Abstract
Purpose :
Meibomian gland (MG) dysfunction is considered the leading cause of dry eye disease, a common, multifactorial disease with a global prevalence ranging from 5 to 50%. MG are modified sebaceous glands (SG) that secrete lipids at the ocular surface which increase the stability of the tear film. MG are composed of several acini organized around a central duct similar to a hair follicle (HF) without a hair shaft. It is well known that the hedgehog (Hh) pathway is required for the growth of HF and implicated in SG differentiation. However, its role in MG development remains unknown. In this study, we investigate how components of the Hh pathway interplay during MG development.
Methods :
To assess the role of Hh signaling in MG development we ablated Smoothened (Smo), required to activate Gli transcription factors, and Ift88, a component of the intraflagellar transport required for trafficking Hh pathway components within the primary cilium. Smo and Ift88 were selectively deleted in keratin 14 (K14)-expressing epithelial cells to generate K14cre;Smofx/fx and K14cre;Ift88fx/fx mice. To monitor the Hh activity, we utilized the Gli1-LacZ reporter mouse line. MG morphology was evaluated by lipid staining, histology, immunostaining, and two-photon microscopy.
Results :
First, we showed that meibocytes are ciliated, mainly in the developing part of the MG central duct and in the ductules at the junction between the central duct and the acini. Using the Gli1-LacZ reporter mouse, we found that in wild-type (WT) mice, Gli1 is highly expressed so the Hh pathway is highly activated in developing MG between E18.5 and P3, but dramatically decreased at P5 and in older mice. Surprisingly, the conditional ablation of the primary cilium in the K14-positive cells (K14cre;Ift88fx/fx mice) leads to an increase of MG size when compared to WT mice, mostly due to the development of supernumerary acini. In contrast, MG size was significantly reduced when Smo is conditionally deleted in K14-positive cells (K14cre;Smofx/fx mice).
Conclusions :
Our data suggest that the Hh pathway is required for MG development and could have implications in the regenerative process of MG. Moreover, ablation of primary cilia or Smo leads to opposite phenotypes during MG development suggesting a possible novel role of primary cilia in Hh regulation in MG tissue.
This is a 2021 ARVO Annual Meeting abstract.