 Hello, I'm Joe Casey and I am Sumplect Loganathan. Today we're going to tell you about some work that we've just published in the journal Human Mutation. If we consider the human eye, the outer surface of the eye is where light comes in, and that surface is known as the cornea. Of course, at the back of the eye are the photoreceptors called the retina. We're going to be talking about problems that occur in the cornea, specifically what happens when water accumulates in the cornea. If we consider a cross-section of the human eye, the cornea is made up of multiple different layers. In the top you'll see the outermost layer called the epithelium. In the center is the stroma layer, and at the back is the endothelial cell layer. Water tends to accumulate osmotically in the stroma of the cornea because of high concentrations of dissolved solute. Countering this, the endothelial cells pump water out of the stroma to maintain the fluid balance in the stroma. If there are problems with this process, then water flow causes accumulation of water in the corneal stroma. This thickens the corneal stroma and this leads to visual aberrations. If we consider the endothelial cell layer and blow it up and look at what's going on, a protein called SLC4A11 is found on the cell surface facing the stroma. Its job is to move water and it works in partnership with aquaporn 1 in the so-called apical surface to gather these to maintain the fluid pumping function of the endothelial cell layer. When this goes wrong, for example, in mutations of SLC4A11, water is not able to be moved out of the stroma. Fluid accumulation occurs and blinding corneal dystrophy disease occurs. In particular, congenital hereditary endothelial dystrophy, Fuchs endothelial corneal dystrophy, and Harboian syndrome are caused by mutations in SLC4A11. Unfortunately, the only viable therapeutic strategy for these diseases is corneal transplantation. Normally, membrane proteins like SLC4A11 are made in an organelle called the endoplasmic reticulum. After their biosynthesis, the protein traffics to the plasma membrane where it can carry out its normal function. In the case of mutant proteins like SLC4A11, the mutant protein may be retained in the endoplasmic reticulum, which means that the protein cannot carry out its normal function and disease arises. The focus of this paper is, therefore, can ER-retained SLC411 mutants be moved to the cell surface? And the second focus is, is this cell surface rescued SLC4A11 functional? And, does accumulation of mutant SLC4A11 cause cell death? So, to answer the first question, we used a couple of strategies to rescue the ER-retained SLC4A11 mutants to the cell surface. And we found that the ER-retained SLC4A11 mutants could be rescued to the plasma membrane. And also we found that using a water flux assay that this cell surface rescued SLC4A11 mutants are functional. So, while we are testing for this functional activity, we came across a bit more details that we established the therapeutic level of SLC4A11 activity for different disease states. So, for example, we found that in homozygous chip, there is less than 10% of SLC4A11 activity. And then in the case of heterozygous FECD condition, where the patient's manifest disease at later stage of life, there is close to 25% SLC4A11 activity. And in the case of chip carrier or the heterozygous chip condition, there is close to 60% SLC4A11 activity. The conclusion of this data is that we established benchmark SLC4A11 activity in order to either delay the disease onset or to cure the disease. So, the third focus of the paper is to investigate whether the accumulation of mutant SLC4A11 causes cell death. So, in order to find whether the mutant SLC4A11 accumulated in the endoplasmic reticulum causes cell death, we carried out a couple of assays and found that mutant SLC4A11 does not cause cell death. Conclusions from this study are that endoplasmic reticulum retained SLC4A11 mutants can be moved to the cell surface. Once that protein is moved to the cell surface, it is functional, and that the accumulation of mutant SLC4A11 in the endoplasmic reticulum by itself does not cause cell death. The implications of this work are quite significant. What this says is that if therapies are found that are able to move SLC4A11 to the cell surface, they should be able to treat the symptoms of corneal dystrophies that are caused by mutations of SLC4A11, holding out hope for people with these diseases. Thank you very much for watching this video.