Hyperlipidemia Affects Tight Junctions and Pump Function in the Corneal Endothelium.

Hyperlipidemia impacts on various diseases, such as atherosclerosis, hypertension, and diabetes mellitus. However, its influence, if any, on ocular tissues is largely unknown. Herein, we developed hyperlipidemic murine models by feeding 4-week-old male wild-type mice with a high-fat diet and apolipoprotein E knockout (ApoE-/-) mice with a high-fat diet or standard diet to investigate the corneal endothelial change under hyperlipidemic conditions. Oil Red O staining showed an accumulation of lipid droplets in corneal endothelial cells (CECs) of hyperlipidemic mice. Other manifestations included a reduced cell density and distorted cell morphology, a disruption of the endothelial cell tight junctions and adhesion junctions, a reduced number of surface microvilli, down-regulation of Na+-K+-ATPase expression and function, activation of oxidative stress, changes in mitochondrial ultrastructure, and increased apoptosis. CEC recovery after injury, moreover, was diminished in hyperlipidemic mice; and high palmitate levels were found in the aqueous humor. In vitro hyperlipemia model, moreover, was found to be associated with dose-dependent CEC cytotoxicity, altered cell morphology, reduced pump function, and an induction of oxidative stress, leading to functional and pathologic changes in the corneal endothelium.

Function of meibomian gland: Contribution of proteins.

The meibomian gland is the major contributor to the tear film lipid layer. It is generally accepted that meibomian gland secretions, i.e, meibum, play a critical role in the homeostasis of the tear film. Lipid components of meibum and their structure, as well as functions were intensively studied. However, the proteins from meibum have not attracted enough attention. This review summarizes current knowledge about protein components of the meibum, particularly their function on tear film and ocular surface, and changes in the proteins during meibomian gland dysfunction (MGD).

High-Fat Diet Induces Inflammation of Meibomian Gland.

Purpose: To determine if a high-fat diet (HFD) induces meibomian gland (MG) inflammation in mice. Methods: Male C57BL/6J mice were fed a standard diet (SD), HFD, or HFD supplemented with the peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist rosiglitazone for various durations. Body weight, blood lipid levels, and eyelid changes were monitored at regular intervals. MG sections were subjected to hematoxylin and eosin staining, LipidTox staining, TUNEL assay, and immunostaining. Quantitative RT-PCR and western blot analyses were performed to detect relative gene expression and signaling pathway activation in MGs. Results: MG acinus accumulated more lipids in the mice fed the HFD. Periglandular CD45-positive and F4/80-positive cell infiltration were more evident in the HFD mice, and they were accompanied by upregulation of inflammation-related cytokines. PPAR-γ downregulation accompanied activation of the mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling pathways in the HFD mice. There was increased acini cell apoptosis and mitochondria damage in mice fed the HFD. MG inflammation was ameliorated following a shift to the standard diet and rosiglitazone treatment in the mice fed the HFD. Conclusions: HFD-induced declines in PPAR-γ expression and MAPK and NF-κB signaling pathway activation resulted in MG inflammation and dysfunction in mice.

A Novel Tissue-Engineered Corneal Stromal Equivalent Based on Amniotic Membrane and Keratocytes.

Purpose: To investigate a novel strategy in constructing tissue-engineered corneal stromal equivalent based on amniotic membrane and keratocytes. Methods: The ultrathin amniotic membrane (UAM) was laminated, with corneal stromal cells (CSCs) distributed between the space of the layered UAMs. Calcein AM staining was used to evaluate cellular viability, morphology, and arrangement. Immunostaining, qRT-PCR, and Western blot were performed to detect gene and protein expression in keratocytes. Optical coherence tomography visualized the cross sections and thickness of the UAM construction. The microstructure of the CSC-secreted extracellular matrix (ECM) was investigated by scanning electron microscopy and transmission electron microscopy (TEM). To evaluate the feasibility of the multilayer UAM-CSC lamination for surgery, the corneal substitute was used to perform lamellar keratoplasty. Slit lamp microscopy and corneal fluorescein staining were performed in postsurgery observation. Results: The CSCs maintained their keratocyte phenotype and secreted well-organized ECM on the aligned UAM surface. The four-layer UAM-CSC lamination attained half thickness of the human cornea (250 ± 18 µm) after 8 weeks' culture, which also showed promising optimal transparency. In TEM images, the CSC-generated ECM displayed stratified, multilayered lamellae with orthogonal fibril arrangement, which was similar to the human cornea microstructure. Furthermore, the stromal equivalent was successfully preformed in lamellar keratoplasty. Four weeks post surgery, the substitute was well integrated into the recipient cornea and completely epithelialized without myofibroblast differentiation. Conclusions: Our study established a novel 3D biomimetic corneal model to replicate the corneal stromal organization with multilayer UAM, which was capable of promoting the development of corneal stroma-like tissues in vitro, establishing a new avenue for basic research and therapeutic potential.

Hyperlipidemia induces meibomian gland dysfunction.

PURPOSE: To investigate the pathological changes of the meibomian gland (MG) and ocular surface in Apolipoprotein E knockout (ApoE-/-) mice and to investigate the association of meibomian gland dysfunction (MGD) with hyperlipidemia. METHODS: Total plasma cholesterol was measured in different ages of ApoE-/- and wild type (WT) mice, whilst the ocular surfaces were observed by slit-lamp biomicroscopy. MG sections were subjected to H&E staining, Oil Red O staining, TUNEL assay and immunostaining. Quantitate RT-PCR and Western blot analyses were performed to detect the relative gene expression in MGs. The 5-month-old ApoE-/- mice were administered with rosiglitazone or GW9662 + rosiglitazone via oral gavage for 2 months to determine their effect on MG pathological change. RESULTS: We found eyelid abnormality, MG dropout, abnormal MG acinar morphology, dilated MG duct and plugging of the MG orifice in ApoE-/- mice. MG acini in ApoE-/- mice showed exaggerated lipid accumulation. Abnormal keratinization increased in MG duct, accompanied with decreased proliferation and increased apoptosis in ApoE-/- mice. Inflammatory cells infiltrated into the surrounding microenvironment of MG acini, and the NF-κB signaling pathway was activated in MG acinar cells. Oxidative stress was evident in MG acinar cells of ApoE-/- mice. Further investigation showed downregulation of PPAR-γ in MG acinar cells of ApoE-/- mice. PPAR-γ agonist rosiglitazone treatment reduced the morbidity of eyelid, as well as corneal pathological changes and MG inflammation in ApoE-/- mice. CONCLUSION: MGD and hyperlipidemia are closely associated in ApoE-/- mice, which represent a new model to study the pathophysiology of MGD related to dyslipidemia.