain, apoptotic proteins, and neuroinflammatory mediators, together with the ¿-synuclein, a specific marker of PD, characterizing this heterogeneous population of cells. Indeed, the human neuroepithelium is composed by a variety of cell types, including olfactory sensory neurons and neuronal precursors, supporting glial-like cells, microvillar cells, and basal stem cells (Brozzetti et al., 2020).
Since in brain regions related to olfaction, as the olfactory bulb, SP-positive neurons have demonstrated to co-localize with a-synuclein, aim of our research is to study the expression of SP and its preferred NK1 receptor in ONs, following the characterization of the cells compositing of the olfactory neuroepithelium and to correlate the values found in control ONs to them from PD patients.
Immunofluorescence analysis will be applied to analyze the presence and the distribution of SP and NK1 positive cells in the olfactory neuroepithelium and the Real-time qPCR analysis to quantify their amount.
Supporting our hypothesis of an involvement of SP in the PD pathogenesis, literature data indicate that PD and other neurodegenerative diseases result primarily from a loss of trophic peptidergic neurotransmitters, possibly SP (Barker, 1989). The involvement of SP and its preferred NK1 receptor, either at central or peripheral level, has been extensively demonstrated in both animal models and epidemiological studies in PD patients.
Recently, analyzing the gene expression profile of the substantia nigra from postmortem human brain of PD patients, druggable targets for PD have been identified. Among the only 15 hub genes involved in PD, the gene TAC1, precursor of SP, represents a prospective aspirant gene for PD diagnosis, indicating SP as a potential PD pharmacological target (Odumpatta and Arumugam, 2021).
Moreover, the possibility to investigate the pattern of expression of SP and NK1 in PD animal models allows to further characterize the involvement of this neuropeptide in the olfactory system, which represents one of the first ¿-synuclein-positive structures in the brain affected in the pre-symptomatic phase of PD.
The analysis of SP in olfactory bulb extracts from neurotoxic (6HOA) lesioned animals in the early phases of the pathology could confirm the contribution of SP and NK1 in the olfactory deficits observed in this pathology.
The innovation of this research project is to address whether SP and its receptor can be considered independent prognostic factors in the early phases of PD, by the analysis of the olfactory neuroepithelium, easily to collect and monitor.
We believe that the team of this project has the most appropriate scientific and technical background as well as instruments required to fulfil the goals of this project and to succeed in its mission.