Genetic and pharmacologic p32-inhibition rescue CHCHD2-linked Parkinson's disease phenotypes in vivo and in cell models.

BACKGROUND: Mutations in CHCHD2 have been linked to Parkinson's disease, however, their exact pathophysiologic roles are unclear. The p32 protein has been suggested to interact with CHCHD2, however, the physiological functions of such interaction in the context of PD have not been clarified. METHODS: Interaction between CHCHD2 and p32 was confirmed by co-immunoprecipitation experiments. We studied the effect of p32-knockdown in the transgenic Drosophila and Hela cells expressing the wild type and the pathogenic variants of hCHCHD2. We further investigated the rescue ability of a custom generated p32-inhibitor in these models as well as in the human fibroblast derived neural precursor cells and the dopaminergic neurons harboring hCHCHD2-Arg145Gln. RESULTS: Our results showed that wildtype and mutant hCHCHD2 could bind to p32 in vitro, supported by in vivo interaction between human CHCHD2 and Drosophila p32. Knockdown of p32 reduced mutant hCHCHD2 levels in Drosophila and in vitro. In Drosophila hCHCHD2 models, inhibition of p32 through genetic knockdown and pharmacological treatment using a customized p32-inhibitor restored dopaminergic neuron numbers and improved mitochondrial morphology. These were correlated with improved locomotor function, reduced oxidative stress and decreased mortality. Consistently, Hela cells expressing mutant hCHCHD2 showed improved mitochondrial morphology and function after treatment with the p32-inhibitor. As compared to the isogenic control cells, large percentage of the mutant neural precursor cells and dopaminergic neurons harboring hCHCHD2-Arg145Gln contained fragmented mitochondria which was accompanied by lower ATP production and cell viability. The NPCs harboring hCHCHD2-Arg145Gln also had a marked increase in α-synuclein expression. The p32-inhibitor was able to ameliorate the mitochondrial fragmentation, restored ATP levels, increased cell viability and reduced α-synuclein level in these cells. CONCLUSIONS: Our study identified p32 as a modulator of CHCHD2, possibly exerting its effects by reducing the toxic mutant hCHCHD2 expression and/or mitigating the downstream effects. Inhibition of the p32 pathway can be a potential therapeutic intervention for CHCHD2-linked PD and diseases involving mitochondrial dysfunction.

A Proteome-Wide Effect of PHF8 Knockdown on Cortical Neurons Shows Downregulation of Parkinson's Disease-Associated Protein Alpha-Synuclein and Its Interactors.

Synaptic dysfunction may underlie the pathophysiology of Parkinson's disease (PD), a presently incurable condition characterized by motor and cognitive symptoms. Here, we used quantitative proteomics to study the role of PHD Finger Protein 8 (PHF8), a histone demethylating enzyme found to be mutated in X-linked intellectual disability and identified as a genetic marker of PD, in regulating the expression of PD-related synaptic plasticity proteins. Amongst the list of proteins found to be affected by PHF8 knockdown were Parkinson's-disease-associated SNCA (alpha synuclein) and PD-linked genes DNAJC6 (auxilin), SYNJ1 (synaptojanin 1), and the PD risk gene SH3GL2 (endophilin A1). Findings in this study show that depletion of PHF8 in cortical neurons affects the activity-induced expression of proteins involved in synaptic plasticity, synaptic structure, vesicular release and membrane trafficking, spanning the spectrum of pre-synaptic and post-synaptic transmission. Given that the depletion of even a single chromatin-modifying enzyme can affect synaptic protein expression in such a concerted manner, more in-depth studies will be needed to show whether such a mechanism can be exploited as a potential disease-modifying therapeutic drug target in PD.

Safeguarding Non-COVID-19 Research: Looking Up from Ground Zero.

The COVID-19 pandemic has kicked off a global race to launch clinical trials of experimental vaccines and treatments for the coronavirus. Worldwide, as resources are directed toward accelerating the research into unravelling the mechanism of COVID-19 pathophysiology, concerns have been raised regarding the future of clinical research in United Kingdom and elsewhere during the current pandemic. However, the real immediate impact of these restrictions due to lock-down is most acutely felt by scientists working on non-COVID-19 biomedical research bench and clinical researchers whose drug trials have to be delayed, suspended or ceased. Here, we highlight our views from "ground zero" as we represent those whose work are deeply affected by the restrictions. We draw attention to some of the practical realities and emotions experienced in the laboratory. In addition, we also highlight the difficulties for policy makers to maintain equanimity in prioritizing their decisions cross the different fields of science.

Mutant PINK1 upregulates tyrosine hydroxylase and dopamine levels, leading to vulnerability of dopaminergic neurons.

PINK1 mutations cause autosomal recessive forms of Parkinson disease (PD). Previous studies suggest that the neuroprotective function of wild-type (WT) PINK1 is related to mitochondrial homeostasis. PINK1 can also localize to the cytosol; however, the cytosolic function of PINK1 has not been fully elucidated. In this study we demonstrate that the extramitochondrial PINK1 can regulate tyrosine hydroxylase (TH) expression and dopamine (DA) content in dopaminergic neurons in a PINK1 kinase activity-dependent manner. We demonstrate that overexpression of full-length (FL) WT PINK1 can downregulate TH expression and DA content in dopaminergic neurons. In contrast, overexpression of PD-linked G309D, A339T, and E231G PINK1 mutations upregulates TH and DA levels in dopaminergic neurons and increases their vulnerability to oxidative stress. Furthermore transfection of FL WT PINK1 or PINK1 fragments with the PINK1 kinase domain can inhibit TH expression, whereas kinase-dead (KD) FL PINK1 or KD PINK1 fragments upregulate TH level. Our findings highlight a potential novel function of extramitochondrial PINK1 in dopaminergic neurons. Deregulation of these functions of PINK1 may contribute to PINK1 mutation-induced dopaminergic neuron degeneration. However, deleterious effects caused by PINK1 mutations may be alleviated by iron-chelating agents and antioxidant agents with DA quinone-conjugating capacity.

The roles of amyloid precursor protein (APP) in neurogenesis: Implications to pathogenesis and therapy of Alzheimer disease.

The amyloid-beta (Aß) peptide is the derivative of amyloid precursor protein (APP) generated through sequential proteolytic processing by ß- and γ-secretases. Excessive accumulation of Aß, the main constituent of amyloid plaques, has been implicated in the etiology of Alzheimer's disease (AD). It was found recently that the impairments of neurogenesis in brain were associated with the pathogenesis of AD. Furthermore recent findings implicated that APP could function to influence proliferation of neural progenitor cells (NPC) and might regulate transcriptional activity of various genes. Studies demonstrated that influence of neurogenesis by APP is conferred differently via its two separate domains, soluble secreted APPs (sAPPs, mainly sAPPα) and APP intracellular domain (AICD). The sAPPα was shown to be neuroprotective and important to neurogenesis, whereas AICD was found to negatively modulate neurogenesis. Furthermore, it was demonstrated recently that microRNA could function to regulate APP expression, APP processing, Aß accumulation and subsequently influence neurotoxicity and neurogenesis related to APP, which was implicated to AD pathogenesis, especially for sporadic AD. Based on data accumulated, secretase balances were proposed. These secretase balances could influence the downstream balance related to regulation of neurogenesis by AICD and sAPPα as well as balance related to influence of neuron viability by Aß and sAPPα. Disruption of these secretase balances could be culprits to AD onset.

Ring finger protein 146/Iduna is a poly(ADP-ribose) polymer binding and PARsylation dependent E3 ubiquitin ligase.

Recent findings suggest that Ring finger protein 146 (RNF146), also called iduna, have neuroprotective property due to its inhibition of Parthanatos via binding with Poly(ADP-ribose) (PAR). The Parthanatos is a PAR dependent cell death that has been implicated in many human diseases. RNF146/Iduna acts as a PARsylation-directed E3 ubquitin ligase to mediate tankyrase-dependent degradation of axin, thereby positively regulates Wnt signaling. RNF146/Iduna can also facilitate DNA repair and protect against cell death induced by DNA damaging agents or γ-irradiation. It can translocate to the nucleus after cellular injury and promote the ubiquitination and degradation of various nuclear proteins involved in DNA damage repair. The PARsylation-directed ubquitination mediated by RNF146/Iduna is analogous to the phosphorylation-directed ubquitination catalyzed by Skp1-Cul1-F-box (SCF) E3 ubiquitin complex. RNF146/Iduna has been found to be implicated in neurodegenerative disease and cancer development. Therefore modulation of the PAR-binding and PARsylation dependent E3 ligase activity of RNF146/Iduna could have therapeutic significance for diseases, in which PAR and PAR-binding proteins play key pathophysiologic roles.