α-Haemolysin of uropathogenic E. coli induces Ca2+ oscillations in renal epithelial cells

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Abstract
Pyelonephritis is one of the most common febrile diseases in children. If not treated appropriately, it causes irreversible renal damage and accounts for a large proportion of end stage renal failures1. Renal scarring can occur in the absence of inflammatory cells, indicating that bacteria may have a direct signalling effect on renal cells2. Intracellular calcium ([Ca2+]i) oscillations can protect cells from the cytotoxic effects of prolonged increases in intracellular calcium3,4. However, no pathophysiologically relevant protein that induces such oscillations has been identified. Here we show that infection by uropathogenic Escherichia coli induces a constant, low-frequency oscillatory [Ca2+]i response in target primary rat renal epithelial cells induced by the secreted RTX (repeats-in-toxin) toxin α-haemolysin. The response depends on calcium influx through L-type calcium channels as well as from internal stores gated by inositol triphosphate. Internal calcium oscillations induced by α-haemolysin in a renal epithelial cell line stimulated production of cytokines interleukin (IL)-6 and IL-8. Our findings indicate a novel role for α-haemolysin in pyelonephritis: as an inducer of an oscillating second messenger response in target cells, which fine-tunes gene expression during the inflammatory response.