Non-contact confocal calcium imaging of murine corneal nerves.

Abnormal corneal nerve function and associated disease is a significant public health concern. It is associated with prevalent ocular surface diseases, including dry eye disease. Corneal nerve dysfunction is also a common side effect of refractive surgeries, as well as a symptom of diseases that cause peripheral neuropathies.

Quantifying the Corneal Nerve Whorl Pattern.

Purpose: The corneal nerves within the sub-basal nerve plexus (SBNP) display a distinctive whorl-like pattern, a highly dynamic structure that could be a marker of diseases. Previous studies have reported a decrease in whorl nerve density in patients with diabetes, indicating an avenue for noninvasive monitoring of diabetic neuropathy. However, conflicting results have since been reported, highlighting the need for improved quantitative analysis of the corneal whorl.

Acyl-CoA:wax alcohol acyltransferase 2 modulates the cone visual cycle in mouse retina.

The daylight and color vision of diurnal vertebrates depends on cone photoreceptors. The capability of cones to operate and respond to changes in light brightness even under high illumination is attributed to their fast rate of recovery to the ground photosensitive state. This process requires the rapid replenishing of photoisomerized visual chromophore (11-cis-retinal) to regenerate cone visual pigments.

Mouse models in studies on the etiology of evaporative dry eye disease.

Evaporative dry eye disease (DED) is a common ocular condition impacting the quality of life of millions of patients worldwide. The etiology of evaporative DED is related to dysfunction of meibomian glands (MGs), resulting in suboptimal yield or lipid composition of secreted meibum. The clinical manifestation of evaporative DED involves mechanical obstruction of the MG orifice and decreased tear film stability that leads to chronic eye irritation, inflammation, and progressive damage to the cornea and surrounding tissue.

Deficiency in Acyl-CoA:Wax Alcohol Acyltransferase 2 causes evaporative dry eye disease by abolishing biosynthesis of wax esters.

Lipids secreted by the meibomian glands (MGs) of the eyelids are essential to the protection of the eye's surface. An altered meibum composition represents the primary cause of evaporative dry eye disease (DED). Despite the critical importance of the meibum, its biosynthetic pathways and the roles of individual lipid components remain understudied.

The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates.

Vitamin A is an essential nutrient necessary for numerous basic physiological functions, including reproduction and development, immune cell differentiation and communication, as well as the perception of light. To evade the dire consequences of vitamin A deficiency, vertebrates have evolved specialized metabolic pathways that enable the absorption, transport, and storage of vitamin A acquired from dietary sources as preformed retinoids or provitamin A carotenoids. This evolutionary advantage requires a complex interplay between numerous specialized retinoid-transport proteins, receptors, and enzymes.

Protective role of carotenoids in the visual cycle.

Exposure to light and accumulation of aberrant visual cycle by-products causes stress in the retina. The physical and chemical properties of carotenoids may provide protection against such scenario. These pigments exist in retinas of many vertebrates, including humans.

Transcription factor ISX mediates the cross talk between diet and immunity.

The intestinal epithelium is a major site for the conversion of dietary β-carotene to retinaldehyde by the enzyme BCO1. The majority of retinaldehyde is further metabolized to retinol (vitamin A), esterified and packaged into triacylglycerol-rich chylomicrons for bodily distribution. Some serve on-site for the synthesis of retinoic acid, a hormone-like compound, which exerts pleiotropic and dominant effects on gastrointestinal immunity.

Impact of LCA-Associated E14L LRAT Mutation on Protein Stability and Retinoid Homeostasis.

Vitamin A (all-trans-retinol) is metabolized to the visual chromophore (11-cis-retinal) in the eyes and to all-trans-retinoic acid, a hormone like compound, in most tissues. A key enzyme in retinoid metabolism is lecithin:retinol acyltransferase (LRAT), which catalyzes the esterification of vitamin A. The importance of LRAT is indicated by pathogenic missense and nonsense mutations, which cause devastating blinding diseases.

Allosteric modulation of the substrate specificity of acyl-CoA wax alcohol acyltransferase 2.

The esterification of alcohols with fatty acids is a universal mechanism to form inert storage forms of sterols, di- and triacylglycerols, and retinoids. In ocular tissues, formation of retinyl esters is an essential step in the enzymatic regeneration of the visual chromophore (11--retinal). Acyl-CoA wax alcohol acyltransferase 2 (AWAT2), also known as multifunctional -acyltransferase (MFAT), is an integral membrane enzyme with a broad substrate specificity that has been shown to preferentially esterify 11--retinol and thus contribute to formation of a readily available pool of retinoids in the eye.

Molecular Basis for Vitamin A Uptake and Storage in Vertebrates.

The ability to store and distribute vitamin A inside the body is the main evolutionary adaptation that allows vertebrates to maintain retinoid functions during nutritional deficiencies and to acquire new metabolic pathways enabling light-independent production of 11- retinoids. These processes greatly depend on enzymes that esterify vitamin A as well as associated retinoid binding proteins. Although the significance of retinyl esters for vitamin A homeostasis is well established, until recently, the molecular basis for the retinol esterification enzymatic activity was unknown.

Genetic dissection in a mouse model reveals interactions between carotenoids and lipid metabolism.

Carotenoids affect a rich variety of physiological functions in nature and are beneficial for human health. However, knowledge about their biological action and the consequences of their dietary accumulation in mammals is limited. Progress in this research field is limited by the expeditious metabolism of carotenoids in rodents and the confounding production of apocarotenoid signaling molecules.

Transport of vitamin A across blood-tissue barriers is facilitated by STRA6.

Vitamin A bound to retinol binding protein 4 (RBP4) constitutes the major transport mode for retinoids in fasting circulation. Emerging evidence suggests that membrane protein, STRA6 (stimulated by retinoic acid 6), is the RBP4 receptor and vitamin A channel; however, the role of STRA6 in vitamin A homeostasis remains to be defined in vivo We subjected Stra6-knockout mice to diets sufficient and insufficient for vitamin A and used heterozygous siblings as controls. We determined vitamin A levels of the eyes, brain, and testis, which highly express Stra6, as well as of tissues with low expression, such as lung and fat.

Characterization of the Role of β-Carotene 9,10-Dioxygenase in Macular Pigment Metabolism.

A family of enzymes collectively referred to as carotenoid cleavage oxygenases is responsible for oxidative conversion of carotenoids into apocarotenoids, including retinoids (vitamin A and its derivatives). A member of this family, the β-carotene 9,10-dioxygenase (BCO2), converts xanthophylls to rosafluene and ionones. Animals deficient in BCO2 highlight the critical role of the enzyme in carotenoid clearance as accumulation of these compounds occur in tissues.

A genetic dissection of intestinal fat-soluble vitamin and carotenoid absorption.

Carotenoids are currently investigated regarding their potential to lower the risk of chronic disease and to combat vitamin A deficiency. Surprisingly, responses to dietary supplementation with these compounds are quite variable between individuals. Genome-wide studies have associated common genetic polymorphisms in the BCO1 gene with this variability.