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  • Interestingly in vivo infusion and

    2021-09-23

    Interestingly, in vivo infusion and uptake of Ang II in intact mice indicated that multiligand endocytic receptor megalin has at least some role in the uptake of Ang II and the downstream signaling process in proximal tubule haloperidol haldol (PTCs) in vivo [173]. Earlier in vivo studies showed that PTCs of the kidney also accumulate both systematically infused 125I-labeled and unlabeled Ang II [[174], [175], [176]]. Live-cell imaging has also simultaneously captured time-lapse images of Ang II type 1a receptors (AT1aR) and intracellular compartments in transfected HEK-293 cells following stimulation with Ang II [172]. It has been reported that a proton-sensing GPCR, ovarian cancer G protein-coupled receptor 1 (OGR1), is related to acidosis and diseases that cause tissue acidification. pH-dependent intracellular trafficking of OGR1 has been visualized in living leukocytes by a real-time fluorescence microscopic method based on sortase A-mediated pulse labeling of OGR1. Quantitative single-cell image analysis and live-cell monitoring demonstrated that the signal transduction activity of OGR1 is regulated by pH-dependent receptor internalization and recycling to the plasma membrane [177]. Recently, internalization of G protein-coupled receptors (GPCRs) was visualized with high spatial resolution near the plasma membrane by means of total internal reflection fluorescence (TIRF) microscopy at a level of discrete single events. Methods have also been developed to determine the relative extent of internalized fluorescent receptor-ligand complexes by comparative fluorescence quantification in living cells of Chinese hamster ovaries (CHO) [178]. Live-cell imaging of other GPCRs using confocal microscopes enabled investigators to observe the internalization and trafficking of receptors in individual cells [179,180]. Confocal imaging revealed detailed receptor neuroanatomy throughout the nervous system of knock-in mice, where δ-opioid receptor (DOR) was replaced by an active DOR-EGFP fusion protein [181]. Real-time imaging in primary neurons allowed dynamic visualization of drug-induced receptor trafficking. In DOR-EGFP animals, drug treatment triggered receptor endocytosis that correlated with the behavioral response. It also has been shown that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors play an important role in brain functions such as learning and memory process. Modulation of synaptic strength through trafficking of AMPA receptors is an essential mechanism underlying synaptic plasticity. Several studies have used live time-lapse imaging of fluorescence-tagged AMPA receptors to directly monitor membrane trafficking in these receptors in their basal state, as well as during synaptic plasticity in vivo using confocal microscopy [182]. Overexpression of lung 5-hydroxytryptamine7 (5-HT7) receptor is an important protective mechanism during lipopolysaccharide (LPS)-induced sepsis-related cell damage. 5-HT7 receptor trafficking has been evaluated using in- vivo and in-vitro models of LPS-induced inflammatory cell injury in rats and LPS-treated A549 cells, which suggested that lung 5-HT7 receptor expression is increased in LPS-induced endotoxemia [183]. Tumor hypoxia is linked with progression of malignant state and resistance to cancer treatments and therapies. It has been indicated that the ligand-bound EGF receptor (EGFR) trafficking is prolonged due to hypoxia-inducible factor (HIF)-medicated delays of endocytic cycle [184]. These authors suggested a role for oxygen-sensing pathway of tumor activation of HIF-associated EGFR-mediated signaling by delayed enocytic trafficking and deactivation of receptor protein. To understand endocytosis, trafficking, and signaling of receptors, more studies with live-cell and animal in-vivo approaches will allow greater detail that should illustrate the mechanistic pathways of NPRA in both physiological and pathophysiological contexts of hormone signaling. The gene-knockout studies of Npr1 in mice have demonstrated that ANP resistance is associated with sodium and volume retention and kidney dysfunction in the mutant animals [45]. Nevertheless, the role of NPRA trafficking in the recycling endosomes and the desensitization of this receptor under pathological conditions is not well understood.