Keratocyte-specific ablation of Tgfbr1, Tgfbr2, and Smad4 manifests differentially keratoconus-like phenotype in mice

Abstract

Purpose : We previously showed that deletion of Transforming Growth Factor beta (TGF-β) signaling pathway via ablation of its type-2 receptor (TbR2) and Smad4 resulted in thin stroma phenotype similar to the human corneal ectasia disease known as keratoglobus. Herein, we tested the role of Tgfbr1 in the same scenario.

Methods : Transforming growth factor-b type 1 receptor (Tgfbr1) was designed to be conditionally knocked out (Tgfbr1^kera-cko) from keratocytes. A novel triple transgenic mice: Kera^rtTA;tetO-Cre;TbR1^f/f, were administered with doxycycline (Dox) from postnatal day 1 (P1) to various developing stages including postnatal day 42 (P42). Optical coherence tomography (OCT) was performed to examine corneal thickness and radius of curvature. Bulging appearance was measured by in vivo microscope and compared to the wild-type littermates (WT). We further compare corneal thickness and morphology among Tgfbr1^Kera-cko, Smad4^Kera-cko and Tgfbr2^Kera-cko mice.

Results : The OCT scanning appeared a doom-shaped cornea in the WT but an ectasia cornea with hyper-reflectivity of the corneal stroma was observed in Tgfbr1^kera-cko. Moreover, overall corneal thickness in Tgfbr1^kera-cko becomes ~60% thinner than that of WT at P42. In the hematoxylin and eosin staining, we observed the uneven thinning and missing stroma in Tgfbr1^kera-cko. Unlike Tgfbr2^Kera-cko or Smad4^Kera-cko which revealed 45-50% thinner stroma throughout the entire cornea, more severe phenotypes including the uneven thinning and disappearing stroma were observed in Tgfbr1^kera-cko. Moreover, the radius of corneal curvature is larger in Tgfbr1^kera-cko as compared to that in the WT. In vivo microscope and OCT imaging also revealed corneal bulging suggesting ectasia in Tgfbr1^kera-cko mice.

Conclusions : These corneal phenotypes in the Tgfbr1^kera-cko transgenic mouse strain suggested that a Smad-independent signaling pathway might play an important role in maintaining stromal thickness. Corneal bulging due to the uneven thinning of stroma is a characteristic of corneal ectasia disease such as keratoglobus and keratoconus. Tgfbr1^kera-cko mimic the morphological changes observed in keratoconus indicates that Smad4-independent signaling pathway, may serve as a potential genetic model for human keratoconus.

This is a 2020 ARVO Annual Meeting abstract.