ABCB1 transporter and Toll-like receptor 4 in trabecular meshwork cells.

Area of Science:

• Ocular Biology
• Immunology
• Pharmacology

Background:

• The aqueous humor nourishes anterior segment tissues, with the trabecular meshwork (TM) regulating substance efflux.
• ATP-binding cassette (ABC) transporters are crucial for cellular detoxification and respond to various stressors.
• The innate immune system in the TM, involving Toll-like receptor 4 (TLR4), maintains ocular homeostasis.

Purpose of the Study:

• To investigate the interaction between the innate immune system (TLR4) and ABCB1 transporter in human TM cells.
• To determine if TLR4 agonists and xenobiotics influence ABCB1-mediated detoxification in the TM.
• To test the hypothesis that innate immune responses modulate ABCB1 activity for xenobiotic detoxification in the aqueous humor.

Main Methods:

• Western blot analysis of human TM cells for TLR4 and ABCB1 expression.
• Challenging TM cells and macrophages with various ligands (lactate, hyaluronic acid, LPS) and inhibitors (naloxone).
• Assessing ABCB1 transporter activity using calcein AM efflux assay and confocal microscopy.

Main Results:

• ABCB1 activity was modulated by inhibitors (verapamil) and activators (digoxin).
• TLR4 agonists, including low-molecular-weight hyaluronic acid (LMW-HA) and lipopolysaccharide (LPS), significantly affected ABCB1 activity.
• Naloxone (TLR4 inhibitor) blocked the effects of LMW-HA and beta-amyloid on ABCB1, while lactate and high-molecular-weight HA reduced its activity.

Conclusions:

• Human TM cells exhibit responsiveness to ABCB1 modulators.
• TLR4 signaling pathways are implicated in the regulation of ABCB1 function.
• The innate immune response within the TM likely plays a critical role in the detoxification of xenobiotics from aqueous humor via ABCB1.