(1) Background: Our previous data indicated that disturbance of the Transforming Growth Factor beta (TGFB) signaling pathway via its Type-2 Receptor (TGFBR2) can cause a Corneal Ectasia (CE)-like phenotype. The purpose of this study is to elucidate whether the SMAD4-dependent signaling pathway is involved in the TGFBR2-related CE-like pathogenesis. (2) Methods:
Smad4 was designed to be conditionally knocked out from keratocytes. Novel triple transgenic mice,
KerartTA; Tet-O-Cre; Smad4flox/flox (
Smad4kera-cko), were administered with doxycycline (Dox). Optical Coherence Tomography (OCT) was performed to examine Central Corneal Thickness (CCT), Corneal Radius, Anterior Chamber and CE-like phenotype and compared to the littermate Control group (
Smad4Ctrl). (3) Results: The OCT revealed normal cornea in the
Smad4Ctrl and a CE-like phenotype in the
Smad4kera-cko cornea, in which the overall CCT in
Smad4kera-cko was thinner than that of
Smad4Ctrl at P42 (
n = 6,
p < 0.0001) and showed no significant difference when compared to that in
Tgfbr2kera-cko. Furthermore, the measurements of the Anterior Chamber and Corneal Radius indicated a substantial ectatic cornea in the
Smad4kera-cko compared to
Smad4Ctrl. The H&E staining of
Smad4kera-cko mimics the finding in the
Tgfbr2kera-cko. The positive immunostaining of cornea-specific marker K12 indicating the cell fate of cornea epithelium remained unchanged in
Smad4kera-cko and the Proliferating Cell Nuclear Antigen (PCNA) immunostaining further indicated an enhanced proliferation in the
Smad4kera-cko. Both immunostainings recapitulated the finding in
Tgfbr2kera-cko. The Masson’s Trichrome staining revealed decreased collagen formation in the corneal stroma from both
Smad4kera-cko and
Tgfbr2kera-cko. The collagen type 1 (Col1a1) immunostaining further confirmed the reduction in collagen type 1 formation in
Smad4kera-cko. (4) Conclusions: The aforementioned phenotypes in the
Smad4kera-cko strain indicated that the SMAD4-dependent signaling pathway is involved in the pathogenesis of the CE-like phenotype observed in
Tgfbr2kera-cko.
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