A GPR119 Signaling System in the Murine Eye Regulates Intraocular Pressure in a Sex-Dependent Manner

Abstract

Purpose: GPR119 is a G protein-coupled receptor that may be the endogenous target for 2-oleoylglycerol (2-OG), a lipid related to the endocannabinoid family of neuromodulators. Interest in GPR119 has centered on its role in regulating insulin secretion; however, the role of GPR119 has not been examined in the eye. The purpose of this study was to explore a potential GPR119-based signaling system in the murine eye.

Methods: We used a combination of RT-PCR, immunohistochemistry, lipid measurement, and IOP measurement in a normotensive mouse model, with GPR119 knockout mice as controls.

Results: We detected GPR119 mRNA and protein in the anterior eye of the mouse and cow, with GPR119 mRNA levels elevated in female relative to male mice. GPR119 protein expression is most prominent in structures near the angle, including trabecular meshwork, as well as iris and corneal epithelium. We detected 2-OG in the anterior eye and detected alterations in lipid levels in GPR119 knockout versus wild type and also by sex. Last, we found that 2-OG preferentially reduces IOP in female mice in a normotensive model.

Conclusions: In summary, we offer evidence for a GPR119-based signaling system in the mammalian eye, with receptors, ligands, and function in the form of a reduction in IOP. Notably this reduction in pressure is restricted to female mice.

Figure 1

GPR119 mRNA is expressed in anterior eye of mouse and cow. (A) RT-PCR shows a band (arrows) at the molecular weight expected for GPR119 mRNA in female mouse anterior eye relative to male. (B) Quantitative PCR shows elevated levels of GPR119 mRNA in female mice relative to male mice. (C) Tissues from cow also express mRNA for GPR119 in corneal epithelium (Epi), corneal endothelium (Endo), retina, and trabecular meshwork (TM).

Figure 2

Overview of GPR119 expression in anterior eye of the mouse. (A, B) GPR119 staining in anterior eye segments of wild-type C57Bl6 female (A) and GPR119 knockout female (B) mice. The most prominent staining in the pigmented tissue is in several structures near the angle (arrows), as well as corneal epithelium. (C) The same antibody in albino/unpigmented CD1 strain mice yields the same staining pattern but also reveals strong iridial staining. (D) Corneal epithelium is also stained. Scale bars: (A, B) 100 μm; (C) 150 μm; (D) 25 μm.

Figure 3

GPR119 expression in anterior eye of the mouse near the angle. (A) Overview of GPR119 staining near the angle with insets (numbered boxes). (A1) Channel-like structure lateral to the angle. (A2) Top image shows structure believed to be trabecular meshwork just distal to the inner end of the angle. Bottom image shows same structure turned 90 degrees (i.e., seen from “above”). (A3) Large blood vessel at the base of iris. (A4) Left image: Z series of box 4 turned to show channel-like structure at tip of angle. Right image shows same structure turned 90 degrees (i.e., seen from the “side”). Scale bars: (A) 50 μm; (A1–A3) 5 μm; (A4) NA.

Figure 4

Cannabinoid-related lipid profile in wild-type versus GPR119 knockout mice and by sex. Left column lists cannabinoid-related lipids out of a panel of lipids that were seen to change in GPR119 knockout versus wild-type mice. Right column shows that 2-OG levels were higher in female versus male GPR119 knockout mice.

Figure 5

Topical 2-OG lowers IOP in female but not male mice. IOP was measured in mice following topical corneal application of 2-OG (5 mM). IOP in female mice was reliably reduced by 2-OG at 1 and 4 hours (A, B) but not male mice (C, D); (E, F) 2-OG does not lower IOP in female GPR119 knockout mice. *P < 0.05, **P < 0.01 by paired t-test.

Figure 6

MBX2982 lowers IOP in female mice. IOP was measured in mice following topical corneal application of synthetic GPR119 ligand MBX2982 (3 mM) which reduced IOP in female mice at 1 hour (A). (B) In female GPR119 knockout mice, MBX2982 raised IOP at 1 hour. *P < 0.05, **P < 0.01 by paired t-test.