skip to main content

Attention:

The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 5:00 PM ET until 11:00 PM ET on Friday, June 21 due to maintenance. We apologize for the inconvenience.


Title: Piezo1 channels mediate trabecular meshwork mechanotransduction and promote aqueous fluid outflow
Key points

Trabecular meshwork (TM) is a highly mechanosensitive tissue in the eye that regulates intraocular pressure through the control of aqueous humour drainage.

Its dysfunction underlies the progression of glaucoma but neither the mechanisms through which TM cells sense pressure nor their role in aqueous humour outflow are understood at the molecular level.

We identified the Piezo1 channel as a key TM transducer of tensile stretch, shear flow and pressure.

Its activation resulted in intracellular signals that altered organization of the cytoskeleton and cell‐extracellular matrix contacts and modulated the trabecular component of aqueous outflow whereas another channel, TRPV4, mediated a delayed mechanoresponse.

This study helps elucidate basic mechanotransduction properties that may contribute to intraocular pressure regulation in the vertebrate eye.

Abstract

Chronic elevations in intraocular pressure (IOP) can cause blindness by compromising the function of trabecular meshwork (TM) cells in the anterior eye, but how these cells sense and transduce pressure stimuli is poorly understood. Here, we demonstrate functional expression of two mechanically activated channels in human TM cells. Pressure‐induced cell stretch evoked a rapid increase in transmembrane current that was inhibited by antagonists of the mechanogated channel Piezo1, Ruthenium Red and GsMTx4, and attenuated in Piezo1‐deficient cells. The majority of TM cells exhibited a delayed stretch‐activated current that was mediated independently of Piezo1 by TRPV4 (transient receptor potential cation channel, subfamily V, member 4) channels. Piezo1 functions as the principal TM transducer of physiological levels of shear stress, with both shear and the Piezo1 agonist Yoda1 increasing the number of focal cell‐matrix contacts. Analysis of TM‐dependent fluid drainage from the anterior eye showed significant inhibition by GsMTx4. Collectively, these results suggest that TM mechanosensitivity utilizes kinetically, regulatory and functionally distinct pressure transducers to inform the cells about force‐sensing contexts. Piezo1‐dependent control of shear flow sensing, calcium homeostasis, cytoskeletal dynamics and pressure‐dependent outflow suggests potential for a novel therapeutic target in treating glaucoma.

 
more » « less
NSF-PAR ID:
10372588
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley-Blackwell
Date Published:
Journal Name:
The Journal of Physiology
Volume:
599
Issue:
2
ISSN:
0022-3751
Page Range / eLocation ID:
p. 571-592
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Age‐related human trabecular meshwork (HTM) cell loss is suggested to affect its ability to regulate aqueous humor outflow in the eye. In addition, disease‐related HTM cell loss is suggested to lead to elevated intraocular pressure in glaucoma. Induced pluripotent stem cell (iPSC)‐derived trabecular meshwork (TM) cells are promising autologous cell sources that can be used to restore the declining TM cell population and function. Previously, an in vitro HTM model is bioengineered for understanding HTM cell biology and screening of pharmacological or biological agents that affect trabecular outflow facility. In this study, it is demonstrated that human iPSC‐derived TM cells cultured on SU‐8 scaffolds exhibit HTM‐like cell morphology, extracellular matrix deposition, and drug responsiveness to dexamethasone treatment. These findings suggest that iPSC‐derived TM cells behave like primary HTM cells and can thus serve as reproducible and scalable cell sources when using this in vitro system for glaucoma drug screening and further understanding of outflow pathway physiology, leading to personalized medicine.

     
    more » « less
  2. In this article, we propose a theoretical model leveraging the analogy between fluid and electric variables to investigate the relation among aqueous humor (AH) circulation and drainage and intraocular pressure (IOP), the principal established risk factor of severe neuropathologies of the optic nerve such as glaucoma. IOP is the steady-state result of the balance among AH secretion (AHs), circulation (AHc), and drainage (AHd). AHs are modeled as a given volumetric flow rate electrically corresponding to an input current source. AHc is modeled by the series of two linear hydraulic conductances (HCs) representing the posterior and anterior chambers. AHd is modeled by the parallel of three HCs: a linear HC for the conventional adaptive route (ConvAR), a nonlinear HC for the hydraulic component of the unconventional adaptive route (UncAR), and a nonlinear HC for the drug-dependent component of the UncAR. The proposed model is implemented in a computational virtual laboratory to study the value attained by the IOP under physiological and pathological conditions. Simulation results (i) confirm the conjecture that the UncAR acts as a relief valve under pathological conditions, (ii) indicate that the drug-dependent AR is the major opponent to IOP increase in the case of elevated trabecular meshwork resistance, and (iii) support the use of the model as a quantitative tool to complement in vivo studies and help design and optimize medications for ocular diseases. 
    more » « less
  3. Abstract A method motivated by the eye’s aqueous veins is described for the imaging and strain calculation within soft biological tissues. A challenge to the investigation of the biomechanics of the aqueous vein—perilimbal sclera tissue complex is resolution of tissue deformations as a function of intraocular pressure and the subsequent calculation of strain (a normalized measure of deformation). The method involves perfusion of the eye with a contrast agent during conduction of non-invasive, optical resolution photoacoustic microscopy. This imaging technique permits three-dimensional displacement measurements of tracked points on the inner walls of the veins which are used in a finite element model to determine the corresponding strains. The methods are validated against two standard strain measurement methods. Representative porcine globe perfusion experiments are presented that demonstrate the power of the method to determine complex strain fields in the veins dependent on intraocular pressure as well as vein anatomy. In these cases, veins are observed to move radially outward during increases in intraocular pressure and to possess significant spatial strain variation, possibly influenced by their branching patterns. To the authors’ knowledge, these are the only such quantitative, data driven, calculations of the aqueous vein strains available in the open literature. 
    more » « less
  4. New Findings

    What is the central question of this study?

    Do endoperoxide 4 and thromboxane A2receptors, which are receptors for cyclooxygenase products of arachidonic metabolism, on thin fibre muscle afferents play a role in the chronic mechanoreflex sensitization present in rats with heart failure with reduced ejection fraction (HF‐rEF)?

    What is the main finding and its importance?

    The data do not support a role for endoperoxide 4 receptors or thromboxane A2receptors in the chronic mechanoreflex sensitization in HF‐rEF rats.

    Abstract

    We investigated the role of cyclooxygenase metabolite‐associated endoperoxide 4 receptors (EP4‐R) and thromboxane A2receptors (TxA2‐R) on thin fibre muscle afferents in the chronic mechanoreflex sensitization in rats with myocardial infarction‐induced heart failure with reduced ejection fraction (HF‐rEF). We hypothesized that injection of either the EP4‐R antagonist L‐161,982 (1 µg) or the TxA2‐R antagonist daltroban (80 µg) into the arterial supply of the hindlimb would reduce the increase in blood pressure and renal sympathetic nerve activity (RSNA) evoked in response to 30 s of static hindlimb skeletal muscle stretch (a model of isolated mechanoreflex activation) in decerebrate, unanaesthetized HF‐rEF rats but not sham‐operated control rats (SHAM). Ejection fraction was significantly reduced in HF‐rEF (45 ± 11%) compared to SHAM (83 ± 6%;P < 0.01) rats. In SHAM and HF‐rEF rats, we found that the EP4‐R antagonist had no effect on the peak increase in mean arterial pressure (peak ΔMAP SHAM= 6, pre: 15 ± 7, post: 15 ± 9,P = 0.99; HF‐rEF= 9, pre: 30 ± 11, post: 32 ± 15 mmHg,P = 0.84) or peak increase in RSNA (peak ΔRSNA SHAM pre: 33 ± 14, post: 47 ± 31%,P = 0.94; HF‐rEF, pre: 109 ± 47, post: 139 ± 150%,P = 0.76) response to stretch. Similarly, in SHAM and HF‐rEF rats, we found that the TxA2‐R antagonist had no effect on the peak ΔMAP (SHAM= 7, pre: 13 ± 7, post: 19 ± 14,P = 0.15; HF‐rEF= 14, pre: 24 ± 13, post: 21 ± 13 mmHg,P = 0.47) or peak ΔRSNA (SHAM pre: 52 ± 43, post: 57 ± 67%,P = 0.94; HF‐rEF, pre: 108 ± 93, post: 88 ± 72%,P = 0.30) response to stretch. The data do not support a role for EP4‐Rs or TxA2‐Rs in the chronic mechanoreflex sensitization in HF‐rEF.

     
    more » « less
  5. Carbonic anhydrase inhibitors (CAIs) have been used for many decades in the treatment of glaucoma. Systemic CAIs were an early treatment option to lower intraocular pressure by reducing aqueous humour production; however, frequent side effects including polyuria and paresthesia contributed to the eventual development of topical CAIs. As topical drug development evolved over time, prostaglandin analogues and beta-blockers have become the gold standard of glaucoma therapies. Although prescribed less often than other classes of topical glaucoma therapies, topical CAIs continue to be used in combination therapies with beta-blockers and alpha agonists. Topical CAIs have also been demonstrated to alter biomarkers of ocular haemodynamics, which have relevance in glaucoma. The purpose of this review is to review and summarise the current state of topical CAI prescribing trends, known efficacy and suggested mechanisms and potential influence on ocular haemodynamics for the future of glaucoma management. 
    more » « less