Senescence‐Associated Secretory Phenotype (SASP) factors down‐regulate glutamate transporter expression in human brainstem astrocytes through a paracrine fashion

Abstract

Glia-neuron crosstalk in the brainstem is emerging as a critical player in the regulation of sympathetic nerve activity (SNA). Specifically, astrocytes modulate SNA by tightly regulating synaptic glutamate levels through transporter mediated re-uptake mechanisms. Pro-inflammatory mediators like TNFα have been shown to negatively affect glutamate transporter expression in astrocytes. Previous studies from our laboratory have provided evidence for oxidative stress-induced senescence and their secretory phenotype (SASP), a potential source of inflammation, in human brainstem astrocytes. Hence, in the present study we hypothesize that inflammatory mediators in SASP factors down-regulate glutamate re-uptake transporter expression in a paracrine manner. To test our hypothesis, we induced senescence in cultured human brainstem astrocytes with hydrogen peroxide (H2O2) treatment at a dose of 300 μM for 2 hours. Senescence induction was confirmed through PCR expression for senescence markers and SA-beta-gal staining 7 days after H2O2 treatment. Conditioned media collected from the senescent and control astrocytes were used to assess the paracrine effect of SASP factors on astrocytic glutamate transporter expression. Following 36 hours of treatment with conditioned media from senescent astrocytes, we observed a significant down-regulation of two of the major astrocytic glutamate re-uptake transporters, EAAT1 (GLAST-1) and EAAT2 (GLT-1) in human brainstem astrocytes. This suggests that soluble SASP factors in the secretome of senescent cells can alter the function of glutamate transporters in the astrocytes through a paracrine action. Increased activity of glutamatergic neurons in the rostral ventrolateral medulla due to reduced glutamate re-uptake at the synapse may be a possible glial mechanism underlying enhanced sympathoexcitation in obesity.