Continuous Large Fluctuations In Intraocular Pressure Change The Trabecular Meshwork Structure

BackgroundGlaucoma is a group of diseases which characterized with the visual field defectcaused by lesions of the optic nerve; elevated intraocular pressure (IOP) is believed to bethe major risk factor for primary open-angle glaucoma (POAG). The current primarytreatment is to reduce IOP through a variety of methods, slowing disease progression.The pathology responsible for ocular hypertension in POAG involves the abnormalaccumulation of ECM proteins and the dysfunction of trabecular meshwork cells thatincrease resistance to the drainage of the aqueous humor through the trabecular pathway,and impair outflow capacity. The mechanisms which leading to the pathological changesin the trabecular meshwork are still unknown.Trabecular meshwork (TM) bridges the sulcus between the scleral spur andSchwabe’s line, consists of flat plate layer of collagen, similar to a sponge-like structure,and TM cells adhesion in the beams. The aqueous humor produced by the ciliary bodymust pass through the trabecular meshwork, to reach the outside of the Schlemm’s canal(SC) juxtacanalicular region (JCT). The JCT and/or SC inner wall endothelium are thesources of aqueous humor outflow resistance and regulate the IOP. Due to uniquephysical location and TM structure, autocrine and paracrine is the main way of TM cellsto adjust outflow resistance. In POAG, Studies confirmed that many cytokines,compounds, and nucleosides in the outflow of aqueous humor impact conventionaloutflow resistance to varying degrees and affect the TM stucture, but how to trigger thesesubstances release in the eye is puzzled.In healthy eye, there is biological rhythm IOP fluctuation and irregular IOPfluctuation caused by daily activities. Due to fluctuations in intraocular pressure andoutflow of aqueous humor, the trabecular meshwork suffers various forms ofbiomechanical. In the process of tissue development and morphogenetic maintenance, the biological stress has an important role for cellular behavior, altering the functional andstructural properties of tissues. Several studies have shown that the short-term variationsin IOP observed in glaucomatous populations are greater than those observed in normalpopulations. TM cells are a type of mechanical sensitive cells, and they are under variouschanges of biological stress in their lifetime, therefore the biological stress also affectedthe TM cells and TM tissue. So we speculate that a large fluctuation in intraocularpressure may be the cause for the pathological changes observed in the TM inglaucomatous eyes, which lead to the intraocular hypertension and glaucoma.To evaluate this hypothesis, we divided the experiment into three parts:1. Establishan animal model of IOP fluctuation in vivo, and proved that the the morphologicalchanges of TM resulted from IOP fluctuation, but not from mechanical injury;2. Afterseveral weeks experiment, the morphology of TM, the expression of extracellular matrix(ECM) and actin expression changed, which were similar to the changes observed inPOAG eye;3. To explore the possible mechanical signaling mechanism induced by IOPfluctuation.ObjectivesEstablish a fluctuating ocular hypertension model in vivo, proved that large IOPfluctuation induced the changes of TM morphological, the expression of ECM and actin,which were similar to the changes observed in POAG eye, and further explore thepossible mechanical signaling mechanism induced by IOP fluctuation.Methods1. After14days experiment, Hematoxylin-eosin (HE) staining was used to evaluatechanges of the thickness of cornea, sclera, density of ganglion cells and the morphology,thickness and density in the TM, ELISA was used to measured IL-6constration inaqueous humor, immunohistochemistry was used to detect CD45positive cells;2. After28days experiment, HE staining was used to evaluate changes of the thickness of cornea,sclera, density of ganglion cells, and the morphology, thickness and density in the TM,immunohistochemistry was used to detect α-smooth muscle actin (α-SMA), laminin (LA)and fibronectin (FN) expression in the TM;3. The conventional signal transductionproteins (Beta-catenin, JNK, ERks, RhoA) also detected by immunohistochemistry. Results1. After two weeks of daily IOP fluctuation, the cornea, sclera, TM thickness andIL-6in aqueous humor remained unchanged, and no CD45positive cells in TM, whereasthe density of TM dramatically increased.2. After several weeks of daily IOP fluctuation,the cornea, sclera and TM thickness remained unchanged, α-SMA, LA and FN werehighly expressed in SD rat TM tissue, and the positive percentage areas significantlyincreased, the density of TM dramatically increased. The IOP and the thickness of TMwere similar in the treated and control eyes.3. Rho A and ERKs positive areaspercentage significantly increased, but JNK and Beta-Catenin were not expressed.Conclusion1. The morphological changes of TM were resulted from IOP fluctuation, but notfrom mechanical injury;2. Large fluctuations in IOP promoted the synthesis of α-SMA, LA and FN in theTM and increased the density of the TM which were similar to the changes observed inPOAG eye;3. Large fluctuations in IOP may induces the Rho A and ERKs signal pathway,which lead to the pathological changes of the TM.