Cardiac-specific expression of heme oxygenase-1 protects against ischemia and reperfusion injury in transgenic mice

Heme oxygenase (HO)-1 degrades the pro-oxidant heme and generates carbon monoxide and antioxidant bilirubin. We have previously shown that in response to hypoxia, HO-1-null mice develop infarcts in the right ventricle of their hearts and that their cardiomyocytes are damaged by oxidative stress. To test whether HO-1 protects against oxidative injury in the heart, we generated cardiac-specific transgenic mice overexpressing different levels of HO-1. By use of a Langendorff preparation, hearts from transgenic mice showed improved recovery of contractile performance during reperfusion after ischemia in an HO-1 dose-dependent manner. In vivo, myocardial ischemia and reperfusion experiments showed that infarct size was only 14.7% of the area at risk in transgenic mice compared with 56.5% in wild-type mice. Hearts from these transgenic animals had reduced inflammatory cell infiltration and oxidative damage. Our data demonstrate that overexpression of HO-1 in the cardiomyocyte protects against ischemia and reperfusion injury, thus improving the recovery of cardiac function.

Cardiac hypertrophy with preserved contractile function after selective deletion of GLUT4 from the heart

Glucose enters the heart via GLUT1 and GLUT4 glucose transporters. GLUT4-deficient mice develop striking cardiac hypertrophy and die prematurely. Whether their cardiac changes are caused primarily by GLUT4 deficiency in cardiomyocytes or by metabolic changes resulting from the absence of GLUT4 in skeletal muscle and adipose tissue is unclear. To determine the role of GLUT4 in the heart we used cre-loxP recombination to generate G4H(-/-) mice in which GLUT4 expression is abolished in the heart but is present in skeletal muscle and adipose tissue. Life span and serum concentrations of insulin, glucose, FFAs, lactate, and beta-hydroxybutyrate were normal. Basal cardiac glucose transport and GLUT1 expression were both increased approximately 3-fold in G4H(-/-) mice, but insulin-stimulated glucose uptake was abolished. G4H(-/-) mice develop modest cardiac hypertrophy associated with increased myocyte size and induction of atrial natriuretic and brain natriuretic peptide gene expression in the ventricles. Myocardial fibrosis did not occur. Basal and isoproterenol-stimulated isovolumic contractile performance was preserved. Thus, selective ablation of GLUT4 in the heart initiates a series of events that results in compensated cardiac hypertrophy.

Increased adenosine monophosphate-activated protein kinase activity in rat hearts with pressure-overload hypertrophy

BACKGROUND

Recent reports suggest that activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), in response to acute changes in cellular energy status in cardiac and skeletal muscles, results in altered substrate utilization. We hypothesized that chronic alterations in myocardial energetics in hypertrophied hearts (left ventricular hypertrophy, LVH) will lead to elevated AMPK activity, which in turn regulates substrate utilization.

METHODS AND RESULTS

Using (31)P NMR spectroscopy and biochemical assays, we found that in LVH hearts, adenosine triphosphate (ATP) concentration decreased by 10%, phosphocreatine concentration decreased by 30%, and total creatine concentration was unchanged. Thus, the ratio of phosphocreatine/creatine decreased to one third of controls, and the ratio of AMP/ATP increased to 5 times above controls. These changes were associated with increased alpha(1) and alpha(2) AMPK activity (3.5- and 4.8-fold above controls, respectively). The increase in AMPK alpha(1) activity was accompanied by a 2-fold increase in alpha(1) expression, whereas alpha(2) expression was decreased by 30% in LVH. The basal rate of 2-deoxyglucose uptake increased by 3-fold in LVH, which was associated with an increased amount of glucose transporters present on the plasma membrane.

CONCLUSIONS

These results demonstrate for the first time that chronic changes in myocardial energetics in hypertrophied hearts are accompanied by significant elevations in AMPK activity and isoform-specific alterations in AMPK expression. It also raises the possibility that AMPK signaling plays an important role in regulating substrate utilization in hypertrophied hearts.

Responses of GLUT4-deficient hearts to ischemia underscore the importance of glycolysis

BACKGROUND

The ischemic heart is dependent on glycolysis for ATP generation, and therapies that increase glucose utilization during ischemia improve survival. Myocardial ischemia results in the translocation of the glucose transporter proteins GLUT1 and GLUT4 to the sarcolemma. The increased glucose entry via these transporters contributes to enhanced glycolysis during ischemia.

METHODS AND RESULTS

To determine the role of GLUT4 in mediating increased glycolytic flux during ischemia, hearts from mice with cardiac-selective GLUT4 deficiency (G4H-/-) were subjected to global low-flow ischemia. During normal perfusion, hearts from fed G4H-/- mice showed increased GLUT1-mediated glucose uptake, higher concentrations of glycogen and phosphocreatine, but delayed recovery after ischemia. When these compensatory changes were eliminated by a 20-hour fast, G4H-/- hearts exhibited depressed glucose utilization during ischemia and developed profound and irreversible systolic and diastolic dysfunction associated with accelerated ATP depletion during ischemia and diminished regeneration of high-energy phosphate compounds on reperfusion.

CONCLUSIONS

GLUT4 is an important mediator of enhanced glycolysis during ischemia and represents an important protective mechanism against ischemic injury.

Impairment of energy metabolism in intact residual myocardium of rat hearts with chronic myocardial infarction

The purpose of this study was to test the hypothesis that energy metabolism is impaired in residual intact myocardium of chronically infarcted rat heart, contributing to contractile dysfunction. Myocardial infarction (MI) was induced in rats by coronary artery ligation. Hearts were isolated 8 wk later and buffer-perfused isovolumically. MI hearts showed reduced left ventricular developed pressure, but oxygen consumption was unchanged. High-energy phosphate contents were measured chemically and by 31P-NMR spectroscopy. In residual intact left ventricular tissue, ATP was unchanged after MI, while creatine phosphate was reduced by 31%. Total creatine kinase (CK) activity was reduced by 17%, the fetal CK isoenzymes BB and MB increased, while the "adult" mitochondrial CK isoenzyme activity decreased by 44%. Total creatine content decreased by 35%. Phosphoryl exchange between ATP and creatine phosphate, measured by 31P-NMR magnetization transfer, fell by 50% in MI hearts. Thus, energy reserve is substantially impaired in residual intact myocardium of chronically infarcted rats. Because phosphoryl exchange was still five times higher than ATP synthesis rates calculated from oxygen consumption, phosphoryl transfer via CK may not limit baseline contractile performance 2 mo after MI. In contrast, when MI hearts were subjected to acute stress (hypoxia), mechanical recovery during reoxygenation was impaired, suggesting that reduced energy reserve contributes to increased susceptibility of MI hearts to acute metabolic stress.

Impaired cardiac energetics in mice lacking muscle-specific isoenzymes of creatine kinase

Our purpose was to determine whether hearts from mice bioengineered to lack either the M isoform of creatine kinase (MCK-/- mice) or both the M and mitochondrial isoforms (M/MtCK-/- mice) have deficits in cardiac contractile function and energetics, which have previously been reported in skeletal muscle from these mice. The phenotype of hearts with deleted creatine kinase (CK) genes is of clinical interest, since heart failure is associated with decreased total CK activity and changes in the relative amounts of the CK isoforms in the heart. We measured isovolumic contractile performance in isolated perfused hearts from wild-type, MCK-/-, and M/MtCK-/- mice simultaneously with cardiac energetics (31P-nuclear magnetic resonance spectroscopy) at baseline, during increased cardiac work, and during recovery. Hearts from wild-type, MCK-/-, and M/MtCK-/- mice had comparable baseline function and responded to 10 minutes of increased heart rate and perfusate Ca2+ with similar increases in rate-pressure product (48+/-5%, 42+/-6%, and 51+/-6%, respectively). Despite a similar contractile response, M/MtCK-/- hearts increased [ADP] by 95%, whereas wild-type and MCK-/- hearts maintained [ADP] at baseline levels. The free energy released from ATP hydrolysis decreased by 3.6 kJ/mol in M/MtCK-/- hearts during increased cardiac work but only slightly in wild-type (1.7 kJ/mol) and MCK-/- (1.5 kJ/mol) hearts. In contrast to what has been reported in skeletal muscle, M/MtCK-/- hearts were able to hydrolyze and resynthesize phosphocreatine. Taken together, our results demonstrate that when CK activity is lowered below a certain level, increases in cardiac work become more "energetically costly" in terms of high-energy phosphate use, accumulation of ADP, and decreases in free energy released from ATP hydrolysis, but not in terms of myocardial oxygen consumption.

Systematic review and meta-analysis comparing three techniques for pancreatic remnant closure following distal pancreatectomy

BACKGROUND

Established closure techniques for the pancreatic remnant after distal pancreatectomy include stapler, suture and anastomotic closure. However, controversy remains regarding the ideal technique; therefore, the aim of this study was to compare closure techniques and risk of postoperative pancreatic fistula (POPF).

METHODS

A systematic review was carried out according to PRISMA guidelines for studies published before January 2014 that compared at least two closure techniques for the pancreatic remnant in distal pancreatectomy. A random-effects model was constructed using weighted odds ratios (ORs).

RESULTS

Thirty-seven eligible studies matched the inclusion criteria and 5252 patients who underwent distal pancreatectomy were included. The primary outcome measure, the POPF rate, ranged 0 from to 70 per cent. Meta-analysis of the 31 studies comparing stapler versus suture closure showed that the stapler technique had a significantly lower rate of POPF, with a combined OR of 0.77 (95 per cent c.i. 0.61 to 0.98; P = 0.031). Anastomotic closure was associated with a significantly lower POPF rate than suture closure (OR 0.55, 0.31 to 0.98; P = 0.042). Combined stapler and suture closure had significantly lower POPF rates than suture closure alone, but no significant difference compared with stapler closure alone.

CONCLUSION

The use of stapler closure or anastomotic closure for the pancreatic remnant after distal pancreatectomy significantly reduces POPF rates compared with suture closure. The combination of stapler and suture closure shows superiority over suture closure alone.

Failure to maintain a low ADP concentration impairs diastolic function in hypertrophied rat hearts

BACKGROUND

Mechanisms in addition to diastolic calcium overload may contribute to diastolic dysfunction in hypertrophied hearts. In this study, we tested the hypothesis that failure to maintain a low ADP concentration in hypertrophied hearts contributes to diastolic dysfunction by inhibiting the rate of cross-bridge cycling.

METHODS AND RESULTS

By perfusing isolated rat hearts with pyruvate and 2-deoxyglucose (2DG), we were able to perturb [ADP] with minimal changes in [ATP] and [inorganic phosphate] or the contribution of glycolytic ATP to ATP synthesis. The effects of 2DG were compared in aortic-banded (LVH, n=5) and sham-operated (control, n=5) rat hearts. 31P NMR spectroscopy was used to measure the concentrations of phosphorus-containing compounds. We found a threefold increase of left ventricular end-diastolic pressure (LVEDP) in LVH during 2DG perfusion, and this increase was concomitant with a threefold increase in intracellular free [ADP]. The [ADP] in the control hearts was maintained <40 micromol/L, and no change in LVEDP was observed. A linear relationship between increases in [ADP] and LVEDP was found (r2=.66, P=.001). Furthermore, the capacity of the creatine kinase reaction, a major mechanism for maintaining a low [ADP], was decreased in LVH (P=.0001).

CONCLUSIONS

Increased [ADP] contributes to diastolic dysfunction in LVH, possibly due to slowed cross-bridge cycling. Decreased capacity of the creatine kinase reaction to rephosphorylate ADP is a likely contributing mechanism to the failure to maintain a low [ADP] in LVH.

Direct targeting of SUZ12/ROCK2 by miR-200b/c inhibits cholangiocarcinoma tumourigenesis and metastasis

Background:

The multidrug resistance and distant metastasis of cholangiocarcinoma result in high postoperative recurrence and low long-term survival rates. It has been demonstrated that the ectopic expression of miR-200 suppresses the multidrug resistance and metastasis of cancer. However, the expression and function of miR-200 in cholangiocarcinoma has not yet been described.

Methods:

In this study, we identified dysregulated microRNAs (miRNAs, miR) in cholangiocarcinoma tissue by microarray analysis, and subsequent real-time PCR and northern blot analyses validated the expression of candidate miR. We performed functional analyses and investigated the relationship between miR-200b/c expression and the properties of cholangiocarcinoma cells. A dual luciferase assay was applied to examine the effect of miRNAs on the 3′-UTR of target genes, and we demonstrated the function of the target gene by siRNA transfection identifying the downstream pathway via western blotting.

Results:

We found significantly downregulated expression of four miR-200 family members (miR-200a/b/c/429) and then confirmed that ectopic miR-200b/200c inhibits the migration and invasion of cholangiocarcinoma cells both in vitro and in vivo. We found that miR-200b/c influenced the tumourigenesis of cholangiocarcinoma cells including their tumour-initiating capacity, sphere formation, and drug resistance. We further found that miR-200b/c regulated migration and invasion capacities by directly targeting rho-kinase 2 and regulated tumorigenic properties by directly targeting SUZ12 (a subunit of a polycomb repressor complex).

Conclusion:

Our study shows that miR-200b/c has a critical role in the regulation of the tumorigenic and metastatic capacity of cholangiocarcinoma and reveals the probable underlying mechanisms.

Role of MgADP in the development of diastolic dysfunction in the intact beating rat heart

Sarcomere relaxation depends on dissociation of actin and myosin, which is regulated by a number of factors, including intracellular [MgATP] as well as MgATP hydrolysis products [MgADP] and inorganic phosphate [Pi], pHi, and cytosolic calcium concentration ([Ca2+]c). To distinguish the contribution of MgADP from the other regulators in the development of diastolic dysfunction, we used a strategy to increase free [MgADP] without changing [MgATP], [Pi], or pHi. This was achieved by applying a low dose of iodoacetamide to selectively inhibit the creatine kinase activity in isolated perfused rat hearts. [MgATP], [MgADP], [Pi], and [H+] were determined using 31P NMR spectroscopy. The [Ca2+]c and the glycolytic rate were also measured. We observed an approximately threefold increase in left ventricular end diastolic pressure (LVEDP) and 38% increase in the time constant of pressure decay (P < 0.05) in these hearts, indicating a significant impairment of diastolic function. The increase in LVEDP was closely related to the increase in free [MgADP]. Rate of glycolysis was not changed, and [Ca2+]c increased by 16%, which cannot explain the severity of diastolic dysfunction. Thus, our data indicate that MgADP contributes significantly to diastolic dysfunction, possibly by slowing the rate of cross-bridge cycling.

Large-scale preparation for efficient polymer-based room-temperature phosphorescence via click chemistry

To achieve efficient polymer-based room-temperature phosphorescence (RTP) materials, covalently embedding phosphors into the polymer matrix appeared as the most appealing approach. However, it is still highly challenging to fabricate RTP materials on a large scale because of the inefficient binding engineering and time-consuming covalent reactions. Here, we have proposed a scalable preparation approach for RTP materials by the facile B─O click reaction between boronic acid-modified phosphors and polyhydroxy polymer matrix. The ab initio molecular dynamics simulations demonstrated that the phosphors were effectively immobilized, resulting in the suppressed nonradiative transitions and activated RTP emission. In comparison to the reported covalent binding time of several hours, such a B─O click reaction can be accomplished within 20 s under ambient environment. The developed strategy simplified the construction of polymer-based RTP polymeric materials by the introduction of facile click chemistry. Our success provides inspirations and possibilities for the scale-up production of RTP materials.

Depletion of energy reserve via the creatine kinase reaction during the evolution of heart failure in cardiomyopathic hamsters

To study the contribution of myocardial energy reserve to the deterioration of cardiac function during the development of heart failure, we defined energy reserve via the creatine kinase (CK) reaction and the isovolumic contractile performance in hearts of cardiomyopathic hamsters at the ages of 1.5, 4, 17, 30 and 43 weeks and in age-matched normal hamsters. Energy reserve via the CK reaction was estimated by the product of total CK activity and the content of total creatine in the heart. Isovolumic contractile performance was measured as rate pressure product (RPP, 10(3) mmHg/min) in isolated hearts. Contractile reserve was assessed as the increase of RPP elicited by high calcium stimulation. Compared to the controls, decreases in total CK activity and content of total creatine were observed in hearts of 17-, 30- and 43-week-old cardiomyopathic hamsters. These changes were not observed in the skeletal muscle. Although the decrease of baseline RPP first occurred at the age of 30 weeks (11.5 +/- 0.9 v 20.5 +/- 0.8, P < 0.05), the contractile reserve was already reduced at the age of 17 weeks (9.9 +/- 1.3 v 23.6 +/- 1.9, P < 0.05). A linear relationship was found between the energy reserve via creatine kinase reaction and the contractile reserve of the heart (r2 = 0.85). Furthermore, concomitant decreases in the CK reaction velocity and the contractile reserve were observed in cardiomyopathic hearts, suggesting that depletion of energy reserve may contribute to the development of heart failure.

Energetic basis for reduced contractile reserve in isolated rat hearts

To study the relationship between myocardial energetics and contractile reserve, we acutely and selectively inhibited creatine kinase (CK) activity in isolated perfused rat hearts, using increasing doses of iodoacetamide. 31P nuclear magnetic resonance spectroscopy was used to measure intracellular pH and the concentrations of ATP, phosphocreatine, and inorganic phosphate. Contractile reserve was assessed as the increase of rate-pressure product (RPP) from baseline during high-calcium perfusion. Contractile reserve was reduced by 9, 35, and 72% in hearts with 26, 6, and 1% CK activity, respectively. An inverse linear relationship between RPP and the free energy release from ATP hydrolysis ([delta G approximately P[) was shown for all groups. Furthermore, the maximal RPPs of all hearts were achieved at the same level of [delta G approximately P[ (52-53 kJ/mol), which is equal to the free energy requirement of sarcoplasmic reticulum Ca2+ adenosine 5'-triphosphatase (ATPase). We suggest that inhibition of the CK reaction caused a decrease of [delta G approximately P[ which, in turn, limits the Ca(2+)-handling capacity of sarcoplasmic reticulum Ca2+ ATPase. In this way, the ability of the heart to increase its contractile performance is restricted.

Mutant ACVR1 Arrests Glial Cell Differentiation to Drive Tumorigenesis in Pediatric Gliomas

Diffuse intrinsic pontine gliomas (DIPGs) are aggressive pediatric brain tumors for which there is currently no effective treatment. Some of these tumors combine gain-of-function mutations in ACVR1, PIK3CA, and histone H3-encoding genes. The oncogenic mechanisms of action of ACVR1 mutations are currently unknown. Using mouse models, we demonstrate that Acvr1G328V arrests the differentiation of oligodendroglial lineage cells, and cooperates with Hist1h3bK27M and Pik3caH1047R to generate high-grade diffuse gliomas. Mechanistically, Acvr1G328V upregulates transcription factors which control differentiation and DIPG cell fitness. Furthermore, we characterize E6201 as a dual inhibitor of ACVR1 and MEK1/2, and demonstrate its efficacy toward tumor cells in vivo. Collectively, our results describe an oncogenic mechanism of action for ACVR1 mutations, and suggest therapeutic strategies for DIPGs.

Genetic variation in the beta, beta-carotene-9', 10'-dioxygenase gene and association with fat colour in bovine adipose tissue and milk

beta, beta-carotene-9', 10'-dioxygenase (BCO2) plays a role in cleaving beta-carotene eccentrically, and may be involved in the control of adipose and milk colour in cattle. The bovine BCO2 gene was sequenced as a potential candidate gene for a beef fat colour QTL on chromosome (BTA) 15. A single nucleotide base change located in exon 3 causes the substitution of a stop codon (encoded by the A allele) for tryptophan(80) (encoded by the G allele) (c. 240G>A, p.Trp80stop, referred to herein as SNP W80X). Association analysis showed significant differences in subcutaneous fat colour and beta-carotene concentration amongst cattle with different BCO2 genotypes. Animals with the BCO2 AA genotype had more yellow beef fat and a higher beta-carotene concentration in adipose tissues than those with the GA or GG genotype. QTL mapping analysis with the BCO2 SNP W80X fitted as a fixed effect confirmed that this SNP is likely to represent the quantitative trait nucleotide (QTN) for the fat colour-related traits on BTA 15. Moreover, animals with the AA genotype had yellower milk colour and a higher concentration of beta-carotene in the milk.

Role of extracellular and intracellular acidosis for hypercapnia-induced inhibition of tension of isolated rat cerebral arteries

The importance of smooth muscle cell pHi and pHo for the hypercapnic vasodilation of rat cerebral arteries was evaluated in vitro. Vessel segments were mounted in a myograph for isometric tension recording; pHi was measured by loading the smooth muscle cells with the fluorescent dye BCECF, and pHo was measured with a glass electrode. In all studies, Ca(2+)-dependent basal tension (in the absence of any agonist) and tension in the presence of arginine vasopressin were investigated. Control solution was physiological saline bubbled with 5% CO2 and containing 25 mmol/L HCO3- (pH 7.45 to 7.50). Induction of hypercapnic acidosis (10% CO2) or normocapnic acidosis (15 mmol/L HCO3-) caused significant inhibition of smooth muscle tension, and both conditions reduced pHi as well as pHo. N-Nitro-L-arginine significantly inhibited the relaxation to hypercapnic acidosis but had no significant effect on relaxation to normocapnic acidosis. Predominant extracellular acidosis, induced by reducing [HCO3-] from 25 to 9 mmol/L and CO2 from 5% to 2.5%, also caused inhibition of tension in steady state. By contrast, predominant intracellular acidosis, induced by increasing [HCO3-] from 25 to 65 mmol/L and CO2 from 5% to 15%, induced a small increase of basal tension and a small decrease of tension in the presence of arginine vasopressin. The responses to predominant intracellular or extracellular acidosis were qualitatively similar in the presence and absence of endothelium and in the presence and absence of N-nitro-L-arginine. It is concluded that the extracellular acidosis and not smooth muscle intracellular acidosis is responsible for the relaxation to hypercapnic acidosis.

L-Arginine improves endothelial function in renal artery of hypertensive Dahl rats

OBJECTIVES

To clarify whether endothelium-derived contracting factor (EDCF) is developed in renal artery of hypertensive Dahl rats and whether prolonged oral L-arginine treatments prevent development of EDCF and hypertension.

DESIGN

The effect of prolonged salt treatment with or without L-arginine on the renal artery was examined.

METHODS AND RESULTS

Dahl salt-sensitive and -resistant rats were fed a 0.4 or an 8% NaCl diet for 4 weeks. High sodium intake increased arterial pressure in Dahl salt-sensitive rats. The rings of renal arteries were suspended for isometric tension recording. Only in the hypertensive rats, more than 1 micromol/l acetylcholine induced an endothelium-dependent contraction response. The contraction was completely inhibited by indomethacin or ONO-3708 [prostaglandin H2 (PGH2)/thromboxane A2 (TXA2) receptor antagonist], and partially inhibited by OKY-046 (TXA2 synthetase inhibitor). Acetylcholine-induced relaxation was significantly depressed in hypertensive rats, which was partially improved by SQ29548 (PGH2/TXA2 receptor antagonist). Oral L-arginine, but not ONO-8809 (orally active PGH2/TXA2 receptor antagonist) treatment, inhibited the contraction and amended the relaxation. The endothelium-independent contraction to TXA2 receptor agonist U46619 and relaxation to nitroprusside were not altered by L-arginine treatment The L-Arginine treatment reduced blood pressure and sodium retention with increases in urinary NO2-/NO3- and cGMP excretion. Hydralazine treatment also inhibited development of EDCF.

CONCLUSIONS

The present results suggest that impaired endothelium-dependent relaxation to acetylcholine is caused in part by induction of EDCF synthesis/release in renal arteries of hypertensive Dahl rats. L-arginine can attenuate sodium retention and development of hypertension, which lead to a decrease in EDCF synthesis in renal arteries.

Derivation of male germ cells from induced pluripotent stem cells in vitro and in reconstituted seminiferous tubules

OBJECTIVES

Previous studies have demonstrated that mouse- and human-induced pluripotent stem (iPS) cells can differentiate into primordial germ cells in vitro. However, up to now it is not known whether iPS cells would be able to differentiate into male germ cells in vivo. The aim of this study was to explore differentiation potential of iPS cells to male germ cells in vitro and in vivo.

MATERIALS AND METHODS

In this study, approaches using in vitro retinoic acid induction and in vivo ectopic transplantation were combined to induce iPS cells to become male germ cells.

RESULTS

RT-PCR showed that expression of pre-meiotic and meiotic germ cell-specific genes was enhanced in iPS cell-derived embryoid bodies (EBs) compared to mRNA transcripts of iPS cells. Immunofluorescence analysis revealed that iPS cell-derived EBs positively expressed germ-cell markers VASA, c-Kit and SCP3. Furthermore, iPS cell-derived cells dissociated from EBs were injected with testicular cells into dorsal skin of mice. Histological examination showed that iPS cell-derived cells could reconstitute seminiferous tubules, and meanwhile, iPS cell-derived germ cells could settle at basement membranes of reconstituted tubules.

CONCLUSION

Our results suggest that iPS cells are able to differentiate into male germ cells in vitro and that reconstituted seminiferous tubules may provide a functional niche for exogenous iPS cell-derived male germ cells. Derivation of male germ cells from iPS cells has potential application for treating male infertility and provides an ideal platform for elucidating molecular mechanisms of male germ-cell development.

Functional map of SARS-CoV-2 3CL protease reveals tolerant and immutable sites

The SARS-CoV-2 3CL protease (3CLpro) is an attractive therapeutic target, as it is essential to the virus and highly conserved among coronaviruses. However, our current understanding of its tolerance to mutations is limited. Here, we develop a yeast-based deep mutational scanning approach to systematically profile the activity of all possible single mutants of the 3CLpro and validate a subset of our results within authentic viruses. We reveal that the 3CLpro is highly malleable and is capable of tolerating mutations throughout the protein. Yet, we also identify specific residues that appear immutable, suggesting that these may be targets for future 3CLpro inhibitors. Finally, we utilize our screening as a basis to identify E166V as a resistance-conferring mutation against the clinically used 3CLpro inhibitor, nirmatrelvir. Collectively, the functional map presented herein may serve as a guide to better understand the biological properties of the 3CLpro and for drug development against coronaviruses.

Effects of endothelin-1 in the isolated heart in ischemia/reperfusion and hypoxia/reoxygenation injury

The effects of the vasoconstrictor peptide endothelin-1 were examined in the isolated heart during hypoxia, reoxygenation and reperfusion. Isovolumic rat hearts were perfused with Krebs-Henseleit buffer at constant pressure. Cumulative dose-response curves were obtained for endothelin-1 boluses of 0.04 to 400 pmol in five groups of hearts. Coronary flow declined with increasing dosages and was almost abolished at 400 pmol in control hearts. In hearts subjected to mild hypoxia (perfusate PO2 approximately 150 mmHg), the constrictor effect of endothelin-1 was attenuated at moderate dose compared to control hearts (4 vs. 16% flow reduction at 40 pmol; P less than 0.05). The constrictor effect was unaltered in hearts subjected to either 60 min of severe hypoxia (PO2 approximately 35 mmHg) followed by reoxygenation or to 10 min of total ischemia followed by reperfusion (stunning). When hearts were reperfused following 30 min of total ischemia (irreversible injury), the constrictor response to endothelin-1 was potentiated compared to control (e.g. 36 vs. 16% flow reduction at 40 pmol; P less than 0.05). We conclude that endothelin-1 is a potent coronary constrictor in hypoxic, reoxygenated and reperfused heart. The constrictor effect is attenuated during hypoxia, most likely due to the presence of counteracting vasodilator metabolites. During reperfusion, the constrictor effect is unchanged in stunned myocardium, but is augmented in irreversibly injured heart, due to either increased endothelin-1 binding sites or loss of counteracting vasodilator mechanisms such as prostaglandins and/or endothelium-derived relaxing factor.

Endogenous nitric oxide enhances coupling between O2 consumption and ATP synthesis in guinea pig hearts

Endogenous nitric oxide (eNO) modulates tissue respiration. To test whether eNO modulates myocardial O2 consumption (MVO2), ATP synthesis, and metabolic efficiency, we used isolated isovolumic guinea pig hearts perfused at a constant flow. N(omega)-nitro-L-arginine (L-NNA; 5 x 10(-5) mol/l) was used to inhibit eNO production. MVO2 was measured at different levels of cardiac work, estimated as the rate-pressure product (RPP). ATP content and synthesis rate were determined using (31)P NMR and magnetization transfer during high cardiac work. L-NNA increased coronary vascular resistance (19 +/- 3%, P < 0.05) and MVO2 (12 +/- 3%, P < 0.05) without an increase in the RPP. In contrast, vehicle infusion resulted in insignificant changes in coronary vascular resistance (3 +/- 2%, P > 0.05) and MVO2 (-2 +/- 1%, P > 0.05). Compared with vehicle, L-NNA caused a higher MVO2 both during KCl arrest (L-NNA 5.6 +/- 0.5 vs. vehicle 3.0 +/- 0.4 micromol x min(-1) x mg x dry wt(-1), P < 0.05) and during increased cardiac work elicited by elevating perfusate Ca2+, indicating an upward shift in the relationship between contractile performance (measured as RPP) and MVO2. However, neither ATP contents nor ATP synthesis rates were different in the two groups during high cardiac work. Thus, because inhibition of eNO production by L-NNA increased MVO2 without a change in the ATP synthesis rate, these data suggest that eNO increases myocardial metabolic efficiency by reducing MVO2 in the heart.

Inhibition of the creatine kinase reaction decreases the contractile reserve of isolated rat hearts

To define the relation between phosphoryl transfer via creatine kinase (CK) and the ability of the intact beating heart to do work, we chemically inhibited CK activity and then measured cardiac performance under physiological and acute stress conditions. Isolated perfused rat hearts were exposed to iodoacetamide (IA) and subjected to one of three cardiac stresses: hypercalcemic (Ca2+ = 3 mM) buffer perfusion (n = 7), norepinephrine (2 mumol/min) infusion (n = 6), or hypoxic buffer perfusion (n = 5). IA decreased CK activity to near zero, measured in intact hearts by 31P magnetization transfer, and to 2% of control CK activity, measured in myocardial homogenates. The CK isoenzyme profile was unchanged, suggesting nonselective IA inhibition of all isoenzymes. Mitochondria isolated from IA-treated hearts had normal ADP:O ratios, state 3 respiratory rates, and unchanged acceptor and respiratory control ratios. Neither actomyosin adenosinetriphosphatase nor adenylate kinase activities were changed. After IA exposure, end-diastolic pressure, left ventricular developed pressure, and heart rate were unchanged for at least 30 min at physiological perfusion pressures, but large changes were observed during stress conditions. The increase in left ventricular developed pressure induced by hypercalcemic perfusion and by norepinephrine infusion decreased by 39 and 54%, respectively. During hypoxia, the rate of phosphocreatine depletion was decreased by 57%, left ventricular developed pressure declined, and end-diastolic pressure increased faster than in controls. These results show that inhibition of CK to < 2% of control activity by IA reduced contractile reserve by approximately 50%. We conclude that CK activity is essential for the expression of the full dynamic range of myocardial performance.

Transfer of the minus strand of DNA during hepadnavirus replication is not invariable but prefers a specific location

The current model for replication of duck hepatitis B virus has reverse transcription initiating and copying a UUAC motif within the encapsidation signal, epsilon, near the 5' end of the RNA template. This results in synthesis of four nucleotides of DNA. This short minus-strand DNA product is then transferred to a complementary position, at DR1, near the 3' end of the RNA template. Elongation of minus-strand DNA then ensues. We have examined the transfer of minus-strand DNA during replication of duck hepatitis B virus in cell culture. The initial aim of this work was to examine the effect of mutations at DR1 on the transfer process. We found that when mutations were introduced into the UUAC motif overlapping DR1, the 5' end of minus-DNA no longer mapped to position 2537 but was shifted two or four nucleotides. Mismatches were predicted to exist at the new sites of elongation. Elongation from nucleotide 2537 could be restored in these mutants by making compensatory changes in the UUAC motif within epsilon. This finding led us to examine limitations in the shifting of the site of transfer. When the UUAC motif in epsilon was changed to six different tetranucleotide motifs surrounding position 2537, transfer of minus-strand DNA shifted predictably, albeit inefficiently. Also, when multiple UUAC motifs were introduced near DR1, the UUAC motif at nucleotide 2537 was used preferentially. Overall, our findings confirm the current minus-strand DNA transfer model and demonstrate a marked preference for the site of the transfer.

Altered creatine kinase enzyme kinetics in diabetic cardiomyopathy. A(31)P NMR magnetization transfer study of the intact beating rat heart

To determine whether the decreased contractile performance in diabetic hearts is associated with a reduced energy reserve due to decreased creatine kinase (CK) activity, we measured total CK activity (V(max)) in vitro and CK reaction velocity in vivo using(31)P NMR spectroscopy in isolated perfused rat hearts after 4 and 6 weeks of diabetes. After 4 weeks of diabetes, V(max)decreased by 22% with a larger decrease of CK MB than of CK MM and mitochondrial-CK isoenzymes. There was no further decrease in these parameters after 6 weeks of diabetes. Isovolumic contractile performance of 4 and 6 week diabetic hearts, estimated as rate-pressure product under identical perfusion and loading conditions (EDP set at 6-8 mmHg), was only 50% of that of control. ATP, PCr and total creatine concentrations were not different in control and 4 or 6 weeks diabetic rat hearts. After 4 weeks of diabetes, CK reaction velocity decreased by 22%. This was in proportion to the decline of V(max)and therefore predicted by the rate equation for the CK reaction. However, the further decline in the CK reaction velocity after 6 weeks of diabetes (45%) was greater than that predicted from the CK rate equation (17% decrease), and cannot be explained by substrate control of the enzyme. When hearts were inotropically stimulated by increasing perfusate calcium concentration, CK reaction velocity increased slightly (approximately 15%) in both control and diabetic hearts, thereby maintaining a constant ATP concentration. We conclude that in the diabetic myocardium, the CK reaction velocity decreases but does not limit the availability of high-energy phosphates for contraction over the range of workloads studied. We also conclude that a mechanism(s) in addition to substrate control regulates CK reaction velocity in the 6 week diabetic hearts.

A flexible repertoire of transcription factor binding sites and a diversity threshold determines enhancer activity in embryonic stem cells

Transcriptional enhancers are critical for development and phenotype evolution and are often mutated in disease contexts; however, even in well-studied cell types, the sequence code conferring enhancer activity remains unknown. To examine the enhancer regulatory code for pluripotent stem cells, we identified genomic regions with conserved binding of multiple transcription factors in mouse and human embryonic stem cells (ESCs). Examination of these regions revealed that they contain on average 12.6 conserved transcription factor binding site (TFBS) sequences. Enriched TFBSs are a diverse repertoire of 70 different sequences representing the binding sequences of both known and novel ESC regulators. Using a diverse set of TFBSs from this repertoire was sufficient to construct short synthetic enhancers with activity comparable to native enhancers. Site-directed mutagenesis of conserved TFBSs in endogenous enhancers or TFBS deletion from synthetic sequences revealed a requirement for 10 or more different TFBSs. Furthermore, specific TFBSs, including the POU5F1:SOX2 comotif, are dispensable, despite cobinding the POU5F1 (also known as OCT4), SOX2, and NANOG master regulators of pluripotency. These findings reveal that a TFBS sequence diversity threshold overrides the need for optimized regulatory grammar and individual TFBSs that recruit specific master regulators.