Rapid Up-Regulation of Endothelial Nitric-Oxide Synthase in a Mouse Model ofEscherichia coliLipopolysaccharide-Induced Bladder Inflammation

Abstract

Increases in the signaling molecule nitric oxide (NO) during inflammation may be linked not only to inducible nitric-oxide synthase (iNOS) but also to endothelial (e)NOS. Escherichia coli lipopolysaccharide (LPS) induces an inflammatory response in the bladder and rapidly increases phosphorylation of Akt/protein kinase B (Akt), a key enzyme regulating proliferation, apoptosis, and inflammation. Activated Akt phosphorylates human eNOS at serine 1177 and subsequently increases NOS activity. Because Akt and eNOS are both localized in the bladder urothelium, phosphorylation of eNOS by Akt provides an attractive mechanism for rapid increases in urinary NO production. Female mice were intraperitoneally injected with LPS (25 mg/kg) or pyrogen-free water (control). Four hours before LPS injection, some mice were injected with wortmannin, which inhibits Akt phosphorylation. Levels of urinary cyclic GMP, a downstream product of NO, increase 75% within 1 h after intraperitoneal injection of LPS, and this increase is blocked by wortmannin. Bladder eNOS and phosphorylated eNOS protein increase 94 and 151%, respectively, 1 h after LPS treatment, whereas iNOS was not detected. Wortmannin decreases eNOS phosphorylation by 60%. Furthermore, bladder Ca 2ϩ -dependent NOS activity (eNOS, neuronal NOS) is increased 79 Ϯ 20% 1 h after LPS treatment, whereas there is no increase in Ca 2ϩ -independent (iNOS) activity (n ϭ 4). Increases in urinary cyclic GMP, NOS activity, and eNOS protein and phosphorylation 1 h after induction of inflammation with LPS, indicate that eNOS plays a role in the early response to bladder inflammation.

Pulmonary vascular iNOS induction participates in the onset of chronic hypoxic pulmonary hypertension

“…L-NIL at 8 mg/l in drinking water markedly reduced exhaled NO levels after LPS, albeit not as much as the nonselective NOS blocker, L-NAME, at 500 mg/l. This is consistent with reports that, in addition to iNOS induction, LPS treatment can increase expression of the remaining NOS isoforms (12,24,30,32). Somewhat surprisingly, even the high L-NAME dose used did not prevent the rise in exhaled NO after LPS completely.…”

Inactivation of Host Akt/Protein Kinase B Signaling by Bacterial Pore-forming Toxins

“…For example, Akt promotes the activation of endothelial nitric-oxide synthase (eNOS) and p47 phox , two key host factors involved in, respectively, the generation of reactive nitrogen and oxygen species that can disable UPEC and other invading pathogens. In response to lipopolysaccharide, eNOS within the bladder is rapidly induced and activated, presumably as part of the host defense against UTIs (Kang et al, 2004). Akt-dependent phosphorylation and subsequent activation of eNOS stimulates the production of nitric oxide, which can have considerable bacteriostatic effects on UPEC (Dimmeler et al, 1999;Fulton et al, 1999;Bower and Mulvey, 2006).…”

Uropathogenic Escherichia coli -Induced Inflammation Alters Mouse Urinary Bladder Contraction via an Interleukin-6-Activated Inducible Nitric Oxide Synthase-Related Pathway

“…LPS is capable of inducing iNOS expression in the urinary bladder (23). A rapid upregulation of endothelial NOS (eNOS) has been demonstrated in a mouse model of E. coli LPS-induced bladder inflammation (12). Moreover, elevated levels of inflammatory cytokines such as IL-6 and IL-8 have been found in the sera and urine specimens of younger infants and children with urinary tract infections (11,24).…”