Behavior of embryonic chick heart cells in culture. 2. Cellular responses to epidermal growth factor and other growth signals

Myocyte proliferation in the developing heart

Regulation of organ growth is critical during embryogenesis. At the cellular level, mechanisms controlling the size of individual embryonic organs include cell proliferation, differentiation, migration, and attrition through cell death. All these mechanisms play a role in cardiac morphogenesis, but experimental studies have shown that the major determinant of cardiac size during prenatal development is myocyte proliferation. As this proliferative capacity becomes severely restricted after birth, the number of cell divisions that occur during embryogenesis limits the growth potential of the postnatal heart. We summarize here current knowledge concerning regional control of myocyte proliferation as related to cardiac morphogenesis and dysmorphogenesis. There are significant spatial and temporal differences in rates of cell division, peaking during the preseptation period and then gradually decreasing toward birth. Analysis of regional rates of proliferation helps to explain the mechanics of ventricular septation, chamber morphogenesis, and the development of the cardiac conduction system. Proliferation rates are influenced by hemodynamic loading, and transduced by autocrine and paracrine signaling by means of growth factors. Understanding the biological response of the developing heart to such factors and physical forces will further our progress in engineering artificial myocardial tissues for heart repair and designing optimal treatment strategies for congenital heart disease.

Effects of transforming growth factor beta1 and dexamethasone on the growth and chondrogenic differentiation of adipose-derived stromal cells

The effects of soluble mediators and medium supplements commonly used to induce chondrogenic differentiation in different cell culture systems were investigated to define their dose-response profiles and potentially synergistic effects on the chondrogenic differentiation of adipose-derived adult stromal (ADAS) cells. Human ADAS cells were suspended within alginate beads and cultured in basal medium with insulin, transferrin, and selenious acid (ITS+) or fetal bovine serum (FBS) and treated with different doses and combinations of TGF-beta1 (0, 1, and 10 ng/mL) and dexamethasone (0, 10, and 100 nM). Cell growth and chondrogenic differentiation were assessed by measuring DNA content, protein and proteoglycan synthesis rates, and proteoglycan accumulation. The combination of ITS+ and TGF-beta1 significantly increased cell proliferation. Protein synthesis rates were increased by TGF-beta1 and dexamethasone in the presence of ITS+ or FBS. While TGF-beta1 significantly increased proteoglycan synthesis and accumulation by 1.5- to 2-fold in the presence of FBS, such effects were suppressed by dexamethasone. In summary, the combination of TGF-beta1 and ITS+ stimulated cell growth and synthesis of proteins and proteoglycans by human ADAS cells. The addition of dexamethasone appeared to amplify protein synthesis but had suppressive effects on proteoglycan synthesis and accumulation.

Synthesis of extracellular matrix and adhesion through beta(1) integrins are critical for fetal ventricular myocyte proliferation

Extracellular matrix (ECM) regulates vascular smooth muscle cell proliferation. The role of ECM in myocardial growth is unexplored. We sought to determine whether human fetal ventricular myocytes (HFVMs) produce ECM and whether synthesis and attachment to ECM are necessary for their epidermal growth factor (EGF)-dependent and -independent proliferation. Cultured HFVMs proliferate in the presence but not absence of serum and EGF, as determined by increase in cell number and [(3)H]thymidine and [(14)C]leucine incorporation (measures of DNA and protein synthesis, respectively). Using a cyanogen bromide digestion technique to measure collagen and elastin and using affinity chromatography for fibronectin, we found that HFVMs synthesized collagen and fibronectin but not elastin. HFVMs grown on exogenous ECM (including fibronectin and type I collagen and laminin) demonstrated no change in proliferation or DNA and protein synthesis with or without EGF. However, inhibition of collagen synthesis using cis-4-hydroxyproline resulted in a decrease in EGF-related HFVM proliferation and DNA and protein synthesis, which was reversed by exposure to L-proline but not by growth on type I collagen. Use of beta(1) but not beta(3) integrin antibody to inhibit cell interaction with ECM resulted in a decrease in HFVM proliferation and DNA and protein synthesis in response to EGF. Furthermore, EGF-dependent proliferation was enhanced by alpha(1)beta(1) and alpha(5)beta(1) antibodies that act as functional ligands, but not alpha(3)beta(1), the only beta(1) subtype expressed in adult myocytes. In conclusion, proliferating HFVMs synthesize collagen and fibronectin. The proliferative response of HFVMs to EGF requires the synthesis of collagen as well as attachment to specific alpha/beta(1) integrin heterodimers.

Influence of growth factors on poultry myogenic satellite cells

Skeletal muscle development in avian and mammalian embryos depends on the proliferation, differentiation, and fusion of embryonic myoblasts. During the late fetal period and following birth or hatching, myogenic satellite cells are responsible for this developmental function. Satellite cells, which are found adjacent to existing skeletal muscle fibers fuse with these fibers and their nuclei direct the synthesis of new protein and function in the maturation of muscle. These events are controlled by specific growth factors that are produced locally by satellite cells and other cells in the muscle. Progress in our understanding of the early events in myogenesis has been made possible by the development of satellite cell cultures and media formulations that allow the assessment of the role of growth factors in skeletal muscle growth and development. Because of the key role that satellite cells play in skeletal muscle growth, development, and regeneration, many scientists in both the agricultural and medical communities have focused their research on understanding the physiology of this cell. From an agricultural perspective, a better understanding of the mechanisms regulating satellite cell activity may lead to procedures to increase the deposition and efficiency of lean muscle (meat) accretion and, perhaps, improve the nutrient composition of meat products.

Indapamide accentuates cardiac chronotropic responses to epidermal growth factor in chick cardiomyocytes

We have previously shown that indapamide [chloro-4-N-(methyl-2-indolinyl-1)-sulfamoyal-3-benzamide] has a direct action on the heart to alter ion fluxes. This study sought to examine the potential interaction between indapamide and epidermal growth factor (EGF). Cardiomyocytes were prepared as primary culture from 7-day-old chick embryo hearts as aggregates that have a pattern of consistent spontaneous contraction. Indapamide enhanced the positive chronotropic response to EGF observed in chick embryonic ventricular myocyte aggregates while indapamide itself did not alter cardiac contractile frequency. Taken in conjunction with data that calcium channel blockade, inhibition of sodium entry or Na(+)-Ca2+ exchange in the cardiomyocyte opposes the positive chronotropic action of EGF on the cardiomyocyte, this study has identified an agent, indapamide, that accentuates the cardiomyocyte response to EGF.

Identification of two types of smooth muscle cells from rabbit urinary bladder

Cells from the muscular layer of neonatal (3-day-old) rabbit urinary bladders were dissociated with collagenase, and cultured in M199 supplemented with 10% fetal bovine serum and antibiotic-antimycotic. Cells in culture were of two types: long and short. The short cells were thick and spindle-shaped, and the long cells were flat and elongated. The long cells can be about 15 times longer than the short cells. The short cells do not divide, but the long cells divide readily. Expressions of smooth muscle and non-muscle myosins, alpha-smooth muscle actin, vimentin, and h-caldesmon were determined by immuno-fluorescence microscopy using specific antibodies. Both types of cells react strongly with antibodies against smooth and non-muscle myosins. Unlike the short cells, the long cells also contain alpha-actin and vimentin. The expression of h-caldesmon was very weak in both cell types. Also, cells dissociated from the smooth muscle layers of adult (6-month-old) rabbit bladder were cultured under the same conditions as the cells from the neonatal bladders to see if the heterogeneity of smooth muscle cells, exhibited by cells from neonatal rabbits, is also shown by cells from adult bladder. Two types of cells were also identified. The cells were then fixed and examined with the same panel of antibodies that we used for the neonatal cells. The long cells from adult bladder muscle express similar proteins to those in the neonatal long cells, and the short cells were stained positively with smooth muscle myosin, non-muscle myosin, alpha-smooth muscle actin, and lightly with caldesmon. Although the absence of vimentin in the short cells from adults is similar to that from neonatal, the strong expression of alpha-actin in the adult short cells is unlike the short cells from neonatal rabbits, in which their expression is barely detectable.

Biopotency of fetal bovine serum, and insulin and insulin-like growth factors I and II in enhancing whole-body protein synthesis of chicken embryos cultured in vitro

Whole-body protein synthesis in chicken embryos was measured to examine the biopotency of fetal bovine serum, bovine insulin, recombinant human insulin, and recombinant human insulin-like growth factors (IGF) I and II. In all experiments chicken embryos at 7 days of incubation age were used and cultured in a synthetic serum-free medium in the presence or absence of the testing substances with a rotatory whole-embryo culture apparatus for up to 30 min. Whole-body protein synthesis was measured from the time course of specific radioactivities of free and protein-bound L-[4-3H]phenylalanine. In addition, the effect of bovine insulin on phenylalanine extraction rate from the culture medium was investigated. Supplementing the medium with fetal bovine serum and human IGF-I significantly enhanced whole-body protein synthesis. In contrast, human IGF-II, bovine insulin, or human insulin did not affect whole-body protein synthesis, although bovine insulin increased phenylalanine extraction rate from the culture medium in a proportional fashion as the dose increased. Therefore, from these results it was concluded that IGF-I, but not IGF-II, might be one of the anabolic factors in fetal bovine serum for stimulating whole-body protein synthesis, and that insulin may play a role in stimulating amino acid transport, but it may not be directly involved in protein synthesis of chicken embryos.

Behavior of embryonic chick heart cells in culture. 3. Spatial distribution of epidermal growth factor in heart muscle cells

Muscle cell-enriched primary cell cultures were prepared from 8-day embryonic chick heart ventricles. Immunostaining with an anti-EGF antibody detected the presence of EGF in the heart muscle cells, in a perinuclear distribution. In addition, some of the EGF appeared to be associated with the sarcomeres. Moreover, immunostaining with an anti-EGF receptor antibody also detected perinuclear localization, albeit not among the sarcomeres. Previous studies have shown that the heart muscle and non-muscle cells in culture respond to EGF to increase [3H]thymidine incorporation and cell division (Lau, 1993b). These data suggest the roles of EGF as a natural regulator in the development of the embryonic chick heart.