PT  - JOURNAL ARTICLE
AU  - Yohei Okubo
AU  - Kazunori Kanemaru
AU  - Junji Suzuki
AU  - Kenta Kobayashi
AU  - Kenzo Hirose
AU  - Masamitsu Iino
TI  - Inositol 1,4,5-trisphosphate receptor type2-independent Ca<sup>2+</sup> release from the endoplasmic reticulum in astrocytes
AID  - 10.1101/321042
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 321042
4099  - http://biorxiv.org/content/early/2018/06/26/321042.short
4100  - http://biorxiv.org/content/early/2018/06/26/321042.full
AB  - Accumulating evidence indicates that astrocytes are actively involved in the physiological and pathophysiological functions of the brain. Intracellular Ca2+ signaling, especially Ca2+ release from the endoplasmic reticulum (ER), is considered to be crucial for the regulation of astrocytic functions. Mice with genetic deletion of inositol 1,4,5-trisphosphate receptor type 2 (IP3R2) are reportedly devoid of astrocytic Ca2+ signaling, and thus widely used to explore the roles of Ca2+ signaling in astrocytic functions. While functional deficits in IP3R2-knockout (KO) mice have been found in some reports, no functional deficit was observed in others. Thus, there remains a controversy regarding the functional significance of astrocytic Ca2+ signaling. To address this controversy, we re-evaluated the assumption that Ca2+ release from the ER is abolished in IP3R2-KO astrocytes using a highly sensitive imaging technique. We expressed the ER luminal Ca2+ indicator G-CEPIA1er in cortical and hippocampal astrocytes to directly visualize spontaneous and stimulus-induced Ca2+ release from the ER. We found attenuated but significant Ca2+ release in response to application of norepinephrine to IP3R2-KO astrocytes. This IP3R2-independent Ca2+ release induced only minimal cytosolic Ca2+ transients but induced robust Ca2+ increases in mitochondria that are frequently in close contact with the ER. These results indicate that ER Ca2+ release is retained and is sufficient to increase the Ca2+ concentration in close proximity to the ER in IP3R2-KO astrocytes.We thank Y. Kawashima for technical assistance and Dr. B. Khakh (University of California at San Francisco) for providing the pZac2.1-gfaABC1D-Lck-GCaMP3 plasmid. This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI [Grant Numbers JP16K08543 (Y.O.), JP15H05648 (K.K.), and JP25117002 and JP25221304 (M.I.)] and grants from the Tokyo Society of Medical Sciences (Y.O.).