Store-operated calcium entry is essential for glial calcium signalling in CNS white matter

Abstract

‘Calcium signalling’ is the ubiquitous response of glial cells to multiple extracellular stimuli. The primary mechanism of glial calcium signalling is by release of calcium from intracellular stores of the endoplasmic reticulum (ER). Replenishment of ER Ca2+ stores relies on store-operated calcium entry (SOCE). However, despite the importance of calcium signalling in glial cells, little is known about their mechanisms of SOCE. Here, we investigated SOCE in glia of the mouse optic nerve, a typical CNS white matter tract that comprises bundles of myelinated axons and the oligodendrocytes and astrocytes that support them. Using quantitative RT-PCR, we identified Orai1 channels, both Stim1 and Stim2, and the transient receptor potential M3 channel (TRPM3) as the primary channels for SOCE in the optic nerve, and their expression in both astrocytes and oligodendrocytes was demonstrated by immunolabelling of optic nerve sections and cultures. The functional importance of SOCE was demonstrated by fluo-4 calcium imaging on isolated intact optic nerves and optic nerve cultures. Removal of extracellular calcium ([Ca2+]o) resulted in a marked depletion of glial cytosolic calcium ([Ca2+]i), which recovered rapidly on restoration of [Ca2+]o via SOCE. 2-aminoethoxydiphenylborane (2APB) significantly decreased SOCE and severely attenuated ATP-mediated calcium signalling. The results provide evidence that Orai/Stim and TRPM3 are important components of the ‘calcium toolkit’ that underpins SOCE and the sustainability of calcium signalling in white matter glia.

TRPM3_miR-204: a complex locus for eye development and disease

“…TRPM3 was also strongly immuno-localized to the inner plexiform layer (IPL) and a subset (~40%) of cells in the GCL with weak immunolabeling of the INL and outer plexiform layer (OPL) of mouse retina [153]. Quantitative PCR revealed that Trpm3 transcripts represented the second most abundant Trpm transcript in mouse optic nerve head (ONH), whereas qPCR and immuno-localization ranked TRPM3 channels as the main TRP channel in optic nerve glial cells (astrocytes and oligodendrocytes) [152,154].…”

Strategies for Neuroprotection in Multiple Sclerosis and the Role of Calcium

“…SOCE occurs in neurons upon Orai1 and Orai2 interaction with STIM1 and/or STIM2 [123], and this process appears to be essential for neuronal growth [124]. Oligodendrocytes and astrocytes (at least in the optic nerve of mice) also express Orai1 as well as STIM1 and STIM2 [125]. Microglia express Orai1 and STIM1 [126].…”

White matter repair and treatment strategy after intracerebral hemorrhage

“…ATP‐mediated inositol 1,4,5‐triphosphate (IP3) relies on the Ca 2+ signaling pathway. Astrocytes and oligodendrocytes express store‐operated calcium entry (SOCE) channels TRPM3 and Orai/Stim, which are essential for glial Ca 2+ calcium signaling and play a role in the conduction, physiological, and pathological, such as in multiple sclerosis, stroke, and traumatic injury . A recent clinical study demonstrated that less white matter hyperintensities on MRI were closely related to a greater cerebral vascular density and diameter and a higher cerebral blood flow (Figures and ) …”