Mitochondrial morphology controls fatty acid utilization by changing CPT1 sensitivity to malonyl-CoA

Changes in mitochondrial morphology are associated with nutrient utilization, but the precise causalities and the underlying mechanisms remain unknown. Here, using cellular models representing a wide variety of mitochondrial shapes, we show a strong linear correlation between mitochondrial fragmentation and increased fatty acid oxidation (FAO) rates. Forced mitochondrial elongation following MFN2 over-expression or DRP1 depletion diminishes FAO, while forced fragmentation upon knockdown or knockout of MFN2 augments FAO as evident from respirometry and metabolic tracing. Remarkably, the genetic induction of fragmentation phenocopies distinct cell type-specific biological functions of enhanced FAO. These include stimulation of gluconeogenesis in hepatocytes, induction of insulin secretion in islet β-cells exposed to fatty acids, and survival of FAO-dependent lymphoma subtypes. We find that fragmentation increases long-chain but not short-chain FAO, identifying carnitine O-palmitoyltransferase 1 (CPT1) as the downstream effector of mitochondrial morphology in regulation of FAO. Mechanistically, we determined that fragmentation reduces malonyl-CoA inhibition of CPT1, while elongation increases CPT1 sensitivity to malonyl-CoA inhibition. Overall, these findings underscore a physiologic role for fragmentation as a mechanism whereby cellular fuel preference and FAO capacity are determined.

Neuroendocrine stress hormones do not recreate the postoperative hypercoagulable state

Surgery causes changes in hemostasis, leading to a hypercoagulable state that has been linked to both arterial and venous thrombotic complications. The etiology of this state is unknown, but many investigators have hypothesized that perioperative neuroendocrine changes are responsible. We have previously demonstrated minimal increases in hemostatic function with a stress hormone infusion. This study was undertaken to further examine the relationship between neuroendocrine hormones and hemostatic function. Seventeen healthy volunteers were administered a stress hormone cocktail i.v. (epinephrine, cortisol, glucagon, angiotensin II, and vasopressin) for 24 h in a blind, placebo-controlled, cross-over design in our clinical research center. Venous blood samples were obtained for measurement of hemostatic function before the infusion and at 2, 8, and 24 h. There were no demonstrable increases in any measure of hypercoagulability. Alternatively, there was an increase in tissue plasminogen activator and protein C activity. These changes are consistent with an inhibition of coagulation and improved fibrinolysis. These data suggest that this combination of neuroendocrine hormones is not responsible for the postoperative hypercoagulable state.

IMPLICATIONS

Infusion of five stress hormones (epinephrine, cortisol, glucagon, vasopressin, and angiotensin II) to normal volunteers does not cause increases in procoagulant proteins and platelet reactivity or decreases in fibrinolytic proteins. Alternatively, these five hormones caused increased levels of fibrinolytic proteins (tissue plasminogen activator) and endogenous anticoagulants (protein C antigen and activity).

A non-canonical Raf function is required for dorsal-ventral patterning during Drosophila embryogenesis

Proper embryonic development requires directional axes to pattern cells into embryonic structures. In Drosophila, spatially discrete expression of transcription factors determines the anterior to posterior organization of the early embryo, while the Toll and TGFβ signalling pathways determine the early dorsal to ventral pattern. Embryonic MAPK/ERK signaling contributes to both anterior to posterior patterning in the terminal regions and to dorsal to ventral patterning during oogenesis and embryonic stages. Here we describe a novel loss of function mutation in the Raf kinase gene, which leads to loss of ventral cell fates as seen through the loss of the ventral furrow, the absence of Dorsal/NFκB nuclear localization, the absence of mesoderm determinants Twist and Snail, and the expansion of TGFβ. Gene expression analysis showed cells adopting ectodermal fates much like loss of Toll signaling. Our results combine novel mutants, live imaging, optogenetics and transcriptomics to establish a novel role for Raf, that appears to be independent of the MAPK cascade, in embryonic patterning.