Year in review 2006: Critical Care--Multiple organ failure, sepsis, and shock

Suppression of PTRF alleviates the polymicrobial sepsis induced by cecal ligation and puncture in mice

BACKGROUND

Sepsis and sepsis-associated organ failure are devastating conditions. Understanding the detailed cellular/molecular mechanisms involved in sepsis should lead to the identification of novel therapeutic targets.

METHODS

Cecal ligation and puncture (CLP) was used as a polymicrobial sepsis model in vivo to determine mortality and end-organ damage. Macrophages were adopted as the cellular model in vitro for mechanistic studies.

RESULTS

PTRF+/- mice survived longer and suffered less organ damage after CLP. Reductions in nitric oxide (NO) and iNOS biosynthesis were observed in plasma, macrophages, and vital organs in the PTRF+/- mice. Using an acute sepsis model after CLP, we found that iNOS-/- mice had a comparable level of survival as the PTRF+/- mice. Similarly, polymerase I transcript release factor (PTRF) deficiency resulted in decreased iNOS and NO/ROS production in macrophages in vitro. Mechanistically, lipopolysaccharide (LPS) enhanced the co-localization and interaction between PTRF and TLR4 in lipid rafts. Deletion of PTRF blocked formation of the TLR4/Myd88 complex after LPS. Consistent with this, lack of PTRF impaired the TLR4 signaling, as shown by the decreased p-JNK, p-ERK, and p-p38, which are upstream factors involved in iNOS transcription.

CONCLUSION

PTRF is a crucial regulator of TLR4 signaling in the development of sepsis.

Lipopolysaccharide effects on the proliferation of NRK52E cells via alternations in gap-junction function

BACKGROUND

Gap junctions regulate proper kidney function by facilitating intercellular communication, vascular conduction, and tubular purinergic signaling. However, no clear relationship has been described between gap-junction function and acute kidney injury induced by the endotoxin lipopolysaccharide (LPS).

METHODS

Normal rat kidney epithelial cells (NRK52E cells) were seeded at high and low densities to promote or impede gap-junction formation, respectively, and establish distinctive levels of intercellular communication in culture. Cells were then challenged with LPS at various concentrations (10-1,000 ng/mL). LPS-induced formation and function of gap junctions were assessed by measuring changes in cell proliferation and colony-forming rates, fluorescent dye transmission to adjacent cells, expression levels of connexin43, and repositioning of confluent cells in response to the gap junction inhibitor oleamide or agonist retinoic acid.

RESULTS

The cell proliferation rate and colony-forming rate of high- and low-density NRK52E cells were decreased upon LPS challenge, in a dose-dependent manner. The colony-forming rate of confluent high-density cells was significantly lower than that of low-density cells. Oleamide treatment raised the LPS-induced colony-forming rate of high-density cells, whereas retinoic acid decreased the rate. Neither oleamide nor retinoic acid significantly affected the LPS-induced colony-forming rate of low-density cells. Fluorescence transmission of high-density cells was reduced by LPS challenge, in a dose-dependent manner, but inclusion of retinoic acid increased the LPS-induced transmission of fluorescence. LPS challenge of either high- or low-density NRK52E cells resulted in down-regulated connexin43 expression.

CONCLUSION

Gap-junction function plays an important role in concentration-dependent cytotoxic effect of LPS on normal rat kidney cells in vitro.

Acute insulin resistance following injury

Hyperglycemia and insulin resistance often occur following injury and/or critical illness. Whereas intensive insulin treatment reduces hyperglycemia, mortality and morbidity in certain patients, little is known regarding the pathophysiology of acute insulin resistance following injury and infection. Studies suggest that acute insulin resistance is complex and might differ in a tissue-specific manner, involving multiple causative factors and intracellular signaling pathways. Therefore, the advantages of intensive insulin therapy might not be uniform to all injuries or critical illnesses. Clearly, the increased incidence of hypoglycemic incidents following intensive insulin therapy indicates a need for understanding the underlying molecular mechanisms of the acute development of insulin resistance, which will allow a more targeted approach to treat altered glucose metabolism of critically ill patients.