Fibroblast Growth Factor Receptor 2 (FGFR2) Is Required for Meibomian Gland Homeostasis in the Adult Mouse

Abstract

PurposeLittle is known about the signaling mechanisms controlling meibomian gland (MG) homeostasis and the pathogenic processes leading to MG atrophy and dysfunction in dry eye disease (DED). We investigated the role of fibroblast growth factor receptor 2 (FGFR2) in the MG homeostasis of adult mice.MethodsA triple transgenic mouse strain (Krt14-rtTA; tetO-Cre; Fgfr2flox/flox), referred to as Fgfr2CKO mice, was generated in which the Fgfr2 gene is ablated by Cre recombinase in keratin 14 (Krt14)-expressing epithelial cells on doxycycline (Dox) induction. FGFR2 expression in normal human and mouse MGs was evaluated by immunohistochemistry. Pathologic MG changes in transgenic mice with conditional deletion of FGFR2 were examined by lipid staining, histology, and immunostaining.ResultsFGFR2 was highly expressed in normal human MGs and adult mouse MGs. Two-month-old Fgfr2CKO mice fed Dox-containing chow for 2 weeks developed severe MG atrophy. MG acinar atrophy in the Fgfr2CKO mice was associated with reduced lipid (meibum) production and the development of clinical findings similar to those in humans with evaporative DED related to MG dysfunction (MGD). Immunohistochemical analyses showed that FGFR2 deletion severely affected proliferation and differentiation of MG acinar cells but affected MG ductal cells to a lesser extent.ConclusionsFGFR2 deletion results in significant MG acinar atrophy and clinical manifestations of MGD in Fgfr2CKO mice, suggesting that MG homeostasis is FGFR2 dependent. The Fgfr2CKO mice with inducible MG atrophy can serve as a valuable animal model for investigating the pathogenesis of MGD and developing novel therapeutic strategies for MGD-related DED.

Meibomian Gland Dysfunction: What Have Animal Models Taught Us?

“…An in vivo mouse genetic study showed that conditional gene deletion of Fgfr2b, an FGF receptor 2 (FGR2) isoform, in epidermal cells causes striking abnormalities in hair and sebaceous glands without affecting animal survival [103]. Reneker and colleagues [104] used a triple transgenic mouse strain (Krt14-rtTA; tetO-Cre; Fgfr2 flox/flox ), referred to as Fgfr2 CKO mice, to study the role of FGFR2 in Meibomian gland homeostasis. After a 2-week induction period, these mice developed severe Meibomian gland atrophy associated with reduced lipid (meibum) production (Oil-red-O staining), as well as evaporative DED symptoms related to MGD in human subjects [42,79].…”

Histopathology and selective biomarker expression in human meibomian glands

“…Downloaded from proliferation and renewal. 20 Nevertheless, the significance of FGFR2 and its ligands in human MG homeostasis awaits further investigations. In summary, while our study is limited by the small sample size due to the poor availability of donor eyelids, the histopathological and biomarker analyses of MG tissues from a young donor with normal-appearing MGs, a young donor with ductal obstruction and two donors in their early 60s shed insights into the diverse underlying pathogenic mechanisms of MGD.…”

“…Using an inducible conditional knockout mouse model, we have demonstrated that FGFR2 signalling plays an essential role in MG acinar proliferation and renewal. 20 Nevertheless, the significance of FGFR2 and its ligands in human MG homeostasis awaits further investigations.…”

“…Tissue sections (5 µm) were treated with xylene; rehydrated in a decreased ethanol series; and subjected to H&E staining, immunofluorescence or immunohistochemistry. 20 For antigen retrieval of immunostaining, tissue sections were boiled in 10 mM sodium citrate buffer for 10 min and then cooled to room temperature. To block endogenous peroxidase activity, sections were treated with 3% hydrogen peroxide in PBS for 20 min.…”

“…Keratin 16 (Krt16) is typically expressed in stratified squamous epithelia and certain glandular tissues. [20][21][22] Overexpression of Krt16 and its type II pair Krt6, along with Krt17 overexpression, is associated with keratinocyte hyperproliferation and considered to be hallmarks for psoriasis, a chronic inflammatory skin disease. 23 24 To explore the role of these cytokeratins in MGD, we examined the expression of keratins 16, 6a and 17 in the MGs of 30M, 36F and 64M ( figure 3).…”