Elimination of dysfunctional mitochondria via mitophagy is essential for cell survival and neuronal functions. But, how impaired mitophagy participates in tissue-specific vulnerability in the brain remains unclear. Here, we find that striatal-enriched protein, Rhes, is a critical regulator of mitophagy and striatal vulnerability in brain. In vivo interactome and density fractionation reveal that Rhes coimmunoprecipitates and cosediments with mitochondrial and lysosomal proteins. Live-cell imaging of cultured striatal neuronal cell line shows Rhes surrounds globular mitochondria, recruits lysosomes, and ultimately degrades mitochondria. In the presence of 3-nitropropionic acid (3-NP), an inhibitor of succinate dehydrogenase, Rhes disrupts mitochondrial membrane potential (ΔΨm) and promotes excessive mitophagy and cell death. Ultrastructural analysis reveals that systemic injection of 3-NP in mice promotes globular mitochondria, accumulation of mitophagosomes, and striatal lesion only in the wild-type (WT), but not in the Rhes knockout (KO), striatum, suggesting that Rhes is critical for mitophagy and neuronal death in vivo. Mechanistically, Rhes requires Nix (BNIP3L), a known receptor of mitophagy, to disrupt ΔΨm and promote mitophagy and cell death. Rhes interacts with Nix via SUMO E3-ligase domain, and Nix depletion totally abrogates Rhes-mediated mitophagy and cell death in the cultured striatal neuronal cell line. Finally, we find that Rhes, which travels from cell to cell via tunneling nanotube (TNT)-like cellular protrusions, interacts with dysfunctional mitochondria in the neighboring cell in a Nix-dependent manner. Collectively, Rhes is a major regulator of mitophagy via Nix, which may determine striatal vulnerability in the brain.
Elimination of dysfunctional mitochondria via mitophagy is essential for cell survival and neuronal functions. But, how impaired mitophagy participates in tissue-specific vulnerability in the brain remains unclear. Here we discovered that Rhes, a striatal-enriched protein, is a major regulator of mitophagy in the striatum. Rhes predominantly interact with dysfunctional mitochondria and degrades them via mitophagy, and this function is exacerbated by the striatal toxin, 3nitropropionic acid (3-NP). 3-NP induces mitochondrial swelling, loss of cristae and neuronal cell death only in WT but not Rhes KO striatum. Mechanistically, Rhes disrupts the mitochondrial membrane potential ( m) and interacts with mitophagy receptor, Nix. In Nix KO cells, Rhes fails to disrupt m or eliminate dysfunctional mitochondria. Moreover, Rhes travels to the neighboring cell and associates with dysfunctional mitochondria via Nix. Collectively, Rhes is a major regulator of mitophagy via Nix which may determine striatal vulnerability in the brain.
The therapeutic benefits of L-3,4-dihydroxyphenylalanine (L-DOPA) in Parkinson disease (PD) patients diminishes with the onset of abnormal involuntary movements (L-DOPA induced dyskinesia), a debilitating motor side effect. L-DOPA induced dyskinesia are due to altered dopaminergic signaling in the striatum, a brain region that controls motor and cognitive functions.However, the molecular mechanisms that promote L-DOPA-induced dyskinesia remain unclear.Here, we have reported that RasGRP1 (also known as CalDAG-GEF-II) physiologically mediated L-DOPA induced dyskinesia in a 6-hydroxy dopamine (6-OHDA) lesioned mouse model of PD. In this study, L-DOPA treatment rapidly upregulated RasGRP1 in the striatum. Our findings showed that RasGRP1 deleted mice (RasGRP1 -/-) had drastically diminished L-DOPAinduced dyskinesia, and RasGRP1 -/mice did not interfere with the therapeutic benefits of L-DOPA. In terms of its mechanism, RasGRP1 mediates L-DOPA-induced extracellular regulated kinase (ERK), the mammalian target of rapamycin kinase (mTOR) and the cAMP/PKA pathway and binds directly with Ras-homolog-enriched in the brain (Rheb), which is a potent activator of mTOR, both in vitro and in the intact striatum. High-resolution tandem mass tag mass spectrometry analysis of striatal tissue revealed significant targets, such as phosphodiesterase (Pde1c), Pde2a, catechol-o-methyltransferase (comt), and glutamate decarboxylase 1 and 2 (Gad1 and Gad2), which are downstream regulators of RasGRP1 and are linked to L-DOPA-induced dyskinesia vulnerability. Collectively, the findings of this study demonstrated that RasGRP1 is a major regulator of L-DOPA-induced dyskinesia in the striatum. Drugs or genedepletion strategies targeting RasGRP1 may offer novel therapeutic opportunities for preventing L-DOPA-induced dyskinesia in PD patients. induced dyskinesia. RESULTS RasGRP1 promoted L-DOPA-induced dyskinesia in a mouse model of Parkinson disease. We hypothesized that RasGRP1 may be an upstream regulator of L-DOPA-induced dyskinesia due to the following reasons: a) L-DOPA treatment of mice with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway augmented striatal ERK and mTOR signaling 1-3 ; b) Rhes, a striatal-enriched protein that activates mTOR, is involved in L-DOPA-induced dyskinesia 6, 17, 18 ; and c) RasGRP1 regulated the synaptic localization of Rhes and RasGRP1, and Rhes co-expression strongly activated both ERK and mTORC1 signaling in a cell culture 16 .To test our hypothesis, we subjected WT and RasGRP1 -/-(RasGRP1 KO) mice to a wellestablished 6-OHDA lesion model of L-DOPA-induced dyskinesia as in our earlier study 6 . Fig 1A shows the timeline of the 6-OHDA lesion and L-DOPA-induced dyskinesia analysis. We observed 6-OHDA-induced PD-like symptoms in the drag test, rotarod, and turning test, which were similar between WT and RasGRP1 KO mice (Fig. 1B). The open field test did not show obvious differences (Fig. 1B). Daily treatment of unilaterally-6-OHDA lesioned mice with 5 mg/kg L-DOPA produced dyski...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.