DIFFERENTIAL ROLE OF NEURONAL AND ASTROGLIAL TRPV4 CHANNELS IN CELLULAR VOLUME AND ION DYSREGULATION DURING ENERGY DEPRIVATION

The role of TRPV4 channels in brain ischemia is controversial, with studies revealing both detrimental and protective functions. This work aims to provide evidence regarding TRPV4 expression and its contribution to cellular swelling and ion disbalance under ischemic and osmotic stress, in order to clarify the role of this channel in brain ischemia.
We conducted immunohistochemical analysis on mouse hippocampal tissue sections, revealing TRPV4 expression in neurons and in a subpopulation of astrocytes. Dynamic confocal imaging and two-photon shadow imaging were performed in acute brain slices to study changes in cellular volume. Metabolic inhibition was induced perfusing brain slices with glucose-free aCSF containing the glucose analogue 2‑deoxyglucose and the cytochrome C antagonist sodium azide (“chemical ischemia”; c.i.). Neuronal swelling caused by hypoosmolar stress or c.i. was reduced by TRPV4 inhibition with HC-067047 or RN-1734, in contrast to the swelling in astrocytes, which was largely independent from TRPV4 activity. Using the membrane-permeable calcium indicator Fluo-4-AM, we show that HC-067047 diminished c.i.-elicited calcium signals in neurons and astrocytes, suggesting that TRPV4 promotes ischemia-induced calcium imbalance. c.i.-triggered astrocyte calcium signals were, however, strongly reduced by TTX, indicating that they arise as an indirect consequence of neuronal TRPV4 activity.
Taken together, our results indicate that TRPV4 contributes differentially to neuronal and astroglial swelling and ion dysregulation during compromised energy metabolism. A better understanding of its molecular mechanisms may reveal novel therapeutic targets to ameliorate ischemic brain injury.
Funded by the DFG, AL 2956/1-1 and RU 2795 ‘Synapses under Stress’ (Ro2327/13-1, 13-2).