Macrovesicular steatosis in greater than 30% of hepatocytes is a significant risk factor for primary graft nonfunction due to increased sensitivity to ischemia reperfusion (I/R) injury. The growing prevalence of hepatic steatosis due to the obesity epidemic, in conjunction with an aging population, may negatively impact the availability of suitable deceased liver donors. Some have suggested that metabolic interventions could decrease the fat content of liver grafts prior to transplantation. This concept has been successfully tested through nutritional supplementation in a few living donors. Utilization of deceased donor livers, however, requires defatting of explanted organs. Animal studies suggest that this can be accomplished by ex vivo warm perfusion in a time scale of a few hours. We estimate that this approach could significantly boost the size of the donor pool by increasing the utilization of steatotic livers. Here we review current knowledge on the mechanisms whereby excessive lipid storage and macrosteatosis exacerbate hepatic I/R injury, and possible approaches to address this problem, including ex vivo perfusion methods as well as metabolically induced defatting. We also discuss the challenges ahead that need to be addressed for clinical implementation.
The controlled differentiation of embryonic stem (ES) cells is of utmost interest to their clinical, biotechnological, and basic science use. Many investigators have combinatorially assessed the role of specific soluble factors and extracellular matrices in guiding ES cell fate, yet the interaction between neighboring cells in these heterogeneous cultures has been poorly defined due to a lack of conventional tools to specifically uncouple these variables. Herein, we explored the role of cell-cell interactions during neuroectodermal specification of ES cells using a microfabricated cell pair array. We tracked differentiation events in situ, using an ES cell line expressing green fluorescent protein (GFP) under the regulation of the Sox1 gene promoter, an early marker of neuroectodermal germ cell commitment in the adult forebrain. We observed that a previously specified Sox1-GFP+ cell could induce the specification of an undifferentiated ES cell. This induction was modulated by the two cells being in contact and was dependent on the age of previously specified cell prior to coculture. A screen of candidate cell adhesion molecules revealed that the expression of connexin (Cx)-43 correlated with the age-dependent effect of cell contact in cell pair experiments. ES cells deficient in Cx-43 showed aberrant neuroectodermal specification and lineage commitment, highlighting the importance of gap junctional signaling in the development of this germ layer. Moreover, this study demonstrates the integration of microscale culture techniques to explore the biology of ES cells and gain insight into relevant developmental processes otherwise undefined due to bulk culture methods.
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