Multiple sclerosis (MS) is a chronic neuroinflammatory disorder, in which activated immune cells directly or indirectly induce demyelination and axonal degradation. Inflammatory stimuli also change phenotype of astrocytes, making them neurotoxic. Resulting “toxic astrocyte” phenotype has been seen in animal models of neuroinflammation and in MS lesions. Proteins secreted by toxic astrocytes are elevated in the cerebrospinal fluid (CSF) of MS patients and reproducibly correlate with the rates of accumulation of neurological disability and brain atrophy. This suggests pathogenic role for toxic astrocytes in MS.
Therefore, the goal of this study is to identify signaling pathways underlying induction of toxic astrogliosis and to detect therapeutic inhibitors for these processes.
Here we applied commercial library of small molecules (Selleck Chemicals LLC; 1431 drugs) that are either Food and Drug Administration (FDA) approved or in clinical development to an in vitro model of toxic astrogliosis to identify drugs and signaling pathways that inhibit inflammatory transformation of astrocytes to neuro-toxic phenotype.
Inhibitors of three pathways related to the endoplasmic reticulum (ER) stress: 1. Proteasome, 2. Heat shock protein 90 (HSP90)- and 3. Mammalian target of rapamycin (mTOR) reproducibly decreased inflammation-induced conversion of astrocytes to toxic phenotype. Dantrolene, an anti-spasticity drug that inhibits calcium release through ryanodine receptors (RyR) expressed in the ER of CNS cells, also exerted inhibitory effect at in vivo-achievable concentrations. We also established CSF SERPINA3 as a relevant pharmacodynamic marker for inhibiting toxic astrocytes in clinical trials.
In conclusion, drug library screening provides mechanistic insight into generation of toxic astrocytes and identifies candidates for immediate proof-of-principle clinical trial(s).