Browsing by Author "Darden, Jordan"

Now showing 1 - 4 of 4
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    Blood Vessel Patterning on Retinal Astrocytes Requires Endothelial Flt-1 (VEGFR-1)
    Chappell, John C.; Darden, Jordan; Payne, Laura Beth; Fink, Kathryn; Bautch, Victoria L. (MDPI, 2019-09-07)
    Feedback mechanisms are critical components of many pro-angiogenic signaling pathways that keep vessel growth within a functional range. The Vascular Endothelial Growth Factor-A (VEGF-A) pathway utilizes the decoy VEGF-A receptor Flt-1 to provide negative feedback regulation of VEGF-A signaling. In this study, we investigated how the genetic loss of flt-1 differentially affects the branching complexity of vascular networks in tissues despite similar effects on endothelial sprouting. We selectively ablated flt-1 in the post-natal retina and found that maximum induction of flt-1 loss resulted in alterations in endothelial sprouting and filopodial extension, ultimately yielding hyper-branched networks in the absence of changes in retinal astrocyte architecture. The mosaic deletion of flt-1 revealed that sprouting endothelial cells flanked by flt-1−/− regions of vasculature more extensively associated with underlying astrocytes and exhibited aberrant sprouting, independent of the tip cell genotype. Overall, our data support a model in which tissue patterning features, such as retinal astrocytes, integrate with flt-1-regulated angiogenic molecular and cellular mechanisms to yield optimal vessel patterning for a given tissue.
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    A Comparison of PET Tracers in Recurrent High-Grade Gliomas: A Systematic Review
    Muthukumar, Sankar; Darden, Jordan; Crowley, James; Witcher, Mark; Kiser, Jackson (MDPI, 2022-12-27)
    Humans with high-grade gliomas have a poor prognosis, with a mean survival time of just 12–18 months for patients who undergo standard-of-care tumor resection and adjuvant therapy. Currently, surgery and chemoradiotherapy serve as standard treatments for this condition, yet these can be complicated by the tumor location, growth rate and recurrence. Currently, gadolinium-based, contrast-enhanced magnetic resonance imaging (CE-MRI) serves as the predominant imaging modality for recurrent high-grade gliomas, but it faces several drawbacks, including its inability to distinguish tumor recurrence from treatment-related changes and its failure to reveal the entirety of tumor burden (de novo or recurrent) due to limitations inherent to gadolinium contrast. As such, alternative imaging modalities that can address these limitations, including positron emission tomography (PET), are worth pursuing. To this end, the identification of PET-based markers for use in imaging of recurrent high-grade gliomas is paramount. This review will highlight several PET radiotracers that have been implemented in clinical practice and provide a comparison between them to assess the efficacy of these tracers.
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    Pericyte Progenitor Coupling to the Emerging Endothelium during Vasculogenesis via Connexin43
    Payne, Laura Beth; Tewari, Bhanu P.; Dunkenberger, Logan; Bond, Samantha; Savelli, Alyssa; Darden, Jordan; Zhao, Huaning; Willi, Caroline; Kanodia, Ronak; Gude, Rosalie; Powell, Michael D.; Oestreich, Kenneth J.; Sontheimer, Harald; Dal-Pra, Sophie; Chappell, John C. (Lippincott Williams & Wilkins, 2022-04-01)
    Background: Vascular pericytes stabilize blood vessels and contribute to their maturation, while playing other key roles in microvascular function. Nevertheless, relatively little is known about involvement of their precursors in the earliest stages of vascular development, specifically during vasculogenesis. Methods: We combined high-power, time-lapse imaging with transcriptional profiling of emerging pericytes and endothelial cells in reporter mouse and cell lines. We also analyzed conditional transgenic animals deficient in Cx43/Gja1 (connexin 43/gap junction alpha-1) expression within Ng2+ cells. Results: A subset of Ng2-DsRed+ cells, likely pericyte/mural cell precursors, arose alongside endothelial cell differentiation and organization and physically engaged vasculogenic endothelium in vivo and in vitro. We found no overlap between this population of differentiating pericyte/mural progenitors and other lineages including hemangiogenic and neuronal/glial cell types. We also observed cell-cell coupling and identified Cx43-based gap junctions contributing to pericyte-endothelial cell precursor communication during vascular assembly. Genetic loss of Cx43/Gja1 in Ng2+ pericyte progenitors compromised embryonic blood vessel formation in a subset of animals, while surviving mutants displayed little-to-no vessel abnormalities, suggesting a resilience to Cx43/Gja1 loss in Ng2+ cells or potential compensation by additional connexin isoforms. Conclusions: Together, our data suggest that a distinct pericyte lineage emerges alongside vasculogenesis and directly communicates with the nascent endothelium via Cx43 during early vessel formation. Cx43/Gja1 loss in pericyte/mural cell progenitors can induce embryonic vessel dysmorphogenesis, but alternate connexin isoforms may be able to compensate. These data provide insight that may reshape the current framework of vascular development and may also inform tissue revascularization/vascularization strategies.
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    A Soluble Platelet-Derived Growth Factor Receptor-β Originates via Pre-mRNA Splicing in the Healthy Brain and Is Upregulated during Hypoxia and Aging
    Payne, Laura Beth; Abdelazim, Hanaa; Hoque, Maruf; Barnes, Audra; Mironovova, Zuzana; Willi, Caroline E.; Darden, Jordan; Houk, Clifton; Sedovy, Meghan W.; Johnstone, Scott R.; Chappell, John C. (MDPI, 2023-04-21)
    The platelet-derived growth factor-BB (PDGF-BB) pathway provides critical regulation of cerebrovascular pericytes, orchestrating their investment and retention within the brain microcirculation. Dysregulated PDGF Receptor-beta (PDGFRβ) signaling can lead to pericyte defects that compromise blood-brain barrier (BBB) integrity and cerebral perfusion, impairing neuronal activity and viability, which fuels cognitive and memory deficits. Receptor tyrosine kinases such as PDGF-BB and vascular endothelial growth factor-A (VEGF-A) are often modulated by soluble isoforms of cognate receptors that establish signaling activity within a physiological range. Soluble PDGFRβ (sPDGFRβ) isoforms have been reported to form by enzymatic cleavage from cerebrovascular mural cells, and pericytes in particular, largely under pathological conditions. However, pre-mRNA alternative splicing has not been widely explored as a possible mechanism for generating sPDGFRβ variants, and specifically during tissue homeostasis. Here, we found sPDGFRβ protein in the murine brain and other tissues under normal, physiological conditions. Utilizing brain samples for follow-on analysis, we identified mRNA sequences corresponding to sPDGFRβ isoforms, which facilitated construction of predicted protein structures and related amino acid sequences. Human cell lines yielded comparable sequences and protein model predictions. Retention of ligand binding capacity was confirmed for sPDGFRβ by co-immunoprecipitation. Visualizing fluorescently labeled sPDGFRβ transcripts revealed a spatial distribution corresponding to murine brain pericytes alongside cerebrovascular endothelium. Soluble PDGFRβ protein was detected throughout the brain parenchyma in distinct regions, such as along the lateral ventricles, with signals also found more broadly adjacent to cerebral microvessels consistent with pericyte labeling. To better understand how sPDGFRβ variants might be regulated, we found elevated transcript and protein levels in the murine brain with age, and acute hypoxia increased sPDGFRβ variant transcripts in a cell-based model of intact vessels. Our findings indicate that soluble isoforms of PDGFRβ likely arise from pre-mRNA alternative splicing, in addition to enzymatic cleavage mechanisms, and these variants exist under normal physiological conditions. Follow-on studies will be needed to establish potential roles for sPDGFRβ in regulating PDGF-BB signaling to maintain pericyte quiescence, BBB integrity, and cerebral perfusion—critical processes underlying neuronal health and function, and in turn, memory and cognition.