Hepatocyte Nuclear Factor-1ß Induces Redifferentiation of Dedifferentiated Tubular Epithelial Cells.

Tubular epithelial cells (TECs) can be dedifferentiated by repetitive insults, which activate scar-producing cells generated from interstitial cells such as fibroblasts, leading to the accumulation and deposition of extracellular matrix molecules. The dedifferentiated TECs play a crucial role in the development of renal fibrosis. Therefore, renal fibrosis may be attenuated if dedifferentiated TECs are converted back to their normal state (re-epithelialization). However, the mechanism underlying the re-epithelialization remains to be elucidated. In the present study, TGF-ß1, a profibrotic cytokine, induced dedifferentiation of cultured TECs, and the dedifferentiated TECs were re-epithelialized by the removal of TGF-ß1 stimulation. In the re-epithelialization process, transcription factor hepatocyte nuclear factor 1, beta (HNF-1ß) was identified as a candidate molecule involved in inducing re-epithelialization by means of DNA microarray and biological network analysis. In functional validation studies, the re-epithelialization by TGF-ß1 removal was abolished by HNF-1ß knockdown. Furthermore, the ectopic expression of HNF-1ß in the dedifferentiated TECs induced the re-epithelialization without the inhibition of TGF-ß/Smad signaling, even in the presence of TGF-ß1 stimulation. In mouse renal fibrosis model, unilateral ureteral obstruction model, HNF-1ß expression in the TECs of the kidney was suppressed with fibrosis progression. Furthermore, the HNF-1ß downregulated TECs resulted in dedifferentiation, which was characterized by expression of nestin. In conclusion, HNF-1ß suppression in TECs is a crucial event for the dedifferentiation of TECs, and the upregulation of HNF-1ß in TECs has a potential to restore the dedifferentiated TECs into their normal state, leading to the attenuation of renal fibrosis.

Activation of PKN mediates survival of cardiac myocytes in the heart during ischemia/reperfusion.

RATIONALE: The function of PKN, a stress-activated protein kinase, in the heart is poorly understood. OBJECTIVE: We investigated the functional role of PKN during myocardial ischemia/reperfusion (I/R). METHODS AND RESULTS: PKN is phosphorylated at Thr774 in hearts subjected to ischemia and reperfusion. Myocardial infarction/area at risk (MI/AAR) produced by 45 minutes of ischemia and 24 hours of reperfusion was significantly smaller in transgenic mice with cardiac-specific overexpression of constitutively active (CA) PKN (Tg-CAPKN) than in nontransgenic (NTg) mice (15+/-5 versus 38+/-5%, P<0.01). The number of TUNEL-positive nuclei was significantly lower in Tg-CAPKN (0.3+/-0.2 versus 1.0+/-0.2%, P<0.05). Both MI/AAR (63+/-9 versus 45+/-8%, P<0.05) and the number of TUNEL-positive cells (7.9+/-1.0 versus 1.3+/-0.9%, P<0.05) were greater in transgenic mice with cardiac-specific overexpression of dominant negative PKN (Tg-DNPKN) than in NTg mice. Thr774 phosphorylation of PKN was also observed in response to H(2)O(2) in cultured cardiac myocytes. Stimulation of PKN prevented, whereas inhibition of PKN aggravated, cell death induced by H(2)O(2), suggesting that the cell-protective effect of PKN is cell-autonomous in cardiac myocytes. PKN induced phosphorylation of alpha B crystallin and increased cardiac proteasome activity. The infarct reducing effect in Tg-CAPKN mice was partially inhibited by epoxomicin, a proteasome inhibitor. CONCLUSIONS: PKN is activated by I/R and inhibits apoptosis of cardiac myocytes, thereby protecting the heart from I/R injury. PKN mediates phosphorylation of alpha B crystallin and stimulation of proteasome activity, which, in part, mediates the protective effect of PKN in the heart.

Secreted Frizzled-related protein 2 is a procollagen C proteinase enhancer with a role in fibrosis associated with myocardial infarction.

Secreted Frizzled-related proteins (sFRPs) have emerged as key regulators of a wide range of developmental and disease processes. Most of the known functions of mammalian sFRPs have been attributed to their ability to antagonize Wnt signalling. Recently however, Xenopus laevis and zebrafish sFRP, Sizzled, was shown to function as an antagonist of Chordin processing by Tolloid-like metalloproteinases. This has led to the proposal that sFRPs may function as evolutionarily conserved antagonists of chordinase activities of this class of proteinases. In contrast to this proposal, we show here that the mammalian sFRP, sFRP2, does not affect Chordin processing, but instead, can serve as a direct enhancer of procollagen C proteinase activity of Tolloid-like metalloproteinases. We also show that the level of fibrosis, in which procollagen processing by Tolloid-like proteinases has a rate-limiting role, is markedly reduced in Sfrp2-null mice subjected to myocardial infarction. Importantly, this reduced level of fibrosis is accompanied by significantly improved cardiac function. This study thus uncovers a function for sFRP2 and a potential therapeutic application for sFRP2 antagonism in controlling fibrosis in the infarcted heart.

Effects of KB-R9032, a new Na+/H+ exchange inhibitor, on canine coronary occlusion/reperfusion-induced ventricular arrhythmias.

We investigated the effects of KB-R9032 (N-(4-isopropyl-2,2-dimethyl-3-oxo-3,4-dihydro-2H-benzo[1,4]oxazine-6-carbonyl) guanidine methanesulfonate), a new Na(+)/H(+) exchange inhibitor, on a coronary artery occlusion/reperfusion-induced arrhythmia model in pentobarbital anesthetized dogs. KB-R9032 reduced the number of ventricular premature contractions seen during the coronary occlusion, while it did not alter the heart rate, mean blood pressure, or electrocardiographic parameters (PR, QRS, or QTc interval). KB-R9032 also decreased the incidence of fatal ventricular fibrillation during coronary artery occlusion and/or after reperfusion. These antiarrhythmic effects were observed not only in the pre-ischemic administration group, but also in the group given KB-R9032 at the 15th min of the 30-min occlusion. These findings support the view that Na(+)/H(+) exchanger may play an important role in inducing coronary ischemia/reperfusion arrhythmias. This suggests that the use of Na(+)/H(+) exchange inhibitors, such as KB-R9032, may be an effective clinical approach to suppress sudden cardiac death due to acute myocardial ischemia/reperfusion such as during coronary bypass surgery, cardiac valve surgery, or percutaneous transluminal coronary angioplasty.