Changes in Epithelial and Stromal Corneal Stiffness Occur with Age and Obesity

Abstract

The cornea is avascular, which makes it an excellent model to study matrix protein expression and tissue stiffness. The corneal epithelium adheres to the basement zone and the underlying stroma is composed of keratocytes and an extensive matrix of collagen and proteoglycans. Our goal was to examine changes in corneas of 8- and 15-week mice and compare them to 15-week pre-Type 2 diabetic obese mouse. Nanoindentation was performed on corneal epithelium in situ and then the epithelium was abraded, and the procedure repeated on the basement membrane and stroma. Confocal imaging was performed to examine the localization of proteins. Stiffness was found to be age and obesity dependent. Young’s modulus was greater in the epithelium from 15-week mice compared to 8-week mice. At 15 weeks, the epithelium of the control was significantly greater than that of the obese mice. There was a difference in the localization of Crb3 and PKCζ in the apical epithelium and a lack of lamellipodial extensions in the obese mouse. In the pre-Type 2 diabetic obese mouse there was a difference in the stiffness slope and after injury localization of fibronectin was negligible. These indicate that age and environmental changes incurred by diet alter the integrity of the tissue with age rendering it stiffer. The corneas from the pre-Type 2 diabetic obese mice were significantly softer and this may be a result of changes both in proteins on the apical surface indicating a lack of integrity and a decrease in fibronectin.

An eye on the dog as the scientist's best friend for translational research in ophthalmology: Focus on the ocular surface

“…16.2-33.1 71,72 1.3 71 1.1 73 25-40 74 6 1.7-3.0 84,85 1.1-1.8 24,85 0.0053 11,24 0.013-0.054 11,24 Abbreviation: The morphology of the canine lacrimal drainage system is remarkably similar to that of humans, except for a longer nasolacrimal duct (notably in long-nosed dogs), and the presence of accessory duct openings into the nasal cavity. 92 In both species, tear drainage begins with the lower and upper nasolacrimal puncta and canaliculi in the medial canthus, joining into a lacrimal sac in the bony lacrimal fossa, and extending into the nasolacrimal duct that runs through an osseous channel towards the nasal cavity.…”

“…71,73 The elastic modulus of the cornea is reportedly higher in rodents, although the methodology used was different. 74,75 Corneal rigidity should be considered in comparative studies in which the biophysical attributes of the cornea are important (e.g., wound healing, keratoprosthesis). The corneal endothelium shares a similar morphological blueprint among species (single cell layer, honey-comb pattern), while the cellular density varies from 3233 cells/mm 2 in rabbits, 2875 cells/mm 2 in mice, 2818 cells/mm 2 in dogs, 2732 cells/mm 2 in humans, and 2242 cells/mm 2 in rats.…”

“…Differences in collagen intertwining, along with the absence of Bowman's membrane in laboratory species, explain the vast disparity in stiffness of the anterior stroma (16.2, 1.3, and 1.1 kPa) and posterior stroma (2.5, 0.5, and 0.4 kPa) in humans, dogs, and rabbits, respectively 71,73 . The elastic modulus of the cornea is reportedly higher in rodents, although the methodology used was different 74,75 . Corneal rigidity should be considered in comparative studies in which the biophysical attributes of the cornea are important (e.g., wound healing, keratoprosthesis).…”

An Eye on the Dog as the Scientist’s Best Friend for Translational Research in Ophthalmology: Focus on the Ocular Surface

“…86,87 The elastic modulus of the cornea is reportedly higher in rodents, although the methodology used was different. 88,89 Corneal rigidity should be considered in comparative studies in which the biophysical attributes of the cornea are important (eg., wound healing, keratoprosthesis). The corneal endothelium shares a similar morphological blueprint among species (single cell layer, honey-comb pattern), while the cellular density varies from 3233 cells/mm 2 in rabbits, 2875 cells/mm 2 in mice, 2818 cells/mm 2 in dogs, 2732 cells/mm 2 in humans, and 2242 cells/mm 2 in rats.…”

Alterations in corneal biomechanics underlie early stages of autoimmune-mediated dry eye disease

“…Mice deficient in autoimmune regulator gene (Aire) have a disruption in central tolerance that results in Th1 polarization of CD4+ T cells (secreting IFNg) [22], an immune cell response that also occurs in patients with a variety of dry eye diseases including Sjögren's [23]. Aire-deficient mice exhibit classic signs of autoimmune-mediated exocrinopathy and associated aqueous-deficient dry eye over a matter of weeks, allowing for an interrogation of the molecular and cellular underpinnings of the disease in the absence of the effects of aging [24][25][26].…”