The eye, like most organs, has an intricate plumbing system. Pressure builds when drainage is impaired, and this condition - glaucoma - can cause irreversible vision loss. Certain popular anti-inflammatory eye medications that contain steroids can in some cases compound the problem, although scientists have been at a loss to understand why.
Now, Cornell researchers have identified the signaling mechanism that triggers steroid-induced glaucoma by creating a 3D "eye-on-a-chip" platform that mimics the flow of ocular fluids.
The findings were published Aug. 27 in Nature Cardiovascular Research. The lead author is Renhao Lu, Ph.D. '24.
"Steroid-induced glaucoma is a major clinical challenge. There's no targeted therapy. We just say you are unlucky," said senior author Esak (Isaac) Lee, assistant professor of biomedical engineering at Cornell Engineering. "There is a clear, unmet need to better understand, and prevent, this major side effect of the steroid in the clinics."
Glaucoma is typically studied in animal models and simple 2D cell cultures, but those approaches often fail to capture the anatomical complexity and responsiveness of the human eye.
The solution from Lee's lab, which studies lymphatic systems in different types of organs, has been to create 3D in-vitro models that can reproduce the systems' layered structures while isolating biological and biophysical factors, all in a highly reproducible and controlled manner. Lee previously co-designed such a device that revealed a protein that jams up the necessary drainage in human skin lymphatic vessels, causing the painful swelling known as lymphedema.
The eye's lymphatic vessels are responsible for draining aqueous humor, a clear, water-like fluid that provides oxygen and nutrients but, when not removed, can cause intraocular pressure (IOP) to build, damaging neurons in the retina that are critical for transmitting light signals to the brain.
Lee's team realized the lymphatics in the eye, known as Schlemm's canal (SC) cells, are quite different from those in the skin, lungs and other organs. These are surrounded by another cell type: trabecular meshwork (TM). Only with both cell layers working in conjunction can the lymphatic system flush the overproduced aqueous humor back into the bloodstream.
The team built a 3D in vitro device, known as a microphysiological system (MPS), with a double layer of TM and SC cells, with a curvature that mimicked the conduit structure of lymphatic vessels in the eye. The researchers treated the "eye-on-a-chip" with the anti-inflammatory steroid dexamethasone, which significantly impaired the drainage.
This enabled the researchers to identify the culprit: A key receptor in TM cells, ALK5, responded to the steroid by downregulating a protein, vascular endothelial growth factor C (VEGFC), which normally loosens the endothelial junctions in SC cells, enabling fluid to pass through the endothelial wall. But that function was disrupted by ALK5/VEGFC signaling.
"This communication causes the Schlemm's canal junction abnormality," Lee said. "The junctions become really thickened or tightened under the steroid, and that junction change increased the resistance of the outflow, causing this glaucoma."
The researchers confirmed the role of the mechanism in a mouse model. The finding opens up two paths to treating glaucoma: blocking ALK5 function; or providing additional VEGFC to the eye along with the steroid treatment.
"We are now aiming to study other targets. There are some genes that people know are important for glaucoma, not just steroid-induced, and we could knock them out in these two cell types," Lee said. "It's complicated and difficult to target one cell type in conventional animal models, but in this system, we could do any genetic modification of these two cell types separately, and then combine them in the device to get a better understanding of these different mechanisms and different types of glaucoma."
Co-authors include postdoctoral researcher Anna Kolarzyk, Ph.D. '25, and W. Daniel Stamer, professor of ophthalmology at Duke University.
The researchers made use of the Cornell NanoScale Science and Technology Facility.
The research was supported by the National Institutes of Health and the BrightFocus Foundation.
