Biology subjects

Ramirez Jarquin, U. N.

Publications and source records attributed to Ramirez Jarquin, U. N..

6 recordsLinked to original sources

bioRxiv2021

Rhes protein transits from neuron to neuron and facilitates mutant huntingtin spreading in the brain.

Rhes (RASD2) is a thyroid hormone-induced gene that regulates striatal motor activity and promotes neurodegeneration in Huntington disease (HD) and tauopathy. Previously, we showed that Rhes moves between cultured striatal neurons and transports the HD protein, polyglutamine-expanded huntingtin (mHTT) via tunneling nanotube (TNT)-like membranous protrusions. However, similar intercellular Rhes transport has not yet been demonstrated in the intact brain. Here, we report that Rhes induces TNT-like protrusions in the striatal medium spiny neurons (MSNs) and transported between dopamine-1 receptor (D1R)-MSNs and D2R-MSNs of intact striatum and organotypic brain slices. Notably, mHTT is robustly transported within the striatum and from the striatum to the cortical areas in the brain, and Rhes deletion diminishes such transport. Moreover, we also found transport of Rhes to the cortical regions following restricted expression in the MSNs of the striatum. Thus, Rhes is a first striatum-enriched protein demonstrated to move and transport mHTT between neurons and brain regions, providing new insights on interneuronal protein transport in the brain.

neuroscience↗

bioRxiv2021

Deletion of Small Ubiquitin-like Modifier-1 Attenuates Behavioral and Anatomical Deficits by Enhancing Functional Autophagic Activities in Huntington Disease

Mutant HTT (mHTT) associated with Huntington disease (HD) affects the central nervous system by prominent atrophy in the striatum and promotes psychiatric, cognitive, and choreiform movements, although the exact mechanism remains obscure. Previous studies have shown that SUMO1 (Small Ubiquitin-like Modifier-1) modification of mHTT promotes cellular toxicity, but the in vivo role and functions of SUMO1 in HD pathogenesis are unclear. Here, we report that SUMO1 deletion in Q175DN HD-het knock-in mice (HD mice) prevented age-dependent HD-like motor and neurological impairments and suppressed the striatal atrophy and inflammatory response. SUMO1 deletion caused a drastic reduction in soluble mHtt levels and nuclear and extracellular mHtt inclusions, while increasing cytoplasmic inclusions in the striatum of HD mice. SUMO1 deletion also enhanced autophagic activity, characterized by augmented interactions between mHTT inclusions and a lysosomal marker (LAMP1), increased LC3B/LAMP1 interaction, and decreased sequestosome-1 (p62) and mHTT and diminished p62/LAMP1 interactions in DARPP-32-positive medium spiny neurons (MSNs) in HD mice. Depletion of SUMO1 in an HD cell model also diminished the mHtt levels and enhanced autophagy flux. In addition, the SUMOylation inhibitor ginkgolic acid strongly enhanced autophagy and diminished mHTT levels in human HD fibroblasts. These results indicate that SUMO is a critical therapeutic target in HD and that blocking SUMO may ameliorate HD pathogenesis by improving autophagy activities.

neuroscience↗

bioRxiv2020

SUMO Modifies GβL and Mediates mTOR Signaling

The mechanistic target of rapamycin (mTOR) signaling is influenced by multiple regulatory proteins and post-translational modifications, however, underlying mechanisms remains unclear. Here, we report a novel role of small ubiquitin-like modifier (SUMO) in mTOR complex assembly and activity. By investigating the SUMOylation status of core mTOR components, we observed that the regulatory subunit, G{beta}L, is modified by SUMO1, 2, and 3 isoforms. Using mutagenesis and mass spectrometry, we identified that G{beta}L is SUMOylated at lysine sites K86, K215, K245, K261 and K305. We found that SUMO depletion reduces mTOR-Raptor and mTOR-Rictor complex formation and diminishes nutrient-induced mTOR signaling. Furthermore, we found that reconstitution with WT G{beta}L but not SUMOylation defective KR mutant G{beta}L promote mTOR signaling in G{beta}L-depleted cells. Taken together, we report for the very first time that SUMO modifies G{beta}L, influences the assembly of mTOR protein complexes, and regulates mTOR activity.

biochemistry↗

bioRxiv2020

cGAS, a DNA Sensor, Promotes Inflammatory Responses in Huntington Disease

The genetic cause of Huntington disease (HD) is attributed to the N-terminal polyglutamine expansion of huntingtin (mHTT). mHTT, which is a ubiquitously expressed protein, induces noticeable damage to the striatum, which affects motor, psychiatric, and cognitive functions in HD individuals. Although inflammatory responses apparently precede striatal damage and an overall progression of HD, the molecular mechanisms at work remain unclear (1-6). In this study, we found that cyclic GMP-AMP synthase (cGAS), a DNA sensor, which regulates inflammation, autophagy, and cellular senescence (7-9), plays a critical role in the inflammatory responses of HD. Ribosome profiling analysis reveals that cGAS mRNA has a high ribosome occupancy at exon 1 and codon-specific pauses at positions 171 (CCG) and 172 (CGT) in HD cells, compared to the control, indicating an altered cGAS expression. Accordingly, cGAS protein levels and activity, as measured by phosphorylation of stimulator of interferon genes (STING) or TANK-binding kinase 1 (TBK1), are increased in HD striatal cells, mouse Q175HD striatum and human postmortem HD striatum, compared to the healthy control. Furthermore, cGAS-dependent inflammatory genes such as Cxcl10 and Ccl5 show enhanced ribosome occupancy at exon 3 and exon 1, respectively and are upregulated in HD cells. Depletion of cGAS via CRISPR/Cas-9 diminishes cGAS activity and decreases expression of inflammatory genes while suppressing the autophagy upregulation in HD cells. We additionally detected the presence of numerous micronuclei, a known inducer of cGAS, in the cytoplasm of HD cells. Overall, the data indicates that cGAS is highly upregulated in HD and mediates inflammatory and autophagy responses. Thus, targeting cGAS may offer therapeutic benefits in HD.

neuroscience↗

bioRxiv2019

RasGRP1 (CalDAG-GEF-II) Mediates L-DOPA-induced Dyskinesia in a Mouse Model of Parkinson Disease

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-DOPA-induced 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 gene-depletion strategies targeting RasGRP1 may offer novel therapeutic opportunities for preventing L-DOPA-induced dyskinesia in PD patients.

neuroscience↗

bioRxiv2019

Rhes, a Striatal-Enriched Protein, Promotes Mitophagy Via Nix.

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, 3-nitropropionic 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 ({Delta}{Psi}m) and interacts with mitophagy receptor, Nix. In Nix KO cells, Rhes fails to disrupt {Delta}{Psi}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.

neuroscience↗