Activation of purinergic receptors induces proliferation and neuronal differentiation in Swiss Webster mouse olfactory epithelium

Abstract

In the central nervous system (CNS), adenosine 5′-triphosphate (ATP) induces the synthesis and release of neurotrophic factors, cell proliferation, and differentiation. The olfactory system is one site where multipotent progenitor cells continue to proliferate and differentiate into neurons throughout life. We tested the hypothesis that ATP initiates proliferation in olfactory epithelium by measuring 5-bromo-2-deoxyuridine incorporation. Adult mice were pre-treated intraperitoneally (i.p.) or intranasally with saline or purinergic receptor antagonists (pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonate+suramin) 30 min prior to nasal instillation of ATP, uridine 5′-triphosphate (UTP), adenosine 5′-(3-thiotriphosphate) (ATPγS) or saline (0 h). Mice received three injections of 5-bromo-2-deoxyuridine between 42 and 46 h, and were sacrificed at 2, 9 or 16 days post–ATP instillation. ATP, UTP or ATPγS significantly increased 5-bromo-2-deoxyuridine incorporation compared to intranasal saline controls in groups pre-treated with saline. Saline, ATP, UTP or ATPγS instillation did not significantly increase 5-bromo-2-deoxyuridine incorporation in groups pre-treated with purinergic receptor antagonists. Similar results were observed in neonates and in a cultured slice preparation. Intranasal instillation of ATP also increased the protein levels of proliferating cell nuclear antigen in adults. Pre-treatment with purinergic receptor antagonists inhibited the ATP-induced increase in proliferating cell nuclear antigen. In adults, a subset of the cells that incorporated 5-bromo-2-deoxyuridine was immunoreactive to neuronal markers mammalian achaete-schute homolog 1, growth-associated protein 43, and olfactory marker protein at 2, 9, and 16 days, respectively. Collectively, these data indicate that purinergic receptor activation induces proliferation and neuronal differentiation in the mouse olfactory epithelium. We propose that extracellular ATP released upon injury could induce proliferation and promote the neuroregeneration of the olfactory epithelium.