Jeffrey A. Golden

The Combined Functions of Proapoptotic Bcl-2 Family Members Bak and Bax Are Essential for Normal Development of Multiple Tissues

Proapoptotic Bcl-2 family members have been proposed to play a central role in regulating apoptosis. However, mice lacking bax display limited phenotypic abnormalities. As presented here, bak(-/-) mice were found to be developmentally normal and reproductively fit and failed to develop any age-related disorders. However, when Bak-deficient mice were mated to Bax-deficient mice to create mice lacking both genes, the majority of bax(-/-)bak(-/-) animals died perinatally with fewer than 10% surviving into adulthood. bax(-/-)bak(-/-) mice displayed multiple developmental defects, including persistence of interdigital webs, an imperforate vaginal canal, and accumulation of excess cells within both the central nervous and hematopoietic systems. Thus, Bax and Bak have overlapping roles in the regulation of apoptosis during mammalian development and tissue homeostasis.

Bronchoalveolar Lavage and Transbronchial Biopsy for the Diagnosis of Pulmonary Infections in the Acquired Immunodeficiency Syndrome

The efficacy of bronchoalveolar lavage and transbronchial biopsy in diagnosing lung infection was determined in 276 fiberoptic bronchoscopic examinations done on 171 patients with known or suspected acquired immunodeficiency syndrome. Of 173 pathogens (Pneumocystis carinii, cytomegalovirus, Mycobacterium avium-intracellulare, Cryptococcus neoformans, M. tuberculosis, Coccidioides immitis, and Histoplasma capsulatum) identified during the initial evaluation or in the subsequent month, the initial bronchoscopic examination detected 166 (96%). Bronchoalveolar lavage and transbronchial biopsy had sensitivities of 86% and 87%, respectively. When bronchoscopy included both bronchoalveolar lavage and transbronchial biopsy, the yield for all pathogens was 98% and the sensitivity for P. carinii infections was 100%. Follow-up for at least 3 weeks after examination failed to detect any additional false-negative results. Fiberoptic bronchoscopy is extremely accurate for the detection of pathogens in patients with the acquired immunodeficiency syndrome, especially when bronchoalveolar lavage and transbronchial biopsy are combined. In patients at high risk of complications from transbronchial biopsy, bronchoalveolar lavage is sufficiently accurate to be used alone.

Intrapulmonary Pharmacokinetics of Linezolid

ABSTRACT In this study, our objective was to determine the steady-state intrapulmonary concentrations and pharmacokinetic parameters of orally administered linezolid in healthy volunteers. Linezolid (600 mg every 12 h for a total of five doses) was administered orally to 25 healthy adult male subjects. Each subgroup contained five subjects, who underwent bronchoscopy and bronchoalveolar lavage (BAL) 4, 8, 12, 24, or 48 h after administration of the last dose. Blood was obtained for drug assay prior to administration of the first dose and fifth dose and at the completion of bronchoscopy and BAL. Standardized bronchoscopy was performed without systemic sedation. The volume of epithelial lining fluid (ELF) recovered was calculated by the urea dilution method, and the total number of alveolar cells (AC) was counted in a hemocytometer after cytocentrifugation. Linezolid was measured in plasma by a high-pressure liquid chromatography (HPLC) technique and in BAL specimens and AC by a combined HPLC-mass spectrometry technique. Areas under the concentration-time curves (AUCs) for linezolid in plasma, ELF, and AC were derived by noncompartmental analysis. Half-lives for linezolid in plasma, ELF, and AC were calculated from the elimination rate constants derived from a monoexponential fit of the means of the observed concentrations at each time point. Concentrations (means ± standard deviations) in plasma, ELF, and AC, respectively, were 7.3 ± 4.9, 64.3 ± 33.1, and 2.2 ± 0.6 μg/ml at the 4-h BAL time point and 7.6 ± 1.7, 24.3 ± 13.3, and 1.4 ± 1.3 μg/ml at the 12-h BAL time point. Linezolid concentrations in plasma, ELF, and AC declined monoexponentially, with half-lives of 6.9, 7.0, and 5.7 h, respectively. For a MIC of 4, the 12-h plasma AUC/MIC and maximum concentration/MIC ratios were 34.6 and 3.9, respectively, and the percentage of time the drug remained above the MIC for the 12-h dosing interval was 100%; the corresponding ratios in ELF were 120 and 16.1, respectively, and the percentage of time the drug remained above the MIC was 100%. The long plasma and intrapulmonary linezolid half-lives and the percentage of time spent above the MIC of 100% of the dosing interval provide a pharmacokinetic rationale for drug administration every 12 h and indicate that linezolid is likely to be an effective agent for the treatment of pulmonary infections.

Noninvasive evaluation of pulmonary artery pressure during exercise by saline-enhanced Doppler echocardiography in chronic pulmonary disease.

To determine the feasibility of noninvasive determination of right ventricular systolic pressure (RVSP) during a graded-exercise protocol, saline contrast-enhanced Doppler echocardiography of tricuspid insufficiency was performed in 36 patients with chronic lung disease and 12 normal controls. In the patients with chronic pulmonary disease, symptom-limited, incremental supine bicycle exercise and pulse oximetry were performed on and off high-flow oxygen. Technically adequate Doppler studies were initially obtained in 20 patients (56%) at rest and 14 (39%) on exercise; these numbers increased to 33 (92%) and 32 (89%), respectively, after enhancement with agitated saline (both p less than 0.001). In 10 patients with chronic lung disease who had simultaneous hemodynamic monitoring during exercise, the correlation between Doppler and catheter measurements of pulmonary artery systolic pressure was close (r = 0.98). Among controls, RVSP increased from 22 +/- 4 at rest (mean +/- SD) to 31 +/- 7 mm Hg at peak exercise. In patients with chronic lung disease, RVSP increased from 46 +/- 20 to 83 +/- 30 mm Hg (both p less than 0.001 vs. controls). Despite normal resting values for RVSP in 28% of study patients, nearly all showed abnormal increases in RVSP during supine bicycle exercise. Increases in RVSP during exercise were greatest in patients who showed oxyhemoglobin desaturation. The short-term administration of oxygen significantly blunted the increase in RVSP during exercise. Saline contrast-enhanced Doppler evaluation of tricuspid insufficiency seems a potentially valuable noninvasive method of determining the exercise response of RVSP in patients with chronic pulmonary disease.

mTOR cascade activation distinguishes tubers from focal cortical dysplasia.

Balloon cells (BCs) in focal cortical dysplasia (FCD) and giant cells (GCs) in tubers of the tuberous sclerosis complex (TSC) share phenotypic similarities. TSC1 or TSC2 gene mutations in TSC lead to mTOR pathway activation and p70S6kinase (phospho‐S6K) and ribosomal S6 (phospho‐S6) protein phosphorylation. Phospho‐S6K, phospho‐S6, and phospho‐S6K–activated proteins phospho‐STAT3 and phospho‐4EBP1 were detected immunohistochemically in GCs, whereas only phospho‐S6 was observed in BCs. Expression of four candidate gene families (cell signaling, cell adhesion, growth factor/receptor, and transcription factor mRNAs) was assayed in single, microdissected phospho‐S6–immunolabeled BCs and GCs as a strategy to define whether BCs and GCs exhibit differential transcriptional profiles. Among 60 genes, differential expression of 24 mRNAs distinguished BCs from GCs and only 4 genes showed similar expression profiles between BCs and GCs. Tuberin mRNA levels were reduced in GCs from TSC patients with TSC2 gene mutations but were unchanged in BCs. Phospho‐S6K, ‐S6, ‐STAT3, and ‐4EBP1 expression in GCs reflects loss of hamartin‐tuberin–mediated mTOR pathway inhibition. Phospho‐S6 expression alone in BCs does not support mTOR cascade activation in FCD. Differential gene expression profiles in BCs and GCs supports the hypothesis that these cell types derive by distinct pathogenic mechanisms. Ann Neurol 2004

Mutations of CASK cause an X-linked brain malformation phenotype with microcephaly and hypoplasia of the brainstem and cerebellum

CASK is a multi-domain scaffolding protein that interacts with the transcription factor TBR1 and regulates expression of genes involved in cortical development such as RELN. Here we describe a previously unreported X-linked brain malformation syndrome caused by mutations of CASK. All five affected individuals with CASK mutations had congenital or postnatal microcephaly, disproportionate brainstem and cerebellar hypoplasia, and severe mental retardation.CASK is a multi-domain scaffolding protein that interacts with the transcription factor TBR1 and regulates expression of genes involved in cortical development such as RELN. Here we describe a previously unreported X-linked brain malformation syndrome caused by mutations of CASK. All five affected individuals with CASK mutations had congenital or postnatal microcephaly, disproportionate brainstem and cerebellar hypoplasia, and severe mental retardation.

Development of the superior temporal neocortex is anomalous in trisomy 21

Abstract. Trisomy 21 (Down syndrome) is the most common inherited form of mental retardation in the United States, however, the basis of impaired cognition is unknown. We have used recently developed stereological cell counting techniques to quantitatively examine the pattern of neuronal migration and maturation in one neocortical area during gestation in normal development and in trisomy 21. Normal development of the cerebral cortex occurs in two general sequences: Beginning at approximately 7-8 weeks gestation, migration of cells destined to become neurons results in the accumulation of cells in the cortical mantle. This process is largely complete by 20-21 weeks. Over the next 7-10 weeks an “inside-out” differentiation into lamina of different neuronal densities occurs. Our data suggest that the second phase of cortical development, the emergence of lamination, is both delayed and disorganized in trisomy 21. The observed pattern of cortical maturation may reflect an abnormality in axonal and dendritic arborization that subsequently subserve the connectional and functional units underlying normal cognition.

Targeted loss of Arx results in a developmental epilepsy mouse model and recapitulates the human phenotype in heterozygous females

Mutations in the X-linked aristaless-related homeobox gene (ARX) have been linked to structural brain anomalies as well as multiple neurocognitive deficits. The generation of Arx-deficient mice revealed several morphological anomalies, resembling those observed in patients and an interneuron migration defect but perinatal lethality precluded analyses of later phenotypes. Interestingly, many of the neurological phenotypes observed in patients with various ARX mutations can be attributed, in part, to interneuron dysfunction. To directly test this possibility, mice carrying a floxed Arx allele were generated and crossed to Dlx5/6(CRE-IRES-GFP)(Dlx5/6(CIG)) mice, conditionally deleting Arx from ganglionic eminence derived neurons including cortical interneurons. We now report that Arx(-/y);Dlx5/6(CIG) (male) mice exhibit a variety of seizure types beginning in early-life, including seizures that behaviourally and electroencephalographically resembles infantile spasms, and show evolution through development. Thus, this represents a new genetic model of a malignant form of paediatric epilepsy, with some characteristics resembling infantile spasms, caused by mutations in a known infantile spasms gene. Unexpectedly, approximately half of the female mice carrying a single mutant Arx allele (Arx(-/+);Dlx5/6(CIG)) also developed seizures. We also found that a subset of human female carriers have seizures and neurocognitive deficits. In summary, we have identified a previously unrecognized patient population with neurological deficits attributed to ARX mutations that are recapitulated in our mouse model. Furthermore, we show that perturbation of interneuron subpopulations is an important mechanism underling the pathogenesis of developmental epilepsy in both hemizygous males and carrier females. Given the frequency of ARX mutations in patients with infantile spasms and related disorders, our data unveil a new model for further understanding the pathogenesis of these disorders.

Stage-specific effects of bone morphogenetic proteins on the oligodendrocyte lineage.

Oligodendrocyte maturation is regulated by multiple secreted factors present in the brain during critical stages of development. Whereas most of these factors promote oligodendrocyte proliferation and survival, members of the bone morphogenetic protein family (BMPs) recently have been shown to inhibit oligodendrocyte differentiation in vitro. Oligodendrocyte precursors treated with BMPs differentiate to the astrocyte lineage. Given that cells at various stages of the oligodendrocyte lineage have distinct responses to growth factors, we hypothesized that the response to BMP would be stage-specific. Using highly purified, stage-specific cultures, we found that BMP has distinct effects on cultured oligodendrocyte preprogenitors, precursors, and mature oligodendrocytes. Oligodendrocyte preprogenitors (PSA-NCAM+, A2B5-) treated with BMP2 or BMP4 developed a novel astrocyte phenotype characterized by a morphological change and expression of glial fibrillary acidic protein (GFAP) but little glutamine synthetase expression and no labeling with A2B5 antibody. In contrast, treating oligodendrocyte precursors with BMPs resulted in the accumulation of cells with the traditional type 2 astrocyte phenotype (GFAP+, A2B5+). However, many of the cells with an astrocytic morphology did not express GFAP or glutamine synthetase unless thyroid hormone was present in the medium. The addition of fibroblast growth factor along with BMP to either oligodendrocyte preprogenitor or the oligodendrocyte precursor cells inhibited the switch to the astrocyte lineage, whereas platelet-derived growth factor addition had no effect. Treatment of mature oligodendrocytes with BMP elicited no change in morphology or expression of GFAP. These data suggest that as cells progress through the oligodendrocyte lineage, they show developmentally restricted responses to the BMPs.

Does Chronic Microaspiration Cause Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is a diffuse fibrotic lung disease of unknown etiology with no effective treatment. Emerging data support a role for chronic microaspiration (ie, subclinical aspiration of small droplets) in the pathogenesis and natural history of idiopathic pulmonary fibrosis. However, the precise relationship between chronic microaspiration and idiopathic pulmonary fibrosis remains unknown. Gastroesophageal reflux, a presumed risk factor for microaspiration, has been strongly associated with idiopathic pulmonary fibrosis with an estimated prevalence of up to 90%. This review aims to describe the relationship between chronic microaspiration and idiopathic pulmonary fibrosis by laying out the clinical and biologic rationale for this relationship and exploring the scientific evidence available. The gaps in our current understanding of the diagnosis of chronic microaspiration and idiopathic pulmonary fibrosis and the ongoing uncertainties in management and treatment will be highlighted. Defining the role of chronic microaspiration in idiopathic pulmonary fibrosis is essential as it has potential clinical, pathobiological, and treatment implications for this deadly disease.