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PubMed2004

Fluctuations of intracellular iron modulate elastin production.

Production of insoluble elastin, the major component of elastic fibers, can be modulated by numerous intrinsic and exogenous factors. Because patients with hemolytic disorders characterized with fluctuations in iron concentration demonstrate defective elastic fibers, we speculated that iron might also modulate elastogenesis. In the present report we demonstrate that treatment of cultured human skin fibroblasts with low concentration of iron 2-20 microm (ferric ammonium citrate) induced a significant increase in the synthesis of tropoelastin and deposition of insoluble elastin. Northern blot and real-time reverse transcription-PCR analysis revealed that treatment with 20 microm iron led to an increase of approximately 3-fold in elastin mRNA levels. Because treatment with an intracellular iron chelator, desferrioxamine, caused a significant decrease in elastin mRNA level and consequent inhibition of elastin deposition, we conclude that iron facilitates elastin gene expression. Our experimental evidence also demonstrates the existence of an opposite effect, in which higher, but not cytotoxic concentrations of iron (100-400 microm) induced the production of intracellular reactive oxygen species that coincided with a significant decrease in elastin message stability and the disappearance of iron-dependent stimulatory effect on elastogenesis. This stimulatory elastogenic effect was reversed, however, in cultures simultaneously treated with high iron concentration (200 microm) and the intracellular hydroxyl radical scavenger, dimethylthiourea. Thus, presented data, for the first time, demonstrate the existence of two opposite iron-dependent mechanisms that may affect the steady state of elastin message. We speculate that extreme fluctuations in intracellular iron levels result in impaired elastic fiber production as observed in hemolytic diseases.

Base Sequence↗
PubMed2006

Cooperativity between the hydrophobic and cross-linking domains of elastin.

The principal protein component of the elastic fiber found in elastic tissues is elastin, an amorphous, cross-linked biopolymer that is assembled from a high molecular weight monomer. The hydrophobic and cross-linking domains of elastin have been considered separate and independent, such that changes to one region are not thought to affect the other. However, results from these solid-state 13C NMR experiments demonstrate that cooperativity in protein folding exists between the two domain types. The sequence of the EP20-24-24 polypeptide has three hydrophobic sequences from exons 20 and 24 of the soluble monomer tropoelastin, interspersed with cross-linking domains constructed from exons 21 and 23. In the middle of each cross-linking domain is a "hinge" sequence. When this pentapeptide is replaced with alanines, as in EP20-24-24[23U], its properties are changed. In addition to the expected increase in alpha-helical content and the resulting increase in rigidity of the cross-linking domains, changes to the organization of the hydrophobic regions are also observed. Using one-dimensional CPMAS (cross-polarization with magic angle spinning) techniques, including spectral editing and relaxation measurements, evidence for a change in dynamics to both domain types is observed. Furthermore, it is likely that the methyl groups of the leucines of the hydrophobic domains are also affected by the substitution to the hinge region of the cross-linking sequences. This cooperativity between the two domain types brings new questions to the phenomenon of coacervation in elastin polypeptides and strongly suggests that functional models for the protein must include a role for the cross-linking regions.

Alanine↗
PubMed1986

Ultrastructural immunolocalization of lysyl oxidase in vascular connective tissue.

The localization of lysyl oxidase was examined in calf and rat aortic connective tissue at the ultrastructural level using polyclonal chicken anti-lysyl oxidase and gold conjugated rabbit anti-chicken immunoglobulin G to identify immunoreactive sites. Electron microscopy of calf aortic specimens revealed discrete gold deposits at the interface between extracellular bundles of amorphous elastin and the microfibrils circumferentially surrounding these bundles. The antibody did not react with microfibrils which were distant from the interface with elastin. There was negligible deposition of gold within the bundles of amorphous elastin and those few deposits seen at these sites appeared to be associated with strands of microfibrils. Lysyl oxidase was similarly localized in newborn rat aorta at the interface between microfibrils and nascent elastin fibers. Gold deposits were not seen in association with extracellular collagen fibers even after collagen-associated proteoglycans had been degraded by chondroitinase ABC. However, the antibody did recognize collagen-bound lysyl oxidase in collagen fibers prepared from purified collagen to which the enzyme had been added in vitro. No reaction product was seen if the anti-lysyl oxidase was preadsorbed with purified lysyl oxidase illustrating the specificity of the antibody probe. The present results are consistent with a model of elastogenesis predicting the radial growth of the elastin fiber by the deposition and crosslinking of tropoelastin units at the fiber-microfibril interface.

Amino Acid Oxidoreductases↗
PubMed1993

Emilin, a component of elastic fibers preferentially located at the elastin-microfibrils interface.

The fine distribution of the extracellular matrix glycoprotein emilin (previously known as glycoprotein gp115) (Bressan, G. M., I. Castellani, A. Colombatti, and D. Volpin. 1983. J. Biol. Chem. 258: 13262-13267) has been studied at the ultrastructural level with specific antibodies. In newborn chick aorta the protein was exclusively found within elastic fibers. In both post- and pre-embedding immunolabeling emilin was mainly associated with regions where elastin and microfibrils are in close contact, such as the periphery of the fibers. This localization of emilin in aorta has been confirmed by quantitative evaluation of the distribution of gold particles within elastic fibers. In other tissues, besides being associated with typical elastic fibers, staining for emilin was found in structures lacking amorphous elastin, but where the presence of tropoelastin has been demonstrated by immunoelectron microscopy. This was particularly evident in the oxitalan fibers of the corneal stroma, in the Descemet's membrane, and in the ciliary zonule. Analysis of embryonic aorta revealed the presence of emilin at early stages of elastogenesis, before the appearance of amorphous elastin. Immunofluorescence studies have shown that emilin produced by chick embryo aorta cells in culture is strictly associated with elastin and that the process of elastin deposition is severely altered by the presence of antiemilin antibodies in the culture medium. The name of the protein was derived from its localization at sites where elastin and microfibrils are in proximity (emilin, elastin microfibril interface located protein).

Animals↗
PubMed1995

Mutations in the human gene for fibrillin-1 (FBN1) in the Marfan syndrome and related disorders.

The extracellular microfibril, 10-14 nm in diameter, performs a number of functions, including serving as the scaffolding for deposition of tropoelastin to form elastic fibers. A variety of proteins compose the structure of microfibrils, the most prominent of which are the two fibrillins. Fibrillin-1 is encoded by FBN1 on human chromosome 15q21 and fibrillin-2 is encoded by FBN2 on 5q23. Each fibrillin monomer contains a large number of epidermal growth factor-like motifs, most capable of binding calcium ions, and a few motifs resembling the binding protein for transforming growth factor beta. In vitro polymerization of fibrillin monomers produces 'beads on a string' structures that look on electron microscopy much like microfibrils purified from the extracellular matrices of a variety of tissues. Mutations in FBN1 produce Marfan syndrome, a pleiotropic autosomal dominant connective tissue disorder with prominent manifestations in the skeleton, eye and cardiovascular system. A number of conditions related to Marfan syndrome are also due to FBN1 mutations. Contractural arachnodactyly is due to mutations in FBN2. In this paper we review the published mutations in these genes, preliminary results of genotype-phenotype correlations, and speculations regarding molecular pathogenesis.

Fibrillin-1↗
PubMed2005

Transcriptional and posttranscriptional inhibition of lysyl oxidase expression by cigarette smoke condensate in cultured rat fetal lung fibroblasts.

Lysyl oxidase (LO) catalyzes crosslinking of collagen and elastin essential for maintaining the structural integrity of the lung extracellular matrix (ECM). To understand mechanisms of cigarette smoke (CS)-induced emphysema, we investigated effects of cigarette smoke condensate (CSC), the particulate matter of CS, on LO mRNA expression in cultured rat fetal lung fibroblasts (RFL6). Exposure of RFL6 cells to 0-120 microg CSC/ml for 24 h induced a dose-dependent inhibition of LO steady-state mRNAs, for example, reducing transcript levels to below 10% of the control in cells incubated with 80-120 microg CSC/ml. Nuclear run-on assays indicated a marked reduction in LO relative transcriptional rates amounting to 27.7% of the control in cells treated with 120 microg CSC/ml. The actinomycin D-chase assay showed that CSC enhanced the instability of LO transcripts. The t1/2 for LO mRNA decay was decreased from 24 h in the control to 4.5 h in cells treated with 120 microg CSC/ml. Moreover, 80-120 microg CSC/ml also inhibited LO promoter activity as revealed by suppression of reporter gene expression in cells transfected with LO promoter-luciferase vectors. Thus, inhibition of LO transcription initiation and enhancement of LO mRNA instability both contributed to downregulation of LO steady-state mRNA in CSC-treated cells. Note that inhibition of LO mRNA expression by CSC was closely accompanied by markedly decreased levels of transcripts of collagen type I and tropoelastin, two substrates of LO. Thus, transcriptional perturbation of LO and its substrates may be a critical mechanism for ECM damage in CS-induced emphysema.

Animals↗
PubMed1988

Cloning of full-length elastin cDNAs from a human skin fibroblast recombinant cDNA library: further elucidation of alternative splicing utilizing exon-specific oligonucleotides.

A human cDNA library was constructed utilizing RNA isolated from cultured skin fibroblasts. Recombinant clones containing elastin sequences were identified by plaque hybridizations with previously characterized human placental elastin cDNAs. Seven positive recombinant clones with inserts of approximately 3.2-2.2 kb were isolated. Characterization of the clones by restriction endonuclease analysis and dot-blot hybridizations with exon-specific synthetic oligonucleotides demonstrated considerable variability in the primary nucleotide sequence. Dideoxy nucleotide sequencing confirmed this finding. The variability is most likely a result of alternative splicing of exons from the primary elastin transcripts. The two largest clones contained approximately 1 kb of 3' untranslated sequence and approximately 2.2 kb of translated sequence encoding 730 amino acids. Six amino acids, encoded by exon 12A, have not been previously noted in human elastin cDNAs. In addition, these human skin fibroblast clones contained a 49 bp 5' untranslated sequence. These results demonstrate that there is considerable variability in the processed nucleotide sequence of the elastin mRNAs. These transcripts may code for isoforms of tropoelastin with different biologic properties.

Amino Acid Sequence↗
PubMed1983

Demonstration of collagenase and elastase activities in the blister fluids from bullous skin diseases. Comparison between dermatitis herpetiformis and bullous pemphigoid.

We have investigated potential mechanisms for blister formation by assaying proteolytic enzymes in the blister fluids of patients with various bullous diseases. Blister fluids were obtained from patients with dermatitis herpetiformis (DH), bullous pemphigoid (BP), chronic bullous disease of childhood (CBDC), and pemphigus vulgaris (PV). The cells were recovered by centrifugation, and the supernatants as well as the cell pellets were assayed first for collagenase activity using [3H]proline-labeled type I collagen as substrate. Collagenase activity could be detected in most cases with DH, BP, and CBDC, while no activity was found in 2 cases of PV or in 5 control blister fluids obtained from suction blisters induced in healthy control subjects. Elastase activity was assayed in the same blister fluids by using a synthetic substrate succinyl-(L-alanyl)3-paranitroanilide or soluble [14C]valine-labeled tropoelastin. High levels of elastase activity were present in all DH patients, while lower, but clearly detectable, levels were found in BP, CBDC, and PV. The enzyme activity in BP was inhibited by Na2EDTA, but not by phenylmethylsulfonyl fluoride (PMSF), and Ca2+ stimulated the activity, suggesting that the enzyme in BP was a metalloproteinase. In cell-free supernatants of the DH blister fluids, the elastase activity was markedly decreased by PMSF, indicating that most of the enzyme activity was due to a serine protease. The cells recovered from DH blister fluids also contained high levels of elastase activity which could be inhibited by PMSF but not by Na2EDTA. Thus, in DH, the elastase activity is probably derived from polymorphonuclear leukocytes abundantly present in the lesions. The results indicate that active proteases are present in the blister fluids of skin diseases, and they may play a mechanistic role in the blister formation by degrading connective tissue components of the dermis and the dermal-epidermal junction.

Adult↗
PubMed1992

Buschke-Ollendorff syndrome associated with elevated elastin production by affected skin fibroblasts in culture.

Buschke-Ollendorff syndrome (BOS; McKusick 16670) is an autosomal dominant connective-tissue disorder characterized by uneven osseous formation in bone (osteopoikilosis) and fibrous skin papules (dermatofibrosis lenticularis disseminata). We describe two patients in whom BOS occurred in an autosomal dominant inheritance pattern. The connective tissue of the skin lesions showed both collagen and elastin abnormalities by electron microscopy. Cultured fibroblasts from both patients produced 2-8 times more tropoelastin than normal skin fibroblasts in the presence of 10% calf serum. Involved skin fibroblasts of one patient produced up to eight times normal levels, whereas apparently uninvolved skin was also elevated more than threefold. In a second patient, whose involvement was nearly complete, elastin production was high in involved areas and less so in completely involved skin. Transforming growth factor-beta 1 (TGF beta 1), a powerful stimulus for elastin production, brought about similar relative increases in normal and BOS strains. Basic fibroblast growth factor, an antagonist of TGF beta 1-stimulated elastin production, was able to reduce elastin production in basal and TGF beta 1 stimulated BOS strains. Elastin mRNA levels were elevated in all patient strains, suggesting that Buschke-Ollendorff syndrome may result, at least in part, from abnormal regulation of extracellular matrix metabolism that leads to increased steady-state levels of elastin mRNA and elastin accumulation in the dermis.

Blotting, Southern↗
PubMed2004

Lysyl oxidase-like and lysyl oxidase are present in the dermis and epidermis of a skin equivalent and in human skin and are associated to elastic fibers.

Elastic fiber formation involves the secretion of tropoelastin which is converted to insoluble elastin by cross-linking, initiated by the oxidative deamination of lysine residues by lysyl oxidase. Five lysyl oxidase genes have been discovered. This study deals with the expression of two isoforms, LOX and LOX-like (LOXL), in human foreskin and in a human skin-equivalent (SE) model that allows the formation of elastic fibers. In this model, keratinocytes are added to a dermal equivalent made of fibroblasts grown on a chitosan-cross-linked collagen-GAG matrix. LOX and LOXL were detected by immunohistochemistry in the dermis and the epidermis of both normal skin and in a SE. This expression was confirmed by in situ hybridization on the SE. LOX and LOXL expression patterns were confirmed in human skin. The ultrastructural localization of LOXL was indicative of its association with elastin-positive materials within the SE and human skin, though interaction with collagen could not be discarded. LOX was found on collagen fibers and could be associated with elastin-positive materials in the SE and human skin. LOXL and LOX were detected in keratinocytes where LOX was mainly expressed by differentiating keratinocytes, in contrast to LOXL that can be found in both proliferating and differentiating fibroblasts. These data favor a role for LOXL in elastic fiber formation, together with LOX, and within the epidermis where both enzymes should play a role in post-translational modification of yet unknown substrates.

Amino Acid Oxidoreductases↗
PubMedDate not supplied

Menkes' kinky hair syndrome: ultrastructural cutaneous alterations of the elastic fibers.

Menkes' kinky hair syndrome is associated with the defective functioning of several copper-dependent enzymes due to impaired copper absorption, transport, or metabolism. Lysyl oxidase is a copper-requiring enzyme that catalyzes the oxidative deamination of lysyl residues linking two adjacent chains of tropoelastin polypeptides into an insoluble network. Elastin of the connective tissue is the responsible protein for the elastic properties of the skin. We report transmission electron microscopy findings concerning elastic fiber alterations of the skin in three patients with Menkes' syndrome. The reticular dermis showed marked changes in the elastic fibers with a paucity of the central amorphous component while retaining normal microfibrillary material. These ultrastructural observations, to the best of our knowledge, are reported for the first time in skin from these patients and may be readily interpreted in terms of a specific biochemical defect in elastogenesis.

Child, Preschool↗
PubMed1996

Biochemistry and molecular regulation of matrix macromolecules in abdominal aortic aneurysms.

Past concepts of aneurysmal dilatation as a passive process of attenuation are oversimplified and inaccurate. Aneurysm formation is a complex remodeling process that involves both synthesis and degradation of matrix proteins. Interstitial procollagen gene expression is increased in AAA compared to AOD or normal aorta, whereas tropoelastin gene expression is decreased in both AOD and AAA. The medial elastin network is disrupted and discontinuous in small AAA. Thus, the growth rate of an established AAA may well relate to the balance between collagen synthesis and degradation. Although the increased procollagen expression found in AAA may represent a compensatory response, understanding the factors that modulate matrix metabolism in AAA may allow for development of pharmacologic strategies which effectively inhibit the growth of small aneurysms.

Animals↗
PubMed2003

Cortisol enhances structural maturation of the hypoplastic fetal lung in sheep.

Although exogenous corticosteroids advance structural maturation of the fetal lung, they can adversely affect fetal lung and body growth. Our aim was to determine whether cortisol, at physiological doses, can enhance structural maturation of the hypoplastic fetal lung without affecting fetal lung growth. Fetal sheep were divided into four groups (n= 5 for each) and lung hypoplasia (LH) was induced in two groups. Increasing doses of cortisol (1.5-4.0 mg) were infused into one group of fetuses with LH and one group without LH; the other two groups received saline. LH retarded structural development, reduced tropoelastin mRNA levels, reduced hydroxyproline and elastin contents, and increased active matrix metalloproteinase-2 (MMP-2) levels in the fetal lung. Cortisol infusions had no effect on fetal lung growth or body weights. In fetuses with LH, cortisol increased the percentage airspace, reduced the interalveolar wall thickness, increased alveolar number and reduced the increase in active MMP-2 levels. Thus, relatively low doses of cortisol can enhance structural maturation of the fetal lung without adversely affecting fetal lung growth. However, cortisol did not correct the abnormal deposition of elastin within the alveolar parenchyma associated with LH, indicating that secondary septal crest formation remained abnormal.

Animals↗
PubMed2005

Aortic aneurysmal disease and cutis laxa caused by defects in the elastin gene.

BACKGROUND: Cutis laxa is an acquired or inherited condition characterized by redundant, pendulous and inelastic skin. Autosomal dominant cutis laxa has been described as a benign disease with minor systemic involvement. OBJECTIVE: To report a family with autosomal dominant cutis laxa and a young girl with sporadic cutis laxa, both with variable expression of an aortic aneurysmal phenotype ranging from mild dilatation to severe aneurysm or aortic rupture. METHODS AND RESULTS: Histological evaluation of aortic aneurysmal specimens indicated classical hallmarks of medial degeneration, paucity of elastic fibres, and an absence of inflammatory or atherosclerotic lesions. Electron microscopy showed extracellular elastin deposits lacking microfibrillar elements. Direct sequencing of genomic amplimers detected defects in exon 30 of the elastin gene in affected individuals, but did not in 121 normal controls. The expression of mutant elastin mRNA forms was demonstrated by reverse transcriptase polymerase chain reaction analysis of cutis laxa fibroblasts. These mRNAs coded for multiple mutant tropoelastins, including C-terminally truncated and extended forms as well as for molecules lacking the constitutive exon 30. CONCLUSIONS: ELN mutations may cause severe aortic disease in patients with cutis laxa. Thus regular cardiac monitoring is necessary in this disease to avert fatal aortic rupture.

Adult↗
PubMed2000

The molecular genetics of Marfan syndrome and related microfibrillopathies.

Mutations in the gene for fibrillin-1 (FBN1) have been shown to cause Marfan syndrome, an autosomal dominant disorder of connective tissue characterised by pleiotropic manifestations involving primarily the ocular, skeletal, and cardiovascular systems. Fibrillin-1 is a major component of the 10-12 nm microfibrils, which are thought to play a role in tropoelastin deposition and elastic fibre formation in addition to possessing an anchoring function in some tissues. Fibrillin-1 mutations have also been found in patients who do not fulfil clinical criteria for the diagnosis of Marfan syndrome, but have related disorders of connective tissue, such as isolated ectopia lentis, familial aortic aneurysm, and Marfan-like skeletal abnormalities, so that Marfan syndrome may be regarded as one of a range of type 1 fibrillinopathies. There appear to be no particular hot spots since mutations are found throughout the entire fibrillin-1 gene. However, a clustering of mutations associated with the most severe form of Marfan syndrome, neonatal Marfan syndrome, has been noted in a region encompassing exons 24 to 32. The gene for fibrillin-2 (FBN2) is highly homologous to FBN1, and mutations in FBN2 have been shown to cause a phenotypically related disorder termed congenital contractural arachnodactyly. Since mutations in the fibrillin genes are likely to affect the global function of the microfibrils, the term microfibrillopathy may be the most appropriate to designate the spectrum of disease associated with dysfunction of these molecules. The understanding of the global and the molecular functions of the fibrillin containing microfibrils is still incomplete and, correspondingly, no comprehensive theory of the pathogenesis of Marfan syndrome has emerged to date. Many, but not all, fibrillin-1 gene mutations are expected to exert a dominant negative effect, whereby mutant fibrillin monomers impair the global function of the microfibrils. In this paper we review the molecular physiology and pathophysiology of Marfan syndrome and related microfibrillopathies.

Abnormalities, Multiple↗
PubMed2005

Regulation of elastin gene transcription by proteasome dysfunction.

Elastin, a major extracellular matrix protein and the core component of elastic fiber, is essential to maintain lung structural integrity and normal physiological function. We previously found that the downregulation of elastin gene transcription by IL-1beta is mediated via activation of NF-kappaB and CCAAT/enhancer binding protein (C/EBP)beta, both targets of the ubiquitin-proteasome pathway. To further investigate the molecular mechanisms that underlie the control of elastin gene expression, we disrupted the ubiquitin-proteasome pathway with specific proteasome inhibitors. We found that specific proteasome inhibitors decreased the steady-state level of elastin mRNA in a dose-responsive manner. Run-on assay and promoter reporter study indicated that the proteasome inhibitor MG-132 repressed the rate of elastin transcription. MG-132 did not affect mRNA levels of NF-kappaB and C/EBPbeta, or the nuclear presence of NF-kappaB, but markedly increased C/EBPbeta isoforms, including liver-enriched transcriptional activating protein and liver-enriched transcriptional inhibitory protein. Addition of cycloheximide blocked these increases and the downregulation of elastin mRNA by MG-132. The MG-132-induced downregulation of elastin transcription was dependent on C/EBPbeta expression as assessed with small interfering RNA. These results indicate that the ubiquitin-proteasome pathway plays an essential role in maintaining elastin gene expression in lung fibroblasts. Disruption of this pathway results in the downregulation of tropoelastin transcription via posttranscriptionally induced C/EBPbeta isoforms.

Animals↗
PubMed1994

Perinatal accumulation of arterial wall constituents: relation to hemodynamic changes at birth.

We compared arterial growth to hemodynamic changes in the perinatal period in lambs. Blood pressure did not change significantly from 120 days gestation to 3 days postpartum, when it was 45.4 +/- 1.9 mmHg; however, pressure rose to 64.8 +/- 2.5 mmHg at 21 days postpartum. Thoracic and abdominal aortic and iliac and carotid arterial blood flows fell > 50% after birth but returned to fetal levels except in the abdominal aorta by 21 days postpartum. Blood flows in mesenteric (BFm) and renal (BFr) arteries increased between 120 days gestation (BFr = 13.4 +/- 1.4; BFm = 41.8 +/- 3.5 ml/min) and 140 days gestation (BFr = 25.9 +/- 1.8; BFm = 189 +/- 18 ml/min) and between 3 and 21 days postpartum (to BFr = 71.1 +/- 14.3; BFm = 334 +/- 59 ml/min). Elastin accumulation accelerated at 140 days gestation in all arteries except the thoracic aorta, in which elastin accumulation was always rapid. Collagen but not DNA accumulation also accelerated in most arteries. Postpartum dexamethasone (0.1 mg/kg twice a day) did not affect abdominal aortic elastin by 10 days of age (23.9 +/- 2.7 vs. 26.4 +/- 4.1 mg for controls); however, dexamethasone upregulated tropoelastin mRNA in fetuses. We hypothesize that cortisol stimulates elastin accumulation in late gestation. Postnatal elastin but neither collagen nor DNA correlated with blood flow changes at birth (r = 0.855, P < 0.05). We infer that accumulation of elastin is sensitive to blood flow rates during perinatal development.

Animals↗
PubMed2002

Insulin-like growth factor I receptor is downregulated after alveolarization in an apoptotic fibroblast subset.

After alveolar formation, >20% of interstitial lung fibroblasts undergo apoptosis, a process that is of critical importance for normal lung maturation. The immature lung contains two morphologically distinct fibroblast populations, lipid-filled interstitial fibroblasts (LIF) and non-LIF (NLIF), which differ with respect to contractile protein content, proliferative capacity, and expression of mRNAs for fibronectin and types I and III collagen, but not tropoelastin. After alveolarization, apoptosis occurs in only one fibroblast population, the LIF. Using flow cytometry to analyze fibroblasts stained with a lipophilic, fluorescent dye, we identified a subset, designated LIF(-), that contained fewer lipid droplets. Unlike LIF that retain lipid, LIF(+), the LIF(-) do not undergo apoptosis after alveolarization. In LIF(+), apoptosis was correlated with downregulation of insulin-like growth factor I receptor (IGF-IR) mRNA and cell surface protein expression. Treatment with anti-IGF-IR decreased total lung fibroblast survival (P = 0.05) as did treatment with the phosphatidylinositol 3-kinase inhibitor LY-294002 and the ras-raf-mitogen-activated protein kinase inhibitor PD-98059 (P < 0.002), which block IGF-I/insulin receptor survival pathways. These observations implicate downregulation of IGF-IR expression in fibroblast apoptosis after alveolar formation.

Aging↗