Angiopoietin-1 Knockout Mice as a Genetic Model of Open-Angle Glaucoma

Abstract

A leading cause of blindness worldwide, glaucoma is often caused by elevated intraocular pressure (IOP) due to impaired aqueous humor outflow from the anterior chamber through Schlemm's canal (SC) and the trabecular meshwork. Despite the large clinical burden, glaucoma research and drug development are hindered by a limited selection of preclinical models that accurately recapitulate human disease. Here, we propose that Angpt1 conditional knockout mice may provide one such model. Angiopoietin/TEK (ANGPT/TEK) signaling is crucial for SC formation and integrity in mice and humans, and mice lacking TEK or its ligand ANGPT1 develop a hypomorphic SC insufficient for normal aqueous humor outflow. Methods: We used a comprehensive histology and physiology approach to characterize the glaucoma phenotype of Angpt1 inducible knockout mice, especially focusing on retina morphology and function. Results: Angpt1 deletion resulted in persistent ocular hypertension beginning in the first month after birth and leading to decreased visual acuity with age due to glaucomatous neuropathy. In the neural retina, we identified marked and specific loss of the retinal ganglion cells, whereas other retinal neurons exhibited largely normal morphology and patterning. Electroretinogram recordings demonstrated reduced scotopic threshold response, further indicating loss of retinal ganglion cell function. Conclusions: These findings highlight the potential of Angpt1 conditional knockout mice as a valuable new glaucoma model. Translational Relevance: Currently, few reliable, rapid-onset genetic glaucoma models are available, and Angpt1 knockout mice will provide an additional tool for studies of IOP-induced neural damage, mechanisms of disease progression, and novel treatment strategies.

Cellular crosstalk regulates the aqueous humor outflow pathway and provides new targets for glaucoma therapies

“…Using neural crest-specific Wnt1 -cre, we have shown that deletion of Angpt1 in the uveal tract recapitulates the glaucoma phenotype of whole-body knockouts, confirming the TM origin of SC-regulating ANGPT1. In comparison to our previous studies in whole body inducible Angpt1 knockouts, neural-crest specific Angpt1 knockout mice showed slightly higher IOP at 10 weeks of age 56 ( Angpt1 ΔNC: Control: 11.5, mutant: 21.2, Δ9.7 mmHg; Angpt1 -whole body: Control: 15.4, mutant: 20.9, Δ5.5 mmHg), possibly due to strain differences or improved excision of TM Angpt1 in Angpt1 ΔNC mice.…”

“…RGCs were quantified as previously described 56 . Briefly, enucleated eyes were immersion fixed (2% formaldehyde in phosphate-buffered saline, pH 7.5) before retinas were dissected and blocked (5% donkey serum, 2.5% BSA, 0.5% Triton X100 in Tris buffered saline pH 7.5, overnight at 4°).…”

Differential roles of neural crest- and endothelial-derived FOXC2 in trabecular meshwork and Schlemm’s Canal in glaucomatous pathology

“…Moreover, sTIE2 is capable of binding angiopoietins to prevent them from activating TIE2 signaling (29). Provided the increase expression of MMPs in NC-Foxc2 -/mice and the crucial role of ANGPT/TIE2 signaling in SC development (25)(26)(27)40), we hypothesized that increased MMP activity in the TM may mediate cleavage of TIE2 in SC endothelium, resulting in higher production of sTIE2, impairment of ANGPT/TIE2 signaling, and impaired SC morphogenesis. To investigate this mechanism, we collected conditioned media from cultured human dermal LECs (HDLECs) treated with either DMSO vehicle or the MMP inhibitor GM-6001 at dosages shown to inhibit sTIE2 shedding in cultured HUVECs (29) or impair tubulogenesis in three-dimensional culture assays (47).…”

“…In contrast to the limbal and conjunctival lymphatics which originate from emergent lymphatic vessels on the nasal side of the developing eye, SC morphogenesis is initiated from the blood limbal and radial vascular plexuses during postnatal development (19,22). Several key lymphatic vascular signaling pathways directly regulate SC morphogenesis and maintenance, such as vascular endothelial growth factor (VEGF)-C/ VEGF receptor (VEGFR)-3 (18), PROX1 (20), and angiopoietin (ANGPT)/TIE2 (21,(23)(24)(25)(26). Of clinical importance, TIE2 mutations have been previously identified in a subset of patients with PCG (23).…”

Angiopoietin-1 Mimetic Nanoparticles for Restoring the Function of Endothelial Cells as Potential Therapeutic for Glaucoma

“…Recently it was demonstrated that the integrity and functionality of SC is maintained by the signaling between angiopoietin 1 (Angpt-1) and its tyrosine kinase receptor Tie [9]. Reduction or even inactivation of the Angpt-1/Tie2 signaling during adulthood in duces SC degeneration and is a key factor for IOP disbalance [4,9,10]. Restoring this path way by adding recombinant Angpt-1 as a therapeutic agent is not straightforward becaus Angpt-1 is prone to aggregation and is therefore not suitable as a therapeutic agent [11] Recently, an Angpt-1 mimetic peptide sequence (HHHRHSF) was discovered [12][13][14].…”