Published ahead of print on February 2, 2006, doi:10.1165/rcmb.2005-0196OC Am. J. Respir. Cell Mol. Biol., Volume 34, Number 6, June 2006, 775-786 A more recent version of this article appeared on June 1, 2006
Submitted on May 23, 2005 Eosinophil-mediated Cholinergic Nerve RemodelingNiamh Durcan1,1 Department of Medicine, Royal College of Surgeons in Ireland, Dublin, Ireland, 2 Department of Pharmacology, University of Liverpool, Liverpool, United Kingdom, 3 Department of Neurology and Neuroscience, Boston University, Boston, USA, 4 Department of Clinical Pharmacology, University of Malta, Malta, Malta, 5 Division of Therapeutics and Molecular Medicine, University of Nottingham, Nottingham, United Kingdom, 6 Department of Dermatology, University of Utah, Utah, USA, 7 Department of Medicine, Queen's University of Belfast, Belfast, United Kingdom * To whom correspondence should be addressed. E-mail: mtwalsh{at}rcsi.ie.
Eosinophils are observed to localize to cholinergic nerves in a variety of inflammatory conditions such as asthma, rhinitis, eosinophilic gastroenteritis and inflammatory bowel disease where they are also responsible for the induction of cell signaling. We hypothesized that a consequence of eosinophil localization to cholinergic nerves would involve a neural remodeling process. Eosinophil co-culture with cholinergic IMR32 cells led to increased expression of the M2 muscarinic receptor with this induction being mediated via an adhesion dependent release of eosinophil proteins, including major basic protein and nerve growth factor. Studies on the promoter sequence of the M2 receptor indicated that this induction was initiated at a transcription start site 145kb upstream of the gene-coding region. This promoter site contains binding sites for a variety of transcription factors including SP1, AP1 and AP2. Eosinophils also induced the expression of several cholinergic genes involved in the synthesis, storage and metabolism of acetylcholine, including the enzymes choline acetyltransferase, vesicular acetylcholine transferase and acetlycholinesterase. The observed eosinophil induced changes in enzyme content were associated with a reduction in intracellular neural acetylcholine but an increase in choline content, suggesting increased acetylcholine turnover and a reduction in acetylcholinesterase activity, in turn suggesting reduced catabolism of acetylcholine. Together these data suggest that eosinophil localization to cholinergic nerves induces neural remodeling, promoting a cholinergic phenotype.
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