Inorganic Polyphosphate Regulates AMPA and NMDA Receptors and Protects Against Glutamate Excitotoxicity via Activation of P2Y Receptors

Abstract

Glutamate is one of the most important neurotransmitters in the process of signal transduction in the CNS. Excessive amounts of this neurotransmitter lead to glutamate excitotoxicity, which is accountable for neuronal death in acute neurological disorders, including stroke and trauma, and in neurodegenerative diseases. Inorganic polyphosphate (PolyP) plays multiple roles in the mammalian brain, including function as a calcium-dependent gliotransmitter mediating communication between astrocytes, while its role in the regulation of neuronal activity is unknown. Here we studied the effect of PolyP on glutamate-induced calcium signal in primary rat neurons in both physiological and pathological conditions. We found that preincubation of primary neurons with PolyP reduced glutamate-induced and AMPA-induced but not the NMDA-induced calcium signal. However, in rat hippocampal acute slices, PolyP reduced ion flux through NMDA and AMPA receptors in native neurons. The effect of PolyP on glutamate and specifically on the AMPA receptors was dependent on the presence of P2Y1 but not of P2X receptor inhibitors and also could be mimicked by P2Y1 agonist 2MeSADP. Preincubation of cortical neurons with PolyP significantly reduced the initial calcium peak as well as the number of neurons with delayed calcium deregulation in response to high concentrations of glutamate and resulted in protection of neurons against glutamate-induced cell death. As a result, activation of P2Y1 receptors by PolyP reduced calcium signal acting through AMPA receptors, thus protecting neurons against glutamate excitotoxicity by reduction of the calcium overload and restoration of mitochondrial function.

Inorganic polyphosphate is produced and hydrolyzed in F0F1-ATP synthase of mammalian mitochondria

“…It also should be noticed that we observed the activity of F 0 F 1 -ATPase in millimolar concentration (Figure 2 and 3). Although the average polyP concentration in the brain is 50-70 mM [3], polyP is highly compartmentalized [13,15,18] and concentration of polyP in some of the compartments (such as mitochondria) can reach millimolar level. Measurements of polyP in isolated mitochondria using polyP-DAPI fluorescence.…”

“…Moreover, the similarity in chemical structure between ATP (three orthophosphates) and polyP (multiple orthophosphates) spreads over to further similarity in the function they both exert in physiology. Thus, polyP plays an important signaling role in the mammalian brain: located to and released from ATP-containing vesicles [13]; it activates neurons and astrocytes through P2Y1 (known to be mostly specific to ATP and ADP) purinoreceptors [14,15]. Interestingly, polyP is shown to be an energy source for extracellular ATP production [16,17].…”

Influence of Energy Deficiency on the Molecular Processes ofSubstantia Nigra Pars CompactaCell for Understanding Parkinsonian Neurodegeneration: A Comprehensive Biophysical Computational Model

“…We suggest that the excitotoxic loss of SNc neurons in PD might be precipitated by energy deficiency (Muddapu et al, 2019). Any therapeutic interventions that can reduce ionic flux through these glutamatergic receptors or enhance energy production can be neuroprotective in nature (Bathina and Das, 2015;Maiolino et al, 2019;Wallace et al, 2010).…”

Oxytocin Receptor Signaling in Vascular Function and Stroke

“…Another current strategy to improve outcomes post-ischemia is the enhancement of cell survival through inhibiting apoptosis (Caglayan et al, 2019;Chen et al, 2020;Jia et al, 2020), reducing excitotoxicity (Maiolino et al, 2019;Jia et al, 2020), and improving metabolism (Ren et al, 2008). The general measures of reduced apoptosis are taken as a reduction in caspase activation and a higher ratio of Bcl-2 to Bax (Chen et al, 2020;Jia et al, 2020).…”

“…The general measures of reduced apoptosis are taken as a reduction in caspase activation and a higher ratio of Bcl-2 to Bax (Chen et al, 2020;Jia et al, 2020). Combatting excitotoxicity often ultimately focuses either on reducing glutamate signaling, mostly through NMDA receptors, or reducing intracellular calcium accumulation and waves in connected cells (Maiolino et al, 2019;Pietrogrande et al, 2019). The improvement of metabolism is closely tied to glucose uptake to sustain cells in the absence of production (Ren et al, 2008).…”