Chronic intake of caffeine during gestation down regulates metabotropic glutamate receptors in maternal and fetal rat heart

Caffeine is the most widely consumed substance in the world which antagonizes adenosine effects. Adenosine acting through A(1) receptors inhibits glutamate release which binds to metabotropic glutamate receptors (mGluRs). Recently, we have shown that maternal caffeine intake during gestation causes down-regulation of A(1) and metabotropic glutamate receptors in the brain of both rat mothers and fetuses. In the present work we provide evidence that caffeine also affects receptors in hearts, causing a decrease in mGluRs from both maternal and fetal hearts. A decrease in G(q/11) and PLC beta(1) proteins level was also observed in both tissues. However, phospholipase C activity was only affected in fetal heart, being significantly decreased. These results suggest an in vivo cross-talk mechanism between adenosine and glutamate receptors in peripheral tissues. Therefore, special attention should be paid to caffeine ingestion during gestation.

Left-right lineage analysis of AV cushion tissue in normal and laterality defective Xenopus hearts

The majority of complex congenital heart defects occur in individuals who are afflicted by laterality disease. We hypothesize that the prevalence of valvuloseptal defects in this population is due to defective left-right patterning of the embryonic atrioventricular (AV) canal cushions, which are the progenitor tissue for valve and septal structures in the mature heart. Using embryos of the frog Xenopus laevis, this hypothesis was tested by performing left-right lineage analysis of myocytes and cushion mesenchyme cells of the superior and inferior cushion regions of the AV canal. Lineage analyses were conducted in both wild-type and laterality mutant embryos experimentally induced by misexpression of ALK4, a type I TGF-beta receptor previously shown to modulate left-right axis determination in Xenopus. We find that abnormalities in overall amount and left-right cell lineage composition are present in a majority of ALK4-induced laterality mutant embryos and that much variation in the nature of these abnormalities exists in embryos that exhibit the same overall body situs. We propose that these two parameters of cushion tissue formation-amount and left-right lineage origin-are important for normal processes of valvuloseptal morphogenesis and that defective allocation of cells in the AV canal might be causatively linked to the high incidence of valvuloseptal defects associated with laterality disease.

Cell type-specific over-expression of chromosome 21 genes in fibroblasts and fetal hearts with trisomy 21

Background

Down syndrome (DS) is caused by trisomy 21 (+21), but the aberrations in gene expression resulting from this chromosomal aneuploidy are not yet completely understood.

Methods

We used oligonucleotide microarrays to survey mRNA expression in early- and late-passage control and +21 fibroblasts and mid-gestation fetal hearts. We supplemented this analysis with northern blotting, western blotting, real-time RT-PCR, and immunohistochemistry.

Results

We found chromosome 21 genes consistently over-represented among the genes over-expressed in the +21 samples. However, these sets of over-expressed genes differed across the three cell/tissue types. The chromosome 21 gene MX1 was strongly over-expressed (mean 16-fold) in senescent +21 fibroblasts, a result verified by northern and western blotting. MX1 is an interferon target gene, and its mRNA was induced by interferons present in +21 fibroblast conditioned medium, suggesting an autocrine loop for its over-expression. By immunohistochemistry the p78^MX1 protein was induced in lesional tissue of alopecia areata, an autoimmune disorder associated with DS. We found strong over-expression of the purine biosynthesis gene GART (mean 3-fold) in fetal hearts with +21 and verified this result by northern blotting and real-time RT-PCR.

Conclusion

Different subsets of chromosome 21 genes are over-expressed in different cell types with +21, and for some genes this over-expression is non-linear (>1.5X). Hyperactive interferon signaling is a candidate pathway for cell senescence and autoimmune disorders in DS, and abnormal purine metabolism should be investigated for a potential role in cardiac defects.

Increased Expression of Vascular Endothelial Growth Factor in Cardiac Structures of Fetus with Hydrops as Compared to Nonhydropic Controls

OBJECTIVE

The hypothesis that severe fetal hydrops is caused by an excess of vascular endothelial growth factor (VEGF), mainly produced in the fetal heart, is tested.

METHODS

Immunohistochemical VEGF-stained postmortem biopsies from the right ventricle and right atrium of 8 hydropic fetuses were compared to those of 8 nonhydropic fetuses. The endocardium, myocardium, epicardium, endothelium, and vascular smooth muscle cells were scored on intensity of VEGF-staining. The Mann-Witney test was used to test for significancy (p < 0.05) of the differences in staining. Increased vascularization as a result of VEGF was measured in both groups by standard randomization count.

RESULTS

The endocardium, epicardium and endothelium of the coronary vessels showed significantly (p < 0.05) more intense VEGF-staining in the hydrops group than in the control group. The atria showed more intense staining than the ventricles in both groups. The hydropic fetuses showed a significantly increased number of coronary vessels in the myocardium. These vessels contained more blood cells than the coronary vessels in nonhydropic fetuses.

CONCLUSION

The fetal heart appears to be a major source of excess VEGF in fetal hydrops.

Hey basic helix-loop-helix transcription factors are repressors of GATA4 and GATA6 and restrict expression of the GATA target gene ANF in fetal hearts

The Hey basic helix-loop-helix transcription factors are downstream effectors of Notch signaling in the cardiovascular system. Mice lacking Hey2 develop cardiac hypertrophy, often associated with congenital heart defects, whereas combined Hey1/Hey2 deficiency leads to severe vascular defects and embryonic lethality around embryonic day E9.5. The molecular basis of these disorders is poorly understood, however, since target genes of Hey transcription factors in the affected tissues remain elusive. To identify genes regulated by Hey factors we have generated a conditional Hey1 knockout mouse. This strain was used to generate paired Hey2- and Hey1/2-deficient embryonic stem cell lines. Comparison of these cell lines by microarray analysis identified GATA4 and GATA6 as differentially expressed genes. Loss of Hey1/2 leads to elevated GATA4/6 and ANF mRNA levels in embryoid bodies, while forced expression of Hey factors strongly represses expression of the GATA4 and GATA6 promoter in various cell lines. In addition, the promoter activity of the GATA4/6 target gene ANF was inhibited by Hey1, Hey2, and HeyL. Protein interaction and mutation analyses suggest that repression is due to direct binding of Hey proteins to GATA4 and GATA6, blocking their transcriptional activity. In Hey2-deficient fetal hearts we observed elevated mRNA levels of ANF and CARP. Expression of ANF and Hey2 is normally restricted to the trabecular and compact myocardial layer, respectively. Intriguingly, loss of Hey2 leads to ectopic ANF expression in the compact layer, suggesting a direct role for Hey2 in limiting ANF expression in this cardiac compartment.

TNF-related apoptosis-inducing ligand and its decoy receptor osteoprotegerin in nonischemic dilated cardiomyopathy

Apoptosis has been attributed an essential role in dilated cardiomyopathy (DCM) recently. We assessed expression of TNF-related apoptosis-inducing ligand (TRAIL) and its decoy receptor osteoprotegerin (OPG) in men with nonischemic DCM, who underwent coronary angiography and endomyocardial biopsy (EMB) after exclusion of coronary artery disease compared to control patients. TRAIL plasma concentrations were elevated in DCM (p=0.02 vs. controls), and were positively correlated with left ventricular enddiastolic diameter (r=0.15, p=0.04), whereas OPG plasma levels did not differ between both groups (p=0.96). In EMB of DCM patients, TRAIL and OPG protein were detected by immunohistochemistry but not in controls. Furthermore, gene expression in EMB or peripheral blood leukocytes (PBL) of DCM patients assessed by real-time PCR showed an increase of TRAIL mRNA in PBL (p=0.01 vs. controls), whereas OPG mRNA was upregulated in endomyocardial specimens (p<0.001 vs. controls). In conclusion, myocardial overexpression of antiapoptotic OPG in DCM patients may represent a compensatory mechanism to limit systemic activation of TRAIL in patients with congestive heart disease.

LMCD1/Dyxin is a novel transcriptional cofactor that restricts GATA6 function by inhibiting DNA binding

The activity of GATA factors is regulated, in part, at the level of protein-protein interactions. LIM domain proteins, first defined by the zinc finger motifs found in the Lin11, Isl-1, and Mec-3 proteins, act as coactivators of GATA function in both hematopoietic and cardiovascular tissues. We have identified a novel GATA-LIM interaction between GATA6 and LMCD1/dyxin. The LIM domains and cysteine-rich domains in LMCD1/dyxin and the carboxy-terminal zinc finger of GATA6 mediate this interaction. Expression of LMCD1/dyxin is remarkably similar to that of GATA6, with high-level expression observed in distal airway epithelium of the lung, vascular smooth muscle, and myocardium. In contrast to other GATA-LIM protein interactions, LMCD1/dyxin represses GATA6 activation of both lung and cardiac tissue-specific promoters. Electrophoretic mobility shift and chromatin immunoprecipitation assays show that LMCD1/dyxin represses GATA6 function by inhibiting GATA6 DNA binding. These data reveal an interaction between GATA6 and LMCD1/dyxin and demonstrate a novel mechanism through which LIM proteins can assert their role as transcriptional cofactors of GATA proteins.

Haploinsufficiency of the cardiac transcription factor Nkx2-5 variably affects the expression of putative target genes

Heterozygous mutations of the cardiac transcription factor Nkx2-5 cause congenital heart disease. To elucidate the molecular pathways of transcription factor mutant phenotypes or diseases, direct targets are commonly sought in studies of homozygous null mutant animals and by heterologous promoter-reporter gene transactivation assays. The expression of putative target genes in a physiologic range of transcription factor concentration, however, is often not examined. Heterozygous Nkx2-5 knockout (Nkx2-5+/-) mice have no more than half-normal levels of Nkx2-5 protein. We therefore measured the mRNA expression of four putative targets of the cardiac transcription factor Nkx2-5 in wild-type and Nkx2-5+/- animals in a variety of developmental and pathologic states. Wild-type and Nkx2-5+/- embryonic hearts expressed similar levels of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), the RNA helicase Csm, and homeodomain only protein HOP. In the failing adult ventricle, ANF and BNP were up-regulated to the same extent in wild-type and Nkx2-5+/- myocardium. Csm and HOP were down-regulated in heart failure, and Nkx2-5+/- hearts expressed about half-normal levels in healthy and failing states. No consistent relationship existed between the expression of putative transcriptional targets and Nkx2-5 gene dosage in the physiologically relevant range. Any dependence of gene expression on Nkx2-5 gene dosage is affected by factors specific to the individual gene and the physiologic context.

The PTEN/PI3K pathway governs normal vascular development and tumor angiogenesis

PTEN is an important tumor suppressor gene. Hereditary mutation of PTEN causes tumor-susceptibility diseases such as Cowden disease. We used the Cre-loxP system to generate an endothelial cell-specific mutation of Pten (Tie2CrePten) in mice. Tie2CrePten(flox/+) mice displayed enhanced tumorigenesis due to an increase in angiogenesis driven by vascular growth factors. This effect was partially dependent on the PI3K subunits p85alpha and p110gamma. In vitro, Tie2CrePten(flox/+) endothelial cells showed enhanced proliferation/migration. Tie2CrePten(flox/flox) mice died before embryonic day 11.5 (E11.5) due to bleeding and cardiac failure caused by impaired recruitment of pericytes and vascular smooth muscle cells to blood vessels, and of cardiomyocytes to the endocardium. These phenotypes depend strongly on p110gamma rather than on p85alpha and were associated with decreased expression of Ang-1, VCAM-1, connexin 40, and ephrinB2 but increased expression of Ang-2, VEGF-A, VEGFR1, and VEGFR2. Pten is thus indispensable for normal cardiovascular morphogenesis and post-natal angiogenesis, including tumor angiogenesis.

Convergent proliferative response and divergent morphogenic pathways induced by epicardial and endocardial signaling in fetal heart development

Heart development requires cardiomyocyte proliferation, coupled with morphogenic differentiation of the inner trabecular myocardium and the outer compact zone myocardium. In mouse embryos lacking the retinoic acid receptor RXRalpha, proliferation and morphogenesis of the compact zone fails. We demonstrated previously that epicardial cells, in response to retinoic acid, secrete an activity that promotes cell proliferation. In this study, we have investigated downstream signaling pathways that are elicited in response to this factor. We find that cells treated in culture activate PI3 kinase and Erk pathways, and that these are required for a proliferative response. In vivo, phosphorylation of Akt and GSK3beta (PI3K pathway) and of Erk1/2 and p90rsk (Erk pathway) is substantially reduced in RXRalpha-deficient heart tissue. Neuregulin, a mitogen secreted from the endocardium which promotes cardiomyocyte proliferation and trabecular differentiation, also activates proliferation via PI3K and Erk pathways. However, the epicardial factor is not neuregulin, and does not function via the neuregulin receptor. Gene markers known to be selectively expressed in trabecular or compact myocardium in vivo are differentially activated in cell culture by treatment with neuregulin or epicardial factor, and are misexpressed in RXRalpha(-/-) heart tissue. We therefore conclude that epicardial and endocardial signals converge on common proliferative components, but diverge in downstream pathways that lead to compact vs. trabecular morphogenic differentiation.

Venn analysis as part of a bioinformatic approach to prioritize expressed sequence tags from cardiac libraries

OBJECTIVES

We needed to sort expressed sequence tags (ESTs) from human cardiac expression libraries.

DESIGN AND METHODS

We annotated DNA sequence text files of 35,152 cardiac ESTs using our search and annotation tool called Multiblast.pl. We generated lists of the most prevalent ESTs in each library, and using a novel Venn tool, we grouped ESTs that were common to all or exclusive to particular libraries.

RESULTS

Hypothetical protein KIAA0553 was expressed 120 times among 917 ESTs from an adult cardiac library (13.1%) compared only once among 8075 ESTs from fetal cardiac libraries (P < 10(-114)), this was confirmed using Northern analysis. We collated biochemical features of KIAA0553 and determined DNA polymorphism frequencies. We also used the Venn tool to specify genes that were uniquely expressed in hypertrophic cardiomyocytes.

CONCLUSIONS

Annotating ESTs and sorting them using Venn analysis can help specify new candidate disease genes from the current lists of "hypothetical proteins".

Temporal and spatial expression pattern of beta1 sodium channel subunit during heart development

OBJECTIVES

The aim of this study is to analyze Scn1b mRNA expression levels and protein distribution of Scn1b, a putative modulator of the pore-forming Na(+) channel subunit in the heart, during mouse cardiac development.

METHODS

Scn1b mRNA levels were determined by real-time RT-PCR using embryonic hearts ranging from E9.5 to E18.5 as well as in postnatal and adult heart. Scn1b protein distribution and subcellular localization during cardiogenesis were analyzed by immunohistochemistry and confocal microscopy.

RESULTS

Scn1b mRNA showed a dynamic expression pattern, peaking at stage E12.5 and decreasing at E15.5. Scn1b mRNA increased at later embryonic and neonatal stages, being maximal in the adult heart. Immunohistochemistry experiments revealed comparable distribution of Scn1b protein between the different cardiac chambers at early embryonic stages. With further development, Scn1b protein showed an enhanced expression in the trabeculated myocardium and the bundle branches. At the subcellular level in later embryonic and postnatal mouse cardiomyocytes, Scn1b was present in T-tubules as identified by immunostaining of alpha-actinin, and in the intercalated disks as identified by immunostaining of connexin 43.

CONCLUSION

These results demonstrate that Scn1b is expressed during mouse heart development, suggesting it can play an important role in the action potential configuration of the cardiomyocytes during heart morphogenesis.

Initiation of embryonic cardiac pacemaker activity by inositol 1,4,5-trisphosphate-dependent calcium signaling

In the adult, the heart rate is driven by spontaneous and repetitive depolarizations of pacemaker cells to generate a firing of action potentials propagating along the conduction system and spreading into the ventricles. In the early embryo before E9.5, the pacemaker ionic channel responsible for the spontaneous depolarization of cells is not yet functional. Thus the mechanisms that initiate early heart rhythm during cardiogenesis are puzzling. In the absence of a functional pacemaker ionic channel, the oscillatory nature of inositol 1,4,5-trisphosphate (InsP3)-induced intracellular Ca2+ signaling could provide an alternative pacemaking mechanism. To test this hypothesis, we have engineered pacemaker cells from embryonic stem (ES) cells, a model that faithfully recapitulates early stages of heart development. We show that InsP3-dependent shuttle of free Ca2+ in and out of the endoplasmic reticulum is essential for a proper generation of pacemaker activity during early cardiogenesis and fetal life.

Effects of cortisol on cardiac myocytes and on expression of cardiac genes in fetal sheep

In 17 fetal sheep aged 129 days, the effects of large-dose infusions of cortisol (72.1 mg/day for 2–3 days) on proliferation, binucleation, and hypertrophy of cardiac myocytes, cardiac expression of angiotensinogen, angiotensin receptor subtypes 1 and 2, Glut-1, glucocorticoid and mineralocorticoid receptors, proteins of the MAPK pathways and calcineurin were studied. Cortisol levels were 8.7 ± 2.3 nM (SE) in 8 control and 1,028 ± 189 nM in 9 treated fetuses ( P < 0.001). Cortisol had no effect on myocyte binucleation. Left ventricular free wall (LVFW) uni- and binucleated myocytes were larger in cortisol-treated fetuses ( P < 0.001, P < 0.05). Cortisol-treated fetuses had higher right ventricular free wall (RVFW) and LVFW angiotensinogen (Aogen) mRNA levels (treated: 2.30 ± 0.37, n = 8 and 2.05 ± 0.45, n = 7 vs. control: 0.94 ± 0.12, n = 8 and 0.67 ± 0.09, n = 7, P < 0.02). Levels of the glucose transporter Glut-1 mRNA were lower in the LVFW of treated fetuses (0.83 ± 0.23 vs. 1.47 ± 0.30 in control, P < 0.05, n = 7, 8). The higher the cortisol level, the greater the Aogen mRNA level (RVFW, r = 0.61, P < 0.01, n = 16; LVFW, r = 0.83, P < 0.0003, n = 14). There were no other changes in mRNA levels nor in levels of extracellular kinase, JNK, p38, their phosphorylated forms, and calcineurin. Thus high levels of cortisol such as occur after birth do not affect fetal cardiac myocyte binucleation or number but are associated with higher levels of ventricular Aogen mRNA, lower levels of Glut-1 mRNA, and hypertrophy of LVFW myocytes. These effects could impact on postnatal cardiac development.

Pathophysiological Significance of T-type Ca2+ Channels: Expression of T-type Ca2+ Channels in Fetal and Diseased Heart

Re-expression of fetal genes has been considered to underlie ionic remodeling in diseased heart. T-type Ca(2+) channels have been reported to be functionally expressed in embryonic hearts. In this review, we summarize developmental changes of T-type Ca(2+) channels in mouse ventricles from 9.5 days postcoitum (dpc) to adulthood, using patch clamp and quantitative PCR. In addition, we introduced T-type Ca(2+) channel expression in hypertrophied ventricles caused by myocardial infarction (MI) and aortic banding (AOB). Substantial T-type Ca(2+) channel current was recorded at both 9.5 and 18 dpc. The currents were inhibited by Ni(2+) at low concentrations. The current was not detectable in the adult stage. Ca(v)3.2 (alpha(1H)) mRNA is expressed dominantly at both 9.5 and 18 dpc. Ca(v)3.1 (alpha(1G)) increases from 9.5 to 18 dpc, but remains at low level compared with Ca(v)3.2. In contrast, Ca(v)3.1 is greater than Ca(v)3.2 at the adult stage. In MI, Ca(v)3.1 mRNA correlates negatively with brain natriuretic peptide (BNP) mRNA, whereas Ca(v)3.2 mRNA correlates positively with BNP mRNA. In AOB, these correlations are weak. We also analyzed the neuron-restrictive silencer factor (NRSF) in these hearts because it is the suppressor of transcription of the fetal cardiac gene program. The negative correlation between NRSF and BNP was stronger in MI than in AOB. Our findings show that Ca(v)3.2 underlies the functional T-type Ca(2+) channel in embryonic heart and suggest that NRSF may regulate Ca(v)3.2 expression in diseased hearts.

Electrophysiology and anatomy of embryonic rabbit hearts before and after septation

Mechanisms of cardiac pacemaking and conduction system (CPCS) development are difficult to study, in part because of the absence of models that are physiologically similar to humans in which we can label the entire CPCS. Investigations of the adult rabbit heart have provided insight into normal and abnormal cardiac conduction. The adult and the embryonic rabbit have an endogenous marker of the entire cardiac conduction system, neurofilament 160 (NF-160). Previous work suggested that ventricular septation correlates with critical phases in avian CPCS development, in contrast to the mouse CPCS. Combining high-resolution optical mapping with immunohistochemical analysis of the embryonic rabbit heart, we investigated the significance of ventricular septation in patterning the rabbit embryonic conduction system. We hypothesized that 1) completion of ventricular septation does not correlate with changes in the ventricular activation sequence in rabbit embryos and 2) CPCS anatomy determines the activation sequence of the embryonic heart. We found that preseptated ( days 11–13, n = 13) and postseptated (day 15, n = 5) hearts had similar “apex-to-base” ventricular excitation. PR intervals were not significantly different in either group. CPCS anatomy revealed continuity of the NF-160-positive tract connecting the presumptive sinoatrial node, atrioventricular (AV) junction, and ventricular conduction system. The presence of collagen in the AV junction coincided with the appearance of an AV interval. We conclude that the apex-to-base ventricular activation sequence in the rabbit embryo is present before completion of ventricular septation. CPCS anatomy reflects global cardiac activation as demonstrated by high-resolution optical mapping.

Reconstruction of the patterns of gene expression in the developing mouse heart reveals an architectural arrangement that facilitates the understanding of atrial malformations and arrhythmias

Firm knowledge about the formation of the atrial components and of the variations seen in congenital cardiac malformations and abnormal atrial rhythms is fundamental to our understanding of the normal structure of the definitive atrial chambers. The atrial region is relatively inaccessible and has continued to be the source of disagreement. Seeking to resolve these controversies, we made three-dimensional reconstructions of the myocardial components of the developing atrium, identifying domains on the basis of differential expression of myocardial markers, connexin40, and natriuretic precursor peptide A. These reconstructions, made from serial sections of mouse embryos, show that from the outset of atrial development, the systemic and pulmonary veins are directly connected to the atrium. Relative to the systemic junctions, however, the pulmonary venous junction appears later. Our experience shows that three-dimensional reconstructions have three advantages. First, they provide clear access to the combined morphological and molecular data, allowing clarification and verification of morphogenetic concepts for nonmorphological experts and setting the scene for further discussion. Second, they demonstrate that, from the outset, the myocardium surrounding the pulmonary veins is distinct from that clothing the systemic venoatrial junctions. Third, they reveal an anatomical and molecular continuity between the entrance of the systemic venous tributaries, the internodal atrial myocardium, and the atrioventricular region. All these regions are derived from primary myocardium, providing a molecular basis for the observed nonrandom distribution of focal right atrial tachycardias.

Differential regulation of Hand1 homodimer and Hand1-E12 heterodimer activity by the cofactor FHL2

The basic helix-loop-helix (bHLH) factor Hand1 plays an essential role in cardiac morphogenesis, and yet its precise function remains unknown. Protein-protein interactions involving Hand1 provide a means of determining how Hand1-induced gene expression in the developing heart might be regulated. Hand1 is known to form either heterodimers with near-ubiquitous E-factors and other lineage-restricted class B bHLH proteins or homodimers with itself in vitro. To date, there have been no reported Hand1 protein interactions involving non-bHLH proteins. Heterodimer-versus-homodimer choice is mediated by the phosphorylation status of Hand1; however, little is known about the in vivo function of these dimers or, importantly, how they are regulated. In an effort to understand how Hand1 activity in the heart might be regulated postdimerization, we have investigated tertiary Hand1-protein interactions with non-bHLH factors. We describe a novel interaction of Hand1 with the LIM domain protein FHL2, a known transcriptional coactivator and corepressor expressed in the developing cardiovascular system. FHL2 interacts with Hand1 via the bHLH domain and is able to repress Hand1/E12 heterodimer-induced transcription but has no effect on Hand1/Hand1 homodimer activity. This effect of FHL2 is not mediated either at the level of dimerization or via an effect of Hand1/E12 DNA binding. In summary, our data describe a novel differential regulation of Hand1 heterodimers versus homodimers by association of the cofactor FHL2 and provide insight into the potential for a tertiary level of control of Hand1 activity in the developing heart.

Relationship between the appearance of preantral follicles in the fetal ovary of Antarctic minke whales (Balaenoptera bonaerensis) and hormone concentrations in the fetal heart, umbilical cord and maternal blood

The present study aimed to determine the relationship among changes in the number of preantral follicles and concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone (P4), androstenedione (A) and estradiol-17beta (E2) in the fetal heart, umbilical cord and maternal blood. Primordial follicles had already appeared in a 20 cm fetus and primary follicles were observed in a 50 cm fetus. In a 70 cm fetus, the number of primordial and primary follicles increased rapidly and secondary follicles were present. The concentrations of LH and FSH did not change between 20 cm and 160 cm in fetal length. When the fetal length became > 70 cm, serum levels in the fetus, umbilical cord and mothers, and E2 levels in umbilical cord increased synchronously (p < 0.05). These results showed increases in the number of preantral follicles in the Antarctic minke whale fetal ovary along with fetal growth during the early gestation period. These findings suggest that the change in preantral follicles was associated with changes in the concentration of steroids in early gestation periods. The changes in steroid concentrations in the fetal and umbilical cord blood and the increased number of preantral follicles were coincident at around 70 cm in fetal length, whereas the growth and differentiation of primordial and primary follicles appeared to be independent of FSH and LH.

Apoptotic/mytogenic pathways during human heart development

OBJECTIVE

The aim of our study was to assess myocytes apoptosis/mitosis and associated intracellular signalling pathways during heart development.

SETTING AND PATIENTS

Eight human fetal hearts (at different gestation ages) and seven human adult hearts were chosen as controls (five normal and two pathological) and studied from both a histological and a molecular point of view.

RESULTS

Our results are as follows: (i) all Shc isoforms are expressed and activated in the human fetal heart; (ii) a progressive fading of Shc and ERK expression are evident during gestation; (iii) JNK is present but it is not activated in the human fetal heart; (iv) CD95 is present in the first week of gestation and fades progressively; (v) apoptotic/proliferative processes are present in the early gestation phase and fades progressively; (vi) in the human heart, Shc isoform with medium weight is 55 kD and not 52 kD and it is upregulated in adult myocardial ischaemia.

CONCLUSIONS

Myocyte underwent apoptosis/mitosis during gestation. Shc isoforms, together with ERK maintain the homeostasis of the heart.

Troponin I Isoform Expression in Human and Experimental Atrial Fibrillation

Background— Atrial fibrillation (AF) is accompanied by re-expression of fetal genes and activation of proteolytic enzymes. In this study both aspects were addressed with respect to troponin I (TnI) isoform expression.

Methods and Results— Western blotting and real-time reverse transcription–polymerase chain reaction were used to study TnI isoform expression in patients with paroxysmal or chronic AF and in goats after 1, 2, 4, 8, and 16 weeks of AF. In addition to cardiac TnI (cTnI), low expression of slow-twitch skeletal TnI (ssTnI) protein was found in 60% of patients in sinus rhythm or paroxysmal AF and in 8% of patients with chronic AF. In adult goat atrium, ssTnI protein expression was undetectable. Calcium-dependent degradation of cTnI protein was found in 1 or 2 of 6 animals after 1 to 4 weeks of AF. Although always low, ssTnI mRNA levels were significantly higher in patients who expressed ssTnI protein than in those who did not. Relative ssTnI mRNA expression was significantly lower in patients with paroxysmal AF and chronic AF than in those in sinus rhythm. In goats there was a tendency toward higher relative levels of ssTnI at the onset of AF followed by a normalization when AF had become sustained.

Conclusions— Atrial re-expression of ssTnI during paroxysmal AF in patients and during the first 2 weeks of pacing-induced AF in goats does not seem to be part of the process of AF-associated cardiomyocyte dedifferentiation but seems to result from transient cardiomyocyte stress at the onset of AF.

Cross-talk of opioid peptide receptor and ?-adrenergic receptor signalling in the heart

Opioid peptide receptor (OPR) and beta-adrenergic receptor (beta-AR) are well-established members of G-protein-coupled receptor (GPCR) superfamily and are involved in regulating cardiac contractility, energy metabolism, myocyte survival or death. OPRs are typical Gi/Go-coupled receptors and activated by opioid peptides derived from the endorphin, dynorphin and enkephalin families, whereas beta-AR stimulated by catecholamines is the model system for Gs-coupled receptors. While it is widely accepted that beta-AR stimulation serves as the most powerful means to increase cardiac output in response to stress or exercise, we have only begun to appreciate functional roles of OPR stimulation in regulating cardiovascular performance. Cardiovascular regulatory effects of endogenous opioids were initially considered to originate from the central nervous system and involved the pre-synaptic co-release of norepinephrine with enkephalin from sympathetic neuronal terminals in the heart. However, opioid peptides of myocardial origin have been shown to play important roles in local regulation of the heart. Notably, OPR stimulation not only inhibits cardiac excitation-contraction coupling, but also protects the heart against hypoxic and ischemic injury via activation of Gi-mediated signalling pathways. Further, OPRs functionally and physically cross-talk with beta-ARs via multiple hierarchical mechanisms, including heterodimerization of these receptors, counterbalance of functional opposing G protein signalling, and interface at downstream signalling events. As a result, the beta-AR-mediated positive inotropic effect and increase in cAMP are markedly attenuated by OPR activation in isolated cardiomyocytes as well as sympathectomized intact rat hearts. This brief review will focus on the interaction between beta-AR and OPR and its potential physiological and pathophysiological relevance in the heart.

Calreticulin in the heart

Calreticulin is a Ca2+ binding/storage chaperone resident protein of the endoplasmic reticulum. This protein plays a key role in the calreticulin/calnexin cycle and the quality control pathways in the endoplasmic reticulum. Calreticulin deficiency is lethal due to impaired cardiac development. However, over-expression of the protein in developing and postnatal heart leads to bradycardia, complete heart block and sudden death. Ultrastructural evidence indicates that the deficiency associated with the absence of calreticulin in the heart may be due to a defect in the development of the contractile apparatus and/or a defect in development of the conductive system as well as a metabolic abnormality. Collectively, we postulate that calreticulin and endoplasmic reticulum plays an important role in cardiac development and postnatal pathologies.

The slow skeletal muscle troponin T gene is expressed in developing and diseased human heart

Cardiac muscle development is characterised by the activation of contractile protein genes and subsequent modulation of expression resulting, ultimately, in the formation of a mature four-chambered organ. Myocardial gene expression is also altered in the adult in response to pathological stimuli and this is thought to contribute to the altered contractile characteristics of the diseased heart. We have examined the expression of the slow skeletal troponin T (TnT) gene in the human heart during development and in disease using whole mount in situ hybridisation and real-time quantitative (TaqMan) polymerase chain reaction (PCR). Slow skeletal TnT mRNA shows transitory and regional expression in the early foetal heart, which occurs at different times in atria and ventricles. In ventricular myocardium, expression is seen in the outer epicardial layer at a time when the coronary circulation is being established. Expression was detected at low levels in the adult human heart and was significantly increased in end-stage heart failure. Similarly, expression was readily detectable during early rat heart development and was up-regulated in pressure overload hypertrophy in adult. Together these data show for the first time that slow skeletal TnT mRNA is readily detectable during early human heart development. They further suggest that slow skeletal TnT may be responsive to myocardial stress and that elevated levels may contribute to myocardial dysfunction in adult disease.