High fat diet induces pre-type 2 diabetes with regional changes in corneal sensory nerves and altered P2X7 expression and localization

Abstract

Type 2 diabetes is one of the leading pathologies that increases the risk of improper wound healing. Obesity has become a major risk factor for this disease that is now considered to be the 4th highest cause of preventable blindness according to the World Health Organization. The cornea is the most densely innervated structure in the human body and senses even the slightest injury. In diabetes, decreased corneal sensitivity secondary to diabetic peripheral neuropathy can lead to increased corneal abrasion, ulceration, and even blindness. In this study, a diet induced obesity (DIO) mouse model of pre-Type 2 diabetes was used to characterize changes in sensory nerves and P2X7, a purinoreceptor, a pain receptor, and an ion channel that is expressed in a number of tissues. Since our previous studies demonstrated that P2X7 mRNA was significantly elevated in diabetic human corneas, we examined P2X7 expression and localization in the DIO murine model at various times after being fed a high fat diet. Fifteen weeks after onset of diet, we found that there was a significant decrease in the density of sub-basal nerves in the DIO mice that was associated with an increase in tortuosity and a decrease in diameter. In addition, P2X7 mRNA expression was significantly greater in the corneal epithelium of DIO mice, and the increase in transcript was enhanced in the central migrating and peripheral regions after injury. Interestingly, confocal microscopy and thresholding analysis revealed that there was a significant increase in P2X7 distal to the injury, which contrasted with a decrease in P2X7-expressing stromal sensory nerves. Therefore, we hypothesize that the P2X7 receptor acts to sense changes at the leading edge following an epithelial abrasion, and this fine-tuned regulation is lost during the onset of diabetes. Further understanding of the corneal changes that occur in diabetes can help us better monitor progression of diabetic complications, as well as develop new therapeutics for the treatment of diabetic corneal dysfunction.

Experimental modeling of cornea wound healing in diabetes: clinical applications and beyond

“…It serves as a pain receptor. Kneer et al 2 previously reported that P2×7 mRNA was significantly overexpressed in diabetic human corneas compared with controls. Therefore, the authors hypothesized that the P2×7 receptor acts to sense changes at the leading edge following an epithelial abrasion, with this form of regulation lost in diabetic eyes.…”

“…Diabetes alters corneal nerve structure44 and downregulate the release of neuropeptides, neurotrophins and growth factors 45. Kneer et al 2 reported a significant decrease in cornea sub-basal nerve density in DIO mice compared with controls, demonstrating similar established phenotypes to that of human diabetics. In this study, a DIO mouse model of type 2 diabetes was used to characterize changes in sensory nerves and P2X purinoceptor 7 (P2×7).…”

“…Briefly, mice are fed for 4–30 weeks with chow containing high fat and sugar (mostly sucrose and occasionally fructose). DIO mice are known to develop obesity, dyslipidemia and impaired glucose tolerance 2. DIO mice are primarily used in studies modeling obesity rather than diabetes, and the induction of sustained hyperglycemia is only achieved at 16–20 weeks after initiation of the diet 9.…”

“…Diabetes mellitus (DM) is an important chronic disease, affecting more than 342 million people worldwide, with a trend of increasing prevalence in the last decade. Patients with DM are at a higher risk of developing ocular complications and account for the major cause of acquired blindness in working-age populations 1–3. In recent years, much of the focus for public health system worldwide has been on secondary prevention of sight-threatening diabetic retinopathy.…”

Physiological assessment of high glucose neurotoxicity in mouse and rat retinal explants

“…An alteration in purinergic receptor subtype expression patterns has been observed in diabetes in the retina and other tissues (Ho et al, ; Kneer, Green, Meyer, Rich, & Minns, ; Mankus, Rich, Minns, & Trinkaus‐randall, ; Seref‐ferlengez, Maung, Schaffler, & Spray, ; Vindeirinho, Santiago, Cavadas, Ambrósio, & Santos, ). For example, in diabetic animals, an increase in levels of P2X 7 R has been reported in corneal epithelium (Kneer et al, ; Mankus et al, ), although a decrease in the expression of these receptors also was shown in osteocytes under HG conditions (Seref‐ferlengez et al, ). Likewise, the metabotropic receptors P2Y 2 R and P2Y 4 R suffer an overexpression in osteoblasts under diabetic conditions (Seref‐ferlengez et al, ), as do some adenosine receptors in the retina (Vindeirinho, Costa, Correia, & Santos, ).…”