Targeted multicolor in vivo imaging over 1,000 nm enabled by nonamethine cyanines.

Recent progress has shown that using wavelengths between 1,000 and 2,000 nm, referred to as the shortwave-infrared or near-infrared (NIR)-II range, can enable high-resolution in vivo imaging at depths not possible with conventional optical wavelengths. However, few bioconjugatable probes of the type that have proven invaluable for multiplexed imaging in the visible and NIR range are available for imaging these wavelengths. Using rational design, we have generated persulfonated indocyanine dyes with absorbance maxima at 872 and 1,072 nm through catechol-ring and aryl-ring fusion, respectively, onto the nonamethine scaffold. Multiplexed two-color and three-color in vivo imaging using monoclonal antibody and dextran conjugates in several tumor models illustrate the benefits of concurrent labeling of the tumor and healthy surrounding tissue and lymphatics. These efforts are enabled by complementary advances in a custom-built NIR/shortwave-infrared imaging setup and software package for multicolor real-time imaging.

GLP-1 metabolite GLP-1(9-36) is a systemic inhibitor of mouse and human pancreatic islet glucagon secretion.

AIMS/HYPOTHESIS: Diabetes mellitus is associated with impaired insulin secretion, often aggravated by oversecretion of glucagon. Therapeutic interventions should ideally correct both defects. Glucagon-like peptide 1 (GLP-1) has this capability but exactly how it exerts its glucagonostatic effect remains obscure. Following its release GLP-1 is rapidly degraded from GLP-1(7-36) to GLP-1(9-36). We hypothesised that the metabolite GLP-1(9-36) (previously believed to be biologically inactive) exerts a direct inhibitory effect on glucagon secretion and that this mechanism becomes impaired in diabetes. METHODS: We used a combination of glucagon secretion measurements in mouse and human islets (including islets from donors with type 2 diabetes), total internal reflection fluorescence microscopy imaging of secretory granule dynamics, recordings of cytoplasmic Ca2+ and measurements of protein kinase A activity, immunocytochemistry, in vivo physiology and GTP-binding protein dissociation studies to explore how GLP-1 exerts its inhibitory effect on glucagon secretion and the role of the metabolite GLP-1(9-36). RESULTS: GLP-1(7-36) inhibited glucagon secretion in isolated islets with an IC50 of 2.5 pmol/l. The effect was particularly strong at low glucose concentrations. The degradation product GLP-1(9-36) shared this capacity. GLP-1(9-36) retained its glucagonostatic effects after genetic/pharmacological inactivation of the GLP-1 receptor. GLP-1(9-36) also potently inhibited glucagon secretion evoked by ß-adrenergic stimulation, amino acids and membrane depolarisation. In islet alpha cells, GLP-1(9-36) led to inhibition of Ca2+ entry via voltage-gated Ca2+ channels sensitive to ω-agatoxin, with consequential pertussis-toxin-sensitive depletion of the docked pool of secretory granules, effects that were prevented by the glucagon receptor antagonists REMD2.59 and L-168049. The capacity of GLP-1(9-36) to inhibit glucagon secretion and reduce the number of docked granules was lost in alpha cells from human donors with type 2 diabetes. In vivo, high exogenous concentrations of GLP-1(9-36) (>100 pmol/l) resulted in a small (30%) lowering of circulating glucagon during insulin-induced hypoglycaemia. This effect was abolished by REMD2.59, which promptly increased circulating glucagon by >225% (adjusted for the change in plasma glucose) without affecting pancreatic glucagon content. CONCLUSIONS/INTERPRETATION: We conclude that the GLP-1 metabolite GLP-1(9-36) is a systemic inhibitor of glucagon secretion. We propose that the increase in circulating glucagon observed following genetic/pharmacological inactivation of glucagon signalling in mice and in people with type 2 diabetes reflects the removal of GLP-1(9-36)'s glucagonostatic action.

Identification of high-performing antibodies for the reliable detection of Tau proteoforms by Western blotting and immunohistochemistry.

Antibodies are essential research tools whose performance directly impacts research conclusions and reproducibility. Owing to its central role in Alzheimer's disease and other dementias, hundreds of distinct antibody clones have been developed against the microtubule-associated protein Tau and its multiple proteoforms. Despite this breadth of offer, limited understanding of their performance and poor antibody selectivity have hindered research progress. Here, we validate a large panel of Tau antibodies by Western blot (79 reagents) and immunohistochemistry (35 reagents). We address the reagents' ability to detect the target proteoform, selectivity, the impact of protein phosphorylation on antibody binding and performance in human brain samples. While most antibodies detected Tau at high levels, many failed to detect it at lower, endogenous levels. By WB, non-selective binding to other proteins affected over half of the antibodies tested, with several cross-reacting with the related MAP2 protein, whereas the "oligomeric Tau" T22 antibody reacted with monomeric Tau by WB, thus calling into question its specificity to Tau oligomers. Despite the presumption that "total" Tau antibodies are agnostic to post-translational modifications, we found that phosphorylation partially inhibits binding for many such antibodies, including the popular Tau-5 clone. We further combine high-sensitivity reagents, mass-spectrometry proteomics and cDNA sequencing to demonstrate that presumptive Tau "knockout" human cells continue to express residual protein arising through exon skipping, providing evidence of previously unappreciated gene plasticity. Finally, probing of human brain samples with a large panel of antibodies revealed the presence of C-term-truncated versions of all main Tau brain isoforms in both control and tauopathy donors. Ultimately, we identify a validated panel of Tau antibodies that can be employed in Western blotting and/or immunohistochemistry to reliably detect even low levels of Tau expression with high selectivity. This work represents an extensive resource that will enable the re-interpretation of published data, improve reproducibility in Tau research, and overall accelerate scientific progress.

Loss of tetraspanin-7 expression reduces pancreatic ß-cell exocytosis Ca2+ sensitivity but has limited effect on systemic metabolism.

BACKGROUND: Tetraspanin-7 (Tspan7) is an islet autoantigen involved in autoimmune type 1 diabetes and known to regulate ß-cell L-type Ca2+ channel activity. However, the role of Tspan7 in pancreatic ß-cell function is not yet fully understood. METHODS: Histological analyses were conducted using immunostaining. Whole-body metabolism was tested using glucose tolerance test. Islet hormone secretion was quantified using static batch incubation or dynamic perifusion. ß-cell transmembrane currents, electrical activity and exocytosis were measured using whole-cell patch-clamping and capacitance measurements. Gene expression was studied using mRNA-sequencing and quantitative PCR. RESULTS: Tspan7 is expressed in insulin-containing granules of pancreatic ß-cells and glucagon-producing α-cells. Tspan7 knockout mice (Tspan7y/- mouse) exhibit reduced body weight and ad libitum plasma glucose but normal glucose tolerance. Tspan7y/- islets have normal insulin content and glucose- or tolbutamide-stimulated insulin secretion. Depolarisation-triggered Ca2+ current was enhanced in Tspan7y/- ß-cells, but ß-cell electrical activity and depolarisation-evoked exocytosis were unchanged suggesting that exocytosis was less sensitive to Ca2+ . TSPAN7 knockdown (KD) in human pseudo-islets led to a significant reduction in insulin secretion stimulated by 20 mM K+ . Transcriptomic analyses show that TSPAN7 KD in human pseudo-islets correlated with changes in genes involved in hormone secretion, apoptosis and ER stress. Consistent with rodent ß-cells, exocytotic Ca2+ sensitivity was reduced in a human ß-cell line (EndoC-ßH1) following Tspan7 KD. CONCLUSION: Tspan7 is involved in the regulation of Ca2+ -dependent exocytosis in ß-cells. Its function is more significant in human ß-cells than their rodent counterparts.

Shortwave Infrared Imaging with J-Aggregates Stabilized in Hollow Mesoporous Silica Nanoparticles.

Tissue is translucent to shortwave infrared (SWIR) light, rendering optical imaging superior in this region. However, the widespread use of optical SWIR imaging has been limited, in part, by the lack of bright, biocompatible contrast agents that absorb and emit light above 1000 nm. J-Aggregation offers a means to transform stable, near-infrared (NIR) fluorophores into red-shifted SWIR contrast agents. Here we demonstrate that J-aggregates of NIR fluorophore IR-140 can be prepared inside hollow mesoporous silica nanoparticles (HMSNs) to result in nanomaterials that absorb and emit SWIR light. The J-aggregates inside PEGylated HMSNs are stable for multiple weeks in buffer and enable high resolution imaging in vivo with 980 nm excitation.

Ex vivo evaluation of a novel surgical guide on the accuracy of closing wedge osteotomies.

OBJECTIVE: To determine the influence of a novel surgical guide on the accuracy and technical difficulty of closing wedge osteotomies (CWO). STUDY DESIGN: Ex vivo experimental study. SAMPLE POPULATION: Canine tibia models (n = 40). METHODS: A 20° cranial CWO (CCWO) was created without (standard procedure; STCCWO) or with the aid of a novel wedge osteotomy guide (WOCCWO). Procedures were performed by diplomate (n = 4) and resident (n = 6) surgeons, with each performing 2 STCCWO followed by 2 WOCCWO. To prevent bias, surgeons were unaware of the study purpose until after completing the STCCWO. The wedges were evaluated by comparing the deviation from the 20° target angle, divergence of the 2 osteotomies (osteotomy divergence angle [ODA]), and measurements of the wedge height at the caudomedial cortex (CMC) and caudolateral cortex (CLC). Technique difficulty was explored through a surgeon questionnaire. RESULTS: The WOCCWO resulted in smaller mean ODA (WOCCWO = 0.86°, SD ± 0.38°, P < .001), and smaller mean difference between CMC and CLC (WOCCWO = 0.29 mm, SD ± 0.19, P < .001) than for the STCCWO (4.22°, SD ± 2.16° and 1.39 mm, SD ± 0.65 respectively). Deviation from the target 20° wedge angle was greater after STCCWO (1.46°, SD ± 1.27°) than after WOCCWO (0.53°, SD ± 0.33°, P = .004). No difference was reported regarding the difficulty of the procedures, but resident surgeons stated that they were more likely to use the guide in a clinical setting compared with diplomates. CONCLUSION: The wedge osteotomy guide improved the accuracy of CCWO compared with standard technique. CLINICAL SIGNIFICANCE: The clinical significance of the differences detected in this study is unclear and warrants in vivo investigation.

Geostatistical Prediction of Microbial Water Quality Throughout a Stream Network Using Meteorology, Land Cover, and Spatiotemporal Autocorrelation.

Predictive modeling is promising as an inexpensive tool to assess water quality. We developed geostatistical predictive models of microbial water quality that empirically modeled spatiotemporal autocorrelation in measured fecal coliform (FC) bacteria concentrations to improve prediction. We compared five geostatistical models featuring different autocorrelation structures, fit to 676 observations from 19 locations in North Carolina's Jordan Lake watershed using meteorological and land cover predictor variables. Though stream distance metrics (with and without flow-weighting) failed to improve prediction over the Euclidean distance metric, incorporating temporal autocorrelation substantially improved prediction over the space-only models. We predicted FC throughout the stream network daily for one year, designating locations "impaired", "unimpaired", or "unassessed" if the probability of exceeding the state standard was ≥90%, ≤10%, or >10% but <90%, respectively. We could assign impairment status to more of the stream network on days any FC were measured, suggesting frequent sample-based monitoring remains necessary, though implementing spatiotemporal predictive models may reduce the number of concurrent sampling locations required to adequately assess water quality. Together, these results suggest that prioritizing sampling at different times and conditions using geographically sparse monitoring networks is adequate to build robust and informative geostatistical models of water quality impairment.

Age as a prognostic factor in relation to surgical evacuation of spontaneous supratentorial intracerebral haemorrhage.

AIM AND CLINICAL RATIONALE FOR THE STUDY: Spontaneous intracerebral haemorrhage (sICH) is an acute life-threatening injury and constitutes 10-15% of first-ever stroke cases. The Surgical Trials in Intracerebral Haematoma studies (STICH and STICH II) represent the two foremost studies in the field, however, with arguable shortcomings. To find more accurate criteria, we aimed to correlate the preoperative neurological and neuroimaging findings with the clinical outcome of operated patients. MATERIALS AND METHODS: In this retrospective study, sICH patients were recruited from the Central Denmark Region from 2010 to 2016. We evaluated the patients' medical records regarding preoperative Glasgow Coma Scale (GCS) 6 months and one year after surgery, focal neurological defects, thrombolytic treatment, pupil status, and haemorrhage localization visualized by neuroimaging. The patients' clinical outcome was assessed using the Glasgow Outcome Scale (GOS). RESULTS: Based on logistic multiple linear analysis, age, basal ganglia haemorrhage and mass effect had significant effect on the mortality rate. Besides, age, basal ganglia haemorrhage, intra ventricular haemorrhage and pupil difference had significant correlation with good outcome (GOS>3). CONCLUSIONS AND CLINICAL IMPLICATIONS: Neurosurgical treatment of the sICH patients is indicated only if age and potentially improved morbidity is carefully evaluated considering the STICH and this study; otherwise, we will just increase the health care burden with a number of extremely care-dependent patients.

Lack of skeletal muscle IL-6 influences hepatic glucose metabolism in mice during prolonged exercise.

The liver is essential in maintaining and regulating glucose homeostasis during prolonged exercise. IL-6 has been shown to be secreted from skeletal muscle during exercise and has been suggested to signal to the liver. Therefore, the aim of this study was to investigate the role of skeletal muscle IL-6 on hepatic glucose regulation and substrate choice during prolonged exercise. Skeletal muscle-specific IL-6 knockout (IL-6 MKO) mice (age, 12-14 wk) and littermate lox/lox (Control) mice were either rested (Rest) or completed a single bout of exercise for 10, 60, or 120 min, and the liver was quickly obtained. Hepatic IL-6 mRNA was higher at 60 min of exercise, and hepatic signal transducer and activator of transcription 3 was higher at 120 min of exercise than at rest in both genotypes. Hepatic glycogen was higher in IL-6 MKO mice than control mice at rest, but decreased similarly during exercise in the two genotypes, and hepatic glucose content was lower in IL-6 MKO than control mice at 120 min of exercise. Hepatic phosphoenolpyruvate carboxykinase mRNA and protein increased in both genotypes at 120 min of exercise, whereas hepatic glucose 6 phosphatase protein remained unchanged. Furthermore, IL-6 MKO mice had higher hepatic pyruvate dehydrogenase (PDH)Ser232 and PDHSer300 phosphorylation than control mice at rest. In conclusion, hepatic gluconeogenic capacity in mice is increased during prolonged exercise independent of muscle IL-6. Furthermore, Skeletal muscle IL-6 influences hepatic substrate regulation at rest and hepatic glucose metabolism during prolonged exercise, seemingly independent of IL-6 signaling in the liver.

Exercise-induced regulation of key factors in substrate choice and gluconeogenesis in mouse liver.

As the demand for hepatic glucose production increases during exercise, regulation of liver substrate choice and gluconeogenic activity becomes essential. The aim of the present study was to investigate the effect of a single exercise bout on gluconeogenic protein content and regulation of enzymes involved in substrate utilization in the liver. Mice were subjected to 1 h of treadmill exercise, and livers were removed immediately, 4 or 10 h after exercise. Glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxylase (PEPCK) mRNA contents in the liver increased immediately after exercise, while the PEPCK protein content increased at 10 h of recovery. Furthermore, 5'AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase (ACC), and pyruvate dehydrogenase (PDH)-E1α Ser(293) phosphorylations decreased immediately after exercise. In addition, PDH kinase 4 (PDK4) mRNA and protein content increased immediately after exercise and at 10 h of recovery, respectively. These findings suggest that acute changes in PEPCK and G6Pase protein contents do not contribute to the regulation of gluconeogenic enzyme activity during 1 h of non-exhaustive exercise. In addition, the observation that PDH-E1α, AMPK, and ACC phosphorylation decreased immediately after exercise may indicate that carbohydrates rather than fatty acids are utilized for oxidation in the liver during non-exhaustive exercise.

Effects of IL-6 on pyruvate dehydrogenase regulation in mouse skeletal muscle.

Skeletal muscle regulates substrate choice according to demand and availability and pyruvate dehydrogenase (PDH) is central in this regulation. Circulating interleukin (IL)-6 increases during exercise and IL-6 has been suggested to increase whole body fat oxidation. Furthermore, IL-6 has been reported to increase AMP-activated protein kinase (AMPK) phosphorylation and AMPK suggested to regulate PDHa activity. Together, this suggests that IL-6 may be involved in regulating PDH. The aim of this study was to investigate the effect of a single injection of IL-6 on PDH regulation in skeletal muscle in fed and fasted mice. Fed and 16-18 h fasted mice were injected with either 3 ng · g(-1) recombinant mouse IL-6 or PBS as control. Fasting markedly reduced plasma glucose, muscle glycogen, muscle PDHa activity, as well as increased PDK4 mRNA and protein content in skeletal muscle. IL-6 injection did not affect plasma glucose or muscle glycogen, but increased AMPK and ACC phosphorylation and tended to decrease p38 protein content in skeletal muscle in fasted mice. In addition IL-6 injection reduced PDHa activity in fed mice and increased PDHa activity in fasted mice without significant changes in PDH-E1α phosphorylation or PDP1 and PDK4 mRNA and protein content. The present findings suggest that IL-6 contributes to regulating the PDHa activity and hence carbohydrate oxidation, but the metabolic state of the muscle seems to determine the outcome of this regulation. In addition, AMPK and p38 may contribute to the IL-6-mediated PDH regulation in the fasted state.

Leucine suppresses α-cell cAMP and glucagon secretion via a combination of cell-intrinsic and islet paracrine signaling.

Glucagon is critical for the maintenance of blood glucose, however nutrient regulation of pancreatic α-cells remains poorly understood. Here, we identified a role for leucine, a well-known ß-cell fuel, in the α-cell intrinsic regulation of glucagon release. In islet perifusion assays, physiological concentrations of leucine strongly inhibited alanine and arginine-stimulated glucagon secretion from human and mouse islets under hypoglycemic conditions. Mechanistically, leucine dose-dependently reduced α-cell cAMP, independently of Ca2+, ATP/ADP, or fatty acid oxidation. Leucine also reduced α-cell cAMP in islets treated with Sstr2 antagonists or diazoxide, compounds that limit paracrine signaling from ß/δ-cells. Studies in dispersed mouse islets confirmed an α-cell intrinsic effect. The inhibitory effect of leucine on cAMP was mimicked by glucose, α-ketoisocaproate, succinate, and the glutamate dehydrogenase activator BCH, and blocked by cyanide, indicating a mechanism dependent on mitochondrial metabolism. Glucose dose-dependently reduced the impact of leucine on α-cell cAMP, indicating an overlap in function, however leucine was still effective at suppressing glucagon secretion in the presence of elevated glucose, amino acids, and the incretin GIP. Taken together, these findings show that leucine plays an intrinsic role in limiting α-cell secretory tone across the physiological range of glucose levels, complementing the inhibitory paracrine actions of ß/δ-cells.

Self-assembled nanoscale DNA-porphyrin complex for artificial light harvesting.

Mimicking green plants' and bacteria's extraordinary ability to absorb a vast number of photons and harness their energy is a longstanding goal in artificial photosynthesis. Resonance energy transfer among donor dyes has been shown to play a crucial role on the overall transfer of energy in the natural systems. Here, we present artificial, self-assembled, light-harvesting complexes consisting of DNA scaffolds, intercalated YO-PRO-1 (YO) donor dyes and a porphyrin acceptor anchored to a lipid bilayer, conceptually mimicking the natural light-harvesting systems. A model system consisting of 39-mer duplex DNA in a linear wire configuration with the porphyrin attached in the middle of the wire is primarily investigated. Utilizing intercalated donor fluorophores to sensitize the excitation of the porphyrin acceptor, we obtain an effective absorption coefficient 12 times larger than for direct excitation of the porphyrin. On the basis of steady-state and time-resolved emission measurements and Markov chain simulations, we show that YO-to-YO resonance energy transfer substantially contributes to the overall flow of energy to the porphyrin. This increase is explained through energy migration along the wire allowing the excited state energy to transfer to positions closer to the porphyrin. The versatility of DNA as a structural material is demonstrated through the construction of a more complex, hexagonal, light-harvesting scaffold yielding further increase in the effective absorption coefficient. Our results show that, by using DNA as a scaffold, we are able to arrange chromophores on a nanometer scale and in this way facilitate the assembly of efficient light-harvesting systems.

Amino acids and the changing face of the α-cell.

Glucagon has long been defined by its glucogenic action and as a result α-cells have been characterised based largely on their interaction with glucose. Recent findings have challenged this preconception, bringing to the fore the significant role glucagon plays in amino acid breakdown and underlining the importance of amino acids in glucagon secretion. The challenge that remains is defining the mechanism that underlie these effects - understanding which amino acids are most important, how they act on the α-cell and how their actions integrate with other fuels such as glucose and fatty acids. This review will describe the current relationship between amino acids and glucagon and how we can use this knowledge to redefine the α-cell.

Kilovoltage X-ray beam quality effect on the relative response of alanine pellet dosemeters.

Determination of beam quality correction factors is crucial for performing accurate alanine pellet dosimetry in non-reference fields. For some complex irradiation geometries, interpolation from literature data is more convenient than an experimental approach to establish these factors. Here we investigate the validity of extracting quality correction factors from literature data based on information on beam qualifiers such as half-value layer (HVL) or effective energy ${E}_{\text{eff}}$. A combination of Monte Carlo calculated dose ratios and a microdosimetric assessment of the relative efficiency allows for numerical evaluation of quality correction factors for a wide array of X-ray qualities. The computational analysis demonstrates that the average energy of the X-ray beam is optimal for characterizing the relative response. Special care should be taken when using the common X-ray beam qualifiers HVL or ${E}_{\text{eff}}$ to determine quality correction factors from literature data.

Metabolic regulation of glucagon secretion.

Since the discovery of glucagon 100 years ago, the hormone and the pancreatic islet alpha cells that produce it have remained enigmatic relative to insulin-producing beta cells. Canonically, alpha cells have been described in the context of glucagon's role in glucose metabolism in liver, with glucose as the primary nutrient signal regulating alpha cell function. However, current data reveal a more holistic model of metabolic signalling, involving glucagon-regulated metabolism of multiple nutrients by the liver and other tissues, including amino acids and lipids, providing reciprocal feedback to regulate glucagon secretion and even alpha cell mass. Here we describe how various nutrients are sensed, transported and metabolised in alpha cells, providing an integrative model for the metabolic regulation of glucagon secretion and action. Importantly, we discuss where these nutrient-sensing pathways intersect to regulate alpha cell function and highlight key areas for future research.

GDF15 increases insulin action in the liver and adipose tissue via a ß-adrenergic receptor-mediated mechanism.

Growth differentiation factor 15 (GDF15) induces weight loss and increases insulin action in obese rodents. Whether and how GDF15 improves insulin action without weight loss is unknown. Obese rats were treated with GDF15 and displayed increased insulin tolerance 5 h later. Lean and obese female and male mice were treated with GDF15 on days 1, 3, and 5 without weight loss and displayed increased insulin sensitivity during a euglycemic hyperinsulinemic clamp on day 6 due to enhanced suppression of endogenous glucose production and increased glucose uptake in WAT and BAT. GDF15 also reduced glucagon levels during clamp independently of the GFRAL receptor. The insulin-sensitizing effect of GDF15 was completely abrogated in GFRAL KO mice and also by treatment with the ß-adrenergic antagonist propranolol and in ß1,ß2-adrenergic receptor KO mice. GDF15 activation of the GFRAL receptor increases ß-adrenergic signaling, in turn, improving insulin action in the liver and white and brown adipose tissue.

Glucose Controls Glucagon Secretion by Regulating Fatty Acid Oxidation in Pancreatic α-Cells.

Whole-body glucose homeostasis is coordinated through secretion of glucagon and insulin from pancreatic islets. When glucose is low, glucagon is released from α-cells to stimulate hepatic glucose production. However, the mechanisms that regulate glucagon secretion from pancreatic α-cells remain unclear. Here we show that in α-cells, the interaction between fatty acid oxidation and glucose metabolism controls glucagon secretion. The glucose-dependent inhibition of glucagon secretion relies on pyruvate dehydrogenase and carnitine palmitoyl transferase 1a activity and lowering of mitochondrial fatty acid oxidation by increases in glucose. This results in reduced intracellular ATP and leads to membrane repolarization and inhibition of glucagon secretion. These findings provide a new framework for the metabolic regulation of the α-cell, where regulation of fatty acid oxidation by glucose accounts for the stimulation and inhibition of glucagon secretion. ARTICLE HIGHLIGHTS: It has become clear that dysregulation of glucagon secretion and α-cell function plays an important role in the development of diabetes, but we do not know how glucagon secretion is regulated. Here we asked whether glucose inhibits fatty acid oxidation in α-cells to regulate glucagon secretion. We found that fatty acid oxidation is required for the inhibitory effects of glucose on glucagon secretion through reductions in ATP. These findings provide a new framework for the regulation of glucagon secretion by glucose.

Reversible hybridization of DNA anchored to a lipid membrane via porphyrin.

The binding of zinc-porphyrin-anchored linear DNA to supported lipid membranes was studied using quartz crystal microbalance with dissipation monitoring (QCM-D). The hydrophobic anchor is positioned at the ninth base of 39-base-pair-long DNA sequences, ensuring that the DNA is positioned parallel to the membrane surface when bound, an important prerequisite for using this type of construct for the creation of two-dimensional (2D) DNA patterns on the surface. The anchor consists of a porphyrin group linked to the DNA via two or three phenylethynylene moieties. Double-stranded DNA where one of the strands was modified with either of these anchors displayed irreversible binding, although binding to the membrane was faster for the derivatives with the short anchor. The binding and subsequent hybridization of single-stranded constructs on the surface was demonstrated at 60 °C, for both anchors, revealing a coverage-dependent behavior. At low coverage, hybridization results in an increase in mass (as measured by QCM-D) by a factor of ~1.5, accompanied by a slight increase in the rigidity of the DNA layer. At high coverage, hybridization expels molecules from the membrane, associated with an initial increase, followed by a decrease in DNA mass (as detected both by QCM-D and by an optical technique). Melting of the DNA on the surface was performed, followed by rehybridization of the single-stranded species left on the surface with their complementary strand, demonstrating the reversibility inherent in using DNA for the formation of membrane-confined nanopatterns.

Sodium, Glucose and Dysregulated Glucagon Secretion: The Potential of Sodium Glucose Transporters.

Diabetes is defined by hyperglycaemia due to progressive insulin resistance and compromised insulin release. In parallel, alpha cells develop dysregulation of glucagon secretion. Diabetic patients have insufficient glucagon secretion during hypoglycaemia and a lack of inhibition of glucagon secretion at higher blood glucose levels resulting in postprandial hyperglucagonaemia, which contributes to the development of hyperglycaemia. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are an efficient pharmacologic approach for the treatment of hyperglycaemia in type 2 diabetes. While SGLT2 inhibitors aim at increasing glycosuria to decrease blood glucose levels, these inhibitors also increase circulating glucagon concentrations. Here, we review recent advances in our understanding of how SGLTs are involved in the regulation of glucagon secretion. Sodium plays an important role for alpha cell function, and a tight regulation of intracellular sodium levels is important for maintaining plasma membrane potential and intracellular pH. This involves the sodium-potassium pump, sodium-proton exchangers and SGLTs. While the expression of SGLT2 in alpha cells remains controversial, SGLT1 seems to play a central role for alpha cell function. Under hyperglycaemic conditions, SGLT1 mediated accumulation of sodium results in alpha cell dysregulation due to altered cellular acidification and ATP production. Taken together, this suggests that SGLT1 could be a promising, yet highly underappreciated drug target to restore alpha cell function and improve treatment of both type 1 and 2 diabetes.