Human Astrocytes Express Functional Protease-Activated Receptors that Increase Their Reactive Phenotype Under Certain...

Protease-activated receptors are G protein-coupled receptors with a novel activation mechanism by which proteases cleave the N-terminus revealing a tethered ligand that binds to the second extracellular loop leading to receptor activation. We have previously shown that protease-activated receptor 2 (PAR2) activation impairs hippocampal synaptic transmission and is neuroprotective in in vitro excitotoxic assays, both of which are astrocyte-dependent. We have also shown that AC264613, a blood-brain barrier-permeable PAR2 activator, results in behavioural changes associated with depression-like behaviour and recently revealed that AC264613 reduces astrocyte reactivity and amyloid load in a mouse model of amyloid pathology. However, whether functional protease-activated receptors are present in human astrocytes and if they alter their reactivity state is unknown.

Commercially available human astrocytes were cultured in serum and serum-free media, and the presence of functional PARs was investigated using standard Ca²⁺ imaging techniques. Immunocytochemistry was used to examine the consequence of PAR activation on their reactive phenotype.

We reveal that functional PAR1 and PAR2 are present in commercially available human astrocytes. Their activation increased glial fibrillary acidic protein (GFAP) expression only after short-term culture but did not affect complement component 3 (C3) or guanylate-binding protein 2 (Gbp2) expression under any conditions tested. In contrast, no change in reactivity was observed following exposure to inflammatory stimuli.

Overall, these data highlight that human astrocytes express functional PARs, but their activation may result in different phenotypic changes from those seen in mouse astrocytes.