Toll-Like Receptor Signalling Pathways Regulate Hypoxic Stress Induced Fibroblast Growth Factor but Not Vascular Endothelial Growth Factor-A in Human Microvascular Endothelial Cells

Abstract

Retinal diseases are the leading causes of irreversible blindness worldwide. The role of toll-like receptor (TLR) signalling mechanisms (MyD88 and TRIF) in the production of pro-angiogenic growth factors from human microvascular endothelial cells (HMEC-1) under hypoxic stress remains unexplored. HMEC-1 was incubated under normoxic (5% CO2 at 37 °C) and hypoxic (1% O2, 5% CO2, and 94% N2; at 37 °C) conditions for 2, 6, 24, and 48 h, respectively. For TLR pathway analysis, HMEC-1 was pre-treated with pharmacological inhibitors (Pepinh-MyD88 and Pepinh-TRIF) and subjected to normoxia and hypoxia conditions. Gene and protein expressions of vascular endothelial growth factor-A (VEGF-A), fibroblast growth factor (FGF-2), hypoxia inducible factor 1-alpha (HIF1-α) were performed using quantitative polymerase chain reaction (qPCR), ELISA, and Western blot methodologies. Levels of TLR3 and TLR4 were analysed by flow cytometry. Under hypoxia, levels of VEGF-A and FGF-2 were elevated in a time-dependent fashion. Inhibition of MyD88 and TRIF signalling pathways decreased FGF-2 levels but failed to modulate the secretion of VEGF-A from HMEC-1. Blocking a known regulator, endothelin receptor (ETR), also had no effect on VEGF-A secretion from HMEC-1. Overall, this study provides the proof-of-concept to target TLR signalling pathways for the management of blinding retinal diseases.

Cytokines and their regulators in rat lung following scorpion envenomation

“…It is known that HIF1-α, which content rise during envenomation was revealed in the results of this study, is one of FGF-2 and VEGF expression activators ( Akhtar et al, 2021 ). Moreover, VEGF levels rise can be also a sign of M1-to-М2 macrophages transition, as M2 phenotype macrophages generate growth factors which promote blood vessel development and cellular proliferation ( Strizova et al, 2023 ).…”

Toll-Like Receptor Signalling Pathways and the Pathogenesis of Retinal Diseases

“…TLR4 levels are raised in response to retinal IR injury (13,140,142,(146)(147)(148)(149) and hypoxia (7,150). In particular, TLR4 levels are highly expressed in the INL (13,146) and GCL (13,142,146) following I/R injury.…”

“…Retinal diseases such as diabetic retinopathy (DR), including diabetic macular oedema (DMO) and proliferative diabetic retinopathy (PDR), and age-related macular degeneration (AMD), are the leading causes of irreversible blindness worldwide (1)(2)(3)(4). These diseases have common pathogenetic themes of inflammation, and ischaemia (5)(6)(7).…”