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Biomedical subjects

A Clement

Publications and source records attributed to A Clement.

At least 55 records · Page 3Linked to original sources
PubMed1997

Idiopathic pulmonary fibrosis in infants.

Idiopathic pulmonary fibrosis is a poorly characterized disease in infants. In the present report, we reviewed our experience with 10 infants during a 10-year period. In 9 patients, onset of symptoms occurred before the age of 2 months and included tachypnea, cough, and inadequate weight gain. However, despite the presence of these symptoms, diagnosis was delayed for 3 months at which time the infants were referred to the pediatric pulmonary department, when the diagnosis was confirmed by open lung biopsy. At the time of admission, bronchoscopy with alveolar lavage was performed in 9 children and showed severe alveolitis with an increase in the neutrophil count. Nine infants were treated with prednisone alone or in combination with chloroquine, colchicine, or cyclophosphamide; all these patients died despite treatment. One infant was treated with pulses of methylprednisolone because of a failure in response to oral prednisone. This girl who displayed similar clinical, radiological, and histological abnormalities as the other children at the time of diagnosis is the only child still alive after 3 years of follow-up. She is now free of respiratory symptoms and has a normal growth curve. The present report raised two important points: (1) a thorough evaluation of characteristic symptoms should lead to an early diagnosis of pulmonary fibrosis in infants; and (2) administration of pulse therapy using corticosteroids has been helpful and needs to be evaluated further.

Biopsy↗
PubMed1997

Effects of dessication on post-planting stress in bare-root Corsican pine seedlings.

We examined the post-planting consequences of pre-planting exposure stress on two-year-old, bare-root Corsican pine (Pinus nigra Arnold. ssp. laricio var. Corsicana) seedlings. Seedlings were lifted from a nursery and exposed to ambient conditions for periods of up to 192 h before being planted in minirhizotrons. Exposure decreased seedling water potential, CO(2) assimilation rate, leaf conductance and new root elongation, and increased mortality after planting. During exposure, needle total nonstructural carbohydrates (TNC) concentration (expressed on a dry mass basis) decreased by 0.31 mg g(dm) (-1) h(-1); however, needle and root TNC concentrations remained high (> 100 mg g(dm) (-1)) at planting, even in those treatments leading to severe seedling mortality. More than 90% of the seedlings with predawn water potentials lower than -1.3 MPa at planting did not elongate new roots and did not survive, whereas a similar percentage of seedlings with a predawn water potential above this value at planting elongated new roots and survived, suggesting that this value corresponds to a turgor threshold below which new root formation is inhibited. At planting, embolization of xylem conduits in roots and shoots was low for seedlings in all of the exposure treatments.

Journal Article↗
PubMed1997

Involvement of the cell cycle inhibitor CIP1/WAF1 in lung alveolar epithelial cell growth arrest induced by glucocorticoids.

Glucocorticoids are known to impair the postnatal development of lung parenchyma by altering the formation of alveoli, and from the current understanding of the processes controlling the growth of the alveolar structure, it is likely that this impairment relies in large part on alteration of alveolar epithelial cell replication. From recent studies on the modulation of cell proliferation by glucocorticoids, it appears that events associated with the G1 phase of the cell cycle are a major target for the actions of these hormones. To gain some insights into the mechanisms involved in the growth arrest of lung alveolar epithelial cells by glucocorticoids, we focused in the present study on the effects of these hormones on the expression of the G1 cyclins and their cell cycle-dependent kinases (CDKs). We observed that when cells were blocked in their proliferation by dexamethasone treatment, no changes in the expression of the various G1 cyclins, D1, D2, D3, or E, could be documented. Also, the levels of CDK2 and CDK4 in glucocorticoid-treated cells did not exhibit significant modifications compared with the levels in proliferating cells. Evaluation of the activity of cyclin-CDK complexes showed that activation of cyclin D-CDK4 was not modified by dexamethasone. By contrast, differences in the activity of cyclin E-CDK2 complexes were found, with a profound decrease in the extracts of cells growth arrested by dexamethasone. Studies of the factors potentially implicated in the inactivation of these complexes strongly suggested a role for p21CIP1, as a dramatic accumulation of this protein was observed in cells treated with dexamethasone. Moreover, changes in p21CIP1 expression appeared to be controlled mostly at the posttranscriptional level. Interestingly, a decrease in the levels of p27KIP1 could be observed. These results indicate that glucocorticoids block entry of alveolar epithelial cells into S phase by specifically altering the activation of cyclin E-CDK2 complexes through induction of the CDK inhibitor p21CIP1.

Animals↗
PubMed1996

Altered regulation of G1 cyclins in oxidant-induced growth arrest of lung alveolar epithelial cells. Accumulation of inactive cyclin E-DCK2 complexes.

The alveolar surface of the lung is a major target for oxidant injury, and its repair following injury is dependent on the ability of its stem cells, the type 2 cells, to initiate proliferation. From previous studies it is likely that events located before the entry into the S phase of the cell cycle and involving several components of the insulin-like growth factor system as well as of transforming growth factor-beta (TGF-beta) play a key role in growth regulation of oxidant-exposed type 2 epithelial cells. To gain further insights into these mechanisms, we explored the effects of O2 exposure on G1 cyclins and their cyclin-dependent kinases (CDKs). We documented an increased expression of these genes in O2-treated type 2 cells. However, despite this induction, a dramatic decrease in cyclin E-CDK2 activity, but not in cyclin D-CDK4 activity, was found. The concomitant induction of CDK inhibitory proteins (CKIs), mainly p21(CIP1), suggests that accumulation of inactive cyclin E-CDK2 activity is due to CKI binding. We also provided evidence that the mechanisms regulating this process involved TGF-beta as anti-TGF-beta antibody treatment was able to reduce the oxidant-induced inhibition of cyclin E-CDK2 activity. Taken together, these results suggest that oxidants may block entry into S phase by acting on a subset of late G1 events whose alterations are sufficient to impair the activation of cyclin E-CDK2 complexes.

Animals↗
PubMed1996

Tau binds to the distal axon early in development of polarity in a microtubule- and microfilament-dependent manner.

Microtubule-associated protein tau is localized to the axon in situ and has been implicated in the development of neuronal polarity. Here we report that tau is extracted differentially in cultured hippocampal neurons yielding an axon-specific localization under conditions that keep the integrity of the plasma membrane. The amount of bound tau increases toward the distal axon and is highest at the transition from the axonal shaft to the growth cone. This distribution is significantly different from the distribution of axonal microtubules that are most concentrated at the proximal axon. Distal binding of tau to one process appears early in development of polarity in culture and correlates with the onset of axon formation (day 2 in culture). Binding to the distal axon requires intact microtubules and microfilaments. Distal tau binding does not stabilize microtubules selectively against drug-induced disassembly, because colchicine-induced microtubule depolymerization is highest distally. We conclude that binding of tau to the distal axon follows a complex mechanism, is an early event in the development of polarity, and reproduces the axon-specific localization of tau in situ.

Actin Cytoskeleton↗
PubMed1996

Rat lung alveolar type II cell line maintains sodium transport characteristics of primary culture.

Culture of primary alveolar type II cells has been widely used to investigate the Na+ transport characteristics of alveolar epithelium. However, this model was restricted by early morphological and physiological dedifferentiation in culture. Recently, a cell line has been obtained by transfection of neonatal type II cells with the simian virus SV40 large T antigen gene (SV40-T2). SV40-T2 cells have retained proliferative characteristics of the primary type II cells (Clement et al., 1991, Exp. Cell Res., 196:198-205.) In the present study, we have characterized Na+ transport pathways in SV40-T2 cells. SV40-T2 cells retained most cardinal properties of the original alveolar epithelial cells. Na+ entry occurred, as in primary cultures, through both Na(+)-cotransporters and amiloride-sensitive Na+ channels. SV40-T2 cells expressed Na(+)-phosphate. Na(+)-amino acid and Na(+)-K(+)-Cl cotransports which are quantitatively similar to that of primary cultures. The existence of amiloride-sensitive Na+ channels was supported by molecular and functional data. SV40-T2 expressed the cloned alpha- and gamma-mRNAs for the rat epithelial Na+ channel (rENaC), whereas beta subunit was not detected, and 22Na+ influx was significantly inhibited by 10 microM amiloride. Na+, which enters SV40-T2 cells, is extruded through a Na+, K(+)-ATPase: mRNA for alpha 1 and beta 1 isoforms of Na+, K(+)-ATPase were present and Na+, K(+)-ATPase activity was evidenced either on intact cells by the presence of a ouabain-sensitive component of 86Rb+ influx or on cell homogenates by the measurement of ouabain-inhibitable ATP hydrolysis. These results indicate that SV40-T2 cell line displays most of the Na+ transport characteristics of well-differentiated primary cells in the first days of culture. We conclude that the SV40-T2 cell line provides a model of differentiated alveolar type II cells and may be a powerful tool to study, in vitro, the modulation of Na+ transport in pathophysiological conditions.

Amiloride↗
PubMed1996

Tenascin-C contains distinct adhesive, anti-adhesive, and neurite outgrowth promoting sites for neurons.

The glia-derived extracellular matrix glycoprotein tenascin-C (TN-C) is transiently expressed in the developing CNS and may mediate neuron-glia interactions. Perturbation experiments with specific monoclonal antibodies suggested that TN-C functions for neural cells are encoded by distinct sites of the glycoprotein (Faissner, A., A. Scholze, and B. Götz. 1994. Tenascin glycoproteins in developing neural tissues--only decoration? Persp. Dev. Neurobiol. 2:53-66). To characterize these further, bacterially expressed recombinant domains were generated and used for functional studies. Several short-term-binding sites for mouse CNS neurons could be assigned to the fibronectin type III (FNIII) domains. Of these, the alternatively spliced insert TNfnA1,2,4,B,D supported initial attachment for both embryonic day 18 (E18) rat and postnatal day 6 (P6) mouse neurons. Only TNfn1-3 supported binding and growth of P6 mouse cerebellar neurons after 24 h, whereas attachment to the other domains proved reversible and resulted in cell detachment or aggregation. In choice assays on patterned substrates, repulsive properties could be attributed to the EGF-type repeats TNegf, and to TNfnA1,2,4. Finally, neurite outgrowth promoting properties for E18 rat hippocampal neurons and P0 mouse DRG explants could be assigned to TNfnB,D, TNfnD,6, and TNfn6. The epitope of mAb J1/tn2 which abolishes the neurite outgrowth inducing effect of intact TN-C could be allocated to TNfnD. These observations suggest that TN-C harbors distinct cell-binding, repulsive, and neurite outgrowth promoting sites for neurons. Furthermore, the properties of isoform-specific TN-C domains suggest functional significance of the alternative splicing of TN-C glycoproteins.

Amino Acid Sequence↗
PubMed1996

Glucocorticoid-induced growth arrest of lung alveolar epithelial cells is associated with increased production of insulin-like growth factor binding protein-2.

Glucocorticoids have been shown to impair lung growth by altering development of the alveolar structure. To characterize the mechanisms involved in this process, we examined the effects of dexamethasone on proliferation of the stem cells of the alveolar epithelium, the type 2 cells. Treatment of type 2 cells with dexamethasone rapidly decreased DNA synthesis, and this effect was observed for concentrations less than 10(-8)M. Inhibition of cell proliferation by glucocorticoids was associated with a marked accumulation of insulin-like growth factor (IGF)-binding protein-2 (IGFBP-2) in the culture medium. Studies of the mechanisms involved in this accumulation indicated that it was associated with an enhanced production of IGFBP-2 and with a similar increase in the level of IGFBP-2 messenger RNA expression without any changes in its stability, as evaluated by actinomycin D experiments. Furthermore, transfection studies using plasmids conveying expression of luciferase gene transcribed from the fragment of rat IBFBP-2 promoter extending from +12 bp relative to the start of transcription plus 1.4 kilobases of the 5'-flanking sequence showed a stimulation of luciferase activity in cells treated with dexamethasone that was similar to the increase in IGFBP-2 messenger RNA and protein. Study of the other components of the IGF system also revealed induction of IGF-II expression upon treatment with dexamethasone. Together with other previously reported results using various modulators of type 2 cell proliferation, the present study strongly suggests that IGFBP-2 is likely to play an important role in the control of alveolar epithelial cell proliferation.

Animals↗
PubMed1996

BAL in children: a controlled study of differential cytology and cytokine expression profiles by alveolar cells in pediatric sarcoidosis.

STUDY OBJECTIVE: The development of BAL in children for both research and clinical purposes has been limited so far by the difficulty in establishing reference values. The aim of the study was (1) to define composition of BAL cellular components in control children and to evaluate the ability of these cells to express various cytokines, and (2) to study modifications of differential cytology and BAL cell cytokine responses in children with interstitial lung disorders. POPULATIONS AND METHODS: Two groups were investigated: a control group of 16 children who were concluded to be free of parenchymal lung disease after complete pulmonary investigation, and a group of 11 children with pulmonary sarcoidosis. Differential cytology was evaluated by standard techniques. BAL cell cytokine expression was studied at the level of messenger RNA (mRNA) by reverse transcription-polymerase chain reaction (RT-PCR) methods. RESULTS: In the control group, differential cell counts appeared to be similar to values reported in adult populations with normal distribution of the data and no influence of age. In this group, no transcripts for interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), IL-6, and transforming (correction of tranforming) growth factor-beta (TGF-beta) could be detected. In children with sarcoidosis, different profiles of IL-1beta, TNF-alpha, IL-6, and TGF-beta expression were individualized which seemed to be related to the activity and/or severity of the disease, IL-6 and TGF-beta mRNA being observed only in the more severe forms. CONCLUSION: These data provide information on BAL cell number and function in children. Characterization of BAL cytokine expression patterns during the course of interstitial lung diseases in children may be of great interest for evaluation of disease activity and/or severity and therefore for planning of therapy.

Actins↗
PubMed1995

Expression of insulin-like growth factor receptors 1 and 2 in the developing lung and their relation to epithelial cell differentiation.

Insulin-like growth factors (IGFs) and their receptors have been implicated as regulators of cell differentiation and cell proliferation in a number of systems and have been shown to play an important role in embryonic development. In this study we examined expression of mRNA for IGF-I and IGF-II, IGF binding protein 2 (IGFBP-2), and IGF receptors 1 (IGFR-1) and 2 (IGFR-2) during fetal lung development and in early postnatal and adult lungs by the polymerase chain reaction (PCR). IGF-I mRNA was found in embryonic and postnatal lungs at all ages as was IGFBP-2, whereas IGF-II mRNA was present only in prenatal lungs. IGFR-1 was present in all but the adult lungs. Lung epithelial cells expressed IGFR-1 at 14 days' gestation but not at 18 days' gestation as measured by PCR and in situ hybridization. Alveolar epithelial cells re-expressed IGFR-1 mRNA in the early postnatal period but not in the adult lung. IGFR-2 was expressed by PCR and in situ hybridization in 14-day embryonic epithelium, was not present at 18 days or at birth, but was re-expressed at high levels in the early postnatal alveolar wall. Immunocytochemical localization of IGFR-2 confirmed its absence in the late fetal and newborn lung. It reappeared in alveoli, exclusively in type 1 cells, in early postnatal and adult lungs. These studies demonstrate the stage- and cell-specific appearance of IGF receptors in the developing and postnatal lung. They also establish IGFR-2 as a marker of the mature alveolar type 1 cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Insulin-like growth factors, their binding proteins, and transforming growth factor-beta 1 in oxidant-arrested lung alveolar epithelial cells.

The epithelium of the pulmonary alveolus is a major target for oxidant injury, and its proper repair following injury is dependent on the proliferative response of its stem cells, the type 2 cells. We have recently shown that hyperoxia arrests proliferation of an immortalized type 2 cell line (SV40T-T2) and that expression of several growth-related genes, normally induced near the G1/S and boundary was altered with a block of translation of their mRNA. In the present study we examined the possible role of the insulin-like growth factor (IGF) system and of transforming growth factor-beta 1 (TGF-beta 1) in the arrest of proliferation induced by hyperoxia. We show that IGF-binding protein 2 (IGFBP-2) accumulates to higher levels in culture medium of SV40T-T2 cells whose proliferation has been arrested by hyperoxia. This proliferation arrest is associated with increased expression of IGFBP-2 mRNA and with induction of type 2 IGF receptor and IGF-II mRNAs. When O2-arrested cells were allowed to resume proliferation in normoxia, the level of expression of these genes rapidly decreased to control levels. We also, found that TGF-beta 1 was induced by O2 exposure, that TGF-beta 1 inhibited SV40T-T2 proliferation, and that TGF-beta 1 itself was a potent stimulator of IGFBP-2 expression. These studies suggest a regulatory link between components of the IGF system and TGF-beta 1 in hyperoxic control of cell proliferation of alveolar epithelial cells.

Animals↗
PubMed1994

Isolation of a neural chondroitin sulfate proteoglycan with neurite outgrowth promoting properties.

Proteoglycans are expressed in various tissues on cell surfaces and in the extracellular matrix and display substantial heterogeneity of both protein and carbohydrate constituents. The functions of individual proteoglycans of the nervous system are not well characterized, partly because specific reagents which would permit their isolation are missing. We report here that the monoclonal antibody 473HD, which binds to the surface of early differentiation stages of murine astrocytes and oligodendrocytes, reacts with the chondroitin sulfate/dermatan sulfate hybrid epitope DSD-1 expressed on a central nervous system chondroitin sulfate proteoglycan designated DSD-1-PG. When purified from detergent-free postnatal days 7 to 14 mouse brain extracts, DSD-1-PG displays an apparent molecular mass between 800-1,000 kD with a prominent core glycoprotein of 350-400 kD. Polyclonal anti-DSD-1-PG antibodies and monoclonal antibody 473HD react with the same molecular species as shown by immunocytochemistry and sequential immunoprecipitation performed on postnatal mouse cerebellar cultures, suggesting that the DSD-1 epitope is restricted to one proteoglycan. DSD-1-PG promotes neurite outgrowth of embryonic day 14 mesencephalic and embryonic day 18 hippocampal neurons from rat, a process which can be blocked by monoclonal antibody 473HD and by enzymatic removal of the DSD-1-epitope. These results show that the hybrid glycosaminoglycan structure DSD-1 supports the morphological differentiation of central nervous system neurons.

Animals↗
PubMed1994

Insulin-like growth factor-II (IGF-II), type 2 IGF receptor, and IGF-binding protein-2 gene expression in rat lung alveolar epithelial cells: relation to proliferation.

Pulmonary alveolar type 2 cells act as a reservoir of stem cells which can be induced to proliferate during periods of lung growth and repair after lung injury. Despite the importance of this process, the mechanisms that regulate type 2 cell proliferation have not been well characterized. We show in this study that insulin-like growth factor (IGF)-binding protein-2 (IGFBP-2) accumulates to high levels in culture medium of growth-arrested type 2 cells. This is associated with an increased expression of IGFBP-2 messenger RNA (mRNA). Study of the other components of the IGF system also reveals induction of IGF-II and type 2 IGF receptor mRNA during the process of type 2 cell block of proliferation. When growth-arrested cells are allowed to resume proliferation by the addition of serum, the level of expression of IGFBP-2, type 2 IGF receptor, and IGF-II rapidly decreased. Despite the similarities in the timing of induction, it is likely that these components are not necessarily linked to mediate effects through a single pathway. Indeed, we show that the addition of conditioned medium from growth-arrested cells on proliferative cells results in down-regulation of IGFBP-2 and increased expression of IGF-II and type 2 IGF receptor mRNA. Treatment of the cells with various concentrations of IGF-II affects only the level of expression of type 2 IGF receptor, whereas IGF-I and insulin appear to influence only the expression of IGFBP-2. From the results presented in this study, it can be suggested that IGFBP-2, IGF-II, and type 2 IGF receptor play an important role in the transition of lung alveolar epithelial cells in and out of the cell cycle.

Animals↗
PubMed1993

Pulmonary sarcoidosis in children: serial evaluation of bronchoalveolar lavage cells during corticosteroid treatment.

The clinical course of sarcoidosis in children has not been well defined. Eight children with symptomatic sarcoidosis included in this study underwent pulmonary function tests and bronchoscopy with bronchoalveolar lavage (BAL) before treatment and during steroid therapy. At the start of therapy, functional parameters, mostly dynamic lung compliance and lung transfer factor for CO, were impaired. This was associated with abnormalities of BAL cell populations: increased total cell number with a high proportion of lymphocytes, modifications of lymphocyte subpopulation with an elevated CD4+/CD8+ ratio, and enhanced ability of alveolar macrophages to release hydrogen peroxide. Although respiratory abnormalities seemed to be similar at the initial stage of sarcoidosis in children and adults, the course of the disease appeared to be different. Despite the absence of respiratory symptoms and disappearance of chest radiographic abnormalities on prolonged steroid treatment, we found slow improvement of pulmonary functions associated with persistence of BAL lymphocytosis and elevated CD4+/CD8+ ratios. However, the ability of alveolar macrophages to release hydrogen peroxide was significantly reduced after 6 months of steroid treatment, and it remained identical to the control group. Therefore, the evaluation of disease activity appears to be critical for therapy in pediatrics, and for this purpose studies of alveolar macrophage activation may be of particular interest.

Adolescent↗
PubMed1993

Planting stress, water status and non-structural carbohydrate concentrations in Corsican pine seedlings.

Two-year-old Corsican pine (Pinus nigra ssp. laricio var. Corsicana) seedlings were either well watered or subjected to a moderate drought for one month before being lifted from the nursery bed on October 9 and transplanted. Well-watered, non-transplanted seedlings served as controls. Needle predawn water potential (Psi(wp)), non-structural carbohydrate concentrations and plant development (survival, bud break, shoot elongation) were assessed before and during the first growing season after transplanting. On April 16, just before bud break, Psi(wp) was lower for the well-watered + transplanted and drought-conditioned + transplanted seedlings (Psi(wp) = -1.45 and -1.83 MPa, respectively) than for the controls (Psi(wp) = -0.56). There was a close relationship between the Psi(wp) measured on April 16 and bud break, shoot elongation and plant survival during the following growing period. Above a Psi(wp) of -1.1 MPa, all plants developed normally. Between -1.1 MPa and -1.6 MPa, bud break, and thus shoot elongation, did not occur in all plants. Between -1.6 MPa and -2.1 MPa, the plants were characterized by the absence of shoot growth, but mortality was zero. Below -2.1 MPa, there was a large increase in plant mortality. On April 16, starch concentrations were markedly lower in the roots of transplanted seedlings than in the controls. There was a positive correlation between Psi(wp) and root starch concentration. The Psi(wp) (-2.3 MPa) at which complete starch depletion was observed in the roots corresponded to the Psi(wp) below which plants did not survive. These results suggest that mechanisms specifically linked to altered water status and metabolic processes associated with altered carbohydrate status are involved in transplanting stress; however, it was not possible to disentangle the two effects. Drought conditioning did not lead to a marked increase in soluble carbohydrate concentrations, as reported for other species, and did not increase plant tolerance to transplanting stress.

Journal Article↗
PubMed1992

Inhibition of lung epithelial cell proliferation by hyperoxia. Posttranscriptional regulation of proliferation-related genes.

The alveolar surface of the lung is a major target for oxidant injury. After injury, repair of the alveolar epithelium is dependent on the ability of epithelial type 2 (T2) cells to proliferate. The regulation of T2 cell proliferation and the effect of reactive oxygen (O2) species on this lung cell proliferation have not been well defined. To investigate this process we focused on the regulation of two late cell cycle genes, histone and thymidine kinase, in T2 cells and fibroblasts exposed in vitro to varying periods of hyperoxia (95% O2). Hyperoxia for 24 to 48 h arrested cell proliferation in a SV40T-immortalized T2 cell line we have developed and in primary and SV40T-immortalized lung fibroblasts. Despite the cessation of proliferation, histone and TK mRNA continued to be expressed at high levels; mRNA half-lives were markedly prolonged but neither protein was translated. Thus proliferation arrest induced by hyperoxia was associated with posttranscriptional control of at least two late cell cycle-related genes. This form of proliferation arrest is also seen when primary and SV40T-T2 cells but not fibroblasts are serum deprived, suggesting that T2 cells in vitro may be uniquely sensitive to alterations in their redox state and that these alterations in turn affect translational control of a subset of proliferation-related genes.

Animals↗