Biomedical subjects

Y Yang

Publications and source records attributed to Y Yang.

At least 451 records · Page 25Linked to original sources

PubMed2000

Immunohistochemical detection of 1,N(6)-ethenodeoxyadenosine, a promutagenic DNA adduct, in liver of rats exposed to vinyl chloride or an iron overload.

Etheno adducts in DNA bases are formed from exogenous agents such as vinyl chloride and urethane, but also via endogenous lipid peroxidation products like trans-4-hydroxy-2-nonenal. An immunohistochemical method was developed to localize the promutagenic 1,N(6)-ethenodeoxyadenosine DNA adduct in liver of rats exposed to vinyl chloride or an iron overload with or without carbon tetrachloride. Six monoclonal antibodies, previously produced through collaborative efforts, were screened for their optimal adduct recognition and low background formation. The antibody generated by clone EM-A-4 was found to be most suitable. Semi-quantitative image analysis of relative pixel intensity showed approximately 1.5 times higher adduct levels (P < 0.05) in the livers of rats treated with vinyl chloride or an iron overload when compared with untreated controls. Significantly elevated adduct levels persisted in vinyl chloride-treated rat liver 14 days after cessation of exposure, suggesting that this adduct is not rapidly eliminated from rat liver DNA. Using the new immunohistochemical method it is possible to visualize this promutagenic etheno-DNA adduct that may play a role in oxidative stress and lipid peroxidation-induced DNA damage in carcinogenesis.

Animals↗

PubMed2000

Tissue targeting of multivalent GalNAc Le(x) terminated N-glycans in mice.

N-Linked biantennary and triantennary oligosaccharides containing multiple terminal GalNAc Le(x) (GalNAcss1-4[Fuc-alpha1-3]GlcNAc) determinants were radioiodinated and their pharmacokinetics, biodistribution, and hepatic cellular localization were determined in mice. Pharmacokinetic analysis revealed GalNAc Le(x) biantennary and triantennary oligosaccharides had a similar mean residence time and steady-state volume of distribution but differed in their total body clearance rate due a shorter alpha half-life for GalNAc Le(x) triantennary. Biodistribution and whole-body-autoradiography studies revealed that both GalNAc Le(x) terminated biantennary and triantennary oligosaccharides predominately targeted to the liver, which accumulated 72% and 79% of the dose 30 min after administration, respectively. Separation of mouse liver parenchymal from non-parenchymal cells demonstrated both N-glycans were almost exclusively (94%) taken up by the parenchymal cells. By comparison, GalNAc terminated biantennary and triantennary N-glycans accumulated in the liver with a targeting efficiency of 73% and 81%, respectively. It is concluded that GalNAc and GalNAc Le(x) terminated N-glycans are recognized in vivo with equivalent affinity by the murine hepatic asialoglycoprotein receptor.

Acetylgalactosamine↗

PubMed2000

Cell-to-cell movement of the 25K protein of potato virus X is regulated by three other viral proteins.

The 25K, 12K, and 8K proteins and coat protein (CP) of Potato virus X (PVX) are required for virus cell-to-cell movement. In this study, experiments were conducted to determine whether the PVX 25K protein moves cell to cell and to explore potential interactions between the PVX 25K, 12K, and 8K proteins and CP. The PVX 25K gene was fused to the green fluorescent protein (GFP) gene and inserted into plasmids adjacent to the cauliflower mosaic virus 35S promoter. These plasmids were introduced by biolistic bombardment to transgenic tobacco expressing the PVX 12K, 8K, and CP genes. The GFP:25K fused proteins moved cell to cell on nontransgenic tobacco and tobacco expressing either the 12K or 8K proteins. However, the GFP:25K proteins did not move on transgenic tobacco expressing the combined 12K/8K genes or the CP gene. Thus, movement of the PVX 25K protein through plasmodesmata may be regulated by interactions with other PVX proteins.

Biological Transport↗

PubMed2000

Selective antagonism of endothelin-A-receptors improves outcome in both head trauma and focal stroke in rat.

Increased levels of endothelin (ET) have been demonstrated in the ischemic brain, and ET receptor antagonism has been shown to improve outcome in cerebral ischemia. However, no previous work has been carried out evaluating the role of ET and its antagonism in brain trauma as compared to experimental stroke. In this study, we evaluated changes in brain ET levels following closed head injury (CHI) and the effects of SB 234551, an endothelin-A- (ET(A)) selective antagonist, and SB 209670, a mixed endothelin-A- and -B- (ET(A)/ET(B)) antagonist, on outcome in CHI and focal stroke. Male Sabra rats were subjected to CHI (weight drop model). Male Sprague Dawley rats were subjected to focal stroke (intraluminal suture model). Motor function(s) were assessed and immunoreactive ET (irET) and the degree of cerebral edema were measured for 24 h after CHI. Brain swelling (edema), neurological deficits and forebrain infarct volumes were measured 24 h after focal stroke. Antagonists (total doses of 7.5, 15, 30 or 60 mg/kg) were administered intravenously for 6-24 h (beginning 15 min after injury). Control rats were infused with vehicle. CHI resulted in increased ET levels in the directly contused hemisphere at 12 and 24 h. In addition, SB 234551 significantly reduced neurological deficits (decreased 30%) and brain edema (decreased 40%) following CHI (p < 0.05 at 60 mg/kg dose). SB 209670 had no effects on CHI outcome. Focal stroke studies yielded similar results. SB 234551 reduced focal stroke-induced neurological deficits by 50%, brain swelling by 54% and the degree of infarction by 36% (p < 0.05 at 30 mg/kg). SB 209670 did not provide any neuroprotection in focal stroke. These data indicate that ET plays a significant role in the pathophysiology of CHI, and that selectively targeting ET(A)-receptors similarly in both CHI and stroke might be a therapeutic opportunity.

Animals↗

PubMed2000

High efficiency and wideband gyro-traveling-wave-tube amplifier

A model is presented for a wideband gyro-traveling-wave-tube amplifier. The model's output bandwidth is comparable to that of the existing wideband model, but its efficiency is improved a lot. In this model, after choosing a proper initial magnitude, the axial magnetic field has a slightly linear decrease from a given position in the interaction section. The interaction mechanism of the beam wave is analyzed and verified by numerical simulation. When the beam current is 7 A, voltage is 90 KV, the velocity ratio is 1.0, and the axial velocity spread is 2%, numerical results show a constant bandwidth of 20% with an efficiency of 42%; the peak power and gain are, respectively, 260 KW and 47 dB.

Journal Article↗

PubMed2000

An enhancer trap line associated with a D-class cyclin gene in Arabidopsis.

In yeast and animals, cyclins have been demonstrated to be important regulators of cell cycle progression. In recent years, a large number of A-, B-, and D-class cyclins have been isolated from a variety of plant species. One class of cyclins, the D-class cyclins, is important for progression through G1 phase of the cell cycle. In Arabidopsis, four D-class cyclins have been isolated and characterized (CYCLIN-D1;1, CYCLIN-D2;1, CYCLIN-D3;1, and CYCLIN-D4;1). In this report we describe the characterization of a fifth D-class cyclin gene, CYCLIN-D3;2 (CYCD3;2), from Arabidopsis. An enhancer trap line, line 5580, contains a T-DNA insertion in CYCD3;2. Enhancer trap line 5580 exhibits expression in young vegetative and floral primordia. In line 5580, T-DNA is inserted in the first exon of the CYCD3;2 gene; in homozygous 5580 plants CYCD3;2 RNA is not detectable. Even though CYCD3;2 gene function is eliminated, homozygous 5580 plants do not exhibit an obvious growth or developmental phenotype. Via in situ hybridization we demonstrate that CYCD3;2 RNA is expressed in developing vegetative and floral primordia. In addition, CYCD3;2 is also capable of rescuing a yeast strain that is deficient in G1 cyclin activity.

Amino Acid Sequence↗

PubMed2000

Anti-DNA antibodies cross-reacting with laminin inhibit trophoblast attachment and migration: implications for recurrent pregnancy loss in SLE patients.

PROBLEM: Systemic lupus erythematosus (SLE), an autoimmune disease, is associated with reduced fetal survival, recurrent abortions, and other pregnancy complications. Some of the autoantibodies found in SLE bind to laminins (LNs), which play an important role in the implantation of the fertilized ovum in humans. METHOD OF STUDY: To elucidate the role of these specific autoantibodies, chorionic villous explants from 6 7-week-old human placentas were established as organ cultures on laminin-1 (LN-1), collagen IV (CN-IV) or uncoated culture dishes. The cultures were then exposed to a mouse monoclonal anti-DNA/anti-LN-1 antibody, to human polyclonal lupus antibodies cross-reacting with LN-1, a function-blocking polyclonal antibody to LN-1, polyclonal antibodies to CN-IV, or IgG control. RESULTS: The explants attached to LN-1 and CN-IV, but not to uncoated culture dishes. LN-1 promoted migration of trophoblast, whereas CN-IV promoted migration of fibroblast-like cells. Trophoblast attachment and migration were abolished in a dose-dependent manner by all three antibodies to LN-1, but not by antibodies to CN-IV or IgG control. Furthermore, the effect of anti-LN antibodies was abolished by preincubating them with LN-1. CONCLUSIONS: These studies suggest that anti-DNA antibodies cross-reacting with LNs may play a role in early pregnancy failure in SLE patients by interfering with placental implantation.

Abortion, Habitual↗

PubMed2000

Hematotoxicity of the chinese herbal medicine Tripterygium wilfordii hook f in CD34-positive human bone marrow cells.

T2, a chloroform/methanol extract of the herb Tripterygium wilfordii Hook f, has been used in China for the treatment of autoimmune and inflammatory diseases for many years. Recent experimental evidence has confirmed that T2 has potent anti-inflammatory and immunosuppressive activity, and a United States Food and Drug Administration-approved clinical trial is currently exploring the efficacy of T2 in the treatment of rheumatoid arthritis. Despite the potential therapeutic benefits of T2, there is ample documentation that T2 is toxic, targeting, among other things, the hematopoietic system, and its use has resulted in cases of leukopenia, thrombocytopenia, and aplastic anemia. This investigation was undertaken to characterize the in vitro effects of T2 on primary human CD34-positive (CD34+) bone marrow cells. Our results demonstrate that T2 has a potent inhibitory effect on the clonogenic response of human bone marrow cells to exogenously added hematopoietic growth factors. The inhibition of colony formation by T2 is not the result of direct cytotoxicity or increased apoptosis and indicates a functional suppression of hematopoiesis. Additional experiments demonstrate that T2 also alters transcriptional regulation in bone marrow cells by inhibiting nuclear factor-kappaB. This transcription factor is found in CD34+ bone marrow cells and has been recently shown to be a requirement for colony formation. These results demonstrate that therapeutic concentrations of T2 exert a significant hematotoxic effect by inhibiting growth factor response in CD34+ bone marrow cells and suggest that inhibition of nuclear factor-kappaB may play a role in the blood dyscrasias encountered with the use of this drug.

Antigens, CD34↗

PubMed2000

Systemic and mucosal immune responses in mice after mucosal immunization with group B streptococcus type III capsular polysaccharide-cholera toxin B subunit conjugate vaccine.

Group B streptococci (GBS) colonize the female genital and rectal tracts and can cause invasive infection in susceptible newborns. An optimally effective GBS vaccine should induce mucosal and systemic immunity. In this study, we investigate the local and systemic immune responses to GBS type III capsular polysaccharide (CPS) after mucosal vaccination of mice via intranasal, peroral, rectal, and vaginal routes, with GBS type III CPS conjugated with recombinant cholera toxin B subunit (GBS III CPS-rCTB). Cholera toxin (CT) was added as an adjuvant. Immunoglobulin G (IgG) and IgA antibodies to the CPS were tested in serum, lungs, and intestinal, rectal, and vaginal extracts by enzyme-linked immunosorbent assay. The conjugated CPS administered by intranasal, peroral, rectal, and vaginal routes was much more effective at inducing both mucosal and systemic antibody responses to GBS III CPS than was unconjugated CPS. The CPS-specific immune responses in various organs were dependent on the route of immunization. Generally, the highest levels of IgA and IgG were generated in the regions or sites of the conjugate exposure. Thus, intranasal vaccination elicited the highest anti-CPS IgA and IgG antibody levels in the lungs, whereas peroral administration in the intestinal site and vaginal vaccination elicited the highest antibody levels in the vagina. Rectal vaccination was superior to the other routes in inducing high antibody levels in the rectum. The four routes of mucosal vaccination also induced distant antibody responses to CPS. Rectal vaccination induced high specific IgA levels in the vagina and intestine, and oral administration induced high specific IgA levels in the lungs and rectum. All four routes of vaccination with the conjugate elicited similarly high levels of anti-CPS IgG in serum. Intranasal vaccination with different doses of the conjugate (10, 30, and 80 microg of CPS) did not have a significant influence on the anti-CPS specific antibody responses. Intranasal immunization induced better antibody responses when one dose of the conjugate was divided and given on three consecutive days compared to administration of the full dose on one occasion. In conclusion, rectal and vaginal vaccination may be the best way of stimulating anti-CPS immune responses in the rectal and vaginal tracts, while high levels of anti-CPS antibodies in the lungs can be achieved after intranasal administration. The vaccination regimen thus might influence the mucosal immune response to CPS. This conjugate may serve as an effective mucosal vaccine for preventing mucosal colonization and invasive infection caused by GBS.

Animals↗

PubMed2000

Salmonella enterica serovar typhi uses type IVB pili to enter human intestinal epithelial cells.

DNA sequencing upstream of the Salmonella enterica serovar Typhi pilV and rci genes previously identified in the ca. 118-kb major pathogenicity island (X.-L. Zhang, C. Morris, and J. Hackett, Gene 202:139-146, 1997) identified a further 10 pil genes apparently forming a pil operon. The product of the pilS gene, prePilS protein (a putative type IVB structural prepilin) was purified, and an anti-prePilS antiserum was raised in mice. Mutants of serovar Typhi either lacking the whole pil operon or with an insertion mutation in the pilS gene were constructed, as was a strain in which the pilN to pilV genes were driven by the tac promoter. The pil(+) strains synthesized type IVB pili, as judged by (i) visualization in the electron microscope of thin pili in culture supernatants of one such strain and (ii) the presence of PilS protein (smaller than the prePilS protein by removal of the leader peptide) on immunoblotting of material pelleted by high-speed centrifugation of either the culture supernatant or sonicates of pil(+) strains. Control pil mutants did not express the PilS protein. A pilS mutant of serovar Typhi entered human intestinal INT407 cells in culture to levels only 5 to 25% of those of the wild-type strain, and serovar Typhi entry was strongly inhibited by soluble prePilS protein (50% inhibition of entry at 1.4 microM prePilS).

Amino Acid Sequence↗

PubMed2000

Characterization of enterovirus isolates from patients with heart muscle disease in a selenium-deficient area of China.

An association of enterovirus infection with endemic cardiomyopathy (Keshan disease [KD]) and outbreaks of myocarditis in selenium-deficient rural areas of southwestern China has been established. Enteroviruses have been isolated from patients with KD or during outbreaks of myocarditis in last two decades. Six of these isolates grew readily in cell lines (Vero or HEp-2) and were investigated by a novel molecular typing method apart from serotyping and pathogenicity. A neutralization assay identified two isolates from KD as coxsackievirus serotype B2 (CVB2) and two isolates from myocarditis as coxsackievirus serotype B6 (CVB6) but failed to type the remaining two isolates, also from myocarditis. Direct nucleotide sequencing of reverse transcription-PCR products amplified from the 5' nontranslated region (5'NTR) of these viruses confirmed that they belong to a phylogenetic cluster consisting of coxsackie B-like viruses, including some echovirus serotypes. Sequence analysis of the coding region for viral capsid protein VP1 showed that two isolates serotyped as CVB2 have the highest amino acid sequence homology with CVB2 and that the remaining four isolates, two CVB6 and the two unknown serotypes, are most closely related to the sequence of CVB6. Sequences among these isolates varied from 82.3 to 99% in the 5'NTR and from 69 to 99% in VP1, indicating no cross contamination. The pathogenicity of these viruses in adult and suckling mice was assessed. None caused pathologic changes in the hearts of adult MF-1 or SWR mice, although pancreatitis was evident. However, the four CVB6-like viruses caused death in suckling mice, similar to a virulent coxsackievirus group B3 laboratory strain. In conclusion, the sequence data confirm that coxsackievirus group B serotypes are predominant in the region in which KD is endemic and may be the etiological agents in outbreaks of myocarditis. VP1 genotyping of enteroviruses is accurate and reliable. Animal experiments indicate that isolates may differ in pathogenicity.

Adolescent↗

PubMed2000

High prevalence of enteroviral genomic sequences in myocardium from cases of endemic cardiomyopathy (Keshan disease) in China.

OBJECTIVE: To verify the aetiological involvement of enterovirus and identify the viral genomic sequences in Keshan disease. DESIGN: Formalin fixed, paraffin embedded myocardial necropsy tissue samples were collected in Keshan disease endemic regions. Fourteen cases with a histologically confirmed diagnosis of subacute or chronic Keshan disease were studied. Control tissue included 10 samples of myocardium from cases of cerebral trauma and one from accidental acid intoxication. One sample from a case of enteroviral myocarditis was used as a positive control. The presence of viral genomic RNA was investigated using an established reverse transcription nested polymerase chain reaction (PCR) coupled with direct nucleotide sequencing. Further investigations of PCR positive samples included in situ antigen detection or hybridisation to confirm positive results. RESULTS: Nine of 14 myocardial samples from Keshan disease cases and the positive control were positive for the enteroviral RNA. All the controls were negative. Six of the PCR positive samples were investigated further by in situ enteroviral antigen or RNA detection and all were positive. DNA sequencing of six representative PCR products confirmed that they were homologous to the 5' non-translated region of enteroviral genomic RNA. Five had highest homology to coxsackievirus B genotypes and one was identical to poliovirus type 3. CONCLUSIONS: These results support an aetiological role for enteroviral infection in Keshan disease. Nucleotide sequence data suggest that coxsackievirus B or coxsackie B like viruses are often involved in Keshan disease.

Adolescent↗

PubMed2000

Flexibility and critical hydrogen bonds in cytochrome c.

We show that protein flexibility can be characterized using graph theory, from a single protein conformation. Covalent and hydrogen bonds are modeled by distance and angular constraints, and a map is constructed of the regions in this network that are flexible or rigid, based on whether their dihedral bonds remain rotatable or are locked by other interactions in the network. This analysis takes only a second on a typical PC, and interatomic potentials; the most time-consuming aspect of molecular dynamics calculations, are not required. Our preliminary work has shown that this approach identifies the experimentally observed, biologically important flexible regions in HIV protease and lysine-arginine-ornithine binding protein. Here we analyze three evolutionarily distant cytochromes c, and find strong similarity between their flexible regions, despite having only 39% sequence identity. Furthermore, we show how the structural flexibility increases as the weaker hydrogen bonds are removed, as would happen under thermal denaturation of the protein. This approach identifies the critical hydrogen bonds that cross-link the tertiary structure.

Amino Acid Sequence↗

PubMed2000

Regulation of stanniocalcin in MDCK cells by hypertonicity and extracellular calcium.

Differential display RT-PCR cloning method was applied to poly(A)(+) RNA isolated from Madin-Darby canine kidney (MDCK) cells in isotonic or hypertonic medium. A differentially expressed 360-bp PCR fragment was isolated, subcloned, sequenced, and used to screen an MDCK cDNA library constructed in lambdaZapII. A composite sequence of two overlapping cDNA clones provided 1,053 bp of sequence that was 93% identical to human stanniocalcin and corresponded to the 3'-end of the mRNA. Although the fish homolog of this hormone inhibits calcium uptake by the gill and intestine, the function of mammalian stanniocalcin remains unknown. Stanniocalcin cDNA probe hybridizes to a 4.4-kb mRNA that is induced eightfold by hypertonicity, in a manner that is dependent on medium organic osmolytes. The mRNA induction correlates with increased total cellular content of the protein and its concomitant release to the medium, consistent with secretion for autocrine or paracrine activity. Furthermore, induction of the mRNA by hypertonicity is dependent on extracellular calcium and displays a threshold phenomenon. The data suggest that kidney stanniocalcin may have a role in the adaptation of kidney cells to osmotic stress, in a manner that is extracellular calcium dependent.

Animals↗

PubMed2000

Genetic analysis of rat chromosome 1 and the Sa gene in spontaneous hypertension.

Linkage studies in segregating populations derived from the spontaneously hypertensive rat (SHR) indicate that a blood pressure quantitative trait locus exists on rat chromosome 1 in the vicinity of the Sa gene. On the basis of these findings and the observation of increased renal expression of the Sa gene in SHR versus normotensive rats, the Sa gene has been proposed as a candidate gene for spontaneous hypertension. In SHR congenic strains, we and others have found that replacement of a segment of SHR chromosome 1 that contains the Sa gene with the corresponding chromosome segment from a normotensive Brown Norway (BN) rat or Wistar-Kyoto rat can reduce blood pressure. To test whether the Sa gene is necessary for the effect of this region of chromosome 1 on blood pressure, we studied a new SHR congenic subline that harbors a smaller segment of BN chromosome 1 that does not include the Sa gene. Transfer of this subregion of chromosome 1 from the BN rat onto the SHR background was associated with significant reductions in blood pressure comparable to those previously observed on transfer of a larger region of chromosome 1 that included the Sa gene. Thus, in the SHR-BN model of hypertension, the results of these mapping studies (1) demonstrate that molecular variation in the Sa gene is not required for the effect of this region of chromosome 1 on blood pressure and (2) should direct attention toward other candidate genes within the differential chromosome segment of the new congenic subline.

Alleles↗

PubMed2000

Identification of echocardiographic "smoke" in a bench model with transcranial Doppler ultrasound.

BACKGROUND AND PURPOSE: Spontaneous echo contrast in cardiac chamber has been indicated as a source of cerebral embolism. The nature of the echocardiographic smokelike signal is still not fully understood. This study was designed to regenerate spontaneous echo contrast and verify its thromboembolic characters in an in vitro model. METHODS: Spontaneous echo contrast was reproduced in an expansion chamber under low flow conditions in a close circulation system. The spontaneous echo contrast was monitored and recorded with a 2-dimensional cardiosonography system and a transcranial Doppler device. Meanwhile, clinically commonly encountered embolic materials such as whole-blood clots, platelet aggregate-rich plasma, air bubbles, and 100-mL normal saline were injected into this monitored circuit. The differentiation of spontaneous echo contrast from emboli was performed by both visual observations of the echo images and offline Doppler signal intensity analysis. Average signal intensities produced by spontaneous contrast and injection of embolic materials and saline were compared. Furthermore, the effect of Doppler-detected flow velocity on generation of spontaneous contrast was also evaluated. RESULTS: Spontaneous echo contrast was reproduced at low flow settings (90 to 120 mL/min) in this model. There was no significant difference in average signal intensity between the flow with spontaneous echo contrast and that without the echo (P=0.71). However, injection of embolic materials or normal saline did not generate smokelike image but caused much higher average signal intensity than the flow with spontaneous contrast (P<0.001). Injection of normal saline also increased average signal intensity. CONCLUSIONS: Our results suggest that smokelike echo is a special echo phenomenon occurring at low flow situations and does not itself produce material capable of embolizing into the systemic circulation.

Blood Flow Velocity↗

PubMed2000

Heparin-binding EGF-like growth factor contributes to reduced glomerular filtration rate during glomerulonephritis in rats.

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the epidermal growth factor (EGF) family, is expressed during inflammatory and pathological conditions. We have cloned the rat HB-EGF and followed the expression of HB-EGF in rat kidneys treated with anti- glomerular basement membrane (anti-GBM) antibody (Ab) to induce glomerulonephritis (GN). We observed glomerular HB-EGF mRNA and protein within 30 minutes of Ab administration and showed by in situ hybridization that glomerular HB-EGF mRNA expression was predominantly in mesangial and epithelial cells. Expression of HB-EGF correlated with the onset of decreased renal function in this model. To test the direct effect of HB-EGF on renal function, we infused the renal cortex with active rHB-EGF, prepared from transfected Drosophila melanogaster cells. This treatment induced a significant decrease in single nephron GFR (SNGFR), single nephron plasma flow, and glomerular ultrafiltration coefficient and an increase in the glomerular capillary hydrostatic pressure gradient. In addition, anti-HB-EGF Ab administered just before anti-GBM Ab blocked the fall in SNGFR and GFR at 90 minutes without any change in the glomerular histologic response. These studies suggest that HB-EGF expressed early in the anti-GBM Ab GN model contributes to the observed acute glomerular hemodynamic alterations.

Animals↗

PubMed2000

Stretch-induced alternative splicing of serum response factor promotes bronchial myogenesis and is defective in lung hypoplasia.

Smooth muscle (SM) develops only in organs and sites that sustain mechanical tensions. Therefore, we determined the role of stretch in mouse and human bronchial myogenesis. Sustained stretch induced expression of SM proteins in undifferentiated mesenchymal cells and accelerated the differentiation of cells undergoing myogenesis. Moreover, bronchial myogenesis was entirely controlled in lung organ cultures by the airway intraluminal pressure. Serum response factor (SRF) is a transcription factor critical for the induction of muscle-specific gene expression. Recently, a SRF-truncated isoform produced by alternative splicing of exon 5 has been identified (SRFDelta5). Here we show that undifferentiated mesenchymal cells synthesize both SRF and SRFDelta5 but that SRFDelta5 synthesis is suppressed during bronchial myogenesis in favor of increased SRF production. Stretch induces the same change in SRF alternative splicing, and its myogenic effect is abrogated by overexpressing SRFDelta5. Furthermore, human hypoplastic lungs related to conditions that hinder cell stretching continue to synthesize SRFDelta5 and show a marked decrease in bronchial and interstitial SM cells and their ECM product, tropoelastin. Taken together, our findings indicate that stretch plays a critical role in SM myogenesis and suggest that its decrease precludes normal bronchial muscle development.

Alternative Splicing↗