Influx Signaling Research Articles

Sodium chloride in the tumor microenvironment enhances T cell metabolic fitness and cytotoxicity

The efficacy of antitumor immunity is associated with the metabolic state of cytotoxic T cells, which is sensitive to the tumor microenvironment. Whether ionic signals affect adaptive antitumor immune responses is unclear. In the present study, we show that there is an enrichment of sodium in solid tumors from patients with breast cancer. Sodium chloride (NaCl) enhances the activation state and effector functions of human CD8+ T cells, which is associated with enhanced metabolic fitness. These NaCl-induced effects translate into increased tumor cell killing in vitro and in vivo. Mechanistically, NaCl-induced changes in CD8+ T cells are linked to sodium-induced upregulation of Na+/K+-ATPase activity, followed by membrane hyperpolarization, which magnifies the electromotive force for T cell receptor (TCR)-induced calcium influx and downstream TCR signaling. We therefore propose that NaCl is a positive regulator of acute antitumor immunity that might be modulated for ex vivo conditioning of therapeutic T cells, such as CAR T cells.

Flow-activated endothelial Piezo1-Pannexin1-TRPV4 signaling is impaired in pulmonary hypertension

Pulmonary hypertension (PH) is a progressive and debilitating disease, characterized by elevated pulmonary arterial pressure (PAP), increased pulmonary artery (PA) contractility and endothelial cell (EC) dysfunction. Endothelial Ca2+ signals dilate resistance-size PAs (rPAs, ~ 50 μm O.D.) and maintain a low PAP. Impaired endothelial Ca2+ signaling mechanisms contribute to exacerbated rPA contraction and elevated PAP in PH. Studies in systemic arteries show that flow/shear stress (F/SS) activates endothelial Ca2+ signals to cause vasodilation. Although rPAs are a “high-flow” vascular bed, flow-induced endothelial Ca2+ signaling mechanisms have not been investigated in PH. In this regard, we recently showed that Ca2+ influx through endothelial transient receptor potential vanilloid 4 (TRPV4EC) ion channels dilates rPAs and lowers resting PAP (Daneva et al., PNAS, 2021). Moreover, F/SS activates the efflux of adenosine triphosphate (ATP, an endogenous vasodilator) through endothelial Pannexin 1 (Panx1EC) in rPAs (Daneva et al., eLife, 2021). Direct mechanosensitivity of Panx1 has been disputed, suggesting the need for an upstream endothelial mechanosensor that responds to increased flow. In this regard, pulmonary endothelial cells express Piezo1, a well-known mechanosensitive ion channel. Therefore, we hypothesized that endothelial Piezo1 (Piezo1EC)-Panx1EC-TRPV4EC signaling mediates flow-induced dilation (FID) of rPAs and regulates PAP. Cannulated and pressurized (15 mmHg) rPAs from inducible EC-specific Piezo1, Panx1 and TRPV4 mice did not dilate to incremental increases of F/SS (4 - 14 dynes/cm2) in comparison to wildtype mice, providing the first evidence that Piezo1EC-Panx1EC-TRPV4EC signaling is necessary for FID of rPAs. Confocal Ca2+ imaging studies in pressurized rPAs from mice expressing GCaMP8, a calcium biosensor, in ECs showed enhanced TRPV4EC sparklet activity (individual Ca2+ influx signals through TRPV4EC channels) in response to F/SS, demonstrating flow-induced activation of TRPV4EC channels in rPAs. Flow-induced TRPV4EC sparklet activity and FID were reduced in rPAs from a mouse model of PH (Sugen 5416 + chronic hypoxia or Su+CH; 4 weeks; 10% O2) when compared to normoxic control mice, suggesting impaired flow-induced endothelial signaling in PH. Bioluminescence measurements of extracellular ATP concentration showed lower baseline ATP levels in rPAs from Su+CH mice suggesting a decrease in ATP efflux in PH. Importantly, F/SS increased the efflux of ATP in rPAs from normal mice, but not in rPAs from Su+CH mice, indicating that F/SS-Panx1EC signaling is also impaired in PH. Together, these data support the idea that flow-induced Piezo1EC-Panx1EC-TRPV4EC signaling is impaired in PH. Future studies will assess the individual signaling linkages in the flow-induced Piezo1EC-Panx1EC-TRPV4EC signaling axis in PH. R01 HL146914, R01 HL157407, R01 HL167208 to SKS; APS Postdoctoral Fellowship to ZD. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

NMDA Receptor Modulation in COVID-19-Associated Acute Respiratory Syndrome in both In Silico and In Vitro Approach.

The normal function of the N-methyl D-aspartate receptors (NMDAR) in human lungs depends on precisely regulated synaptic glutamate levels. Pathophysiology of the lungs is brought on by the changes in homeostasis of glutamate in the synapsis that leads to abnormal NMDAR activity. Severe acute respiratory syndrome (SARS) primarily results in lung infections, particularly lung muscle stiffening, and NMDA receptor potentiation may increase calcium ion influx and support downstream signaling mechanisms. Hence, NMDAR modulators that depend on glutamate levels could be therapeutically useful medications with fewer unintended side effects. A compound called THP (tetrahydropalmatine) that amplifies Ca2+ influx and potentiates NMDA receptors has been identified in the current study. In asthmatic human airway smooth muscle (HASM) cells, THP regulates the NMDA receptor and helps in asthmatic ASM contraction, and the pharmacological stimulation of ASM depends on both brain and respiratory NMDA receptors. Glutamate potency is altered by this substance without any voltage-dependent side effects. Additionally, a GGPP (geranylgeranyl pyrophosphate)-dependent mechanism of THP reduced the production of pro-inflammatory cytokines in ASM. THP is distinctive in terms of its chemical makeup, functioning, and agonist concentration-dependent and allosteric modulatory activity. To treat COVID-19-related SARS, THP, or any future-related compounds will make good drug-like molecule candidates.

Characterization of the role of TMEM175 in an in vitro lysosomal H+ fluxes model.

Lysosome acidification is a dynamic equilibrium of H+ influx and efflux across the membrane, which is crucial for cell physiology. The vacuolar H+ ATPase (V-ATPase) is responsible for the H+ influx or refilling of lysosomes. TMEM175 was identified as a novel H+ permeable channel on lysosomal membranes, and it plays a critical role in lysosome acidification. However, how TMEM175 participates in lysosomal acidification remains unknown. Here, we present evidence that TMEM175 regulates lysosomal H+ influx and efflux in enlarged lysosomes isolated from COS1 treated with vacuolin-1. By utilizing the whole-endolysosome patch-clamp recording technique, a series of integrated lysosomal H+ influx and efflux signals in a ten-of-second time scale under the physiological pH gradient (luminal pH 4.60, and cytosolic pH 7.20) was recorded from this in vitro system. Lysosomal H+ fluxes constitute both the lysosomal H+ refilling and releasing, and they are asymmetrical processes with distinct featured kinetics for each of the H+ fluxes. Lysosomal H+ fluxes are entirely abolished when TMEM175 losses of function in the F39V mutant and is blocked by the antagonist (2-GBI). Meanwhile, lysosomal H+ fluxes are modulated by the pH-buffering capacity of the lumen and the lysosomal glycosylated membrane proteins, lysosome-associated membrane protein 1 (LAMP1). We propose that the TMEM175-mediated lysosomal H+ fluxes model would provide novel thoughts for studying the pathology of Parkinson's disease and lysosome storage disorders.

Impairment of endothelial Pannexin1-TRPV4 signaling and flow-induced vasodilation in obesity-induced pulmonary hypertension

Obesity is a highly prevalent and debilitating disease that significantly contributes to the development of other pathologies, such as pulmonary hypertension (PH). However, the mechanisms triggering obesity-induced PH (OiPH) are currently unknown. Endothelial cell (EC) Ca 2+ signals dilate small pulmonary arteries (PAs) and maintain a low resting pulmonary arterial pressure (PAP). Impairment of endothelial Ca 2+ signaling mechanisms is a crucial contributor to elevated PAP in PH. Although PAs are a “high-flow” vascular bed, flow-induced endothelial Ca 2+ signaling mechanisms have not been investigated in OiPH. In this regard, we recently showed that Ca 2+ influx through endothelial transient receptor potential vanilloid 4 (TRPV4 EC ) ion channels dilates PAs and lowers resting PAP (Daneva et al., PNAS, 2021). Moreover, flow/shear stress (F/SS) activates the efflux of adenosine triphosphate (ATP) through endothelial Pannexin 1 (Panx1 EC ) in PAs. Panx1 EC -effluxed ATP, in turn, stimulates endothelial purinergic P2Y2 receptor (P2Y2R EC ) to increase TRPV4 EC channel activity (Daneva et al., eLife, 2021). Therefore, I hypothesized that impaired Panx1 EC -P2Y2R EC -TRPV4 EC signaling axis reduces flow-induced dilation of PAs and elevates PAP in OiPH. Right ventricular systolic pressure, an indicator of PAP, was significantly higher in mice exposed to a high-fat diet (HFD, 60%, 24 weeks) compared to normal chow-fed mice, confirming OiPH in these mice. F/SS (4–15 dynes/cm 2 )-induced dilation was drastically reduced in small PAs (~ 50 μm), cannulated at both ends and pressurized to 15 mm Hg, from HFD mice, possibly indicating impaired flow-induced endothelial signaling in OiPH. Confocal Ca 2+ imaging studies in fluo-4-loaded PAs showed that the baseline and agonist (GSK1016790A)-induced activity of TRPV4 EC sparklets (unitary Ca 2+ influx signals through TRPV4 EC channels) is reduced in HFD mice compared to normal mice, confirming a decrease in TRPV4 EC channel activity in OiPH. F/SS (4–15 dynes/cm 2 ) resulted in increased activity of TRPV4 EC sparklets in PAs from normal mice, but not in PAs from HFD mice, suggesting that flow-induced TRPV4 EC activity is reduced in OiPH. Bioluminescence measurements of extracellular ATP concentration showed lower baseline ATP levels in PAs from HFD mice than normal mice. Importantly, F/SS (4 – 15 dynes/cm 2 ) increased ATP efflux in PAs from normal mice, but not in PAs from HFD mice, indicating that flow-Panx1 EC signaling is also impaired in OiPH. Together, these data support the idea that flow-induced Panx1 EC -TRPV4 EC signaling is impaired in OiPH. Targeting the individual elements of this pathway may provide novel therapies in OiPH. Future studies will assess the signaling linkages of the flow-Panx1 EC -P2Y2R EC -TRPV4 EC signaling axis in OiPH. R01 HL142808, R01 HL146914, R01 HL157407 to Dr. S.K. Sonkusare; APS Postdoctoral Fellowship Award to Dr. Z. Daneva This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Role of PARP and TRPM2 in VEGF Inhibitor-Induced Vascular Dysfunction.

Background Hypertension and vascular toxicity are major unwanted side effects of antiangiogenic drugs, such as vascular endothelial growth factor inhibitors (VEGFis), which are effective anticancer drugs but have unwanted side effects, including vascular toxicity and hypertension. Poly (ADP-ribose) polymerase (PARP) inhibitors, used to treat ovarian and other cancers, have also been associated with elevated blood pressure. However, when patients with cancer receive both olaparib, a PARP inhibitor, and VEGFi, the risk of blood pressure elevation is reduced. Underlying molecular mechanisms are unclear, but PARP-regulated transient receptor potential cation channel, subfamily M, member 2 (TRPM2), a redox-sensitive calcium channel, may be important. We investigated whether PARP/TRPM2 plays a role in VEGFi-induced vascular dysfunction and whether PARP inhibition ameliorates the vasculopathy associated with VEGF inhibition. Methods and Results Human vascular smooth muscle cells (VSMCs), human aortic endothelial cells, and wild-type mouse mesenteric arteries were studied. Cells/arteries were exposed to axitinib (VEGFi) alone and in combination with olaparib. Reactive oxygen species production, Ca2+ influx, protein/gene analysis, PARP activity, and TRPM2 signaling were assessed in VSMCs, and nitric oxide levels were determined in endothelial cells. Vascular function was assessed by myography. Axitinib increased PARP activity in VSMCs in a reactive oxygen species-dependent manner. Endothelial dysfunction and hypercontractile responses were ameliorated by olaparib and a TRPM2 blocker (8-Br-cADPR). VSMC reactive oxygen species production, Ca2+ influx, and phosphorylation of myosin light chain 20 and endothelial nitric oxide synthase (Thr495) were augmented by axitinib and attenuated by olaparib and TRPM2 inhibition. Proinflammatory markers were upregulated in axitinib-stimulated VSMCs, which was reduced by reactive oxygen species scavengers and PARP-TRPM2 inhibition. Human aortic endothelial cells exposed to combined olaparib and axitinib showed nitric oxide levels similar to VEGF-stimulated cells. Conclusions Axitinib-mediated vascular dysfunction involves PARP and TRPM2, which, when inhibited, ameliorate the injurious effects of VEGFi. Our findings define a potential mechanism whereby PARP inhibitor may attenuate vascular toxicity in VEGFi-treated patients with cancer.

Targeting Host Sulphonyl Urea Receptor 2 Can Reduce Severity of Helicobacter pylori Associated Gastritis.

While most Helicobacter pylori-infected individuals remain asymptomatic throughout their lifetime, in a significant proportion, the resulting severe chronic gastritis drives the development of gastric cancer. In this study, we examine a new therapeutic target, a host potassium channel regulatory subunit, SUR2 (encoded by ABCC9), with potential to protect against H pylori-associated diseases. SUR2 gene (ABCC9) expression in human gastric biopsies was analyzed by quantitative polymerase chain reactions. Helicobacter-infected mice were administered the SUR2-channel agonists, pinacidil and nicorandil, then gastric tissues analyzed by histology, immunohistochemistry and quantitative polymerase chain reaction, and splenic tissues by enzyme-linked immunosorbent assays. Invitro studies were performed on human and mouse macrophages, human gastric epithelial cells and mouse splenocytes. ABCC9 expression in human and mouse stomachs is downregulated with H pylori infection. Treatment of Helicobacter-infected mice with SUR2 channel modulators, pinacidil or nicorandil, significantly reduced gastritis severity. In gastric epithelial cells, nicorandil-induced opening of the SUR2 channel increased intracellular K+ and prevented H pylori-mediated Ca2+ influx and downstream pro-inflammatory signaling. SUR2 is a novel host factor that regulates Helicobacter pathogenesis. Pharmacological targeting of SUR2 provides a potential approach for reducing the severity of H pylori-associated gastritis, without eradicating infection.

Abstract P134: Tnfα Impairs Endothelial Calcium Signaling And Elevates Blood Pressure In Obesity.

Endothelial dysfunction in small arteries is a hallmark of obesity-induced hypertension. Recent studies show that endothelial upregulation of inducible nitric oxide synthase (iNOS) and NADPH oxidase 1 (NOX1) plays a critical role in obesity-induced endothelial dysfunction. Endothelial upregulation of iNOS and NOX1 results in excessive formation of peroxynitrite, a reactive nitrogen species, which impairs endothelium-dependent vasodilation. It is well-known that inflammatory mediators elevate cellular iNOS, NOX1, and peroxynitrite levels. In this regard, tumor necrosis factor-alpha (TNFα) signaling has been proposed as a critical contributor to endothelial dysfunction in obesity. Notably, vascular SMCs TNFα levels were increased in heart failure and diabetes. Therefore, we hypothesized that vascular wall-derived TNFα acts locally to impair endothelial function in obesity. Flow cytometry studies showed an increase in TNFα levels in freshly isolated SMCs from small mesenteric arteries (MAs) of high-fat diet-fed obese mice compared to normal chow-fed control mice. However, TNFα levels in ECs from obese mice were not different from those in ECs from control mice. The pro-inflammatory effects of TNFα are mediated mainly through TNFα receptor I activation. Treating the obese mice with a selective inhibitor of TNFα receptor I signaling reduced the blood pressure to normal levels in obese mice but did not affect blood pressure in control mice. Treatment with R7050 also abolished the obesity-induced increase in iNOS and NOX1 expression in endothelial cells. Further, R7050 administration restored acetylcholine-induced, endothelium-dependent vasodilation of MAs in pressure myography experiments. Previous studies showed a decrease in Ca 2+ influx through endothelial TRPV4 channels contributes to blood pressure elevation in obese mice. Notably, R7050 administration restored the Ca 2+ influx signals through endothelial TRPV4 channels in MAs, as studied using high-speed confocal Ca 2+ imaging. Our findings collectively indicate that TNFα signaling contributes to the impairment of endothelial calcium signaling and blood pressure elevation in obesity and highlights the role of SMCs as a source of TNFα in obesity

The Janus-faced role of TRPM2-S in retroperitoneal liposarcoma via increasing ROS levels

BackgroundRetroperitoneal liposarcoma (RPLS) is a specific soft tissue sarcoma with a high recurrence rate. The short isoform of transient receptor potential cation channel subfamily M member 2 (TRPM2-S) plays an important role in the regulation of reactive oxygen species (ROS). However, the association between TRPM2-S and RPLS and its underlying mechanisms remains unclear.MethodsThe expression of both TRPM2-S and TRPM2-L in RPLS tissues was verified by kimmunohistochemistry (IHC). The regulation on Ca2+ influx by TRPM2-S was evaluated by Fluo-4 AM staining. The effect of TRPM2-S on cell proliferation and apoptosis was tested by 5-Ethynyl-2′-deoxyuridine (EdU) staining and Flow cytometry respectively. The level of cellular ROS was assessed by the DCFH-DA probe. Different concentrations of H2O2 were used to provide oxidative stress on RPLS cells. The underlying mechanisms were further explored by Western blotting.ResultsThe IHC assays showed that TRPM2-S, but not TRPM2-L, was prognostic in RPLS. Low TRPM2-S level was associated with poor disease-free survival (DFS). Calcium influx signal intensity was significantly decreased under TRPM2-S overexpression, which resulted in a decrease in the levels of FOXO3a and PTEN. Correspondingly, the levels of pERK, pAKT, pP65, pGSK-3β, Bcl-2, and β-catenin were upregulated, and cellular ROS was gently increased under TRPM2-S overexpression. Moreover, TRPM2-S slightly promoted cell proliferation and inhibited apoptosis of RPLS cell lines under normoxia, but largely increased apoptosis rates under oxidative stress. The cleaved caspase3 was significantly upregulated by TRPM2-S overexpression under oxidative stress. N-Acetyl-l-cysteine (NAC), a small molecule antioxidant, could largely rescue RPLS cells from the apoptosis induced by H2O2.ConclusionTRPM2-S exerts Janus-faced effects in RPLS by increasing the ROS levels via inhibition on FOXO3a, which promotes cell proliferation under normoxia but induces apoptosis under oxidative stress.FQgJQSptf854GdLd9y3hLjVideo abstract

Exploring the mechanism of sweetener neohesperidin dihydrochalcone on oral tolerance via a network pharmacology approach combined with vivo and vitro methods

Neohesperidin dihydrochalcone (NHDC) is a kind of sweetener widely used in food processing. Some artificial sweeteners induce food allergy by breaking oral tolerance (OT). The relationship between NHDC and oral tolerance are important in food safety. We explored the possible effects of NHDC on OT via network pharmacology combined with vivo and vitro experiments. NHDC was predicted to have effects on OT. It was focus on immunoglobulin production, inflammation and immunity. Then, OT mouse model and mast cell degranulation were applied to further explore the mechanism. NHDC could affect the Th2 response by suppressing the sIgG1 level in the serum and GATA-3 expression in the colon. NHDC could inhibit RBL-2H3 cells degranulation by suppressing the Ca2+ influx and MAPK signaling pathways. Results showed that NHDC can be safely applied in food processing and had promotional effects on oral tolerance.

TNFα signaling impairs endothelial calcium signaling and elevates blood pressure in obesity

Endothelial dysfunction in small arteries is a hallmark of obesity‐induced hypertension. Recent studies show that endothelial upregulation of inducible nitric oxide synthase (iNOS) and NADPH oxidase 1 (NOX1) plays a critical role in obesity‐induced endothelial dysfunction. Endothelial upregulation of iNOS and NOX1 results in excessive formation of peroxynitrite, a reactive nitrogen species, which impairs endothelium‐dependent vasodilation. It is well‐known that inflammatory mediators elevate cellular iNOS, NOX1, and peroxynitrite levels. In this regard, tumor necrosis factor alpha (TNFa) signaling has been proposed as a key contributor to endothelial dysfunction in obesity. Notably, vascular smooth muscle cells (SMCs) were shown to generate TNFa in heart failure and diabetes. Therefore, we hypothesized that vascular wall‐derived TNFa acts locally to impair endothelial function in obesity. Flow cytometry studies showed an increase in TNFa levels in freshly isolated SMCs from small mesenteric arteries (MAs) of high‐fat diet‐fed (14 weeks) obese mice compared to normal chow‐fed control mice. However, TNFa levels in endothelial cells (ECs) from obese mice were not different from those in ECs from control mice. The levels of two other cytokines, IL‐1b and IL‐6, were not different between in SMCs and ECs from normal and obese mice. Additionally, qPCR studies in endothelium‐denuded MAs provided further evidence that TNFa expression is increased in SMCs from obese mice compared to control mice. The pro‐inflammatory effects of TNFa are mediated mainly through TNFa receptor I activation. Treating the obese mice with a selective inhibitor of TNFa receptor I signaling (R7050, 10 mg/kg, i.p., once a day for 14 days) reduced the blood pressure to normal levels in obese mice, but had no effect on blood pressure in control mice. Treatment with R7050 also abolished obesity‐induced increase in iNOS and NOX1 expression in endothelial cells. Further, R7050 administration restored acetylcholine‐induced, endothelium‐dependent vasodilation of MAs in pressure myography experiments. Previous studies showed that a decrease in Ca2+ influx through endothelial transient receptor potential vanilloid 4 (TRPV4) channels contributes to blood pressure elevation in obese mice. Notably, R7050 administration restored the Ca2+ influx signals through endothelial TRPV4 channels in MAs, as studied using high‐speed confocal Ca2+ imaging. Collectively, our findings indicate that TNFa signaling contributes to the impairment of endothelial calcium signaling and blood pressure elevation in obesity, and highlight the role of SMCs as a source of TNFa in obesity.

Smooth Muscle TRPV4 Channels Signaling Nanodomains in Blood Pressure Regulation

Transient receptor potential vanilloid 4 (TRPV4) channel is a crucial Ca2+influx pathway in arterial smooth muscle cells (SMCs). However, the effect of SMC TRPV4 (TRPV4SMC) channel activity on resting blood pressure has not been investigated. We hypothesized that SMC TRPV4 (TRPV4SMC) channels regulate blood pressure under homeostatic and hypertensive conditions. Radiotelemetric recordings showed lower resting blood pressure in SMC‐specific TRPV4‐/‐ (TRPV4SMC‐/‐) mice than control mice, suggesting that TRPV4SMC channels elevate the resting blood pressure. α1 adrenergic receptor (α1AR) stimulation–induced constriction was blunted in small mesenteric arteries (MAs) from TRPV4SMC‐/‐ mice, whereas intraluminal pressure–induced (myogenic) constriction was increased. Moreover, both α1AR stimulation and increased intraluminal pressure activated elementary Ca2+ influx signals through TRPV4SMC channels (TRPV4SMC sparklets) in MAs from control mice. These data supported the concept that TRPV4SMC channels contribute to α1AR–induced vasoconstriction but oppose myogenic vasoconstriction. Inhibition of Ca2+‐sensitive K+ (BK) channels abolished the effect of TRPV4SMC channels on myogenic vasoconstriction, indicating a crucial role for TRPV4SMC–BK channel signaling in limiting myogenic vasoconstriction. Accordingly, a direct activation of TRPV4SMC channels with GSK1016790A (30 nM) increased BK channel currents in SMC patch‐clamp experiments. α1AR stimulation, however, was unable to increase BK channel currents, implying two functionally opposite pools of TRPV4SMC channels. Direct STORM superresolution imaging revealed a1AR:TRPV4SMC and TRPV4SMC:BK channel co‐localization, and almost no co‐localization of a1ARs and BK channels. Together, these data supported the idea of spatially separated and functionally opposite nanodomains of TRPV4SMC channels. We further hypothesized that an imbalance between these two nanodomains contributes to elevated blood pressure in hypertension. In skeletal muscle arteries from hypertensive patients, a1AR activation of TRPV4SMC channel currents was accentuated whereas TRPV4SMC activation of BK channel currents was impaired. Similarly, MAs from angiotensin II‐infused hypertensive mice showed increased activity of constrictor a1AR–TRPV4SMC signaling and impairment of dilatory TRPV4SMC–BK channel signaling. Collectively, our data identify novel smooth muscle Ca2+ signaling nanodomains that regulate blood pressure and demonstrate their impairment in hypertension.

Endothelial Pannexin1‐purinergic signaling pulmonary hypertension

Endothelial cell (EC) Ca2+ signals dilate small pulmonary arteries (PAs) and maintain a low resting pulmonary arterial pressure (PAP). Impairment of endothelial Ca2+ signaling mechanisms is a crucial contributor to elevated PAP in pulmonary hypertension (PH). Studies in systemic arteries show that flow/shear stress activates endothelial Ca2+ signals to cause vasodilation. Although PAs are a “high‐flow” vascular bed, flow‐induced endothelial Ca2+ signaling mechanisms have not been investigated in PH. In this regard, we recently showed that Ca2+ influx through endothelial transient receptor potential vanilloid 4 (TRPV4EC) ion channels dilates PAs and lowers resting PAP (Daneva et al., PNAS, 2021). Moreover, flow/shear stress activates the efflux of adenosine triphosphate (ATP) through endothelial Pannexin 1 (Panx1EC) in PAs. Panx1EC‐effluxed ATP, in turn, stimulates endothelial purinergic P2Y2 receptor (P2Y2REC) to increase TRPV4EC channels activity (Daneva et al., eLife, 2021). I hypothesized that impaired Panx1EC—P2Y2REC—TRPV4EC signaling axis reduces flow‐induced dilation of PAs and elevates PAP in PH. Confocal Ca2+ imaging studies in fluo‐4‐loaded en face PAs (~ 50 mm) showed that the baseline and agonist (GSK1016790A or GSK101)‐induced activity of TRPV4EC sparklets (individual Ca2+ influx signals through TRPV4EC channels) is reduced in the mice exposed to Sugen 5416 + chronic hypoxia (Su+CH; 3 weeks; 10% O2) compared to the normoxic control mice, indicating a decrease in TRPV4EC channel activity in PH. The expression of TRPV4 channels at the mRNA level, however, was not altered in Su+CH mice. The activation of TRPV4EC sparklets by exogenous ATP (1 mM) was also reduced in PAs from Su+CH mice, suggesting an impairment of ATP‐P2Y2REC‐TRPV4EC channel signaling axis in PH. Accordingly, ATP‐induced, endothelium‐dependent dilation was absent in PAs from Su+CH mice. We previously showed that basal ATP efflux in PAs predominantly occurs through endothelial Panx1, and flow/shear stress increases ATP efflux entirely through the activation of endothelial Panx1. Bioluminescence measurements of extracellular ATP concentration showed lower baseline ATP levels in PAs from Su+CH mice than control mice, suggesting a decrease in ATP efflux in PH. Importantly, flow/shear stress (4 – 15 dynes/cm2) increased the efflux of ATP from normal mice, but not in PAs from Su+CH mice, indicating that flow/shear stress‐Panx1EC signaling is also impaired in PH. Together, these data support the idea that flow‐Panx1EC and P2Y2REC‐TRPV4EC signaling are impaired in PH. Targeting individual elements of this pathway may provide novel therapeutic options in PH and other pulmonary vascular disorders characterized by endothelial dysfunction. Future studies will assess the individual signaling linkages of the flow‐Panx1EC‐P2Y2REC‐TRPV4EC signaling axis in PH.

Induction of hemolysis and eryptosis by occupational pollutant nickel chloride is mediated through calcium influx and p38 MAP kinase signaling.

Nickel (Ni) is an abundant environmental hazard and an occupational pollutant. Exposure to Ni compounds is prevalent in electroplating workers and in the printing industry, among others. The toxicity of Ni manifests as dermatological, gastrointestinal, respiratory, allergic, and cardiovascular symptoms. In particular, hyperbilirubinemia and reticulocytosis have been detected in intoxicated subjects; an observation possibly implicating selective red blood cell (RBC) toxicity. Herein, the interaction of nickel chloride (NiCl2) with human RBCs and associated molecular mechanisms are described. Cells from healthy donors were incubated for 24 h at 37°C in the presence or absence of 0.5‒10 mM of NiCl2, and cytotoxicity was determined through hemoglobin leakage by colorimetry under different experimental conditions. Eryptotic markers were also identified by flow cytofluorometry using Annexin-V-FITC tagging for phosphatidylserine (PS) exposure, light scatter properties for cellular dimensions, Fluo4/AM labeling for intracellular calcium, and H2DCFDA staining for reactive oxygen species (ROS). Additionally, small molecule inhibitors were used to probe the signaling pathways involved. It was found that NiCl2 at 10 mM caused profound intracellular calcium overload and significant calcium-dependent hemolysis. Also, NiCl2 reduced forward scatter and increased side scatter, Annexin- positive cells, and ROS levels. Importantly, NiCl2-induced hemolysis was significantly attenuated by the exclusion of extracellular calcium, and in the presence of p38 MAP kinase (MAPK) inhibitor SB203580. It is concluded that NiCl2 induces p38 MAPK-dependent hemolysis, and stimulates the canonical features of premature eryptosis. This report presents the first description of the molecular mechanisms underlying the hemolytic and eryptotic potential of NiCl2 and, thus, may explain changes in hematological parameters observed in poisoning victims. Int J Occup Med Environ Health. 2022;35(1):1-11.

Compression enhances invasive phenotype and matrix degradation of breast cancer cells via Piezo1 activation

BackgroundUncontrolled growth in solid breast cancer generates mechanical compression that may drive the cancer cells into a more invasive phenotype, but little is known about how such compression affects the key events and corresponding regulatory mechanisms associated with invasion of breast cancer cells including cellular behaviors and matrix degradation.ResultsHere we show that compression enhanced invasion and matrix degradation of breast cancer cells. We also identified Piezo1 as the putative mechanosensitive cellular component that transmitted compression to not only enhance the invasive phenotype, but also induce calcium influx and downstream Src signaling. Furthermore, we demonstrated that Piezo1 was mainly localized in caveolae, and both Piezo1 expression and compression-enhanced invasive phenotype of the breast cancer cells were reduced when caveolar integrity was compromised by either knocking down caveolin1 expression or depleting cholesterol content.ConclusionsTaken together, our data indicate that mechanical compression activates Piezo1 channels to mediate enhanced breast cancer cell invasion, which involves both cellular events and matrix degradation. This may be a critical mechanotransduction pathway during breast cancer metastasis, and thus potentially a novel therapeutic target for the disease.

Chronic neuronal excitation leads to dual metaplasticity in the signaling for structural long-term potentiation.

Synaptic plasticity is long-lasting changes in synaptic currents and structure. When neurons are exposed to signals that induce aberrant neuronal excitation, they increase the threshold for the induction of long-term potentiation (LTP), known as metaplasticity. However, the metaplastic regulation of structural LTP (sLTP) remains unclear. We investigate glutamate uncaging/photoactivatable (pa)CaMKII-dependent sLTP induction in hippocampal CA1 neurons after chronic neuronal excitation by GABAA receptor antagonists. We find that the neuronal excitation decreases the glutamate uncaging-evoked Ca2+ influx mediated by GluN2B-containing NMDA receptors and suppresses sLTP induction. In addition, single-spine optogenetic stimulation using paCaMKII indicates the suppression of CaMKII signaling. While the inhibition of Ca2+ influx is protein synthesis independent, the paCaMKII-induced sLTP suppression depends on it. Our findings demonstrate that chronic neuronal excitation suppresses sLTP in two independent ways (i.e., dual inhibition of Ca2+ influx and CaMKII signaling). This dual inhibition mechanism may contribute to robust neuronal protection in excitable environments.

Abstract 12772: Regulation of Blood Pressure by Smooth Muscle TRPV4 Channels Under Normal and Hypertensive Conditions

Introduction: Recent studies suggest that transient receptor potential vanilloid 4 (TRPV4) channel is a functionally important Ca 2+ influx pathway in arterial smooth muscle cells (SMCs). Hypothesis: We hypothesized that SMC TRPV4 (TRPV4 SMC ) channels regulate blood pressure under normal conditions and in hypertension. Results: Radiotelemetric recordings showed lower blood pressures in the SMC-specific TRPV4 -/- (TRPV4 SMC -/- ) mice than the control mice. Phenylephrine (PE, α1 adrenergic receptor or α1AR agonist)-induced constriction was blunted in small mesenteric arteries (MAs) from TRPV4 SMC -/- mice, whereas intraluminal pressure-induced constriction was increased. These data demonstrated that TRPV4 SMC channels contribute to α1AR-induced vasoconstriction but oppose pressure-induced vasoconstriction. Both PE and intraluminal pressure increased the activity of elementary Ca 2+ influx signals through TRPV4 SMC channels (TRPV4 SMC sparklets). TRPV4 agonist GSK1016790A (30 nM) activated the currents through large-conductance, Ca 2+ -sensitive K + (BK) channels in SMCs, whereas phenylephrine had no effect on BK channel currents. These data implied the presence of two functionally distinct pools of TRPV4 SMC channels: 1) α1AR-activated, constrictor TRPV4 SMC channels; and 2) pressure-activated, dilator TRPV4 SMC channels. Next, direct STORM imaging demonstrated that ~30% TRPV4 SMC channels co-localize with α1ARs and ~10% TRPV4 SMC channels co-localize with BK channels. Importantly, only ~3% TRPV4 SMC channels co-localized with both α1ARs and BK channels, supporting the concept of spatially distinct constrictor and dilator TRPV4 SMC channels. Angiotensin II (Ang II, 7-14 days) infusion resulted in a lower increase in blood pressure in TRPV4 SMC -/- mice than the control mice, demonstrating a crucial role of TRPV4 SMC channels in blood pressure elevation in hypertension. Moreover, Ang II infusion in C57BL6 mice increased α1AR-TRPV4 SMC signaling; reduced pressure-activation of TRPV4 SMC channels; and reduced TRPV4 SMC -BK channel signaling. Conclusions: Our results show that increased constrictor TRPV4 SMC channel activity and reduced dilator TRPV4 SMC channel activity combine to elevate blood pressure in hypertension.

Abstract 10294: Endothelial Pannexin1-TRPV4 Signaling Regulates Pulmonary Arterial Pressure

The pulmonary endothelial cells (EC) dilate small pulmonary arteries (PAs) and maintain low pulmonary arterial pressure (PAP). Importantly, the loss of EC function contributes to elevated PAP in pulmonary hypertension (PH). Recent studies show that Pannexin 1 (Panx1), an ATP efflux pathway at the cell membrane, is a critical regulator of endothelial function. However, the impact of endothelial Panx1 (Panx1 EC ) on PA contractility and PAP is unknown. We observed that the extracellular ATP (eATP) levels are reduced in PAs from inducible, EC-specific Panx1 -/- (Panx1 EC -/- ) mice, identifying Panx1 EC as an important ATP release pathway in PAs. Our recently published findings demonstrated that eATP dilates PAs via activation of Ca 2+ influx through endothelial transient receptor potential vanilloid 4 (TRPV4 EC ) ion channels. Therefore, we hypothesized that endothelial Panx1—eATP—TRPV4 channel signaling dilates PAs and lowers resting PAP. Apyrase (10 U/mL), an ATP hydrolyzing enzyme, reduced the activity of TRPV4 EC sparklets (individual Ca 2+ influx signals through TRPV4 EC channels) in PAs, implying a constitutive regulation of TRPV4 EC channels by ATP. The activity of TRPV4 EC sparklets was lower in PAs from Panx1 EC -/- mice than controls, identifying Panx1 EC as a novel promoter of TRPV4 EC channel activity. Pressure myography studies in PAs (~ 50 μm) from Panx1 EC -/- and TRPV4 EC -/- mice showed higher constriction to thromboxane A2 receptor agonist U46619 (1-300 nM) compared to PAs from controls. Finally, right ventricular systolic pressure was higher in Panx1 EC -/- and TRPV4 EC -/- mice compared to the respective controls. These data indicated that Panx1 EC —eATP—TRPV4 EC channel signaling lowers PA contractility and PAP. ATP is an endogenous activator of purinergic receptor signaling. Inhibition of P2Y1 and P2X receptors did not alter ATP activation of TRPV4 EC sparklets in PAs. However, P2Y2 receptor inhibition and EC-specific P2Y2 receptor deletion abolished ATP activation of TRPV4 EC sparklets. Together, these data identify a novel Panx1 EC —eATP—P2Y2R EC signaling pathway that enhances TRPV4 EC channel activity and lowers PAP. Individual elements of this pathway may provide novel therapeutic targets for treating pulmonary vascular disorders.

Regulation of Pulmonary Arterial Pressure by Endothelial Pannexin1–TRPV4 Channel Signaling

Endothelial cells (EC) dilate small pulmonary arteries (PAs) and lower the resting pulmonary arterial pressure (PAP). Moreover, the loss of endothelial function is a key contributor to elevated PAP in pulmonary hypertension. Therefore, an in-depth understanding of endothelial mechanisms controlling PAP is necessary for designing novel therapeutic strategies against pulmonary hypertension. Pannexin 1 (Panx1), an ATP efflux pathway on the EC membranes, has emerged as a crucial controller of endothelial function. However, the impact of endothelial Panx1 (Panx1EC) on PA contractility and PAP is not known. Recent studies support the idea that endothelial transient receptor potential vanilloid 4 (TRPV4EC) channels dilate small PAs, and are activated by extracellular ATP (eATP). Since Panx1EC is an ATP efflux pathway, we hypothesized that Panx1EC-TRPV4EC channel signaling dilates PAs and lowers resting PAP. Right ventricular systolic pressure (RVSP), an indirect indicator of PAP, was higher in inducible, EC-specific Panx1 (Panx1EC-/-) and TRPV4 channel knockout (TRPV4EC-/-) mice compared to the respective control mice. The activity of TRPV4EC channels was recorded as individual Ca2+ influx signals (TRPV4EC sparklets) in fluo 4-loaded en face PAs using spinning disk confocal imaging. The TRPV4EC sparklet activity was lower in PAs from Panx1EC-/- mice than the control mice, identifying Panx1EC as a novel promoter of TRPV4EC channel activity. Apyrase (10 U/mL), an ATP hydrolyzing enzyme, also reduced the activity of TRPV4EC sparklets in PAs from control mice but not Panx1EC-/- mice. Pressurized PAs (15 mm Hg) from Panx1EC-/- and TRPV4EC-/- mice showed higher constriction to thromboxane A2 receptor agonist U46619 (1-300 nM) compared to PAs from the respective control mice. These data indicated that Panx1EC-eATP-TRPV4EC signaling lowers PA contractility and PAP. Consistent with previous findings that eATP dilates PAs via purinergic P2Y2 receptor (P2Y2R) signaling, ATP activation of TRPV4EC channels was lost in PAs from inducible P2Y2EC-/- mice. Together, these data identify a novel Panx1EC-eATP-P2Y2REC signaling pathway that promotes TRPV4EC channel activity in PAs. Panx1, P2Y2R, and TRPV4 channels have been shown to localize with the scaffolding protein caveolin 1 (Cav-1), raising the possibility that Cav-1EC may provide a signaling scaffold for Panx1EC-P2Y2REC-TRPV4EC signaling in PAs. Accordingly, P2Y2REC-activation of TRPV4EC channels was lost in PAs from inducible Cav-1EC-/- mice, and these mice showed higher resting RVSPs compared to the control mice. Additionally, in situ proximity ligation assay confirmed the nanometer proximity of Cav-1EC with Panx1EC, P2Y2REC, and TRPV4EC channel in PAs. Overall, our findings identify Cav-1EC-dependent Panx1EC-P2Y2REC-TRPV4EC channel pathway that dilates PAs and lowers PAP. Targeting individual elements of this pathway may provide novel therapeutic options in pulmonary vascular disorders.

Dichotomous effects of smooth muscle TRPV4 channels on vascular contractility

Ca2+ signaling mechanisms in smooth muscle cells (SMCs) determine vascular contractility. Transient receptor potential vanilloid 4 (TRPV4) ion channels have been described as a crucial Ca2+ influx pathway in SMCs from small, resistance-sized arteries. However, the impact of SMC TRPV4 (TRPV4SMC) channel activity on blood pressure remains unknown, mostly due to the lack of studies in SMC-specific knockout mice. We hypothesized that TRPV4SMC channels control the resting blood pressure. Radiotelemetric blood pressure recordings showed reduced daytime and nighttime blood pressures in the inducible, SMC-specific TRPV4 knockout (TRPV4SMC-/-) mice compared to the control mice. The effect of TRPV4SMC-/- on vascular contractility was assessed using two endogenous vasoconstrictor mechanisms- 1) SMC α1 adrenergic receptor (α1AR) stimulation and 2) increased intraluminal pressure. Phenylephrine (α1AR agonist)-induced constriction of pressurized mesenteric arteries (MAs, 80 mm Hg, 1 nM-10 mM phenylephrine) and blood pressure elevation (10 mg/kg phenylephrine, i.p.) were blunted in TRPV4SMC-/- mice, identifying a central role of TRPV4SMC channels in α1AR-induced vasoconstriction and blood pressure elevation. Individual Ca2+ influx signals through TRPV4SMC channels (TRPV4SMC sparklets) were recorded using spinning disk confocal imaging in fluo-4-loaded MAs pressurized to 80 mm Hg. Phenylephrine (1 mM) activated TRPV4SMC sparklets, an effect abolished by protein kinase C (PKC) inhibitor (Go6976, 1 mM). These results indicated that PKC-TRPV4SMC channel signaling is a major contributor to α1AR-induced vasoconstriction. In direct contrast with PE-induced constriction, intraluminal pressure-induced constriction was higher in MAs from TRPV4SMC-/- mice, suggesting that SMC TRPV4 channels limit pressure-induced vasoconstriction. Previous studies have shown that TRPV4SMC channels can activate large-conductance, Ca2+-sensitive K+ (BK) channels, thereby decreasing pressure-induced vasoconstriction. Consistent with these findings, vasoconstriction in response to BK channel inhibitor (paxilline, 1 mM) was reduced in MAs from TRPV4SMC-/- mice, supporting a dilatory TRPV4SMC channel-BK channel signaling under resting conditions. In situ proximity ligation assay revealed co-localization of TRPV4SMC channels with both α1ARs and BK channels. Overall, TRPV4SMC channels increase the resting blood pressure but have divergent effects on vascular contractility. TRPV4SMC channels contribute to α1AR-induced vasoconstriction but limit pressure-induced vasoconstriction. Therefore, selective vasoactive stimulus-TRPV4SMC channel coupling may determine the impact of TRPV4SMC channels on vascular resistance.