Effects of Dyslipidemia in Diet-Induced Obesity and Aging on the Meibomian Gland and Ocular Surface

Purpose: Using a mouse model of diet-induced obesity where dyslipidemia is present, this dissertation evaluates the hypothesis that dyslipidemia alters meibum composition which in turn impacts the tear film, meibomian gland and ocular surface morphology. The first aim determines if alterations in plasma (systemic) lipids during dyslipidemia are mirrored by changes in meibum lipids and tear production using a diet-induced mouse model of obesity. The second aim determines if meibomian glands and the ocular surface morphology change during dyslipidemia and the third aim determines if dyslipidemia is associated with changes in meibum-synthesizing peroxisomes. Methods: 5-week-old male C57/BL6 mice were fed a normal (ND; 15% kcal fat) or an obesogenic high-fat diet (HFD; 42% kcal milk fat) for 10 weeks. Body weight and adiposity (epidydimal adipose tissue weight) were recorded. Plasma and meibum samples were obtained for targeted lipidomic analysis of cholesteryl esters (CE), triglycerides (TG), ceramides (Cer) and sphingomyelins (SM) using Nano-ESI-MS/MS and LC-ESI-MS/MS. Eyelids were harvested for meibomian gland morphological analysis and corneas obtained for scanning electron evaluation of ocular surface microplicae. Aged mice were also included for comparison. Meibocyte peroxisomes were evaluated by transcriptomic and immunohistochemical analysis of peroxisomal PEX 14, ABCD1, ABCD3 and ACOX1. Results: HFD mice gained ≈ 30% more weight and showed significant dyslipidemia with ≈ 2-3-fold increase in plasma CE, TG, and SM than ND mice. Increased body weight correlated with plasma CE, TG and SM, p<0.01-<0.0001. HFD mice also showed increased saturation in most meibum lipid species. The change in plasma TGs mirrored meibum TGs. Alterations in meibum were accompanied by excessive (2-fold more) aqueous tear production and ≈ 25% larger meibomian gland area and reductions in corneal epithelial microplicae coverage. Aging was associated with a downregulation (≈2-4) in peroxisomal enzymes PEX14, ABCD1 and ABCD3 in the presence of dyslipidemia. Conclusions: Dyslipidemia (diet-induced or age-induced) is linked to MGD. The increased saturation of meibum and the associated excessive aqueous tear production as well as re-organization of ocular surface (corneal) epithelial microplicae are consistent with MGD and dry eye. Controlling the plasma lipid profile may be an effective strategy for managing MGD patients

Dyslipidemia and Meibomian Gland Dysfunction: Utility of Lipidomics and Experimental Prospects with a Diet-Induced Obesity Mouse Model

Meibomian gland dysfunction (MGD) is the leading cause of dry eye disease and loss of ocular surface homeostasis. Increasingly, several observational clinical studies suggest that dyslipidemia (elevated blood cholesterol, triglyceride or lipoprotein levels) can initiate the development of MGD. However, conclusive evidence is lacking, and an experimental approach using a suitable model is necessary to interrogate the relationship between dyslipidemia and MGD. This systematic review discusses current knowledge on the associations between dyslipidemia and MGD. We briefly introduce a diet-induced obesity model where mice develop dyslipidemia, which can serve as a potential tool for investigating the effects of dyslipidemia on the meibomian gland. Finally, the utility of lipidomics to examine the link between dyslipidemia and MGD is considered

Obese Mice with Dyslipidemia Exhibit Meibomian Gland Hypertrophy and Alterations in Meibum Composition and Aqueous Tear Production

Background: Dyslipidemia may be linked to meibomian gland dysfunction (MGD) and altered meibum lipid composition. The purpose was to determine if plasma and meibum cholesteryl esters (CE), triglycerides (TG), ceramides (Cer) and sphingomyelins (SM) change in a mouse model of diet-induced obesity where mice develop dyslipidemia. Methods: Male C57/BL6 mice (8/group, age = 6 wks) were fed a normal (ND; 15% kcal fat) or an obesogenic high-fat diet (HFD; 42% kcal fat) for 10 wks. Tear production was measured and meibography was performed. Body and epididymal adipose tissue (eAT) weights were determined. Nano-ESI-MS/MS and LC-ESI-MS/MS were used to detect CE, TG, Cer and SM species. Data were analyzed by principal component analysis, Pearson's correlation and unpaired t-tests adjusted for multiple comparisons; significance set at p <= 0.05. Results: Compared to ND mice, HFD mice gained more weight and showed heavier eAT and dyslipidemia with higher levels of plasma CE, TG, Cer and SM. HFD mice had hypertrophic meibomian glands, increased levels of lipid species acylated by saturated fatty acids in plasma and meibum and excessive tear production. Conclusions: The majority of meibum lipid species with saturated fatty acids increased with HFD feeding with evidence of meibomian gland hypertrophy and excessive tearing. The dyslipidemia is associated with altered meibum composition, a key feature of MGD