The protein alpha-synuclein (aSN) has long been known as a main cause in Parkinson’s disease and Lewy Body Dementia, for example, when it forms lumpy protein aggregates that destroy cell function – but aSN in its natural form, without clumping, has not had a concrete, known function.
An international research team – led by Poul Nissen and Poul Henning Jensen from DANDRITE – has now demonstrated that natural aSN is an important activator of an essential calcium pump in the cell membrane.
Previously, the protein calmodulin was the only known activation factor of PMCA, but the researchers now add another important player and show that the activation of PMCA by aSN takes place in negatively charged membrane environments, complementary to calmodulin, which acts in neutral and possibly positively charged lipid environments.
Nissen explains: “The activation appears to be of particular importance in the presynaptic area of neurons, which is responsible for transmitting signals in the brain’s neural network. It is known that aSN accumulates in the presynaptic compartment, and our study shows, for the first time, that aSN and PMCA appear together in this area. In addition, we show that aSN stimulates calcium excretion from neurons, and not least that aSN significantly increases the activity of the PMCA.”
In addition, the researchers show by mathematical network modelling that PMCA activation likely to be of key importance for the calcium homeostasis, when neurons signal repeatedly, and calcium therefore enters the cell constantly. aSN’s activation of PMCA thus prevents a build up of calcium that would be toxic to the cell.
Henning Jensen elaborates: “Our laboratory has previously shown that early clump stages of aSN activate another calcium pump, SERCA, which sits in an internal organelle of the cell (endoplasmic reticulum), but SERCA is not activated much by soluble aSN. Oppositely, PMCA is activated a lot by soluble aSN and almost not by clumped aSN.”
Calcium regulation by PMCA and SERCA is essential for all cells, not least neurons, so if a pathological condition is associated with transitioning from natural aSN to clumped aSN, there is also a shift in aSN activation from PMCA to SERCA, and calcium regulation is thus strongly affected. It changes a multitude of processes, and ultimately leads to cell death.