Biomedical subjects

Zhenlin Li

Publications and source records attributed to Zhenlin Li.

At least 19 recordsLinked to original sources

PubMed2006

Delayed liver regeneration in mice lacking liver serum response factor.

Various immediate early genes (IEGs) upregulated during the early process of liver regeneration are transcriptional targets of the serum response factor (SRF). We show here that the expression of SRF is rapidly induced in rodent liver after partial hepatectomy. Because the inactivation of the SRF gene in mice is embryonic lethal, the in vivo role of SRF in liver regeneration after partial hepatectomy was analyzed in mutant mice conditionally deleted for SRF in the liver. We demonstrate that SRF is not an essential factor for liver ontogenesis. However, adult mutant mice show impaired liver regeneration after partial hepatectomy, associated with a blunted upregulation of various SRF target IEGs. In conclusion, our work suggests that SRF is an early response transcription factor that may contribute to the initial phases of liver regeneration through its activation of IEGs.

Animals↗

PubMed2006

Conditional inactivation of the murine serum response factor in the pancreas leads to severe pancreatitis.

The Serum Response Factor (SRF) is widely expressed transcription factor acting at the confluence of multiple signaling pathways and has been implicated in the control of differentiation, growth, and cell death. In the present study, we found that SRF is expressed in the developing and adult pancreas. To explore the possible role of SRF in this organ, we have generated mutant mice with conditional disruption of the Srf gene. Such mutants presented normal development of both the exocrine and endocrine pancreas indicating that SRF is dispensable for pancreas ontogenesis. However, after weaning, these mice developed profound morphological alterations of the exocrine pancreas, which were reminiscent of severe pancreatitis. In these mice, massive acinar injury, Nuclear Factor Kappa B activation and proinflammatory cytokines release led to complete destruction of the exocrine pancreas and its replacement by adipose tissue. Despite these changes, the organization and function of the endocrine islets of Langerhans remained well-preserved. This new animal model of spontaneous pancreatitis could prove a valuable tool to gain further insight into the physiopathology of this disease.

Animals↗

PubMed2006

Interactions of intermediate filament protein synemin with dystrophin and utrophin.

Synemin is a unique, very large intermediate filament (IF) protein present in all types of muscle cells, which forms heteropolymeric intermediate filaments (IFs) with the major IF proteins desmin and/or vimentin. We show herein that tissue-purified avian synemin directly interacts with both dystrophin and utrophin, and that specific expressed regions of both of the mammalian (human) synemin isoforms (alpha-synemin and beta-synemin) directly interact with specific expressed domains/regions of the dystrophin and utrophin molecules. Mammalian synemin is also shown to colocalize with dystrophin within muscle cell cultures. These results indicate that synemin is an important IF protein in muscle cells that helps fortify the linkage between the peripheral layer of cellular myofibrils and the costameric regions located along the sarcolemma and the sarcolemma region located within the neuromuscular and myotendinous junctions (NMJs and MTJs).

Animals↗

PubMed2006

Transgenic mice overexpressing the 5-hydroxytryptamine transporter gene in smooth muscle develop pulmonary hypertension.

One intrinsic abnormality of pulmonary artery smooth muscle cells (PA-SMCs) in human idiopathic pulmonary hypertension (iPH) is an exaggerated proliferative response to internalized serotonin (5-HT) caused by increased expression of the 5-HT transporter (5-HTT). To investigate whether 5-HTT overexpression in PA-SMCs is sufficient to produce PH, we generated transgenic mice overexpressing 5-HTT under the control of the SM22 promoter. Studies in SM22-LacZ(+) mice showed that the transgene was expressed predominantly in SMCs of pulmonary and systemic vessels. Compared with wild-type mice, SM22-5-HTT(+) mice exhibited a 3- to 4-fold increase in lung 5-HTT mRNA and protein, together with increased lung 5-HT uptake activity, but no changes in platelet 5-HTT activity or blood 5-HT levels. At 8 weeks of age, SM22-5-HTT(+) mice exhibited PH, with marked increases in right ventricular systolic pressure (RVSP), right ventricle/left ventricle+septum ratio, and muscularization of distal pulmonary vessels, but no changes in systemic arterial pressure. PH worsened with age. Except a marked decrease in Kv channels, no changes in the lung expression of mediators of pulmonary vascular remodeling were observed in SM22-5-HTT(+) mice. Compared with wild-type mice, SM22-5-HTT(+) mice showed depressed hypoxic pulmonary vasoconstriction contrasting with greater severity of hypoxia- or monocrotaline-induced PH. These results show that increased 5-HTT expression in PA-SMCs, to a level close to that found in human iPH, lead to PH in mice. They further support a central role for 5-HTT in the pathogenesis of PH, making 5-HTT a potential therapeutic target.

Acute Disease↗

PubMed2006

New role for serum response factor in postnatal skeletal muscle growth and regeneration via the interleukin 4 and insulin-like growth factor 1 pathways.

Serum response factor (SRF) is a crucial transcriptional factor for muscle-specific gene expression. We investigated SRF function in adult skeletal muscles, using mice with a postmitotic myofiber-targeted disruption of the SRF gene. Mutant mice displayed severe skeletal muscle mass reductions due to a postnatal muscle growth defect resulting in highly hypotrophic adult myofibers. SRF-depleted myofibers also failed to regenerate following injury. Muscles lacking SRF had very low levels of muscle creatine kinase and skeletal alpha-actin (SKA) transcripts and displayed other alterations to the gene expression program, indicating an overall immaturity of mutant muscles. This loss of SKA expression, together with a decrease in beta-tropomyosin expression, contributed to myofiber growth defects, as suggested by the extensive sarcomere disorganization found in mutant muscles. However, we observed a downregulation of interleukin 4 (IL-4) and insulin-like growth factor 1 (IGF-1) expression in mutant myofibers which could also account for their defective growth and regeneration. Indeed, our demonstration of SRF binding to interleukin 4 and IGF-1 promoters in vivo suggests a new crucial role for SRF in pathways involved in muscle growth and regeneration.

Animals↗

PubMed2005

Temporally controlled onset of dilated cardiomyopathy through disruption of the SRF gene in adult heart.

BACKGROUND: Serum response factor (SRF) is a cardiac transcription factor involved in cell growth and differentiation. We have shown, using the Cre/loxP system, that cardiac-specific disruption of SRF gene in the embryonic heart results in lethal cardiac defects. The role of SRF in adult heart is unknown. METHODS AND RESULTS: We disrupted SRF in the adult heart using a heart-specific tamoxifen-inducible Cre recombinase. This disruption led to impaired left ventricular function with reduced contractility, subsequently progressing to dilated cardiomyopathy, as demonstrated by serial echocardiography, including tissue Doppler imaging. The cytoarchitecture of cardiomyocytes was altered in the intercalated disks. All mutant mice died from heart failure 10 weeks after treatment. These functional and structural defects were preceded by early alterations in the cardiac gene expression program: major decreases in mRNA levels for cardiac alpha-actin, muscle creatine kinase, and calcium-handling genes. CONCLUSIONS: SRF is crucial for adult cardiac function and integrity. We suggest that the rapid progression to heart failure in SRF mutant mice results primarily from decreased expression of proteins involved in force generation and transmission, low levels of polymerized actin, and changes in cytoarchitecture, without hypertrophic compensation. These cardiac-specific SRF-deficient mice have the morphological and clinical features of acquired dilated cardiomyopathy in humans and may therefore be used as an inducible model of this disorder.

Animals↗

PubMed2005

[Imaging technique and clinical application of 16-slice spiral CT for coronary artery].

This study was conducted in pursuit of the optimal imaging technique and for a primary clinical application of 16-slice multislice spiral computed tomography (MSCT) for coronary artery. Unenhanced and contrast-enhanced 16-slice SCT imaging was performed in 38 cases with retrospective electrocardiographic gating. MPR, MIP and VRT reconstruction of enhanced scan images were made in all cases, and CPR, VE reconstruction images were made in some cases. The demonstration of coronary artery was evaluated. The influencing factors of the image quality were analyzed. The results showed that the detection rates of RCA, PDA, LMA, LAD, DB, LCX and LMB were 36 (94.7%), 34 (89.5%), 37 (97.4%), 36 (94.7%), 34 (94.4%), 36 (94.7%), 34 (89.5%) on axial images, respectively, which were higher than those of the arteries on 3D images (P < 0.01). Therefore, 16-slice spiral CT is a reliable and accurate technique to demonstrate coronary artery and its branches, and is a noninvasive method to screen, diagnose and postoperatively evaluate coronary artery diseases. The factors influencing the image quality include the heart rate, the cardiac rhythm, the respiratory movement of patients and the trigger delays of imaging processing.

Adult↗

PubMed2004

Desmin: a major intermediate filament protein essential for the structural integrity and function of muscle.

Desmin is a muscle-specific protein and a key subunit of the intermediate filament in cardiac, skeletal and smooth muscles. Desmin filaments are mainly located at the periphery of Z-disk of striated muscles and at the dense bodies of smooth muscle cells, and they have been postulated to play a critical role in the maintenance of structural and mechanical integrity of the contractile apparatus in muscle tissues. This review summarizes the findings in the regulation of the desmin gene and function of the desmin protein. The expression of desmin gene is regulated by a combination of different transcription control regions in muscle cells. The results from mice deficient in desmin reveal the fundamental role of desmin filaments in cell architecture, force transmission and mitochondrial function. Mice lacking desmin postnatally develop a dilated cardiomyopathy, a skeletal myopathy and smooth muscle defects. Some of desmin-related myopathies are attributable to a missense mutations and deletions in the desmin gene. Other desmin-related myopathies, in which the desmin gene is not mutated, could be related to mutations of the genes encoding the proteins that interact with desmin.

Animals↗

PubMed2004

Tax protein of human T-cell leukaemia virus type 1 induces interleukin 17 gene expression in T cells.

Tax protein of human T-cell leukaemia virus type 1 (HTLV-1) induces the expression of several cellular genes that are involved in T cell activation and proliferation. In this study, it was observed that Tax upregulated the expression of human interleukin 17 (IL17), a cytokine mainly produced by activated CD4(+) memory T cells. Indeed, IL17 mRNA was highly expressed in HTLV-1-infected T cells as well as in Tax-expressing Jurkat T cells, whereas it was not detectable in HTLV-1-negative T cell lines. The clinical relevance of these observations was further demonstrated by quantitative assessment of IL17 expression in lymphocytes isolated from one HTLV-1-infected patient. To define the transcriptional activation of the IL17 gene by Tax, the 5'-flanking region of this gene was cloned and a reporter gene analysis performed. The presence of a Tax-responsive region spanning 614 bp upstream of the initiation start site was identified, in HeLa as well as in Jurkat cells, stimulated with phorbol myristate acetate and Ca(2+) ionophore. Finally, Tax mutants were used to show that the transcriptional activation of the IL17 promoter by Tax was dependent on the CREB/ATF pathway. As IL17 upregulates the expression of several pro-inflammatory cytokines, these observations provide new insights into the involvement of the Tax protein in the pathophysiology of HTLV-1-associated inflammatory disorders.

Base Sequence↗

PubMed2004

Targeted inactivation of serum response factor in the developing heart results in myocardial defects and embryonic lethality.

Serum response factor (SRF) is at the confluence of multiple signaling pathways controlling the transcription of immediate-early response genes and muscle-specific genes. There are active SRF target sequences in more than 50 genes expressed in the three muscle lineages including normal and diseased hearts. However, the role of SRF in heart formation has not been addressed in vivo thus far due to the early requirement of SRF for mesoderm formation. We have generated a conditional mutant of SRF by using Cre-LoxP strategy that will be extremely useful to study the role of SRF in embryonic and postnatal cardiac functions, as well as in other tissues. This report shows that heart-specific deletion of SRF in the embryo by using a new beta MHC-Cre transgenic mouse line results in lethal cardiac defects between embryonic day 10.5 (E10.5) and E13.5, as evidenced by abnormally thin myocardium, dilated cardiac chambers, poor trabeculation, and a disorganized interventricular septum. At E9.5, we found a marked reduction in the expression of essential regulators of heart development, including Nkx2.5, GATA4, myocardin, and the SRF target gene c-fos prior to overt maldevelopment. We conclude that SRF is crucial for cardiac differentiation and maturation, acting as a global regulator of multiple developmental genes.

Animals↗

PubMed2003

Temporal patterns of bone marrow cell differentiation following transplantation in doxorubicin-induced cardiomyopathy.

OBJECTIVE: Recent studies have suggested benefits of bone marrow cell transplantation for the regeneration of ischemic cardiac tissue. To extend the potential of cell transplantation, we assessed this treatment in a mouse model of acute nonischemic doxorubicin-induced cardiomyopathy. METHODS: To allow detection of engrafted cells, we used transgenic mice expressing the nuclear-located LacZ under the control of either desmin or vimentin promoters, which identify muscle lineage and mesenchymal cells, respectively. All transplanted cells were also labeled with the fluorescent dye DIL. One week after the administration of doxorubicin (15 mg/kg), mice were intramyocardially injected with either allogeneic unpurified bone marrow cells (6 x 10(6) in 30 microl, n=59) or purified sca-1(pos) cells (4 x 10(5) in 30 microl, n=22). In parallel, control normal mice received only unpurified bone marrow cells (n=28). Hearts were harvested at serial intervals until 2 weeks after transplantation and analyzed by immunohistochemistry to assess the degree of engraftment and transplanted cell differentiation. RESULTS: In control mice, no differentiation of bone marrow cells was detected. In contrast, unpurified bone marrow cells grafted into diseased myocardium featured two successive phases of cell differentiation. The first yielded cells with a mesenchymal phenotype (44.1+/-10.1 cells/3 x 10(-2) mm(3) at 2 days), was transient and lasted 1 week. The second phase was characterized by cells with a muscular phenotype detected in a small number of cells (5.6+/-2.3 cells/3 x 10(-2) mm(3) at 7 days). Two weeks after transplantation, some of these cells appeared phenotypically close to cardiomyocytes, as evidenced by morphology and positive staining for myosin binding protein C, vinculin and myosin heavy chain. In sca-1(pos) hematopoietic progenitor grafted mice hearts, no transdifferentiation into cardiac cells was detected at any time point. CONCLUSION: These data support the hypothesis of the potential for a myogenic differentiation of bone marrow cells following engraftment in a nonischemic model of global cardiomyopathy. Bone marrow-derived cells amenable to cardiac differentiation are present in total unpurified bone marrow but not in the sca-1(pos) hematopoietic progenitor cell population. However, the very small number of transdifferentiated cells raises concerns over their functional efficacy.

Animals↗

PubMed2003

Expression of the intermediate filament protein synemin in myofibrillar myopathies and other muscle diseases.

Synemin is a member of the intermediate protein superfamily. Previous studies in avian and rodent skeletal and cardiac muscles have demonstrated that synemin localises at the Z-band, where it associates with desmin and alpha-actinin. In the present study, the distribution of synemin was examined using immunohistochemistry in muscle biopsy specimens from patients suffering from myofibrillar myopathy (MM, n=6), dermatomyositis (DM, n=3), inclusion body myositis (IBM, n=5), oculopharyngeal muscular dystrophy (OPD, n=3) and denervation atrophy (DA, n=3), to investigate the possible participation of this protein in the pathogenesis of various muscular diseases. Of patients affected by MM, two showed the presence of mutations in the desmin gene; none had mutations in the alphaB-crystallin gene; and no mutations were identified in synemin or syncoilin genes of three patients. Synemin immunohistochemistry disclosed a faint staining corresponding to the Z-bands in the cytoplasm of control muscle fibres; in contrast, focal aggregates of synemin were seen in patients with MM. Increased synemin immunoreactivity was identified diffusely or in the subsarcolemmal space of scattered fibres in patients with DM, and in vacuolated fibres of patients with IBM and OPD. Strong synemin immunoreactivity was observed in target formations and atrophic fibres of patients with denervating disorders, as well as in atrophic fibres, regardless of their origin, in all patients studied. Synemin co-localised with desmin, as seen on consecutive serial sections immunostained with anti-synemin or anti-desmin antibodies. These observations demonstrate abnormal accumulations containing both synemin and desmin in muscle fibres in patients with MM, IBM, DM, OPD and DA. Considering the important role of synemin as one of intermediate filaments of skeletal and cardiac muscle, its destruction and accumulation in the intracellular debris suggest that synemin may participate in the pathogenesis of these disorders.

Adult↗

PubMed2003

On noxious desmin: functional effects of a novel heterozygous desmin insertion mutation on the extrasarcomeric desmin cytoskeleton and mitochondria.

Recent studies in desmin (-/-) mice have shown that the targeted ablation of desmin leads to pathological changes of the extrasarcomeric intermediate filament cytoskeleton, as well as structural and functional abnormalities of mitochondria in striated muscle. Here, we report on a novel heterozygous single adenine insertion mutation (c.5141_5143insA) in a 40-year-old patient with a distal myopathy. The insertion mutation leads to a frameshift and a truncated desmin (K239fs242). Using transfection studies in SW13 and BHK21 cells, we show that the K239fsX242 desmin mutant is incapable of forming a desmin intermediate filament network. Furthermore, it induces the collapse of a pre-existing desmin cytoskeleton, alters the subcellular distribution of mitochondria and leads to abnormal cytoplasmic protein aggregates reminiscent of desmin-immunoreactive granulofilamentous material seen in the ultrastructural analysis of the patient's muscle. Analysis of mitochondrial function in isolated saponin-permeablized skeletal muscle fibres from our patient showed decreased maximal rates of respiration with the NAD-dependent substrate combination glutamate and malate, as well as a higher amytal sensitivity of respiration, indicating an in vivo inhibition of complex I activity. Our findings suggest that the heterozygous K239fsX242 desmin insertion mutation has a dominant negative effect on the polymerization process of desmin intermediate filaments and affects not only the subcellular distribution, but also biochemical properties of mitochondria in diseased human skeletal muscle. As a consequence, the intermediate filament pathology-induced mitochondrial dysfunction may contribute to the degeneration/regeneration process leading to progressive muscle dysfunction in human desminopathies.

Adenine↗

PubMed2003

Synemin expression in developing normal and pathological human retina and lens.

Synemin (Syn) is an intermediate filament (IF) protein. To gain insight into a morphogenetic role of Syn, we have studied its expression patterns in the developing human retina and lens and compared it with those of other IF proteins. In addition, we have tested Syn expression in fetuses (23 and 28 weeks) affected by Walker-Warburg syndrome (WWS), Meckel syndrome, and trisomy 13. In the retina, Syn expression starts in the nerve fiber and ganglion cell layers (NFL and GCL) at 15 weeks, remains there in up to 20 weeks, and spreads to other layers and may be colocalized with vimentin, GFA, or neurofilaments in the subsequent 16 weeks. This expansion of Synemin expression from 20 to 28 weeks is not observed in WWS in which Syn immunoreactivity in NFL is reduced and Vim expression is increased. Changes are seen in Syn or vimentin expressions in the retinae of 23-week-old Meckel syndrome or 28-week-old trisomy 13 fetuses. Syn expression in the lens is, at first (16 weeks), uniformly distributed, becoming stronger in the epithelium of the anterior part at 25 weeks and later. As in the retina, Syn expression in lens is also selectively affected in WWS. The colocalization of Synemin with vimentin, GFA, or NF supports the idea that Syn is a key cross-linking protein that connects different cytoskeletal structures. Moreover, stagnant Syn expression in WWS retina and lens reinforces the notion of a significant role of this protein in morphogenesis.

Fetal Diseases↗

PubMed2003

Spontaneous muscular dystrophy caused by a retrotransposal insertion in the mouse laminin alpha2 chain gene.

We identified a novel spontaneous mouse model of human congenital muscular dystrophy with laminin alpha2 chain deficiency, named dy(Pas)/dy(Pas). Homozygous animals rapidly developed a progressive muscular dystrophy leading to premature death. Immunohistological and biochemical analyses demonstrated the absence of laminin alpha2 chain expression in skeletal muscle. Analysis of the laminin alpha2 chain cDNA showed the insertion of the long terminal repeat of an intracisternal A-particle gene. In addition, a 6.1 kb insertion composed of retrotransposon elements was identified in the Lama2 sequence. The dy(Pas)/dy(Pas) mouse is thus the first spontaneous mutant with a complete laminin alpha2 chain deficiency in which the mutation has been identified.

Animals↗

PubMed2002

Excessive microvascular adaptation to changes in blood flow in mice lacking gene encoding for desmin.

OBJECTIVE: Desmin, an intermediate filament, has a key role in the integrity of myocytes, and its absence induces cardiomyopathies. Mice lacking desmin (Des-/- group) exhibit microvascular dysfunction leading to smooth muscle hyporeactivity. We investigated the effect of the absence of desmin in mice (Des-/- mice versus Des+/+ mice) on the adaptation of mesenteric arteries to changes in blood flow. METHODS AND RESULTS: With the use of selective ligations of second-order mesenteric arteries, blood flow was either diminished (low flow [LF]) or elevated (high flow [HF]); respective LF to HF values were 136+/-18 to 206+/-29 microL/min for Des+/+ mice and 119+/-14 to 189+/-24 microL/min for Des-/-mice in daughter arteries. Two weeks after ligation, arteries were mounted in an arteriograph, allowing the measurement of diameter under controlled conditions of pressure and flow. In HF arteries, diameter changes in response to increases in pressure were higher in Des-/- mice than in Des+/+ mice. Conversely, in LF arteries, diameter was lower in Des-/- mice. Flow-dependent dilation was higher in HF arteries and lower in LF arteries than in control arteries. This adaptation was lower in Des-/- mice than in Des+/+ mice (11.6+/-3.1% versus 25.5+/-4.8% dilation, respectively). Endothelial NO synthase expression increased in HF arteries in both strains. CONCLUSIONS: These findings provide a demonstration of the role of the intermediate filament desmin in microvascular remodeling. This dysfunction might take place in desmin-related myopathies.

Adaptation, Physiological↗

PubMed2002

Comparative study of immune responses induced after immunization with plasmids encoding the HIV-1 Nef protein under the control of the CMV-IE or the muscle-specific desmin promoter.

The objective of this study was to compare immune responses induced against HIV-1 Nef after DNA immunization with Nef encoding plasmids under the control of an ubiquitous or a muscle-specific promoter. To this end, plasmids containing HIV-1 nef under the control of the Cytomegalovirus or the human desmin promoters, specifically expressed in muscle cells, were constructed. Different groups of BALB/c mice were immunized with 10 or 100 microg of both constructs, controls were the pcDNA3 vector or the Nef protein in Freund's adjuvant (Nef-CFA). Our data showed that both plasmids stimulated anti-Nef humoral responses in a dose-dependent manner. The anti-Nef antibody response, however, was earlier and higher with the CMV-IE promoter than with the desmin promoter. We also showed that Nef expressing plasmids induced high titers of anti-Nef antibodies (10(4)), comparable to those obtained in the Nef-CFA group (4x10(4)). Analysis of the specificity of anti-Nef antibodies revealed no influence of the promoter, and in contrast to Nef-CFA, plasmid immunization elicited anti-Nef antibodies directed principally against conformational-dependent epitopes. Data on the lymphoproliferative response showed that the specificity of expression, or the plasmid dose, did not affect the onset-time or the intensity of the response. The predominant IgG2a isotype of anti-Nef antibodies and the cytokine profile, mostly IL-2 and IFN-gamma, produced by Nef-stimulated spleen cells indicated a Th1 response in plasmid-immunized mice, in contrast to mice immunized with Nef-CFA, where a Th2 response was induced. In conclusion, these data indicate that antigen expression by muscle cells is sufficient to stimulate a Th1 immune response.

AIDS Vaccines↗

PubMed2002

Mechanical function of intermediate filaments in arteries of different size examined using desmin deficient mice.

Protein composition and mechanical function of intermediate filaments were examined in arteries of different sizes using desmin deficient mice (Des-/-) and their wild-type controls (Des+/+). Using SDS-PAGE gels and Western blots we found a gradient in desmin expression in the arterial tree; the desmin content increased from the elastic artery aorta, via the muscular mesenteric artery to the resistance-sized mesenteric microarteries approximately 150 microm in diameter in Des+/+ mice. Mechanical experiments were performed on the aorta, the mesenteric artery and resistance-sized arteries using wire myographs. For aorta and mesenteric artery, no differences in passive or active circumference- stress relations were found between Des-/- and Des+/+ mice. In microarteries, both passive and active stress were lower in the Des-/- group. In conclusion, large elastic and muscular arteries contain a relatively low amount of desmin, and the desmin intermediate filaments do not seem to play a major role in the mechanical properties of these larger arterial vessels. In the microarteries, where expression of desmin is high, desmin plays a role in supporting both passive and active tension.

Animals↗