Excess glutamate secreted from astrocytes drives upregulation of P-glycoprotein in endothelial cells in amyotrophic lateral sclerosis

Abstract

In amyotrophic lateral sclerosis (ALS), upregulation in expression and activity of the ABC transporter P-glycoprotein (P-gp) driven by disease advancement progressively reduces CNS penetration and efficacy of the ALS drug, riluzole. Post-mortem spinal cord tissues from ALS patients revealed elevated P-gp expression levels in endothelial cells of the blood-spinal cord barrier compared to levels measured in control, non-diseased individuals. We recently found that astrocytes expressing familial ALS-linked SOD1 mutations regulate expression levels of P-gp in endothelial cells, which also exhibit a concomitant, significant increase in reactive oxygen species production and NFκB nuclear translocation when exposed to mutant SOD1 astrocyte conditioned media. In this study, we found that glutamate, which is abnormally secreted by mutant SOD1 and sporadic ALS astrocytes, drives upregulation of P-gp expression and activity levels in endothelial cells via activation of N-Methyl-D-Aspartic acid (NMDA) receptors. Surprisingly, astrocytesecreted glutamate regulation of endothelial P-gp levels is not a mechanism shared by all forms of ALS. C9orf72-ALS astrocytes had no effect on endothelial cell P-gp expression and did not display increased glutamate secretion. Utilizing an optimized in vitro human BBB model consisting of patient-derived induced pluripotent stem cells, we showed that co-culture of endothelial cells with patient-derived astrocytes increased P-gp expression levels and transport activity, which was significantly reduced when endothelial cells were incubated with the NMDAR antagonist, MK801. Overall, our findings unraveled a complex molecular interplay between astrocytes of different ALS genotypes and endothelial cells potentially occurring in disease that could differentially impact ALS prognosis and efficacy of pharmacotherapies.

Effect of heat stress on blood-brain barrier integrity in iPS cell-derived microvascular endothelial cell models

“…We also found that heat stress could induce the expression of P-gp. As previously published, heat stress-induced some molecules, such as HIF-1α [21] and cyclooxygenase-2 (COX-2) [22], could induce the expression of P-gp. Notably, P-gp is known to play an important role in the efflux of various chemical mediators.…”

Astrocyte-Derived Paracrine Signals: Relevance for Neurogenic Niche Regulation and Blood–Brain Barrier Integrity

“…Activated astrocytes release large amounts of glutamate that act on endothelial NMDA receptors and promote oxidative stress (Scott et al, 2007), TJ disruption, and increased BBB permeability (Andras et al, 2007). Further, glutamate increases the expression of P-gp, as reported in endothelial cells cultured with astrocytes derived from amyotrophic lateral sclerosis (ALS) patients (Mohamed et al, 2019). This condition can justify "P-gp–mediated pharmacoresistance" (Mohamed et al, 2017), often observed in diseases including ALS and epilepsy (Avemary et al, 2013; Feldmann et al, 2013).…”

Riluzole does not ameliorate disease caused by cytoplasmic TDP-43 in a mouse model of amyotrophic lateral sclerosis

“…This is also important to consider in the case of riluzole, since it has been shown that although riluzole alone had no effect in SOD1 G93A mice, when combined with elacridar, a drug which inhibits transporters including P-glycoprotein that control drug efflux from the central nervous system, motor function was improved and survival was significantly extended (43). P-glycoprotein is up-regulated in ALS at least in part in response to astrocytic release of glutamate, and this upregulation may decrease penetration of riluzole into the central nervous system (44).…”