Systems Biology Will Direct Vascular-Targeted Therapy for Obesity

Axl and Vascular Endothelial Growth Factor Receptors Exhibit Variations in Membrane Localization and Heterogeneity Across Monolayer and Spheroid High-Grade Serous Ovarian Cancer Models

Vascular endothelial growth factor receptors (VEGFRs) and Axl are receptor tyrosine kinases (RTK) that are targeted in ovarian cancer therapy. Two-dimensional monolayer culture and three-dimensional spheroids are common models for RTK-targeted drug screening: monolayers are simple and economical while spheroids include several genetic and histological tumor features. RTK membrane localization dictates RTK signaling and drug response, however, it is not characterized in these models. We quantify plasma membrane RTK concentrations and show differential RTK abundance and heterogeneity in monolayers versus spheroids. We show VEGFR1 concentrations on the plasma membrane to be 10 times higher in OVCAR8 spheroids than in monolayers; OVCAR8 spheroids are more heterogeneous than monolayers, exhibiting a bimodal distribution of a low-Axl (6200/cell) and a high-Axl subpopulation (25,000/cell). In addition, plasma membrane Axl concentrations differ by 100 times between chemosensitive (OVCAR3) and chemoresistant (OVCAR8) cells and by 10 times between chemoresistant cell lines (OVCAR5 vs. OVCAR8). These systematic findings can guide ovarian cancer model selection for drug screening.

Absolute Quantification of Plasma Membrane Receptors Via Quantitative Flow Cytometry

Plasma membrane receptors are transmembrane proteins that initiate cellular response following the binding of specific ligands (e.g., growth factors, hormones, and cytokines). The abundance of plasma membrane receptors can be a diagnostic or prognostic biomarker in many human diseases. One of the best techniques for measuring plasma membrane receptors is quantitative flow cytometry (qFlow). qFlow employs fluorophore-conjugated antibodies against the receptors of interest and corresponding fluorophore-loaded calibration beads offers standardized and reproducible measurements of plasma membrane receptors. More importantly, qFlow can achieve absolute quantification of plasma membrane receptors when phycoerythrin (PE) is the fluorophore of choice. Here we describe a detailed qFlow protocol to obtain absolute receptor quantities on the basis of PE calibration. This protocol is foundational for many previous and ongoing studies in quantifying tyrosine kinase receptors and G-protein-coupled receptors with in vitro cell models and ex vivo cell samples.

Chronic VEGFR-3 signaling preserves dendritic arborization and sensitization under stress

Dendritic arborization is critical for the establishment and maintenance of precise neural circuits. Vascular endothelial growth factor D (VEGF-D), well-characterized as a "lymphangiogenic" growth factor, reportedly maintains dendritic arborization and synaptic strength in the hippocampus of adult mice through VEGF receptor (VEGFR-3) signaling. Here, we investigated the effect of chronic VEGFR-3-specific activation on adipose arbor morphometry using the Adipo-VD mouse, a model of inducible, adipose-specific VEGF-D overexpression. We examined whether adipose tissue innervation was preserved or functionally different in Adipo-VD mice during stress in vivo and if VEGFR-3 signaling afforded neuroprotection to challenged neurons in vitro. Chronic VEGFR-3 signaling in Adipo-VD subcutaneous adipose tissue resulted in a reduction in the dendrite length, dendritic terminal branches (filament length), and dendritic terminal branch volume (filament volume), but increased dendrite branching. We also identified reduced stimulus-evoked excitatory sympathetic nerve activity in Adipo-VD mice. Following 6-hydroxydopamine (6-OHDA) denervation, Adipo-VD dendritic arbors were preserved, including improved dendritic branch volume, length, and dendritic branches than in wildtype tissues. In vitro, we found that chronic elevation of VEGFR-3 signaling in developing mVC neurons changes the dendritic arbor complexity and improves stress-induced structure remodeling. Developing neurons are conferred neuroprotection against stress, potentially by upregulation of proteolytic conversion of pro-BDNF to mature BDNF. Mature neurons, however, display improved dendritic arbor complexity, and unaltered dendritic structural remodeling and improved resistance to stress with VEGFR-3 signaling. Overall, chronically increasing VEGFR-3 signaling in neurons has a synergistic impact on neurosensitization and neuroprotection during stress.

Transcriptomic Changes of Murine Visceral Fat Exposed to Intermittent Hypoxia at Single Cell Resolution

Intermittent hypoxia (IH) is a hallmark of obstructive sleep apnea (OSA) and induces metabolic dysfunction manifesting as inflammation, increased lipolysis and insulin resistance in visceral white adipose tissues (vWAT). However, the cell types and their corresponding transcriptional pathways underlying these functional perturbations are unknown. Here, we applied single nucleus RNA sequencing (snRNA-seq) coupled with aggregate RNA-seq methods to evaluate the cellular heterogeneity in vWAT following IH exposures mimicking OSA. C57BL/6 male mice were exposed to IH and room air (RA) for 6 weeks, and nuclei from vWAT were isolated and processed for snRNA-seq followed by differential expressed gene (DEGs) analyses by cell type, along with gene ontology and canonical pathways enrichment tests of significance. IH induced significant transcriptional changes compared to RA across 14 different cell types identified in vWAT. We identified cell-specific signature markers, transcriptional networks, metabolic signaling pathways, and cellular subpopulation enrichment in vWAT. Globally, we also identify 298 common regulated genes across multiple cellular types that are associated with metabolic pathways. Deconvolution of cell types in vWAT using global RNA-seq revealed that distinct adipocytes appear to be differentially implicated in key aspects of metabolic dysfunction. Thus, the heterogeneity of vWAT and its response to IH at the cellular level provides important insights into the metabolic morbidity of OSA and may possibly translate into therapeutic targets.