Glypican-4 regulated actin cytoskeletal reorganization in glucocorticoid treated trabecular meshwork cells and involvement of Wnt/PCP signaling

Fibrosis and Src Signalling in Glaucoma: From Molecular Pathways to Therapeutic Prospects

Glaucoma, a leading cause of irreversible blindness, is characterised by progressive optic nerve damage, with elevated intraocular pressure (IOP) and extracellular matrix (ECM) remodelling in the lamina cribrosa (LC) contributing to its pathophysiology. While current treatments focus on IOP reduction, they fail to address the underlying fibrotic changes that perpetuate neurodegeneration. The Src proto-oncogene, a non-receptor tyrosine kinase, has emerged as a key regulator of cellular processes, including fibroblast activation, ECM deposition, and metabolism, making it a promising target for glaucoma therapy. Beyond its well-established roles in cancer and fibrosis, Src influences pathways critical to trabecular meshwork function, aqueous humour outflow, and neurodegeneration. However, the complexity of Src signalling networks remains a challenge, necessitating further investigation into the role of Src in glaucoma pathogenesis. This paper explores the therapeutic potential of Src inhibition to mitigate fibrotic remodelling and elevated IOP in glaucoma, offering a novel approach to halting disease progression.

Protocol for the Extraction and Characterization of Trabecular Meshwork Cell Cytoskeleton Fraction

Among various cellular attributes modulating aqueous humor (AH) outflow through the trabecular pathway and eventually intraocular pressure, the involvement of actomyosin regulated cellular contraction and relaxation, cell-extracellular matrix adhesion and cell-cell junctions, and mechanotransduction are well recognized. Although various biological and pharmacological agent-modulated AH outflows were associated with altered actin cytoskeletal organization and cell adhesive interactions of trabecular meshwork (TM) cells, these changes were analyzed largely with a biased approach to examine the specific proteins, but there were very few efforts in examining them with hypothesis-free unbiased approach in their native state. Therefore, in this chapter, we describe a protocol tailored to characterize the cytoskeleton of TM cells. This simple protocol can be applied to identifying the differentially regulated TM cell cytoskeleton proteins under any given treatment condition in conjunction with quantitative proteomic analysis.

Dysregulation of septin cytoskeletal organization in the trabecular meshwork contributes to ocular hypertension

Ocular hypertension, believed to result partly from increased contractile activity, cell adhesive interactions, and stiffness within the trabecular meshwork (TM), is a major risk factor for glaucoma, a leading cause of blindness. However, the identity of molecular mechanisms governing organization of actomyosin and cell adhesive interactions in the TM remains limited. Based on our previous findings, in which proteomics analyses revealed elevated levels of septins, including septin-9 in human TM cells treated with the ocular hypertensive agent dexamethasone, here, we evaluated the effects of septin-9 overexpression, deficiency, and pharmacological targeting in TM cells. These studies demonstrated a profound impact on actomyosin organization, cell adhesion, contraction, and phagocytosis. Overexpression raised intraocular pressure (IOP) in mice, while inhibition increased cell permeability. In addition, we replicated a significant association between a common variant (rs9038) in SEPT9 with IOP in the Genetic Epidemiology Research on Adult Healthy and Aging (GERA) cohort. Collectively, these data reveal a link between dysregulated septin cytoskeletal organization in the TM and increased IOP, likely due to enhanced cell contraction, adhesive interactions, and fibrotic activity. This suggests that targeting the septin cytoskeleton could offer a novel approach for lowering IOP in patients with glaucoma.

Effects of SIPA1L1 on trabecular meshwork extracellular matrix protein accumulation and cellular phagocytosis in POAG

Accumulation of extracellular matrix (ECM) proteins in trabecular meshwork (TM), which leads to increased outflow resistance of aqueous humor and consequently high intraocular pressure, is a major cause of primary open-angle glaucoma (POAG). According to our preliminary research, the RapGAP protein superfamily member, signal-induced proliferation-associated 1-like 1 protein (SIPA1L1), which is involved in tissue fibrosis, may have an impact on POAG by influencing ECM metabolism of TM. This study aims to confirm these findings and identify effects and cellular mechanisms of SIPA1L1 on ECM changes and phagocytosis in human TM (HTM) cells. Our results showed that the expression of SIPA1L1 in HTM cells was significantly increased by TGF-β2 treatment in label-free quantitative proteomics. The aqueous humor and TM cell concentration of SIPA1L1 in POAG patients was higher than that of control. In HTM cells, TGF-β2 increased expression of SIPA1L1 along with accumulation of ECM, RhoA, and p-cofilin 1. The effects of TGF-β2 were reduced by si-SIPA1L1. TGF-β2 decreased HTM cell phagocytosis by polymerizing cytoskeletal actin filaments, while si-SIPA1L1 increased phagocytosis by disassembling actin filaments. Simultaneously, overexpressing SIPA1L1 alone exhibited comparable effects to that of TGF-β2. Our studies demonstrate that SIPA1L1 not only promotes the production of ECM, but also inhibits its removal by reducing phagocytosis. Targeting SIPA1L1 degradation may become a significant therapy for POAG.

Chemical mapping of the surface interactome of PIEZO1 identifies CADM1 as a modulator of channel inactivation

The propeller-shaped blades of the PIEZO1 and PIEZO2 ion channels partition into the plasma membrane and respond to indentation or stretching of the lipid bilayer, thus converting mechanical forces into signals that can be interpreted by cells, in the form of calcium flux and changes in membrane potential. While PIEZO channels participate in diverse physiological processes, from sensing the shear stress of blood flow in the vasculature to detecting touch through mechanoreceptors in the skin, the molecular details that enable these mechanosensors to tune their responses over a vast dynamic range of forces remain largely uncharacterized. To survey the molecular landscape surrounding PIEZO channels at the cell surface, we employed a mass spectrometry-based proteomic approach to capture and identify extracellularly exposed proteins in the vicinity of PIEZO1. This PIEZO1-proximal interactome was enriched in surface proteins localized to cell junctions and signaling hubs within the plasma membrane. Functional screening of these interaction candidates by calcium imaging and electrophysiology in an overexpression system identified the adhesion molecule CADM1/SynCAM that slows the inactivation kinetics of PIEZO1 with little effect on PIEZO2. Conversely, we found that CADM1 knockdown accelerates inactivation of endogenous PIEZO1 in Neuro-2a cells. Systematic deletion of CADM1 domains indicates that the transmembrane region is critical for the observed effects on PIEZO1, suggesting that modulation of inactivation is mediated by interactions in or near the lipid bilayer.

Dichotomous Effects of Glypican-4 on Cancer Progression and Its Crosstalk with Oncogenes

Glypicans are linked to various aspects of neoplastic behavior, and their therapeutic value has been proposed in different cancers. Here, we have systematically assessed the impact of GPC4 on cancer progression through functional genomics and transcriptomic analyses across a broad range of cancers. Survival analysis using TCGA cancer patient data reveals divergent effects of GPC4 expression across various cancer types, revealing elevated GPC4 expression levels to be associated with both poor and favorable prognoses in a cancer-dependent manner. Detailed investigation of the role of GPC4 in glioblastoma and non-small cell lung adenocarcinoma by genetic perturbation studies displays opposing effects on these cancers, where the knockout of GPC4 with CRISPR/Cas9 attenuated proliferation of glioblastoma and augmented proliferation of lung adenocarcinoma cells and the overexpression of GPC4 exhibited a significant and opposite effect. Further, the overexpression of GPC4 in GPC4-knocked-down glioblastoma cells restored the proliferation, indicating its mitogenic effect in this cancer type. Additionally, a survival analysis of TCGA patient data substantiated these findings, revealing an association between elevated levels of GPC4 and a poor prognosis in glioblastoma, while indicating a favorable outcome in lung carcinoma patients. Finally, through transcriptomic analysis, we attempted to assign mechanisms of action to GPC4, as we find it implicated in cell cycle control and survival core pathways. The analysis revealed upregulation of oncogenes, including FGF5, TGF-β superfamily members, and ITGA-5 in glioblastoma, which were downregulated in lung adenocarcinoma patients. Our findings illuminate the pleiotropic effect of GPC4 in cancer, underscoring its potential as a putative prognostic biomarker and indicating its therapeutic implications in a cancer type dependent manner.

Influence of Growth Differentiation Factor 15 on Intraocular Pressure in Mice

Growth differentiation factor 15 (GDF15), a stress-sensitive cytokine, and a distant member of the transforming growth factor β superfamily, has been shown to exhibit increased levels with aging, and in various age-related pathologies. Although GDF15 levels are elevated in the aqueous humor (AH) of glaucoma (optic nerve atrophy) patients, the possible role of this cytokine in the modulation of intraocular pressure (IOP) or AH outflow is unknown. The current study addresses this question using transgenic mice expressing human GDF15 and GDF15 null mice, and by perfusing enucleated mouse eyes with recombinant human GDF15 (rhGDF15). Treatment of primary cultures of human trabecular meshwork cells with a telomerase inhibitor, an endoplasmic reticulum stress-inducing agent, hydrogen peroxide, or an autophagy inhibitor resulted in significant elevation in GDF15 levels relative to the respective control cells. rhGDF15 stimulated modest but significant increases in the expression of genes encoding the extracellular matrix, cell adhesion proteins, and chemokine receptors (C-C chemokine receptor type 2) in human trabecular meshwork cells compared with controls, as deduced from the differential transcriptional profiles using RNA-sequencing analysis. There was a significant increase in IOP in transgenic mice expressing human GDF15, but not in GDF15 null mice, compared with the respective wild-type control mice. The AH outflow facility was decreased in enucleated wild-type mouse eyes perfused with rhGDF15. Light microcopy-based histologic examination of the conventional AH outflow pathway tissues did not reveal identifiable differences between the GDF15-targeted and control mice. Taken together, these results reveal the modest elevation of IOP in mice expressing human GDF15 possibly stemming from decreased AH outflow through the trabecular pathway.

Influence of the calcium voltage-gated channel auxiliary subunit (CACNA2D1) absence on intraocular pressure in mice

The etiology of elevated intraocular pressure (IOP), a major risk factor for glaucoma (optic nerve atrophy), is poorly understood despite continued efforts. Although the gene variant of CACNA2D1 (encoding α2δ1), a calcium voltage-gated channel auxiliary subunit, has been reported to be associated with primary open-angle glaucoma, and the pharmacological mitigation of α2δ1 activity by pregabalin lowers IOP, the cellular basis for α2δ1 role in the modulation of IOP remains unclear. Our recent findings reveled readily detectable levels of α2δ1 and its ligand thrombospondin in the cytoskeletome fraction of human trabecular meshwork (TM) cells. To understand the direct role of α2δ1 in the modulation of IOP, we evaluated α2δ1 null mice for changes in IOP and found a moderate (∼10%) but significant decrease in IOP compared to littermate wild type control mice. Additionally, to gain cellular insights into α2δ1 antagonist (pregabalin) induced IOP changes, we assessed pregabalin's effects on human TM cell actin cytoskeletal organization and cell adhesive interactions in comparison with a Rho kinase inhibitor (Y27632), a known ocular hypotensive agent. Unlike Y27632, pregabalin did not have overt effects on cell morphology, actin cytoskeletal organization, or cell adhesion in human TM cells. These results reveal a modest but significant decrease in IOP in α2δ1 deficient mice, and this response appears to be not associated with the contractile and cell adhesive characteristics of TM cells based on the findings of pregabalin effects on isolated TM cells. Therefore, the mechanism by which pregabalin lowers IOP remains elusive.

miR-196b-5p regulates inflammatory process and migration via targeting Nras in trabecular meshwork cells

Glaucoma, an insidious ophthalmic pathology, is typified by an aberrant surge in intraocular pressure (IOP) which culminates in the degeneration of retinal ganglion cells and optical neuropathy. The mitigation of IOP stands as the principal therapeutic strategy to forestall vision loss. The trabecular meshwork's (TM) integrity and functionality are pivotal in modulating aqueous humor egress. Despite their potential significance in glaucomatous pathophysiology, the implications of microRNAs (miRNAs) on TM functionality remain largely enigmatic. Transcriptomic sequencing was employed to delineate the miRNA expression paradigm within the limbal region of rodent glaucoma models, aiming to elucidate miRNA-mediated mechanisms within the glaucomatous milieu. Analytical scrutiny of the sequencing data disclosed 174 miRNAs with altered expression profiles, partitioned into 86 miRNAs with augmented expression and 88 with diminished expression. Notably, miRNAs such as hsa-miR-196b-5p were identified as having substantial expression discrepancies with concomitant statistical robustness, suggesting a potential contributory role in glaucomatous progression. Subsequent in vitro assays affirmed that miR-196b-5p augments the inflammatory cascade within immortalized human TM (iHTM) and glaucoma-induced human TM (GTM3) cells, concurrently attenuating cellular proliferation, motility, and cytoskeletal architecture. Additionally, miR-196b-5p implicates itself in the regulation of IOP and inflammatory processes in rodent models. At a mechanistic level, miR-196b-5p modulates its effects via the targeted repression of Nras (neuroblastoma RAS viral oncogene homolog). Collectively, these transcriptomic investigations furnish a comprehensive vista into the regulatory roles of miRNAs within the glaucomatous framework, and the identification of differentially expressed miRNAs alongside their targets could potentially illuminate novel molecular pathways implicated in glaucoma, thereby aiding in the development of innovative therapeutic avenues.

Glucocorticoid-Induced Ocular Hypertension and Glaucoma

Glucocorticoid (GC) therapy is indicated in many diseases, including ocular diseases. An important side-effect of GC therapy is GC-induced ocular hypertension (GIOHT), which may cause irreversible blindness known as GC-induced glaucoma (GIG). Here, we reviewed the pathological changes that contribute to GIOHT including in the trabecular meshwork and Schlemm's canal at cellular and molecular levels. We also discussed the clinical aspects of GIOHT/GIG including disease prevalence, risk factors, the type of GCs, the route of GC administration, and management strategies.