Mechanosensitive Piezo2 channels are functionally expressed in retinal astrocytes: implications for blood flow autoregulation.

Question: Retinal astrocytes are known to play a critical role in the development of the retinal vasculature, in regulating retinal homeostasis and in maintaining the inner blood retinal barrier. They have also been implicated in retinal blood flow control, but the mechanisms through which they modulate vascular tone are poorly understood. Here we show that astrocytes express the novel mechanosensitive ion channel, Piezo2, which we believe may allow them to monitor and modulate the contractile state of the retinal vasculature.
Methods: Piezo2 expression was investigated by immunolabelling of rat retinal flatmount preparations and human retinal astrocytes in culture. siRNA knockdown and Fura-2 calcium microfluorimetry in human retinal astrocytes was used to investigate functional Piezo2 channel activity.
Results: Piezo2 was expressed in retinal astrocytes. Piezo2 expressing end foot projections were observed to wrap around the vasculature and connexion 43 (GJP1) was observed to be expressed in the regions between the end foot processes and the underlying smooth muscle layer of retinal arterioles. Cultured human retinal astrocytes also expressed Piezo2. Hypotonic-induced stretch of retinal astrocytes evoked a transient increase in intracellular calcium which was maintained in the presence of the swell-activated chloride channel inhibitor 1mM DIDS. This response was significantly inhibited in cells transfected with siRNA against Piezo2, but not scrambled siRNA, strongly suggesting that this stretch-activated response is produced by the action of the Piezo2 channel.
Conclusion: Piezo 2 channels are expressed at a molecular and functional level in retinal astrocytes. Their potential activation in astrocytic end-feet during periods of increased blood pressure and their precise role in modulating retinal vascular tone now warrants further investigation.