A New Sleep Staging System for Type III Sleep Studies Equipped with a Tracheal Sound Sensor

Type III sleep studies record cardio-respiratory channels only. Compared with polysomnography, which also records electrophysiological channels, they present many advantages: they are less expensive, less time-consuming, and more likely to be performed at home. However, their accuracy is limited by missing sleep information. That is why many studies present specific cardio-respiratory parameters to assess the causal effects of sleep stages upon cardiac or respiratory activities. For this paper, we gathered many parameters proposed in literature, leading to 1,111 features. The pulse oximeter, the PneaVoX sensor (recording tracheal sounds), respiratory inductance plethysmography belts, the nasal cannula and the actimeter provided the 112 worthiest ones for automatic sleep scoring. Then, a 3-step model was implemented: classification with a multi-layer perceptron, sleep transition rules corrections (from the AASM guidelines), and sequence corrections using a Viterbi hidden Markov model. The whole process was trained and tested using 300 and 100 independent recordings provided from patients suspected of having sleep breathing disorders. Results indicated that the system achieves substantial agreement with manual scoring for classifications into 2 stages (wake vs. sleep: mean Cohen's Kappa of 0.63 and accuracy rate Acc of 87.8%) and 3 stages (wake vs. R stage vs. NREM stage: mean of 0.60 and Acc of 78.5%). It indicates that the method could provide information to help specialists while diagnosing sleep. The presented model had promising results and may enhance clinical diagnosis.

Diagnosis of sleep apnea without sensors on the patient's face

STUDY OBJECTIVES

Thermistors, nasal cannulas, and respiratory inductance plethysmography (RIP) are the recommended reference sensors of the American Academy of Sleep Medicine (AASM) for the detection and characterization of apneas and hypopneas; however, these sensors are not well tolerated by patients and have poor scorability. We evaluated the performance of an alternative method using a combination of tracheal sounds (TSs) and RIP signals.

METHODS

Consecutive recordings of 70 adult patients from the Pays de la Loire Sleep Cohort were manually scored in random order using the AASM standard signals and the combination TS and RIP signals, without respiratory sensors placed on the patient's face. The TS-RIP scoring used the TS and RIP-flow signals for detection of apneas and hypopneas, respectively, and the suprasternal pressure and RIP belt signals for the characterization of apneas.

RESULTS

Sensitivity and specificity of the TS-RIP combination were 96.21% and 91.34% for apnea detection and 89.94% and 93.25% for detecting hypopneas, respectively, with a kappa coefficient of 0.87. For the characterization of apneas, sensitivity and specificity were 98.67% and 96.17% for obstructive apneas, 92.66% and 99.36% for mixed apneas, and 96.14% and 98.89% for central apneas, respectively, with a kappa coefficient of 0.94. The TS-RIP scoring revealed a high agreement for classifying obstructive sleep apnea into severity classes (none, mild, moderate, and severe obstructive sleep apnea) with a Cohen's kappa coefficient of 0.96.

CONCLUSIONS

Compared with the AASM reference sensors, the TS-RIP combination allows reliable noninvasive detection and characterization of respiratory events with a high degree of sensitivity and specificity. TS-RIP combination could be used for diagnosis of obstructive sleep apnea in adults, either as an alternative to the AASM sensors or in combination with the recommended AASM sensors.

Tracheal sounds for the scoring of sleep respiratory events in children

STUDY OBJECTIVES

Oronasal thermistor and nasal cannula are recommended for the scoring of respiratory events (RE) but these sensors are poorly tolerated in children. The aim of the study was to evaluate tracheal sounds (TS) and suprasternal pressure (SSP) for the scoring of RE during sleep in children.

METHODS

We compared the detection and characterization of RE by AASM-recommended sensors ("AASM" scoring), with the detection and characterization of RE by the combination of TS and SSP with respiratory inductance plethysmography-sum (TS-RIP scoring), and TS and SSP only (TS scoring).

RESULTS

The recordings of 17 patients were analyzed. The TS, SSP, and RIP flow signals were present during 95%, 95%, and 99% of the validated recording time, respectively, as compared to 79% and 86% for nasal cannula and oronasal thermistor. A total of 1,456 RE were scored with the "AASM" scoring, 1,335 with the TS-RIP scoring, and 1,311 with the TS scoring. Sensitivity for apnea and hypopnea detection was 88% and 84% for the TS-RIP scoring, and 86% and 77% for the TS scoring. For apnea characterization, the TS-RIP scoring sensitivities and specificities were 97% and 100%, 76% and 98%, and 95% and 97%, for obstructive, mixed, and central apnea, respectively. For the TS scoring, they were 95% and 100%, 95% and 97%, and 91% and 97%, respectively.

CONCLUSIONS

TS and SSP + RIP-sum has a good sensitivity and specificity for the detection and characterization of apnea and hypopnea in children. TS and SSP alone have good sensitivity and specificity for apnea detection and characterization but lower sensitivity for hypopnea detection.

Automatic identification of sleep and wakefulness using single-channel EEG and respiratory polygraphy signals for the diagnosis of obstructive sleep apnea

Polysomnography (PSG) is necessary for the accurate estimation of total sleep time (TST) and the calculation of the apnea-hypopnea index (AHI). In type III home sleep apnea testing (HSAT), TST is overestimated because of the lack of electrophysiological sleep recordings. The aim of this study was to evaluate the accuracy and reliability of a novel automated sleep/wake scoring algorithm combining a single electroencephalogram (EEG) channel with actimetry and HSAT signals. The study included 160 patients investigated by PSG for suspected obstructive sleep apnea (OSA). Each PSG was recorded and scored manually using American Academy of Sleep Medicine (AASM) rules. The automatic sleep/wake-scoring algorithm was based on a single-channel EEG (FP2-A1) and the variability analysis of HSAT signals (airflow, snoring, actimetry, light and respiratory inductive plethysmography). Optimal detection thresholds were derived for each signal using a training set. Automatic and manual scorings were then compared epoch by epoch considering two states (sleep and wake). Cohen's kappa coefficient between the manual scoring and the proposed automatic algorithm was substantial, 0.74 ± 0.18, in separating wakefulness and sleep. The sensitivity, specificity and the positive and negative predictive values for the detection of wakefulness were 76.51% ± 21.67%, 95.48% ± 5.27%, 81.84% ± 15.42% and 93.85% ± 6.23% respectively. Compared with HSAT signals alone, AHI increased by 22.12% and 27 patients changed categories of OSA severity with the automatic sleep/wake-scoring algorithm. Automatic sleep/wake detection using a single-channel EEG combined with HSAT signals was a reliable method for TST estimation and improved AHI calculation compared with HSAT.

Validation of a Suprasternal Pressure Sensor for Sleep Apnea Classification in Children

STUDY OBJECTIVES

The recognition and characterization of respiratory events is crucial when interpreting sleep studies. The aim of the study was to validate the PneaVoX sensor, which integrates the recording of respiratory effort by means of suprasternal pressure (SSP), respiratory flow, and snoring for the classification of sleep apneas in children.

METHODS

Sleep recordings of 20 children with a median age of 7.5 (0.5-16.5) years were analyzed. Scoring of apneas according to the American Academy of Sleep Medicine (AASM) guidelines using nasal pressure, oronasal thermal sensor and respiratory efforts by means of respiratory inductance plethysmography (RIP), was compared to a scoring using the PneaVoX sensor and nasal pressure, without the oronasal thermal sensor nor RIP, during a dual blind study.

RESULTS

The percentage of sleep time recording without artifacts was 97%, 97%, 87%, 65%, and 98% for the respiratory flow and SSP from the PneaVoX sensor, oronasal thermal sensor, nasal pressure, and RIP, respectively. As compared to the AASM scoring with RIP, sensitivity and specificity of the SSP for the scoring of central apneas were 75% and 99% for the first reader, and 70% and 100% for the second reader, respectively. Sensitivity and specificity for the scoring of obstructive apneas were 98% and 75%, and 100% and 70%, respectively. A significant number of apneas scored as central by RIP were scored as obstructive by the SSP.

CONCLUSIONS

The PneaVoX sensor has a high degree of scorability in children. The PneaVoX sensor is a useful adjunct for characterizing apneas.

The B[a]P-increased intercellular communication via translocation of connexin-43 into gap junctions reduces apoptosis

Gap junctions are channels in plasma membrane composed of proteins called connexins. These channels are organized in special domains between cells, and provide for direct gap junctional intercellular communication (GJIC), allowing diffusion of signalling molecules <1 kD. GJIC regulates cell homeostasis and notably the balance between proliferation, cell cycle arrest, cell survival and apoptosis. Here, we have investigated benzo[a]pyrene (B[a]P) effects on GJIC and on the subcellular localization of the major protein of gap junction: connexin-43 (Cx43). Our results showed that B[a]P increased GJIC between mouse hepatoma Hepa1c1c7 cells via translocation of Cx43 from Golgi apparatus and lipid rafts into gap junction plaques. Interestingly, inhibition of GJIC by chlordane or small interference RNA directed against Cx43 enhanced B[a]P-induced apoptosis in Hepa1c1c7 cells. The increased apoptosis caused by inhibition of GJIC appeared to be mediated by ERK/MAPK pathway. It is suggested that B[a]P could induce transfer of cell survival signal or dilute cell death signal via regulation of ERK/MAPK through GJIC.

Characterization of goldfish fin cells in culture: some evidence of an epithelial cell profile

Comprehensive characterization of cultured cells in fish was little explored and cell origin is often deduced from morphological analogies with either epithelial of fibroblastic cells. This study aims to characterize cell origin in goldfish fin culture using morphological, immunochemical, and molecular approaches. Time lapse analysis revealed that cultured cell morphology changed within minutes. Therefore, cell morphology cannot predict whether cells are from fibroblastic or epithelial origin. The labeling pattern of heterologous anti-cytokeratin and anti-vimentin antibodies against goldfish epithelial cells and fibroblasts was first tested on skin sections and the corresponding labeling of the cultured cells was analyzed. No cell origin specificity could be obtained with the chosen antibodies. In the molecular approach, detection levels of three cytokeratin (CauK8-IIS, CauK49-IE and CauK50-Ie) and one vimentin transcripts were assessed on skin and fin samples. Specificity for epithelial cells of the most abundant mRNA, CauK49-Ie, was thereafter validated on skin sections by in situ hybridization. The selected markers were used afterwards to characterize fin cultures. CauK49-IE riboprobe labeled every cell in young cultures whereas no labeling was observed in older cultures. Accordingly, CauK49-IE transcript levels decreased after 15 days culture while CauK8-IIS ones increased. The use of homologous marker gave evidence that young cultured cells from goldfish fin are homogeneously of epithelial type and that cell characteristics may change over culture time.

RNAi-mediated ERK2 knockdown inhibits growth of tumor cells in vitro and in vivo

The MAPK MEK/ERK pathway is often upregulated in cancer cells and represents an attractive target for development of anticancer drugs. Only few data concerning the specific functions of ERK1 and 2 are reported in the literature. In this report, we investigated the specific role of ERK1 and 2 in liver tumor growth both in vitro and in vivo. DNA synthesis and cells in S phase analysed by flow cytometry, correlated with strong inhibition of Cdk1 and cyclin E levels, are strongly reduced after exposure to the MEK inhibitor, U0126. We obtained a significant reduction of colony formation in soft agar assays and a reduction in the size of tumor xenografts in nude mice treated with U0126. Then, we could specifically abolished ERK1 or 2 expression by small-interfering RNA (siRNA) and demonstrated that ERK2 knockdown but not ERK1 interferes with the process of replication. Moreover, we found that colony formation and tumor growth in vivo were significantly inhibited by targeting ERK2 using stable chemically modified siRNA. Taken together, our results emphasize the importance of the MEK/ERK pathway in liver cancer cell growth in vitro and in vivo and argue for a crucial role of ERK2 in this regulation.

Orientation fields of nonlinear biological fibrils by second harmonic generation microscopy

The orientation of fibrils within biological tissues is of primary importance. In this study, we propose a simple method based on second harmonic generation (SHG) microscopy to map, pixel by pixel, the orientation of the symmetry axis of the second-order nonlinear susceptibility tensor of fibrils that produce SHG. The method uses only four images acquired at specific polarizations of the input laser beam, and can be easily and cheaply implemented on a confocal microscope. In addition to orientation informations, the method also provides polarization independent images and estimations of the ratio of the nonlinear susceptibility components. We demonstrate the relevance of our concept by studying the orientation fields of the collagen meshwork in a healthy rat liver that provides well separated fibrils. By correlating the mean orientation of the nonlinear susceptibility to the fibril orientation itself for many fibril segments, and using circular statistics, it is shown that both orientations are truly parallel at the fibril scale. Our polarimetric method allows to map fibril orientation fields, independently of individual fibril contrast in the SHG image.

Mechanism in the sequential control of cell morphology and S phase entry by epidermal growth factor involves distinct MEK/ERK activations

Cell shape plays a role in cell growth, differentiation, and death. Herein, we used the hepatocyte, a normal, highly differentiated cell characterized by a long G1 phase, to understand the mechanisms that link cell shape to growth. First, evidence was provided that the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) cascade is a key transduction pathway controlling the hepatocyte morphology. MEK2/ERK2 activation in early G1 phase did not lead to cell proliferation but induced cell shape spreading and demonstration was provided that this MAPK-dependent spreading was required for reaching G1/S transition and DNA replication. Moreover, epidermal growth factor (EGF) was found to control this morphogenic signal in addition to its mitogenic effect. Thus, blockade of cell spreading by cytochalasin D or PD98059 treatment resulted in inhibition of EGF-dependent DNA replication. Our data led us to assess the first third of G1, is exclusively devoted to the growth factor-dependent morphogenic events, whereas the mitogenic signal occurred at only approximately mid-G1 phase. Moreover, these two growth factor-related sequential signaling events involved successively activation of MEK2-ERK2 and then MEK1/2-ERK1/2 isoforms. In addition, we demonstrated that inhibition of extracellular matrix receptor, such as integrin beta1 subunit, leads to cell arrest in G1, whereas EGF was found to up-regulated integrin beta1 and fibronectin in a MEK-ERK-dependent manner. This process in relation to cytoskeletal reorganization could induce hepatocyte spreading, making them permissive for DNA replication. Our results provide new insight into the mechanisms by which a growth factor can temporally control dual morphogenic and mitogenic signals during the G1 phase.

The mitogen-activated protein kinase kinase/extracellular signal-regulated kinase cascade activation is a key signalling pathway involved in the regulation of G(1) phase progression in proliferating hepatocytes

In this study, activation of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signalling pathway was analyzed in proliferating rat hepatocytes both in vivo after partial hepatectomy and in vitro following epidermal growth factor (EGF)-pyruvate stimulation. First, a biphasic MEK/ERK activation was evidenced in G(1) phase of hepatocytes from regenerating liver but not from sham-operated control animals. One occurred in early G(1) (30 min to 4 h), and the other occurred in mid-late G(1), peaking at around 10.5 h. Interestingly, the mid-late G(1) activation peak was located just before cyclin D1 induction in both in vivo and in vitro models. Second, the biological role of the MEK/ERK cascade activation in hepatocyte progression through the G(1)/S transition was assessed by adding a MEK inhibitor (PD 98059) to EGF-pyruvate-stimulated hepatocytes in primary culture. In the presence of MEK inhibitor, cyclin D1 mRNA accumulation was inhibited, DNA replication was totally abolished, and the MEK1 isoform was preferentially targeted by this inhibition. This effect was dose dependent and completely reversed by removing the MEK inhibitor. Furthermore, transient transfection of hepatocytes with activated MEK1 construct resulted in increased cyclin D1 mRNA accumulation. Third, a correlation between the mid-late G(1) MEK/ERK activation in hepatocytes in vivo after partial hepatectomy and the mitogen-independent proliferation capacity of these cells in vitro was established. Among hepatocytes isolated either 5, 7, 9, 12 or 15 h after partial hepatectomy, only those isolated from 12- and 15-h regenerating livers were able to replicate DNA without additional growth stimulation in vitro. In addition, PD 98059 intravenous administration in vivo, before MEK activation, was able to inhibit DNA replication in hepatocytes from regenerating livers. Taken together, these results show that (i) early induction of the MEK/ERK cascade is restricted to hepatocytes from hepatectomized animals, allowing an early distinction of primed hepatocytes from those returning to quiescence, and (ii) mid-late G(1) MEK/ERK activation is mainly associated with cyclin D1 accumulation which leads to mitogen-independent progression of hepatocytes to S phase. These results allow us to point to a growth factor dependency in mid-late G(1) phase of proliferating hepatocytes in vivo as observed in vitro in proliferating hepatocytes and argue for a crucial role of the MEK/ERK cascade signalling pathway.

Skp2 induction and phosphorylation is associated with the late G1 phase of proliferating rat hepatocytes

The changes in phosphoproteins purified with the affinity peptide p9CKShs1 were analyzed from extracts of regenerating rat livers in order to define some G1 and G1/S regulations characteristic of mature hepatocytes stimulated to proliferate. We observed a 47 kDa phosphoprotein that occurred first at the end of G1 before peaking in the S phase. P47 was also found to be phosphorylated in late G1 in primary hepatocyte cultures stimulated with mitogens. P47 was still phosphorylated in extracts depleted of Cdc2, but to a lesser extent after Cdk2 depletion. This phosphoprotein was identified as Skp2. (i) P47 shared the same electrophoretic mobility than Skp2, a cell cycle protein essential for S phase entry in human fibroblasts; (ii) Skp2, like P47, started to be expressed and was highly phosphorylated during the G1/S transition of hepatocytes stimulated to proliferate in vivo and in vitro; (iii) P47 was specifically immunoprecipitated by an antibody directed against Skp2. In addition, cyclin A/Cdk2 complexes from regenerating liver clearly interacted with Skp2. This is the first demonstration that Skp2 is induced and phosphorylated in the late G1 and S phase of hepatocytes in vivo in regenerating liver as well as in vitro in mitogen-stimulated hepatocytes.

Deferoxamine arrests in vitro the proliferation of porcine hepatocyte in G1 phase of the cell cycle

Iron is required for cell proliferation of all living species. Moreover, iron excess may be involved in the development of hepatocellular carcinoma. In this study we analyzed the effects of deferoxamine, an iron chelator, on normal porcine hepatocyte proliferation. We confirmed that hepatocytes isolated from young pigs proliferate in the presence of insulin and fetal calf serum as shown by [3H] methyl-thymidine incorporation, presence of mitotic figures and increase in cell number. This was paralleled by nuclear expression of p34cdc2 and its associated histone H1 kinase activity. In the presence of deferoxamine, [3H] methyl-thymidine incorporation, expression of nuclear proteins (p34cdc2 and PCNA) and H1 kinase activity were drastically reduced. In addition, in contrast with control cultures, cells in S-phase were not detected by flow cytometry. These data suggest that iron chelation by deferoxamine can arrest the progression of porcine hepatocytes in the G1 phase of the cell cycle.

Growth factor dependence of progression through G1 and S phases of adult rat hepatocytes in vitro. Evidence of a mitogen restriction point in mid-late G1

Several hepatocyte mitogens have been identified, but the signals triggering the G0/G1 transition and cell cycle progression of hepatocytes remain unknown. Using hepatocyte primary cultures, we investigated the role of epidermal growth factor/pyruvate during the entry into and progression through the G1 phase and analyzed the expression of cell cycle markers. We show that the G0/G1 transition occurs during hepatocyte isolation as evidenced by the expression of early genes such as c-fos, c-jun, and c-myc. In culture, hepatocytes progress through G1 regardless of growth factor stimulation until a restriction point (R point) in mid-late G1 beyond which they cannot complete the cell cycle without mitogenic stimulation. Changes in cell cycle gene expression were associated with progression in G1; the cyclin E mRNA level is low early in G1 but increases at the G1/S boundary, while the protein is constantly detected during cell cycle but undergoes a change of electrophoretic mobility in mid-late G1 after the R point. In addition, a drastic induction of cyclin D1 mRNA and protein, and to a lesser extent of cyclin D2 mRNA, takes place in mitogen-stimulated cells after the R point. In contrast, cyclin D3 mRNA appears early in G1, remains constant in stimulated cells, but accumulates in unstimulated arrested cells, paralleling the cyclin-dependent kinase 4 mRNA expression. These results characterize the different steps of G1 phase in hepatocytes.

The liver-specific response to phenobarbital involves a transient increase in phosphorylation of a 34-kda nuclear protein in rat liver and in hepatocytes in culture

We have examined the influence of phenobarbital, a liver detoxication gene inducer and a potent tumor promoter, on the phosphorylation status of nuclear-enriched proteins in primary rat hepatocyte cultures and in whole livers. Freshly isolated cells were plated on plastic dishes in presence of serum for 4 h and 2 mM phenobarbital was added for various times, following serum withdrawal. A transient increase in phosphorylation of a 34-kda nuclear protein was detected at 6 h. In whole livers, but not in kidneys, a nuclear protein with the same electrophoretic mobility was also transiently over-phosphorylated, following injection of 80 mg/kg phenobarbital, although the peak activity was attained after 30 min only. No immunological relatedness between major histones and the 34-kda protein was found. Our results demonstrate a specific, yet undescribed, transient effect of phenobarbital on the phosphorylation status of a 34-kda nuclei-enriched protein in rat hepatocytes and in rat liver.

[Intercellular communications in cell differentiation and in hepatic carcinogenesis]

The liver epoch like other tissue epochs occurs after that different events have induced heterogeneity in embryonic cells which results in distinct evolutionary processes. These events and those of organogenesis like "induction" are deeply dependent on cell-cell communications. Cell-cell interactions involve either soluble factors (hormones, growth factors), extracellular matrix or plasma membrane proteins responsible for cell-cell recognition and/or adhesion. All these plasma membrane signals are transduced to the nucleus and modulate the expression of groups of genes. To be functionally stable along the adult stage the liver has to maintain an ordered activity of cell renewal. This balance between proliferation and differentiation is, at least in part, controlled by cell-cell communications. Therefore, it is not surprising that intercellular communications are altered during hepatocarcinogenesis. They involve changes in the distribution of junctions, in the amounts of extracellular matrix components and/or growth factors which all result in modifying the differentiation/proliferation balance. Cell culture models have been used for these different studies; new in vitro systems should be set up in the near future by taking advantage of the targeted hepatocarcinogenesis in transgenic mouse.

Expression and activation of cdks (1 and 2) and cyclins in the cell cycle progression during liver regeneration

In normal adult liver, hepatocytes are arrested in G0, and they rapidly respond to a mass loss by a definite number of divisions. Thus, taking advantage of the in vivo regenerative capacity of the liver following partial hepatectomy, we have analyzed both expression and activation of p34cdc2 (= cdk1) and p33cdk2 through the cell cycle, particularly during the long lasting G1 phase and in the G1/S transition. While p33cdk2 is constantly expressed during the cell cycle, p34cdc2 is completely absent in resting hepatocytes and remains unexpressed for up to 20 h after partial hepatectomy, a time period corresponding to the G1 phase and G1/S transition, and then accumulates in the S, G2, and M phases. No histone H1 kinase activity is detected during the G1 phase, while two peaks of p34cdc2 kinase activity are observed during the S and M phases and only one peak of p33cdk2 kinase activity in the S phase. p34cdc2 forms complexes with both cyclins A and B while p33cdk2 is associated with cyclin A only. Surprisingly, cyclins E and D1 are present in resting liver and with modest variation throughout the cell cycle. Taken together, our data provide evidence that the pattern of G1-associated proteins in hepatocytes during liver regeneration is distinct from that described in other cell types.

[Role of intercellular communications in hepatic differentiation and carcinogenesis]

The liver epoch like other tissue epochs, occurs after that different events have induced heterogeneity in embryonic cells which result in distinct evolutionary processes. These events and those of organogenesis like "induction", are deeply dependent on cell-cell communications. Cell-cell interactions involve either soluble factors (hormones, growth factors), extracellular matrix or plasma membrane proteins responsible for cell-cell recognition and/or adhesion. All these plasma membrane signals are transduced to the nucleus and modulate the expression of groups of genes. To be functionally stable along the adult stage the liver has to maintain an ordered activity of cell renewal. This balance between proliferation and differentiation is at least in part, controlled by cell-cell communications. Therefore, it is not surprising that intercellular communications are altered during hepatocarcinogenesis. They involve changes in the distribution of junctions, in the amounts of extracellular matrix components and/or growth factors which all result in modifying the differentiation/proliferation balance. Cell culture models have been used for these different studies; new in vitro systems should be set up in the near future by taking advantage of the targeted hepatocarcinogenesis in transgenic mouse.

A plasma membrane protein is involved in cell contact-mediated regulation of tissue-specific genes in adult hepatocytes

We have identified the liver-regulating protein (LRP), a cell surface protein involved in the maintenance of hepatocyte differentiation when cocultured with rat liver epithelial cells (RLEC). LRP was defined by immunoreactivity to a monoclonal antibody (mAb L8) prepared from RLEC. mAb L8 specifically detected two polypeptides of 85 and 73 kD in immunoprecipitation of both hepatocyte- and RLEC-iodinated plasma membranes. The involvement of these polypeptides, which are integral membrane proteins, in cell interaction-mediated regulation of hepatocytes was assessed by evaluating the perturbing effects of the antibody on cocultures with RLEC. Several parameters characteristic of differentiated hepatocytes were studied, such as liver-specific and house-keeping gene expression, cytoskeletal organization and deposition of extracellular matrix (ECM). An early cytoskeletal disturbance was evidenced and a marked alteration of hepatocyte functional capacity was observed in the presence of the antibody, together with a loss of ECM deposition. By contrast, cell-cell aggregation or cell adhesion to various extracellular matrix components were not affected. These findings suggest that LRP is distinct from an extracellular matrix receptor. The fact that early addition of mAb L8 during cell contact establishment was necessary to be effective may indicate that LRP is a novel plasma membrane protein that plays an early pivotal role in the coordinated metabolic changes which lead to the differentiated phenotype of mature hepatocytes.

Distinct effects of cell-cell communication and corticosteroids on the synthesis and distribution of cytokeratins in cultured rat hepatocytes

Cytokeratins CK 8 and CK 18 are the two keratins expressed in the liver. They are known to undergo extensive changes in expression with alteration of the hepatocyte phenotype in vitro. In this study, we have investigated the variation in levels of these two cytokeratins in hepatocytes selected from different situations in vivo. The amounts of corresponding transcripts were compared; cytokeratin 8 and 18 mRNAs were present at similar levels in hepatocytes freshly isolated from adult liver and, unexpectedly, from 17-day-old foetuses and newborn rats, whereas they were markedly higher in regenerating hepatocytes isolated early after partial hepatectomy. In order to investigate whether the different factors that can promote hepatocyte differentiation also produce a similar set of cytoskeletal changes, we have analysed both the expression and the distribution of cytokeratins in hepatocytes under different culture conditions allowing modulation of differentiation. Establishment of cell-cell contacts and addition of glucocorticoids were used as two modulating factors. Coculturing hepatocytes with rat liver epithelial cells (RLEC), which favours active expression of liver-specific genes, resulted in a gradual decline of cytokeratin mRNAs, whereas pure hepatocyte cultures, which exhibit rapid phenotypic changes, expressed increasing levels of CK 8 and CK 18 transcripts. Furthermore, intracellular CK distribution was dramatically modified in parallel: the CK-positive material formed a fine network of fibrils uniformly distributed in the cytoplasm of hepatocytes in pure culture, whereas in cocultured cells CK immunofluorescence appeared principally located at the cellular periphery and it was regularly arranged in long fibrils just beneath the plasma membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of coagulation factor V gene by normal adult human hepatocytes in primary culture

Normal human adult hepatocytes were examined for their ability to synthesize and secrete factor V using primary culture. The culture medium contained both factor V and factor Va as determined by bioassay and activation experiments. Immunoprecipitation of newly synthesized labelled factor V showed the presence of both native factor V (m.w. 330,000) and two fragments of respective molecular weight 300,000 and 265,000. Northern blot analysis revealed the presence of a single 7 kb factor V mRNA in cultured human hepatocytes as in liver biopsies, together with fibrinogen beta and albumin transcripts. Relative levels of factor V, fibrinogen beta and albumin mRNAs differed when the cells cultured, suggesting that expression of the three corresponding genes might in part be independently regulated. Furthermore, addition of glucocorticoids enhanced factor V and fibrinogen beta mRNA levels 1.6- and 5-fold respectively, but did not significantly increase that of albumin. These results provide evidence that human hepatocytes actively participate in the synthesis of plasma factor V and constitute a valuable model to study the common and specific regulations involved in the control of the expression of this gene in human liver.

Autocrine activity of interleukin 6 secreted by hepatocarcinoma cell lines

Among several rat hepatoma cell lines known to secrete interleukin 6 (IL6), the HTC.JZ1 line stands out as a high-level producer. HTC.JZ1 cells were stimulated to secrete up to fourfold increased amounts of IL6 over 24 hours by treatment with lipopolysaccharides (LPS). Both functional IL6 levels, measured as hepatocyte stimulating factor (HSF) activity, and IL6 mRNA concentrations were increased proportionally by exposure to LPS. Similarly, IL6 mRNA was induced by LPS treatment in cultured primary rat hepatocytes. The induction of Il6 mRNA by LPS was inhibited both in primary hepatocyte and hepatoma cell cultures by treatment with the synthetic glucocorticoid dexamethasone, consistent with the known analogous repression of the IL6 gene by dexamethasone in macrophages, monocytes and fibroblasts. IL6 secreted by HTC.JZ1 cells was utilized as an autocrine inducer of endogenous acute phase gene expression: HTC cells expressed constitutive levels of alpha 2-macroglobulin (alpha 2M) mRNA specified by the major rat acute phase gene, the alpha 2M gene, which is known to be regulated by IL6. By contrast, normal rat liver biopsy material and a number of other rat hepatoma cell lines lacked endogenous IL6 production and showed very low to zero expression of endogenous alpha 2M mRNA. Expression of alpha 2M mRNA in HTC.JZ1 cells was inducible by treatment with LPS. The constitutive and the LPS-induced production of alpha 2M mRNA were significantly reduced (up to 50% inhibition) by addition of an anti IL6 serum to the culture medium and removal of the immune complexes. However, complete neutralization of the alpha 2M-inducing HSF activity could not be obtained with anti-IL6 serum alone, probably because HTC.JZ1 cells secrete comparable quantities of a second HSF activity. This activity, the cytokine leukemia inhibitory factor (LIF), is also known to stimulate transcription of the rat alpha 2M gene but was not reactive with anti-IL6 sera. The induction of IL6 mRNA in HTC cells by LPS was regulated at the transcriptional level, as demonstrated by a series of mutagenesis and transfection experiments. Progressive deletion of 5' flanking sequences from the IL6 gene promoter region reduced the basal level, and the LPS-induced promoter activity after transfection into HTC.JZ1 hepatoma cells. IL6 has been shown to act as an autocrine regulator of growth for certain B lymphoid cell lines derived from human multiple myelomas. The results presented here establish that IL6 secreted by certain hepatoma cell lines also acts in an autocrine fashion to induce expression of the endogenous acute phase alpha 2M gene.

Gene regulation by interleukin 6

Interleukin 6 (IL-6) is a central alarm hormone of the mammalian body. During acute and chronic inflammations, it induces acute phase plasma protein synthesis by liver hepatocytes, modulates the immune response and participates in the regulation of body temperature (fever). In addition, it is a growth factor for certain tumor cells, such as myeloma cells. The details of the IL-6 signal transduction mechanism are unknown. We have contributed to this problem at 2 levels: (a), we have mapped an IL-6-response element (IL-6-RE) in the 5' flanking region of the alpha 2-macroglobulin gene (alpha 2M), a prototype rat liver acute phase gene. This element, CTGGGA, serves as a binding site for nuclear factors that facilitate hormone induced transcription. We have begun to characterize these factors from hepatic cells and demonstrated that they undergo characteristic IL-6-induced changes. Similar factors were also discovered in human Burkitt tumor derived cell lines (B cells). These bound at the IL-6-RE of the rat alpha 1M gene and formed indistinguishable protein DNA complexes, as the corresponding hepatic factors. Thus, common elements probably operate in the IL-6 signal transduction cascade in liver cells and B cells; (b), we have cloned the rat liver IL-6 receptor (IL-6-R) and derived its amino acid sequence. It was 53% identical to the human leukocyte IL-6-R and all functional domains were highly conserved. Therefore, the cell-type specific responses to IL-6 in liver cells and lymphocytes were probably not due to cell-type specific forms of the receptor, but to other so far unknown elements of the signal transduction cascade.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of laminin chains and receptor (LBP-32) in fetal and neoplastic hepatocytes compared to normal adult hepatocytes in vivo and in culture

Laminin deposition is increased in fetal liver and in a variety of liver diseases, including the development of carcinoma. We investigated the role of the hepatocyte in the synthesis of both laminin and its 32- to 67-kd receptor in normal adult, fetal, and diethylnitrosamine-treated rat livers, and in adult rat hepatocyte primary cultures. Laminin was localized by immunoelectron microscopy in the endoplasmic reticulum of hepatocytes in fetal-derived and in 18-month-old diethylnitrosamine-treated rat livers. Steady-state mRNA levels for the three chains of laminin (A, B1, and B2) and the laminin receptor (LBP-32) were examined. Northern-blot analyses showed that hepatocytes at all stages lacked the A-chain mRNA. B1-chain mRNA was undetectable in normal adult hepatocytes, while significant levels of B1-chain mRNA were found in fetal hepatocytes and in adult hepatocyte primary culture. In hepatocytes from diethylnitrosamine-treated rats, B1-chain mRNAs were abundant and were present mainly in nodular formations rather than in the nontumorous areas. B2-chain mRNAs were barely detectable in either normal adult or fetal hepatocytes. In diethylnitrosamine-treated rats, the steady-state B2-chain mRNA level was higher in nodules than in nontumorous areas. In primary culture, B2-chain mRNAs were present as early as 4 hours after adult hepatocyte seeding, and dramatically increased during the following 2 days. Only low levels of laminin-receptor (LBP-32) mRNAs were present in normal adult hepatocytes, whereas the levels were high in the fetal and in the tumor-containing livers. In diethylnitrosamine-treated rats, LBP-32 mRNAs were more abundant in nodular formations rather than in nontumorous areas. In hepatocyte primary culture, the expression of the LBP-32 mRNA dramatically increased during the first 24 hours. These results show that in hepatocytes, expression of laminin chains and its receptor LBP-32 are not coordinated and depends on the maturation of the cells. In addition, they suggest that the expression of B1 and B2 chains in adult hepatocytes is related to changes of the normal phenotype and/or the pericellular environment.

Production of interleukin 6 by hepatoma cells

Five rat hepatoma cell lines were shown to secrete hepatocyte-stimulating factors (HSFs) capable of inducing a characteristic spectrum of acute phase genes. Three of these lines, but not normal rat livers or livers from rats with an experimentally induced acute inflammation, produced interleukin 6 (IL6) mRNA. An anti-rat IL6 serum was prepared against synthetic peptides derived from the rat IL6 cDNA sequence. This antiserum cleared authentic rat IL6 and a fraction of the HSF activities secreted by the hepatoma cell lines. After concentration of culture supernatants from FTO2B hepatoma cells, IL6 was detected with the anti-IL6 serum by immuno-blot analysis. Biosynthesis of IL6 in the HTC line was demonstrated by metabolic labeling and immunoprecipitation. Secretion of HSF activities by hepatoma cells was increased by serum factors. These data suggest that different rat hepatoma lines each secrete different characteristic sets of HSF activities and establish unambiguously that IL6 is secreted by at least some of these lines.

Increased level of the mitochondrial ND5 transcript in chemically induced rat hepatomas

We have constructed a cDNA library from a hepatoma cell line (HTC cells) and isolated the clones corresponding to mRNAs present at a much higher level in hepatomas than in normal hepatocytes. The characterization of one of these clones is described in this paper. This clone is homologous to part of the mitochondrial ND5 gene (a subunit of NADH-ubiquinone oxidoreductase). The level of this mRNA was found increased in HTC cells and in hepatocytes from diethylnitrosamine-treated rats long before the development of tumors and strongly increased in carcinoma nodules as compared to hepatocytes from nontreated rats. Southern blot analysis showed a mitochondrial DNA heterogeneity in hepatomas with an alteration of the structure of part of the molecules.

DNA sequences homologous to mitochondrial genes in nuclei from normal rat tissues and from rat hepatoma cells

Using specific probes we show that sequences homologous to NADH dehydrogenase Subunit 6, and Cytochrome oxidase Subunits I, II, and III mitochondrial genes are present in nuclear DNA from various tissues. These mitochondrial-like sequences are also present in rat hepatoma nuclear DNA but with an abnormal organization and a higher copy number than in normal hepatocytes.

RNAs containing mitochondrial ND6 and COI sequences present an abnormal structure in chemically induced rat hepatomas

We have constructed a cDNA library prepared from an hepatoma cell line (HTC cells) and isolated a clone, pHT 13, which corresponds to mRNAs present at a much higher level in rat hepatomas than in normal hepatocytes. The sequence of the pHT 13 insert has been previously published (Nucleic Acids Res. 1988, 16,10935). This clone contains mitochondrial DNA sequences with an abnormal organization, since it includes part of the NADH dehydrogenase subunit 6 (ND6) and of the cytochrome oxidase subunit I (COI) genes separated by 230 bases instead of 9 kb in mitochondrial genome from normal hepatocytes. In this work we show (1) that RNAs homologous to this clone are present in hepatoma cells but not in normal hepatocytes, (2) that a 3 kb fragment of tumor mitochondrial DNA contains both the ND6 and the COI sequences. The abnormal structure of the DNA is confirmed by Southern blot analysis which shows that distinct types of mitochondrial DNAs are present in hepatoma cells.

Biosynthesis of factor V by normal adult rat hepatocytes

The synthesis of coagulation factor V was investigated in isolated rat hepatocytes maintained in long-term primary culture. Two culture conditions were compared. A clotting assay and an immunoprecipitation experiment with rabbit anti rat factor V IgG were used to demonstrate not only the presence of factor V in the cells but also active secretion into the culture medium. Both the inhibition of the clotting reaction in presence of the antibody and absence of thrombin in culture media confirmed the specificity of the clotting assays. Electron microscopic examination located factor V in the endoplasmic reticulum and Golgi apparatus of hepatocytes in common with other liver specific plasma proteins. Examination of liver tissue sections confirmed the production of factor V in hepatocytes but not in hepatic endothelial cells although it did not exclude a transit pathway of factor V through these cells. Addition of Russell viper venom factor V activating enzyme to the culture medium had no effect on the factor V activity. In contrast, treatment of cell extracts did increase the coagulant activity. This suggests that hepatocytes contained principally an unactivated form or procofactor, whereas factor V present into the culture medium was mainly in an activated form. These data provide evidence for synthesis and secretion of an hepatocytic factor V.

Chronic iron overload inhibits protein secretion by adult rat hepatocytes maintained in long-term primary culture

Short-term pure cultures and long-term cocultures of adult rat hepatocytes with rat liver epithelial cells, presumably derived from primitive biliary cells, were used to define in vitro models of iron overloaded hepatocytes in order to understand the molecular mechanism responsible for liver damage occurring in patients with hemochromatosis. In vitro iron overload was obtained by daily addition of ferric nitrilotriacetate to the culture medium. A concentration of 20 microM ferric salt induced hepatocyte iron overload with minimal cytotoxicity as evaluated by cell viability, morphological changes of treated cells and cytosolic enzyme leakage into the culture medium. The effects of iron overload on protein biosynthesis and secretion were studied in both short-term pure cultures and long-term cocultures of hepatocytes. The amounts of intracellular and newly synthesized proteins were never modified by the iron treatment. Furthermore, neither the relative amounts of transferrin and albumin mRNAs nor their translational products were altered by iron overload. Moreover, no change in the transferrin isomeric forms were observed in treated cells. In contrast, a prolonged exposure of cocultured hepatocytes to 20 microM ferric salt led to a significant decrease in the amount of proteins secreted in the medium. This decrease included the two major secreted proteins, namely albumin and transferrin, and probably all other secreted proteins. These results demonstrate that iron loading alters neither the total nor the liver specific protein synthesis activity of cultured hepatocytes. They suggest that chronic overload may impede the protein secretion process.

Hepatocytes may produce laminin in fibrotic liver and in primary culture

Previous studies have shown that laminin is present in basement membranes in normal liver but failed to identify cellular sources. We have investigated the extracellular and intracellular distribution of laminin in normal rat and human liver, in fibrotic human liver and in primary hepatocyte cultures from both species by light and electron microscopy using the indirect immunoperoxidase technique. In normal liver from both species, antibodies to laminin strongly stained basement membranes and formed discontinuous discrete deposits in the wall of the sinusoid. Vascular endothelial and bile duct cells as well as fat-storing cells and sinusoidal endothelial cells strongly stained for this glycoprotein while hepatocytes were negative. In fibrotic human liver, increased amounts of extracellular laminin were usually found. Continuous deposition in the space of Disse was observed in some cases. In addition to fat-storing cells and endothelial cells, hepatocytes were also sometimes positive. Normal rat and human hepatocytes synthesize and secrete laminin in conventional culture, but it remains soluble in the medium. By contrast, in coculture with another rat liver cell type, laminin accumulated around hepatocyte cords. These observations suggest that fat-storing cells and endothelial cells are the major sites of production of laminin in normal liver. However, when their environment is altered (e.g., liver injury, culture), adult hepatocytes are able to synthesize detectable amounts of laminin.

Use of hepatocyte co-cultures in the assessment of drug toxicity from chronic exposure

1. In rat hepatocyte cultures, clonidine and malotilate were cytotoxic at 170 microM but did not induce changes at lower concentrations during 24 h exposure. Amitriptyline induced cell injury at 20 microM but was ineffective at 2 microM. 2. In co-culture of rat or human hepatocytes with rat liver epithelial cells, 2 microM amitriptyline was cytotoxic after 7 days treatment whereas 70 to 100 microM clonidine or malotilate gave no significant effect. 3. These results suggest that co-cultured hepatocytes which retain their differentiated state for several days or weeks, represents a promising tool for studying hepatotoxicity from chronic treatment in vitro.

Differential response of primary cultures of human and rat hepatocytes to aflatoxin B1-induced cytotoxicity and protection by the hepatoprotective agent (+)-cyanidanol-3

The acute hepatotoxicity induced by aflatoxin B1 (AFB1) and the potential protective effect of (+)-cyanidanol-3 (Catergen) were evaluated in both human and rat hepatocytes in primary cultures. AFB1-induced acute toxicity was visualized by light microscope observation and quantified by measurement of lactic dehydrogenase activity in the medium. Human hepatocytes were susceptible to AFB1-induced cytotoxicity but no evident relationship between the concentration of mycotoxin and the extent of cellular damage was established. (+)-Cyanidanol-3 was not toxic at concentrations up to 2 x 10(-3)M, but no obvious protective effect from AFB1-induced injury was evidenced in human cells. By contrast, rat hepatocytes responded in a dose-related manner to AFB1. (+)-Cyanidanol was toxic at 10(-3)M, but even at this concentration exerted a strong protective effect against AFB1-induced cytotoxicity. Such species differences suggest the existence of metabolic differences in both AFB1 and (+)-cyanidanol-3 activating and deactivating mechanisms.

Modulation of alkaline phosphodiesterase I in cultured rat hepatocytes

Alkaline phosphodiesterase I activity was measured in adult and foetal rat hepatocytes maintained in primary culture under various conditions. This enzyme was found to be expressed in both cell populations and could be resolved into two bands having apparent molecular weights of 130,000 and 250,000, respectively. Alkaline phosphodiesterase I activity was already at high levels in 15 day foetal liver and, as early as the 19th day of gestation, it reached adult levels. Alkaline phosphodiesterase I levels were well maintained during culture. In the absence of serum, its level continued to increase with time in foetal cells. It dramatically increased by days 4 and 5, in adult cells maintained on fibronectin and plastic, respectively. Dexamethasone stimulated alkaline phosphodiesterase I activity after a lag phase of 8 h, with a maximum reached after 40 h. As this induction was prevented by addition of actinomycin D or cycloheximide, it could be concluded that it required RNA and protein synthesis. Only the major Mr 250,000 form responded to dexamethasone and was sensitive to serum.

Immunocytochemical evidence for the maintenance of cytochrome P-450 isozymes, NADPH cytochrome C reductase, and epoxide hydrolase in pure and mixed primary cultures of adult human hepatocytes

Specific polyclonal antibodies were used to investigate the distribution of two cytochrome P-450 isozymes (5 and 8), NADPH cytochrome c reductase, and epoxide hydrolase in adult human hepatocytes cultured alone or co-cultured with rat liver epithelial cells. The enzymes were localized by the indirect immunoperoxidase technique following fixation with a paraformaldehyde-glutaraldehyde mixture and membrane permeabilization with saponin. The pattern of distribution of the four enzymes after 24 hr in culture was similar to that found in vivo. Virtually all the hepatocytes exhibited nearly homogeneous positive staining for cytochrome P-450-8, whereas only 60-80% were positive for cytochrome P-450-5. Nearly homogeneous staining was also observed in all hepatocytes for NADPH cytochrome c reductase and epoxide hydrolase. During the first 12 days in pure culture, the intensity of staining, as well as the number of positively stained cells, decreased slightly except for epoxide hydrolase, which did not show any obvious change. In contrast, even after 15 days in co-culture the extent of staining for all the enzymes decreased less than in pure culture. These results indicate that adult human hepatocytes continue to express specific drug-metabolizing enzymes for several days in culture and provide further evidence that those cells are more stable than rodent hepatocytes in primary culture.

Highly selective extraction of spiralin from the Spiroplasma citri cell membrane with alkyl-N-sulfobetaines

The extraction of proteins from the membrane of the mollicute (mycoplasma) Spiroplasma citri by sodium N-dodecyl-N,N-dimethyl-3-amino-1-propane sulfonate (SB12) and sodium N-tetradecyl-N,N-dimethyl-3-amino-1-propane sulfonate (SB14) was studied with electrophoretic methods. The membranes were prepared by osmotic lysis of the cells and depleted of the bulk of extrinsic proteins. It was possible to extract up to 35 and 45% of membrane proteins with SB12 and SB14, respectively. Maximal yield was obtained in both cases with detergent concentrations greater than or equal to 5 mumoles/mg of membrane protein. Spiralin, the major protein in the S. citri membrane, was highly selectively solubilized without the loss of antigenicity, with a yield of about 90% with SB12 and close to 100% with SB14, for a detergent concentration greater than or equal to 0.2 M. The degree of selectivity in favour of spiralin was higher with SB12 (purity approximately equal to 70%) than with SB14 (purity approximately equal to 50%). Treatment of the S. citri membrane with high concentrations of SB12 is a simple and fast procedure for partial purification of spiralin. This example shows that, in some cases, it should be possible to modulate the selectivity of the extraction of membrane proteins simply by varying the relative concentration of detergent.

Synthesis and phosphorylation of cytoskeleton components in foetal, regenerating and adult normal rat hepatocytes during culture

Detergent insoluble material (DIM) was prepared by gentle treatment with detergent from foetal, regenerating and adult normal rat hepatocytes cultured for various times. It retained to some degree the morphology of the cells. After incubation of intact cells with 35S-methionine, most of the labelled DIM proteins were found to be components of the cytoskeleton. They included several cytokeratins, vimentin and actin. The synthesis rate varied with the age of animals and culture conditions. The high synthetic rate of vimentin in foetal and regenerating hepatocytes could be associated with cell proliferation. No correlation was found between cytokeratin synthesis and hepatocyte growth. Most of the cytoskeleton proteins could be phosphorylated in intact cells and in DIM from cultured hepatocytes. However the degree of phosphorylation of these proteins was not related to their synthetic rate. The decreased phosphorylation level in cultured adult rat hepatocytes could be related to the rapid loss of specific functions.

Maintenance and reversibility of active albumin secretion by adult rat hepatocytes co-cultured with another liver epithelial cell type

When adult rat hepatocytes were co-cultured with another liver epithelial cell type in a medium supplemented or not with fetal calf serum (FCS), it was found that 1. They survived for more than 2 months 2. Albumin secretion levels remained high over the whole culture period 3. Decreased secretion might be reversed 4. This protein secretion activity appeared to be dependent upon both the presence of cell-cell contacts and the production of an extracellular material. The results demonstrate for the first time long-term stabilization and reversibility of a specific function (albumin secretion) at high levels by adult hepatocytes cultured in serum-free medium and suggest that both the presence of other liver cell type(s) and the production of an extracellular matrix are needed for the maintenance of specific functions in cultured hepatocytes.