Modulation of Peptidyl Arginine Deiminase 2 and Implication for Neurodegeneration

Abstract

Purpose: To demonstrate that elevated pressure increases the peptidyl arginine deiminase 2 (PAD2) expression in cultured astrocytes in vitro that can be modulated by pharmacological agents modulating intracellular calcium. Methods: Isolated rat brain astrocytes were subjected to pressure treatment. Western and immunohistochemical analyses detected PAD2 protein expression. Calcium measurements were achieved employing fluorescence-based microscopic imaging and quantification system. Experiments were repeated with human optic nerve head–derived astrocytes. Results: PAD2 has recently been shown to be associated with glaucomatous optic nerve. Astrocytes subjected to pressure (25–100 mmHg) show elevated level of PAD2, increased intracellular calcium, and concomitant citrullination but not significant cell death. PAD2 expression in response to elevated pressure may play a role in glaucomatous neurodegeneration. Pressure-treated astrocytes were also subjected to thapsigargin (50–250 nM) treatment, but it is unclear whether this had any further effect in increasing PAD2 expression. Conversely, treatment with calcium chelating agent BAPTA-AM (50–250 nM) results in decreased intracellular calcium concentration and PAD2. Conclusions: These results suggest calcium modulation could be exploited as therapeutic strategy to modulate pressure-induced PAD2 expression and citrullination.