Glaucoma is popularly understood as a disease in which overpressure in the eye results in damage to the optic nerve, the nerve responsible for vision, and ultimately blindness. 

BY MIRIAM KOLKO

Miriam Kolko (b. 1972) is a specialist in ophthalmology. She conducted research in the USA for five years where she held both a Fulbright Scholarship and completed a PhD and subsequently a postdoctoral degree. Miriam completed her original medical specialisation in the Capital Region of Denmark and subsequently took up a fellowship in glaucoma. She has been an associate professor at the University of Copenhagen since 2012. In 2014, Miriam was appointed consultant physician with responsibility for the glaucoma unit at Roskilde University Hospital. In addition, she is the principal investigator in a team of researchers at the Department of Neuroscience and Pharmacology at the Panum Insti - tute, University of Copenhagen.

Project: ’Glaucoma beyond IOP - importance of mitochondrial function in Müller cells' ability to protect retinal ganglion cells’ 

Grantee: Miriam Kolko and the Department of Neuroscience and Pharmacology, University of Copenhagen

Amount: DKK 3,841,007 from VELUX FONDEN

Eye pressure, called Intraocular Pressure (IOP), is still recognised as the main risk factor for the eye disease called glaucoma, but the cause of the optic nerve damage has not been established. As such, the consensus is that glaucoma is a spectrum of different eye diseases, all of which result in damage to the optic nerve.

Imbalance and inadequate energy supply cause optic nerve damage

At one end of the spectrum, an imbalance in IOP results in damage to the optic nerve, but at the other end, the cause of glaucoma is more complex and is conceivably due to inadequate energy supply to the retinal nerve cells and the optic nerve.

Müller cells are essential in maintaining nerve cell energy supply. Another important function is the ability of the cells to maintain balance in a substance called glutamate, which aids nerve signalling to the brain. Although glutamate is essential for signalling between nerve cells, and hence crucial for vision, an accumulation of glutamate will cause the nerve cells to die o f due to overstimulation. Müller cells prevent this very type of overstimulation by removing excess glutamate from nerve cells.

Oxidative stress affects the ability of support cells to project nerve cells

During the project period, a number of laboratory models were set up for glaucoma to observe interactions between nervecells and Müller cells. The hypothesis is that in people with glaucoma, the Müller cells are impaired and therefore unable to protect the nerve cells. 

The aim is consequently to investigate how the energy level of Müller cells in fuences their ability to protect nerve cells. This was investigated in the frst instance by altering energy availability and by subjecting Müller cells to so-called oxidative stress. 

Collaboration with the center for healthy aging

The grant has made it possible to elaborate on research to date by applying translational research concepts. To that end, a collaborative project has been initiated with the Center for Healthy Aging (University of Copenhagen) and Rigshospitalet (Denmark's leading teaching hospital) which includes patients with glaucoma. 

The project has been approved by a medical ethics committee, and the patients are subjected to oxidative stress. Besides measuring blood fow, blood samples are obtained before and after oxidative stress. The samples are analysed for mitochondrial activity in order to determine mitochondrial performance in glaucoma patients as compared with peer control patients.

Nerve cell energy generator put through its paces

The preliminary findings indicate that the ability of Müller cells to remove excess glutamate from nerve cells is impaired by the different types of stress. Both oxidative stress and variable energy availability affects the functioning of Müller cells. Because cells' main energy production is handled by their ‘energy generators’ (the mitochondria), these are focal for the project's research. 

Through a number of collaborative projects, the investigators are thus seeking to demonstrate the importance of mitochondrial functioning for Müller cell function. A study currently nearing completion clearly demonstrates that mitochondria are essential for Müller cell maintenance in response to reduced energy availability. 

The hypothesis is thus that well-functioning mitochondria are particularly vital during stress. In order to demonstrate this, a cell model was set up in which cultured nerve cells had ‘wells’ of cultured Müller cells inserted in them. This system forms the basis for studying the two cell types in close proximity to each other. 

The investigators examine how a change in the habitual state (homeostasis) of the Müller cell a fects its ability to sustain nerve cells. So far, the research has demonstrated that a change in energy availability impairs the ability of Müller cells to absorb glutamate and hence their ability to sustain nerve cells. 

It has also been demonstrated that mitochondrial function is crucial for Müller cells' gene and protein expression, which also a fects their homeostasis and ultimately their ability to protect nerve cells. 

Figure 3. The period 1996-2011 has seen a significant increase in the incidence of glaucoma cases. Women with glaucoma age 50+ are represented in 10-year age intervals. (Kolko et al., PLoS One. 2015 Jul 16;10(7)). Figure: Miriam Kolko