RESUMEN
The effect of ring stiffness and pressure on the glassy dynamics of a thermal assembly of two-dimensional ring polymers is investigated using extensive coarse-grained molecular dynamics simulations. In all cases, dynamical slowing down is observed with increasing pressure, and thereby, a phase space for equilibrium dynamics is identified in the plane of the obtained monomer density and ring stiffness. When the rings are highly flexible, i.e., have low ring stiffness, glassiness sets in via the crowding of crumpled polymers, which take on a globular form. In contrast, at large ring stiffness, when the rings tend to have large asphericity under compaction, we observe the emergence of local domains having orientational ordering at high pressures. Therefore, our simulations highlight how varying the deformability of rings leads to contrasting mechanisms in driving the system toward the glassy regime.
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Endothelial cell (EC) migration is critical for the repair of monolayer disruption following angioplasties, but migration is inhibited by lipid oxidation products, including lysophosphatidylcholine (lysoPC), which open canonical transient receptor potential 6 (TRPC6) channels. TRPC6 activation requires an increase in intracellular Ca2+ concentration ([Ca2+]i), the source of which is unknown. LysoPC can activate phospholipase A2 to release arachidonic acid (ArA). ArA can activate arachidonic acid-regulated calcium (ARC) channels that are formed by stromal interaction molecule 1 (STIM1) and Orai1 and Orai3 proteins. Both lysoPC and ArA can activate p38 mitogen-activated protein kinase (MAPK) that induces the phosphorylation required for STIM1-Orai3 association. This is accompanied by an increase in [Ca2+]i and TRPC6 externalization. The effect of lysoPC and ArA is not additive, suggesting activation of the same pathway. The increase in [Ca2+]i activates an Src kinase that leads to TRPC6 activation. Downregulation of Orai3 using siRNA blocks the lysoPC- or ArA-induced increase in [Ca2+]i and TRPC6 externalization and preserves EC migration. These data show that lysoPC induces activation of p38 MAPK, which leads to STIM1-Orai3 association and increased [Ca2+]i. This increase in [Ca2+]i activates an Src kinase leading to TRPC6 externalization, which initiates a cascade of events ending in cytoskeletal changes that disrupt EC migration. Blocking this pathway preserves EC migration in the presence of lipid oxidation products.NEW & NOTEWORTHY The major lysophospholipid component in oxidized LDL, lysophosphatidylcholine (lysoPC), can activate p38 MAP kinase, which in turn promotes externalization of Orai3 and STIM1-Orai3 association, suggesting involvement of arachidonic acid-regulated calcium (ARC) channels. The subsequent increase in intracellular calcium activates an Src kinase required for TRPC6 externalization. TRPC6 activation, which has been shown to inhibit endothelial cell migration, is blocked by p38 MAP kinase or Orai3 downregulation, and this partially preserves endothelial migration in lysoPC.
Asunto(s)
Lisofosfatidilcolinas , Proteínas Quinasas p38 Activadas por Mitógenos , Canal Catiónico TRPC6/genética , Proteínas Quinasas p38 Activadas por Mitógenos/metabolismo , Calcio/metabolismo , Molécula de Interacción Estromal 1/genética , Ácido Araquidónico/farmacología , Canales de Calcio/metabolismo , Familia-src Quinasas/metabolismo , Proteína ORAI1/genéticaRESUMEN
Estimating the burden of COVID-19 in India is difficult because the extent to which cases and deaths have been undercounted is hard to assess. Here, we use a 9-component, age-stratified, contact-structured epidemiological compartmental model, which we call the INDSCI-SIM model, to analyse the first wave of COVID-19 spread in India. We use INDSCI-SIM, together with Bayesian methods, to obtain optimal fits to daily reported cases and deaths across the span of the first wave of the Indian pandemic, over the period Jan 30, 2020 to Feb 15, 2021. We account for lock-downs and other non-pharmaceutical interventions (NPIs), an overall increase in testing as a function of time, the under-counting of cases and deaths, and a range of age-specific infection-fatality ratios. We first use our model to describe data from all individual districts of the state of Karnataka, benchmarking our calculations using data from serological surveys. We then extend this approach to aggregated data for Karnataka state. We model the progress of the pandemic across the cities of Delhi, Mumbai, Pune, Bengaluru and Chennai, and then for India as a whole. We estimate that deaths were undercounted by a factor between 2 and 5 across the span of the first wave, converging on 2.2 as a representative multiplier that accounts for the urban-rural gradient. We also estimate an overall under-counting of cases by a factor of between 20 and 25 towards the end of the first wave. Our estimates of the infection fatality ratio (IFR) are in the range 0.05-0.15, broadly consistent with previous estimates but substantially lower than values that have been estimated for other LMIC countries. We find that approximately 35% of India had been infected overall by the end of the first wave, results broadly consistent with those from serosurveys. These results contribute to the understanding of the long-term trajectory of COVID-19 in India.
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COVID-19 , Humanos , COVID-19/epidemiología , India/epidemiología , Teorema de Bayes , Control de Enfermedades Transmisibles , PandemiasRESUMEN
Amorphous solids are known to fail catastrophically via fracture, and cavitation at nano-metric scales is known to play a significant role in such a failure process. Micro-alloying via inclusions is often used as a means to increase the fracture toughness of amorphous solids. Modeling such inclusions as randomly pinned particles that only move affinely and do not participate in plastic relaxations, we study how the pinning influences the process of cavitation-driven fracture in an amorphous solid. Using extensive numerical simulations and probing in the athermal quasistatic limit, we show that just by pinning a very small fraction of particles, the tensile strength is increased, and also the cavitation is delayed. Furthermore, the cavitation that is expected to be spatially heterogeneous becomes spatially homogeneous by forming a large number of small cavities instead of a dominant cavity. The observed behavior is rationalized in terms of screening of plastic activity via the pinning centers, characterized by a screening length extracted from the plastic-eigenmodes.
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During vascular interventions, oxidized low-density lipoprotein and lysophosphatidylcholine (lysoPC) accumulate at the site of arterial injury, inhibiting endothelial cell (EC) migration and arterial healing. LysoPC activates canonical transient receptor potential 6 (TRPC6) channels, leading to a prolonged increase in intracellular calcium ion concentration that inhibits EC migration. However, an initial increase in intracellular calcium ion concentration is required to activate TRPC6, and this mechanism remains elusive. We hypothesized that lysoPC activates the lipid-cleaving enzyme phospholipase A2 (PLA2), which releases arachidonic acid (AA) from the cellular membrane to open arachidonate-regulated calcium channels, allowing calcium influx that promotes externalization and activation of TRPC6 channels. The focus of this study was to identify the roles of calcium-dependent and/or calcium-independent PLA2 in lysoPC-induced TRPC6 externalization. We show that lysoPC induced PLA2 enzymatic activity and caused AA release in bovine aortic ECs. To identify the specific subgroup and the isoform(s) of PLA2 involved in lysoPC-induced TRPC6 activation, transient knockdown studies were performed in the human endothelial cell line EA.hy926 using siRNA to inhibit the expression of genes encoding cPLA2α, cPLA2γ, iPLA2ß, or iPLA2γ. Downregulation of the ß isoform of iPLA2 blocked lysoPC-induced release of AA from EC membranes and TRPC6 externalization, as well as preserved EC migration in the presence of lysoPC. We propose that blocking TRPC6 activation and promoting endothelial healing could improve the outcomes for patients undergoing cardiovascular interventions.
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Ácido Araquidónico/metabolismo , Señalización del Calcio , Células Endoteliales/metabolismo , Fosfolipasas A2/metabolismo , Canal Catiónico TRPC6/metabolismo , Animales , Bovinos , Células Cultivadas , Activación Enzimática , Lipoproteínas LDL/metabolismo , Lisofosfatidilcolinas/metabolismoRESUMEN
In soft amorphous materials, shear cessation after large shear deformation leads to configurations having residual shear stress. The origin of these states and the distribution of the local shear stresses within the material is not well understood, despite its importance for the change in material properties and consequent applications. In this work, we use molecular dynamics simulations of a model dense non-Brownian soft amorphous material to probe the non-trivial relaxation process towards a residual stress state. We find that, similar to thermal glasses, an increase in shear rate prior to the shear cessation leads to lower residual stress states. We rationalise our findings using a mesoscopic elasto-plastic description that explicitly includes a long range elastic response to local shear transformations. We find that after flow cessation the initial stress relaxation indeed depends on the pre-sheared stress state, but the final residual stress is majorly determined by newly activated plastic events occurring during the relaxation process, a scenario consistent with the phenomenology of avalanche dynamics in the low shear rate limit of steadily sheared amorphous solids. Our simplified coarse grained description not only allows capturing the phenomenology of residual stress states but also rationalising the altered material properties that are probed using small and large deformation protocols applied to the relaxed material.
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Using extensive numerical simulations, we investigate the flow behaviour of a model glass-forming binary mixture whose constituent particles have a large size ratio. The rheological response to applied shear is studied in the regime where the larger species are spatially predominant. We demonstrate that the macroscopic rigidity that emerges with increasing density occurs in the regime where the larger species undergo a glass transition while the smaller species continue to be highly diffusive. We analyse the interplay between the timescale imposed by the shear and the quiescent relaxation dynamics of the two species to provide a microscopic insight into the observed rheological response. Finally, by tuning the composition of the mixture, we illustrate that the systematic insertion of the smaller particles affects the rheology by lowering of viscosity of the system.
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Using extensive molecular dynamics simulations, we investigate the slowdown of dynamics in a 3D system of ring polymers by varying the ambient pressure and the stiffness of the rings. Our study demonstrates that the stiffness of the rings determines the dynamics of the ring polymers, leading to glassiness at lower pressures for stiffer rings. The threading of the ring polymers, a unique feature that emerges only due to the topological nature of such polymers in three dimensions, is shown to be the determinant feature of dynamical slowdown, albeit only in a certain stiffness range. Our results suggest a possible framework for exploring the phase space spanned by ring stiffness and pressure to obtain spontaneously emerging topologically constrained polymer glasses.
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Extensive molecular dynamics computer simulations of an equimolar, glass-forming AB mixture with a large size ratio are presented. While the large A particles show a glass transition around the critical density of mode-coupling theory ρc, the small B particles remain mobile with a relatively weak decrease in their self-diffusion coefficient DB with increasing density. Surprisingly, around ρc, the self-diffusion coefficient of species A, DA, also starts to show a rather weak dependence on density. We show that this is due to finite-size effects that can be understood from the analysis of the collective interdiffusion dynamics.
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Endothelial cell (EC) migration is critical for healing arterial injuries, such as those that occur with angioplasty. Impaired re-endothelialization following arterial injury contributes to vessel thrombogenicity, intimal hyperplasia, and restenosis. Oxidized lipid products, including lysophosphatidylcholine (lysoPC), induce canonical transient receptor potential 6 (TRPC6) externalization leading to increased [Ca2+]i, activation of calpains, and alterations of the EC cytoskeletal structure that inhibit migration. The p110α and p110δ catalytic subunit isoforms of phosphatidylinositol 3-kinase (PI3K) regulate lysoPC-induced TRPC6 externalization in vitro. The goal of this study was to assess the in vivo relevance of those in vitro findings to arterial healing following a denuding injury in hypercholesterolemic mice treated with pharmacologic inhibitors of the p110α and p110δ isoforms of PI3K and a general PI3K inhibitor. Pharmacologic inhibition of the p110α or the p110δ isoform of PI3K partially preserves healing in hypercholesterolemic male mice, similar to a general PI3K inhibitor. Interestingly, the p110α, p110δ, and the general PI3K inhibitor do not improve arterial healing after injury in hypercholesterolemic female mice. These results indicate a potential new role for isoform-specific PI3K inhibitors in male patients following arterial injury/intervention. The results also identify significant sex differences in the response to PI3K inhibition in the cardiovascular system, where female sex generally has a cardioprotective effect. This study provides a foundation to investigate the mechanism for the sex differences in response to PI3K inhibition to develop a more generally applicable treatment option.
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Dominio Catalítico/fisiología , Fosfatidilinositol 3-Quinasa Clase I/antagonistas & inhibidores , Fosfatidilinositol 3-Quinasa Clase I/metabolismo , Hipercolesterolemia/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Cicatrización de Heridas/fisiología , Animales , Bovinos , Línea Celular , Células Endoteliales/metabolismo , Femenino , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Isoformas de Proteínas/metabolismo , Transducción de Señal/fisiologíaRESUMEN
Lipid oxidation products, including lysophosphatidylcholine (lysoPC) inhibit endothelial cell (EC) migration in vitro and impair EC healing of arterial injuries in vivo, in part by activating phosphatidylinositol 3-kinase (PI3K), which increases the externalization of canonical transient receptor potential 6 (TRPC6) channels and the subsequent increase in intracellular calcium. Inhibition of PI3K is a potential method to decrease TRPC6 activation and restore migration, but PI3K is involved in multiple intracellular signaling pathways and has multiple downstream effectors. The goal of this study is to identify the specific p110 catalytic subunit isoforms responsible for lysoPC-induced TRPC6 externalization to identify a target for intervention while minimizing impact on alternative signaling pathways. Down-regulation of the p110α and p110δ isoforms, but not the p110ß or p110γ isoforms, with small interfering RNA significantly decreased phosphatidylinositol (3,4,5)-trisphosphate production and TRPC6 externalization, and significantly improved EC migration in the presence of lysoPC. These results identify an additional role of p110α in EC and reveal for the first time a specific role of p110δ in EC, providing a foundation for subsequent in vivo studies to investigate the impact of p110 isoform inhibition on arterial healing after injury.
Asunto(s)
Movimiento Celular/efectos de los fármacos , Fosfatidilinositol 3-Quinasa Clase I/metabolismo , Células Endoteliales/efectos de los fármacos , Lisofosfatidilcolinas/farmacología , Canal Catiónico TRPC6/metabolismo , Animales , Señalización del Calcio , Dominio Catalítico , Bovinos , Línea Celular , Fosfatidilinositol 3-Quinasa Clase I/genética , Células Endoteliales/enzimología , Humanos , Isoenzimas , Cinética , Fosfatos de Fosfatidilinositol/metabolismoRESUMEN
We develop a framework to study the mechanical response of athermal amorphous solids via a coupling of mesoscale and microscopic models. Using measurements of coarse-grained quantities from simulations of dense disordered particulate systems, we present a coherent elastoplastic model approach for deformation and flow of yield stress materials. For a given set of parameters, this model allows us to match consistently transient and steady state features of driven disordered systems with diverse preparation histories under both applied shear-rate and creep protocols.
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Polycrystals are partially ordered solids where crystalline order extends over mesoscopic length scales, namely, the grain size. We study the Poisuielle flow of such materials in a rough channel. In general, similar to yield stress fluids, three distinct dynamical states, namely, flowing, stick-slip, and jammed can be observed, with a yield threshold dependent on channel width. Importantly, the interplay between the finite channel width, and the intrinsic ordering scale (the grain size) leads to a new type of spatiotemporal heterogeneity. In wide channels, although the average flow profile remains pluglike, at the underlying granular level, there is vigorous grain remodeling activity resulting from the velocity heterogeneity among the grains. As the channel width approaches typical grain size, the flowing polycrystalline state breaks up into a spatially heterogeneous mixture of flowing liquid like patches and chunks of nearly static grains. Despite these static grains, the average velocity still shows a parabolic profile, dominated by the moving liquidlike patches. However, the solid-liquid front moves at nearly constant speed in the opposite direction of the external drive.
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The response of a model two-dimensional colloidal glass former to an externally imposed spatially random potential, which acts as a quenched disorder, is investigated using numerical simulations, motivated by recent experiments and also mean field predictions. The external potential induces the onset of the glassy dynamics at increasingly smaller field roughness, with increasing packing fraction of the particulate assembly, and the existence of aging processes within the glassy regime is also observed. Furthermore, along the axis of increasing field roughness, the dynamical slowdown is not correlated to the hexatic order within the supercooled regime.
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Using numerical simulations, we have studied the yielding response, in the athermal quasistatic limit, of a model amorphous material having inclusions in the form of randomly pinned particles. We show that, with increasing pinning concentration, the plastic activity becomes more spatially localized, resulting in smaller stress drops, and a corresponding increase in the magnitude of strain where yielding occurs. We demonstrate that, unlike the spatially heterogeneous and avalanche led yielding in the case of the unpinned glass, for the case of large pinning concentration, yielding takes place via a spatially homogeneous proliferation of localized events.
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Via extensive numerical simulations, we study the fluidisation process of dense amorphous materials subjected to an external shear stress, using a three-dimensional colloidal glass model. In order to disentangle possible boundary effects from finite size effects in the process of fluidisation, we implement a novel geometry-constrained protocol with periodic boundary conditions. We show that this protocol is well controlled and that the longtime fluidisation dynamics is, to a great extent, independent of the details of the protocol parameters. Our protocol, therefore, provides an ideal tool to investigate the bulk dynamics prior to yielding and to study finite size effects regarding the fluidisation process. Our study reveals the existence of precursors to fluidisation observed as a peak in the strain-rate fluctuations, that allows for a robust definition of a fluidisation time. Although the exponents in the power-law creep dynamics seem not to depend significantly on the system size, we reveal strong finite size effects for the onset of fluidisation.
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Lipid oxidation products, including lysophosphatidylcholine (lysoPC), activate canonical transient receptor potential 6 (TRPC6) channels leading to inhibition of endothelial cell (EC) migration in vitro and delayed EC healing of arterial injuries in vivo. The precise mechanism through which lysoPC activates TRPC6 channels is not known, but calmodulin (CaM) contributes to the regulation of TRPC channels. Using site-directed mutagenesis, cDNAs were generated in which Tyr(99) or Tyr(138) of CaM was replaced with Phe, generating mutant CaM, Phe(99)-CaM, or Phe(138)-CaM, respectively. In ECs transiently transfected with pcDNA3.1-myc-His-Phe(99)-CaM, but not in ECs transfected with pcDNA3.1-myc-His-Phe(138)-CaM, the lysoPC-induced TRPC6-CaM dissociation and TRPC6 externalization was disrupted. Also, the lysoPC-induced increase in intracellular calcium concentration was inhibited in ECs transiently transfected with pcDNA3.1-myc-His-Phe(99)-CaM. Blocking phosphorylation of CaM at Tyr(99) also reduced CaM association with the p85 subunit and subsequent activation of phosphatidylinositol 3-kinase (PI3K). This prevented the increase in phosphatidylinositol (3,4,5)-trisphosphate (PIP3) and the translocation of TRPC6 to the cell membrane and reduced the inhibition of EC migration by lysoPC. These findings suggest that lysoPC induces CaM phosphorylation at Tyr(99) by a Src family kinase and that phosphorylated CaM activates PI3K to produce PIP3, which promotes TRPC6 translocation to the cell membrane.
Asunto(s)
Señalización del Calcio/fisiología , Calmodulina/metabolismo , Membrana Celular/metabolismo , Movimiento Celular/fisiología , Células Endoteliales/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Canales Catiónicos TRPC/metabolismo , Animales , Calcio/metabolismo , Calmodulina/genética , Bovinos , Membrana Celular/genética , Células Endoteliales/citología , Activación Enzimática/fisiología , Humanos , Lisofosfatidilcolinas/genética , Lisofosfatidilcolinas/metabolismo , Fosfatidilinositol 3-Quinasas/genética , Transporte de Proteínas/fisiología , Canales Catiónicos TRPC/genética , Canal Catiónico TRPC6RESUMEN
Lipid oxidation products, including lysophosphatidylcholine (lysoPC), activate canonical transient receptor potential 6 (TRPC6) channels, and the subsequent increase in intracellular Ca2+ leads to TRPC5 activation. The goal of this study is to elucidate the steps in the pathway between TRPC6 activation and TRPC5 externalization. Following TRPC6 activation by lysoPC, extracellular regulated kinase (ERK) is phosphorylated. This leads to phosphorylation of p47phox and subsequent NADPH oxidase activation with increased production of reactive oxygen species. ERK activation requires TRPC6 opening and influx of Ca2+ as evidenced by the failure of lysoPC to induce ERK phosphorylation in TRPC6-/- endothelial cells. ERK siRNA blocks the lysoPC-induced activation of NADPH oxidase, demonstrating that ERK activation is upstream of NADPH oxidase. The reactive oxygen species produced by NADPH oxidase promote myosin light chain kinase (MLCK) activation with phosphorylation of MLC and TRPC5 externalization. Downregulation of ERK, NADPH oxidase, or MLCK with the relevant siRNA prevents TRPC5 externalization. Blocking MLCK activation prevents the prolonged rise in intracellular calcium levels and preserves endothelial migration in the presence of lysoPC.
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Movimiento Celular/fisiología , Células Endoteliales/metabolismo , NADPH Oxidasas/metabolismo , Canales Catiónicos TRPC/metabolismo , Animales , Bovinos , Movimiento Celular/efectos de los fármacos , Células Endoteliales/efectos de los fármacos , Activación Enzimática/fisiología , Humanos , Lisofosfatidilcolinas/farmacología , Ratones , Ratones Endogámicos C57BL , Especies Reactivas de Oxígeno/metabolismo , Canal Catiónico TRPC6RESUMEN
We study the rheology of confined suspensions of neutrally buoyant rigid monodisperse spheres in plane-Couette flow using direct numerical simulations. We find that if the width of the channel is a (small) integer multiple of the sphere diameter, the spheres self-organize into two-dimensional layers that slide on each other and the effective viscosity of the suspension is significantly reduced. Each two-dimensional layer is found to be structurally liquidlike but its dynamics is frozen in time.
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OBJECTIVE: After arterial injury, endothelial cell (EC) migration is essential for healing, but lipid oxidation products activate TRPC6 and TRPC5 ion channels, leading to increased intracellular calcium and inhibition of EC migration in vitro. The objective of this study was to further evaluate the role of TRPC channels in EC migration in vitro and to validate in vitro findings in an in vivo model. METHODS: Mouse aortic ECs were cultured, and the effect of lysophosphatidylcholine, the major lysophospholipid in oxidized low-density lipoprotein, on migration was assessed in a razor-scrape assay. EC healing after a carotid injury with electrocautery was evaluated in wild-type (WT), TRPC6(-/-), and TRPC5(-/-) mice receiving either a chow or high-cholesterol (HC) diet. RESULTS: Lysophosphatidylcholine inhibited EC migration of WT ECs to 22% of baseline and of TRPC5(-/-) ECs to 53% of baseline but had minimal effect on TRPC6(-/-) EC migration. Hypercholesterolemia severely impaired EC healing in vivo, with 51.4% ± 1.8% and 24.9% ± 2.0% of the injury resurfaced with ECs at 5 days in chow-fed and HC-fed WT mice, respectively (P < .001). Hypercholesterolemia did not impair healing in TRPC6(-/-) mice, with coverage of 48.4% ± 3.4% and 46.8% ± 1.6% in chow-fed and HC-fed TRPC6(-/-) mice, respectively. Hypercholesterolemia had a reduced inhibitory effect in TRPC5(-/-) mice, with EC coverage of 51.7% ± 3.0% and 37.% ± 1.4% in chow-fed and HC-fed TRPC5(-/-) mice, respectively. CONCLUSIONS: Results suggest that activation of TRPC6 and TRPC5 channels is the key contributor to impaired endothelial healing of arterial injuries in hypercholesterolemic mice.