Apoptosis in lung pathophysiology

As recently as 1993, fewer than 10 manuscripts had been published on the topic of apoptosis specifically in the lung. Although that number is increasing, far fewer papers appear each year on apoptosis in the lung than in the other major organs. Therefore, our knowledge of this important aspect of lung cell physiology is relatively rudimentary. Recent literature is beginning to define important roles for apoptosis in normal lung cell turnover, lung development, and the pathogenesis of diseases such as interstitial pulmonary fibrosis, acute respiratory distress syndrome, and chronic obstructive pulmonary disease. Although the involvement of lung cell apoptosis in each of these examples seems clear, the many factors comprising the normal and abnormal regulation of cell death remain to be elucidated and are likely to be different in each situation. The definition of those factors will be an exciting and challenging field of research for many years to come. In that context, the goal of this symposium was to discuss, from a physiological perspective, some of the most recent and exciting advances in the definition of signaling mechanisms involved in the regulation of apoptosis specifically in lung cell populations.

Lack of seasonal variation in blood pressure in patients on hemodialysis in a North American center

Seasonal variation in blood pressure in patients undergoing hemodialysis in Europe has recently been described. If confirmed, this has important therapeutic, research, and epidemiological implications. All normotensive patients not administered antihypertensive drugs in our unit were studied. Predialysis blood pressures were measured before each dialysis treatment over two 2-month periods, January through February and July through August, in Winnipeg, Canada, a city with one of the most extreme seasonal temperature variations in North America. No difference in blood pressures was found between summer and winter (141 +/- 5/75 +/- 2 versus 140 +/- 4/74 +/- 2 mm Hg; P = not significant). Average daily temperatures were -16 degrees C in winter and 23 degrees C in summer. Interdialytic weight gain was the same in both groups. In conclusion, season has no effect on blood pressure in hemodialysis patients in a North American center. Reported seasonal changes in blood pressure in Europe may be related to nonclimatic factors.

Effect of hemoglobin levels in hemodialysis patients with asymptomatic cardiomyopathy

BACKGROUND

Hemoglobin levels below 10 g/dL lead to left ventricular (LV) hypertrophy, LV dilation, a lower quality of life, higher cardiac morbidity, and a higher mortality rate in end-stage renal disease. The benefits and risks of normalizing hemoglobin levels in hemodialysis patients without symptomatic cardiac disease are unknown.

METHODS

One hundred forty-six hemodialysis patients with either concentric LV hypertrophy or LV dilation were randomly assigned to receive doses of epoetin alpha designed to achieve hemoglobin levels of 10 or 13.5 g/dL. The study duration was 48 weeks. The primary outcomes were the change in LV mass index in those with concentric LV hypertrophy and the change in cavity volume index in those with LV dilation.

RESULTS

In patients with concentric LV hypertrophy, the changes in LV mass index were similar in the normal and low target hemoglobin groups. The changes in cavity volume index were similar in both targets in the LV dilation group. Treatment-received analysis of the concentric LV hypertrophy group showed no correlation between the change in mass index and a correlation between the change in LV volume index and mean hemoglobin level achieved (8 mL/m2 per 1 g/dL hemoglobin decrement, P = 0.009). Mean hemoglobin levels and the changes in LV mass and cavity volume index were not correlated in patients with LV dilation. Normalization of hemoglobin led to improvements in fatigue (P = 0.009), depression (P = 0.02), and relationships (P = 0.004).

CONCLUSIONS

Normalization of hemoglobin does not lead to regression of established concentric LV hypertrophy or LV dilation. It may, however, prevent the development of LV dilation, and it leads to improved quality of life.

Health care systems: the emperor has no clothes

Hospitals that merged and joined systems in the last 10 years need to revisit their decisions and determine whether their good intentions have actually paid off.

Comparative hospitalization of hemodialysis and peritoneal dialysis patients in Canada

BACKGROUND

Most comparisons of hemodialysis (HD) and peritoneal dialysis (PD) have used mortality as an outcome. Relatively few studies have directly compared the hospitalization rates, an outcome of perhaps equal importance, of patients using these different dialysis modalities.

METHODS

Eight hundred twenty-two consecutive patients at 11 Canadian institutions with irreversible renal failure had an extensive assessment of comorbid illness and initial mode of dialysis collected prospectively immediately prior to starting dialysis therapy. The cohort was assembled between March 1993 and November 1994. The mean follow-up was 24 months. Admission data were used to compare hospitalization rates in HD and PD.

RESULTS

Thirty-four percent of patients at baseline and 50% at three months used PD. Twenty-five percent of HD and 32% of PD patients switched dialysis modality at least once after their first treatment (P = NS). Nine percent of HD patients and 30% of PD patients switched modality after three months (P < 0. 001). Total comorbidity was higher in HD patients at baseline (P < 0. 001) and at three months (P = 0.001). The overall hospitalization rate was 40.2 days per 1000 patient days after baseline and 38.0 days per 1000 patient days after three months. When an adjustment was made for baseline comorbid conditions, patients on PD had a lower rate of hospitalization in intention-to-treat analysis according to the type of dialysis in use at baseline (RR 0.85, 95% CI, 0.82 to 0.87, P < 0.001), but a higher rate according to the type of dialysis in use three months after study entry (RR 1.31, 95% CI, 1.27 to 1.34, P < 0.001). In analyses based on the amount of time actually spent on each treatment modality, PD was associated with a higher rate of hospitalization when analyzed according to the type of dialysis in use at baseline (RR 1.10, 95% CI, 1.07 to 1.13, P < 0.001) and according to the type of dialysis in use three months after study entry (RR 1.26, 95% CI, 1.23 to 1.30, P < 0.001).

CONCLUSIONS

Conclusions regarding comparative hospitalization rates are heavily dependent on the analytic starting point and on whether intention-to-treat or treatment-received analyses are used. When early treatment switches are accounted for, HD is associated with a lower rate of hospitalization than PD, but the effect is modest.

TRAIL expression in vascular smooth muscle

TRAIL is a cell-associated tumor necrosis factor-related apoptosis-inducing ligand originally identified in immune cells. The ligand has the capacity to induce apoptosis after binding to cell surface receptors. To examine TRAIL expression in murine vascular tissue, we employed in situ hybridization and immunohistochemistry. In these studies, we found that TRAIL mRNA and protein were specifically localized throughout the medial smooth muscle cell layer of the pulmonary artery. Notably, a similar pattern of expression was observed in the mouse aorta. Consistent with these findings, we found that cultures of primary human aorta and pulmonary artery smooth muscle cells express abundant TRAIL mRNA and protein. We also found that these cells and endothelial cells undergo cell lysis in response to exogenous addition of TRAIL. Last, we confirmed that TRAIL specifically activated a death program by confirming poly(ADP ribose) polymerase cleavage. Overall, we believe that these findings are relevant to understanding the factors that regulate cell turnover in the vessel wall.

Comparative mortality of hemodialysis and peritoneal dialysis in Canada

BACKGROUND

Comparisons of mortality rates in patients on hemodialysis versus those on peritoneal dialysis have been inconsistent. We hypothesized that comorbidity has an important effect on differential survival in these two groups of patients.

METHODS

Eight hundred twenty-two consecutive patients at 11 Canadian institutions with irreversible renal failure had an extensive assessment of comorbid illness collected prospectively, immediately prior to starting dialysis therapy. The cohort was assembled between March 1993 and November 1994; vital status was ascertained as of January 1, 1998.

RESULTS

The mean follow-up was 24 months. Thirty-four percent of patients at baseline, 50% at three months, and 51% at six months used peritoneal dialysis. Values for a previously validated comorbidity score were higher for patients on hemodialysis at baseline (4.0 vs. 3.1, P < 0.001), three months (3.7 vs. 3.2, P = 0.001), and six months (3.6 vs. 3.2, P = 0.005). The overall mortality was 41%. The unadjusted peritoneal dialysis/hemodialysis mortality hazard ratios were 0.65 (95% CI, 0. 51 to 0.83, P = 0.0005), 0.84 (95% CI, 0.66 to 1.06, P = NS), and 0. 83 (95% CI, 0.64 to 1.08, P = NS) based on the modality of dialysis in use at baseline, three months, and six months, respectively. When adjusted for age, sex, diabetes, cardiac failure, myocardial infarction, peripheral vascular disease, malignancy, and acuity of renal failure, the corresponding hazard ratios were 0.79 (95% CI, 0. 62 to 1.01, P = NS), 1.00 (95% CI, 0.78 to 1.28, P = NS), and 0.95 (95% CI, 0.73 to 1.24, P = NS). Adjustment for a previously validated comorbidity score resulted in hazard ratios of 0.74 (95% CI, 0.58 to 0.94, P = 0.01), 0.94 (95% CI, 0.74 to 1.19, P = NS), and 0.88 (95% CI, 0.68 to 1.13, P = NS) at baseline, three months, and six months. There was no survival advantage for either modality in any of the major subgroups defined by age, sex, or diabetic status.

CONCLUSIONS

The apparent survival advantage of peritoneal dialysis in Canada is due to lower comorbidity and a lower burden of acute onset end-stage renal disease at the inception of dialysis therapy. Hemodialysis and peritoneal dialysis, as practiced in Canada in the 1990s, are associated with similar overall survival rates.

Role of activator protein-1 in TCR-mediated regulation of the murine fasl promoter

The present study demonstrates that transcription factor interactions are important in regulating the murine fasl promoter following TCR-mediated activation. We used DNase I-footprinting, EMSAs, and transient transfection assays to identify the minimal TCR signal-responsive region within the fasl promoter. This region contains the previously identified binding sites for NF-kappaB and Egr and the AP-1 site identified in this study. We found that TCR signaling induces AP-1 binding to this site and regulates the fasl promoter function in a fashion dependent on NF-kappaB binding. However, mutation in the AP-1 site alone did not show a significant effect on the promoter function. The data suggest that the minimal promoter required at least two transcription factors to function.

A multicenter study of noncompliance with continuous ambulatory peritoneal dialysis exchanges in US and Canadian patients

Recent evidence suggested that noncompliance (NC) with continuous ambulatory peritoneal dialysis (CAPD) exchanges may be more common in US than in Canadian dialysis centers. This issue was investigated using a questionnaire-based method in 656 CAPD patients at 14 centers in the United States and Canada. NC was defined as missing more than one exchange per week or more than two exchanges per month. Patients were ensured of the confidentiality of their individual results. Mean patient age was 56 +/- 16 years, 52% were women, and 39% had diabetes. The overall admitted rate of NC was 13%, with a rate of 18% in the United States and 7% in Canada (P < 0.001). NC was more common in younger patients (P < 0.0001), those without diabetes (P < 0.001), and employed patients (P < 0.05). It was also more common in black and Hispanic than in Asian and white patients (P < 0.001). NC was more common in patients prescribed more than four exchanges daily (P < 0.0001) but was not affected by dwell volume. On multiple regression analysis, the independent predictors of NC, in order of importance, were being prescribed more than four exchanges per day, black race, being employed, younger age, and not having diabetes. Being treated in a US unit did not quite achieve significance as a multivariate independent predictor. These findings suggest that NC is not uncommon in CAPD patients and is more frequent in US than in Canadian patients. However, country of residence is less powerful as a predictor of NC than a variety of other demographic and prescription factors.

Molecular characterization of the mouse Fas ligand promoter in airway epithelial cells

Constitutively expressed Fas ligand in several distinct epithelial cell types appears to protect tissues by inducing apoptosis of Fas(+) immune cells during inflammatory reactions. To study the transcriptional regulation of Fas ligand gene in airway epithelial cells, a 618-bp 5'-flanking region of mouse Fas ligand gene was cloned, sequenced, and the transcriptional start site was determined by using 5'-RACE. Deletion analysis, gel mobility shift assays and site-directed mutagenesis indicated that a CCAAT box located -214 bp upstream from the transcription start site served as a major positive regulatory cis-element in an airway epithelial cell line. This element was not required for constitutive Fas ligand expression in Sertoli cells. Furthermore, the activity of the site did not involve the NF-Y protein complex or c/EBP protein family. UV-cross linking proteins to this element indicated that a approximately 23-kDa transcription factor bound to the Fas ligand promoter CCAAT box and, thus, likely plays an important role in the regulation of Fas ligand expression in airway epithelial cells.

The role of pathology in an investigation of an outbreak of West Nile encephalitis in New York, 1999

An outbreak of encephalitis occurred in New York City in late August 1999, the first caused by West Nile virus in North America. Histopathologic and immunopathologic examinations performed on human autopsy materials helped guide subsequent laboratory and epidemiologic investigations that led to identification of the etiologic agent.

FasL promoter activation by IL-2 through SP1 and NFAT but not Egr-2 and Egr-3

Recently activated peripheral T cells treated with IL-2 for 4 days expressed Fas ligand (FasL)-mediated cytotoxicity. These IL-2-treated T cells had high nuclear expression of SP1 and NFAT, but lacked the Egr-2 and Egr-3 that could be induced by anti-CD3 stimulation and had been implicated in FasL gene activation. A minimal promoter region that responded to IL-2 was identified by transient transfection assays using deletion mutants. The data suggests that the GGGCGGAAA site present in the 5' end of the minimal FasL promoter is critical to IL-2-induced FasL gene activation. The GGGCGGAAA sequence contains an overlapping site used by two transcription factor families, one (GGGCGG) for the SP1 family and the other (GGAAA) for the NFAT family. FasL promoter activity was partially but statistically significantly reduced with constructs mutated at either site. More activity was lost with a construct mutated at both sites. In contrast, mutation at the Egr site had no effect on IL-2-induced FasL promoter activity. Our study identified a new FasL promoter site responding to IL-2-induced SP1 and NFAT factors. Furthermore, the nuclei of IL-2-treated cells express SP1 and NFAT, but not Egr-2 and Egr-3, for FasL gene activation.

Lessons learned from a review of the development of selected vaccines. National Vaccine Advisory Committee

BACKGROUND

Although the vaccine research and development network in the United States remains vibrant, its continued success requires maintaining harmonious interaction among its many components. Changing one component is likely to affect the system overall. An examination of case studies of the development of selected vaccines would allow an examination of the network as a whole. This article presents conclusions drawn from the case study review undertaken.

OBJECTIVE

Successful development of vaccines is a time-intensive process requiring years of commitment from a network of scientists and a continuum of regulatory and manufacturing entities. We undertook this work to shed light on how well the vaccine development system in the United States performs.

METHOD

The National Vaccine Advisory Committee examined the research and development pathways of several vaccines that reached licensure expeditiously (hepatitis B vaccine, Haemophilus influenzae type b conjugate vaccines); some that became licensed only after considerable delay (oral typhoid Ty21a vaccine, varicella vaccine); some that are at the point of imminent or recent licensure (reassortant Rhesus rotavirus vaccine, which was licensed by the Food and Drug Administration on August 30, 1998) or near submission for licensure (intranasal cold adapted influenza vaccine); and one for which clinical development is slow because of hurdles that must be overcome (respiratory syncytial virus vaccines).

RESULTS

Some common themes emerged from the reviews of these vaccine "case histories": the expediting influence of a strong scientific base and rationale; the need for firm quantitation of disease burden and clear identification of target populations; the critical role played by individuals or teams who act as "champions" to overcome the inevitable obstacles; availability of relevant animal models, high-quality reagents and standardized assays to measure immune response; the absolute requirement for well designed, meticulously executed clinical trials of vaccine safety, immunogenicity, and efficacy; postlicensure measurements of the public health impact of the vaccine and a track record of the vaccine's safety and acceptance with large-scale use; and the critical need for international collaborations to evaluate vaccines against diseases of global importance that are rare in the United States (eg, typhoid fever). It was clear that the critical step-up from bench scale to pilot lots and then to large-scale production, which depends on a small group of highly trained individuals, is often a particularly vulnerable point in the development process.

CONCLUSIONS

One fundamental lesson learned is that within the varied and comprehensive US vaccine development infrastructure, multiple and rather distinct paths can be followed to reach vaccine licensure. The National Vaccine Advisory Committee review process should be conducted periodically in the future to ascertain that the US vaccine development network, which has been enormously productive heretofore and has played a leadership role globally, is adapting appropriately to ensure that new, safe, and efficacious vaccines become available in a timely manner.

Characterization of a novel cis-element that regulates Fas ligand expression in corneal endothelial cells

Constitutively expressed Fas ligand in the cornea, Sertoli cell of the testes, Paneth cell of the intestines, and Clara cell of the airway protect surrounding parenchymal tissue by inducing apoptosis of Fas(+) immune cells during inflammatory reactions. Indeed, the action of corneal Fas ligand has been suggested to facilitate successful allogeneic cornea transplantation. To study the transcriptional regulation of Fas ligand in the eye, we employed an immortalized mouse corneal endothelial cell line (C3H3) that constitutively expresses Fas ligand. By deletion analysis of the mouse Fas ligand promoter, gel mobility shift assays, and site-directed mutagenesis, we found that a TCCT motif located -299 base pairs upstream from the transcriptional start site served as a major positive regulatory cis-element in C3H3 cells. In contrast, this element was not required for Fas ligand transcriptional activity in Sertoli cells and airway epithelial cells. By UV cross-linking analysis, we found that an approximately 30-kDa corneal nuclear protein binds to the Fas ligand promoter TCCT box and, thus, likely plays an important role in Fas ligand expression in corneal endothelial cells.

Calcium use increases risk of calciphylaxis: a case-control study

OBJECTIVE

To investigate the risk factors for the development of calciphylaxis in renal failure, a poorly understood and often fatal condition characterized by calcium deposition in tissues.

DESIGN

Retrospective case-control study.

SETTING

University hospital peritoneal dialysis center.

PATIENTS

Eight continuous ambulatory peritoneal dialysis (CAPD) patients with calciphylaxis were identified in a 3-year period. We matched up to five controls for dialysis modality and length of time on dialysis with each case.

STATISTICS

Multivariate conditional logistic regression analysis for matched case-controls.

MAIN OUTCOME MEASURES

Laboratory data and demographics were collected as well as cumulative calcium and vitamin D ingestion over the year prior to disease onset.

RESULTS

All the patients were female, versus only 38% (14/37) of controls (p < 0.0001). While not statistically significant, a majority of the patients were diabetic [62.5% (5/8) vs 32% (12/37)]. Peak and average levels of serum calcium, phosphate, calcium x phosphate product, parathyroid hormone (PTH), albumin, iron, total iron-binding capacity (TIBC), and ferritin were not significantly different in cases compared with controls. The use of calcitriol alone or with calcium carbonate was not found to be a significant risk factor for the development of calciphylaxis. In a multivariate analysis, iron intake seemed to be protective, contrary to previous reports, while the use of calcium carbonate was associated with a strong trend to increased risk of calciphylaxis development (odds ratio = 1.029/g and 1.011/g calcium ingested per month, at 1 and 2 - 3 months prior to calciphylaxis development; p = 0.0556 and 0.0565, respectively).

CONCLUSION

These data, although limited by the small numbers of index cases, suggest that calcium ingestion is a risk factor for calciphylaxis. The increased use of calcium salts as a phosphate binder in recent years might explain the apparent increased incidence of calciphylaxis in our and other centers. The preponderance of female diabetics among cases reported elsewhere was confirmed in our study.

Provider sponsored organizations: emerging opportunities for growth

As providers struggle to identify mechanisms to serve the Medicare population, the Medicare program continues to evolve. Of course, providers may serve the beneficiaries through traditional Medicare, Medicare HMOs, or a Medicare Select product, but as this book shows, under the appropriate conditions, the best way may be through the formation of a PSO.

Single synaptic events evoke NMDA receptor-mediated release of calcium from internal stores in hippocampal dendritic spines

We have used confocal microscopy to monitor synaptically evoked Ca2+ transients in the dendritic spines of hippocampal pyramidal cells. Individual spines respond to single afferent stimuli (<0.1 Hz) with Ca2+ transients or failures, reflecting the probability of transmitter release at the activated synapse. Both AMPA and NMDA glutamate receptor antagonists block the synaptically evoked Ca2+ transients; the block by AMPA antagonists is relieved by low Mg2+. The Ca2+ transients are mainly due to the release of calcium from internal stores, since they are abolished by antagonists of calcium-induced calcium release (CICR); CICR antagonists, however, do not depress spine Ca2+ transients generated by backpropagating action potentials. These results have implications for synaptic plasticity, since they show that synaptic stimulation can activate NMDA receptors, evoking substantial Ca2+ release from the internal stores in spines without inducing long-term potentiation (LTP) or depression (LTD).

Identification of two NF-kappa B sites in mouse CD95 ligand (Fas ligand) promoter: functional analysis in T cell hybridoma

Fas ligand (FasL) gene expression is critically involved in peripheral T cell tolerance and lymphocyte homeostasis. Previous studies have suggested that nuclear translocation of NF-kappaB during T cell activation is a critical event for FasL gene activation. In the present study we have identified two NF-kappaB sites (designated FasL-kappaB1 and FasL-kappaB2) on the promoter (approximately 700 bp) of FasL. The NF-kappaB sites were identified by electrophoretic mobility shift assay. Transient transfection reporter analyses showed that the FasL promoter activity was comparable between a construct that contains both sites and a shorter construct (433 bp) that contains only the FasL-kappaB1 site. Furthermore, elimination of FasL-kappaB1 by site-directed mutagenesis significantly inhibited FasL promoter activity. These observations provide strong evidence that NF-kappaB directly binds to the FasL-kappaB1 site and up-regulates FasL gene expression.

Neuropsychiatric systemic lupus erythematosus and the syndrome of inappropriate secretion of antidiuretic hormone: a case report with very late onset systemic lupus erythematosus

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) associated with neuropsychiatric lupus (NP-SLE) is rare. We report a case of SIADH associated with the new onset of SLE in an 88-yr-old female. The unique features of this case include the extreme age of onset of SLE presenting with neuropsychiatric manifestations and positive antiribosomal P antibody titres. Both the NP manifestations of SLE and SIADH were highly correlated with the SLE disease activity. This case illustrates a novel presentation of NP-SLE with SIADH which may develop due to antibody-mediated hypothalamic dysfunction.

Effect of pergolide on restless legs and leg movements in sleep in uremic patients

Restless legs syndrome (RLS) and periodic limb movements in sleep (PLMS) are disorders that are common and disturbing to uremic patients. The treatment of these is problematic. Eight patients on chronic hemodialysis and continuous peritoneal dialysis completed a double-blind placebo-controlled crossover study using incremental doses of pergolide up to 0.25 mg at bedtime for treatment of RLS and sleep disruption. Five patients (62.5%) noted subjective improvement in restless legs symptoms and sleep quality. Objective results were improved only slightly by treatment. The percentage of the first hour in bed during which leg movements occurred decreased from 20.5 +/- 6.0 to 11.5 +/- 3.3, p < 0.05. However, findings during sleep were less positive. The following measures were not significant between placebo and treatment: leg movements per hour of sleep [53.7 +/- 22.3 vs 35.8 +/- 11.8 (p = 0.2)]; and percentage of sleep time spent with leg movements [5.5% +/- 3.2 vs 4.4% +/- 1.4 (p = 0.37)]. Patients continued to have very disrupted sleep, and we could not document an objective improvement in sleep architecture. Thus, although pergolide at the dose of 0.25 mg at bedtime provided subjective improvement in symptoms of restless legs and quality of sleep, and objectively decreased leg movements during the first hour in bed, objectively sleep continued to be disrupted. In this small patient group, the response to pergolide was not uniform, and further investigation is required to test effectiveness at higher doses.

Loss of adenylyl cyclase I activity disrupts patterning of mouse somatosensory cortex

The somatosensory (SI) cortex of mice displays a patterned, nonuniform distribution of neurons in layer IV called the 'barrelfield' (ref. 1). Thalamocortical afferents (TCAs) that terminate in layer IV are segregated such that each barrel, a readily visible cylindrical array of neurons surrounding a cell-sparse center, represents a distinct receptive field. TCA arbors are confined to the barrel hollow and synapse on barrel-wall neurons whose dendrites are oriented toward the center of the barrel. Mice homozygous for the barrelless (brl) mutation, which occurred spontaneously in ICR stock at Université de Lausanne (Switzerland), fail to develop this patterned distribution of neurons, but still display normal topological organization of the SI cortex. Despite the absence of barrels and the overlapping zones of TCA arborization, the size of individual whisker representations, as judged by 2-deoxyglucose uptake, is similar to that of wild-type mice. We identified adenylyl cyclase type I (Adcy1) as the gene disrupted in brl mutant mice by fine mapping of proximal chromosome 11, enzyme assay, mutation analysis and examination of mice homozygous for a targeted disruption of Adcy1. These results provide the first evidence for involvement of cAMP signalling pathways in pattern formation of the brain.

Sp3 regulates fas expression in lung epithelial cells

By transducing an apoptotic signal in immune effector cells, Fas has been directly implicated in the control of immunological activity. Expression and functional results, however, have also suggested a role for Fas in regulating cell turnover in specific epithelial populations. To characterize factors responsible for Fas expression in epithelial cells, approximately 3 kb of the 5' flanking region of the mouse Fas gene was isolated. By rapid amplification of cDNA ends and primer extension, transcriptional start sites were identified within 50 bp upstream of the translation start site. Transient transfection of promoter-luciferase constructs in a mouse lung epithelial cell line, MLE-15, localized promoter activity to the first 77 bp of upstream sequence. By using a 60 bp DNA probe (-18 to -77) in electrophoretic mobility-shift assays, three shifted complexes were found. Incubation with excess cold Sp1 oligonucleotide or an anti-Sp3 antibody inhibited complex formation. Site-directed mutagenesis of the Sp1 site resulted in 60-70% loss of promoter activity. In Drosophila SL-2 cells, promoter activity was markedly increased by co-transfection of an Sp3 expression construct. These results show that the Sp3 protein is involved in regulating Fas gene expression in lung epithelial cells.

Programmed cell death contributes to postnatal lung development

The rat lung undergoes the phase of maturation of the alveolar septa and of the parenchymal microvascular network mainly during the third postnatal week. Speculating that programmed cell death may contribute to the thinning of the alveolar septa, we searched for the presence of DNA fragmentation in rat lungs between postnatal days 6 and 36 using the TUNEL procedure. The number of positive nuclei was compared at different days. We observed an 8-fold increase of programmed cell death toward the end of the third week as compared to the days before and after this time point. The precise timing of the appearance of the peak depended on the size of the litter. Double-labeling for DNA fragmentation (TUNEL) and for type I and type II epithelial cells (antibodies E11 and MNF-116), as well as morphologic studies at electron microscopic level, revealed that during the peak of programmed cell death mainly fibroblasts and type II epithelial cells were dying. While both dying cell types were TUNEL-positive, nuclear fragments and apoptotic bodies were exclusively observed in the dying fibroblasts. We conclude that programmed cell death is involved in the structural maturation of the lung by reducing the number of fibroblasts and type II epithelial cells in the third postnatal week. We observed that the dying fibroblasts are cleared by neighboring fibroblasts in a later stage of apoptosis, and we hypothesize that type II epithelial cells are cleared by alveolar macrophages in early stages of the programmed cell death process.