u-0126 and Escherichia-coli-Infections

Infection with enterohemorrhagic Escherichia coli (EHEC) can result in severe disease, including hemorrhagic colitis and the hemolytic uremic syndrome. Shiga toxins (Stx) are the key EHEC virulence determinant contributing to severe disease. Despite inhibiting protein synthesis, Shiga toxins paradoxically induce the expression of proinflammatory cytokines from various cell types in vitro, including intestinal epithelial cells (IECs). This effect is mediated in large part by the ribotoxic stress response (RSR). The Shiga toxin-induced RSR is known to involve the activation of the stress-activated protein kinases (SAPKs) p38 and JNK. In some cell types, Stx also can induce the classical mitogen-activated protein kinases (MAPKs) or ERK1/2, but the mechanism(s) by which this activation occurs is unknown. In this study, we investigated the mechanism by which Stx activates ERK1/2s in IECs and the contribution of ERK1/2 activation to interleukin-8 (IL-8) expression. We demonstrate that Stx1 activates ERK1/2 in a biphasic manner: the first phase occurs in response to StxB1 subunit, while the second phase requires StxA1 subunit activity. We show that the A subunit-dependent ERK1/2 activation is mediated through ZAK-dependent signaling, and inhibition of ERK1/2 activation via the MEK1/2 inhibitors U0126 and PD98059 results in decreased Stx1-mediated IL-8 mRNA. Finally, we demonstrate that ERK1/2 are activated in vivo in the colon of Stx2-intoxicated infant rabbits, a model in which Stx2 induces a primarily neutrophilic inflammatory response. Together, our data support a role for ERK1/2 activation in the development of Stx-mediated intestinal inflammation.

Topics: Animals; Butadienes; Cell Line; Enterohemorrhagic Escherichia coli; Enzyme Activation; Epithelial Cells; Escherichia coli Infections; Extracellular Signal-Regulated MAP Kinases; Flavonoids; Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating); HEK293 Cells; Hemolytic-Uremic Syndrome; Humans; Inflammation; Interleukin-8; Intestinal Mucosa; JNK Mitogen-Activated Protein Kinases; MAP Kinase Kinase Kinases; Nitriles; p38 Mitogen-Activated Protein Kinases; Protein Kinases; Rabbits; RNA Interference; RNA, Small Interfering; Shiga Toxin 1; Shiga Toxin 2

Hippocampus endogenous neurogenesis has been postulated to play a favorable role in brain restoration after injury. However, the underlying molecular mechanisms have been insufficiently deciphered. Here we investigated the potential regulatory capacity of MAPK/ERK signaling on neurogenesis and the associated cognitive performance in prenatally infected neonatal rats. From our data, intrauterine infection could induce hippocampal neuronal apoptosis and promote endogenous repair by evoking neural stem cell proliferation and survival. We also found intrauterine infection could induce increased levels of p-ERK, p-CREB and BDNF, which might be responsible for the potential endogenous rescue system. Furthermore, inhibition of MAPK/ERK signaling could aggravate hippocampal neuronal apoptosis, decrease neurogenesis, and impair the offspring's cognitive performances and could also down-regulate the levels of p-ERK, p-CREB and BDNF. Our data strongly suggest that the activation of MAPK/ERK signaling may play a significant role in promoting survival of newly generated neural stem cells via an anti-apoptotic mechanism, which may be particularly important in endogenous neuroprotection associated with cognitive performance development in prenatally infected rats.

Topics: Animals; Animals, Newborn; Apoptosis; Behavior, Animal; Brain-Derived Neurotrophic Factor; Butadienes; Cognition Disorders; Cyclic AMP Response Element-Binding Protein; Enzyme Inhibitors; Escherichia coli Infections; Extracellular Signal-Regulated MAP Kinases; Female; Hippocampus; MAP Kinase Signaling System; Neurogenesis; Neurons; Nitriles; Pregnancy; Pregnancy Complications, Infectious; Rats

Bacterial infection of the kidney is associated with renal tubule dysfunction and dysregulation of systemic electrolyte balance. Whether bacterial molecules directly affect renal tubule transport is unknown. We examined the effects of LPS on HCO3(-) absorption in the isolated rat and mouse medullary thick ascending limb (MTAL). LPS decreased HCO3(-) absorption when added to bath or lumen. The MEK/ERK inhibitor U0126 eliminated inhibition by bath LPS but had no effect on inhibition by lumen LPS. Conversely, the mammalian target of rapamycin (mTOR) inhibitor rapamycin eliminated inhibition by lumen LPS but had no effect on inhibition by bath LPS. Inhibiting basolateral Na(+)/H(+) exchange with amiloride eliminated inhibition of HCO3(-) absorption by lumen but not bath LPS. Confocal immunofluorescence showed expression of TLR4 in basolateral and apical membrane domains. Inhibition of HCO3(-) absorption by bath and lumen LPS was eliminated in MTALs from TLR4(-/-) mice. Thus LPS inhibits HCO3(-) absorption through distinct TLR4-dependent pathways in basolateral and apical membranes. These results establish that bacterial molecules can directly impair the transport function of renal tubules, identifying a new mechanism contributing to tubule dysfunction during bacterial infection. The LPS-induced reduction in luminal acidification may contribute to Gram-negative pathogenicity by promoting bacterial adherence and growth and impairing correction of infection-induced systemic acid-base disorders.

Topics: Amiloride; Animals; Bicarbonates; Butadienes; Disease Progression; Endotoxemia; Escherichia coli Infections; Escherichia coli K12; Immunity, Innate; In Vitro Techniques; Kidney Tubules; Lipid A; Lipopolysaccharides; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Nitriles; Rats; Rats, Sprague-Dawley; Serum; Signal Transduction; Sirolimus; Toll-Like Receptor 4; Urinary Tract Infections