FGF-signaling in Meibomian Gland (MG) Homeostasis of Adult Mice

Abstract

Purpose : Meibomian glands (MGs) secret lipids (meibum) via a holocrine mechanism which requires perpetual regeneration and renewal of acinar cells to maintain MG homeostasis. We investigate the role of fibroblast growth factor (FGF) as one of the potential modulating mechanism(s) of MG homeostasis in this study.

Methods : Individual MGs were isolated from tarsal plates of adult mice of either sex by laser capture microdissection. RNAs from either MGs or surrounding eyelid tissue were extracted for RT-PCR to examine the expression of FGFs and FGF receptors (FGFRs). To delineate the role of FGFR2 in MGs, a triple transgenic mouse line (Krt14-rtTA; tetO-Cre, Fgfr2^flox/flox, referred as Fgfr2^CKO) was generated, in which the floxed Fgfr2 gene in keratin-14 (Krt14)-expressing epithelial cells can be ablated by Cre recombinase upon doxycycline (Dox) induction. Pathological changes in the MGs of mutant mice were examined by immunohistochemical analyses of various MG markers.

Results : Among the 22 FGF members examined, at least 9 different FGFs were detected by RT-PCR using the RNAs from either MGs or eyelids of adult mice (n=3) . Among them, FGF-7 and FGF-10 (both being FGFR2 ligand) were expressed at a higher level than other FGFs. Three of the four FGFRs, FGFR 1, 2 and 3, were highly expressed in the MGs. To investigate the role of FGFR2 in MGs, two-month old Fgfr2^CKO mice were fed with Dox chow to induce gene deletion in MGs and other Krt-14 expressing cells. After receiving Dox for two weeks, Fgfr2^CKO mice developed severe MG atrophy, associated with reduced meibum production and development of ocular surface abnormalities similar to those noted in human evaporative dry eye disease (DED). Further immunohistochemical analyses showed that FGFR2 deletion led to poor MG basal cell proliferation and impaired acinar cell differentiation with only minimal impact on MG ductal cells.

Conclusions : Three FGFRs are expressed in adult mouse MGs which can be regulated by various FGF ligands produced in MGs and in eyelids. Activation of FGFR2 by FGF-7 and/or FGF-10 is likely to be essential for MG homeostasis via regulating MG proliferation and differentiation.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.