Nickel Sulfate Induces Location-Dependent Atrophy of Mouse Olfactory Epithelium: Protective and Proliferative Role of Purinergic Receptor Activation

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Abstract
Exposure to nickel sulfate (NiSO4) leads to impaired olfaction and anosmia through an unknown mechanism. We tested the hypothesis that ATP is released following NiSO4-induced injury and that ATP promotes regenerative cell proliferation in the olfactory epithelium (OE). Male Swiss Webster mice were intranasally instilled with NiSO4 or saline followed by ATP, purinergic receptor antagonists, or saline. We assessed the olfactory epithelium for NiSO4-induced changes using histology and immunohistochemistry 1–7 days postinstillation and compared results to olfactory bulb ablation-induced toxicity. Intranasal instillation of NiSO4 produced a dose- and time-dependent reduction in the thickness of turbinate OE. These reductions were due to sustentacular cell loss, measured by terminal dUTP nick-end labeling (TUNEL) staining at 1-day postinstillation and caspase-3–dependent apoptosis of olfactory sensory neurons at 3 days postinstillation. A significant increase in cell proliferation was observed at 5 and 7 days postinstillation of NiSO4 evidenced by BrdU incorporation. Treatment with purinergic receptor antagonists significantly reduced NiSO4-induced cell proliferation and posttreatment with ATP significantly increased cell proliferation. Furthermore, posttreatment with ATP had no effect on sustentacular cell viability but significantly reduced caspase-3–dependent neuronal apoptosis. In a bulbectomy-induced model of apoptosis, exogenous ATP produced a significant increase in cell proliferation that was not affected by purinergic receptor antagonists, suggesting that ATP is not released during bulbectomy-induced apoptosis. ATP is released following NiSO4-induced apoptosis and has neuroproliferative and neuroprotective functions. These data provide therapeutic strategies to alleviate or cure the loss of olfactory function associated with exposure to nickel compounds.

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