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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2021)

Atherosclerosis is a chronic inflammatory disease of arteries that leads to heart attack and stroke in over 3 million people per year in the US. The main risk factors for atherosclerotic cardiovascular disease (ASCVD) include dyslipidemia and disorders of metabolism. Moreover, there is a strong association between arterial flow characteristics and the local regulation of the inflammation that promotes ASCVD. Triglyceride rich lipoproteins (TGRL) are elevated in the circulation of individuals at risk for ASCVD and were shown to act synergistically with low magnitude shear stress (SS) to promote an inflammatory response by cultured human aortic endothelial cells (HAECs). This response was characterized by maximal vascular cell adhesion molecule (VCAM)-1 expression and was dependent upon an endoplasmic reticulum (ER) stress response. The magnitude of this response correlated strongly with enrichment in certain polyunsaturated fatty acid (PUFA) metabolites within the circulating lipoproteins that may be further metabolized by several enzymatic pathways in endothelial cells to produce an array of inflammatory mediators. We hypothesized that shifting endothelial cyclooxygenase (COX)-2-dependent PUFA metabolism alters the ER stress-mediated VCAM 1 upregulation in response to TGRLs.

TGRLs isolated from postprandial human plasma following a high fat test meal were characterized via flow cytometry as pro- or anti-inflammatory based on their impact on up- or down-regulation of VCAM-1 expression by HAEC relative to stimulation with tumor necrosis factor (TNF)α. TNFα stimulated HAEC monolayers were exposed to a SS gradient via artery-on-a-chip (AOC) microfluidics in the presence of TGRL and/or pharmacological intervention to induce or inhibit COX-2. ER stress markers that promote maximal VCAM-1 expression by TGRL in inflamed HAEC were analyzed by western blot. Despite a strong inverse correlation between COX-2 and VCAM-1 expression observed in the SS gradient, the results did not strongly support a direct effect of COX-2 in mediating ER stress-induced VCAM-1 expression but implicated cross talk with other metabolic pathways. COX-2 expression was suppressed by low magnitude (atherosusceptible) SS and enhanced by high magnitude (atheroprotective) SS in the AOC device, registering a 37% increase from static control at 12 dynes/cm2. COX-2 induction with phorbal-12,13-dibutyrate attenuated VCAM-1 across the SS gradient, reducing peak expression at 2 dynes/cm2 by 62%. COX-2 upregulation by pharmacological induction or high magnitude SS suppressed ER stress-mediated VCAM-1 elicited by TNFα and TGRLs. These results are consistent with a protective role for COX- 2 in reducing endothelial inflammation that promotes atherosclerosis and reveal the potential for endothelial PUFA metabolism to modulate an inflammatory response to TGRL. Furthermore, a potent effect of low SS to enhance VCAM-1 expression while suppressing COX-2 expression was observed, consistent with its ability to promote an atherosusceptible phenotype, and demonstrating its importance when studying the inflammation promoting atherosclerosis.

    Cover page: COX-2 Induction Suppresses Endothelial Inflammation Elicited by Lipoproteins and Low Shear Stress
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2023)
    Human induced pluripotent stem cells (hiPSCs) not only provide an abundant source of vascular cells for potential therapeutic applications in vascular disease but also constitute an excellent model for understanding the mechanisms that regulate the differentiation and the functionality of vascular cells. Here, we reported that myocyte enhancer factor 2C (MEF2C) transcription factor, but not any other members of the MEF2 family, was robustly upregulated during the differentiation of vascular progenitors and endothelial cells (ECs) from hiPSCs. Vascular endothelial growth factors (VEGF) strongly induced MEF2C expression in endothelial lineage cells. The specific upregulation of MEF2C during the commitment of endothelial lineage was dependent on the extracellular signal regulated kinase (ERK). Moreover, knockdown of MEF2C with shRNA in hiPSCs did not affect the differentiation of ECs from these hiPSCs, but greatly reduced the migration and tube formation capacity of the hiPSC-derived ECs. Through a chromatin immunoprecipitation-sequencing, genome-wide RNA-sequencing, quantitative RT-PCR, and immunostaining analyses of the hiPSC-derived endothelial lineage cells with MEF2C inhibition or knockdown compared to control hiPSC-derived ECs, we identified TNF-related apoptosis inducing ligand (TRAIL) and transmembrane protein 100 (TMEM100) as novel targets of MEF2C. This study demonstrates an important role for MEF2C in regulating human EC functions and highlights MEF2C and its downstream effectors as potential targets to treat vascular malfunction-associated diseases.
      Cover page: Role of MEF2C in the Endothelial Cells Derived from Human Induced Pluripotent Stem Cells
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2017)
      Continuous contraction-relaxation cycles of the heart require strong and stable connections of cardiac myocytes (CMs) with the extracellular matrix (ECM) to preserve sarcolemmal integrity. CM attachment to the ECM is mediated by integrin complexes localized at the muscle adhesion sites termed costameres. The ubiquitously expressed cytoskeletal protein talin (Tln) is a component of muscle costameres that links integrins ultimately to the sarcomere. There are two talin genes, Tln1 and Tln2. Here, we tested the function of these two Tln forms in myocardium where Tln2 is the dominant isoform in postnatal CMs. Surprisingly, global deletion of Tln2 in mice caused no structural or functional changes in heart, presumably because CM Tln1 became up-regulated. Tln2 loss increased integrin activation, although levels of the muscle-specific β1D-integrin isoform were reduced by 50%. With this result, we produced mice that had simultaneous loss of both CM Tln1 and Tln2 and found that cardiac dysfunction occurred by 4 wk with 100% mortality by 6 mo. β1D integrin and other costameric proteins were lost from the CMs, and membrane integrity was compromised. Given that integrin protein reduction occurred with Tln loss, rescue of the phenotype was attempted through transgenic integrin overexpression, but this could not restore WT CM integrin levels nor improve heart function. Our results show that CM Tln2 is essential for proper β1D-integrin expression and that Tln1 can substitute for Tln2 in preserving heart function, but that loss of all Tln forms from the heart-muscle cell leads to myocyte instability and a dilated cardiomyopathy.
        Cover page: Loss of mouse cardiomyocyte talin-1 and talin-2 leads to β-1 integrin reduction, costameric instability, and dilated cardiomyopathy
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