Biology subjects

Shahani, N.

Publications and source records attributed to Shahani, N..

3 recordsLinked to original sources

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↗

bioRxiv2019

Global ribosome profiling reveals that mutant huntingtin stalls ribosomes and represses protein synthesis independent of fragile X mental retardation protein

The regulators that stall ribosome translocation are poorly understood. We find that polyglutamine-expanded mutant Huntingtin (mHtt), the Huntingtons disease (HD) causing protein, promotes ribosome stalling and physiologically suppresses protein synthesis. A comprehensive, genome-wide analysis of ribosome footprint profiling (Ribo-Seq) revealed widespread ribosome stalling on mRNA transcripts and a shift in the distribution of ribosomes toward the 5 end, with single-codon unique pauses on selected mRNAs in HD cells. In Ribo-Seq, we found fragile X mental retardation protein (FMRP), a known regulator of ribosome stalling, translationally upregulated and it co-immunoprecipitated with mHtt in HD cells and postmortem brain. Depletion of FMRP gene, Fmr1, however, did not affect the mHtt-mediated suppression of protein synthesis or ribosome stalling in HD cells. Consistent with this, heterozygous deletion of Fmr1 in Q175FDN-Het mouse model, Q175FDN-Het; Fmr1+/-, showed no discernable phenotype, but a subtle deficit in motor skill learning. On the other hand, depletion of mHtt, which binds directly to ribosomes in an RNase-sensitive manner, enhanced global protein synthesis, increased ribosome translocation and decreased stalling. This mechanistic knowledge advances our understanding of the inhibitory role of mHtt in ribosome translocation and may lead to novel target(s) identification and therapeutic approaches that modulate ribosome stalling in HD.\n\nOne Sentence SummaryHuntingtons disease (HD) protein, mHtt, binds to ribosomes and affects their translocation and promotes stalling independent of the fragile X mental retardation protein.

neuroscience↗