Biology subjects

Sharma, S. S.

Publications and source records attributed to Sharma, S. S..

4 recordsLinked to original sources

bioRxiv2026

Bile Acids Regulate Accumbal Cholinergic Circuitry and Dopamine Release through TGR5 Activation

BackgroundFatty foods and alcohol (i.e., ethanol) produce strong reinforcing effects, in part by altering cholinergic interneuron (CIN) activity and tonic dopamine (DA) release within the nucleus accumbens (NAc). Ethanol and fatty foods also both stimulate hepatic and possibly local brain bile acid (BA) synthesis, which raises the possibility that BAs may act as a common upstream regulator of these substances shared mesolimbic effects. MethodsThe current study investigated whether BAs can directly alter mesolimbic activity. Electrophysiological data from acute mouse brain slices was collected to assess BA effects on NAc CIN firing, as well as on excitatory and inhibitory postsynaptic CIN inputs. Bile effects on NAc DA release and clearance rates were measured through voltammetry. ResultsWe found that low concentrations of a 1:1 mixture of BAs cholic acid (CA) and deoxycholic acid (DCA; 1-10 M) increased CIN firing rate, whereas high BA concentrations (1-10 mM) decreased CIN firing. We further demonstrated that BA-induced excitatory effects on CIN firing are independently mediated by at least two mechanisms: Takeda G-protein-coupled receptor 5 (TGR5) activation and suppression of inhibitory CIN currents. Additionally, our results indicate that BAs modulate inhibitory input in a complex manner, reducing frequency at low concentrations, but increasing at high concentrations, and increasing amplitude at low concentrations current amplitude, and the distribution of postsynaptic current amplitude sizes across concentrations. Finally, our voltammetry data indicate that while low BA concentrations enhance NAc DA release without affecting DA uptake, high BA concentrations robustly inhibit accumbal DA release. ConclusionOur findings provide evidence that BAs exert direct modulatory effects on neural activity in the striatum.

neuroscience↗

bioRxiv2026

Enhanced co-expression of cyclin F and USP7 in luminal A breast cancer correlates with endocrine resistance, high oxidative phosphorylation, and low inflammatory signatures

Cyclin F is a non-canonical cyclin that functions as the substrate-recognition subunit of the SCFCyclin F E3-ubiquitin ligase complex. By targeting specific proteins for degradation, cyclin F plays an important role in proteostasis and genomic stability. We recently showed that cyclin F interacts with USP7, a deubiquitylating enzyme. USP7-mediated stabilization of ER and PHF8 is linked to breast carcinogenesis. On the other hand, recent studies have implicated SCFCyclin F in modulating the CDK4/6-RB axis, a pathway that plays a crucial role in tumorigenesis and progression in the HR+/HER2- breast cancer. Herein, we performed an in-silico analysis to investigate the role of USP7-cyclin F axis in HR+/HER2-breast cancer. Cyclin F and USP7 transcripts were positively correlated across cancer cell lines and the luminal A breast cancer in the TCGA cohort. In both the METABRIC and TCGA breast cancer cohorts, high cyclin F-USP7 co-expression was synergistically associated with poor survival only in the endocrine-treated luminal A group, but not in those without endocrine treatment, suggesting an association with endocrine resistance. Notably, the transcriptomic profiles of high cyclin F-USP7 tumors were associated with signatures of endocrine resistance. Cancer Dependency Map analysis of CRISPR knockout of cyclin F or USP7 on cellular fitness suggested cyclin F influences the CDK4-RB pathway via RBL2 and/or PLK4, while USP7 might influence the ESR1-CDK4 network via HUWE1. Further, pathway analysis of differentially abundant proteins in the TCGA cohort identified enrichment of upregulated proteins in the oxidative phosphorylation and cell cycle pathways, and downregulated proteins in the immune pathways.

cancer biology↗

bioRxiv2025

Syntaxin 1A Transmembrane Domain Palmitoylation 1 Induces a Fusogenic Conformation

Neurotransmitter release is triggered by the fusion of synaptic vesicles with the plasma membrane, orchestrated by SNARE proteins Synaptobrevin 2 (Syb2), Syntaxin 1A (Stx1A), and SNAP25. Recent experimental studies showed that Stx1A palmitoylation of C271/C272 promotes spontaneous neurotransmitter release. However, the mechanistic role of SNARE transmembrane domain (TMD) palmitoylation in membrane fusion remains unclear. To investigate the structural and functional implications of TMD palmitoylation, we employed coarse-grained molecular dynamics simulations with the MARTINI force field. In simulations of individual SNAREs and of SNAP-25/Stx1A (t-SNARE) complexes in a membrane the palmitoyl chains of Syb2 and Stx1A localize to the membrane midplane, with Stx1A palmitoyl chains bending toward the extracellular leaflet. Non-palmitoylated Stx1A assumed a conformation where the SNARE domain was lying flat, adhering to the intracellular surface of the membrane. Stx1A dual palmitoylation induced dramatic changes, reducing the tilt of its TMD and stabilizing a more upright conformation of its SND. This conformation resembles the Stx1A conformation in a s Stx1A-SNAP25 t-SNARE complex, providing a potential mechanistic explanation of how Stx1A TMD palmitoylation facilitates early steps in SNARE complex formation and thus promotes spontaneous release. In simulations of the late steps of layers 5 to 8 SNARE complex zippering in a system of 4 SNARE complexes bridging a 10-nm nanodisc and a planar membrane, FPs spontaneously opened after a few hundred nanoseconds, preceded by distal leaflet lipid transfer and followed by FP flickering conductance before FP closure. At this stage, Stx1A TMD palmitoylation delayed lipid transfer and FP formation and decreased FP flicker open times, whereas the palmitoylation of Syb2 did not affect fusion pore dynamics. These findings suggest that after facilitation of priming before FP opening, Stx1A TMD palmitoylation, directly affects FP dynamics. These results highlight the essential role of SNARE TMD palmitoylation at multiple stages of neurotransmitter release. Statement of SignificanceSynaptic vesicle fusion is critical for neurotransmitter release, enabling neuron-to-neuron communication at synapses. Post-translational modifications, such as palmitoylation, are known to influence this process. Using MARTINI coarse-grained molecular dynamics simulations, we examined the impact of SNARE transmembrane domain (TMD) palmitoylation on SNARE protein conformation and fusion dynamics. Stx1A palmitoylation reduces its TMD tilting and changes its SNARE domain conformation, facilitating SNARE complex formation. In fusion pore (FP) simulations, Stx1A palmitoylation delayed FP opening, decreased FP flicker open times, and shortened FP conductance flicker durations by direct interactions with the FP. Interestingly, dual palmitoylation of Stx1A and Syb2 restored flickering duration but decreased FP opening probability within 4 s, suggesting a nuanced role of TMD palmitoylation in modulating neurotransmitter release.

biophysics↗

bioRxiv2023

Restoration of locomotor function following stimulation of the A13 region in Parkinson's mouse models

Parkinsons disease (PD) is characterized by extensive motor and non-motor dysfunction, including gait disturbance, which is difficult to treat effectively. This study explores the therapeutic potential of targeting the A13 region, a heterogeneous region of the medial zona incerta (mZI) containing dopaminergic, GABAergic, and glutamatergic neurons that has shown relative preservation in PD models. The A13 is identified to project to the mesencephalic locomotor region (MLR), with a subpopulation of cells displaying activity correlating to movement speed, suggesting its role in locomotion. We show that photoactivation of this A13 region can alleviate bradykinesia and akinetic features, while increasing turning in a mouse model of PD. These effects combine disease-specific rescue of function with a possible gain of function. We identified areas of preservation and plasticity within the A13 region using whole-brain imaging. Our findings suggest a global remodeling of afferent and efferent projections of the A13 region, highlighting the zona incertas role as a crucial hub for the rapid selection of motor function. The study unveils the significant pro-locomotor effects of the A13 region and suggests its promising potential as a therapeutic target for PD-related gait dysfunction. SIGNIFICANCE STATEMENTThis work examines the function of the A13 region in locomotion, an area with direct connectivity to locomotor regions in the brainstem. A13 stimulation can restore locomotor function and improve bradykinesia in a PD mouse model.

neuroscience↗