The pyrrolysyl-tRNA synthetase/tRNAPyl pair is the most versatile and widespread system for the incorporation of non-canonical amino acids (ncAAs) into proteins in mammalian cells. However, low yields of ncAA incorporation severely limit its applicability to relevant biological targets. Here, we generate two tRNAPyl variants that significantly boost the performance of the pyrrolysine system. Compared to the original tRNAPyl, the engineered tRNAs feature a canonical hinge between D- and T-loop, show higher intracellular concentrations and bear partially distinct post-transcriptional modifications. Using the new tRNAs, we demonstrate efficient ncAA incorporation into a G-protein coupled receptor (GPCR) and simultaneous ncAA incorporation at two GPCR sites. Moreover, by incorporating last-generation ncAAs for bioorthogonal chemistry, we achieve GPCR labeling with small organic fluorophores on the live cell and visualize stimulus-induced GPCR internalization. Such a robust system for incorporation of single or multiple ncAAs will facilitate the application of a wide pool of chemical tools for structural and functional studies of challenging biological targets in live mammalian cells.

Overweight has become a major health care problem in Western societies and is accompanied by an increasing incidence and prevalence of non-alcoholic fatty liver disease (NAFLD). The progression from NAFLD to non-alcoholic steatohepatitis (NASH) marks a crucial tipping point in the progression of severe and irreversible liver diseases. This study aims to gain further insight into the molecular processes leading to the evolution from steatosis to steatohepatitis. Steatosis was induced in cultures of primary human hepatocytes by continuous five-day exposure to free fatty acids (FFAs). The kinetics of lipid accumulation, lipotoxicity, and oxidative stress were measured. Additionally, ER stress was evaluated by analyzing the protein expression profiles of its key players: PERK, IRE1a, and ATF6a. Our data revealed that hepatocytes are capable of storing enormous amounts of lipids without showing signs of lipotoxicity. Prolonged lipid accumulation did not create an imbalance in hepatocyte redox homeostasis or a reduction in antioxidative capacity. However, we observed an FFA-dependent increase in ER stress, revealing thresholds for triggering the activation of pathways associated with lipid stress, inhibition of protein translation, and apoptosis. Our study clearly showed that even severe lipid accumulation can be attenuated by cellular defenses, but regenerative capacities may be reduced.

Background and Purpose-Granulocyte colony-stimulating factor (GCSF) showed robust neuroprotective and neuroregenerative properties after stroke in rodents but failed to meet study end points in patients. Because immunologic side effects of GCSF may have escaped preclinical testing because of nonallometric dose translation, we hypothesized those as possible reasons. Methods-Stroke was induced in C57BL/6 mice by 45-minute filament middle cerebral artery occlusion. GCSF was administered at 50 and 832.5 μg/kg body weight. Treatment was controlled by vehicle injection, sham surgery, and naive animals. Immune cell counts were assessed in blood, spleen, and brain by multidimensional flow cytometry 1 day after stroke. Results-High-dose GCSF significantly altered myeloid and T-cell subpopulations in blood and spleen and caused a tremendous increase of monocytes/macrophages infiltrating the ischemic brain. Conclusions-Dose-dependent immunomodulation superimposes central nervous system-specific effects of GCSF after stroke. Adaption of dose or treatment time may overcome this drawback. (Stroke. 2014;45:623-626.)