Mutation of a putative S-nitrosylation site of TRPV4 protein facilitates the channel activates

Flipping Off and On the Redox Switch in the Microcirculation

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: (a) regulating peripheral vascular resistance and blood pressure and (b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: (a) smooth muscle to endothelial communication for vasoconstriction, (b) endothelial to smooth muscle cell cross talk for vasodilation, and (c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward.

FAT10 Induces cancer cell migration by stabilizing phosphorylated ABI3/NESH

The WAVE regulatory complex (WRC) is involved in various cellular processes by regulating actin polymerization. The dysregulation of WRC components is associated with cancer development. ABI family member 3 (ABI3)/new molecule including SH3 (NESH) is one of the WRC components and it has been reported that ABI3 phosphorylation can affect WRC function. Although several residues of ABI3 have been reported to be possible phosphorylation sites, it is still unclear which residues are important for the function of ABI3. Furthermore, it is unclear how the phosphorylated form of ABI3 is regulated. Here, we demonstrate that ABI3 is stabilized by its interaction with human leukocyte antigen-F adjacent transcript 10 (FAT10). Using phospho-dead or phospho-mimetic mutants of ABI3, we showed that serine 213 and 216 are important phosphorylation sites of ABI3. In particular, FAT10 has a higher affinity for the phosphorylated form of ABI3 than the non-phosphorylated form, and it stabilizes the phosphorylated form more than the non-phosphorylated form through this differential affinity. The interaction between FAT10 and the phosphorylated form of ABI3 promoted cancer cell migration. Therefore, our results suggest that FAT10 stabilizes the phosphorylated form of ABI3, which may lead to WRC activation, thereby promoting cancer cell migration.

TRPV4-A Missing Link Between Mechanosensation and Immunity

Transient receptor potential vanilloid-type 4 (TRPV4) cation channel is widely expressed in all tissues as well as in immune cells and its function as mechanosensitive Ca2+ channel seems to be conserved throughout all mammalian species. Of late, emerging evidence has implicated TRPV4 in the activation and differentiation of innate immune cells, especially in neutrophils, monocytes, and macrophages. As such, TRPV4 has been shown to mediate neutrophil adhesion and chemotaxis, as well as production of reactive oxygen species in response to pro-inflammatory stimuli. In macrophages, TRPV4 mediates formation of both reactive oxygen and nitrogen species, and regulates phagocytosis, thus facilitating bacterial clearance and resolution of infection. Importantly, TRPV4 may present a missing link between mechanical forces and immune responses. This connection has been exemplary highlighted by the demonstrated role of TRPV4 in macrophage activation and subsequent induction of lung injury following mechanical overventilation. Mechanosensation via TRPV4 is also expected to activate innate immune cells and establish a pro-inflammatory loop in fibrotic diseases with increased deposition of extracellular matrix (ECM) and substrate stiffness. Likewise, TRPV4 may be activated by cell migration through the endothelium or the extracellular matrix, or even by circulating immune cells squeezing through the narrow passages of the pulmonary or systemic capillary bed, a process that has recently been linked to neutrophil priming and depriming. Here, we provide an overview over the emerging role of TRPV4 in innate immune responses and highlight two distinct modes for the activation of TRPV4 by either mechanical forces ("mechanoTRPV4") or by pathogens ("immunoTRPV4").

Redox regulation of transient receptor potential channels in the endothelium

ROS and RNS are important mediators of signaling pathways in the endothelium. Specific members of the TRP superfamily of cation channels act as important Ca²⁺ influx pathways in endothelial cells and are involved in endothelium-dependent vasodilation, regulation of barrier permeability, and angiogenesis. ROS and RNS can modulate the activity of certain TRP channels mainly by modifying specific cysteine residues or by stimulating the production of second messengers. In this review, we highlight the recent literature describing redox regulation of TRP channel activity in endothelial cells as well as the physiological importance of these pathways and implication for cardiovascular diseases.

Dual contribution of TRPV4 antagonism in the regulatory effect of vasoinhibins on blood-retinal barrier permeability: diabetic milieu makes a difference

Breakdown of the blood-retinal barrier (BRB), as occurs in diabetic retinopathy and other chronic retinal diseases, results in vasogenic edema and neural tissue damage, causing vision loss. Vasoinhibins are N-terminal fragments of prolactin that prevent BRB breakdown during diabetes. They modulate the expression of some transient receptor potential (TRP) family members, yet their role in regulating the TRP vanilloid subtype 4 (TRPV4) remains unknown. TRPV4 is a calcium-permeable channel involved in barrier permeability, which blockade has been shown to prevent and resolve pulmonary edema. We found TRPV4 expression in the endothelium and retinal pigment epithelium (RPE) components of the BRB, and that TRPV4-selective antagonists (RN-1734 and GSK2193874) resolve BRB breakdown in diabetic rats. Using human RPE (ARPE-19) cell monolayers and endothelial cell systems, we further observed that (i) GSK2193874 does not seem to contribute to the regulation of BRB and RPE permeability by vasoinhibins under diabetic or hyperglycemic-mimicking conditions, but that (ii) vasoinhibins can block TRPV4 to maintain BRB and endothelial permeability. Our results provide important insights into the pathogenesis of diabetic retinopathy that will further guide us toward rationally-guided new therapies: synergistic combination of selective TRPV4 blockers and vasoinhibins can be proposed to mitigate diabetes-evoked BRB breakdown.

Transient Receptor Potential Vanilloid 4 and Serum Glucocorticoid-regulated Kinase 1 Are Critical Mediators of Lung Injury in Overventilated Mice In Vivo

BACKGROUND

Mechanical ventilation can cause lung endothelial barrier failure and inflammation cumulating in ventilator-induced lung injury. Yet, underlying mechanotransduction mechanisms remain unclear. Here, the authors tested the hypothesis that activation of the mechanosensitive Ca channel transient receptor potential vanilloid (TRPV4) by serum glucocorticoid-regulated kinase (SGK) 1 may drive the development of ventilator-induced lung injury.

METHODS

Mice (total n = 54) were ventilated for 2 h with low (7 ml/kg) or high (20 ml/kg) tidal volumes and assessed for signs of ventilator-induced lung injury. Isolated-perfused lungs were inflated with continuous positive airway pressures of 5 or 15 cm H2O (n = 7 each), and endothelial calcium concentration was quantified by real-time imaging.

RESULTS

Genetic deficiency or pharmacologic inhibition of TRPV4 or SGK1 protected mice from overventilation-induced vascular leakage (reduction in alveolar protein concentration from 0.84 ± 0.18 [mean ± SD] to 0.46 ± 0.16 mg/ml by TRPV4 antagonization), reduced lung inflammation (macrophage inflammatory protein 2 levels of 193 ± 163 in Trpv4 vs. 544 ± 358 pmol/ml in wild-type mice), and attenuated endothelial calcium responses to lung overdistension. Functional coupling of TRPV4 and SGK1 in lung endothelial mechanotransduction was confirmed by proximity ligation assay demonstrating enhanced TRPV4 phosphorylation at serine 824 at 18% as compared to 5% cyclic stretch, which was prevented by SGK1 inhibition.

CONCLUSIONS

Lung overventilation promotes endothelial calcium influx and barrier failure through a mechanism that involves activation of TRPV4, presumably due to phosphorylation at its serine 824 residue by SGK1. TRPV4 and SGK1 may present promising new targets for prevention or treatment of ventilator-induced lung injury.

TRPV4: Molecular Conductor of a Diverse Orchestra

Transient receptor potential vanilloid type 4 (TRPV4) is a calcium-permeable nonselective cation channel, originally described in 2000 by research teams led by Schultz (Nat Cell Biol 2: 695-702, 2000) and Liedtke (Cell 103: 525-535, 2000). TRPV4 is now recognized as being a polymodal ionotropic receptor that is activated by a disparate array of stimuli, ranging from hypotonicity to heat and acidic pH. Importantly, this ion channel is constitutively expressed and capable of spontaneous activity in the absence of agonist stimulation, which suggests that it serves important physiological functions, as does its widespread dissemination throughout the body and its capacity to interact with other proteins. Not surprisingly, therefore, it has emerged more recently that TRPV4 fulfills a great number of important physiological roles and that various disease states are attributable to the absence, or abnormal functioning, of this ion channel. Here, we review the known characteristics of this ion channel's structure, localization and function, including its activators, and examine its functional importance in health and disease.

Control of the neurovascular coupling by nitric oxide-dependent regulation of astrocytic Ca(2+) signaling

Neuronal activity must be tightly coordinated with blood flow to keep proper brain function, which is achieved by a mechanism known as neurovascular coupling. Then, an increase in synaptic activity leads to a dilation of local parenchymal arterioles that matches the enhanced metabolic demand. Neurovascular coupling is orchestrated by astrocytes. These glial cells are located between neurons and the microvasculature, with the astrocytic endfeet ensheathing the vessels, which allows fine intercellular communication. The neurotransmitters released during neuronal activity reach astrocytic receptors and trigger a Ca²⁺ signaling that propagates to the endfeet, activating the release of vasoactive factors and arteriolar dilation. The astrocyte Ca²⁺ signaling is coordinated by gap junction channels and hemichannels formed by connexins (Cx43 and Cx30) and channels formed by pannexins (Panx-1). The neuronal activity-initiated Ca²⁺ waves are propagated among neighboring astrocytes directly via gap junctions or through ATP release via connexin hemichannels or pannexin channels. In addition, Ca²⁺ entry via connexin hemichannels or pannexin channels may participate in the regulation of the astrocyte signaling-mediated neurovascular coupling. Interestingly, nitric oxide (NO) can activate connexin hemichannel by S-nitrosylation and the Ca²⁺-dependent NO-synthesizing enzymes endothelial NO synthase (eNOS) and neuronal NOS (nNOS) are expressed in astrocytes. Therefore, the astrocytic Ca²⁺ signaling triggered in neurovascular coupling may activate NO production, which, in turn, may lead to Ca²⁺ influx through hemichannel activation. Furthermore, NO release from the hemichannels located at astrocytic endfeet may contribute to the vasodilation of parenchymal arterioles. In this review, we discuss the mechanisms involved in the regulation of the astrocytic Ca²⁺ signaling that mediates neurovascular coupling, with a special emphasis in the possible participation of NO in this process.

Human skeletal dysplasia caused by a constitutive activated transient receptor potential vanilloid 4 (TRPV4) cation channel mutation

The transient receptor potential vanilloid 4 (TRPV4) cation channel, a member of the TRP vanilloid subfamily, is expressed in a broad range of tissues where it participates in the generation of Ca²⁺ signals and/or depolarization of the membrane potential. Regulation of TRPV4 abundance at the cell surface is critical for osmo- and mechanotransduction. Defects in TRPV4 are the cause of several human diseases, including brachyolmia type 3 (MIM:113500) (also known as brachyrachia or spondylometaphyseal dysplasia Kozlowski type [MIM:118452]), and metatropic dysplasia (MIM:156530) (also called metatropic dwarfism or parastremmatic dwarfism [MIM:168400]). These bone dysplasia mutants are characterized by severe dwarfism, kyphoscoliosis, distortion and bowing of the extremities, and contractures of the large joints. These diseases are characterized by a combination of decreased bone density, bowing of the long bones, platyspondyly, and striking irregularities of endochondral ossification with areas of calcific stippling and streaking in radiolucent epiphyses, metaphyses, and apophyses. In this review, we discuss the potential effect of the mutation on the regulation of TRPV4 functions, which are related to human diseases through deviated function. In particular, we emphasize how the constitutive active TRPV4 mutant affects endochondral ossification with a reduced number of hypertrophic chondrocytes and the presence of cartilage islands within the zone of primary mineralization. In addition, we summarize current knowledge about the role of TRPV4 in the pathogenesis of several diseases.

The nuclear localization of glycogen synthase kinase 3β is required its putative PY-nuclear localization sequences

Glycogen synthase kinase-3β(GSK-3β), which is a member of the serine/threonine kinase family, has been shown to be crucial for cellular survival, differentiation, and metabolism. Here, we present evidence that GSK-3β is associated with the karyopherin β2 (Kap β2) (102-kDa), which functions as a substrate for transportation into the nucleus. A potential PY-NLS motif ((109)IVRLRYFFY(117)) was observed, which is similar with the consensus PY NLS motif (R/K/H)X(2-5)PY in the GSK-3β catalytic domain. Using a pull down approach, we observed that GSK-3β physically interacts with Kap β2 both in vivo and in vitro. Secondly, GSK-3β and Kap β2 were shown to be co-localized by confocal microscopy. The localization of GSK-3β to the nuclear region was disrupted by putative Kap β2 binding site mutation. Furthermore, in transient transfection assays, the Kap β2 binding site mutant induced a substantial reduction in the in vivo serine/threonine phosphorylation of GSK-3β, where- as the GSK-3β wild type did not. Thus, our observations indicated that Kap β2 imports GSK-3β through its putative PY NLS motif from the cytoplasm to the nucleus and increases its kinase activity.

The negative feedback regulation of TRPV4 Ca2+ ion channel function by its C-terminal cytoplasmic domain

The transient receptor potential vanilloid 4 (TRPV4) cation channel, a member of the TRP vanilloid subfamily, is expressed in a broad range of tissues where it participates in the generation of a Ca(2+) signal and/or depolarization of the membrane potential. Regulation of the abundance of TRPV4 at the cell surface is critical in osmo- and mechanotransduction. In this review, we discussed that the potential effect of Ca(2+) occurs via its action at an intracellular site in the C-terminus of the channel protein by the effect of the modulation on TRPV4 (such as 824 Ser residue phosphorylation), and its regulation for TRPV4 functions related with cell surface spread, wound healing or its polarity reorientation through its differential affinity with actin or tubulin.

Endoplasmic Reticulum (ER) Stress Enhances Tip60 (A Histone Acetyltransferase) Binding to the Concanavalin A

Herein, we report that the concanavalin A binding of Tip60 (a target of the human immunodeficiency virus type 1-encoded transactivator Tat interacting protein 60 KD; a histone acetyltransferase; HAT) is enhanced as the result of endoplasmic reticulum (ER) stress. The cell expression of Tip60 combined with site-directed mutagenesis analysis was used to identify the glutamine 324 residue as the lecithin binding (Concanavalin A; Con A) site. The Tip60 N324A mutant strain, which seems to be the Con A binding-deficient, was attenuated the protein-protein interactions with FE65 and its protein stability, but its ability of G0-G1 cell cycle arrest was not interrupted. Interestingly, both HAT activity and the nuclear localization of Tip60 N324A mutant were enhanced than those of Tip60 WT. Thus, our results indicate that the Con A binding deficient of Tip60 seems to be one of the most pivotal posttranslational modifications (such as N-glycosylation) for its functional regulation signal, which is generated in response to ER stress.