Conditioned medium from overly excitatory primary astrocytes induced by La³⁺ increases apoptosis in primary neurons via upregulating the expression of NMDA receptors

Abstract

Lanthanum (La) can accumulate in the brain and impair learning and memory. However, the underlying mechanism of La-induced neurotoxicity has remained elusive. Under physiological conditions, it has been reported that moderately excitatory astrocytes play an important role in the regulation of neuronal signals and synaptic plasticity. However, under pathological conditions, overly excitatory astrocytes can release excess excitatory transmitters, such as glutamate (Glu) and d-serine, and induce the over-activation of NMDA receptors (NMDAR) in neurons, ultimately leading to neuronal excitotoxicity. To date, limited work has been performed with respect to whether La can induce neuronal excitotoxicity by inducing astrocytes to become overexcited. In this study, in vitro models of primary culture rat cortical astrocytes and neurons were established. First, the astrocytes were treated with 0.125 mM, 0.25 mM and 0.5 mM lanthanum chloride (LaCl3) for 24 h, and the supernatants were collected as a conditioned medium (CM) which is denoted as CM (La3+); then, the neurons were treated with CM (La3+) for 48 h. The results illustrate that LaCl3 treatment significantly upregulated the mRNA and protein expression levels of metabotropic glutamate receptor 5 (mGLUR5), phospholipase C (PLC), connexin 43 (Cx43) and Cx30, increased the concentrations of inositol trisphosphate (IP3) and [Ca2+]i, and promoted the synthesis and release of Glu and d-serine in astrocytes. Moreover, the CM (La3+) could increase the mRNA and protein expression levels of NMDAR subunits (NR1, NR2A, NR2B), the concentration of [Ca2+]i and the rate of apoptosis in neurons. Furthermore, after removal of La, CM (La-free) had a similar effect on neurons which could be antagonized by MK-801, DCKA and DAAO. These results suggest that the neuron apoptosis induced by La is closely related to the excessive release of Glu and d-serine from overly excitatory astrocytes.

Ampelopsin (AMP) preserves glutamate homeostasis between astrocyte and neuron against cerebral ischemia injury

“…When the presynaptic reuptake of Glu is hindered, the extracellular accumulation of Glu is increased, and NMDAR in neurons is over-activated by Glu, which directly causes excitatory neurotoxic reactions [26,27].…”

Activation of TREK-1 Potassium Channel Improved Cognitive Deficits in Alzheimer's Disease Model Mice by Modulation of Glutamate Metabolic Pathway

“…Glu is involved in many processes in the brain, including cognition, movement and development (Hascup et al 2008). Paradoxically, overloaded Glu mediates excessive activation of neurotoxic effect (Sun et al 2018). The dynamic balance of Glu content is maintained by glutamate transport system on membrane of astrocytes (Mahmoud et al 2019).…”

Molecular neurochemistry of the lanthanides

“…The expressions of glutamate/aspartate transporters (GLAST and GLT‐1), glutamine syntethase (GS), and phosphate‐activated glutaminase (PAG) were decreased. This NMDA receptor overactivation causes glutamate‐induced excitotoxic neuronal injury and is usually connected with Ca 2+ excess and apoptosis (Sun et al, ).…”