Evidence for low nanocompaction of heterochromatin in living embryonic stem cells

Despite advances in the identification of chromatin regulators and genome interactions, the principles of higher-order chromatin structure have remained elusive. Here, we applied FLIM-FRET microscopy to analyse, in living cells, the spatial organisation of nanometre range proximity between nucleosomes, which we called "nanocompaction." Both in naive embryonic stem cells (ESCs) and in ESC-derived epiblast-like cells (EpiLCs), we find that, contrary to expectations, constitutive heterochromatin is much less compacted than bulk chromatin. The opposite was observed in fixed cells. HP1α knockdown increased nanocompaction in living ESCs, but this was overridden by loss of HP1β, indicating the existence of a dynamic HP1-dependent low compaction state in pluripotent cells. Depletion of H4K20me2/3 abrogated nanocompaction, while increased H4K20me3 levels accompanied the nuclear reorganisation during EpiLCs induction. Finally, the knockout of the nuclear cellular-proliferation marker Ki-67 strongly reduced both interphase and mitotic heterochromatin nanocompaction in ESCs. Our data indicate that, contrary to prevailing models, heterochromatin is not highly compacted at the nanoscale but resides in a dynamic low nanocompaction state that depends on H4K20me2/3, the balance between HP1 isoforms, and Ki-67.

Targeting the methyltransferase SETD8 impairs tumor cell survival and overcomes drug resistance independently of p53 status in multiple myeloma

Background

Multiple myeloma (MM) is a malignancy of plasma cells that largely remains incurable. The search for new therapeutic targets is therefore essential. In addition to a wide panel of genetic mutations, epigenetic alterations also appear as important players in the development of this cancer, thereby offering the possibility to reveal novel approaches and targets for effective therapeutic intervention.

Results

Here, we show that a higher expression of the lysine methyltransferase SETD8, which is responsible for the mono-methylation of histone H4 at lysine 20, is an adverse prognosis factor associated with a poor outcome in two cohorts of newly diagnosed patients. Primary malignant plasma cells are particularly addicted to the activity of this epigenetic enzyme. Indeed, the inhibition of SETD8 by the chemical compound UNC-0379 and the subsequent decrease in histone H4 methylation at lysine 20 are highly toxic in MM cells compared to normal cells from the bone marrow microenvironment. At the molecular level, RNA sequencing and functional studies revealed that SETD8 inhibition induces a mature non-proliferating plasma cell signature and, as observed in other cancers, triggers an activation of the tumor suppressor p53, which together cause an impairment of myeloma cell proliferation and survival. However, a deadly level of replicative stress was also observed in p53-deficient myeloma cells treated with UNC-0379, indicating that the cytotoxicity associated with SETD8 inhibition is not necessarily dependent on p53 activation. Consistent with this, UNC-0379 triggers a p53-independent nucleolar stress characterized by nucleolin delocalization and reduction of nucleolar RNA synthesis. Finally, we showed that SETD8 inhibition is strongly synergistic with melphalan and may overcome resistance to this alkylating agent widely used in MM treatment.

Conclusions

Altogether, our data indicate that the up-regulation of the epigenetic enzyme SETD8 is associated with a poor outcome and the deregulation of major signaling pathways in MM. Moreover, we provide evidences that myeloma cells are dependent on SETD8 activity and its pharmacological inhibition synergizes with melphalan, which could be beneficial to improve MM treatment in high-risk patients whatever their status for p53.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-021-01160-z.

The 20S proteasome activator PA28γ controls the compaction of chromatin

PA28γ (also known as PSME3), a nuclear activator of the 20S proteasome, is involved in the degradation of several proteins regulating cell growth and proliferation and in the dynamics of various nuclear bodies, but its precise cellular functions remain unclear. Here, using a quantitative FLIM-FRET based microscopy assay monitoring close proximity between nucleosomes in living human cells, we show that PA28γ controls chromatin compaction. We find that its depletion induces a decompaction of pericentromeric heterochromatin, which is similar to what is observed upon the knockdown of HP1β (also known as CBX1), a key factor of the heterochromatin structure. We show that PA28γ is present at HP1β-containing repetitive DNA sequences abundant in heterochromatin and, importantly, that HP1β on its own is unable to drive chromatin compaction without the presence of PA28γ. At the molecular level, we show that this novel function of PA28γ is independent of its stable interaction with the 20S proteasome, and most likely depends on its ability to maintain appropriate levels of H3K9me3 and H4K20me3, histone modifications that are involved in heterochromatin formation. Overall, our results implicate PA28γ as a key factor involved in the regulation of the higher order structure of chromatin.

Cell-cycle regulation of non-enzymatic functions of the Drosophila methyltransferase PR-Set7

Tight cell-cycle regulation of the histone H4-K20 methyltransferase PR-Set7 is essential for the maintenance of genome integrity. In mammals, this mainly involves the interaction of PR-Set7 with the replication factor PCNA, which triggers the degradation of the enzyme by the CRL4CDT2 E3 ubiquitin ligase. PR-Set7 is also targeted by the SCFβ-TRCP ligase, but the role of this additional regulatory pathway remains unclear. Here, we show that Drosophila PR-Set7 undergoes a cell-cycle proteolytic regulation, independently of its interaction with PCNA. Instead, Slimb, the ortholog of β-TRCP, is specifically required for the degradation of the nuclear pool of PR-Set7 prior to S phase. Consequently, inactivation of Slimb leads to nuclear accumulation of PR-Set7, which triggers aberrant chromatin compaction and G1/S arrest. Strikingly, these phenotypes result from non-enzymatic PR-Set7 functions that prevent proper histone H4 acetylation independently of H4K20 methylation. Altogether, these results identify the Slimb-mediated PR-Set7 proteolysis as a new critical regulatory mechanism required for proper interphase chromatin organization at G1/S transition.

Histone H4K20 tri-methylation at late-firing origins ensures timely heterochromatin replication

Among other targets, the protein lysine methyltransferase PR-Set7 induces histone H4 lysine 20 monomethylation (H4K20me1), which is the substrate for further methylation by the Suv4-20h methyltransferase. Although these enzymes have been implicated in control of replication origins, the specific contribution of H4K20 methylation to DNA replication remains unclear. Here, we show that H4K20 mutation in mammalian cells, unlike in Drosophila, partially impairs S-phase progression and protects from DNA re-replication induced by stabilization of PR-Set7. Using Epstein-Barr virus-derived episomes, we further demonstrate that conversion of H4K20me1 to higher H4K20me2/3 states by Suv4-20h is not sufficient to define an efficient origin per se, but rather serves as an enhancer for MCM2-7 helicase loading and replication activation at defined origins. Consistent with this, we find that Suv4-20h-mediated H4K20 tri-methylation (H4K20me3) is required to sustain the licensing and activity of a subset of ORCA/LRWD1-associated origins, which ensure proper replication timing of late-replicating heterochromatin domains. Altogether, these results reveal Suv4-20h-mediated H4K20 tri-methylation as a critical determinant in the selection of active replication initiation sites in heterochromatin regions of mammalian genomes.

Coupling mitosis to DNA replication: the emerging role of the histone H4-lysine 20 methyltransferase PR-Set7

To ensure accurate inheritance of genetic information through cell proliferation, chromosomes must be precisely copied only during S phase, and then correctly condensed and segregated during mitosis. Several new findings suggest that this tight coupling between DNA replication and mitosis is in part controlled by cell cycle regulated chromatin modifications, in particular due to the changing activity of lysine methyltransferase PR-Set7/SET8 that is responsible for the monomethylation of histone H4 at lysine 20. Cell cycle oscillation of PR-Set7 is orchestrated by ubiquitin-mediated proteolysis, and interference with this regulatory process leads to unscheduled licensing of replication origins and altered timing of mitotic chromosome compaction. This review provides an overview of how PR-Set7 regulates these two cell cycle events and highlights questions that remain to be addressed.

Form and function of dosage-compensated chromosomes--a chicken-and-egg relationship

Does the three-dimensional (3D) conformation of interphase chromosomes merely reflect their function or does it actively contribute to gene regulation? The analysis of sex chromosomes that are subject to chromosome-wide dosage compensation processes promises new insight into this question. Chromosome conformations are dynamic and largely determined by association of distant chromosomal loci in the nuclear space or by their anchoring to the nuclear envelope, effectively generating chromatin loops. The type and extent of such interactions depend on chromatin-bound transcription regulators and therefore reflects function. Dosage compensation adjusts the overall transcription activity of X chromosomes to assure balanced expression in the two sexes. Initial analyses of mammalian and Drosophila X chromosomes have led to the hypothesis that their conformations may not only reflect their functional state but may in turn contribute to the coordination of chromosome-wide tuning of transcription.

The dosage compensation complex shapes the conformation of the X chromosome in Drosophila

The dosage compensation complex (DCC) in Drosophila globally increases transcription from the X chromosome in males to compensate for its monosomy. We discovered a male-specific conformation of the X chromosome that depends on the associations of high-affinity binding sites (HAS) of the DCC. The core DCC subunits MSL1-MSL2 are responsible for this male-specific organization. Contrary to emerging concepts, we found that neither DCC assembly nor the conformation of the male X chromosome are influenced by nuclear pore components. We propose that nuclear organization of HAS is central to the faithful distribution of the DCC along the X chromosome.

From genetics to epigenetics: the tale of Polycomb group and trithorax group genes

The Polycomb gene was discovered 60 years ago as a mutation inducing a particular homeotic phenotype. Subsequent work showed that Polycomb is a general repressor of homeotic genes. Other genes with similar function were identified and named Polycomb group (PcG) genes, while trithorax group (trxG) genes were shown to counteract PcG-mediated repression of homeotic genes. We now know that PcG and trxG proteins are conserved factors that regulate hundreds of different genomic loci. A sophisticated pathway is responsible for recruitment of these proteins at regulatory regions that were named PcG and trxG response elements (PRE and TRE). Once recruited to their targets, multimeric PcG and trxG protein complexes regulate transcription by modulating chromatin structure, in particular via deposition of specific post-translational histone modification marks and control of chromatin accessibility, as well as regulation of the three-dimensional nuclear organization of PRE and TRE. Here, we recapitulate the history of PcG and trxG gene discovery, we review the current evidence on their molecular function and, based on this evidence, we propose a revised classification of genes involved in PcG and trxG regulatory pathways.

RNAi Components Are Required for Nuclear Clustering of Polycomb Group Response Elements

Drosophila Polycomb group (PcG) proteins silence homeotic genes through binding to Polycomb group response elements (PREs). Fab-7 is a PRE-containing regulatory element from the homeotic gene Abdominal-B. When present in multiple copies in the genome, Fab-7 can induce long-distance gene contacts that enhance PcG-dependent silencing. We show here that components of the RNA interference (RNAi) machinery are involved in PcG-mediated silencing at Fab-7 and in the production of small RNAs at transgenic Fab-7 copies. In general, these mutations do not affect the recruitment of PcG components, but they are specifically required for the maintenance of long-range contacts between Fab-7 copies. Dicer-2, PIWI, and Argonaute1, three RNAi components, frequently colocalize with PcG bodies, and their mutation significantly reduces the frequency of PcG-dependent chromosomal associations of endogenous homeotic genes. This suggests a novel role for the RNAi machinery in regulating the nuclear organization of PcG chromatin targets.

Recruitment of Drosophila Polycomb group proteins to chromatin by DSP1

Polycomb and trithorax group (PcG and trxG) proteins maintain silent and active transcriptional states, respectively, throughout development. In Drosophila, PcG and trxG proteins associate with DNA regions named Polycomb and trithorax response elements (PRE and TRE), but the mechanisms of recruitment are unknown. We previously characterized a minimal element from the regulatory region of the Abdominal-B gene, termed Ab-Fab. Ab-Fab contains a PRE and a TRE and is able to maintain repressed or active chromatin states during development. Here we show that the Dorsal switch protein 1 (DSP1), a Drosophila HMGB2 homologue, binds to a sequence present within Ab-Fab and in other characterized PREs. Addition of this motif to an artificial sequence containing Pleiohomeotic and GAGA factor consensus sites is sufficient for PcG protein recruitment in vivo. Mutations that abolish DSP1 binding to Ab-Fab and to a PRE from the engrailed locus lead to loss of PcG protein binding, loss of silencing, and switching of these PREs into constitutive TREs. The binding of DSP1 to PREs is therefore important for the recruitment of PcG proteins.

Inheritance of Polycomb-dependent chromosomal interactions in Drosophila

Maintenance of cell identity is a complex task that involves multiple layers of regulation, acting at all levels of chromatin packaging, from nucleosomes to folding of chromosomal domains in the cell nucleus. Polycomb-group (PcG) and trithorax-group (trxG) proteins maintain memory of chromatin states through binding at cis-regulatory elements named PcG response elements or cellular memory modules. Fab-7 is a well-defined cellular memory module involved in regulation of the homeotic gene Abdominal-B (Abd-B). In addition to its action in cis, we show here by three-dimensional FISH that the Fab-7 element leads to association of transgenes with each other or with the endogenous Fab-7, even when inserted in different chromosomes. These long-distance interactions enhance PcG-mediated silencing. They depend on PcG proteins, on DNA sequence homology, and on developmental progression. Once long-distance pairing is abolished by removal of the endogenous Fab-7, the derepressed chromatin state induced at the transgene locus can be transmitted through meiosis into a large fraction of the progeny, even after reintroduction of the endogenous Fab-7. Strikingly, meiotic inheritance of the derepressed state involves loss of pairing between endogenous and transgenic Fab-7. This suggests that transmission of nuclear architecture through cell division might contribute to inheritance of chromatin states in eukaryotes.

[Development of a self-administered questionnaire to assess women's satisfaction with maternity care]

OBJECTIVES

We describe the development and the validation of a French self-administered questionnaire which measures women satisfaction concerning care given during pregnancy. The analysis includes pregnancy monitoring, hospitalization for delivery and homecoming.

METHODS

We considered the content validity, internal-consistency and the reproducibility by test-retest estimates. This survey also compared the characteristics of respondents and non-respondents.

RESULTS

Response rate was 61% and the rate of reply per question was greater than 90%. Eleven dimensions are identified by principal-components analysis. Ten of them had good Cronbach's alpha coefficients (0.58 to 0.83). The convergence between open comments and questions and between the different methods to measure satisfaction was good. The test-retest estimates for each dimension were correct.

CONCLUSION

This questionnaire is reliable. It is a valid tool for evaluation of satisfaction after pregnancy. Designed to be sent to the woman's residence 2 months after childbirth, it can be easily used in common practice.

Laryngeal afferents activated by phenyldiguanide and their response to cold air or helium-oxygen

In anesthetized cats, sensory neurons in the superior laryngeal nerves (SLN) were identified with respect to their response to (1) phenyldiguanide (PDG) i.v., (2) mechanical stimulation and (3) lowering temperature in an isolated tracheolaryngeal segment. The activity originating from 107 SLN afferent units activated by PDG was recorded using glass microelectrodes advanced in the nodose ganglion. All tested afferent units increased their discharge rate during direct touching of the airway mucosa. None showed flow or pressure related activity during abrupt changes in constant laryngeal flow or transmural pressure in the isolated segment. Fifteen units were inhibited by cold air. Sixty-two units significantly increased their firing rate when the temperature approached 18 degrees C, reached a peak discharge near 15 degrees C, then their activity decreased or stopped. The response to cold air was compared to cold heliox (79% He-21% O2), which enhanced the respiratory heat loss by conduction. The peak firing rate was significantly higher with heliox (+356% compared to +246% with air), the temperature threshold higher (25 degrees C +/- 1.0 degree C) and the temperature range broader (25-11.5 degrees C). Present results show that a large proportion (58%) of afferent SLN fibres activated by PDG are likely non-proprioceptive units, which are stimulated by cooling the inspired gas. Thermosensitive units in the upper airways may act as sensors of the thermal flux through the airway wall more than as detectors of the absolute value of temperature in the airway lumen.

Role of vagal and spinal sensory pathways in diaphragmatic response to resistive loading

The effects of severe inspiratory (I) or expiratory (E) resistive loads on diaphragmatic activity were studied in two groups of cats anaesthetized with sodium pentobarbital or ethylcarbamate-chloralose. In intact cats, I or E loading never changed the amplitude of integrated diaphragmatic electric myogram (EMG) measured at 1.0 s (Edi 1.0); only I loading, prolonged the duration of diaphragmatic activity (Tdi). After selective procaine block of non-volume related vagal sensory inputs, I or E loading markedly increased Edi 1.0 and changes in Tdi due to I loading persisted. After bivagotomy, which also suppressed volume related vagal feed back, Edi 1.0 increased during I or E loading but change in Tdi disappeared. Initial spinal section at C8 level only reduced changes in Tdi with inspiratory loading. Bivagotomy plus spinal section abolished all load induced changes in diaphragmatic activity. These results suggest that all vagal information from the lungs participate in the mechanism of load compensation but that spinal sensory pathways play a minor role in this response in anaesthetized cats.

Increased ventilatory chemosensitivity induced by domperidone, a dopamine antagonist, in healthy humans

Respiratory and cardiovascular effects of domperidone (0.1 mg X kg-1 i.v.) and placebo given on separate test days to eleven healthy volunteers were assessed in a double-blind study. Domperidone caused no significant change in ventilation, heart rate and blood pressure while they were resting and breathing room air. However, it produced an increase in the slope of the hypoxia-induced ventilatory response, from 2.35 +/- 1.10 to 3.71 +/- 2.91 1 X min-1 per 1% decrease in SaO2 (mean +/- SD; p less than 0.05). We conclude that domperidone augments hypoxic responsiveness in humans, presumably by blocking the dopaminergic receptors that modulate the activity of carotid body chemoreceptors, as it does not readily cross the blood-brain barrier.

Breathing discomfort in asthma: role of adaptation level

In asthmatic patients, Helson's adaptation level theory was applied to breathing discomfort to investigate the discrepancy between the subjective severity of breathlessness and their objective airflow obstruction. The data from a signal detection methodology show a considerable loss of sensitivity in twelve asthmatic patients with permanent airflow obstruction compared to the high sensitivity of six normal subjects to the same four external resistive loads (range 2.5 to 8.0 cmH2O X l-1 X s). Furthermore, when subjective ratings are examined, the absence of any contrast effect between adjacent load intensities in asthmatics suggests that these subjects evaluate the discomfort induced by the loads with reference to a strong internal comparison (adaptation level) rather than to the experimental stimuli. There was no relationship between physiological parameters and the low sensitivity of asthmatics. Also salbutamol-induced bronchodilation in six asthmatics did not improve sensitivity or induce any contrast effect. These two observations bring out the necessity to consider the role of past experience of breathing discomfort on adaptation level and sensitivity.

The effects of ischemia, lactic acid and hypertonic sodium chloride on phrenic afferent discharge during spontaneous diaphragmatic contraction

In 9 sodium pentobarbital anaesthetized cats, 50 single-unit phrenic afferent recordings were determined during spontaneous ventilation, retrograde carotid arterial injection of lactic acid (LA, 0.1 N) and NaCl (5%), and a 2-min occlusion of the superior thoracic aorta. Fifty percent of the units had tonic low-frequency spontaneous discharge; 50% had phasic high-frequency discharge. Tonic fiber activity increased significantly with LA, NaCl and occlusion, while phasic fiber activity decreased in all 3 conditions. These results suggest that the diaphragm contains sensory endings sensitive to ischemia and extracellular metabolic changes.

Effects of airflow resistance variations on resistive load detection in normal subjects

The sensitivity to airflow resistance variations produced by externally added resistive loads, with modification of background load, was studied in 15 normal subjects, using "Sensory Decision Theory" (SDT), a psychophysical method that gives an index of accuracy, P(A), unaffected by response bias. In six subjects, asked to detect three increasingly added loads (delta R) at different levels of basal resistance (1.6 and 3.6 cmH2O X 1(-1) X s), inspiratory resistive load detection (RLD) improved with background loading, and a highly significant relationship was found between P(A) and peak mouth pressure (Pm). The relationship between P(A) and the change in Pm, i.e. delta Pm, was less significant. These results suggest that, although tension developed by the respiratory muscles reflected by mouth pressure may be an important stimulus to respiratory RLD, other factors must also be considered. In seven subjects, in whom airway resistance was increased at least 50% by inhalation of carbachol, inconsistent variations in P(A) were found. In seven subjects, in whom airflow resistance was decreased by inhalation of heliox, and in six of seven subjects after salbutamol inhalation, RLD was significantly impaired. The results of this study lead us to the conclusion that Weber's law is not verified for weak internal or external background loading.

Phrenic afferents and their role in inspiratory control

In anesthetized cats, with vagi cut and the spinal cord severed at the C8 level, phrenic motor and/or sensory discharge was recorded. Small afferent phrenic fibers were identified through their activation by lactic acid, hyperosmotic NaCl solution, or phenyl diguanide. They exhibited a spontaneous but irregular low-frequency discharge. Block of their conduction by procaine had no effect on eupneic motor phrenic activity. Large afferent phrenic fibers showed a spontaneous rhythmic discharge, and cold block (6 degrees C) of these fibers significantly prolonged the phrenic discharge time (Tphr) and total breath duration (TT) during eupnea. The stimulation of all afferent phrenic fibers lowered the impulse frequency of phrenic motoneurons (f impulses) and shortened both Tphr and TT. When the stimulation was performed during cold block all of the effects on phrenic output persisted, but changes in timing were less pronounced. Under procaine block, only the effects of phrenic nerve stimulation on Tphr persisted. These results suggest that both large and small afferent phrenic fibers control the inspiratory activity with a prominent role of small fibers on phrenic motoneuron impulse frequency.

Cold-induced bronchospasm in normal and sensitized rabbits

In anesthetized, paralyzed and artificially ventilated rabbits, changes in lung resistance induced by cooling the inspired air were studied under dry air conditions. Airway response to cold was measured in normal animals and in rabbits sensitized to bovine serum albumin. The magnitude of cold-induced bronchospasm was significantly greater in sensitized than in normal rabbits but the time course for recovery of control lung resistance during rewarming was the same in both groups and lasted longer than 4 min. Inhalation of a nebulized aerosol of sodium cromoglycate (SCG) markedly reduced cold-induced bronchospasm and shortened the recovery period, which then lasted only 20 to 30 sec. Vagotomy abolished the airway response to cold air in all cases and this was observed whether the vagus nerves were cut before or after SCG inhalation. SCG or vagotomy exerted the same effect on the response to cold air in normal or sensitized rabbits. Sensitized animals showed an hyperresponsiveness to histamine as well as to cold air. These results suggest that cold-induced bronchospasm results from a vagally mediated reflex whose effects are only enhanced and prolonged by a local release of humoral factors, linked to the reflex path. The increased response to cold air in the sensitized rabbits seems to correspond to non-specific hyperresponsiveness of bronchial smooth muscle rather than to an increased local release of inflammatory mediators.

Role of vagal and spinal sensory pathways on eupneic diaphragmatic activity

The interactions between vagal and spinal afferents in the control of eupneic diaphragmatic activity were studied in two groups of cats anesthetized either with pentobarbital sodium (SPB) or with ethyl carbamate-alpha-chloralose (ECC), which enhanced spinal reflexes. Under both conditions of anesthesia two experimental protocols were performed: 1) bilateral cervical vagotomy followed by spinal section at C8 level or 2) spinal section followed by vagotomy. Changes in integrated diaphragmatic activity (Edi) were studied during eupneic ventilation and tracheal occlusion at end expiration. Vagotomy always significantly increased the amplitude of Edi during eupnea (SPB + 30%; ECC + 15%) and prolonged its duration (Tdi) (SPB + 110%; ECC + 75%) but did not modify the overall shape of the Edi vs. time relationship. Spinal section induced reverse changes in the amplitude of Edi, whether vagal afferents were present or suppressed and modified the shape of the Edi wave, but did not significantly modify Tdi. These results indicate that both vagal and spinal afferents may participate in the control of eupneic inspiration but exert different and interdependent influences on the recruitment and firing time of phrenic motoneurons. In addition, Tdi measured during tracheal occlusion (Todi) was markedly prolonged under ECC anesthesia. In this situation spinal section reduced Todi, which became close to the values obtained in intact or spinal cats under SPB anesthesia. Thus the response to tracheal occlusion at end expiration cannot be interpreted as resulting from the sole suppression of volume related vagal information.

Pulmonary function and electromyographic study of respiratory muscles in myotonic dystrophy

Ten adult myotonic dystrophy patients underwent measurements of lung function, maximal dynamic and static ventilatory efforts, and respiratory muscle electromyography (EMG). EMG studies were performed during spontaneous breathing or when subjects breathed through high inspiratory or expiratory resistive loads. Present results show that (1) a moderate restriction of lung volumes with hypoxemia plus normocapnia is often observed; (2) patients sustain dynamic ventilatory efforts more easily than static work; and (3) abnormalities in respiratory muscle EMG exist with spontaneous expiratory and inspiratory intercostal activities during quiet breathing and changes in muscular response to resistive loads. Inspiratory loading evokes contraction of expiratory muscles, with a marked decrease in inspiratory activities. Expiratory resistive loads prolong the diaphragmatic contraction throughout the expiratory time, and in some patients, relaxation of the diaphragm does not occur during the loaded run. These EMG data suggest that the reciprocal inhibition among respiratory neurons is enhanced in myotonic dystrophy and that myotonia also occurs in the diaphragm when loads oppose its relaxation.

Ventilatory effects of domperidone, a new dopamine antagonist, in anaesthetized rabbits

The ventilatory effects of domperidone (DP), a dopamine antagonist that does not cross the blood-brain barrier, were studied on rabbits anaesthetized with pentobarbitone. DP induced hyperventilation (+20%), which was not dose-dependent, without any marked change in arterial blood gases. This effect was abolished by previous transection of both carotid sinus nerves. On an average, steady state hypoxia (PaO2 approximately 45 mmHg for 5 min) doubled ventilation before, and increased itself threefold after DP (0.10 mg kg-1 i.v.). Prazosin (PZ, 0.1 mg kg-1 i.v.), an alpha 1-adrenoceptor antagonist, induced hyperventilation (+16%) but decreased systemic arterial blood pressure. PZ did not modify the ventilatory response to steady state hypoxia. In short, DP has a slight stimulating effect on resting ventilation and potentiates the ventilatory response to steady state hypoxia. This last effect would not depend on additional alpha 1-adrenoceptor antagonism of DP, as PZ does not change the ventilatory response to hypoxia.

Inspiratory and expiratory resistive load detection in normal and asthmatic subjects. A sensory decision theory analysis

The ability to detect added external inspiratory and expiratory resistive loads was studied in normal and asthmatic subjects using sensory decision theory as a psychophysical method. Performances P(A)/delta R [where P(A) represents the index of sensitivity and delta R the additional resistor] were similar in normal and asthmatic subjects, but when sensitivity was expressed in relation to airway resistance [P(A)/delta R/Raw], asthmatics showed higher inspiratory and expiratory performances than normal subjects. After bronchodilation the relative sensitivity in the asthmatic group was impaired and approached that of normal subjects. Comparing inspiratory and expiratory load detection, normal subjects showed a higher sensitivity for expiratory than for inspiratory loads. In contrast, there was no difference in the asthmatic group. The response bias remained the same across conditions. If one accepts the assumption that the variability of sensitivity presented by asthmatic and normal subjects might be related to the variable state of their pulmonary function, our results can be interpreted as demonstrating a relationship between sensitivity and pulmonary distension or airway obstruction. These results are in agreement with the hypothesis that the site of perception for respiratory load detection is the chest wall.

[Influence of chronic smoking on leukocytes]

The authors showed a significant increase in total leukocyte count (2p less than 0.001), neutrophil concentration (2p less than 0.001) and lymphocyte concentration (2p less than 0.01) in 21 chronic smokers compared to 22 non-smokers. However, only the total leukocyte count and the neutrophil count proved to be correlated to carboxyhemoglobin saturation. Slightly different hypotheses are proposed to explain the increase in leukocyte count: the carbon monoxide and/or the carboxyhemoglobin acts directly on peripheral blood leukocytes or indirectly, via the adrenalin secretion. The average leukocyte count in smokers corresponds to the upper borderline in nonsmokers; therefore, it seems pertinent to take into consideration the number of cigarettes smoked per day when assessing a smoker's leukocytosis.

Comparative reflex action of histamine, acetylcholine and serotonin on dog airways

To dissociate airway stimulation from airway response, a segment of the cervical trachea was isolated from the rest of the bronchial tree in 15 anesthetized dogs; nerve and blood supplies of the segment were preserved. Patency of the intrathoracic airways was assessed with lung resistance (RL) measurements. When doses of aerosolized histamine (His), acetylcholine (ACh) and serotonin (Ser) causing comparable increases in RL were delivered into the intrathoracic airways, concomitant increases in pressure were recorded in the tracheal segment (indicating constriction) with His being the most effective. When the hypoxemia accompanying His- and ACh-induced bronchoconstriction was prevented by inhaling an air-oxygen mixture, the tracheal response persisted (2 dogs). Vagotomy decreased the RL response to His, ACh and Ser and abolished tracheal response (13 dogs). The tracheal response was still abolished when larger doses of His and ACh were given in order to induce an increase in RL similar to that observed before vagotomy (7 dogs). These data suggest the existence of a positive feed-back mechanism in the airways, pharmacological bronchoconstriction causing vagally mediated reflex bronchoconstriction. Direct stimulation of lung irritant receptors by histamine may explain the larger degree of reflex bronchoconstriction observed with this agent.

[Tobacco consumption and carboxyhemoglobin levels in blood donors]

The authors studied the tobacco consumption of 283 blood donors and its consequences. 151 were nonsmokers and 132 were smokers (47.7% smoke more than 10 g/day). Their mean HbCO level was 4.3 +/- 0.2% (highest level 15%). HbCO levels are significantly correlated with daily tobacco consumption (p less than 0.001) and can be estimated with the following regression equation: HbCO% = 0.176 (tobacco in grams/day) + 1.976. For a similar consumption, inhalers exhibit significantly (p less than 0.001) higher HbCO levels than noninhalers and the increase is significantly higher (p less than 0.02) in inhalers who smoked 1 h or less prior to blood sampling. High HbCO levels have two consequences: in the donors they have caused a tobacco polycythemia syndrome and in the recipients they have caused acute problems in cases of massive blood transfusion and cardiovascular surgery with extracorporeal circulation.

Airway response of asthmatics to carbachol and to deep inspiration

Dose-response curves were established in asthmatics by using graded doses of aerosolized carbachol and specific airway conductance (SGaw) measurements. After carbachol inhalation, we evaluated the influence on SGaw of a deep inspiration to total lung capacity followed by a passive expiration to functional residual capacity. When SGaw had returned to its pre-deep-inspiration value, forced expiratory volume in one second (FEV1) was obtained. Two groups of patients were selected according to the effect of deep inspiration on SGaw: group A (22 patients) with a less than 25% SGaw increase after deep inspiration, and group B (21 patients) with a more than 75% SGaw increase. Both groups were comparable in age and initial SGaw and FEV1 values. Carbachol inhalation induced a similar SGaw decrease in both groups, whereas FEV1 decreased more (p less than 0.05) in group A than in group B. The two groups did not differ significantly regarding the dose of carbachol causing a 25% SGaw decrease and in the slope of the dose-response curve. We conclude that, in asthmatic patients, airway response to an inhaled broncho-constrictor agent is not related to the airway response to deep inspiration. This suggests that previous studies of airway response to bronchoconstrictor agents which have been performed by using only FEV1 measurements, may need to be reassessed.

Ventilatory responses to muscular vibrations in healthy humans

In healthy humans, we studied the effect of high-frequency mechanical vibrations applied unilaterally to the tendon of the biceps or triceps brachialis on ventilation and the breathing pattern. This stimulus preferentially activates the muscle spindle afferents. Increase of respiratory frequency and changes in the ventilatory timing started at the first or second inspiration during tendon stimulation, and no adaptation occurred as long as the vibrations continued. The tidal volume and mean inspiratory flow rate were only enhanced in individuals having high-frequency breathing during eupnea. The changes in ventilatory variables were observed when the motor response to vibrations was tested under isometric or isotonic conditions. Various experimental procedures enabled us to induce a tonic reflex contraction in either the vibrated muscle or the antagonist of no reflex contraction in either group of muscles. In all cases the increase in minute ventilation was identical. These changes in breathing pattern was not associated with a significant decrease in alveolar CO2 pressure and did not seem to be responsible for important variations in respiratory gas exchanges. The response to high-frequency vibrations was also studied after ventilation was increased with added dead space. The magnitude of hyperventilation an the pattern of ventilatory response produced by tendon stimulation did not change with increased ventilation. In conclusion, the stimulation of muscle spindles in human induces changes in ventilation and pattern of breathing , and the occurrence of a reflex muscular contraction does not seem necessary in order to obtain such effects.

Changes in activity of vagal bronchopulmonary C fibres by chemical and physical stimuli in the cat

1. In eighteen anaesthetized cats, action potentials in non-myelinated vagal afferent neurones were recorded in the nodose ganglion by means of extracellular micro-electrodes. 2. The pulmonary or bronchial origin of these C fibres was assessed in closed chest preparations by injecting phenyl diguanide into either the right atrium or the ascending aorta (bronchial circulation). This was confirmed in two animals by local mechanical stimulation. 3. Eighty per cent of bronchopulmonary C fibres increased their discharge frequency when the end-tidal CO2 concentration (FA,CO2) increased from 0.02 to 0.10. Most of these C endings showed a maximal response when FA,CO2 reached 0.04. For the others a further increase in discharge occurred when CO2 concentration reached 0.08-0.10. Continuous measurement of C fibre discharge frequency indicated that they detected preferentially changes in the inspired CO2 content, but adapted when a high CO2 level was maintained. Their activation by hypercapnia was followed by an increase in lung resistance. 4. Lowering the O2 content of the inspired gas had no effect on the spontaneous activity of bronchopulmonary C endings. 5. When the stroke volume of the pump was doubled, the spontaneous activity of bronchopulmonary C fibres decreased in intact chest preparations. Inflation of the lungs had the opposite effect after the chest was opened. In both cases hyperdeflation was a potent stimulus to these receptors. 6. In tracheotomized cats, the tracheal temperature was 28-29 degrees C. When normal thermal conditions were restored in the tracheal lumen (33-34 degrees C) the spontaneous discharge frequency of some bronchial C fibres was greatly increased. 7. It is concluded that the spontaneous activity of most of the bronchial or pulmonary C fibres was maximal when chemical and physical physiological conditions were restored in the lungs. It appears that changes in alveolar CO2 concentration constitute the usual stimulus for these fibres.

Influence of anxiolytic drugs (Prazepam and Diazepam) on respiratory center output and CO2 chemosensitivity in patients with lung diseases

Occlusion pressure at 0.1 s (P0.1) and its evolution during progressive hyperoxic hypercapnia (CO2 chemosensitivity) were measured in 40 patients. Most of them (26) were affected by asthma and /or chronic bronchitis and had mild obstruction and hypoxemia. Measurements were made after 2 days of oral prazepam, diazepam or a placebo (single-blind study). Diazepam induced a significant decrease in P0.1 without affecting CO2 chemosensitivity. In contrast, prazepam did not significantly modify P0.1 or CO2 chemosensitivity. However, P0.1 decreased in 5/18 individual cases. 1 week of treatment by prazepam has advantages over diazepam by not depressing respiratory center output.

Pulmonary mechanics during hypoxia in spontaneously breathing anesthetized rabbits

Changes in lung mechanics were measured during hypoxia (FIO2 = 0.10 during 5 min) in spontaneously breathing anesthetized rabbits. In intact animals, hypoxia induced scattered variations in total lung resistance (RL) (decrease, increase or no alteration) and dynamic lung compliance (CL), whereas in carotid body denervated animals it was accompanied by an almost constant decrease in RL (-12%); but if a subsequent vagotomy was performed, there was no significant variation in RL. In animals which had been only vagotomized, CL decreased significantly during hypoxia (-23%) without any associated change in RL. So, the arterial chemoreceptor mediated bronchoconstrictor effects due to hypoxia could be normally masked by the dilator effects (metabolic and/or sympathetic) on the airways.

The interaction between indomethacin and contractile agents on human isolated airway muscle

1 Concentration-effect curves to acetylcholine and histamine were produced in fresh human bronchial muscle (2 to 4 h after removal from the patients) and in preparations previously stored at 4 degrees C for 12 h. 2 Sensitivities of fresh human airway muscle preparations to acetylcholine (pD2 value, 5.89 +/- 0.03; n = 4) and histamine (pD2 values, 5.41 +/- 0.03; n = 13) were similar. There was no significant difference in the sensitivities of stored preparations (acetylcholine: pD2 value, 5.70 +/- 0.06; n = 23 and histamine: pD2 value, 5.44 +/- 0.07; n = 16) when compared to the fresh preparations. 3 Indomethacin did not significantly change the basal tone in preparations of either fresh or stored human airway muscle. 4 A low concentration of indomethacin (0.17 muM) significantly reduced responsiveness and sensitivity to histamine in stored bronchi but not in fresh bronchi. The acetylcholine concentration-effect curves were unaltered by exposure to this concentration of indomethacin in either fresh or stored tissues. High concentrations (1.7 muM and 17 muM) depressed the maximal responsiveness of the bronchi to both agonists. 5 These results suggest indirectly that the regulatory role of prostaglandins in human airway muscle may be different from that in other species.

[Asthma-tobacco interaction and alterations of maximal expiratory flow in air and in helium-oxygen (author's transl)]

The eventual interaction between tobacco and asthma and the sensitivity of different functional tests on small airways are compared in 4 groups of subjects (n = 49): non-smokers and control smokers, asthmatic non-smokers and smokers. All subjects have a normal vital capacity (VC) and a normal forced expiratory volume in one second (FEV1). The measurement of mid expiratory time (MET) and maximal flow at 50% (V Max 50) and at 25% (V Max 25) of the flow volume curve in air (FEMV) does not have any discriminating advantages over the simple measurement of the ratio FEV1/VC. The latter, although always normal, differentiates the controls from the asthmatic non-smokers. Besides, helium independency (characterized by an increase in the V Max 50 air-helium less than 20% and an increase of volume iso flow [V iso V] beyond 20% of VC) is mostly linked to tobacco addiction but is definitely worsened when associated to asthma.

Assessment of the central chemosensitivity in man under transient or progressive hypercapnia

In healthy man, the central chemosensitivity to CO2 was studied after depression of the arterial chemoreflex drive by inhalation of pure oxygen. The effectiveness of the functional decrease of arterial chemoreceptor function was assessed by the delayed hyperventilation which followed transient inhalation of hypercapnic gas mixtures for 3 or 5 breaths in hyperoxic conditions. In such a case the first significant increase in tidal volume (VT) occurred 13.9 +/- 3.2 (SE) sec later than the early change in this variable measured in normoxic conditions. The stimulus strength was estimated by the change in CO2 partial pressure in end-tidal alveolar gas (delta PETCO2). The central chemosensitivity (SCO2), defined as the ratio between change in ventilation (delta V) and delta PETCO2, was assessed either by transient inhalation of gas mixtures containing 5 to 8% CO2 in pure O2 ("varying transients") or by progressive hypercapnia (rebreathing in pure O2). In both cases, the first significant change in ventilation was due to an increase in VT, but, for a given delta PETCO2, VT changes were higher during rebreathing than after transient hypercapnia; (2) The respiratory frequency (fR) was progressively enhanced during rebreathing (shortening of expiratory duration in all cases and of inspiratory time in some subjects) but the ventilatory rhythm diminished after transient stimulation as soon as delta PETCO2 reached one kPa, and this was due to an increase in inspiratory duration; (3) The associated changes in VT and fR during rebreathing could explain that SCO2 values given by this method were 5.2 times greater than after transient hypercapnia ("varying tests"). The differences are discussed in terms of, (1) isolated changes in arterial PCO2 or associated decrease in pH of the cerebrospinal fluid; (2) changes in brain blood flow, and (3) stimulation of lung stretch receptors by the important increase in VT during rebreathing.

[Smoking and carbon monoxide consumption (author's transl)]

Among 2,069 patients subjected to pulmonary function tests, 20% were smokers with a mean oxyhemoglobin (HbCO) level of 5.2%. Similar values for HbCO (2.4%) were found in non-smokers and ex-smokers. A positive correlation was observed between daily tobacco consumption and HbCO level, i.e. HbCO = 0.123 (g/day) + 3.433. For a similar consumption (16 g/day), smokers who inhaled the smoke had a significantly higher level of HbCO than smokers who did not (5.8 vs. 4.7%). The interval separating the time when the last cigarette was smoked from HbCO measurement is of utmost importance: for a similar tobacco consumption (10 g/day) HbCO ranged from 6.5 +/- 0.5% when the interval was 1 h to 4.6 +/- 0.3% when it was 3 h (p < 0.005). In some cases, there were discrepancies between the number of cigarettes smoked as indicated by the subjects and the measured levels of HbCO. Possible inhalation of exogenous CO from other sources than smoking or increased production of endogenous CO could account for these differences.

Pattern of the ventilatory response to transient hypoxia in man: differences from transient hypercapnic test

The pattern of change in ventilatory variables after inhalation of pure N2 for two breaths was studied in normal children and adults. In six subjects the trends of change were compared to the ventilatory response to transient hypercapnia. We observed differences in the patterns of increasing ventilation with an initial abrupt increase of tidal volume for transient hypoxia and a progressive change for hypercapnia. In both cases respiratory frequency was progressively but unsystematically enhanced. A highly significant positive correlation was demonstrated between individual sensitivities to CO2 and O2, with a greater response to hypercapnia (5.6 time) than to hypoxia. Finally, a very short-latency decrease in expiratory duration occurred in the first breath after inhalation of hypercapnic mixture, supporting the recent data of Cunningham et al. (1977).

Mechanisms of the bronchoconstrictor effects of deep inspiration in asthmatic patients

A single deep inspiration (DI) is commonly followed by transient airflow obstruction in asthmatic patients. In some patients, however, DI results in a sustained response which suggests that more than one mechanism may be responsible. We have studied the characteristics of the response to repeated DI, and their modificatiion by various pharmacological agents, by measuring specific airway resistance (sRaw) in ten subjects who showed reproducible and consistent increases in sRaw after DI. Two types of reaction were observed: type A (n = 8) had an immediate maximum and usually short persistence; type B (n = 2) had a delayed maximum with a progressive increase. In type A reactions repetition of DI showed different patterns of response--either a reproducible reaction to each DI or a plateau effect. In type B reactions the response spontaneously increased with repeated DI. Type A responses to DI were inhibited completely by a beta-adrenergic stimulant (BAS), largely by an anticholinergic drug (AC, ipratropium bromide), but in no case by disodium cromoglycate (DSCG). Type B responses were inhibited completely by BAS, largely by DSCG, and partially by AC. These findings suggest that the response to DI is due to bronchoconstriction, which in type A reactions is of reflex origin, vagally mediated, and is due in part or wholly to mediator-release in type B reactions.

Transient hypoxia: ventilatory response after vagotomy and during artificial phasic inflation

The early ventilatory response to transient hypoxia was examined in the anaesthetized rabbit. In intact spontaneously breathing animals, an increase in tidal volume (VT) with an accompanying slight increase in inspiratory duration (TI) and a decrease in the expiratory duration (TE) was observed. After vagotomy, the ventilatory response was distinguished by a greater increase in VT and a significant decrease in TI and TE. In another group of artificially ventilated rabbits, an increase in inspiratory volume with a simultaneous decrease in breathing frequency was found to involve a smaller reflex increase in phrenic inspiratory discharge after onset of transient hypoxia. These observations suggest that afferents from pulmonary vagal stretch receptors inhibit those from arterial chemoreceptors.

[Hemoglobin oxygen combining capacity power. Reproducibility, variability; the effect of carboxyhemoglobin (author's transl)]

Hemoglobin oxygen combining power (HOCP) was measured in blood samples of 41 non smoking subjects and 36 smokers. The reproductibility and the varibility of this value were established (maximal variability was 2,5% in individual measurement). When the oxygen carrying capacity is reported to total hemoglobin (Hbt.), these two groups are not significantly different (1,344 +/- 0,004 ml O2 g-1 Hbt--n = 77-). However, when oxygen carrying capacity is reported to functional hemoglobin (Hbf = Hbt -- HbCO) there is a significative difference between smokers and non smokers (Student's t test 2 p less than 0,001) (1,404 +/- 0,005 ml O2 Hbf -- n = 77-).

[Correlations between the changes in the affinity of hemoglobin of oxygen and the anaerobic metabolism during muscular exercise in 20 silicotic patients (author's transl)]

This study investigated the changes in hemoglobin affinity for oxygen -- P50 standard [P50 (7.40)]; P50 in vivo (P50 IV), and 2,3-diphosphoglycerate concentration (2,3-DPG) -- and the anaerobic metabolism during a short muscular exercise in 20 silicotic patients. P50 (7.40) and 2,3-DPG remained unchanged at the end of the exercise but P50 IV increased significantly. A negative correlation was found between the increase in the arterial lactates and the increase in P50 IV. Such a shift to the right of the oxyhemoglobin dissociation curve probably improves the tissular oxygenation and can be regarded as a compensatory mechanism in patients with pulmonary impairment during exercise.