Impact of institutional variables on centre performance in long-term survival after heart transplant.

OBJECTIVES: The gold standard metric for centre-level performance in orthotopic heart transplantation (OHT) is 1-year post-OHT survival. However, it is unclear whether centre performance at 1 year is predictive of longer-term outcomes. This study evaluated factors impacting longer-term centre-level performance in OHT. METHODS: Patients who underwent OHT in the USA between 2010 and 2021 were identified using the United Network of Organ Sharing data registry. The primary outcome was 5-year survival conditional on 1-year survival following OHT. Multivariable Cox proportional hazard models assessed the impact of centre-level 1-year survival rates on 5-year survival rates. Mixed-effect models were used to evaluate between-centre variability in outcomes. RESULTS: Centre-level risk-adjusted 5-year mortality conditional on 1-year survival was not associated with centre-level 1-year survival rates [hazard ratio: 0.99 (0.97-1.01, P = 0.198)]. Predictors of 5-year mortality conditional on 1-year survival included black recipient race, pre-OHT serum creatinine, diabetes and donor age. In mixed-effect modelling, there was substantial variability between centres in 5-year mortality rates conditional on 1-year survival, a finding that persisted after controlling for recipient, donor and institutional factors (P < 0.001). In a crude analysis using Kaplan-Meier, the 5-year survival conditional on 1-year survival was: low volume: 86.5%, intermediate volume: 87.5%, high volume: 86.7% (log-rank P = 0.52). These measured variables only accounted for 21.4% of the between-centre variability in 5-year mortality conditional on 1-year survival. CONCLUSIONS: Centre-level risk-adjusted 1-year outcomes do not correlate with outcomes in the 1- to 5-year period following OHT. Further research is needed to determine what unmeasured centre-level factors contribute to longer-term outcomes in OHT.

Conservation of Atypical Allostery in C. elegans UDP-Glucose Dehydrogenase.

Human UDP-glucose dehydrogenase (hUGDH) oxidizes uridine diphosphate (UDP)-glucose to UDP-glucuronic acid, an essential substrate in the phase II metabolism of drugs. The activity of hUGDH is controlled by an atypical allosteric mechanism in which the feedback inhibitor UDP-xylose competes with the substrate for the active site and triggers a buried allosteric switch to produce an inactive complex (EΩ). Previous comparisons with a nonallosteric UGDH identified six large-to-small substitutions that produce packing defects in the protein core and provide the conformational flexibility necessary for the allosteric transition. Here, we test the hypothesis that these large-to-small substitutions form a motif that can be used to identify allosteric UGDHs. Caenorhabditis elegans UGDH (cUGDH) conserves this motif with the exception of an Ala-to-Pro substitution in position 109. The crystal structures of unliganded and UDP-xylose bound cUGDH show that the A109P substitution is accommodated by an Asn-to-Ser substitution at position 290. Steady-state analysis and sedimentation velocity studies show that the allosteric transition is conserved in cUGDH. The enzyme also exhibits hysteresis in progress curves and negative cooperativity with respect to NAD+ binding. Both of these phenomena are conserved in the human enzyme, which is strong evidence that these represent fundamental features of atypical allostery in UGDH. A phylogenetic analysis of UGDH shows that the atypical allostery motif is ancient and identifies a potential transition point in the evolution of the UGDH family.

The entropic force generated by intrinsically disordered segments tunes protein function.

Protein structures are dynamic and can explore a large conformational landscape1,2. Only some of these structural substates are important for protein function (such as ligand binding, catalysis and regulation)3-5. How evolution shapes the structural ensemble to optimize a specific function is poorly understood3,4. One of the constraints on the evolution of proteins is the stability of the folded 'native' state. Despite this, 44% of the human proteome contains intrinsically disordered peptide segments greater than 30 residues in length6, the majority of which have no known function7-9. Here we show that the entropic force produced by an intrinsically disordered carboxy terminus (ID-tail) shifts the conformational ensemble of human UDP-α-D-glucose-6-dehydrogenase (UGDH) towards a substate with a high affinity for an allosteric inhibitor. The function of the ID-tail does not depend on its sequence or chemical composition. Instead, the affinity enhancement can be accurately predicted based on the length of the intrinsically disordered segment, and is consistent with the entropic force generated by an unstructured peptide attached to the protein surface10-13. Our data show that the unfolded state of the ID-tail rectifies the dynamics and structure of UGDH to favour inhibitor binding. Because this entropic rectifier does not have any sequence or structural constraints, it is an easily acquired adaptation. This model implies that evolution selects for disordered segments to tune the energy landscape of proteins, which may explain the persistence of intrinsic disorder in the proteome.

A naturalistic evaluation and audit database of agomelatine: clinical outcome at 12 weeks.

OBJECTIVE: To determine the effectiveness of agomelatine in routine clinical practice and explore factors associated with response and continuation. METHOD: Consecutive patients prescribed agomelatine in participating psychiatric services were included. Patient demographic and outcome data were collected at treatment initiation and then at weeks 4, 8 and 12. Outcomes were analysed with respect to clinical and demographic factors. RESULTS: A total of 110 patients from nine NHS trusts were followed through 12 weeks of treatment. Agomelatine was largely used in difficult-to-treat or refractory patients: 83 (75%) had failed to respond to, or relapsed on, prior antidepressants. There were high rates of physical (54.5%) and psychiatric (50.0%) comorbidity. At 12 weeks of treatment, 68 (62%) continued agomelatine treatment. Overall, 69 subjects (62.7%) improved by at least one point of the Clinical Global Impression (severity) scale. Of 42 who discontinued, 23 (56%) discontinued because of lack of efficacy and 10 (24%) due to an adverse event. Of all variables examined, only a history of more than five episodes of depression significantly predicted discontinuation of treatment (OR continuation - 0.36, 95% CI 0.14, 0.95). CONCLUSION: Agomelatine was effective and generally well tolerated in a cohort of difficult-to-treat patients in clinical practice.

Exendin-4 stimulation of cyclin A2 in beta-cell proliferation.

OBJECTIVE: Beta-cell proliferation is an important mechanism underlying beta-cell mass adaptation to metabolic demands. We have examined effects, in particular those mediated through intracellular cAMP signaling, of the incretin hormone analog exendin-4 on cell cycle regulation in beta-cells. RESEARCH DESIGN AND METHODS: Changes in islet protein levels of cyclins and of two critical cell cycle regulators cyclin kinase inhibitor p27 and S-phase kinase-associated protein 2 (Skp2) were assessed in mice treated with exendin-4 and in a mouse model with specific upregulation of nuclear cAMP signaling exhibiting increased beta-cell proliferation (CBP-S436A mouse). Because cyclin A2 was stimulated by cAMP, we assessed the role of cylcin A2 in cell cycle progression in Min6 and isolated islet beta-cells. RESULTS: Mice treated with exendin-4 showed increased beta-cell proliferation, elevated islet protein levels of cyclin A2 with unchanged D-type cyclins, elevated PDX-1 and Skp2 levels, and reduced p27 levels. Exendin-4 stimulated cyclin A2 promoter activity via the cAMP-cAMP response element binding protein pathway. CBP-S436A islets exhibited elevated cyclin A2, reduced p27, and no changes in D-type cyclins, PDX-1, or Skp2. In cultured islets, exendin-4 increased cyclin A2 and Skp2 and reduced p27. Cyclin A2 overexpression in primary islets increased proliferation and reduced p27. In Min6 cells, cyclin A2 knockdown prevented exendin-4-stimulated proliferation. PDX-1 knockdown reduced exendin-4-stimulated cAMP synthesis and cyclin A2 transcription. CONCLUSIONS: Cyclin A2 is required for beta-cell proliferation, exendin-4 stimulates cyclin A2 expression via the cAMP pathway, and exendin-4 stimulation of cAMP requires PDX-1.

Increased pancreatic beta-cell proliferation mediated by CREB binding protein gene activation.

The cyclic AMP (cAMP) signaling pathway is central in beta-cell gene expression and function. In the nucleus, protein kinase A (PKA) phosphorylates CREB, resulting in recruitment of the transcriptional coactivators p300 and CREB binding protein (CBP). CBP, but not p300, is phosphorylated at serine 436 in response to insulin action. CBP phosphorylation disrupts CREB-CBP interaction and thus reduces nuclear cAMP action. To elucidate the importance of the cAMP-PKA-CREB-CBP pathway in pancreatic beta cells specifically at the nuclear level, we have examined mutant mice lacking the insulin-dependent phosphorylation site of CBP. In these mice, the CREB-CBP interaction is enhanced in both the absence and presence of cAMP stimulation. We found that islet and beta-cell masses were increased twofold, while pancreas weights were not different from the weights of wild-type littermates. beta-Cell proliferation was increased both in vivo and in vitro in isolated islet cultures. Surprisingly, glucose-stimulated insulin secretion from perfused, isolated mutant islets was reduced. However, beta-cell depolarization with KCl induced similar levels of insulin release from mutant and wild-type islets, indicating normal insulin synthesis and storage. In addition, transcripts of pgc1a, which disrupts glucose-stimulated insulin secretion, were also markedly elevated. In conclusion, sustained activation of CBP-responsive genes results in increased beta-cell proliferation. In these beta cells, however, glucose-stimulated insulin secretion was diminished, resulting from concomitant CREB-CBP-mediated pgc1a gene activation.

Light quantity controls leaf-cell and chloroplast development in Arabidopsis thaliana wild type and blue-light-perception mutants.

Plants acclimate to changes in light quantity by altering leaf-cell development and the accumulation of chloroplast components, such that light absorption is favoured under limiting illumination, and light utilisation under non-limiting conditions. Previous evidence suggests an involvement of a high-light photosynthetic redox signal in the down-regulation of the accumulation of the light-harvesting complexes of photosystem 11 (Lhcb) and the expression of the Lhcb genes. and of a blue-light signal in the control of leaf development and in the increase in photosynthetic capacity, as affected by the accumulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We examined the internal anatomy of leaves, the ultrastructure of chloroplasts and accumulation of light-harvesting complexes and Rubisco in wild-type Arabidopsis thaliana (L.) Heynh. and in mutants in each of the three known blue-light photoreceptors, cryptochrome 1, cryptochrome 2 and phototropin, as well as a mutant in both cryptochromes. Our results indicate an extensive capacity of the Arabidopsis mesophyll cells to adapt to high light fluence rate with an increase in palisade elongation. Under high light, chloroplasts showed increased starch accumulation and reductions in the amount of granal thylakoids per chloroplast, in the proportion of chlorophyll b relative to chlorophyll a, and in the accumulation of the major Lhcb polypeptides. The responses were similar for all four mutants, with respect to their wild types. The results are consistent with either a complete redundancy in function between cryptochromes and phototropin, or their absence of involvement in the light-quantity responses tested. We observed minimal effects of light quantity on Rubisco accumulation over the range of fluence rates used, and conclude that elongation of palisade mesophyll cells and accumulation of Rubisco are controlled separately. This indicates that light acclimation must be the result of a number of individual elementary responses. Quantitative differences in the acclimatory responses were observed between the Landsberg erecta and Columbia wild-type ecotypes used.

Small-cell carcinoma of the esophagus: treatment by chemotherapy alone.

Small-cell carcinoma of the esophagus is a rare tumor. In most reported cases, surgery has been the major mode of therapy. Most patients have relapsed rapidly with disseminated disease. We treated a patient with small-cell carcinoma of the esophagus with a multi-drug regimen being used in small cell-carcinoma of the lung. Within two months of beginning therapy, the primary lesion, as evaluated by barium esophogram, had completely resolved. Residual disease was seen on panendoscopy. The patient was considered to be in partial remission. She relapsed nine months after starting therapy and died with widespread metastases. Small-cell carcinoma of the esophagus should not be treated surgically but rather in the same fashion as is small-cell carcinoma of the lung, i.e., with multi-drug chemotherapy and radiation therapy.