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1. The pericyte microenvironment during vascular development

   https://doi.org/10.1111/micc.12554  

   Payne, Laura B. ; Zhao, Huaning ; James, Carissa C. ; Darden, Jordan ; McGuire, David ; Taylor, Sarah ; Smyth, James W. ; Chappell, John C. ( May 2019 , Microcirculation)

   Vascular pericytes provide critical contributions to the formation and integrity of the blood vessel wall within the microcirculation. Pericytes maintain vascular stability and homeostasis by promoting endothelial cell junctions and depositing extracellular matrix (ECM) components within the vascular basement membrane, among other vital functions. As their importance in sustaining microvessel health within various tissues and organs continues to emerge, so does their role in a number of pathological conditions including cancer, diabetic retinopathy, and neurological disorders. Here, we review vascular pericyte contributions to the development and remodeling of the microcirculation, with a focus on the local microenvironment during these processes. We discuss observations of their earliest involvement in vascular development and essential cues for their recruitment to the remodeling endothelium. Pericyte involvement in the angiogenic sprouting context is also considered with specific attention to crosstalk with endothelial cells such as through signaling regulation and ECM deposition. We also address specific aspects of the collective cell migration and dynamic interactions between pericytes and endothelial cells during angiogenic sprouting. Lastly, we discuss pericyte contributions to mechanisms underlying the transition from active vessel remodeling to the maturation and quiescence phase of vascular development.

    

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2. Variations in mechanical stiffness alter microvascular sprouting and stability in a PEG hydrogel model of idiopathic pulmonary fibrosis

   https://doi.org/10.1111/micc.12817  

   Leonard‐Duke, Julie ; Bruce, Anthony C. ; Peirce, Shayn M. ; Taite, Lakeshia J. ( May 2023 , Microcirculation)

   Microvascular remodeling is governed by biomechanical and biochemical cues which are dysregulated in idiopathic pulmonary fibrosis. Understanding how these cues impact endothelial cell‐pericyte interactions necessitates a model system in which both variables can be independently and reproducibly modulated. In this study we develop a tunable hydrogel‐based angiogenesis assay to study how varying angiogenic growth factors and environmental stiffness affect sprouting and vessel organization.

   Lungs harvested from mice were cut into 1 mm long segments then cultured on hydrogels having one of seven possible stiffness and growth factor combinations. Time course, brightfield, and immunofluorescence imaging were used to observe and quantify sprout formation.

   Our assay was able to support angiogenesis in a comparable manner to Matrigel in soft 2 kPa gels while enabling tunability to study the effects of stiffness on sprout formation. Matrigel and 2 kPa groups contained significantly more samples with sprouts when compared to the stiffer 10 and 20 kPa gels. Growth factor treatment did not have as obvious an effect, although the 20 kPa PDGF + FGF‐treated group had significantly longer vessels than the vascular endothelial growth factor‐treated group.

   We have developed a novel, tunable hydrogel assay for the creation of lung explant vessel organoids which can be modulated to study the impact of specific environmental cues on vessel formation and maturation.

    

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3. A Soluble Platelet-Derived Growth Factor Receptor-β Originates via Pre-mRNA Splicing in the Healthy Brain and Is Upregulated during Hypoxia and Aging

   https://doi.org/10.3390/biom13040711  

   Payne, Laura Beth ; Abdelazim, Hanaa ; Hoque, Maruf ; Barnes, Audra ; Mironovova, Zuzana ; Willi, Caroline E. ; Darden, Jordan ; Houk, Clifton ; Sedovy, Meghan W. ; Johnstone, Scott R. ; et al ( April 2023 , Biomolecules)

   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. 

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4. Pericytes Contribute to Dysfunction in a Human 3D Model of Placental Microvasculature through VEGF‐Ang‐Tie2 Signaling

   https://doi.org/10.1002/advs.201900878  

   Haase, Kristina ; Gillrie, Mark R. ; Hajal, Cynthia ; Kamm, Roger D. ( October 2019 , Advanced Science)

   Placental vasculopathies are associated with a number of pregnancy‐related diseases, including pre‐eclampsia (PE)—a leading cause of maternal–fetal morbidity and mortality worldwide. Placental presentations of PE are associated with endothelial dysfunction, reduced vessel perfusion, white blood cell infiltration, and altered production of angiogenic factors within the placenta (a candidate mechanism). Despite maintaining vascular quiescence in other tissues, how pericytes contribute to vascular growth and signaling in the placenta remains unknown. Here, pericytes are hypothesized to play a detrimental role in the pathogenesis of placental vascular growth. A perfusable triculture model is developed, consisting of human endothelial cells, fibroblasts, and pericytes, capable of recapitulating growth and remodeling in a system that mimics inflamed placental microvessels. Placental pericytes are shown to contribute to growth restriction of microvessels over time, an effect that is strongly regulated by vascular endothelial growth factor and Angiopoietin/Tie2 signaling. Furthermore, this model is capable of recapitulating essential processes including tumor necrosis factor alpha (TNFα)‐mediated vascular leakage and leukocyte infiltration, both important aspects associated with placental PE. This placental vascular model highlights that an imbalance in endothelial–pericyte crosstalk can play a critical role in the development of vascular pathology and associated diseases.

    

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5. Advanced age protects resistance arteries of mouse skeletal muscle from oxidative stress through attenuating apoptosis induced by hydrogen peroxide

   https://doi.org/10.1113/JP278255  

   Norton, Charles E. ; Sinkler, Shenghua Y. ; Jacobsen, Nicole L. ; Segal, Steven S. ( July 2019 , The Journal of Physiology)

   Vascular oxidative stress increases with advancing age.

   We hypothesized that resistance vessels develop resilience to oxidative stress to protect functional integrity and tested this hypothesis by exposing isolated pressurized superior epigastric arteries (SEAs) of old and young mice to H₂O₂.

   H₂O₂‐induced death was greater in smooth muscle cells (SMCs) than endothelial cells (ECs) and lower in SEAs from oldvs. young mice; the rise in vessel wall [Ca²⁺]_iinduced by H₂O₂was attenuated with ageing, as was the decline in noradrenergic vasoconstriction; genetic deletion of IL‐10 mimicked the effects of advanced age on cell survival.

   Inhibiting NO synthase or scavenging peroxynitrite reduced SMC death; endothelial denudation or inhibiting gap junctions increased SMC death; delocalization of cytochrome C activated caspases 9 and 3 to induce apoptosis.

   Vascular cells develop resilience to H₂O₂during ageing by preventing Ca²⁺overload and endothelial integrity promotes SMC survival.

   Advanced age is associated with elevated oxidative stress and can protect the endothelium from cell death induced by H₂O₂. Whether such protection occurs for intact vessels or differs between smooth muscle cell (SMC) and endothelial cell (EC) layers is unknown. We tested the hypothesis that ageing protects SMCs and ECs during acute exposure to H₂O₂(200 µm, 50 min). Mouse superior epigastric arteries (SEAs; diameter, ∼150 µm) were isolated and pressurized to 100 cmH₂O at 37˚C. For SEAs from young (4 months) mice, H₂O₂killed 57% of SMCs and 11% of ECs in malesvs. 8% and 2%, respectively, in females. Therefore, SEAs from males were studied to resolve the effect of ageing and experimental interventions. For old (24 months) mice, SMC death was reduced to 10% with diminished accumulation of [Ca²⁺]_iin the vessel wall during H₂O₂exposure. In young mice, genetic deletion of IL‐10 mimicked the protective effect of ageing on cell death and [Ca²⁺]_iaccumulation. Whereas endothelial denudation or gap junction inhibition (carbenoxolone; 100 µm) increased SMC death, inhibiting NO synthase (l‐NAME, 100 µm) or scavenging peroxynitrite (FeTPPS, 5 µm) reduced SMC death along with [Ca²⁺]_i. Despite NO toxicity via peroxynitrite formation, endothelial integrity protects SMCs. Caspase inhibition (Z‐VAD‐FMK, 50 µm) attenuated cell death with immunostaining for annexin V, cytochrome C, and caspases 3 and 9 pointing to induction of intrinsic apoptosis during H₂O₂exposure. We conclude that advanced age reduces Ca²⁺influx that triggers apoptosis, thereby promoting resilience of the vascular wall during oxidative stress.

    

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