Excitotoxic glutamate causes neuronal insulin resistance by inhibiting insulin receptor/Akt/mTOR pathway

• Published in: Molecular brain Vol. 12; no. 1; p. 112
• Main Authors: Pomytkin, Igor, Krasil'nikova, Irina, Bakaeva, Zanda, Surin, Alexander, Pinelis, Vsevolod
• Format: Journal Article
• Language: English
• Published: England BioMed Central 19-12-2019; BMC
• Subjects: AKT protein; Calcium (intracellular); Calcium (mitochondrial); Central insulin resistance; Excitotoxicity; Fluorescent indicators; Gene expression; Glutamate excitotoxicity; Glycogen; Glycogen synthase kinase 3; Insulin; Insulin resistance; Kinases; Micro Report; Mitochondria; Phosphorylation; Rapamycin; Rhodamine; Serine; Signal transduction; TOR protein; Traumatic brain injury; Tyrosine; Variance analysis; Central insulin resistance; Insulin; Glutamate excitotoxicity
• ISSN: 1756-6606; 1756-6606
• DOI: 10.1186/s13041-019-0533-5

An impaired biological response to insulin in the brain, known as central insulin resistance, was identified during stroke and traumatic brain injury, for which glutamate excitotoxicity is a common pathogenic factor. The exact molecular link between excitotoxicity and central insulin resistance remains unclear. To explore this issue, the present study aimed to investigate the effects of glutamate-evoked increases in intracellular free Ca
concentrations [Ca
]
and mitochondrial depolarisations, two key factors associated with excitotoxicity, on the insulin-induced activation of the insulin receptor (IR) and components of the Akt/ mammalian target of rapamycin (mTOR) pathway in primary cultures of rat cortical neurons.
Changes in [Ca
]
and mitochondrial inner membrane potentials (ΔΨ
) were monitored in rat cultured cortical neurons, using the fluorescent indicators Fura-FF and Rhodamine 123, respectively. The levels of active, phosphorylated signalling molecules associated with the IR/Akt/mTOR pathway were measured with the multiplex fluorescent immunoassay.
When significant mitochondrial depolarisations occurred due to glutamate-evoked massive influxes of Ca
into the cells, insulin induced 48% less activation of the IR (assessed by IR tyrosine phosphorylation, pY
), 72% less activation of Akt (assessed by Akt serine phosphorylation, pS
), 44% less activation of mTOR (assessed by mTOR pS
), and 38% less inhibition of glycogen synthase kinase β (GSK3β) (assessed by GSK3β pS
) compared with respective controls. These results suggested that excitotoxic glutamate inhibits signalling via the IR/Akt/mTOR pathway at multiple levels, including the IR, resulting in the development of acute neuronal insulin resistance within minutes, as an early pathological event associated with excitotoxicity.