Maprotiline restores ER homeostasis and rescues neurodegeneration via Histamine Receptor H1 inhibition in retinal ganglion cells

When the protein or calcium homeostasis of the endoplasmic reticulum (ER) is adversely altered, cells experience ER stress that leads to various diseases including neurodegeneration. Genetic deletion of an ER stress downstream effector, CHOP, significantly protects neuron somata and axons. Here we report that three tricyclic compounds identified through a small-scale high throughput screening using a CHOP promoter-driven luciferase cell-based assay, effectively inhibit ER stress by antagonizing their common target, histamine receptor H1 (HRH1). We further demonstrated that systemic administration of one of these compounds, maprotiline, or CRISPR-mediated retinal ganglion cell (RGC)-specific HRH1 inhibition, delivers considerable neuroprotection of both RGC somata and axons and preservation of visual function in two mouse optic neuropathy models. Finally, we determine that maprotiline restores ER homeostasis by inhibiting HRH1-mediated Ca2+ release from ER. In this work we establish maprotiline as a candidate neuroprotectant and HRH1 as a potential therapeutic target for glaucoma.

The elimination criteria of outliers were based on the visible health status of the individual mice. The mice underwent significant weight loss or appearing sick were excluded from data analysis.
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For cell based experiments in vitro seeded cell populations were randomly allocated to treatment groups prior to treatment. All mice were randomly allocated into experimental groups before the start of the treatment. Important findings were repeated with independent experiments.
Investigators were blinded to group allocation. For observer-based microscopy data assessment and collection, observers were masked to the treatment of the samples. For in vivo SLO, PERG, OKR and SD-OCT recording, the data collection was undertaken in a double blinded fashion, with observers unaware of treatment groupings or prior determined measurements. Key experiments were validated in independent experiments. Selected data was analyzed by different investigators to validate findings.
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Only highly cited and thoroughly validated antibodies were chosen and used. All primary antibodies used in this study work well for immunoblotting and immunohistochemistry in human or mouse samples. The expression pattern for each antibody matches pervious reports in the literature.
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