Udvikling af Parkinson's: Interaktionen mellem Hedgehog-signalering, PINK1/PARK2 og mitokondriel dysfunktion i C. elegans: Nye originale fund og indsigter

Abstract

Parkinsons sygdom (PD) er en udbredt neurodegenerativ lidelse, som er karakteriseret ved tab af dopaminerge neuroner, hvor dysfunktionelle mitokondrier spiller en central rolle i sygdomsprogressionen – muligvis forårsaget af nedsat mitofagi som følge af mutationer i PINK1/PARK2. Præliminære data viser markant forhøjede niveauer af Hedgehog (Hh)-signalering i fibroblastceller fra PD-patienter med sygdomsfremkaldende varianter i PINK1/PARK2, hvilket antyder, at der kan være en sammenhæng mellem Hh-signalering og PD. Hh-signalering er blevet impliceret i en lang række processer, herunder neurogenese og neurobeskyttende effekter, men det er endnu uklart, om det påvirker udviklingen af PD. I dette studie blev C. elegans anvendt som modelorganisme til at undersøge mulige interaktioner mellem PINK1/PARK2-medieret mitokondriel kvalitetskontrol og Hh-signalering – og om dette kan indikere en mulig forbindelse til PD. For at besvare disse spørgsmål blev forskellige transgene orme-stammer udsat for RNAi-medieret knockdown af pdr-1 (homolog til det humane PARK2), hhat-2 (homolog til det humane HHAT) eller det Hh-relaterede gen grl-1 (uden direkte menneskelig homolog). Dopaminerg neurodegeneration blev vurderet ved kvalitativ vurdering af morfologien af CEP-neuroner. Derudover blev ændringer i mitokondriemorfologi kvantificeret ved brug af den fluorescerende probe MitoTracker som markør for mitokondriel sundhed. Til sidst blev tra-1-ekspression målt som et potentielt mål for komponenter af Hh-signalering. Knockdown af hhat-2 i en PD-model reducerede α-synuclein-induceret toksicitet og aldersbetinget neurodegeneration i CEP-neuroner, hvilket antyder, at Hh-signalering har neurotoksiske effekter i dopaminerge neuroner. Overraskende havde knockdown af pdr-1 ingen effekt på neurodegeneration i PD-modellen. Desuden medførte knockdown af grl-1 ændringer i mitokondriemorfologi, hvilket antyder, at komponenter af Hh-signalering potentielt regulerer mitokondriedynamik. Endelig førte knockdown af pdr-1 og grl-1 til ændringer i tra-1-ekspression, hvilket tyder på, at begge fungerer som regulatorer af komponenter i Hh-signalvejen. Samlet set fremhæver disse fund en potentiel funktionel forbindelse mellem Hh-signalering, PINK1/PARK2 og PD-neuropatologi.

Parkinson’s disease (PD) is a prevalent neurodegenerative disorder characterized by the loss of dopaminergic neurons, with dysfunctional mitochondria playing a central role in disease progression, potentially caused by reduced mitophagy by PINK1/PARK2 mutations. Preliminary data shows substantially elevated levels of Hedgehog (Hh) signaling in fribroplast cells of PD patients with disease causing variants in PINK1/PARK2, indicating that there might be a correlation between Hh-signaling & PD. Hh-signaling has been implicated in a wide range of processes, including neurogenesis & neuroprotective e`ects, yet it is not clear whether it impacts development of PD. In this study, C. elegans was used as a model organism to explore possible interactions between PINK1/PARK2-mediated mitochondrial quality control & Hh-signaling, & if this underlines a possible connection to PD. To answer these questions, di`erent transgenic worm strains were subjected to RNAimediated knockdown of pdr-1 (homolog of human PARK2), hhat-2 (homolog of human HHAT) or the Hh-related gene grl-1 (no direct human homolog). Dopaminergic neurodegeneration was assessed by qualitatively scoring the morphology of CEP-neurons. Furthermore, changes in mitochondrial morphology were quantified using the fluorescent probe MitoTracker as a marker for mitochondrial health. Lastly, tra-1 expression was measured as a potential readout of components of Hh-signaling activity. Knockdown of hhat-2 in a PD model reduced α-synuclein induced toxicity & age dependent neurodegeneration in CEP-neurons, suggesting neurotoxic e`ects of Hh-signaling in dopaminergic neurons. Surprisingly, pdr-1 knockdown didn’t a`ect neurodegeneration in a PD model. Furthermore, knockdown of grl-1 induced changes in mitochondrial morphology, suggesting components of Hh-signaling as a potential regulator of mitochondrial dynamics. Lastly, pdr-1 & grl-1 knockdown resulted in changes in tra-1 expression, suggesting both as a regulator of components of the Hh-signaling pathway. This indicates that the PINK1/PARK2 system potentially regulates PD-development, mediated by upregulation of Hh-signaling, that has neurotoxic e`ects on dopaminergic neurons. Together, these findings highlight a potential functional link between Hh-signaling, PINK1/PARK2 & PD-neuropathology.

A master thesis from Aalborg University

Udvikling af Parkinson's: Interaktionen mellem Hedgehog-signalering, PINK1/PARK2 og mitokondriel dysfunktion i C. elegans: Nye originale fund og indsigter

[Parkinson's Disease Development: The Interaction Between Hedgehog Signaling, PINK1/PARK2, and Mitochondrial Dysfunction in C. elegans: Novel findings and insights]