Biology subjects

Vargas, D. A.

Publications and source records attributed to Vargas, D. A..

3 recordsLinked to original sources

bioRxiv2020

Macrophage metallothioneins participate in the antileishmanial activity of antimonials

SYNOPSISO_ST_ABSBackgroundC_ST_ABSHost cell functions that participate in the pharmacokinetics and pharmacodynamics (PK/PD) of pentavalent antimonials for treatment of American cutaneous leishmaniasis (CL) are critical for drug efficacy. ObjectivesIn this study, we investigated whether macrophage mechanisms of xenobiotic detoxification contribute to drug-dependent elimination of intracellular Leishmania. MethodsTranscriptomes of primary macrophages from CL patients (n=6), exposed ex vivo to Leishmania infection and SbV were generated. Candidate genes were selected and validated using short harping RNA interference (shRNA) in THP-1 cells. ResultsStrong induction of metallothionein (MT) genes was observed upon Leishmania infection and exposure to SbV, with 7 MT genes (MT1 and MT2 family members) appearing within the top 20 up-regulated genes. Tandem knockdown (KD) of MT2-A and MT1-E, 1F, and 1X in THP-1 cells was achieved using a pan-MT shRNA., Intracellular parasite survival after SbV exposure was unaffected in tandem-KD cells, and this was a consequence of strong transcriptional upregulation of MTs by infection and SbV, overcoming the KD effect. Gene silencing of the metal transcription factor-1 (MTF-1) abrogated expression of MT1 and MT2-A genes. Upon exposure to SbV, intracellular survival of Leishmania in MTF-1KD cells was significantly enhanced (p [≤] 0.05). ConclusionsMTs are potent scavengers of heavy metals, and central elements of the mammalian cell machinery for xenobiotic detoxification. Results from this study highlight the participation of macrophage MTs in Sb-dependent parasite killing, revealing novel strategies for host-targeted optimization of antileishmanial drugs.

molecular biology↗

bioRxiv2019

Intercellular adhesion stiffness moderates cell decoupling on stiff substrates

The interplay between cell-cell and cell-substrate interactions is complex yet necessary for the formation and well-functioning of tissues. The same mechanosensing mechanisms used by the cell to sense its extracellular matrix, also play a role in intercellular interactions. We used the discrete element method to develop a computational model of a deformable cell that includes subcellular components responsible for mechanosensing. We modeled a cell pair in 3D on a patterned substrate, a simple laboratory setup to study intercellular interactions. We explicitly modeled focal adhesions between the cells and the substrate, and adherens junctions between cells. These mechanosensing adhesions matured; their disassembly rate was dictated by the force they carry. We also modeled stress fibers which bind the discrete adhesions and contract. The mechanosensing fibers strengthened upon stalling and exerted higher forces. Traction exerted on the substrate was used to generate maps displaying the magnitude of the tractions along the cell-substrate interface. Simulated traction maps are compared to experimental maps obtained via traction force microscopy. The model recreates the dependence on substrate stiffness of the tractions spatial distribution across the cell-substrate interface, the contractile moment of the cell pair, the intercellular force, and the number of focal adhesions. It also recreates the phenomenon of cell decoupling, in which cells exert forces separately when substrate stiffness increases. More importantly, the model provides viable molecular explanations for decoupling. It shows that the implemented mechanosensing mechanisms are responsible for competition between different fiber-adhesion configurations present in the cell pair. The point at which an increasing substrate stiffness becomes as high as that of the cell-cell interface is the tipping point at which configurations that favor cell-substrate adhesion dominate over those favoring cell-cell adhesion. This competition is responsible for decoupling. Additionally, we learn that extent of decoupling is modulated by adherens junction maturation.\n\nStatement of SignificanceCells are sensitive to mechanical factors of their extracellular matrix while simultaneously in contact with other cells. This creates complex intercellular interactions that depend on substrate stiffness and play a role in processes such as development and diseases like cardiac arrhythmia, asthma, and cancer. The simplest cell collective system in vitro is a cell pair on a patterned substrate. We developed a computational model of this system which explains the role of molecular adhesions and contractile fibers in the dynamics of cell-cell interactions on substrates with different stiffness. It is one of the first models of a deformable cell collective based on mechanical principles. It recreates cellular decoupling, a phenomenon in which cells exert forces separately, when substrate stiffness increases.

bioengineering↗

bioRxiv2017

Tandem histone-binding domains enhance the activity of a synthetic chromatin effector

Fusion proteins that specifically interact with biochemical marks on chromosomes represent a new class of synthetic transcriptional regulators that decode cell state information rather than DNA sequences. In multicellular organisms, information relevant to cell state, tissue identity, and oncogenesis is often encoded as biochemical modifications of histones, which are bound to DNA in eukaryotic nuclei and regulate gene expression states. We have previously reported the development and validation of the \"Polycomb-based transcription factor\" (PcTF), a fusion protein that recognizes histone modifications through a protein-protein interaction between its polycomb chromodomain (PCD) motif and trimethylated lysine 27 of histone H3 (H3K27me3) at genomic sites. We demonstrated that PcTF activates genes at methyl-histone-enriched loci in cancer-derived cell lines. However, PcTF induces modest activation of a methyl-histone associated reporter compared to a DNA-binding activator. Therefore, we modified PcTF to enhance its target affinity. Here, we demonstrate the activity of a modified regulator called Pc2TF, which has two tandem copies of the H3K27me3-binding PCD at the N-terminus. Pc2TF shows higher affinity for H3K27me3 in vitro and shows enhanced gene activation in HEK293 cells compared to PcTF. These results provide compelling evidence that the intrinsic histone-binding activity of the PCD motif can be used to tune the activity of synthetic histone-binding transcriptional regulators.

synthetic biology↗