Linking ascorbic acid production in Ribes nigrum with fruit development and changes in sources and sinks

Background and Aims

Understanding the synthesis of ascorbic acid (l-AsA) in green tissues in model species has advanced considerably; here we focus on its production and accumulation in fruit. In particular, our aim is to understand the links between organs which may be sources of l-AsA (leaves) and those which accumulate it (fruits). The work presented here tests the idea that changes in leaf and fruit number influence the accumulation of l-AsA. The aim was to understand the importance of leaf tissue in the production of l-AsA and to determine how this might provide routes for the manipulation of fruit tissue l-AsA.

Methods

The experiments used Ribes nigrum (blackcurrant), predominantly in field experiments, where the source–sink relationship was manipulated to alter potential leaf l-AsA production and fruit growth and accumulation of l-AsA. These manipulations included reductions in reproductive capacity, by raceme removal, and the availability of assimilates by leaf removal and branch phloem girdling. Natural variation in fruit growth and fruit abscission is also described as this influences subsequent experimental design and the interpretation of l-AsA data.

Key Results

Results show that fruit l-AsA concentration is conserved but total yield of l-AsA per plant is dependent on a number of innate factors many of which relate to raceme attributes. Leaf removal and phloem girdling reduced fruit weight, and a combination of both reduced fruit yields further. It appears that around 50 % of assimilates utilized for fruit growth came from apical leaves, while between 20 and 30 % came from raceme leaves, with the remainder from ‘storage’.

Conclusions

Despite being able to manipulate leaf area and therefore assimilate availability and stored carbohydrates, along with fruit yields, rarely were effects on fruit l-AsA concentration seen, indicating fruit l-AsA production in Ribes was not directly coupled to assimilate supply. There was no supporting evidence that l-AsA production occurred predominantly in green leaf tissue followed by its transfer to developing fruits. It is concluded that l-AsA production occurs predominantly in the fruit of Ribes nigrum.     

Immune modulation of effector CD4+ and regulatory T cell function by sorafenib in patients with hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a difficult to treat cancer characterized by poor tumor immunity with only one approved systemic drug, sorafenib. If novel combination treatments are to be developed with immunological agents, the effects of sorafenib on tumor immunity are important to understand. In this study, we investigate the impact of sorafenib on the CD4+CD25? effector T cells (Teff) and CD4+CD25+ regulatory T cells (Tregs) from patients with HCC. We isolated Teff and Treg from peripheral mononuclear cells of HCC patients to determine immune reactivity by thymidine incorporation, ELISA and flow cytometry. Teff cultured alone or with Treg were supplemented with different concentrations of sorafenib. The effects of sorafenib on Teff responses were dose-dependent. Pharmacologic doses of sorafenib decreased Teff activation by down regulating CD25 surface expression. In contrast, sub-pharmacologic concentrations of sorafenib resulted in Teff activation. These low doses of sorafenib in the Teff cultures led to a significant increase in Teff proliferation, IL2 secretion and up-regulation of CD25 expression on the cell surface. In addition, low doses of sorafenib in the suppression Teff/Treg cocultures restored Teff responses by eliminating Treg suppression. The loss of Treg suppressive function correlated with an increase in IL2 and IL6 secretion. Our findings show that sub-pharmacologic doses of sorafenib impact subsets of T cells differently, selectively increasing Teff activation while blocking Treg function. In conclusion, this study describes novel immune activating properties of low doses of sorafenib by promoting immune responsiveness in patients with HCC.     

Publications of Anthony Calhoun Clement (1909–1984)

Summary

Two zoeae and the megalopa of the majid crab Macropodia parva were obtained from laboratory material. At 25±1°C and 35% salinity, the first crab appeared 12 days after hatching; survival to the first crab instar was 27%. The larval stages are described in detail and compared with those of the previously described species of the genus Macropodia. Zoeal characteristics of M. parva that differentiate it from other known Macropodia larvae are the naked telson furcae and the absence, in zoea II, of the exopodal setae on the basis of the maxillule.     

Human Core Temperature Responses during Exercise and Subsequent Recovery: An Important Interaction between Diurnal Variation and Measurement Site

Chronobiological investigations into core temperature during and after exercise can involve ambulatory measurements of intestinal temperature during actual competitions, esophageal temperature measurements in laboratory simulations, or rectal temperature, which can be measured in both the field and laboratory. These sites have yet to be compared during both morning and afternoon exercise and subsequent recovery. At 08∶00 and 17∶00 h, seven recreationally active males exercised at 70% peak oxygen uptake for 30 min and then recovered passively for 30 min. During the experiment, esophageal, rectal, intestinal, and skin temperatures, plus sweat loss, heart rate, and ratings of perceived exertion (RPE), were monitored. We found that the diurnal variation in intestinal temperature responses (0.45±0.32°C; mean±SD) was significantly larger compared with rectal (0.33±0.24°C) and, particularly, esophageal temperature responses (0.21±0.20°C; p= 0.019). This reflected a greater difference of 0.25–0.40°C between the esophagus and the other two sites in the afternoon, compared to inter‐site differences of only 0.13–0.16°C in the morning. Diurnal variation was small for skin temperature, heart rate, sweat loss, and RPE responses during exercise (p>0.05). Our data suggest that the relative differences between intestinal, rectal, and esophageal temperature during exercise and subsequent recovery depend on time of day to the extent that inferences from studies on experimental and applied chronobiology will be affected.     

Structural, kinetic and computational investigation of Vitis vinifera DHDPS reveals new insight into the mechanism of lysine-mediated allosteric inhibition

Lysine is one of the most limiting amino acids in plants and its biosynthesis is carefully regulated through inhibition of the first committed step in the pathway catalyzed by dihydrodipicolinate synthase (DHDPS). This is mediated via a feedback mechanism involving the binding of lysine to the allosteric cleft of DHDPS. However, the precise allosteric mechanism is yet to be defined. We present a thorough enzyme kinetic and thermodynamic analysis of lysine inhibition of DHDPS from the common grapevine, Vitis vinifera (Vv). Our studies demonstrate that lysine binding is both tight (relative to bacterial DHDPS orthologs) and cooperative. The crystal structure of the enzyme bound to lysine (2.4 Å) identifies the allosteric binding site and clearly shows a conformational change of several residues within the allosteric and active sites. Molecular dynamics simulations comparing the lysine-bound (PDB ID 4HNN) and lysine free (PDB ID 3TUU) structures show that Tyr132, a key catalytic site residue, undergoes significant rotational motion upon lysine binding. This suggests proton relay through the catalytic triad is attenuated in the presence of lysine. Our study reveals for the first time the structural mechanism for allosteric inhibition of DHDPS from the common grapevine.     

Discovery of an intravenous hepatoselective glucokinase activator for the treatment of inpatient hyperglycemia

Glucokinase (hexokinase IV) continues to be a compelling target for the treatment of type 2 diabetes given the wealth of supporting human genetics data and numerous reports of robust clinical glucose lowering in patients treated with small molecule allosteric activators. Recent work has demonstrated the ability of hepatoselective activators to deliver glucose lowering efficacy with minimal risk of hypoglycemia. While orally administered agents require a considerable degree of passive permeability to promote suitable exposures, there is no such restriction on intravenously delivered drugs. Therefore, minimization of membrane diffusion in the context of an intravenously agent should ensure optimal hepatic targeting and therapeutic index. This work details the identification a hepatoselective GKA exhibiting the aforementioned properties.     

Characterization of Adherent Bacteroidales from Intestinal Biopsies of Children and Young Adults with Inflammatory Bowel Disease

There is extensive evidence implicating the intestinal microbiota in inflammatory bowel disease [IBD], but no microbial agent has been identified as a sole causative agent. Bacteroidales are numerically dominant intestinal organisms that associate with the mucosal surface and have properties that both positively and negatively affect the host. To determine precise numbers and species of Bacteroidales adherent to the mucosal surface in IBD patients, we performed a comprehensive culture based analysis of intestinal biopsies from pediatric Crohn''s disease [CD], ulcerative colitis [UC], and control subjects. We obtained biopsies from 94 patients and used multiplex PCR or 16S rDNA sequencing of Bacteroidales isolates for species identification. Eighteen different Bacteroidales species were identified in the study group, with up to ten different species per biopsy, a number higher than demonstrated using 16S rRNA gene sequencing methods. Species diversity was decreased in IBD compared to controls and with increasingly inflamed tissue. There were significant differences in predominant Bacteroidales species between biopsies from the three groups and from inflamed and uninflamed sites. Parabacteroides distasonis significantly decreased in inflamed tissue. All 373 Bacteroidales isolates collected in this study grew with mucin as the only utilizable carbon source suggesting this is a non-pathogenic feature of this bacterial order. Bacteroides fragilis isolates with the enterotoxin gene [bft], previously associated with flares of colitis, were not found more often at inflamed colonic sites or within IBD subjects. B. fragilis isolates with the ability to synthesize the immunomodulatory polysaccharide A [PSA], previously shown to be protective in murine models of colitis, were not detected more often from healthy versus inflamed tissue.     

Fatty Acid‐Derived Pro‐Toxicants of the Rat Selective Toxicant Norbormide

Norbormide [5‐(α‐hydroxy‐α‐2‐pyridylbenzyl)‐7‐(α‐2‐pyridylbenzylidene)‐5‐norbornene‐2,3‐dicarboximide] (NRB), an existing but infrequently used rodenticide, is known to be uniquely toxic to rats but relatively harmless to other rodents and mammals. However, as an acute vasoactive, NRB has a rapid onset of action which makes it relatively unpalatable to rats, often leading to sublethal uptake and accompanying bait shyness. A series of NRB‐derived pro‐toxicants ( 3a  –  i , 4a  –  i , and 5a  –  i ) were prepared in an effort to ‘mask’ this acute response and improve both palatability and efficacy. Their synthesis, in vitro biological evaluation (vasocontractile response in rat vasculature, stability in selected rat media) and palatability/efficacy in Sprague–Dawley, wild Norway, and wild ship rats is described. Most notably, pro‐toxicant 3d was revealed to be free of all pre‐cleavage vasoconstrictory activity in rat caudal artery and was subsequently demonstrated to release NRB in the presence of rat blood, liver, and pancreatic enzymes. Moreover, it consistently displayed a high level of acceptance by rats in a two‐choice bait‐palatability and efficacy trial, with accompanying high mortality. On this evidence, fatty acid ester prodrugs would appear to offer a promising platform for the further development of NRB‐derived toxicants with enhanced palatability and efficacy profiles.     

Atg5-dependent autophagy contributes to the development of acute myeloid leukemia in an MLL-AF9-driven mouse model

Acute myeloid leukemia (AML) is a hierarchical hematopoietic malignancy originating from leukemic stem cells (LSCs). Autophagy is a lysosomal degradation pathway that is hypothesized to be important for the maintenance of AML as well as contribute to chemotherapy response. Here we employ a mouse model of AML expressing the fusion oncogene MLL-AF9 and explore the effects of Atg5 deletion, a key autophagy protein, on the malignant transformation and progression of AML. Consistent with a transient decrease in colony-forming potential in vitro, the in vivo deletion of Atg5 in MLL-AF9-transduced bone marrow cells during primary transplantation prolonged the survival of recipient mice, suggesting that autophagy has a role in MLL-AF9-driven leukemia initiation. In contrast, deletion of Atg5 in malignant AML cells during secondary transplantation did not influence the survival or chemotherapeutic response of leukemic mice. Interestingly, autophagy was found to be involved in the survival of differentiated myeloid cells originating from MLL-AF9-driven LSCs. Taken together, our data suggest that Atg5-dependent autophagy may contribute to the development but not chemotherapy sensitivity of murine AML induced by MLL-AF9.Acute myeloid leukemia (AML) is a clonal hematopoietic malignancy characterized by the uncontrolled proliferation of immature myeloid cells within the bone marrow (BM), eventually suppressing normal hematopoiesis.¹ Recurrent chromosomal translocations frequently occur in AML, one of which involves the fusions of the KMT2A gene on chromosome 11 to a number of potential partners that are diagnosed as prognostically intermediate to poor.¹ Among these fusions, the MLL-AF9 fusion oncogene, resulting from the t(9;11)(p22;q23) translocation, is well studied owing to its robust phenotype in various mouse models of AML.^{2, 3, 4} It has been previously reported that BM transplantation of hematopoietic progenitors expressing exogenous MLL-AF9 leads to rapid in vivo transformation and progression of AML in a syngeneic, immunocompetent mouse model and recapitulates the poor chemotherapy response of t(9;11)(p22;q23) fusion human AML.^{2, 5}Autophagy is an evolutionarily conserved catabolic pathway by which cellular components are engulfed by double-membraned vesicles, called autophagosomes, and delivered to the lysosome for degradation and recycling. Autophagy is best characterized to be induced under stressful conditions, such as organelle damage or nutrient deprivation, and is followed by the elongation of the autophagosome membrane around its cargo. In Atg5-dependent autophagy, the conversion of LC3-I to LC3-II by lipidation is crucial for autophagosome membrane expansion, which is mediated by a series of ubiquitin-like conjugation systems.⁶ Within this pathway, the Atg5-Atg12-Atg16 complex acts as an E3-ubiquitin-ligase-like enzyme that specifically mediates the conjugation of LC3-I to phosphatidylethanolamine to form LC3-II, which inserts to the autophagosomal membrane. Autophagosome maturation is followed by fusion to lysosomes, at which time the inner compartment is degraded. The genetic ablation of Atg5 leads to a complete and highly selective inhibition of LC3-dependent autophagosome formation.^{6, 7}Autophagy is known to be implicated in cancer as both a tumor promoter and a tumor suppressor.⁸ The genetic ablation of autophagy in mouse hematopoietic stem cells (HSCs) has been shown to result in severe impairments to HSC maintenance.^{9, 10, 11, 12, 13} Autophagy dysregulation has also been implicated in AML,^{12, 13, 14} suggesting that targeting autophagy could be promising for AML treatment. As an expanding arsenal of pharmacological autophagy modulators are being developed,^{15, 16} it has become increasingly important to specifically determine whether autophagy has an important role in AML using a genetic mouse model. Therefore, we sought to dissect the role of autophagy through the in vivo homozygous deletion of Atg5 in MLL-AF9-driven murine AML. We discover in this study that Atg5 deletion during primary transplantation prolongs the survival of animals, whereas Atg5 deletion after secondary transplantation has no effect on animal survival, suggesting a role for autophagy in the initiation, but not maintenance, of AML in our model. We additionally assessed the effect of autophagy in chemotherapeutic response and found that Atg5 deletion in our MLL-AF9 model had no effect on the in vivo response to cytarabine and doxorubicin combination therapy, suggesting that autophagy does not significantly contribute to chemotherapy response in this model.