Activation of AMPK by Bitter Melon Triterpenoids Involves CaMKKβ

We recently showed that bitter melon-derived triterpenoids (BMTs) activate AMPK and increase GLUT4 translocation to the plasma membrane in vitro, and improve glucose disposal in insulin resistant models in vivo. Here we interrogated the mechanism by which these novel compounds activate AMPK, a leading anti-diabetic drug target. BMTs did not activate AMPK directly in an allosteric manner as AMP or the Abbott compound (A-769662) does, nor did they activate AMPK by inhibiting cellular respiration like many commonly used anti-diabetic medications. BMTs increased AMPK activity in both L6 myotubes and LKB1-deficient HeLa cells by 20–35%. Incubation with the CaMKKβ inhibitor, STO-609, completely attenuated this effect suggesting a key role for CaMKKβ in this activation. Incubation of L6 myotubes with the calcium chelator EGTA-AM did not alter this activation suggesting that the BMT-dependent activation was Ca²⁺-independent. We therefore propose that CaMKKβ is a key upstream kinase for BMT-induced activation of AMPK.     

Mammalian cell processing of a unique uracil residue in simian virus 40 DNA.

The processing of a unique uracil in DNA has been studied in mammalian cells. A synthetic oligodeoxyribonucleotide carrying a potential Bgl II restriction site, where one base has been substituted with a uracil, was inserted in the early intron of SV40 genome. Various heteroduplexes were constructed in such a manner that the restitution of an active Bgl II restriction site corresponds in each case to the specific substitution of the uracil by one of the four bases normally present in the DNA. DNA cuts by this restriction enzyme in one or several constructed heteroduplexes immediately determine the type of base pair substitution produced at the site of the U residue. When the uracil is inserted opposite a purine it is fully repaired; when facing a guanine it is replaced by a cytosine and opposite an adenine it is replaced by a thymine. These results indicate the error-free repair of uracil when it appears in the cell with the usual mechanisms such as cytosine deamination or incorporation of dUTP in place of dTTP during replication. When the uracil is inserted opposite a pyrimidine no error free repair at all is detected for U:C or U:T mismatches. It appears, moreover, that in approximately 18% of the cases U:T mismatch leads to a C:G base pairing. In the majority of the U:pyrimidine mismatches, mutations occur in the vicinity of the uracil, including base substitutions and frameshifts by addition of one or several bases.     

Role of malolactic fermentation in lactic acid bacteria

Although decarboxylation of malate to lactate by malolactic enzyme does not liberate biologically available energy (e.g., ATP, NADH), the growth rate of many malolactic bacteria is greatly enhanced by malolactic fermentation. The deacidification of the medium due to malate dissipation cannot fully account for this situation. The chemiosmotic theory postulates that another form of energy could generated by translocation of protons through the membrane coupled to end-product efflux. Konings et al. showed that this theory is indeed applicable to lactate efflux in Streptococcus cremoris at pH 7.0. A similar mechanism could account for the observed increased activity in malolactic bacteria. The study in wild type and mutant strains of Streptococcus lactis unable to carry out malolactic fermentation led us to the following conclusions: (1) under glucose non-limiting conditions, malolactic fermentation helps to maintain pH of the medium at a certain level; (2) during glucose limited growth, malolactic fermentation could be coupled with an energetic process independent from that mentioned above.     

Opposite effects of two ligands for peripheral type benzodiazepine binding sites, PK 11195 and RO5-4864, in a conflict situation in the rat

The effects of two drugs acting at the peripheral type benzodiazepine binding sites, PK 11195 and RO5-4864, were examined in shock-induced suppression of drinking in rats. These two compounds have opposite effects : RO5-4864 (3.1-1205 mg/kg i.p.) enhanced whereas PK 11195 (25-50 mg/kg i.p.) decreased the punished responding, and PK 11195 (6.25 mg/kg, a dose which did not alter the punished responding) blocked the proconflict action of RO5-4864 (6.25 and 12.5 mg/kg). The effects of RO5-4864 and PK 11195 were not antagonized by RO15-1788, a selective antagonist of the central benzodiazepine site. In addition, PK 11195 (6.25 mg/kg) did not reverse the proconflict effect of two beta-carbolines : beta-CEE and FG 7142. AS picrotoxin did not change the punished responding, these data imply that the effects of RO5-4864 and PK 11195 on the one hand and those of chlordiazepoxide and beta-carbolines on the other hand are differentially mediated and suggest that the peripheral type benzodiazepine binding sites are involved in this conflict model.     

Peripheral benzodiazepine binding sites: Effect of PK 11195, 1-(2-chlorophenyl)-n-methyl-n-(1-methylpropyl)-3-isoquinolinecarboxamide: I. In vitro studies

[³H] R05-4864 binding sites have been characterized in kidney, heart, brain, adrenals and platelets in the rat. In all these organs the following order of potency in the R05-4864 displacement was found : R05-4864 > diazepam > clonazepam indicating that they correspond to the “peripheral type” of benzodiazepine binding sites. PK 11195, an isoquinoline carboxamide derivative, displaces [³H] R05-4864 from its binding sites in all the organs. PK 11195 was as potent as R05-4864 in the platelets, heart, adrenals, kidney and several brain regions (midbrain, hypothalamus, medulla + pons and hippocampus. However it was 5 to 10 times more effective in cortex and striatum. In conclusion PK 11195 might represent a new tool to elucidate the physiological relevance of “peripheral type” benzodiazepine binding sites and might help to discriminate the hypothetical subclasses of these binding sites.     

Product of the Lactococcus lactis gene required for malolactic fermentation is homologous to a family of positive regulators.

Malolactic fermentation is a secondary fermentation that many lactic acid bacteria can carry out when L-malate is present in the medium. The activation of the malolactic system in Lactococcus lactis is mediated by a locus we call mleR. Induction of the genes necessary to perform malolactic fermentation occurs only in bacteria with a functional copy of mleR. The mleR gene consists of one open reading frame capable of coding for a protein with a calculated molecular mass of 33,813 daltons. The amino acid sequence of the predicted MleR gene product is homologous to that of positive activators in gram-negative bacteria: LysR, IlvY gene products of Escherichia coli, MetR, CysB of Salmonella typhimurium, AmpR of Enterobacter cloacae, NodD of Rhizobium sp., and TrpI of Pseudomonas aeruginosa.     

Imbalance of leucine flux in Lactococcus lactis and its use for the isolation of diacetyl-overproducing strains.

Diacetyl is a by-product of pyruvate metabolism in Lactococcus lactis, where pyruvate is first converted to alpha-acetolactate, which is slowly decarboxylated to diacetyl in the presence of oxygen. L. lactis usually converts alpha-acetolactate to acetoin enzymatically, by alpha-acetolactate decarboxylase encoded by the aldB gene. We took advantage of the fact that this enzyme also has a central role in the regulation of branched-chain amino acids, to select spontaneous aldB mutants in an unbalanced concentration of leucine versus those of valine and isoleucine in the medium. Industrial dairy strains of L. lactis subsp. lactis biovar diacetylactis containing point mutations and deletions of aldB were isolated and characterized. Their growth in milk was not affected, but they rapidly accumulated a large amount of alpha-acetolactate instead of acetoin from citrate in milk. Under aerated condition, strains devoid of AldB produced about 10 times more diacetyl than did the parental strains.     

Three major mesoplanktonic communities resolved by in situ imaging in the upper 500 m of the global ocean

Aim

The distribution of mesoplankton communities has been poorly studied at global scale, especially from in situ instruments. This study aims to (1) describe the global distribution of mesoplankton communities in relation to their environment and (2) assess the ability of various environmental-based ocean regionalizations to explain the distribution of these communities.

Location

Global ocean, 0–500 m depth.

Time Period

2008–2019.

Major Taxa Studied

Twenty-eight groups of large mesoplanktonic and macroplanktonic organisms, covering Metazoa, Rhizaria and Cyanobacteria.

Methods

From a global data set of 2500 vertical profiles making use of the Underwater Vision Profiler 5 (UVP5), an in situ imaging instrument, we studied the global distribution of large (>600 μm) mesoplanktonic organisms. Among the 6.8 million imaged objects, 330,000 were large zooplanktonic organisms and phytoplankton colonies, the rest consisting of marine snow particles. Multivariate ordination (PCA) and clustering were used to describe patterns in community composition, while comparison with existing regionalizations was performed with regression methods (RDA).

Results

Within the observed size range, epipelagic plankton communities were Trichodesmium-enriched in the intertropical Atlantic, Copepoda-enriched at high latitudes and in upwelling areas, and Rhizaria-enriched in oligotrophic areas. In the mesopelagic layer, Copepoda-enriched communities were also found at high latitudes and in the Atlantic Ocean, while Rhizaria-enriched communities prevailed in the Peruvian upwelling system and a few mixed communities were found elsewhere. The comparison between the distribution of these communities and a set of existing regionalizations of the ocean suggested that the structure of plankton communities described above is mostly driven by basin-level environmental conditions.

Main Conclusions

In both layers, three types of plankton communities emerged and seemed to be mostly driven by regional environmental conditions. This work sheds light on the role not only of metazoans, but also of unexpected large protists and cyanobacteria in structuring large mesoplankton communities.