In a new genetic βb1-CTGF mouse model for primary open-angle glaucoma elevated intraocular pressure is accompanied by apoptotic retinal ganglion cell loss

Abstract

Purpose : Primary open-angle glaucoma is one of the most common causes for blindness worldwide. Although an elevated intraocular pressure (IOP) is the main risk factor, the exact pathology remained indistinguishable. Therefore, it is necessary to have appropriate models to investigate these mechanisms. In this study, we analyzed a transgenic glaucoma mouse model (βb1-CTGF) to elucidate new possible mechanisms of the disease focusing on the early onset of the axonal loss driven by the increased IOP.

Methods : IOP was measured in βb1-CTGF and wildtype (Co) mice at 5, 10, and 15 weeks of age. At 15 weeks, retinal flatmounts (n=12/group) and cross-sections (n=9/group) were prepared. Immunohistology was performed with markers against retinal ganglion cells (RGCs; Brn-3a), apoptosis (cleaved caspase 3), microglia (Iba1), activated microglia (ED1), and the complement system (C3 and membrane attack complex = MAC). Cells were counted via ImageJ. Groups were compared using Student’s t-test.

Results : At 5 and 10 weeks, the IOP in the βb1-CTGF and Co group was comparable (p>0.05). After 15 weeks, a significant elevated IOP was measured in βb1-CTGF mice (Co: 11.6±0.3 mmHg, CTGF: 15.1±0.9 mmHg; p<0.001). On flatmounts, significantly fewer Brn-3a⁺ RGCs was observed in the βb1-CTGF group (3399.4±114.6 cells/mm²) compared to Co (4186.9±282.9 cells/mm²; p=0.02). These results were confirmed on retinal cross-sections. Here, a significant loss of RGCs was noted in the βb1-CTGF mice (Co: 43.6±3.0 cells/mm, CTGF: 25.5±2.8 cells/mm; p<0.001). Additionally, significant more cleaved caspase 3⁺ RGCs were seen in the βb1-CTGF group (15.4±1.8 %) compared to Co (6.6±1.6 %; p=0.002). Neither the total number of microglia nor the number of activated microglia was altered in 15 weeks old mice (p>0.05). Additionally, no changes were observed regarding the complement components C3 and MAC at the investigated points in time (p>0.05).

Conclusions : A previous study revealed a loss of axons in optic nerves of the βb1-CTGF mouse model. Here, we observed a loss of RGCs after IOP elevation. At this point, no alterations could be noted regarding the microglia and the complement system. However, we assume that the CTGF mouse could serve as a good model for better understanding the pathomechanisms in primary open-angle glaucoma.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.