[AMP-activated protein kinase: how a mistake in energy gauge causes glycogen storage].

Mutation in PRKAG2 encoding the gamma2 subunit of the AMP activated protein kinase (AMPK) cause human cardiomyopathy characterized by hypertrophy, Wolff-Parkinson-White syndrome, conduction system disease and glycogen storage in the myocardium. AMPK is a master metabolic regulator activated by hormones and energy deficient states. A heterotrimer enzyme comprising the catalytic alpha- and regulatory beta-and gamma-subunits was preserved through evolution and is ubiquitously expressed among mammalian tissues. AMPK is activated by AMP and inhibited by ATP that competes for binding to the regulatory sites on the gamma-subunit. Upstream kinases which phosphorylate Thr172 on the catalytic subunit activate the enzyme during exercise, ischemia, in response to sympathetic stimulation and hormones such as leptin and adiponectin. AMPK operates by phosphorylating its target proteins such as Acetyl CoA Carboxylase. Its classic functions include decreased fat synthesis in liver and adipose tissues, increased fatty acid oxidation, stimulating muscle glucose uptake and glycolysis. Altogether, these activities serve to restore the cellular and whole body energy balance. Human mutations which disrupt the nucleotide-binding affinity of the gamma2 subunit lead to loss of inhibition by ATP and inappropriate activate AMPK under resting conditions. As a result, myocytes recruit energy metabolites in excess of demand, causing storage of glycogen. Will AMPK ever emerge as a therapeutic target? Bench experiments suggest its potential in treating diabetes, ischemia and cell cycle regulation but much work is needed until these developments reach the bedside.

Diminished selection for thymidine-analog mutations associated with the presence of M184V in Ethiopian children infected with HIV subtype C receiving lamivudine-containing therapy.

BACKGROUND: We retrospectively studied the effect of the lamivudine-induced reverse transcription mutation M184V on selection of thymidine analog mutations (TAMs) in HIV subtype C-infected children and on clinical outcome. METHODS: We genotyped 135 blood samples from 55 children. TAMs accumulation, viral load and clinical outcome were compared in children maintained on zidovudine/stavudine + lamivudine + protease inhibitor/nonnucleoside reverse transcriptase inhibitor (PI/NNRTI) despite loss of viral suppression and in children treated with, or switched to, other nucleoside reverse transcriptase inhibitors (NRTIs). Drug susceptibility and replication capacity of selected samples were measured. RESULTS: M184V developed in 18 of 22 of children who had received only zidovudine/stavudine + lamivudine + PI/NNRTI during a mean of 23.2 +/- 3.2 months versus in 3 of 14 children treated with other drugs and/or having multiple regimen changes (P = 0.001). TAMs appeared, respectively, in 2 of 22 versus 12 of 14 (P < 0.0001). The 2 groups did not differ significantly in baseline HIV-RNA or CD4 count, sampling time, and follow-up period. In M184V-containing samples, we found large reductions in susceptibility to lamivudine and emtricitabine but not to other NRTIs. When T215Y was present without M184V, susceptibility to zidovudine was reduced 8-fold. When both M184V + T215Y occurred, susceptibility to zidovudine was substantially increased. Average inhibition concentration 50 values were similar to those documented in the Stanford database for subtype B HIV with these mutation patterns. CONCLUSIONS: Maintaining a thymidine analog + lamivudine-based regimen reduced accumulation of TAMs and increased zidovudine susceptibility. This is likely the result of an increased susceptibility to thymidine analog (zidovudine) in the context of M184V documented here for the first time in subtype C-infected children. This retrospective study supports the strategy of maintaining lamivudine-containing therapy in subtype C-infected children. This strategy may be beneficially applied in the treatment of children in Africa, where thymidine analog + lamivudine-based regimen became available recently but further options are limited.

Increased glycogen stores due to gamma-AMPK overexpression protects against ischemia and reperfusion damage.

During ischemia, endogenous glycogen becomes the principal substrate for energy through glycolysis. Cardiac-specific manipulation of AMP-activated protein kinase (AMPK) by over-expression of its regulatory gamma-subunit induces glycogen storage. The aim of this study was to examine whether heart glycogen in transgenic mice overexpressing PRKAG2 may protect from ischemia and reperfusion injury. Isolated hearts were mounted on Langendorff apparatus and subjected to 30 min 'no-flow' or 'low-flow' ischemia and 60 min reperfusion. Hemodynamic measurements, tetrazolium staining, glycogen and lactate were used to monitor ischemia reperfusion damage. After low-flow ischemia, left ventricular pressure, coronary flow (CF) and the area of viable myocardium were 20-30% higher in PRKAG2 mice compared to controls. The basal levels of glycogen in PRKAG2 were 9.2 microg/g, markedly higher than in controls, but after low-flow ischemia they declined concomitantly with increased lactate washout in the coronary effluent. During no-flow ischemia there was neither protection nor consumption of glycogen in PRKAG2 hearts. Cardioprotection was also eliminated when PRKAG2 hearts were depleted of glycogen prior to low-flow ischemia. AMPK alpha Thr172 phosphorylation did not differ between PRKAG2 hearts and controls either during low-flow ischemia or reperfusion. We conclude that PRKAG2 hearts resist low-flow ischemia injury better than controls. Improved recovery was associated with increased consumption of glycogen, and was unrelated to AMPK activation. These findings demonstrate the potential of heart protection from ischemia and reperfusion injury through metabolic manipulation increasing the level and utilization of myocardial glycogen.