Myotrophin in human heart failure

Indigenous people from Amazon show genetic signatures of pathogen-driven selection

Ecological conditions in the Amazon rainforests are historically favorable for the transmission of numerous tropical diseases, especially vector-borne diseases. The high diversity of pathogens likely contributes to the strong selective pressures for human survival and reproduction in this region. However, the genetic basis of human adaptation to this complex ecosystem remains unclear. This study investigates the possible footprints of genetic adaptation to the Amazon rainforest environment by analyzing the genomic data of 19 native populations. The results based on genomic and functional analysis showed an intense signal of natural selection in a set of genes related to Trypanosoma cruzi infection, which is the pathogen responsible for Chagas disease, a neglected tropical parasitic disease native to the Americas that is currently spreading worldwide.

The ATO/miRNA-885-5p/MTPN axis induces reversal of drug-resistance in cholangiocarcinoma

PURPOSE

Cholangiocarcinoma (CCA) is the second most malignant tumor of the hepatobiliary system. Due to its cumbersome early diagnosis and rapid progression, chemotherapy has become the main treatment option. Primary drug resistance is a major cause of the poor efficacy of chemotherapeutic drugs. Therefore, it is considered urgent to explore new drugs to overcome primary drug resistance of CCA.

METHODS

Western blot and qRT-PCR assays were used to assess the expression of myotrophin (MTPN) and microRNA-885-5p (miR-885-5p) in CCA tissues and cells. The viability of CCA cells treated with arsenic trioxide (ATO), 5-fluorouracil (5-Fu) and cisplatin (CDDP) was analyzed using a CCK-8 assay. A luciferase reporter assay was used to assess the interaction between miR-885-5p and MTPN. Kaplan-Meier analyses were used for survival assessments.

RESULT

We found that ATO can reduce the resistance of CCA cells to 5-Fu and CDDP and promote the killing effect of 5-Fu and CDDP. Low-dose ATO showed an anti-drug-resistance effect through up-regulation of the expression of miR-885-5p. Combined with sequencing results and database predictions, we found that MTPN may serve as a direct target of miR-885-5p. After MTPN knockdown, the sensitivity of CCA cells to 5-FU and CDDP was increased. Finally, we found that ATO can reverse chemotherapy resistance induced by overexpression of MTPN.

CONCLUSION

Our data indicate that the ATO/miR-885-5p/MTPN axis may serve as a target for improving the sensitivity of CCA cells to chemotherapy.

Platelet proteome changes in dogs with congestive heart failure

BACKGROUND

Platelets play a central role in the development of cardiovascular diseases and changes in their proteins are involved in the pathophysiology of heart diseases in humans. There is lack of knowledge about the possible role of platelets in congestive heart failure (CHF) in dogs. Thus, this study aimed to investigate the changes in global platelet proteomes in dogs with CHF, to clarify the possible role of platelets in the physiopathology of this disease. Healthy-dogs (n = 10) and dogs with acute CHF due to myxomatous mitral valve disease (MMVD, n = 10) were used. Acute CHF was defined based on the clinical (increased respiratory rate or difficulty breathing) and radiographic findings of pulmonary edema. Dogs Blood samples were collected into tubes with acid-citrate-dextrose, and platelet-pellets were obtained by centrifuge and washing steps. Platelet-proteomes were identified using LC-MS based label-free differential proteome expression analysis method and matched according to protein database for Canis lupus familiaris.

RESULTS

Totally 104 different proteins were identified in the platelets of the dogs being 4 out of them were significantly up-regulated and 6 down-regulated in acute CHF dogs. Guanine-nucleotide-binding protein, apolipoproteins (A-II and C-III) and clusterin levels increased, but CXC-motif-chemokine-10, cytochrome-C-oxidase-subunit-2, cathepsin-D, serine/threonine-protein-phosphatase-PP1-gamma-catalytic-subunit, creatine-kinase-B-type and myotrophin levels decreased in acute CHF dogs. These proteins are associated with several molecular functions, biological processes, signaling systems and immune-inflammatory responses.

CONCLUSION

This study describes by first time the changes in the protein composition in platelets of dogs with acute CHF due to MMVD. Our findings provide a resource for increase the knowledge about the proteome of canine platelets and their roles in CHF caused by MMVD and could be a tool for further investigations about the prevention and treatment of this disease.

The Human Myotrophin Variant Attenuates MicroRNA-Let-7 Binding Ability but Not Risk of Left Ventricular Hypertrophy in Human Essential Hypertension

Myotrophin, known as a myocardial hypertrophy-inducing factor, is responsible for the initiation of cardiac hypertrophy that transits to heart failure. MicroRNAs are small noncoding RNAs that down-regulate posttranscriptional expression of target molecules. We investigated the role of variants of the microRNA-binding site in myotrophin in affecting its expression and any association with cardiac hypertrophy. Bioinformatics demonstrated that variant rs17168525 was identified to be located in the let-7/miR-98-binding site of myotrophin. We further experimentally test to effects of the identified variant on myotrophin translation using luciferase reporter assay and Western blotting. We found that the C allele of rs17168525 suppressed myotrophin translation by facilitating let-7c binding, but not the T allele. Let-7c overexpression caused a significant decrease in the level of myotrophin protein. Next, we investigated the association of the variant with cardiac hypertrophy in 1614 hypertensive patients, including 552 with left ventricular hypertrophy and 1062 without left ventricular hypertrophy, as well as 591 healthy control subjects from a Han Chinese population. No significant association between the variant rs17168525 and left ventricular hypertrophy in hypertensive patients in a Han Chinese population (P>0.05). In conclusion, our experimental results provide evidence that the T allele of rs17168525 in the 3'-UTR of myotrophin might influence the level of myotrophin protein by interfering with let-7/miR-98 binding.

Circulating levels of the vasoactive peptide urotensin II in patients with acute coronary syndrome and stable coronary artery disease

Urotensin II (UII) is a vasoactive peptide with various roles in cardiovascular physiology and pathophysiology. There is an accumulating evidence implicating UII in atherosclerosis and coronary artery disease, making it an important target in acute coronary syndrome (ACS). In this study, we sought to determine the plasma levels of UII in ACS patients within 48 h of clinical presentation and after a 12-week recovery period. We compared them to patients with stable coronary artery disease (CAD) and a control group of normolipidemic subjects without known CAD. Using a highly sensitive ELISA technique, we measured plasma UII in 27 ACS patients, 26 stable CAD patients and 22 age-matched controls. ACS patients had significantly elevated plasma UII during the first 48 h of clinical presentation compared to stable CAD patients and controls. We also found significant positive correlations between UII and CRP and with triglycerides and a significant negative correlation between UII and EF. There was no correlation with LDL-C. In conclusion, plasma UII levels were elevated in patients with acute coronary syndrome, particularly immediately after clinical presentation. This suggests an upregulation of UII expression in ACS.

Protein profiling of human nonpigmented ciliary epithelium cell secretome: the differentiation factors characterization for retinal ganglion cell line

The purpose of this paper was to characterize proteins secreted from the human nonpigmented ciliary epithelial (HNPE) cells, which have differentiated a rat retinal ganglion cell line, RGC-5. Undifferentiated RGC-5 cells have been shown to express several marker proteins characteristic of retinal ganglion cells. However, RGC-5 cells do not respond to N-methyl-D aspartate (NMDA), or glutamate. HNPE cells have been shown to secrete numbers of neuropeptides or neuroproteins also found in the aqueous humor, many of which have the ability to influence the activity of neuronal cells. This paper details the profile of HNPE cell-secreted proteins by proteomic approaches. The experimental results revealed the identification of 132 unique proteins from the HNPE cell-conditioned SF-medium. The biological functions of a portion of these identified proteins are involved in cell differentiation. We hypothesized that a differentiation system of HNPE cell-conditioned SF-medium with RGC-5 cells can induce a differentiated phenotype in RGC-5 cells, with functional characteristics that more closely resemble primary cultures of rat retinal ganglion cells. These proteins may replace harsh chemicals, which are currently used to induce cell differentiation.

Anchoring skeletal muscle development and disease: the role of ankyrin repeat domain containing proteins in muscle physiology

The ankyrin repeat is a protein module with high affinity for other ankyrin repeats based on strong Van der Waals forces. The resulting dimerization is unusually resistant to both mechanical forces and alkanization, making this module exceedingly useful for meeting the extraordinary demands of muscle physiology. Many aspects of muscle function are controlled by the superfamily ankyrin repeat domain containing proteins, including structural fixation of the contractile apparatus to the muscle membrane by ankyrins, the archetypical member of the family. Additionally, other ankyrin repeat domain containing proteins critically control the various differentiation steps during muscle development, with Notch and developmental stage-specific expression of the members of the Ankyrin repeat and SOCS box (ASB) containing family of proteins controlling compartment size and guiding the various steps of muscle specification. Also, adaptive responses in fully formed muscle require ankyrin repeat containing proteins, with Myotrophin/V-1 ankyrin repeat containing proteins controlling the induction of hypertrophic responses following excessive mechanical load, and muscle ankyrin repeat proteins (MARPs) acting as protective mechanisms of last resort following extreme demands on muscle tissue. Knowledge on mechanisms governing the ordered expression of the various members of superfamily of ankyrin repeat domain containing proteins may prove exceedingly useful for developing novel rational therapy for cardiac disease and muscle dystrophies.

Influence of p53 in the transition of myotrophin-induced cardiac hypertrophy to heart failure

AIMS

Cardiac-specific overexpression of myotrophin (myo) protein in transgenic (myo-Tg) mice results in hypertrophy at 4 weeks that progresses to heart failure (HF) by 36 weeks. Gene profiling showed that p53 expression increases as hypertrophy worsens to HF, suggesting that p53 may influence myo-induced HF. We aimed to define how the p53 signalling cascade affects the spectrum of cardiac hypertrophy (CH)/HF.

METHODS AND RESULTS

Immunoblot analysis showed that in myo-Tg mice (Mus musculus), upregulation of p53 occurs only when hypertrophy transitions to HF (16 weeks onward). To elucidate the role of p53, a double-Tg mouse line (p53(-/-)/myo(+/+)) was developed by crossing myo-Tg mice with p53-null mice. A significant reduction in cardiac mass with improved cardiac function was observed in p53(-/-)/myo(+/+) mice, suggesting that absence of p53 prevents hypertrophy from turning into HF. Analysis via real-time reverse-transcription PCR revealed changes in transcripts of the p53 pathway in p53(-/-)/myo(+/+) mice. Ingenuity Pathway Analysis indicated that cross-talk among several key nodal molecules (e.g. cyclin-dependent kinase inhibitor 1A, caspase-3, nuclear factor kappa-light-chain enhancer of activated B cells etc.) may play a regulatory role in the transition of CH to HF.

CONCLUSION

Our data provide evidence, for the first time, that the coherence of p53 with myo plays an active role during the transition of CH to HF in a model of HF induced by myo overexpression. Transition from CH to HF can be prevented in the absence of p53 in myo-induced hypertrophy. Therefore, deletion/inhibition of p53 could be a therapeutic strategy to prevent CH from transitioning to HF.

Nuclear co-translocation of myotrophin and p65 stimulates myocyte growth. Regulation by myotrophin hairpin loops

Myotrophin, a 12-kDa ankyrin repeat protein, stimulates protein synthesis and cardiomyocyte growth to initiate cardiac hypertrophy by activating the NF-kappaB signaling cascade. We found that, after internalization into myocytes, myotrophin cotranslocates into the nucleus with p65 to stimulate myocyte growth. We used structure-based mutations on the hairpin loops of myotrophin to determine the effect of the loops on myotrophin and p65 localization, induction of protein synthesis, and cardiac hypertrophy. Loop mutants, most prominently glutamic acid 33-->alanine (E33A), stimulated protein synthesis much less than wild type. Myotrophin-E33A internalized into myocytes but did not translocate into the nucleus and failed to promote nuclear translocation of p65. In addition, two cardiac hypertrophy marker genes, atrial natriuretic factor and beta-myosin heavy chain, were not up-regulated in E33A-treated cells. Myotrophin-induced myocyte growth and initiation of hypertrophy thus require nuclear co-translocation of myotrophin and p65, in a manner that depends crucially on the myotrophin hairpin loops.

Urotensin II is raised in acute myocardial infarction and low levels predict risk of adverse clinical outcome in humans

BACKGROUND

UII is elevated in patients with heart failure; however its role in acute myocardial infarction (AMI) is unknown. We sought to compare levels of UII in patients with AMI to controls. We also compared UII to N terminal pro B type natriuretic peptide (NT-BNP) to evaluate whether levels of UII can be used to predict the risk of adverse clinical outcome (ACO).

METHODS AND RESULTS

129 patients were studied with serial blood measurements and echocardiogram during their index admission. Plasma concentration of median UII was significantly elevated in AMI compared to controls (median 1.40 vs. 0.42 fmol/ml p<0.012). Over the median follow up of 102 days (range 0-189) there were 14 deaths and 14 readmissions with AMI or heart failure. Using a Cox proportional hazards model the only independent predictors of ACO were UII (OR 0.29, p=0.046) and NT-BNP (OR 4.78, p=0.012) between 73 and 96 h. The Kaplan-Meier survival curve revealed a significantly better clinical outcome in patients with UII above the median compared with UII below the median.

CONCLUSIONS

UII levels are raised in AMI and is an independent predictor of ACO. Patients with a poor outcome mount a lower UII response suggesting a possible cardioprotective role for this peptide.

Myotrophin is a more powerful predictor of major adverse cardiac events following acute coronary syndrome than N-terminal pro-B-type natriuretic peptide

Myotrophin is a 12 kDa protein initially isolated from hypertrophied hearts of spontaneously hypertensive rats and acts by modulating NF-kappaB (nuclear factor kappaB) activity. We have reported previously the presence of myotrophin in patients with human systolic heart failure; however, its role as a predictor of MACE (major adverse cardiac events) in patients with ACS (acute coronary syndrome) is unclear. In the present study, we sought to investigate this and compared myotrophin with NTproBNP (N-terminal pro-B-type natriuretic peptide), a marker of MACE. We studied 356 patients with ACS {276 men; mean age, 63.0+/-12.8 years; 80.6% STEMI [ST segment elevation MI (myocardial infarction)]; and 19.4% NSTEMI (non-STEMI)}. Blood measurement was made at 25-48 h after the onset of chest pain. The plasma concentration of myotrophin and NTproBNP was determined using in-house non-competitive immunoassays. Patients were followed-up for the combined end point of death, MI or need for urgent revascularization. Over the median follow-up period of 355 (range 0-645) days, there were 28 deaths, 27 non-fatal MIs and 73 patients required urgent revascularization. Myotrophin was raised in patients with MACE compared with survivors [510.7 (116.0-7445.6) fmol/ml compared with 371.5 (51.8-6990.4) fmol/ml respectively; P=0.001; values are medians (range)]. Using a Cox proportional hazards model, myotrophin {HR (hazard ratio), 1.64 [95% CI (confidence interval), 0.97-2.76]; P=0.05} and Killip class above 1 [HR, 1.52 (95% CI, 0.93-2.42); P=0.10] were the only independent predictors of MACE. A Kaplan-Meier survival curve revealed a significantly better clinical outcome in patients with myotrophin below the median compared with those with myotrophin above the median (log rank, 7.63; P=0.006). In conclusion, after an ACS, levels of myotrophin are more informative at predicting MACE than NTproBNP and may be useful to risk stratify patients.

A Binding Free Energy Hot Spot in the Ankyrin Repeat Protein GABPβ Mediated Protein–Protein Interaction

The frequently observed ankyrin repeat motif represents a structural scaffold evolved for mediating protein-protein interactions. As such, these repeats modulate a diverse range of cellular functions. We thermodynamically characterized the heterodimeric GA-binding protein (GABP) alphabeta complex and focused specifically on the interaction mediated by the ankyrin repeat domain of the GABPbeta. Our isothermal titration calorimetric analysis of the interaction between the GABP subunits determined an association constant (K(A)) of 6.0 x 10(8) M(-1) and that the association is favorably driven by a significant change in enthalpy (DeltaH) and a minor change in entropy (-TDeltaS). A total of 16 GABPbeta interface residues were chosen for alanine scanning mutagenesis. The calorimetrically measured differences in the free energy of binding were compared to computationally calculated values resulting in a correlation coefficient r = 0.71. We identified three spatially contiguous hydrophobic and aromatic residues that form a binding free energy hot spot (DeltaDeltaG > 2.0 kcal/mol). One residue provides structural support to the hot spot residues. Three non-hot spot residues are intermediate contributors (DeltaDeltaG approximately 1.0 kcal/mol) and create a canopy-like structure over the hot spot residues to possibly occlude solvent and orientate the subunits. The remaining interface residues are located peripherally and have weak contributions. Finally, our mutational analysis revealed a significant entropy-enthalpy compensation for this interaction.

Characterization and functional significance of myotrophin: a gene with multiple transcripts

The underlying mechanism for the development of cardiac hypertrophy that advances to heart failure is not known. Many factors have been implied to play a role in this process. Among others, we have isolated and identified myotrophin, a factor that stimulates myocytes growth, from spontaneously hypertensive rat (SHR) heart and patients with dilated cardiomyopathy. The gene encoding myotrophin has been cloned and expressed in E. coli. Recently, myotrophin gene has been mapped and shown to be a novel gene localized in human chromosome 7q-33. To define the characteristics of each transcript and its pathophysiological significance, we examined transcripts of myotrophin in SHR heart during progression of hypertrophy. Northern blot analysis of myotrophin mRNA showed multiple transcripts. We isolated and characterized various myotrophin cDNA clones corresponding to the multiple transcripts by 5' "stretch plus" rat heart cDNA library screening. Sequence analysis of these cDNA clones indicates that each clone has a unique 5' UTR and multiple 3' UTR with varying lengths, repeated ATTTA motifs and many polyadenylation signals. In vitro transcripts generated from all these myotrophin-specific cDNA clones translate in vitro to a 12-kD protein. Among pathophysiological significance, we determined mRNA expression in 9 days old, 3 weeks old and 31 weeks old and observed a linear increased during the progression of hypertrophy. In WKY, this mRNA level remained the same throughout the growth and development of hypertrophy. Our data strongly suggest that myotrophin appears to be a candidate gene for cardiac hypertrophy and heart failure.

Capping protein: new insights into mechanism and regulation

Temporal and spatial control of the actin cytoskeleton are crucial for a range of eukaryotic cellular processes. Capping protein (CP), a ubiquitous highly conserved heterodimer, tightly caps the barbed (fast-growing) end of the actin filament and is an important component in the assembly of various actin structures, including the dynamic branched filament network at the leading edge of motile cells. New research into the molecular mechanism of how CP interacts with the actin filament in vitro and the function of CP in vivo, including discoveries of novel interactions of CP with other proteins, has greatly enhanced our understanding of the role of CP in regulating the actin cytoskeleton.