Monoclonal antibodies to desmin: evidence for stage-dependent intermediate filament immunoreactivity during cardiac and skeletal muscle development

Permanent myopathy caused by mutation of SCN4A Metl592Val: Observation on myogenesis in vitro and on effect of basic fibroblast growth factor on the muscle

OBJECTIVE

The present study is to observe in vitro the proliferation ability of the muscle cells from permanent myopathy (PM) patients of nomokalaemic periodic paralysis (normKPP), which is caused by mutations of Met1592Val in the skeletal muscle voltage gated sodium channel (SCN4A) gene on chromosome 17q23.1. We also evaluate the possible effect of the foreign basic fibroblast growth factor (bFGF) in preventing and curing PM.

METHODS

The gastrocnemius muscle cells were taken from two male patients with PM of the same Chinese family with Met1592Val mutation of SCN4A, determined by gene screening. Four male patients suffering from the skeletal injury without PM were taken as control. All preparations were protogenerationally cultured in vitro. Proliferation of the cultured preparations was measured by MTT. Activities of the lactic dehydrogenase (LDH), creatine kinase (CK), and protein content in these cells were also detected. The effects of bFGF with different doses (10 ng/mL, 20 ng/mL, 40 ng/mL, 80 ng/mL, 120 ng/mL and 160 ng/mL) on the above mentioned parameters were also evaluated.

RESULTS

Cells from both PM and control subjects were successfully cultured in vitro. The cultivation of the muscle cells from PM patients in vitro was not yet seen. Results indicated the obvious stimulation of bFGF on cell proliferation, activities of LDH and CK, protein synthesis, in a dose dependent manner. The optimal dose of bFGF was 120 ng/mL (P<0.05), beyond which greater dose caused a less effect. The effect of bFGF on 160 ng /mL was stronger than that on 80 ng/mL, but there was no significant difference (P>0.05).

CONCLUSION

Myoblastic cells from patients with PM had a weaker ability of developing into the myotubules, thus they were unable to perform effective regeneration, which resulted in a progressive necrosis. The exogenous bFGF could promote the division and proliferation of the muscle cells in vitro. These results shield a light on bFGFos potential role in preventing and treating PM.

Loss of stem cell regenerative capacity within aged niches

This work uncovers novel mechanisms of aging within stem cell niches that are evolutionarily conserved between mice and humans and affect both embryonic and adult stem cells. Specifically, we have examined the effects of aged muscle and systemic niches on key molecular identifiers of regenerative potential of human embryonic stem cells (hESCs) and post-natal muscle stem cells (satellite cells). Our results reveal that aged differentiated niches dominantly inhibit the expression of Oct4 in hESCs and Myf-5 in activated satellite cells, and reduce proliferation and myogenic differentiation of both embryonic and tissue-specific adult stem cells (ASCs). Therefore, despite their general neoorganogenesis potential, the ability of hESCs, and the more differentiated myogenic ASCs to contribute to tissue repair in the old will be greatly restricted due to the conserved inhibitory influence of aged differentiated niches. Significantly, this work establishes that hESC-derived factors enhance the regenerative potential of both young and, importantly, aged muscle stem cells in vitro and in vivo; thus, suggesting that the regenerative outcome of stem cell-based replacement therapies will be determined by a balance between negative influences of aged tissues on transplanted cells and positive effects of embryonic cells on the endogenous regenerative capacity. Comprehensively, this work points toward novel venues for in situ restoration of tissue repair in the old and identifies critical determinants of successful cell-replacement therapies for aged degenerating organs.

Expression of intermediate filament desmin and vimentin in the human fetal heart

BACKGROUND

The intermediate filament (IF) desmin provides support for contractile machinery in muscle cells, and vimentin plays an important role in maintaining the stability of mesenchymal cells and in signal transduction. However, development of IFs in heart tissue during intrauterine life in human is not well established.

METHODS

In the present study, development of desmin and vimentin in human fetal hearts aged 9-28 weeks of gestation (n = 41) were investigated by immunohistochemistry with monoclonal antibodies against desmin and vimentin. Relative density of fluorescence of each sample was determined by densitometry. Left ventricle (LV) tissues from a 1-year-old child (n = 1) were examined by immunohistochemistry for postnatal comparison. Western blot analyses were done with only a few randomly selected LV tissues from fetuses of 9, 20, and 28 weeks gestation to assess trends of desmin and vimentin expression.

RESULTS

By Western blot analyses, 53-kDa desmin and 54-kDa vimentin were present in all fetal heart tissues examined. Desmin intensity was progressively increased with increasing fetal age, whereas vimentin intensity decreased. Desmin was present only in cardiomyocytes. In the earlier period (10-14 weeks gestation), desmin was localized along the cardiomyocyte membrane and/or Z lines in regular intervals, and later (25-28 weeks gestation) it was structurally well integrated; however, its network was incomplete. Only cardiomyocytes from a 1-year-old child revealed highly developed and integrated desmin lattices. However, vimentin was present in the mesenchymal tissue including fibroblasts and surrounding blood vessels. In part, some cardiomyocytes showed a weakly positive reaction with monoclonal antibody against vimentin in 9-14 weeks gestation. Vimentin-positive areas, however, were progressively diminished with increasing fetal age. Vimentin was present only in the connective tissue and coverings of the 1-year-old child's heart. Relative density of fluorescence of desmin was increased with increasing fetal age, whereas that of vimentin decreased.

CONCLUSIONS

These results indicate that there is a fetal age (or gestation)-dependent expression of IFs in human fetal heart: desmin increases with increasing fetal age, whereas vimentin decreases.

Establishment of the mesodermal cell line QCE-6. A model system for cardiac cell differentiation

The QCE-6 cell line was derived from precardiac mesoderm of the Japanese quail. As previously reported, these cells are able to differentiate into two distinct cardiac cell types with myocardial or endocardial endothelial cell properties. This present communication describes in detail the derivation of this cell line and further characterizes the nontreated and induced myocardial and endothelial phenotypes of these cells. The QCE-6 cells exhibit an epithelial morphology, as well as the pattern of protein expression, that is characteristic of precardiac mesoderm. Treatment with retinoic acid, basic fibroblast growth factor (bFGF), transforming growth factor (TGF)-beta 2, and TGF-beta 3 induces these cells to differentiate and produce mixed cultures of epithelial and mesenchymal cells. The epithelial cells express myosin, desmin, and cardiac troponin I in a punctate pattern throughout the cytoplasm. These sarcomeric proteins become organized in a premyofibrillar pattern when TGF-beta 1, platelet-derived growth factor (PDGF)-BB, and insulin-like growth factor (IGF) II are added in combination along with retinoic acid, bFGF, TGF-beta 2, and TGF-beta 3. Also, these treatments induce Na+,K(+)-ATPase expression. When the QCE-6 cells are cultured on collagen type I, the mesenchymal cells that are promoted by retinoic acid, bFGF, TGF-beta 2, and TGF-beta 3 will invade the gel. These mesenchymal cells are positive for QH1 and JB3, which are both markers for presumptive endocardial cells within the early cardiogenic mesoderm. The addition of both PDGF-BB and IGF II to QCE-6 cell cultures will inhibit the ability of retinoic acid, bFGF, TGF-beta 2, and TGF-beta 3 to induce both the mesenchymal morphology and QH1 and JB3 expression. Collectively, these results suggest that the proces of cardiac cell differentiation is regulated by multiple signals and that early cardiogenic mesoderm contains a bipotential stem cell that can give rise to both the myocardial and endocardial lineages. More important, since the QCE-6 cells are representative of early cardiogenic cells, this cell line offers a unique model system to study cardiac cell differentiation.

Antisense suppression of skeletal muscle myosin light chain-1 biosynthesis impairs myofibrillogenesis in cultured myotubes

Although the alkali or essential light chains of skeletal muscle myosin are not required for actin-activated myosin ATPase activity, these myosin subunits are necessary for force transmission with in vitro actin motility assays and are believed to stabilize the alpha-helical neck region of myosin subfragment-1. To probe the functions of the essential light chains during myofibril assembly, we used recombinant DNA procedures to deplete this light chain in cultured muscle. Retroviral expression vectors were constructed which encoded the exon-1 sequence of the myosin light chain-1 gene in antisense orientation. These vectors were applied to myogenic cells from embryonic chick and quail pectoralis muscle. Colonies expressing antisense RNA were selected in growth medium containing the neomycin analogue G-418, plus 5-bromo-2'-deoxyuridine (BrdU) and triggered to differentiate by removal of the latter. Expression of antisense myosin light chain-1 mRNA impaired muscle development. In the antisense cultures there were more mononucleated cells, fewer and smaller myotubes which had poorly developed myofibrils and high levels of diffusely staining myosin heavy chain, not apparent in control myotubes. Protein synthesis in the myotube cultures was analyzed by 35S-methionine labelling and two-dimensional gel electrophoresis. Except for a suppression of approximately 80% of myosin light chain-1f synthesis, the overall pattern of protein synthesis was not altered significantly. These studies suggest that retardation of myosin light chain-1f accumulation inhibits or delays myofibrillogenesis.

Inhibition of desmin expression blocks myoblast fusion and interferes with the myogenic regulators MyoD and myogenin

The muscle-specific intermediate filament protein, desmin, is one of the earliest myogenic markers whose functional role during myogenic commitment and differentiation is unknown. Sequence comparison of the presently isolated and fully characterized mouse desmin cDNA clones revealed a single domain of polypeptide similarity between desmin and the basic and helix-loop-helix region of members of the myoD family myogenic regulators. This further substantiated the need to search for the function of desmin. Constructs designed to express anti-sense desmin RNA were used to obtain stably transfected C2C12 myoblast cell lines. Several lines were obtained where expression of the anti-sense desmin RNA inhibited the expression of desmin RNA and protein down to basal levels. As a consequence, the differentiation of these myoblasts was blocked; complete inhibition of myoblast fusion and myotube formation was observed. Rescue of the normal phenotype was achieved either by spontaneous revertants, or by overexpression of the desmin sense RNA in the defective cell lines. In several of the cell lines obtained, inhibition of desmin expression was followed by differential inhibition of the myogenic regulators myoD and/or myogenin, depending on the stage and extent of desmin inhibition in these cells. These data suggested that myogenesis is modulated by at least more than one pathway and desmin, which so far was believed to be merely an architectural protein, seems to play a key role in this process.

Vimentin and desmin expression in degenerating and regenerating dystrophic murine muscles

The distribution of the intermediate filament proteins (IFP) desmin and vimentin was studied in gastrocnemius, plantaris and soleus muscles of the dystrophic mouse strain ReJ 129 during postnatal development. Special attention was paid to the overall morphological changes in the distribution of these cytoskeletal constituents in degenerating and regenerating muscle fibres. In contrast to their normal counterparts, the dystrophic mice (ReJ 129 dy/dy) appeared to develop four types of distinct muscle fibres with immunohistochemically detectable aberrant IFP patterns. The distribution of desmin IFP differed in the dystrophic muscle fibres as compared to the normal fibres in that juxtanuclear aggregates of IFP were frequently seen. In contrast to the recent literature we conclude that these cells are regenerated myofibres exhibiting defective nuclear migration.

Myogenic cytodifferentiation of the precardiac mesoderm in the rat

The contractile cells of the primitive heart are derived from a subpopulation of the lateral plate splanchnic mesoderm. While the formation of the cardiac primordia has been studied in the avian embryo, little is known about this cell population in the mammal. To investigate the distribution and cellular differentiation of the myocardial precursors in the early mammalian embryo, we studied the sequential immunohistochemical appearance of desmin and myosin in whole mounts of rat embryos from the presomite (gestational day 9) through the 6-8 somite, straight heart tube (gestational day 10) stages of early cardiac morphogenesis. In contrast to the chicken, and previous reports in the mouse, our results show that myogenic differentiation of the muscle precursor cells of the heart begins in the presomite embryo prior to formation of the anterior intestinal portal or foregut. In addition, this cell population of the precardiac mesoderm appears as a single crescent-shaped population of cells in continuity across the midline which extends caudally during development and then fuses in the midline to form the primitive heart tube. Unlike skeletal myogenesis, desmin and myosin appear simultaneously and are codistributed throughout this initial period of heart development. These results suggest that myocardial differentiation in the rat is precocious when compared to the chicken and precedes the morphogenetic processes involved in formation of the primitive heart tube. Furthermore, this study provides the first description in the mammal of the spatial distribution of the myogenic precardiac mesoderm.

Assembly, disassembly, and exchange of glial fibrillary acidic protein

The kinetics and dynamics of glial fibrillary acidic protein (GFAP) assembly was explored by a fluorescence energy transfer assay method. Purified GFAP was stoichiometrically labeled at a single cysteine residue with fluorescein-maleimide. Soluble labeled GFAP in a low ionic strength buffer was assembled into 10 nm filaments by rapidly increasing the ionic strength, and the kinetics of GFAP assembly was monitored by the reduction in fluorescence due to self-quenching of fluorescein. The extent of fluorescence quench correlated with both the formation of 10 nm filament morphology and the amount of protein pelleted at 12,000g. The assembly of GFAP is critically dependent upon both protein and magnesium ion concentration, and at the critical concentration for GFAP assembly is approximately 40 micrograms/ml. Disassembly of GFAP filaments was also observed as a relief of fluorescence quenching after dilution of labeled GFAP filaments. When labeled GFAP filaments were mixed with an excess of unlabeled filaments, a rapid increase of fluorescence was observed, which is due to an exchange of subunits between labeled and unlabeled GFAP filaments. These results indicate that GFAP filaments are dynamic structures and that a small pool of kinetically active unassembled GFAP subunits are in a dynamic equilibrium with assembled GFAP filaments. The ability of GFAP to assemble, disassemble, and undergo subunit exchange has important implications for the organization and dynamics of astroglia cell cytoskeleton during development and in response to injury.

Arrangement of cytoskeletal filaments at the equator of chicken intrafusal muscle fibers

The organization of the cytoskeleton at the equator of chicken intrafusal fibers was examined with immunofluorescence light microscopy, using monoclonal antibodies against myosin heavy chains, desmin, actin and tropomyosin. Actin was localized in the cytosol and in equatorial nuclei, while myosin heavy chains, desmin and tropomyosin were only observed in the cytosol. Although all four proteins were present at the equator and at the pole, the fluorescence produced after incubation with the different antibodies varied considerably between the two regions. Staining at the pole was in the form of striations, but at the equator it was non-striated and more uniform. The observed fluorescent patterns suggest that at the equator filaments are assembled into looser arrays than in the sarcomeres of the pole. A flexible cytoskeleton at the equator would be an appropriate substrate for distorting the affixed sensory endings during an applied stress.

Expression of intermediate filament proteins in fetal and adult human lung tissues

The expression patterns of intermediate filament proteins in fetal and normal or nonpathological adult human lung tissues are described using (chain-specific) monoclonal antibodies. In early stages of development (9-10 weeks and 25 weeks of gestation) only so-called simple cytokeratins such as cytokeratins 7 (minor amounts). 8, 18 and 19 are detected in bronchial epithelial cells. At later stages of development, the cytokeratin expression patterns become more complex. The number of bronchial cells positive for cytokeratin 7 increases, but basal cells in the bronchial epithelium remain negative. These latter cells show, however, expression of cytokeratin 14 in the third trimester of gestation. Developing alveolar epithelial cells express cytokeratins 7, 8, 18 and 19. In adult human bronchial epithelium cytokeratins 4 (varying amounts), 7, 8, 13 (minor amounts), 14, 18 and 19 can be detected, with the main expression of cytokeratins 7, 8, and 18 in columnar cells and the main expression of cytokeratin 14 in basal cells. Vimentin is detected in all mesenchymal tissues. In addition, fetal lung expresses vimentin in bronchial epithelium, however, to a lesser extent with increasing age, resulting in the expression of vimentin in only few scattered bronchial cells at birth. Also in adult bronchial epithelium the expression of vimentin is noticed in part of the basal and columnar epithelial cells. Desmin filaments, present in smooth muscle cells of the lung, appear to alter their protein structure with age. In early stages of development smooth muscle cells surrounding blood vessels are partly reactive with some cytokeratin antibodies and with a polyclonal desmin antibody. At week 9-10 and week 25 of gestation a monoclonal antibody to desmin, however, is not reactive with blood vessel smooth muscle cells but is only reactive with smooth muscle cells surrounding bronchi. With increasing age the reactivity of cytokeratin antibodies with smooth muscle cells in blood vessels decreases, while the reactivity with the monoclonal desmin antibody increases. Our results show that during differentiation profound changes in the intermediate filament expression patterns occur in the different cell types of the developing lung.

Assembly and exchange of intermediate filament proteins of neurons: neurofilaments are dynamic structures

We have explored the dynamics of intermediate filament assembly and subunit exchange using fluorescently labeled neurofilament proteins and a fluorescence resonance energy transfer assay. Neurofilaments (NFs) are assembled from three highly phosphorylated proteins with molecular masses of 180 (NF-H), 130 (NF-M), and 66 kD (NF-L) of which NF-L forms the structural core. The core component, NF-L, was stoichiometrically labeled at cysteine 321 with fluorescein, coumarin, or biotin-maleimide to produce assembly-competent fluorescent or biotinylated derivatives, respectively. Using coumarin-labeled NF-L as fluorescence donor and fluorescein-labeled NF-L as the fluorescence acceptor, assembly of NF filaments was induced by rapidly raising the NaCl concentration to 170 mM, and the kinetics was followed by the decrease in the donor fluorescence. Assembly of NF-L subunits into filaments does not require nucleotide binding or hydrolysis but is strongly dependent on ionic strength, pH, and temperature. The critical concentration of NF-L, that concentration that remains unassembled at equilibrium with fully formed filaments, is 38 micrograms/ml or 0.6 microM. Under physiological salt conditions NF-L filaments also undergo extensive subunit exchange. Kinetic analysis and evaluation of several possible mechanisms indicate that subunit exchange is preceded by dissociation of subunits from the filament and generation of a kinetically active pool of soluble subunits. Given the concentration of NF-L found in nerve cells and the possibility of regulating this pool, these results provide the first information that intermediate filaments are dynamic structures and that NF-L within the NF complex is in dynamic equilibrium with a small but kinetically active pool of unassembled NF-L units.

The intraclonal and interclonal phenotypic heterogeneity in a rhabdomyosarcoma cell line with abortive imitation of embryonic myogenesis

Three distinct subpopulations (A, B, C) derived from a dimethylbenzanthracene-induced rat rhabdomyosarcoma were established as permanent cell lines. Although the clonal nature of each of these subpopulations was confirmed by repeated recloning procedures, a striking intraclonal phenotypic heterogeneity was observed. By means of immunofluorescence microscopy and transmission electron microscopy, it could be shown that these subpopulations closely recapitulate stages of embryonic rhabdomyogenesis both in vitro and in vivo, but differ in their particular range of maximum differentiation. Embryonic rhabdomyogenesis is imitated most perfectly by subpopulation C, in which multinuclear myotubes are formed in vitro by fusion of mononuclear cells, and alpha-sarcomeric actin is expressed in the multinuclear cells and in a few mononuclear cells. After retransplantation in vivo, subpopulation C further proceeds in fine structural differentiation, now exhibiting myofibrils with a sarcomeric organization in the myotube-like giant cells. The cells of subpopulation B do not exceed the stage of mononuclear desmin-positive cells in vitro, but synthesize thin and thick myofilaments after retransplantation in vivo. The cells of subpopulation A recapitulate embryonic rhabdomyogenesis least successfully being confined to the stage of mononuclear desmin-positive cells. Thus, the coexistence of diverse subpopulations and the cellular maturation within these subpopulations together contribute to the phenotypic heterogeneity of rhabdomyosarcomas.

Transient coexpression of desmin and cytokeratins 8 and 18 in developing myocardial cells of some vertebrate species

During myogenesis the intermediate-sized filament (IF) cytoskeleton is characterized by increasing proportions of desmin. While skeletal and smooth muscle formation occurs in free mesenchymal cells containing vimentin-type IFs, myocardial development starts from a polar epithelium containing cytokeratin IFs and desmosomes. Therefore, we have studied the formation of the epicardium and the myocardium in different vertebrate species, combining light and electron microscopic immunolocalization techniques with gel-electrophoretic analyses of cytoskeletal proteins of microdissected myocardial tissue at differing developmental stages. In this report, we describe results obtained from advanced stages of myocardial differentiation. In all species studied the myocardial cell possess IFs abundant in desmin, often together with smaller amounts of vimentin, and the mesothelial layer of the epicardium contains cytokeratin IFs. However, we have observed remarkable interspecies differences with respect to the occurrence of cytokeratins in embryonic myocardial cells. In fetal human myocardium, from week 10 of pregnancy on, but not in juvenile and adult myocardium, and in chicken myocardium of all stages examined (until several days after hatching) specific immunostaining was seen with certain broad-range cytokeratin antibodies as well as with antibodies specific for cytokeratins 18 (in both species) and 8 (showing significant reaction only in human). This cytokeratin immunoreaction, however, did not appear in IFs extending throughout the cytoplasm or at Z-lines, but was localized in punctate arrays representing aggregates of dense material. The aggregates were often enriched at, but not restricted to, the desmosomal plaques of the intercalated discs. These observations were supported by gel-electrophoretic demonstration of small but significant amounts of cytokeratins 18 (in both species) and 8 (detected only in human) in microdissected myocardial tissue. We also observed cytokeratins in smooth muscle cells of some cardiac blood vessels. In contrast, bovine myocardium of advanced fetal age as well as rat and mouse myocardium (from fetal day 12 on) were negative for cytokeratins with all methods, although epicardial cytokeratin IFs were demonstrable. These observations are discussed in relation to myocardial histogenesis and to general problems of cytokeratin gene expression control in epithelial and nonepithelial cells.

Modulation of desmin intermediate filament assembly by a monoclonal antibody

We have used a monoclonal antibody against desmin to examine the assembly of intermediate filaments (IF) from their building blocks, the tetrameric protofilaments. The antibody, designated D76, does not cross react with any other IF proteins (Danto, S.I., and D.A. Fischman. 1984. J. Cell Biol. 98:2179-2191). It binds to a region amino-terminal to cys-324 of avian desmin that is resistant to chymotrypsin and trypsin digestion, and in the electron microscope appears to bind to the ends of tetrameric protofilaments. In combination, these findings suggest that the epitope of the antibody resides at the amino-terminal end of the alpha-helical rod domain. Preincubation of desmin protofilaments with an excess of D76 antibodies blocks their subsequent assembly into IF. In the presence of sub-stoichiometric amounts of antibodies, IF are assembled from protofilaments but they are morphologically aberrant in that (a) they are capped by IgG molecules at one or both ends; (b) they are unraveled to varying degree, revealing a characteristic right-handed helical arrangement of sub-filamentous strands of different diameters. The antibody binds only to the ends but not along the length of desmin IF. The most straightforward explanation for this is that the epitope resides in a part of the desmin molecule that becomes buried within the core of the filament upon polymerization and is therefore inaccessible to the antibody.

Expression of desmin, laminin and fibronectin during in situ differentiation (decidualization) of rat uterine stromal cells

Immunocytochemical analysis of frozen rat uterine sections containing decidual tissue, formed in response to normal or artificial stimulation of uteri sensitized by endogenous or exogenous hormonal regimens, demonstrated an elevated expression of the intermediate filament protein desmin in decidual cells. Changes in the expression of extracellular matrix (ECM) components were coordinated with the elevated expression of desmin as stromal cells underwent decidualization. In parallel with the pattern of regional decidualization, as determined by elevated desmin expression, laminin accumulated in ECM of decidual cells while an apparent decrease in fibronectin was associated with altered organization at the decidual cell surface. The in situ observations confirm previous results, which indicated that the expression of desmin in decidual cells formed in vivo or in vitro is a valid marker of their differentiation, and resolve questions unanswered in the previous study: (a) desmin (and laminin) appear to be constitutively expressed in non-decidualized stroma at barely detectable levels, (b) desmin is a valid marker of stromal cell differentiation because it is expressed similarly in decidual cells, irrespective of varying experimental protocols for uterine sensitization and stimulation, and (c) desmin expression follows the same regional progression described for the process of decidualization in morphological and histochemical studies.