NF‐Y‐dependent regulation of glutamate receptor 4 expression and cell survival in cells of the oligodendrocyte lineage

Abstract

Glutamate receptor subunit 4 (GluA4) is highly expressed by neural cells sensitive to excitotoxicity, and is the predominant subunit expressed by oligodendrocyte precursor cells (OPC) during a key period of vulnerability to hypoxic‐ischemic injury. Therefore, transcriptional networks downstream of excitotoxic GluA4 activation represent a promising area for therapeutic intervention. In this work, we identify the CCAAT binding transcription factor NF‐Yb as a novel transcriptional regulator of Gria4 (GluA4 gene), and a controller of excitotoxic death in the oligodendroglial lineage. We describe a novel regulatory region within Gria4 containing CCAAT sequences whose binding by NF‐Yb is regulated by excitotoxicity. Excitotoxicity‐induced alterations in NF‐Yb binding are associated with changes in Gria4 transcription, while knockdown of NF‐Yb alters the transcription of reporter constructs containing this regulatory region. Data from immortalized and primary OPC reveal that RNAi and pharmacological disruption of NF‐Yb alter Gria4 transcription, with the latter inducing apoptosis and influencing a set of apoptotic genes similarly regulated during excitotoxicity. These data provide the first definition of a trans‐acting mechanism regulating Gria4, and identify the NF‐Y network as a potential source of pharmacological targets for promoting OPC survival.

Glutamatergic signaling between neurons and oligodendrocyte lineage cells: Is it synaptic or non‐synaptic?

“…Upon synaptic glutamate release, AMPARs in OPCs are exposed to agonist only briefly (few milliseconds at most), while in vitro exposure is sustained (several hours) and likely results in desensitization of AMPARs (Robert & Howe, ). In addition, prolonged exposure of OPCs and Oli‐neu cells to AMPAR agonists is known to trigger downregulation of AMPAR subunits, particularly those which render AMPARs Ca 2+ ‐permeable (Begum et al, ; Hossain, Liu, Fragoso, & Almazan, ; Jourdi et al, ; Mangiavacchi & Wolf, ). Therefore, decrease in proliferation and lineage progression of OPCs upon prolonged exposure to AMPAR agonists observed in vitro may be mediated by reduced entry of Ca 2+ which is a key regulator of proliferation and differentiation (Hamilton, Hubbard, & Butt, ; Toth, Shum, & Prakriya, ; Yang, Xiong, & Yao, ).…”

Glial Cell AMPA Receptors in Nervous System Health, Injury and Disease

“…The prominent expression of Ca 2+ permeable AMPAR in the OL lineage places these cells at threat of injury from excitotoxic conditions (Figure 2B). Indeed, AMPAR-mediated excitotoxicity has been described in numerous in vitro studies using cultures of both OPC/preOL [45,170,171] and differentiated OL [65,163,197]. Importantly, excitotoxicity in these cells is associated with excessive Ca 2+ influx [65,171], thus expression of Ca 2+ permeable AMPAR, as described in Section 2.2, appears to render these cells vulnerable to high levels of extracellular glutamate.…”

“…Apoptosis is closely regulated by the induction of pro- and anti-apoptotic Bcl-2 genes [322,323], so the pathways connecting pathophysiological AMPAR stimulation may provide an interesting range of targets for therapeutic research. Related to this idea, we recently examined the transcriptional events induced in OPC following pathophysiological AMPAR stimulation [45]. To focus our work we searched for potential regulators of Gria4, the gene encoding GluA4, via an in silico analysis.…”

“…AMPAR function in the nervous system is not restricted to neuronal cells. Indeed many glial cells exhibit functional AMPAR whose activation regulates a range of important cellular activities including cell migration [38,39], morphological development and re-structuring [40,41] proliferation and differentiation [42,43], transcriptional regulation [44,45], survival [46], and the regulation of various ion channels [42,47,48]. Importantly, overactivation of AMPAR plays a key role in mediating cellular injury to neuronal and glial cells alike.…”

“…The high levels of Ca 2+ uptake by mitochondria have also been related to the inhibition of mitochondrial respiration and the release of cytochrome c, thus triggering apoptosis [75,86,87]. Glutamate excitotoxicity also increases the expression of pro-apoptotic Bak protein, while also decreasing anti-apoptotic Bcl-2 protein levels [71], and altering the transcription and function of the nuclear factor Y (NF-Y) complex [45], a transcription factor closely linked to the control of apoptotic cell death [88] (see Section 8).…”