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Biomedical subjects

Howard J Worman

Publications and source records attributed to Howard J Worman.

At least 19 recordsLinked to original sources
PubMed2007

Emery-Dreifuss muscular dystrophy.

Emery-Dreifuss muscular dystrophy (EDMD) is inherited in an X-linked or autosomal manner. X-linked EDMD is caused by mutations in EMD, which encodes an integral protein of the nuclear envelope inner membrane called emerin. Autosomally inherited EDMD is caused by mutations in LMNA, which encodes A-type nuclear lamins, intermediate filament proteins associated with inner nuclear membrane. Although the causative mutations have been described and mouse models have been created, the pathogenic processes by which mutations in genes encoding nuclear envelope proteins cause striated muscle abnormalities in EDMD remain obscure. Working hypotheses include effects on nuclear structural integrity, increased cellular susceptibility to mechanical stress damage, alterations in gene expression in response to nuclear envelope changes, and effects on cell proliferation and differentiation.

History, 20th Century↗
PubMed2006

Proteasome-mediated degradation of integral inner nuclear membrane protein emerin in fibroblasts lacking A-type lamins.

We previously identified and characterized a homozygous LMNA nonsense mutation leading to the absence of A-type lamins in a premature neonate who died at birth. We show here that the absence of A-type lamins is due to degradation of the aberrant mRNA transcript with a premature termination codon. In cultured fibroblasts from the subject with the homozygous LMNA nonsense mutation, there was a decreased steady-state expression of the integral inner nuclear membrane proteins emerin and nesprin-1alpha associated with their mislocalization to the bulk endoplasmic reticulum and a hyperphosphorylation of emerin. To determine if decreased emerin expression occurred post-translationally, we treated cells with a selective proteasome inhibitor and observed an increase in expression. Our results show that mislocalization of integral inner nuclear membrane proteins to the endoplasmic reticulum in human cells lacking A-type lamins leads to their degradation and provides the first evidence that their degradation is mediated by the proteasome.

Cells, Cultured↗
PubMed2006

Pathology and nuclear abnormalities in hearts of transgenic mice expressing M371K lamin A encoded by an LMNA mutation causing Emery-Dreifuss muscular dystrophy.

Mutations in LMNA, which encodes nuclear lamins A and C, cause a broad range of diseases, including autosomal dominant Emery-Dreifuss muscular dystrophy (EDMD) and related disorders with a predominant cardiomyopathy. Homozygous Lmna model "knock-in" and null mice develop cardiomyopathy, whereas heterozygous mice do not. Overexpression of lamin A mutants that cause cardiomyopathy in cultured cells induces morphological abnormalities in the nuclear envelope and lamina; however, effects on tissue and organ pathology have not been determined. We used the heart-selective alpha-myosin heavy chain promoter to drive expression in transgenic mice of human wild-type and M371K lamin A, which causes EDMD. Mice expressing M371K lamin A were born at approximately 0.07 of the expected frequency and those born typically died at 2-7 weeks of age. Histological analysis showed increased eosinophilia and fragmentation of cardiomyofibrils, nuclear pyknosis and edema without fibrosis or significant inflammation, indicative of acute or subacute injury. Mice expressing human wild-type lamin A were born at only slightly less than the expected frequency and had normal life spans. Confocal immunofluorescence microscopy demonstrated abnormal nuclear envelopes with intranuclear foci of lamins in cardiac cells expressing M371K lamin A. Electron microscopy revealed extensively convoluted nuclear envelopes, intranuclear inclusions and chromatin clumps in cardiomyocyte nuclei. These results demonstrate that expression of a lamin A mutant that induces alterations in nuclear morphology can cause tissue and organ damage in mice with a normal complement of wild-type lamins.

Animals↗
PubMed2006

The carboxyl-terminal nucleoplasmic region of MAN1 exhibits a DNA binding winged helix domain.

MAN1 is an integral protein of the inner nuclear membrane that interacts with nuclear lamins and emerin, thus playing a role in nuclear organization. It also binds to chromatin-associated proteins and transcriptional regulators, including the R-Smads, Smad1, Smad2, and Smad3. Mutations in the human gene encoding MAN1 cause sclerosing bone dysplasias, which sometimes have associated skin abnormalities. At the molecular level, these mutations lead to loss of the MAN1-R-Smads interaction, thus perturbing transforming growth factor beta superfamily signaling pathway. As a first step to understanding the physical basis of MAN1 interaction with R-Smads, we here report the structural characterization of the carboxyl-terminal nucleoplasmic region of MAN1, which is responsible for Smad binding. This region exhibits an amino-terminal globular domain adopting a winged helix fold, as found in several Smad-associated sequence-specific DNA binding factors. Consistently, it binds to DNA through the positively charged recognition helix H3 of its winged helix motif. However, it does not show the predicted carboxyl-terminal U2AF homology domain in solution, suggesting that the folding and stability of such a domain in MAN1 depend upon binding to an unidentified partner. Modeling the complex between DNA and the winged helix domain shows that the regions involved in DNA binding are essentially distinct from those reported to be involved in Smad binding. This suggests that MAN1 binds simultaneously to R-Smads and their targeted DNA sequences.

Amino Acid Sequence↗
PubMed2006

Inner nuclear membrane and regulation of Smad-mediated signaling.

Smads mediate signal transduction by cytokines of the transforming growth factor-beta family. Recent data show that intrinsic and extrinsic proteins of the inner nuclear membrane affect the activities of Smads. MAN1, an integral protein of the inner nuclear membrane, binds to receptor-regulated Smads and antagonizes signaling by transforming growth factor-beta, activin and bone morphogenic protein. Lamins A and C, extrinsic intermediate filament proteins of the inner nuclear membrane that are mutated in several human diseases, appear to regulate phosphorylation of Smads. These data demonstrate that proteins within and associated with the inner nuclear membrane lipid bilayer regulate signal transduction pathways involved in numerous developmental, physiological and pathophysiological processes.

Animals↗
PubMed2006

Dependence of diffusional mobility of integral inner nuclear membrane proteins on A-type lamins.

Integral proteins of the nuclear envelope inner membrane have been proposed to reach their sites by diffusion after their co-translational insertion in the rough endoplasmic reticulum. They are then retained in the inner nuclear membrane by binding to nuclear structures. One such structure is the nuclear lamina, an intermediate filament meshwork composed of A-type and B-type lamin proteins. Emerin, MAN1, and LBR are three integral inner nuclear membrane proteins. We expressed these proteins fused to green fluorescent protein in embryonic fibroblasts from wild-type mice and Lmna -/- mice, which lack A-type lamins. We then studied the diffusional mobilities of emerin, MAN1, and LBR using fluorescence recovery after photobleaching. We show that emerin and MAN1, but not LBR, are more mobile in the inner nuclear membrane of cells from Lmna -/- mice than in cells from wild-type mice. In cells from Lmna -/- mice expressing exogenous lamin A, the protein mobilities were similar to those in cells from wild-type mice. This supports a model where emerin and MAN1 are at least partly retained in the inner nuclear membrane by binding to A-type lamins, while LBR depends on other binding partners for its retention.

Animals↗
PubMed2006

Nuclear lamin A inhibits adipocyte differentiation: implications for Dunnigan-type familial partial lipodystrophy.

Mutations in the LMNA gene encoding A-type lamins cause several diseases, including Emery-Dreifuss muscular dystrophy and Dunnigan-type familial partial lipodystrophy (FPLD). We analyzed differentiation of 3T3-L1 preadipocytes to adipocytes in cells overexpressing wild-type lamin A as well as lamin A with amino acid substitutions at position 482 that cause FPLD. We also examined adipogenic conversion of mouse embryonic fibroblasts lacking A-type lamins. Overexpression of both wild-type and mutant lamin A inhibited lipid accumulation, triglyceride synthesis and expression of adipogenic markers. This was associated with inhibition of expression of peroxisome-proliferator-activated receptor gamma 2 (PPARgamma2) and Glut4. In contrast, embryonic fibroblasts lacking A-type lamins accumulated more intracellular lipid and exhibited elevated de novo triglyceride synthesis compared with wild-type fibroblasts. They also had increased basal phosphorylation of AKT1, a mediator of insulin signaling. We conclude that A-type lamins act as inhibitors of adipocyte differentiation, possibly by affecting PPARgamma2 and insulin signaling.

3T3 Cells↗
PubMed2006

Here come the SUNs: a nucleocytoskeletal missing link.

The nuclear envelope has traditionally been thought of as a barrier that separates the nucleoplasm from the cytoplasm in eukaryotic cells. Increasing evidence shows that the nuclear envelope also links the inside of the nucleus to the cytoskeleton. Here we discuss recent papers showing that this link occurs through complexes of lamins on the inner aspect of the inner nuclear membrane, transmembrane proteins of the inner nuclear membrane called SUNs and large nesprin isoforms localized specifically to the outer nuclear membrane. These discoveries have implications for nuclear positioning, nuclear migration and pathogenesis of inherited diseases that are caused by mutations in nuclear envelope proteins.

Animals↗
PubMed2006

Correlation of initial autoantibody profile and clinical outcome in primary biliary cirrhosis.

Although there have been significant advances in understanding the clinical and biochemical features of primary biliary cirrhosis (PBC), there is still a paucity of data on the usefulness of biomarkers as prognostic indicators. This is particularly important at the time of initial diagnosis. Indeed, the widespread use of antimitochondrial antibody testing has led to an earlier diagnosis of asymptomatic PBC and it is difficult to predict which patients will experience a benign versus a rapidly progressive course. To address this issue, we examined a unique population of 127 newly diagnosed patients with PBC during a 15-year period of observation that began in January 1990. Sera from these patients were analyzed for antimitochondrial, antinuclear, and anti-smooth muscle antibodies, and immunoblotting was performed for nuclear pore complex (NPC). The patients were then followed up longitudinally using biochemical liver function tests. No patient was under any medical therapy for PBC at the time of the initial sera collection. Data were analyzed based not only on the clinical features, but also the Mayo score and specific outcome measures, including time to death, need for liver transplantation, and complication free survival. Among patients with early disease, bilirubin increased to >2 mg/dL in the anti-NPC(+) patients (26% vs. 5%, P = .019). Anti-NPC antibodies remained stable or slightly increased over the period of observation. In condusion, anti-NPC identifies patients likely to experience an unfavorable clinical course and more rapid disease progression.

Adult↗
PubMed2005

Inner nuclear membrane and signal transduction.

Recent research has shown that the inner nuclear membrane is a site for regulation of signal transduction from the plasma membrane to the nucleus. This has coincided with discoveries showing that mutations in extrinsic and intrinsic inner nuclear membrane proteins cause a variety of inherited diseases. In most instances, the mechanisms by which mutations in inner nuclear membrane proteins cause disease are not understood. In at least one case, however, an alteration in signal transduction appears to underlie disease pathogenesis.

Animals↗
PubMed2005

Dermal fibroblasts in Hutchinson-Gilford progeria syndrome with the lamin A G608G mutation have dysmorphic nuclei and are hypersensitive to heat stress.

BACKGROUND: Hutchinson-Gilford progeria syndrome (HGPS, OMIM 176670) is a rare sporadic disorder with an incidence of approximately 1 per 8 million live births. The phenotypic appearance consists of short stature, sculptured nose, alopecia, prominent scalp veins, small face, loss of subcutaneous fat, faint mid-facial cyanosis, and dystrophic nails. HGPS is caused by mutations in LMNA, the gene that encodes nuclear lamins A and C. The most common mutation in subjects with HGPS is a de novo single-base pair substitution, G608G (GGC>GGT), within exon 11 of LMNA. This creates an abnormal splice donor site, leading to expression of a truncated protein. RESULTS: We studied a new case of a 5 year-old girl with HGPS and found a heterozygous point mutation, G608G, in LMNA. Complementary DNA sequencing of RNA showed that this mutation resulted in the deletion of 50 amino acids in the carboxyl-terminal tail domain of prelamin A. We characterized a primary dermal fibroblast cell line derived from the subject's skin. These cells expressed the mutant protein and exhibited a normal growth rate at early passage in primary culture but showed alterations in nuclear morphology. Expression levels and overall distributions of nuclear lamins and emerin, an integral protein of the inner nuclear membrane, were not dramatically altered. Ultrastructural analysis of the nuclear envelope using electron microscopy showed that chromatin is in close association to the nuclear lamina, even in areas with abnormal nuclear envelope morphology. The fibroblasts were hypersensitive to heat shock, and demonstrated a delayed response to heat stress. CONCLUSION: Dermal fibroblasts from a subject with HGPS expressing a mutant truncated lamin A have dysmorphic nuclei, hypersensitivity to heat shock, and delayed response to heat stress. This suggests that the mutant protein, even when expressed at low levels, causes defective cell stability, which may be responsible for phenotypic abnormalities in the disease.

Cell Nucleus↗
PubMed2005

Intracellular trafficking and dynamics of double homeodomain proteins.

Double homeodomain (DUX) proteins are encoded by a family of 3.3-kilobase repeated elements dispersed in the human genome. One of these elements named D4Z4 is found in a tandem repeat array on chromosome 4 that is partially deleted in facioscapulohumeral muscular dystrophy. We have evaluated the trafficking and mobility of two DUX proteins, DUX1 and DUX4. We transfected C2C12 myoblasts with cDNA encoding these proteins fused to the green fluorescent protein and studied their intracellular localization and diffusional mobilities using fluorescence recovery after photobleaching and fluorescence loss in photobleaching. We also studied truncated forms of the proteins, containing one or both homeodomains or a region outside the homeodomains. We show that both full-length proteins are actively transported into the nucleus, and that the homeodomains contain the signals required for this localization. DUX1 is more mobile than DUX4 within the nucleus (t(1/2) = 4.8 s for DUX1 and 13.4 s for DUX4), suggesting differences in the way the two proteins interact with nuclear components.

Active Transport, Cell Nucleus↗
PubMed2005

Risk factors and comorbidities in primary biliary cirrhosis: a controlled interview-based study of 1032 patients.

Primary biliary cirrhosis (PBC) is an autoimmune disease of unknown etiology, often associated with other autoimmune conditions. Controlled studies have so far provided conflicting data on risk factors and comorbidity rates in PBC. We enrolled patients with PBC (n = 1032) from 23 tertiary referral centers for liver diseases in the United States and random-digit-dialed controls (n = 1041) matched for sex, age, race, and geographical location. Patients and controls were administered a modified version of the US National Health and Nutrition Examination Study (NHANES III) questionnaire by trained personnel to evaluate associations between PBC and social, demographic, personal and family medical histories, lifestyle, and reproductive factors and the rates of comorbidity in affected individuals. Data indicate that having a first-degree relative with PBC (adjusted odds ratio [AOR] 10.736; 95% confidence interval 4.227-27.268), history of urinary tract infections (AOR 1.511, 95% CI 1.192-1.915), past smoking (AOR 1.569, 95% CI 1.292-1.905), or use of hormone replacement therapies (AOR 1.548, 95% CI 1.273-1.882) were significantly associated with increased risk of PBC. The frequent use of nail polish slightly increased the risk of having PBC. Other autoimmune diseases were found in 32% of cases and 13% of controls (P<0.0001). In conclusion, environmental factors, possibly including infectious agents through urinary tract infections or chemicals contained in cigarette smoke, may induce PBC in genetically susceptible individuals. Exogenous estrogens may also contribute to explain the female predominance of the disease.

Aged↗
PubMed2005

Nuclear envelope, nuclear lamina, and inherited disease.

The nuclear envelope is composed of the nuclear membranes, nuclear lamina, and nuclear pore complexes. In recent years, mutations in nuclear-envelope proteins have been shown to cause a surprisingly wide array of inherited diseases. While the mutant proteins are generally expressed in most or all differentiated somatic cells, many mutations cause fairly tissue-specific disorders. Perhaps the most dramatic case is that of mutations in A-type lamins, intermediate filament proteins associated with the inner nuclear membrane. Different mutations in the same lamin proteins have been shown to cause striated muscle diseases, partial lipodystrophy syndromes, a peripheral neuropathy, and disorders with features of severe premature aging. In this review, we summarize fundamental aspects of nuclear envelope structure and function, the inherited diseases caused by mutations in lamins and other nuclear envelope proteins, and possible pathogenic mechanisms.

Animals↗
PubMed2005

Hepatic steatosis in Dunnigan-type familial partial lipodystrophy.

OBJECTIVES: Characterization of familial clusters of subjects with metabolic derangements predisposing to hepatic steatosis and nonalcoholic steatohepatitis could facilitate genomic studies to identify risk factors for their development. Dunnigan-type familial partial lipodystrophy (FPLD) is an autosomal dominantly inherited disorder caused by mutations in the LMNA gene. Affected subjects have loss of subcutaneous fat from the extremities and symptoms similar to those characterizing the metabolic syndrome, including insulin resistance and dyslipidemia. The goal of this study was to determine the prevalence of steatosis in subjects with FPLD. METHODS: We examined 18 subjects from six families with FPLD for mutations in LMNA and analyzed plasma lipid and serum glucose concentrations. Liver ultrasound and serum aminotransferase activities were used as indicators of steatosis or steatohepatitis. In two subjects, histological examination of hepatic tissue was performed. RESULTS: All subjects had FPLD-causing mutations in LMNA. Plasma lipids were measured in 17 subjects, 16 of whom had hyperlipidemia and 14 presented with either documented insulin resistance or diabetes mellitus. Hepatic steatosis was present in 15 subjects who had ultrasound examinations and 9 of these had elevated serum aminotransferase activities. Liver biopsy confirmed steatosis in 2 subjects. CONCLUSIONS: Hepatic steatosis is part of the clinical phenotype of FPLD. This familial disorder may provide a human metabolic model system to facilitate genomic and environmental studies to determine risk factors for hepatic steatosis and nonalcoholic steatohepatitis.

Adipose Tissue↗
PubMed2005

Components of the nuclear envelope and their role in human disease.

The nuclear envelope is composed of the nuclear lamina, nuclear pore complexes and nuclear membranes. The outer nuclear membrane is very similar to the rough endoplasmic reticulum. The pore membranes contain unique integral proteins and are associated with nuclear pore complexes. The inner nuclear membrane is associated with heterochromatin and the nuclear lamina, a meshwork of intermediate filament proteins called lamins. In humans, lamins are encoded by three genetic loci, LMNA, LMNB1 and LMNB2. Mutations in LMNA cause a spectrum of inherited diseases, including autosomal dominant Emery-Dreifuss muscular dystrophy and related striated muscle disorders, partial lipodystrophies, a peripheral neuropathy and progeria syndromes. Eighty or more transmembrane proteins may reside primarily in the inner nuclear membrane but only several have been fairly well characterized. These include emerin, which is mutated in X-linked Emery-Dreifuss muscular dystrophy, LAP2, MAN1 and LBR. LBR binds to B-type lamins and chromatin proteins and shares sequence similarities with sterol reductases. Heterozygous mutations in LBR cause Pelger-Huët anomaly, characterized by morphologically abnormal neutrophil nuclei, and homozygous mutations cause HEM/Greenberg skeletal dysplasia, characterized by developmental abnormalities and 3 beta-hydroxysterol-epsilon-14-reductase deficiency. Further studies of nuclear envelope proteins may uncover additional unsuspected relationships to human disease.

Animals↗
PubMed2004

MAN1, an integral protein of the inner nuclear membrane, binds Smad2 and Smad3 and antagonizes transforming growth factor-beta signaling.

MAN1 (also known as LEMD3) is an integral protein of the inner nuclear membrane. Recently, mutations in MAN1 have been shown to result in osteopoikilosis, Buschke-Ollendorff syndrome and melorheostosis. We show that the nucleoplasmic, C-terminal domain of human MAN1 binds to Smad2 and Smad3 and antagonizes signaling by transforming growth factor-beta (TGF-beta). In a yeast two-hybrid screen using the C-terminal domain of MAN1 as bait, eight positive clones were obtained that encoded Smad3. In direct two-hybrid assays, this portion of MAN1 bound to Smad2 and Smad3. In glutathione-S-transferase precipitation assays, the C-terminal domain of MAN1 bound to Smad2 and Smad3 under stringent conditions. Antibodies against MAN1 were able to co-immunoprecipiate Smad2 from cells, demonstrating that they reside in the same complex in vivo. TGF-beta treatment stimulated transcription from a reporter gene in control cells, but reporter gene stimulation was significantly inhibited in cells overexpressing MAN1 or its C-terminal domain but not its N-terminal domain. TGF-beta-induced cell proliferation arrest was also inhibited in stable cell lines overexpressing MAN1. These results show that the nuclear envelope regulates a signal transduction pathway and have implications for how mutations in nuclear envelope proteins cause different human diseases.

Cell Line↗