We all know that your eyes can be affected by many things such as your nutrition, your lifestyle, and the sun, but did you know that the cilia in your body could affect your eyesight? Cilia are hair like projections and are found in many organisms that have multiple functions. In humans, cilia are found in and on the outside of almost all cell types and are adapted for various cellular functions such as signal transduction, sensory perception, and protein trafficking.
There are two types of cilia, motile and non-motile. Motile cilia are generally used for moving particles across the membrane and are found in the respiratory tract and ear. Non-motile, or immotile cilia, are non-moving cilia that are generally used to receive signals from other cells and can be found in the kidney and eye. These two different types of cilia are very important for the proper functioning of many systems in the human body and when the cilia do not function properly it is known as ciliopathy.
Ciliopathy refers to a group of disorders associated with mutations in the cilia proteins which can lead to abnormal formation and function of the cilia. Defects in the normal function of the cilia are seen in many disorders such as Senior-Loken syndrome, Bardet-Biedl syndrome, Joubert syndrome, Meckel-Gruber syndrome, and Retinitis Pigmentosa (RP). RP is the most common retinal degeneration worldwide and is characterized by non-functional photoreceptors which give rise to night blindness, tunnel vision, and can also lead to blindness (example of a scene viewed by a person with RP pictured to the right). The photoreceptors that become affected are known as the rods and cones, which provide acuity and color to your vision. These photoreceptors are composed of immotile cilia which are also known as the connecting cilium. The connecting cilium mediates the bi-directional transport of proteins and lipids and is dedicated to photoreception and signal transduction to the brain. This movement of proteins and lipids to the inner and outer segments of the photoreceptors is called intraflagellar transport (IFT).
Mutations in the IFT can affect the transportation of the proteins and can lead to photoreceptor degeneration. One such mutation that occurs commonly in X-linked RP is a mutation to the GTPase regulator protein (RPGR) of the cilia-centrosomal protein. This specific protein is known to affect the IFT directly and indirectly due to interactions with several other cilia proteins like IFT88/Polaris and RPGRIP1. This mutation in RPGR can be seen in vision loss, hearing dysfunctions, respiratory infections, and primary ciliary dyskinesia.
Currently, research on ciliopathies are becoming more and more relevant in literature and are being studied to better understand the effects of immotile cilia in mammals and the consequences of their mutations. One such example is gene therapy which is currently being tested for the potential in restoring long-term sight in dogs, mice, and some humans suffering from RP. RP is just one example of how a change to the cilia can affect the overall functions of the human body. The inability of the cilia to transport the needed proteins to the inner and outer segments of the photoreceptor cells will undeniably result in a progressive loss of vision, potentially leading to blindness.