Mitochondria undergo fragmentation in response to electron transport chain (ETC) poisons and mitochondrial DNA–linked disease mutations, yet how these stimuli mechanistically connect to the mitochondrial fission and fusion machinery is poorly understood. We found that the energy-sensing adenosine monophosphate (AMP)–activated protein kinase (AMPK) is genetically required for cells to undergo rapid mitochondrial fragmentation after treatment with ETC inhibitors. Moreover, direct pharmacological activation of AMPK was sufficient to rapidly promote mitochondrial fragmentation even in the absence of mitochondrial stress. A screen for substrates of AMPK identified mitochondrial fission factor (MFF), a mitochondrial outer-membrane receptor for DRP1, the cytoplasmic guanosine triphosphatase that catalyzes mitochondrial fission. Nonphosphorylatable and phosphomimetic alleles of the AMPK sites in MFF revealed that it is a key effector of AMPK-mediated mitochondrial fission.

Metformin is the most widely prescribed drug for the treatment of type-2 diabetes. However, knowledge of the full effects of metformin on biochemical pathways and processes in its primary target tissue, the liver, is limited. One established effect of metformin is to decrease cellular energy levels. The AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) are key regulators of metabolism that are respectively activated and inhibited in acute response to cellular energy depletion. Here we show that metformin robustly inhibits mTORC1 in mouse liver tissue and primary hepatocytes. Using mouse genetics, we find that at the lowest concentrations of metformin that inhibit hepatic mTORC1 signaling, this inhibition is dependent on AMPK and the tuberous sclerosis complex (TSC) protein complex (TSC complex). Finally, we show that metformin profoundly inhibits hepatocyte protein synthesis in a manner that is largely dependent on its ability to suppress mTORC1 signaling.

SUMMARY The AMP-activated protein kinase (AMPK) is a highly conserved master regulator of metabolism, whose activation has been proposed to be therapeutically beneficial for the treatment of several metabolic diseases, including nonalcoholic fatty liver disease (NAFLD). NAFLD, characterized by excessive accumulation of hepatic lipids, is the most common chronic liver disease and a major risk factor for development of nonalcoholic steatohepatitis, type 2 diabetes, and other metabolic conditions. To assess the therapeutic potential of AMPK activation, we have generated a genetically engineered mouse model, termed iAMPKCA, where AMPK can be inducibly activated in vivo in mice in a spatially and temporally restricted manner. Using this model, we show that liver-specific AMPK activation reprograms lipid metabolism, reduces liver steatosis, decreases expression of inflammation and fibrosis genes, and leads to significant therapeutic benefits in the context of diet-induced obesity. These findings further support AMPK as a target for the prevention and treatment of NAFLD.

During the development of research to compare the processes and impact of inclusive education in Sweden with results obtained from a study undertaken in Ireland, a pilot study was conducted and documented. The pilot study had three aims: (1) to gather data to provide guidance for a substantive study adapted to Swedish conditions through modification of Irish research procedures and instruments, (2) to critically interrogate how we as researchers could most effectively conduct a pilot study utilizing observational and video-recorded data, and (3) to use the Irish theoretical model as a tool of analysis for studying inclusion in two Swedish schools. Although pilot studies are frequently conducted to assess the efficacy of research instruments for use in qualitative research projects, few publications have drawn upon empirical findings related to such studies. Additionally, while methodological texts recommend the use of pilot studies in qualitative research, there is a lack of reported research focusing on how to conduct such pilot studies. We argue that our methodological findings may contribute to greater awareness of the important role that a pilot study may have for full-scale qualitative research projects, for example, in case study research where semi-structured qualitative interviews are used. This argument is based on the assumption that researchers, and especially novice researchers, having conducted a pilot study will be better informed and prepared to face the challenges that are likely to arise in the substantive study and more confident in the instruments to be used for data collection. A proper analysis of the procedures and results from the pilot study facilitates the identification of weaknesses that may be addressed. A carefully organized and managed pilot study has the potential to increase the quality of the research as results from such studies can inform subsequent parts of the research process.