Canonical and noncanonical contribution of thyroid hormone receptor isoforms alpha and beta to cardiac hypertrophy and heart rate in male mice

BACKGROUND

Stimulation of ventricular hypertrophy and heart rate are two major cardiac effects of thyroid hormone (TH). Aim of this study was to determine in vivo which TH receptor (TR), α or β, and which mode of TR action, canonical gene expression or DNA binding independent noncanonical action, mediate these effects.

MATERIAL AND METHODS

We compared global TRα and TRβ knockout mice (TRαKO; TRβKO) with wild-type (WT) mice to determine the TR isoform responsible for T3 effects. The relevance of TR DNA binding was studied in mice with a mutation in the DNA-binding domain that selectively abrogates DNA binding and canonical TR action (TRαGS; TRβGS). Hearts were studied with echocardiography at baseline and after seven weeks T3 treatment. Gene expression was measured with real-time PCR. Heart rate was recorded with radiotelemetry transmitters for seven weeks in untreated, hypothyroid and T3-treated mice.

RESULTS

T3 induced ventricular hypertrophy in WT and TRβKO mice, but not in TRαKO mice. Hypertrophy was also induced in TRαGS mice. Thus, hypertrophy is mostly mediated by noncanonical TRα action. Similarly, repression of Mhy7 occurred in WT and TRαGS mice. Basal heart rate was largely dependent on canonical TRα action. But responsiveness to hypothyroidism and T3 treatment as well as expression of pacemaker gene Hcn2 were still preserved in TRαKO mice, demonstrating that TRβ could compensate for absence of TRα.

CONCLUSION

T3-induced cardiac hypertrophy could be attributed to noncanonical TRα action, whereas heart rate regulation was mediated by canonical TRα action. TRβ could substitute for canonical, but not noncanonical TRα action.

Cardiac recovery from pressure overload is not altered by thyroid hormone status in old mice

Introduction

Thyroid hormones (THs) are known to have various effects on the cardiovascular system. However, the impact of TH levels on preexisting cardiac diseases is still unclear. Pressure overload due to arterial hypertension or aortic stenosis and aging are major risk factors for the development of structural and functional abnormalities and subsequent heart failure. Here, we assessed the sensitivity to altered TH levels in aged mice with maladaptive cardiac hypertrophy and cardiac dysfunction induced by transverse aortic constriction (TAC).

Methods

Mice at the age of 12 months underwent TAC and received T4 or anti-thyroid medication in drinking water over the course of 4 weeks after induction of left ventricular pressure overload.

Results

T4 excess or deprivation in older mice had no or only very little impact on cardiac function (fractional shortening), cardiac remodeling (cardiac wall thickness, heart weight, cardiomyocyte size, apoptosis, and interstitial fibrosis), and mortality. This is surprising because T4 excess or deprivation had significantly changed the outcome after TAC in young 8-week-old mice. Comparing the gene expression of deiodinases (Dio) 2 and 3 and TH receptor alpha (TRα) 1 and the dominant-negative acting isoform TRα2 between young and aged mice revealed that aged mice exhibited a higher expression of TRα2 and Dio3, while expression of Dio2 was reduced compared with young mice. These changes in Dio2 and 3 expressions might lead to reduced TH availability in the hearts of 12-month-old mice accompanied by reduced TRα action due to higher TRα2.

Discussion

In summary, our study shows that low and high TH availability have little impact on cardiac function and remodeling in older mice with preexisting pressure-induced cardiac damage. This observation seems to be the result of an altered expression of deiodinases and TRα isoforms, thus suggesting that even though cardiovascular risk is increasing with age, the response to TH stress may be dampened in certain conditions.

Structural and Biochemical Investigation of the Heterodimeric Murine tRNA-Guanine Transglycosylase

In tRNA^Asp, tRNA^Asn, tRNA^Tyr, and tRNA^His of most bacteria and eukaryotes, the anticodon wobble position may be occupied by the modified nucleoside queuosine, which affects the speed and the accuracy of translation. Since eukaryotes are not able to synthesize queuosine de novo, they have to salvage queuine (the queuosine base) as a micronutrient from food and/or the gut microbiome. The heterodimeric Zn²⁺ containing enzyme tRNA-guanine transglycosylase (TGT) catalyzes the insertion of queuine into the above-named tRNAs in exchange for the genetically encoded guanine. This enzyme has attracted medical interest since it was shown to be potentially useful for the treatment of multiple sclerosis. In addition, TGT inactivation via gene knockout leads to the suppressed cell proliferation and migration of certain breast cancer cells, which may render this enzyme a potential target for the design of compounds supporting breast cancer therapy. As a prerequisite to fully exploit the medical potential of eukaryotic TGT, we have determined and analyzed a number of crystal structures of the functional murine TGT with and without bound queuine. In addition, we have investigated the importance of two residues of its non-catalytic subunit on dimer stability and determined the Michaelis-Menten parameters of murine TGT with respect to tRNA and several natural and artificial nucleobase substrates. Ultimately, on the basis of available TGT crystal structures, we provide an entirely conclusive reaction mechanism for this enzyme, which in detail explains why the TGT-catalyzed insertion of some nucleobases into tRNA occurs reversibly while that of others is irreversible.

Bacterial microcompartments for isethionate desulfonation in the taurine-degrading human-gut bacterium Bilophila wadsworthia

Background

Bilophila wadsworthia, a strictly anaerobic, sulfite-reducing bacterium and common member of the human gut microbiota, has been associated with diseases such as appendicitis and colitis. It is specialized on organosulfonate respiration for energy conservation, i.e., utilization of dietary and host-derived organosulfonates, such as taurine (2-aminoethansulfonate), as sulfite donors for sulfite respiration, producing hydrogen sulfide (H₂S), an important intestinal metabolite that may have beneficial as well as detrimental effects on the colonic environment. Its taurine desulfonation pathway involves the glycyl radical enzyme (GRE) isethionate sulfite-lyase (IslAB), which cleaves isethionate (2-hydroxyethanesulfonate) into acetaldehyde and sulfite.

Results

We demonstrate that taurine metabolism in B. wadsworthia 3.1.6 involves bacterial microcompartments (BMCs). First, we confirmed taurine-inducible production of BMCs by proteomic, transcriptomic and ultra-thin sectioning and electron-microscopical analyses. Then, we isolated BMCs from taurine-grown cells by density-gradient ultracentrifugation and analyzed their composition by proteomics as well as by enzyme assays, which suggested that the GRE IslAB and acetaldehyde dehydrogenase are located inside of the BMCs. Finally, we are discussing the recycling of cofactors in the IslAB-BMCs and a potential shuttling of electrons across the BMC shell by a potential iron-sulfur (FeS) cluster-containing shell protein identified by sequence analysis.

Conclusions

We characterized a novel subclass of BMCs and broadened the spectrum of reactions known to take place enclosed in BMCs, which is of biotechnological interest. We also provided more details on the energy metabolism of the opportunistic pathobiont B. wadsworthia and on microbial H₂S production in the human gut.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02386-w.

The Importance of Charge in Perturbing the Aromatic Glue Stabilizing the Protein-Protein Interface of Homodimeric tRNA-Guanine Transglycosylase

Bacterial tRNA-guanine transglycosylase (Tgt) is involved in the biosynthesis of the modified tRNA nucleoside queuosine present in the anticodon wobble position of tRNAs specific for aspartate, asparagine, histidine, and tyrosine. Inactivation of the tgt gene leads to decreased pathogenicity of Shigella bacteria. Therefore, Tgt constitutes a putative target for Shigellosis drug therapy. Since it is only active as homodimer, interference with dimer-interface formation may, in addition to active-site inhibition, provide further means to disable this protein. A cluster of four aromatic residues seems important to stabilize the homodimer. We mutated residues of this aromatic cluster and analyzed each mutated variant with respect to the dimer and thermal stability or enzyme activity by applying native mass spectrometry, a thermal shift assay, enzyme kinetics, and X-ray crystallography. Our structural studies indicate a strong influence of pH on the homodimer stability. Apparently, protonation of a histidine within the aromatic cluster supports the collapse of an essential structural motif within the dimer interface at slightly acidic pH.

High-affinity peroxisome proliferator-activated receptor β/δ-specific ligands with pure antagonistic or inverse agonistic properties

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is a ligand-regulated nuclear receptor with essential functions in metabolism and inflammation. We have synthesized a new derivative [methyl 3-(N-(4-(hexylamino)-2-methoxyphenyl)sulfamoyl)thiophene-2-carboxylate (ST247) structurally related to the published PPARβ/δ inhibitory ligand methyl 3-(N-(2-methoxy-4-(phenylamino)phenyl)sulfamoyl)thiophene-2-carboxylate (GSK0660). ST247 has a higher affinity to PPARβ/δ than GSK0660, and at equimolar concentrations, it more efficiently 1) induces the interaction with corepressors both in vitro and in vivo, 2) inhibits the agonist-induced transcriptional activity of PPARβ/δ, and 3) down-regulates basal level expression of the peroxisome proliferator responsive element-driven PPARβ/δ target gene ANGPTL4. Methyl 3-(N-(4-(tert-butylamino)-2-methoxyphenyl)sulfamoyl)thiophene-2-carboxylate (PT-S58), another high-affinity derivative from our series, also efficiently inhibits agonist-induced transcriptional activation, but in contrast to ST247, it does not enhance the interaction of PPARβ/δ with corepressors. PT-S58 rather prevents corepressor recruitment triggered by the inverse agonist ST247. These findings classify ST247 as an inverse agonist, whereas PT-S58 is the first pure PPARβ/δ antagonist described to date. It is noteworthy that ST247 and PT-S58 are also effective on PPRE-independent functions of PPARβ/δ: in monocytic cells, both ligands modulate expression of the activation marker CCL2 in the opposite direction as an established PPARβ/δ agonist. The possibility to differentially modulate specific functions of PPARβ/δ makes these novel compounds invaluable tools to advance our understanding of PPARβ/δ biology.

[Early symptoms and findings in optic nerve meningiomas]

PURPOSE OF THE STUDY

While evaluating radiotherapy results in patients with primary and secondary optic nerve sheath meningiomas (ONSM) treated between 1993 and 2002, a large amount of data about early signs and symptoms has been collected which might be helpful for establishing an early diagnosis.

METHODS

We have reviewed the charts of the patients available at the Centre of Ophthalmology, collecting especially pretreatment data.

RESULTS

112 patients, 4 with bilateral tumours, 83 % female were included. Mean age was 51.7 years. Visual acuity loss with relative afferent pupillary defect was the main symptom and sign in primary ONSM (38 patients). Median interval between first symptoms and diagnosis was 12 months. Optic discs were in approximately one half atrophic, the other half were swollen, and only rarely normal (3 cases only). Retinociliary shunt vessels were seen in 10 cases. Nerve fibre bundle defects were the major visual field finding (including constriction and central scotoma). Visual acuity was better than 0.5 (20 / 40) in 46 % and worse than 0.1 (20 / 200) in 30 %. In secondary ONSM, the interval to diagnosis was with a median of 6 months shorter than in primary ONSM. Approximately half of the optic discs were atrophic, only 6 % were swollen. Even here nerve fibre bundle defects were dominating, only 7 % had vertical hemianopic defect. Visual acuity was better than 0.5 (20 / 40) in 30 % and in worse than 0.1 (20 / 200) 22 %. 45 % had ocular motility disorders.

DISCUSSION

Vertical hemianopic defects were surprisingly rare. The high rate of nerve fibre bundle defects and the relatively high number of patients with good visual acuity might explain why this disorder is occasionally mistaken for glaucoma. A typical clinical appearance can be outlined: mainly mid-aged women, slowly progressing visual loss, frequently motility disorders, relative afferent pupillary defect, nerve fibre bundle defects and atrophic or--mainly in primary ONSM--swollen optic disc form the characteristic picture.

Targeting the open-flap conformation of HIV-1 protease with pyrrolidine-based inhibitors

HIV protease is a well-established drug target in antiviral chemotherapy. Immense research efforts have been made to discover effective inhibitors, thus making the enzyme one of the most studied and best characterized proteins. Although the protease exhibits high flexibility, all approved drugs target virtually the same protein conformation. The development of viral cross-resistance demands the generation of inhibitors with novel scaffolds and deviating modes of binding. Herein we report the design and the short, high-yielding stereoselective synthesis of a series of chiral, symmetric pyrrolidine-based inhibitors targeting the open-flap conformation of the protease. The obtained co-crystal structure with one derivative provides a valuable starting point for further inhibitor design.

Single preoperative oral application of ascorbic acid does not affect postoperative plasma levels of ascorbic acid

BACKGROUND AND AIMS

A decrease in ascorbic acid (AA) plasma concentration is well known during the postoperative period and postulated to be caused by increased radical scavenging activity in response to surgical trauma. This often affects postoperative patients and is associated with multiple organ failure. Therefore, substitution of AA could potentially decrease the risk of postoperative complications. This study examines the effect of preoperative oral administration of 1,000 mg AA on the postoperative AA plasma concentration.

METHODS

54 patients were randomly split into two groups; patients in group 1 received no AA preoperatively while group 2 received oral AA (1,000 mg). Plasma samples were obtained preoperatively and on the first postoperative day for AA analysis (HPLC).

RESULTS

In both groups the AA concentration was normal preoperatively and reduced postoperatively.

CONCLUSION

A preoperative substitution of 1,000 mg AA is not sufficient to prevent postoperative lowered plasma concentration.

Phenotypic findings due to trisomy 7p15.3-pter including the TWIST locus

We report on a three-month-old boy with a 46,XY,der(Y)t(Y;7)(p11.32;p15.3) karyotype and growth deficiency, postnatal microcephaly with large fontanels, wide sagittal and metopic sutures, hypertelorism, choanal stenosis, micrognathia, bilateral cryptorchidism, hypospadias, abnormal fingers and toes, and severe developmental delay. FISH studies showed partial trisomy 7p resulting from a de novo unbalanced translocation. The application of molecular probes from the TWIST gene region (7p15.3-p21.1) and probes from the pseudoautosomal region (PAR) demonstrated that the 7p15.3-pter fragment was translocated onto Yp with the breakpoint within approximately 20 kb from the Yp telomere. We discuss the possible role of the TWIST gene in abnormal skull development and suggest that trisomy 7p cases with delayed closure of fontanels can be a result of TWIST gene dosage effect.

Kabuki syndrome-like features associated with a small ring chromosome X and XIST gene expression

Although clinical features in Kabuki syndrome (KS; Niikawa-Kuroki syndrome) have been well defined, the underlying genetic mechanism still remains unclear. We report a 9-year-old girl with typical KS-like facial appearance, skeletal and dermatoglyphic abnormalities, severe mental retardation, and growth deficiency. In 60 of 100 GTG-banded metaphases from peripheral blood lymphocytes, a ring chromosome smaller than a G group chromosome was found, which, according to reverse painting, consisted of Xq11.1q13. The proband's karyotype was described as mos45,X/46,X,+r(X). Several loci were analyzed with fluorescence in situ hybridization (FISH) and microsatellite markers revealing that one r(X) breakpoint mapped proximal to DXS422 (Xp11.21) and the second mapped distal to XIST gene, between loci DXS128E and DXS441 (Xq13.2). Uniparental disomy for X and r(X) was excluded and the paternal origin of r(X) was identified. XIST expression was demonstrated by nested reverse transcription polymerase chain reaction (RT-PCR) using primers spanning exons 5, 6i, and 6 in RNA prepared from lymphocytes. The observation of XIST expression is in contrast to two other cases in which the XIST gene was either not present on r(X) or not expressed. To our knowledge, this is the first case of Kabuki-like syndrome manifestations with r(X) and XIST expression.

Construction of a detailed physical and transcript map of the candidate region for Russell-Silver syndrome on chromosome 17q23-q24

Russell-Silver syndrome (RSS) is a heterogeneous disorder characterized mainly by pre- and postnatal growth retardation and characteristic dysmorphic features. The genetic cause of this syndrome is unknown. However, two autosomal translocations involving chromosome 17q25 were reported in association with RSS. Molecular analysis of the breakpoint on chromosome 17 of the de novo translocation previously described as t(1;17)(q31;q25) enabled us to refine the localization of the chromosome 17 breakpoint to 17q23-q24. Since no detailed mapping data were available for this region, we established a contig of yeast artificial chromosomes, P1 artificial chromosomes, bacterial artificial chromosomes, and cosmid clones for a 17q segment flanked by the sequence-tagged site (STS) markers D17S1557 and D17S940. This contig covers a physical distance of 4-5 Mb encompassing several novel markers. A transcript map was constructed by assigning genes and expressed sequence tags to the clone contig, and altogether 74 STS markers were mapped. Furthermore, the locus order and content provide insight into several duplication events that have occurred in the chromosomal region 17q23-q24. On the basis of our refined map, we have reduced the translocation breakpoint region to 65 kb between the newly derived markers 58T7 and CF20b. These data provide the molecular tools for the final identification of the RSS gene in 17q23-q24.

Color constancy in goldfish: the limits

Color constancy was investigated in behavioral training experiments on colors ranging from blue to yellow, located in the color space close to Planck's locus representing the main changes in natural skylight. Two individual goldfish were trained to peck at a test field of medium hue out of a series of 13-15 yellowish and bluish test fields presented simultaneously on a black background. During training the tank in which the fish were swimming freely was illuminated with white light. Correct choices were rewarded with food. During the tests differently saturated yellow or blue illumination was used. The degree of color constancy was inferred from the choice behavior under these illuminations. Perfect color constancy was found up to a certain degree of saturation of the colored light. Beyond this level test fields other than the training test field were chosen, indicating imperfect color constancy. Color constancy was quantified by applying color metrics on the basis of the goldfish cone sensitivity functions.

Simultaneous color contrast in goldfish--a quantitative study

A set of 9-15 colored test fields was presented to goldfish. In Experiment 1, test field hues ranged from green through yellow to red; in Experiment 2, the hues varied from blue through gray to yellow. In the training conditions, the test fields were presented with a gray or black surround. The fish learned to choose one intermediate test field hue by rewarding them with food. In the test conditions, the color of the surround was changed from gray to green, or red (Experiment 1), and from black to blue, or yellow (Experiment 2). The choice behavior of the goldfish changed substantially: one of the test fields other than the training test field was preferred. Direction and strength of simultaneous color contrast was quantified in goldfish color space. The effect of spatial stimulus configuration was investigated by changing test field size and using narrow annular surrounds. With test field radii ranging between 2 and 7.5 mm simultaneous color contrast was optimal whenever the ratio between surround width and test field radius had a value of about 1:1.

The goldfish--a colour-constant animal

A series of either thirteen or fifteen coloured test fields with hues from blue through grey to yellow were presented on a black background. Goldfish were trained on a bluish-grey test field by food reward. In the training situation, the setup with the coloured papers was illuminated with white light. In the test situation, the colour of the illumination was changed to blue or yellow. In both test illuminations the goldfish preferred the training field in the same way as under white illumination despite the fact that this test field stimulated the cone types very differently from the training situation. As test fields were present that excited the cones in exactly the same way as under white light, but were not chosen, colour constancy can be concluded. By means of colour metrics, it was possible to quantify direction and strength of colour constancy.

Wavelength discrimination of the goldfish in the ultraviolet spectral range

Wavelength discrimination ability of the goldfish was measured with a behavioural training technique in the UV spectral range. First, spectral sensitivity was determined for the two fish to adjust the monochromatic lights (between 334 and 450 nm) to equal subjective brightness. The results of the wavelength discrimination experiment show that, independent of which wavelength the fish were trained on, the relative choice frequency reached values above 70% only at wavelengths longer than 410 nm. Wavelength discrimination between 344 and 404 nm was not possible. Accordingly, the delta lambda function increases steeply between 400 and 380 nm, with values between about 12 and 90 nm, respectively. Model computations indicate that the delta lambda function cannot be explained on the basis of the cone sensitivity spectra. Instead, inhibitory interactions have to be assumed which suppress the short wavelength flanks of the short-, mid-, and long-wavelength sensitive cone types in the UV range.