Diet and Adaptive Evolution of Alanine-Glyoxylate Aminotransferase Mitochondrial Targeting in Birds.

Adaptations to different diets represent a hallmark of animal diversity. The diets of birds are highly variable, making them an excellent model system for studying adaptive evolution driven by dietary changes. To test whether molecular adaptations to diet have occurred during the evolution of birds, we examined a dietary enzyme alanine-glyoxylate aminotransferase (AGT), which tends to target mitochondria in carnivorous mammals, peroxisomes in herbivorous mammals, and both mitochondria and peroxisomes in omnivorous mammals. A total of 31 bird species were examined in this study, which included representatives of most major avian lineages. Of these, 29 have an intact mitochondrial targeting sequence (MTS) of AGT. This finding is in stark contrast to mammals, which showed a number of independent losses of the MTS. Our cell-based functional assays revealed that the efficiency of AGT mitochondrial targeting was greatly reduced in unrelated lineages of granivorous birds, yet it tended to be high in insectivorous and carnivorous lineages. Furthermore, we found that proportions of animal tissue in avian diets were positively correlated with mitochondrial targeting efficiencies that were experimentally determined, but not with those that were computationally predicted. Adaptive evolution of AGT mitochondrial targeting in birds was further supported by the detection of positive selection on MTS regions. Our study contributes to the understanding of how diet drives molecular adaptations in animals, and suggests that caution must be taken when computationally predicting protein subcellular targeting.

Activation of autophagy improved the neurologic outcome after cardiopulmonary resuscitation in rats.

OBJECTIVE: Recent studies have shown the existence of autophagy in cerebral ischemia; however, there has been no research on the role of autophagy in cerebral injury after cardiopulmonary resuscitation (CPR). This study was conducted to determine the role of autophagy in an animal model of ventricular fibrillation (VF)/CPR. METHODS: Experiment 1: A total of 48 adult Wistar rats were untreated for 7 minutes after induction of VF using an external transthoracic alternating current, and subsequent CPR was performed to observe the existence of autophagy after the return of spontaneous circulation (ROSC). Experiment 2: A total of 72 rats were pretreated with intracerebroventricular injection of physiologic saline (control group), the autophagy inducer (rapamycin group), or the autophagy inhibitor 3-methyladenine (3-methyladenine group) before ROSC to evaluate the contribution of autophagy to neuronal injury after ROSC. RESULTS: The activation of autophagy was attenuated 2 to 4 hours after ROSC, which was related to the activity decrease of 5'-adenosine monophosphate-activated protein kinase after ROSC. Rapamycin treatment significantly increased the expressions of LC3-II and Beclin-1 after ROSC, attenuated the activation of caspase-3, promoted neuronal survival and decreased neuronal apoptosis, and improved the neurologic deficit score after CPR. CONCLUSIONS: The activation of autophagy after ROSC offered a remarkable tolerance to VF/CPR ischemic insult and improved the neurologic outcomes.

Competitive oxidation and ubiquitylation on the evolutionarily conserved cysteine confer tissue-specific stabilization of Insig-2.

Insig-2 is an ER membrane protein negatively controlling lipid biosynthesis. Here, we find that Insig-2 is increased in the tissues, including liver, but unaltered in the muscle of gp78-deficient mice. In hepatocytes and undifferentiated C2C12 myoblasts, Insig-2 is ubiquitylated on Cys215 by gp78 and degraded. However, the C215 residue is oxidized by elevated reactive oxygen species (ROS) during C2C12 myoblasts differentiating into myotubes, preventing Insig-2 from ubiquitylation and degradation. The stabilized Insig-2 downregulates lipogenesis through inhibiting the SREBP pathway, helping to channel the carbon flux to ATP generation and protecting myotubes from lipid over-accumulation. Evolutionary analysis shows that the YECK (in which C represents Cys215 in human Insig-2) tetrapeptide sequence in Insig-2 is highly conserved in amniotes but not in aquatic amphibians and fishes, suggesting it may have been shaped by differential selection. Together, this study suggests that competitive oxidation-ubiquitylation on Cys215 of Insig-2 senses ROS and prevents muscle cells from lipid accumulation.