Siponimod (BAF312) Activates Nrf2 While Hampering NFκB in Human Astrocytes, and Protects From Astrocyte-Induced Neurodegeneration

Abstract

Multiple sclerosis (MS) is an inflammatory neurodegenerative disease of the central nervous system (CNS) with heterogeneous pathophysiology. In its progressive course oligodendrocyte and neuroaxonal damage is sustained by compartmentalized inflammation due to glial dysregulation. Siponimod (BAF312), a modulator of two sphingosine-1-phosphate (S1P) receptors (S1P1 and S1P5) is the first oral treatment specifically approved for active secondary progressive MS. To address potential direct effects of BAF312 on glial function and glia-neuron interaction, we set up a series of in vitro functional assays with astrocytes generated from human fibroblasts. These cells displayed the typical morphology and markers of astroglia, and were susceptible to the action of inflammatory mediators and BAF312, because expressing receptors for IL1, IL17, and S1P (namely S1P1 and S1P3). Targeting of S1P signaling by BAF312 inhibited NFκB translocation evoked by inflammatory cytokines, indicating a direct anti-inflammatory activity of the drug on the human astrocyte. Further, while glia cells exposed to IL1 or IL17 downregulated protein expression of glutamate transporters, BAF312-treated astrocytes maintained high levels of GLAST and GLT1 regardless of the presence of inflammatory mediators. Interestingly, despite potential glial susceptibility to S1P signaling via S1P3, which is not targeted by BAF312, NFκB translocation and downregulation of glutamate transporters in response to S1P were inhibited at similar levels by BAF312 and FTY720, another S1P signaling modulator targeting also S1P3. Accordingly, specific inhibition of S1P1 via NIBR-0213 blocked S1P-evoked NFκB translocation, demonstrating that modulation of S1P1 is sufficient to dampen signaling via other S1P receptors. Considering that NFκB-dependent responses are regulated by Nrf2, we measured activation of this critical transcription factor for anti-oxidant reactions, and observed that BAF312 rapidly induced nuclear translocation of Nrf2, but this effect was attenuated in the presence of an inflammatory milieu. Finally, in vitro experiments with spinal neurons exposed to astrocyte-conditioned media showed that modulation of

Protective Functions of Reactive Astrocytes Following Central Nervous System Insult

“…Exogenously administered agents require a high permeability through the BBB and a persisting bioavailability to ensure longlasting therapeutic effects (279). Only a limited number of small molecules has shown beneficial "protective" effects on glial cells following acute CNS insult so far, which is best documented during neuroinflammation (92, [280][281][282][283][284][285][286]. Thus, there is a dire need for novel strategies that mediate recovery after acute CNS insult and lead to long-term regeneration in chronic inflammatory and degenerative diseases.…”

Reactive astrocyte nomenclature, definitions, and future directions

“…In addition to astrocytes from postmortem samples and biopsies 59 ( Fig. 1b), hiPSC-derived astrocytes, which can be generated with a fast protocol in 2D layers 104 or integrated in 3D systems such as spheroids and organoids [105][106][107][108] , are rapidly becoming commonplace in basic research 11,82 and therapy development 109 . Researchers need to be aware of the pros and cons of the various protocols available, as discussed in previous sections and elsewhere [110][111][112] .…”

Sphingosine-1-Phosphate Receptor Modulators and Oligodendroglial Cells: Beyond Immunomodulation

“…The compound decreased the level of ROS and enhanced the expression and activity of protective factors, such as nuclear factor erythroid 2–related factor 2 (Nrf2), heme oxygenase-1(HO-1), and NAD(P)H: Quinone acceptor oxidoreductases-1 (NQO1) [ 131 ]. Consistently, increased expression of Nrf2 was observed in human iPSC-derived astrocytes treated with 100 nM of S1PR modulators, fingolimod, and siponimod [ 132 ]. More recently, increased oligodendrocyte loss and demyelination have been observed in the cuprizone-induced demyelination in Nrf2-knockout mice [ 133 ].…”

“…However, a high level of inflammatory mediators leads to decreased receptors’ expression resulting in an increased glutamate amount. In this context, it has been recently observed that, in human iPSC-induced astrocytes, the treatment with high concentrations of siponimod (100 nM) maintains the expression of GLAST and GLT-1 [ 132 ], contributing to restoring the imbalanced glutamate transmission.…”