Alteration of the alveolar-capillary membrane diffusing capacity in chronic left heart disease

During left heart disease, the chronic increase in pulmonary capillary wedge pressure (PCWP) results both in vascular alterations with increased pulmonary vascular resistance (PVR), and in progressive thickening of the alveolar-capillary membrane, which diffusing capacity (Dm) is reduced. However, the total lung diffusing capacity for carbon monoxide (TLco) is inconstantly impaired, depending on the degree of pulmonary congestion. We evaluated the relation between the pulmonary hemodynamic repercussions of chronic heart disease and the 2 components of TLco, i.e., Dm and capillary blood volume. Forty-seven patients with chronic left heart disease (28 with valve disease, 19 with cardiomyopathy) underwent right heart catheterization with determination of PCWP and PVR. Pulmonary function tests, including spirometry, determination of TLco, and of its 2 components (percentage of predicted values) were performed in patients and in 15 healthy subjects. TLco and Dm, but not capillary blood volume, were significantly decreased in patients. Dm was related to PVR (p = 0.0006), and was markedly reduced in patients with high PVR (> or = 3 Wood U): 54 +/- 8% vs 80 +/- 19% in patients with normal PVR (p <0.0001). Dm < or = 66% identified all high PVR patients (sensitivity = 100%, specificity = 77%). Capillary blood volume was related to PCWP (p = 0.02), and was increased in patients with high PCWP (> 15 mm Hg): 126 +/- 30% vs 99 +/- 23% (p <0.01), but with a marked overlap. TLco values, although reduced in patients with high PVR (p <0.001), were not predictive of high PVR or high PCWP. Determination of Dm allows a more accurate detection of pulmonary hypertension complicating chronic left heart disease than the other pulmonary parameters.

Age-dependent changes in myocardial susceptibility to zero flow ischemia and reperfusion in isolated perfused rat hearts: relation to antioxidant status

Ageing is associated with an increase in myocardial susceptibility to ischemia and a decrease in post-ischemic recovery of function. In the present study, we have examined the effects of ageing on (i) myocardial ischemic contracture, (ii) the reperfusion syndrome and lipid peroxidation upon reperfusion, and (iii) the activity of enzymes involved in reactive oxygen species elimination. Hearts from male Wistar rats aged 4 (adults), 16 (old) or 24 months (senescent) were subjected to 20-min zero flow ischemia and 30-min reperfusion ex vivo. Cardiac activity of superoxide dismutase, catalase, and glutathione peroxidase, as well as cardiac content of thiobarbituric acid reactants were assessed in frozen heart samples. The effects of ageing on ischemic contracture of the sarcomeres were assessed on electromicrographs of tissues taken at the end of ischemia. In our experimental conditions, ischemic contracture of the sarcomeres increased progressively during ageing. In contrast, the severity of the reperfusion syndrome increased between 4 and 16 months of age, and then decreased up to 24 months of age. We propose that the peak of susceptibility of the myocardium to reperfusion observed during moderate ageing might be related to a decrease in the ability of cardiomyocytes to dismutate hydrogen peroxide as suggested by the observed decrease in catalase activity. Finally, the better resistance to the reperfusion syndrome exhibited by senescent rats compared to old rats might be due to a natural selection of a subpopulation of rats which is particularly resistant to oxidative stress.

Species-dependent enantioselective glucuronidation of carprofen

1. The stereoselective glucuronidation of carprofen, a non-steroidal anti-inflammatory drug, was investigated in vitro using microsomes prepared from liver of different species (rat, dog, horse, sheep and man) or UGT2B1 expressed in fibroblasts. 2. The Km towards the drug was very similar among these species and for the two enantiomers, whereas the Vmax varied substantially according to the animal used. The rat exhibited a high stereoselective glucuronidation whereas other species, including man, presented a low stereoselectivity. The R-enantiomer was glucuronidated at a more efficient rate than its enantiomorph, and was a better substrate (in terms of Vmax/Km). 3. To explain the enantioselective disposition of carprofen in man and in the different species, the ratio of the enzymatic efficacies (Vmax/Km) were compared with the ratio of the pharmacokinetic parameters AUCs. The basic hypothesis that the intrinsic clearance reflect the enantioselective behaviour of carprofen seemed substantiated when we focused on man and rat glucuronidation, but the in vivo-in-vitro correlation was not possible in other species. 4. In conclusion, the chiral pharmacokinetics of carprofen is less dependent on the stereoselective glucuronidation than other stereoselective processes such as protein binding of carprofen, enzymatic hydrolysis, or renal elimination of glucuronides.

Effects of sustained low-flow ischemia on myocardial function and calcium-regulating proteins in adult and senescent rat hearts

OBJECTIVE

Both aging and myocardial ischemia are associated with alterations of calcium-regulating proteins. We investigated the effects of graded levels of low-flow ischemia on myocardial function and on SR Ca(2+)-ATPase (SERCA2), Na(+)-Ca2+ exchanger (NCX) and ryanodine receptor (RyR2), at mRNA and protein levels in both adult and senescent myocardium.

METHODS

Isolated hearts from 4 and 24 month old (mo) rats were retrogradely perfused during 180 min at 100% (100% CF, n = 11 and n = 11 respectively. 30% (30% CF, n = 10 and n = 12) or 15% (15% CF, n = 13 and n = 8) of their initial coronary flow, and active tension and coronary resistance (in % of their baseline value) were recorded. After 180 min of perfusion. NCX, RyR2 and SERCA2 mRNAs (in % of age-matched 100% CF group value) and protein levels were quantitated in the left ventricles by slot blot and Western blot analysis, respectively.

RESULTS

In 24 mo hearts, low-flow ischemia induced a greater fall in active tension (-65 +/- 7% vs. -40 +/- 4% in 4 mo 30% CF, p, 0.01 and -82 +/- 2% vs. -60 +/- 5% in 4 mo 15% CF groups, p < 0.05 after 15 min of ischemia) and a greater increase in coronary resistance (+357 +/- 44% vs. +196 +/- 39% in 4 mo 30% CF, p < 0.05 and +807 +/- 158% vs. +292 +/- 61% in 4 mo 15% CF groups, p < 0.001 after 15 min of ischemia). An increased accumulation of SERCA2 (+36% and NCX (+46%) transcripts, but not RyR2, already occurred in 24 mo 30% CF group while the 3 transcripts accumulated in 24 mo 15% CF group. In 4 mo rats SERCA2 (+26%), NCX (+35%) and RyR2 (+81%) mRNA levels only increased in the 15% CF group. Corresponding calcium-regulating protein levels were unaltered whatever the degree of flow reduction in both 4 mo and 24 mo hearts.

CONCLUSION

Low-flow ischemia does not induce calcium-regulating protein loss in both adult and senescent hearts. The increase in mRNAs coding for calcium-handling proteins and the impairment of myocardial function which occur at a lesser degree of coronary flow reduction in senescent hearts, indicate a higher vulnerability to low-flow ischemia during aging.

Ultrastructural localization of interferon-inducible double-stranded RNA-activated enzymes in human cells

The protein kinase PKR and the 2',5'-oligoadenylate (2-5A) synthetase are two interferon-induced and double-stranded RNA-activated enzymes which are implicated in the mechanism of action of interferon. Their distribution was undertaken here at the ultrastructural level by the immunogold procedure, following the use of specific monoclonal antibodies directed against PKR and 69- and 100-kDa forms of the 2-5A synthetase. These enzymes were detected as a pool of nonaggregated proteins scattered throughout the cell and as aggregates often associated with electron-dense doughnut-like structures showing a similar aspect whatever their subcellular localization: the cytoplasm, the nuclear envelope, and the nucleus. In general, the 2-5A synthetases were present in much more lower amounts than the PKR, probably due to the difficulty of detecting traces of proteins by electron microscopy. To circumvent this, we used a human lymphoblastoid cell line overexpressing the 69-kDa form of the 2-5A synthetase. In such cells, the synthetase was then clearly observed in both the cytoplasm and the nucleus; isolated or small clusters of gold particles were numerous in the cell mainly over the RNP fibrils of the interchromatin space, nucleolus, and ribosomes. Interestingly, gold particles were also found to be associated with the membranes of nuclear envelope and rough endoplasmic reticulum probably due to the myristilated motif of this form of 2-5A synthetase. Finally, intensely labeled electron-opaque dots sometimes associated with the nuclear pore complexes were present in the nucleus and in the cytoplasm of cells which might suggest their transport from the nucleus to the cytoplasm or reciprocally through the nuclear pore complexes. These observations indicate the wider distribution of the dsRNA-activated enzymes in the cell, thus pointing out their potential implication in as yet undetermined physiological function(s) necessary for various cellular metabolic reactions.

Trace elements and cardioprotection: increasing endogenous glutathione peroxidase activity by oral selenium supplementation in rats limits reperfusion-induced arrhythmias

Oxyradicals have been implicated as a possible cause of reperfusion-arrhythmias (RA). However, the use of diverse exogenous oxyradical scavengers designed to reduce RA has given contradictory results. The aim of the present study was to determine whether enhancing the activity of the main endogenous enzyme involved in peroxide elimination in cardiac cells, namely glutathione peroxidase, may limit RA in isolated heart preparations by increasing their antioxidant status. For this purpose, a group of 15 male Wistar rats received a selenium enriched diet for ten weeks (1.5 mg Se/kg diet). Control animals (n = 15) received a standard diet containing 0.05 mg Se/kg diet. The incidence of early ventricular arrhythmias was investigated during the reperfusion period following 10 min regional ischemia induced ex-vivo by left coronary artery ligation. Our results show that selenium-supplementation significantly increased the global selenium status of the animals. In the isolated heart preparations, the selenium supplementation induced a significant reduction of the severity of RA as assessed by the arrhythmia score and the limitation of the incidence of both ventricular tachycardia (control: 91% vs selenium: 36%, p < 0.05) and irreversible ventricular fibrillation (control: 45% vs selenium: 0%, p < 0.05). These effects were associated with a significant increase in cardiac mitochondrial and cytosolic glutathione peroxidase activities in both the left and the right ventricles. These results illustrate the potential protective effect of selenium against ischemia-reperfusion injury and suggest that peroxides might play a key role in the genesis of some aspects of the reperfusion syndrome.

Release of viruses and viral DNA from nucleus to cytoplasm of HeLa cells at late stages of productive adenovirus infection as revealed by electron microscope in situ hybridization

Considerable progress has been made over the past 10 years towards a full understanding of the functional significance of the structural changes resulting from the production of adenoviruses in permissive cells. Similarly, the host-virus interactions which are involved in viral replication and gene expression as well as in RNA nuclear export have been investigated. Post-embedding nonisotopic in situ hybridization has been proven to be a powerful tool for the study of nucleic acids in infected cells provided that controlled elimination of artifacts by appropriate treatments was undertaken. Adenovirus infected cells present two biological characteristics which could lead to false positive or negative results. First, they contain large amounts of single-stranded portions of viral DNA which are revealed with viral RNA molecules. Second, DNA-binding proteins are present which hide some nucleic acid sequences. By using a DNA probe and appropriate variations in the experimental protocol, it is possible to reveal specifically different kinds of targets, simultaneously single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), or only ssDNA, or only dsDNA, or only RNA. By using two probes labeled with different haptens, biotine and digoxigenin, it is possible to detect concomitantly two nucleic acid targets and, therefore, to study their relationships. In order to gain insight into the changes in the nucleus before cell lysis and to improve our knowledge on the series of steps leading to the release of adenoviruses from the nucleus, examination of cells at 41 h post-infection and identification of structures containing adenoviral nucleic acids were undertaken. In addition to the ultrastructural changes and precise distribution of cellular DNA and viral nucleic acid molecules already described in cells up to 24 h post-infection (for a review, see Puvion E, Puvion-Dutilleul F (1996) Exp Cell Res 229, 217-225), new results were obtained. Routine observation revealed the presence of: i) viruses in the cytoplasm, some being located next to nuclear pores; ii) abnormally large portions of the nuclear envelope devoid of underlying condensed chromatin; iii) proliferation of either the inner nuclear membrane only or both membranes of the nuclear envelope; and iv) electron-opaque grains in the nuclear compartment involved in viral genome transcription, and also in the clusters of interchromatin granules known to contain mature viral messenger RNA (Bridge E et al (1996) J Cell Biol 135, 303-314). In situ hybridization revealed the presence of: i) dsDNA in the cytoplasmic viruses indicating that they were mature viruses; ii) free viral dsDNA and ssDNA molecules in the cytoplasm whereas host DNA remained confined at the nuclear border; and iii) viral RNA in the newly-described electron-opaque grains we call, therefore, viral-RNA containing grains. Immunodetection of bromodeoxyuridine (BrdU) incorporated into DNA in pulse and pulse-chase experiments allowed us to ascertain that cells at 41 h post-infection were truly living cells and that at least part of the newly-synthesized viral DNA migrated from the nucleus to the cytoplasm. Taken together, the data suggest that modifications of the nuclear matrix, cytoskeleton, and nucleo-cytoplasmic interactions might occur near the termination of adenovirus infection inducing the progressive release of viruses, vial dsDNA and ssDNA molecules in the cytoplasm. In addition, the observation of a new structural support for the intranuclear viral RNA in the clusters of interchromatin granules emphasizes the role of these cellular structures in the intranuclear trafficking of messenger RNA leading to the regulation of its nuclear export.

Molecular characteristics of cocaine-induced cardiomyopathy in rats

Cocaine abuse induces severe cardiomyopathy. To investigate the molecular effects of acute and prolonged administration of cocaine, mRNAs encoding markers of either mechanical overload, as atrial natriuretic factor (ANF) and alpha- and beta-myosin heavy chains, or fibrosis as type I and III procollagens, were quantitated in the left ventricle of rats 4 h after one injection of cocaine (40 mg/kg, n = 7), or 14 (n = 15) and 28 days (n = 10) after chronic infusion of cocaine (40 mg/kg per day). Plasma cocaine and benzylecgonine concentrations were both significantly augmented during the infusion while plasma levels of triiodothyronine and thyroxine were lowered. Acute injection of cocaine induced ANF gene expression. Cocaine treatment during 28 days resulted in left ventricular hypertrophy (+ 20% after 24 days, P < 0.05) with normal blood pressure, associated with an accumulation of mRNAs encoding ANF and type I and III collagens (+66% and +55%, P < 0.05). Such a chronic treatment also induced a shift from the alpha- to the beta-myosin heavy chain gene expression (-40% and +50%, P < 0.05). In conclusion, cocaine activates markers of both hemodynamic overload and fibrosis. Such an activation may result from direct and/or indirect effects of the drug such as myocardial ischemia, mechanical overload and/or hypothyroidism.

Differential regulation of matrix metalloproteinases associated with aging and hypertension in the rat heart

We compared two models of cardiac fibrosis in which collagen synthesis is controlled at different levels. Regulation is pretranslational in aldosterone-salt-induced hypertension in young rats and posttranslational in 24-month-old rats. However, little is known about the role of matrix metalloproteinases (MMP) in fibrosis development. Ventricular MMP activities were studied by zymography, and MMP-2 and MMP-1 mRNA levels were determined using slot-blot and ribonuclease protection assay, respectively. After 1 month of aldosterone-salt treatment, proMMP-2, MMP-2, and proMMP-1 collagenolytic activities and their gene expression were unchanged compared with sham-operated rats. After 2 months, total MMP-2 activity was increased by 40% with parallel stimulation of its gene expression. These changes were localized by in situ zymography within the media of coronary vessels. These results suggest that MMP play a prominent role in vascular remodeling during the first steps of hypertension. During aging, however, there were 40% and 45% decreases in MMP-2 and proMMP-1 activity, respectively, with a corresponding down-regulation of MMP-2 mRNA. These observations suggest that depression of the degradative pathway is partly responsible for age-associated fibrosis. Thus, MMP have differing involvements in the cardiac remodeling associated with hypertension or aging.

Senescent heart compared with pressure overload-induced hypertrophy

Although systolic left ventricular (LV) function is normal in the elderly, aging is associated in rat papillary muscle with mechanical and sarcoplasmic reticulum Ca2+ ATPase alterations similar to those observed in the hypertrophied heart. However, alterations in the other calcium-regulating proteins implicated in contraction and relaxation are still unknown. To investigate alterations in LV function and calcium-regulating proteins, we measured hemodynamics and Na(+)-Ca2+ exchanger (NCx), ryanodine receptor (RyR2), and sarcoplasmic reticular Ca2+ ATPase (SERCA2) mRNA levels (expressed in densitometric scores normalized to that of poly(A+) mRNA) in left ventricle from 4-month-old (adult, n = 13) and 24-month-old (senescent, n = 15) rats. For ex vivo contractile function, active tension was measured during isolated heart perfusion in adult (n = 11) and senescent (n = 11) rats. For comparison of age-dependent effects of moderate hypertension on both hemodynamics and calcium proteins, renovascular hypertension was induced or a sham operation performed at 2 (n = 11 and n = 6) and 22 (n = 26 and n = 5) months of age. In senescent rats, LV systolic pressure and maximal rates of pressure development were unaltered, although active tension was depressed (4.7 +/- 0.4 versus 8.3 +/- 0.7 g/g heart weight in adults, P < .0001). SERCA2 mRNA levels were decreased in senescent left ventricle (0.98 +/- 0.05 versus 1.18 +/- 0.05 in adults, P < .01), without changes in NCx and RyR2 mRNA accumulation. Renovascular hypertension resulted in 100% mortality in aged rats; in adults, renovascular hypertension resulted, 2 months later, in an increase of LV systolic pressure (170 +/- 7 versus 145 +/- 3 mm Hg in sham-operated rats, P < .05) and in mild LV hypertrophy (+18%, P < .01) associated with a decrease in SERCA2 mRNA levels (1.02 +/- 0.03 versus 1.18 +/- 0.03 in sham-operated rats, P < .001). Contractile dysfunction in senescent isolated heart and decreased SERCA2 mRNA levels were associated with in vivo normal LV function at rest, indicating the existence of in vivo compensatory mechanisms. RyR2 and NCx gene expressions were not implicated in the observed contractile dysfunction. In aged rats, renovascular hypertension resulted in 100% mortality, probably related to elevated levels of circulating angiotensin II, whereas in adult rats, renovascular hypertension induced a mild LV hypertrophy associated with a selective alteration in SERCA2 gene expression.

Molecular basis of the regression of cardiac hypertrophy

Cardiac failure is a disease which involves three different mechanisms: (1) the limits and imperfections of the general process of myocardial adaptation to mechanical stress, which includes various changes in genetic expression, including an increased collagen mass, but an unchanged collagen concentration; (2) the limits and imperfections of the adaptational process at the peripheral level which allows the entire organism to adapt to the low cardiac output; (3) fibrosis, an augmented collagen concentration, which is not a direct consequence of mechanical overload, but depends on aging, myocardial ischemia or hormonal changes. Middle-aged spontaneously hypertensive rats (SHRs) represent a good model of the common clinical situation. Three-month treatment with a CEI reduces, in parallel, arterial hypertension, left ventricular hypertrophy and ventricular fibrosis. Holter monitoring was also performed in these animals. Untreated SHRs when compared to age-matched Wistar rats have an increased number of ventricular premature beats which are suppressed by the treatment. In addition, heart rate variability has been quantified by using the pseudo Wigner-Villé transformation, a time and frequency domain method. The low frequency oscillations are hampered in SHRs. CEI normalizes this parameter.

Distribution of ribosomal genes in nucleoli of herpes simplex virus type 1 infected cells

Herpes simplex virus type 1 (HSV-1) infection of HeLa cells induces profound changes in the structure of the nucleoli. They become markedly elongated, and their fibrillar centers become greatly diminished in number, but larger than in non-infected HeLa cells, and only partially surrounded by the dense fibrillar component. The effect of prolonged HSV-1 infection on the distribution of the rRNA genes was studied by means of postembedding electron microscope in situ hybridization using a biotinylated ribosomal DNA (rDNA) probe, which spans about half of the rRNA gene, and subsequent immunogold labeling of the resulting hybrids. Gold particles accumulated over two structures: a large solitary, finely fibrillar, moderately electron opaque area which was detectable only in a few sections of nucleoli and corresponded to the virus-modified fibrillar center, and over limited areas of the nucleolus-associated chromatin. In non-infected HeLa cells, foci of clustered rRNA genes were observed in the more frequently detected fibrillar centers and in association with condensed chromatin. It would be expected that foci of extended rDNA molecules might contain active or potentially active genes, whereas foci of highly compacted rDNA molecules might contain inactive genes. The ribosomal RNA molecules which were detected with the same probe over the dense fibrillar component and the granular component of the nucleoli of both infected and non-infected cells were not found within the rDNA-containing foci. The data strongly suggest that the changes in the size and number of fibrillar centers induced by the intranuclear development of HSV-1 might be directly linked to the well-known decrease of the nucleolar activity.

In situ hybridization and immuno-electron microscope analyses of the Us11 gene of herpes simplex virus type 1 during transient expression

The distribution of Us11 RNA and of its encoded protein have been investigated at the ultrastructural level in HeLa cells transiently expressing the Us11 gene of herpes simplex virus type 1. In these transfected cells, Us11 protein accumulates at sites identical to those of lytically infected cells, i.e., in nucleoli and in regions of the cytoplasm that contain ribosomes. Us11 RNA and polyadenylated RNA are scattered over the ribosome-rich areas of the cytoplasm. They also accumulate in the nucleoplasm on clustered ribonucleoprotein (RNP) fibrils but also in clusters of interchromatin granules, some of them contiguous to nucleoli. However they are never found in nucleoli. These data reveal the involvement of interchromatin granules in some steps of Us11 mRNA maturation and/or transport.

Intranuclear retention of ribosomal RNAs in response to herpes simplex virus type 1 infection

The localization of ribosomal RNA (rRNA) was investigated at the ultrastructural level in herpes simplex virus type 1 infected HeLa cells using three distinct biotinylated probes which bind in sequence to three different segments of the ribosomal genes. Comparison of the above with the signal levels obtained from non-infected cells reveals information about the effects of HSV-1 infection on ribosome biogenesis. A probe specific for the 5′ end portion of pre-rRNA labeled all nucleoli of both non-infected and infected cells in the same way, that is, it mainly labeled the dense fibrillar component and the border of the fibrillar centers but only slightly labeled the granular component. This indicates that the initial cleavage of pre-rRNA in herpes infection still occurs in the 5′ region of the 5′ external transcribed spacer. However, a probe specific for 18 S rRNA labeled the granular component of the nucleoli more intensely after infection. In addition, significant amounts of rRNA molecules were present within the intranuclear viral region, except over the enclosed viral dense bodies, and within the virus-enlarged clusters of interchromatin granules. The data indicate that the still enigmatic viral dense bodies, which are nucleolus-related structures, are excluded from the marked intranuclear retention of ribosomal RNAs and, in addition, reveal a possible role for the interchromatin granules of infected cells in the regulation of the export of the ribosomal subunits towards the cytoplasm.

Molecular and cellular biology of the senescent hypertrophied and failing heart

During aging, experimental studies have revealed various cellular changes, principal among which is myocyte hypertrophy, which compensates for the loss of myocytes and is associated with fibrosis. The expression of alpha-myosin heavy chain is replaced by that of the isogene beta-myosin, which leads to decreased myosin adenosine triphosphatase (ATPase) activity. In consequence, contraction is slower and more energetically economical. The Ca(2+)-ATPase of the sarcoplasmic reticulum and Na+/Ca2+ exchange activity are decreased, which probably explains the reduced velocity of relaxation. Membrane receptors are also modified, since the density of both the total beta-adrenergic and muscarinic receptors is decreased. The senescent heart is able to hypertrophy in response to overload and to adapt to the new requirements. Similar alterations are observed both in the senescent heart and in the overloaded heart, in clinical as well as in experimental studies; however, differences do exist, especially in terms of fibrosis and arrhythmias.

p80-coilin: a component of coiled bodies and interchromatin granule-associated zones

We investigated at the electron microscope level the fate of the three intranuclear structures known to accumulate snRNPs, and which correspond to the punctuate immunofluorescent staining pattern (the coiled bodies, the clusters of interchromatin granules and the interchromatin granule-associated zones) after exposure to either a low salt medium which induces a loosening and partial spreading of nucleoprotein fibers or a high ionic strength salt medium and subsequent DNase I digestion, in order to obtain DNA-depleted nuclear matrices. The loosened clusters of interchromatin granules and the coiled bodies could no longer be distinguished from surrounding nucleoprotein fibers solely by their structure, but constituents of the clusters of interchromatin granules could be detected by in situ hybridization with both U1 and U2 DNA probes, and constituents of the coiled bodies were detectable mainly with the U2 DNA probe. The interchromatin granule-associated zones, the electron-opacity and compactness of which were preserved despite the loosening treatment, remained labeled with the U1 DNA probe only. In DNA-depleted nuclear matrices, the snRNA content of the coiled bodies, the clusters of interchromatin granules and their associated zones, which were all easily recognizable within the residual nuclear ribonucleoprotein network, was unmodified. The data indicate, therefore, that the loosening procedure as well as the high salt extraction procedure preserve the snRNA content of all three spliceosome component-accumulation sites and reveal that interchromatin granule-associated zones are elements of the nuclear matrix. The p80-coilin content coiled bodies was also preserved whatever the salt treatment used. An intriguing new finding is the detection of abundant p80-coilin within the interchromatin granule-associated zones, both before and after either low or high salt treatment of cells. Therefore, p80-coilin is an integral constituent of the interchromatin granule-associated zones.

Synthesis and maturation of viral transcripts in herpes simplex virus type 1 infected HeLa cells: the role of interchromatin granules

The response of the cellular RNA processing machinery to herpes simplex virus type 1 (HSV-1) infection was studied at the ultrastructural level in HeLa cells and compared to the distribution of RNA polymerase II molecules and viral RNA. Immunogold labeling of RNA polymerase II molecules revealed that viral genome transcription was restricted to filaments in an intranuclear, virus-induced region. This region also contained viral RNAs as revealed by in situ hybridization of two biotinylated viral DNA probes: a probe encompassing a limited portion of the viral genome (the F fragment) and a probe for the total genome. In addition, the latter probe revealed large amounts of viral RNA within the clusters of interchromatin granules, intranuclear structures of normal cells that became enlarged during HSV-1 infection. Components of spliceosomes were localized by in situ hybridization with biotinylated U1 and U2 DNA probes. The large viral region contained only traces of U1 and U2 RNAs, probably because of the low frequency of splices of viral transcripts. The clusters of interchromatin granules, however, accumulated U1 and U2 RNAs with the same frequency as in noninfected cells. Poly(A) RNA was detected by in situ hybridization of a biotinylated poly(dT) probe. Some was present over the filaments of the virus-induced region but most was accumulated in the clusters of interchromatin granules. Our data suggest, therefore, that the clusters of interchromatin granules, in addition to their involvement in spliceosome component assembly, might also be a transient storage site for some families of viral mRNA, possibly a sorting site that regulates their migration.

Anchorage of adenoviral RNAs to clusters of interchromatin granules

Previous in situ hybridization experiments have revealed that clusters of interchromatin granules in adenovirus type 5 infected HeLa cells contain not only spliceosome components but also significant amounts of viral RNA and poly(A)+ RNA molecules whereas nonpolyadenylated viral RNA molecules are present within the still enigmatic viral compact rings. To determine the levels of association of the viral RNA molecules with cellular clusters of interchromatin granules and viral compact rings, we investigated the effects of a cell extraction technique on these structures. The spreading apart of the nucleoproteins by exposure of infected cells to a detergent-containing hypotonic solution, which exclusively preserves structurally linked components, resulted in the persistence within the clusters of interchromatin granules of U1 snRNA, U2 snRNA, viral RNA, and poly(A)+ RNA. These data clearly reveal that, in addition to the well-known strong binding of spliceosome components within the clusters of interchromatin granules, there also is an anchorage of viral RNA and messenger RNA molecules to these structures, which suggests functional relationships. Taken together, the data indicate that the clusters of interchromatin granules might be the sites of accumulation and retention of those cell and viral messenger RNA molecules that are transiently stored in the nucleus before their degradation or their transport to the cytoplasm. In addition, the firm binding of nonpolyadenylated viral RNA to the viral compact rings suggests a role for these structures in the transient storage of the nonused portions of the viral primary late transcripts.

Nonsynchronous changes in myocardial collagen mRNA and protein during aging: effect of DOCA-salt hypertension

Myocardial fibrosis has been investigated in 3-, 16-, and 24-mo-old normal rats and also in 24-mo-old rats subjected to deoxycorticosterone acetate (DOCA)-salt treatment-induced-hypertension. Collagen content was assessed both histologically and by hydroxyproline assay. Type I and III procollagen mRNA levels were quantitated by Slot Blot analyses. Aging is associated with fibrosis as shown both biochemically (hydroxyproline concentration in 3-, 16-, and 24-mo-old rats was 0.70 +/- 0.05, 0.92 +/- 0.07, and 1.57 +/- 0.13 mg/g of left ventricle, respectively, P < 0.05 and P < 0.0001 vs. 3 mo) and histologically. By contrast, type I procollagen mRNA levels decreased during aging (from -63%, P < 0.001 in 16-mo-old rats and -51%, P < 0.01 in 24-mo-old rats vs. 3-mo-old rats) as well as type III procollagen mRNA levels. DOCA-salt treatment in 24-mo-old rats had no effect on either the degree of fibrosis or the mRNA levels. We conclude that nonsynchronous changes in myocardial collagen mRNA and protein occur during aging, indicating translational and/or posttranslational mechanisms in collagen regulation. Hypertension during senescence did not modify collagen deposition at either the protein or mRNA levels.

Is the senescent heart overloaded and already failing?

Heart failure mainly occurs during the last decades of life, and it is important to know if the senescent heart is not an already failing heart. During aging, both contraction and relaxation of papillary muscle are impaired. Such an impairment is compensated in vivo and the cardiac output remains normal. In spite of a loss in myocytes, the heart weight/body weight ratio is unchanged, but the myocytes are bigger. Arrhythmias are permanent and are accompanied by a loss of the normal heart rate variability. Changes in specific mRNAs include: a shift in myosin heavy chain (MHC) isogene expression leading to an increased beta MHC content; decreased densities of Ca2+ ATPase of the sarcoplasmic reticulum, beta 1-adrenergic receptor, and muscarinic receptors; and attenuation of the Na+/Ca2+ exchange activity. Most of these changes, but not all, resemble those observed during cardiac overload and are accompanied by an increased duration of both the action potential and the intracellular calcium transient. However, the senescent heart is still able to further modify its phenotype in response to mechanical overload. The senescent heart is a diseased heart, and the origin of the "disease" is multifactorial and includes the general process of senescence, hormonal changes, and the myocardial consequences of senescence of the vessels.

Induction of complete segregation of cellular DNA and non-encapsidated viral genomes in herpes simplex virus type 1 infected HeLa cells as revealed by in situ hybridization

The intranuclear distribution of human Alu elements and herpes simplex virus type 1 (HSV-1) genomes was examined in HeLa cells by post-embedding in situ hybridization using in parallel appropriate biotinylated DNA probes. The bound probes were detected by direct immunogold labeling. In non-infected cells, human Alu elements detected by BLUR 8 were randomly scattered over the masses and strands of chromatin throughout the nucleus. The marked asynchrony of the HSV-1 cycle in individual HeLa cells of 17 h infected cultures allowed us to study the respective distributions of cell and viral DNA during the course of the infectious cycle. Labeling of human Alu elements revealed that cellular DNA had become confined to the border of infected nuclei without extension of cellular DNA fibers into the newly formed electron-translucent regions that occupied the centers of the infected nuclei. Labeling of HSV-1 DNA detected by a viral DNA probe revealed that non-encapsidated viral genomes were present exclusively within this centrally located viral region whereas encapsidated HSV-1 genomes, which were more widely distributed in the infected cell, were seen within the marginated host chromatin as well as the central viral region. Therefore, HSV-1 infection induces a regrouping of human Alu elements, that is, of host chromatin at the nuclear border. Non-encapsidated HSV-1 genomes and cellular DNA do not co-localize. Instead, they always constitute two adjacent compartments without spatial interrelationships.

High resolution localization of replicating viral genome in adenovirus-infected HeLa cells

Previous autoradiographical and in situ hybridization experiments have revealed that the replication of viral genomes in adenovirus type 5 infected HeLa cells induces changes in nuclear structure of which one of the more striking is the formation of distinctive replicative foci. The latter consist of a viral ssDNA accumulation site and a surrounding fibrillogranular network. We have reexamined these structures and processes by a more direct and higher resolution approach, that is, incorporation of bromodeoxyuridine (BrdU) by the infected cells and subsequent immunogold detection of the BrdU incorporated into DNA. Short pulses with BrdU in pulse-chase experiments confirmed that viral DNA replication at the early stage of nuclear transformation was confined within small virus-induced structures, the so-called early replicative sites, and revealed the persistence of the newly synthesized viral DNA at those sites for at least 2 h. At intermediate and late stages of nuclear transformation, the intensity of viral DNA replication, which varies from one type of replicative focus to another, was most intense in that layer of the fibrillogranular network which was in closest proximity to the viral single-stranded DNA (ssDNA) accumulation sites, whereas replication was weakest over the latter. Subsequently, BrdU-containing viral DNA molecules became more widely distributed in the viral ssDNA accumulation sites and the fibrillogranular network, the two constituents of the viral replicative machinery. Two hours later, some labeled molecules attained the viral genome storage site and/or became encapsulated. The most striking observation is the presence of a limited region in the replicative focus which is the preferential site for viral genome replication. The data also indicated that viral DNA molecules which were labeled during the short pulses remained in the replicative foci themselves, to be replicated and transcribed prior to attaining the pool of inactive genomes and/or becoming encapsulated.