Cardiac fibroblasts: function, regulation of gene expression, and phenotypic modulation

Cardiac fibroblasts constitute the majority of the non-myocyte cell population in the ventricular myocardium. These cells are located in the interstitium, in areas between and surrounding cardiac myocytes. Cardiac fibroblasts are responsible for the synthesis of extracellular matrix proteins such as fibrillar collagen types I and III, basement membrane type IV collagen, fibronectin, and laminin. In addition to its role in muscle development and myoblast differentiations, extracellular matrix consisting primarily of fibrillar collagen is an intricate and highly organized structure that serves to support cardiac myocytes and to maintain functional integrity of the myocardium. Balanced synthesis and degradation of this matrix is the key to normal development of cardiac muscle and perfect myocardial function. Collagen remodeling and accumulation has been demonstrated in several experimental models of cardiac hypertrophy. To gain insights into molecular and cellular mechanisms that affect cardiac fibroblast behavior, cardiac fibroblasts from rat and rabbit ventricular myocardium were cultured and the impact of neurotransmitters and growth factors such as norepinephrine and transforming growth factor--beta (TGF-beta 1), to which cardiac fibroblasts are exposed in vivo, was studied. Results of these studies, with regards to gene expression, proliferation and differentiation of cardiac fibroblasts in culture, and their biological implications are discussed.

An immunoassay for qualitative estimation of collagenase activity in mammalian tissues

Collagen, the most abundant protein of the mammalian body, is specifically degraded by collagenase. Collagenase activity and subsequent collagen degradation are the main aspects of essential biological processes such as bone remodeling, tissue repair and wound healing. Measurement of collagenase activity is of interest to a wide variety of investigations using mammalian tissues, including clinical specimens. Most assays for collagenase activity are based on chemical modification of the substrate collagen. A unique feature of the present method is that it allows the rapid, qualitative measurement of collagenase activity without the requirement of substrate modification. It is based upon both substrate digestion by collagenase and reaction of undigested collagen with its antibody. Collagenase activity is measured by quantitation of immunoreactivity of undigested collagen using an enzyme-linked immunosorbent assay (ELISA). The assay is performed in 96-well microtiter plates used for ELISA. The advantages of this method are several: (a) a highly specific reaction between substrate collagen and its antibody that rules out the possibility of nonspecific quantitation; (b) the use of a nonmodified substrate; (c) the ease and rapidity of performance of a microassay. Application of the microassay to mammalian tissue homogenates was demonstrated in rat uterus tissue and ventricular myocardium of normal and hypertensive rats.

Effect of norepinephrine on myocardial collagen gene expression and response of cardiac fibroblasts after norepinephrine treatment

Biosynthesis of the collagen matrix of the heart has been shown to be regulated under various physiologic and pathologic conditions. Biogenic amines have known effects on myocardial function. The authors studied the effects of norepinephrine on myocardial collagen gene expression in the rat heart. Norepinephrine was administered intravenously in a sustained-release manner. Within 1 hour after treatment, the abundance of mRNA for pro alpha 2 (I) collagen increased by 212% (P = 0.05), TGF-beta 1 by 91% (P = 0.05), and cytoskeletal actin by 429% (P less than 0.01) in the ventricular myocardium of the treated rats compared with that in control untreated rats. In extended period of treatment, the abundance of mRNA for pro alpha 2 (I) collagen reached a peak (206% increase, P less than 0.01) at day 3, remained elevated through day 6, and returned to the control levels at 2 weeks after treatment. The expression of mRNA for TGF-beta 1 was coregulated with that of pro alpha 2 (I) collagen. The abundance of mRNA for cytoskeletal actin showed a sharp increase (323%, P less than 0.05) at day 1 and remained elevated through day 6 in treated hearts compared with that in control hearts and returned to the control levels at 2 weeks after treatment. Coadministration of alpha-receptor blocker, phentolamine, led to modest reversal, whereas coadministration of beta-receptor blocker, propranolol, led to about 50% reversal of norepinephrine effects on the abundance of mRNAs. At day 3 of treatment, collagen content of ventricular tissue, as determined by hydroxyproline measurement was increased by 13% (P less than 0.05) in treated hearts. Immunofluorescent light microscopy showed increased collagen deposition and focal areas of necrosis in the endocardial regions in hearts of animals treated with norepinephrine for 2 weeks. In vitro studies on cultured cardiac fibroblasts showed that although norepinephrine treatment does not lead to significant changes in the abundance of mRNA for pro alpha 2 (I) collagen, it leads to increased mRNA for cytoskeletal actin and increased (113%, P less than 0.05) 3H-thymidine incorporation into the cell nuclei of treated cells compared with that in untreated cells. The authors conclude that although norepinephrine has no direct in vitro effects on collagen type I biosynthesis, its in vivo effects may lead to a cascade of events such as induction of growth factors that ultimately result in increased expression of collagen type I in the myocardium.

Properties of heart fibroblasts of adult rats in culture

In the heart of the adult rat, fibroblasts are mainly responsible for the synthesis and deposition of the collagenous matrix. Because these cells in vitro may serve as an important model system for studies of collagen metabolism in heart tissue, we have cultured and characterized rat-heart fibroblasts from young adult and old animals. Conditions included use of media of different compositions with and without addition of ascorbate. Cells used were either cultured directly from fresh tissues or thawed previously frozen cells. Cultured cells were studied with respect to growth properties, morphology and ultrastructure and patterns of collagen. Heart fibroblasts generally resembled fibroblasts cultured from other tissues, but were more like skeletal muscle fibroblasts in that they deposited, in addition to type I collagen, type IV collagen and laminin. The fibroblasts showed a typical appearance in phase-contrast microscopy and electron microscopy. In the case of cells grown with added ascorbate, aligned collagen fibrils in the extracellular matrix showed a periodicity typical of type I collagen. The deposition of type I collagen occurred only in medium supplemented with ascorbate, and in that circumstance increased as a function of time past confluence; this was independent of the age of the animal from which the cells were obtained or of other changes of medium composition studied. Immunofluorescence studies with specific antibodies revealed that the cells deposited types I and IV collagens, laminin and fibronectin. In contrast to the case of type I collagen, the deposition of type IV collagen occurred in cells grown either with or without ascorbate.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of transforming growth factor-beta 1 and phorbol myristate acetate on cardiac fibroblasts. Regulation of fibrillar collagen mRNAs and expression of early transcription factors

Cardiac fibroblasts are responsible for synthesis and deposition of fibrillar collagen types I and III. Transforming growth factor-beta 1 (TGF-beta 1) has been proved to increase collagen biosynthesis in various systems, both in vivo and in vitro. We have investigated the effect of TGF-beta 1 on collagen gene expression in cultured cardiac fibroblasts and have compared this effect with that of a mitogenic agent, phorbol myristate acetate (PMA). The regulation of collagen types I and III gene expression was examined by using cDNA probes to rat alpha 2 (I) and mouse alpha 1 (III) procollagens. Quiescent cultured cardiac fibroblasts from rabbit heart were treated with TGF-beta 1 (10-15 ng/ml) and PMA (200 ng/ml). After 24 hours of treatment with TGF-beta 1, the abundance of mRNA for pro-alpha 2 (I) and pro-alpha 1 (III) collagens was increased by 112% (p less than 0.001) and 97% (p = 0.05), respectively, in treated fibroblasts compared with untreated cells. However, PMA-treated cells showed an opposite response: a 42% (p = 0.01) decrease in mRNA levels for pro-alpha 2 (I) collagen was observed. Immunofluorescent staining of cardiac fibroblasts in culture with anti-type I collagen antibody showed that alterations in mRNA levels led to altered collagen synthesis: cellular collagen was relatively increased in TGF-beta 1-treated cells and significantly diminished in PMA-treated cells. The abundance of mRNA for pro-alpha 1 (III) collagen was not affected by PMA treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac fibroblasts are predisposed to convert into myocyte phenotype: specific effect of transforming growth factor beta

Cardiac fibroblasts are mainly responsible for the synthesis of major extracellular matrix proteins in the heart, including fibrillar collagen types I and III and fibronectin. In this report we show that these cells, when stimulated by transforming growth factor beta 1 (TGF-beta 1), acquire certain myocyte-specific properties. Cultured cardiac fibroblasts from adult rabbit heart were treated with TGF-beta 1 (10-15 ng/ml) for different periods of time. Northern hybridization analysis of total RNA showed that cells treated with TGF-beta 1 for 24 hr expressed mRNA corresponding to sarcomeric actin mRNA. Immunofluorescence staining and light microscopy showed that cultured cardiac fibroblasts treated with TGF-beta 1 became stained with a monoclonal antibody to muscle-specific actin. After treatment of quiescent cells with TGF-beta 1, cell proliferation (as measured by [3H]thymidine incorporation) was moderately increased (1.5-fold, P less than 0.001). NIH 3T3 cells and human skin fibroblasts, treated with TGF-beta 1, did not express sarcomeric actin mRNA. Treatment of cardiac fibroblasts with the mitogenic agent phorbol 12-myristate 13-acetate or with norepinephrine, angiotensin II, or interleukin 1 beta did not induce myocyte-specific actin mRNA. Cultured cardiac fibroblasts at the subconfluent stage, when exposed to TGF-beta 1 in the presence of 10% fetal bovine serum, gave rise to a second generation of slowly growing cells that expressed muscle-specific actin filaments. Our findings demonstrate that cardiac fibroblasts can be made to differentiate into cells that display many characteristics of cardiac myocytes. TGF-beta 1 seems to be a specific inducer of such conversion.

Regulation of fibrillar collagen types I and III and basement membrane type IV collagen gene expression in pressure overloaded rat myocardium

Left ventricular hypertrophy is based on cardiac myocyte growth. The hypertrophic process can be considered heterogeneous based on whether it also includes a remodeling and accumulation of fibrillar types I and III collagens that are responsible for impaired myocardial stiffness. In the heart, the messenger RNA (mRNA) for fibrillar collagen types I and III has been detected only in cardiac fibroblasts, whereas mRNA for basement membrane collagen type IV is present in both fibroblasts and myocytes. We studied the early and long-term expression of these collagenous proteins in rat myocardium after abdominal aortic banding with renal ischemia. Complementary DNA probes for rat pro-alpha 2 (I), mouse type III and mouse type IV collagens, and chicken beta-actin were used. Northern and dot blot analysis on total RNA extracted from left ventricular tissue indicated a sixfold increase in steady-state levels of mRNA for collagen type I on day 3 of abdominal aortic banding, which had declined to control levels by day 7 where it remained rather constant at 4 and 8 weeks. Type III collagen showed a similar pattern of gene expression after banding. mRNA levels for type IV collagen, on the other hand, were elevated on day 1 after banding, returning to control at day 7 and remaining constant. Actin mRNA levels also increased on day 1 of banding, followed by a rapid return to control levels. Monospecific antibody to types I and III collagens and immunofluorescent light microscopy on frozen sections of the myocardium revealed that at 1 week after banding, the distribution and density of these collagens were similar to those of control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen and the myocardium: fibrillar structure, biosynthesis and degradation in relation to hypertrophy and its regression

The extracellular matrix of the myocardium contains an elaborate structural matrix composed mainly of fibrillar types I and III collagen. This matrix is responsible for the support and alignment of myocytes and capillaries. Because of its alignment, location, configuration and tensile strength, relative to cardiac myocytes, the collagen matrix represents a major determinant of myocardial stiffness. Cardiac fibroblasts, not myocytes, contain the mRNA for these fibrillar collagens. In the hypertrophic remodeling of the myocardium that accompanies arterial hypertension, a progressive structural and biochemical remodeling of the matrix follows enhanced collagen gene expression. The resultant significant accumulation of collagen in the interstitium and around intramyocardial coronary arteries, or interstitial and perivascular fibrosis, represents a pathologic remodeling of the myocardium that compromises this normally efficient pump. This report reviews the structural nature, biosynthesis and degradation of collagen in the normal and hypertrophied myocardium. It suggests that interstitial heart disease, or the disproportionate growth of the extracellular matrix relative to myocyte hypertrophy, is an entity that merits greater understanding, particularly the factors regulating types I and III collagen gene expression and their degradation.

Expression of fibrillar types I and III and basement membrane collagen type IV genes in myocardium of tight skin mouse

STUDY OBJECTIVE

The aim was to study the expression of fibrillar collagen types I and III and basement membrane type IV collagen in the heart of the tight skin mouse, a genetic mutant with collagen overproduction in various organs.

DESIGN

Collagen gene expression was measured in the ventricular tissues of the heart of the tight skin mouse and the age matched homozygous (+/+) litter mates by the use of cDNA probes to alpha 2 (I), alpha 1 (III) and alpha 2 (IV) procollagen and northern and dot blot analysis. Collagen deposition was examined by immunofluorescent light microscopy using monospecific antibodies to types I, III and IV collagens.

EXPERIMENTAL MATERIAL

Heterozygous male (TSK/+) and normal (+/+) mice, 1.5-2 months old of the C57BL/6 strain were used. The animals were anaesthetised and the hearts were rapidly excised and processed for RNA extraction and antibody staining.

MEASUREMENTS AND RESULTS

The results of northern and dot blot analyses showed a 41% increase in mRNA level for collagen type I, a 63% increase in mRNA level for type III and a 33% increase in type IV collagen in the ventricular myocardium (right and left ventricles) of the tight skin mouse compared to its counterpart in age matched homozygous (+/+) litter mates. mRNA levels for beta actin showed no significant increase. Immunofluorescent light microscopy and monospecific antibodies to types I, III and IV collagens were used to examine collagen deposition. The results showed that collagen type I fibres are thicker and denser in perivascular areas of the tight skin mouse heart compared to normal heart. No abnormal accumulation of type III fibres was observed.

CONCLUSIONS

The heart of the tight skin mouse may be an appropriate model for studying the up regulation of cardiac collagen gene expression and its potential contribution to myocardial diseases.

Ito-cell gene expression and collagen regulation

Ito cells are perisinusoidal cells thought to be a major source of collagen in normal and fibrotic livers. These cells appear to have features similar to several cell types but when cultured assume a fibroblast-like morphology. In this study we evaluated the phenotype of both freshly isolated and cultured Ito cells by examining their gene expression. To better define the modulators of Ito-cell collagen synthesis, we also examined the effect of transforming growth factor-beta 1, tumor necrosis factor-alpha and dexamethasone on collagen synthesis by these cells. Northern hybridization analysis revealed that cultured Ito cells expressed different types of procollagen mRNAs than did freshly isolated cells. Cultured cells contained large amounts of type I procollagen mRNA and lesser amounts of types III and IV, whereas freshly isolated cells contained more type IV procollagen mRNA than types I and III. Treatment of cultured cells with either transforming growth factor-beta 1 or tumor necrosis factor-alpha resulted in a greater than three-fold increase in total collagen content, and the effects of these cytokines on Ito-cell collagen synthesis involved different levels of gene regulation. Transforming growth factor-beta 1-treated cells had an approximately threefold increase in their type I procollagen mRNA levels, whereas no increase in this mRNA level was found in tumor necrosis factor-alpha-treated cells. Transforming growth factor-beta 1 treatment induced a twofold increase in transforming growth factor-beta 1 mRNA content in cultured cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen accumulation in heart ventricles as a function of growth and aging

Increase in resting tension of left ventricular papillary muscle with age has been attributed to the amount of collagen present. We therefore studied the total amount and structure of myocardial collagen as a function of age in the hearts of male Fischer 344 rats. Using amino acid analysis and quantification of hydroxyproline, we showed that collagen accumulates in relation to ventricular protein after 3 months of age and continues in that mode with increased age of the animal, levelling off at 22 months. In this strain of rats, collagen increased in the left ventricle from 5.5% of total protein in a 1 month old animal to approximately 12% in 22 and 26 month old animals; in the right ventricle the increase was from 7% in the 1 month old animal to approximately 19.5% in 22-26 month old animals. The larger percentages of collagen in the right ventricle relative to the left agree with findings of others. Collagen accumulates in intrinsic collagenous structures where the pre-existing fibres are thickened and are more extensive. These structures were detected with light microscopy and scanning electron microscopy and include perimysial weaves, coiled perimysial fibres and struts. Regions of fibrosis were also increased in size and volume in older animals.

Cellular origin and distribution of transforming growth factor-beta in the normal rat myocardium

Transforming growth factor-beta (TGF-beta) is a biologically active polypeptide present in normal tissues as well as transformed cells. Two structurally related forms of this peptide are TGF-beta 1 and TGF-beta 2. Using freshly isolated cardiomyocytes and non-myocyte heart cells, and a [32P]- labelled cDNA probe to human TGF-beta 1, we demonstrated that mRNA for TGF-beta 1 could be detected only in the nonmyocyte fraction of heart cells. In the present study, the distribution of TGF-beta 1 in the heart was determined by immunofluorescence staining by use of a polyclonal antibody to porcine TGF-beta 1 in cryostat sections of rat heart. Immunofluorescence staining was intense around the blood vessels and radially diffuse in the surrounding myocardium.

Collagenase activity in the normal rat myocardium. An immunohistochemical method

Fibrillar collagen in the myocardium provides a supportive framework for myocytes and capillaries. Disruption of this organized framework has been observed in certain pathological states. Collagen degradation is primarily mediated by the specific enzyme collagenase, which has been found to exist in various tissues including the myocardium. In this report we describe a method that detects collagenase activity in sections of cardiac tissue. This method is on the basis of degradation of collagen by collagenase on one hand and the visualization of disrupted collagen fibers by immunofluorescence on the other. Frozen rat heart sections were incubated under optimal conditions for collagenase activity (37 degrees C in the presence of 0.1 M calcium at pH 7.4) for 24 h and 48 h. Subsequently, immunofluorescence staining with antibody to type I collagen was performed and the collagenous structures were visualized by immunofluorescence light microscopy. As control, untreated rat heart sections and sections incubated in the absence of calcium were similarly treated with antibody. After the 24 h of incubation, we found no change in the structural integrity of collagen fibers. Marked disruption of the type I collagen fibers was observed 48 h after incubation. No evidence of collagen fiber disruption was found in control sections. Experiments with exogenous collagenase resulted in similar collagen fiber disruption in the frozen rat heart sections. We conclude that the disruption of collagen type I fibers after 48 h of incubation, under optimal conditions for collagenolytic digestion, is the result of collagen degradation by intrinsic collagenase of the myocardium.

Localization of types I, III and IV collagen mRNAs in rat heart cells by in situ hybridization

Previous studies investigating the cellular origins of several collagens in young adult rat hearts (Eghbali et al., 1988) demonstrated that the mRNAs for types I and III collagen occurred in non-myocyte cells, mostly fibroblasts, whereas the mRNA for type IV collagen was observed in both myocytes and non-myocyte cells. In the present study, cellular localization of collagen mRNAs has been achieved by in situ hybridization in rat heart tissue and in isolated heart cells. Frozen tissue sections, isolated cardiomyocytes, cultured neonatal cardiomyocytes and fibroblasts were hybridized with DNA probes for type-specific collagens, actin, and myosin heavy chain. Silver grains were visualized by dark field imaging. In heart sections, types I and III mRNAs were observed predominantly adjacent to myocytes and in the interstitium, where fibroblasts are known to be present. In contrast, type IV collagen mRNA was identified both within the myocytes and the interstitium. In freshly isolated adult cardiomyocytes and in cultured neonatal cardiomyocytes, collagen type IV mRNA was observed but type I collagen mRNA was not. In cultured neonatal fibroblasts, both types IV and I collagen mRNAs were abundant.

Visualization of collagenase-sensitive acetylcholinesterase in isolated cardiomyocytes and in heart tissue

Previous studies have indicated that the asymmetric form of acetylcholinesterase (collagen-tailed) is localized in the basal lamina of the neuromuscular junction of skeletal muscle. The present study shows localization of the asymmetric acetylcholinesterase in the heart of the rat. Antiserum to 14 + 18 S acetylcholinesterase of the electric eel was raised in rabbits. The purified antibody did not react with collagen type I or laminin. Collagenase reduced the immunoreactivity of the enzyme with the purified antibody. Isolated cardiomyocytes and frozen sections of the heart were stained for acetylcholinesterase with the antibody. Diffuse immunofluorescence appeared over the surface of the cardiomyocytes. In the frozen sections, the immunofluorescence was most intense at the cell boundaries. These data suggest that collagenase-sensitive acetylcholinesterase in the heart is present in the myocytes and occurs in the vicinity of the basal lamina.

Characterization and visualization of rat and guinea pig brain kappa opioid receptors: evidence for kappa 1 and kappa 2 opioid receptors

kappa opioid receptors (kappa receptors) have been characterized in homogenates of guinea pig and rat brain under in vitro binding conditions. kappa receptors were labeled by using the tritiated prototypic kappa opioid ethylketocyclazocine under conditions in which mu and delta opioid binding was suppressed. In the case of guinea pig brain membranes, a single population of high-affinity kappa opioid receptor sites (kappa sites; Kd = 0.66 nM, Bmax = 80 fmol/mg of protein) was observed. In contrast, in the case of rat brain, two populations of kappa sites were observed--high-affinity sites at low density (Kd = 1.0 nM, Bmax = 16 fmol/mg of protein) and low-affinity sites at high density (Kd = 13 nM, Bmax = 111 fmol/mg of protein). To test the hypothesis that the high- and low-affinity kappa sites represent two distinct kappa receptor subtypes, a series of opioids were tested for their abilities to compete for binding to the two sites. U-69,593 and Cambridge 20 selectively displaced the high-affinity kappa site in both guinea pig and rat tissue, but were inactive at the rat-brain low-affinity site. Other kappa opioid drugs, including U-50,488, ethylketocyclazocine, bremazocine, cyclazocine, and dynormphin (1-17), competed for binding to both sites, but with different rank orders of potency. Quantitative light microscopy in vitro autoradiography was used to visualize the neuroanatomical pattern of kappa receptors in rat and guinea pig brain. The distribution patterns of the two kappa receptor subtypes of rat brain were clearly different. The pattern of rat high-affinity kappa sites paralleled that of guinea pig in the caudate-putamen, mid-brain, central gray substance of cerebrum, and substantia nigra; interspecies differences were apparent throughout most of the rest of the brain. Collectively, these data provide direct evidence for the presence of two kappa receptor subtypes; the U-69,593-sensitive, high-affinity kappa 1 site predominates in guinea pig brain, and the U-69,593-insensitive, low-affinity kappa 2 site predominates in rat brain.

Structure and function of connective tissue in cardiac muscle: collagen types I and III in endomysial struts and pericellular fibers

Heart myocytes and capillaries are enmeshed in a complex array of connective tissue structures arranged in several levels of organization: epimysium, the sheath of connective tissue that surrounds muscles; perimysium, which is associated with groups of cells; and endomysium, which surrounds and interconnects individual cells. The present paper is a review of work in this field with an emphasis on new, unpublished findings, including composition of endomysial fibers and disposition of newly described perimysial fibers. The role of scanning electron microscopy in the development of current understanding is also outlined. Biaxially arranged epimysial fibers form a sheath around papillary muscles and trabeculae that becomes increasingly well-oriented with the muscle axis during stretch. Perimysial structures are associated with groups of cells, and include weaves and septa of collagen, tendon-like fibers between weaves, ribbon-like fibers perpendicular to myocytes, and the newly described coiled perimysial fibers, which form an array in parallel with the myocytes and the epimysial net. The endomysium includes struts that bridge cells and pericellular fibers; both contain collagen types I and III. The evidence for the latter is presented in this paper and depends upon the use of antibody localization with fluorescent markers in light microscopy and colloidal gold for scanning electron microscopy. The implications of the composition of collagen fibers for myocardial function are discussed in relation to intra-cellular and other extra-cellular structures.

Collagen chain mRNAs in isolated heart cells from young and adult rats

Collagen is the predominant component of the extracellular matrix of the heart, where it is organized in a hierarchy of structures. To establish the cellular origin of the various collagen types, type I-procollagen alpha 2 chain and types III and IV collagen mRNAs were examined in preparations of myocytes and non-myocyte heart cells freshly isolated from rats 1 to 6 months old. The cardiomyocytes appeared morphologically intact and functionally competent. Fibroblast-like cells predominated in the non-myocyte cell fractions but endothelial and smooth muscle cells were also present. RNA from whole ventricular tissue served as a control. Northern and dot blot analyses were used to establish the presence or absence of mRNAs. In RNA prepared from whole ventricular tissue, the mRNAs for alpha-, beta-, and gamma-actin isotypes were detected whereas mRNA for alpha-actin was found in myocytes and those for beta- and gamma-actins were found in non-myocyte cells, confirming further the nature of the cell populations. Procollagen types I and III mRNAs were not detected in the total RNA of cardiomyocytes but mRNA for type IV collagen was present. The mRNAs for all three collagen types were present in the non-myocyte cells. These results suggest that in the rat heart the non-myocyte cells, probably fibroblasts, are responsible for interstitial collagen production. Both cell populations may engage in the formation of basement membrane collagen type IV.

Differential effects of gamma-interferon on collagen and fibronectin gene expression

The interferons are a group of endogenous proteins that exhibit a variety of biological functions in addition to their ability to induce resistance to viruses. In order to evaluate the anti-fibrogenic actions of interferon, we have delineated the level of regulation responsible for gamma-interferon-induced changes in collagen and fibronectin gene expression in cultured fibroblasts. Confluent human skin fibroblasts were exposed to 500 anti-viral units/ml of gamma-interferon. RNA was then extracted from the cells, and steady-state mRNA levels were determined by Northern and dot blot hybridization studies. Cells exposed to interferon had type I procollagen mRNA levels that were 23% of control and type III procollagen mRNA levels only 7% of control. The interferon-treated cells also had beta-actin mRNA levels that were decreased to 51% that of untreated cells but had fibronectin steady-state mRNA levels that were 560% of control levels. Nuclear run-on assays revealed that interferon did not affect the transcriptional rates of types I and III collagen or beta-actin, but it did increase the transcriptional rate of fibronectin to 670% of control levels. These findings demonstrate that gamma-interferon causes a marked decrease in types I and III procollagen mRNA levels in vitro by a post-transcriptional mechanism while inducing fibronectin expression at a transcriptional level.

Visualization of multiple opioid-receptor types in rat striatum after specific mesencephalic lesions

In order to gain insight into a possible modulatory role for mu, delta, and kappa opioid receptors of the nigrostriatal dopaminergic pathway, we investigated the topographical organization of the receptors with respect to pre- and postsynaptic membranes. Dopaminergic terminals projecting from the substantia nigra to the corpus striatum were destroyed by unilateral injection of 6-hydroxydopamine into the substantia nigra. Quantitative receptor assays using highly specific radioligands were used to measure the density of striatal mu, delta, and kappa receptors before and after denervation. Denervation caused a 34 +/- 2% loss of striatal mu receptors and a 32 +/- 1% loss of striatal delta receptors on the lesioned side of the brain; in contrast, kappa receptors did not change significantly in density. Quantitative in vitro autoradiography was used to visualize the neuroanatomical pattern of receptors on lesioned and nonlesioned sides of the brain under the light microscope. Loss of mu receptors in striatal patches was striking in the ventrolateral areas of the striatum, whereas the most notable loss of delta receptors was found in the central striatum. Other brain areas did not differ significantly in mu receptor density between the lesioned and nonlesioned sides, as determined by autoradiography. These findings suggest that a high percentage of mu and delta receptors in the striatum are located on the nigrostriatal dopaminergic terminals and support the concept of a modulatory role for mu and delta opioid peptides in the nigrostriatal dopaminergic pathway.

Enzyme-antibody histochemistry. A method for detection of collagens collectively

Different types of distinct molecular forms of collagen are components of the extracellular matrix in most tissues. The common types can usually be detected by immunohistochemical methods but others may escape detection for lack of specific antisera. However, all these collagens are substrates for the collagenase of Clostridium histolyticum. In this report we describe a method that allows the visualization of collagens, collectively, in a tissue preparation. The method is based on the affinity between clostridial collagenase and collagen on one hand, and collagenase and its antibody on the other. Under the conditions of low temperature used in the procedure, collagenase binds to collagen, but digestion does not occur. Subsequent reaction of the bound collagenase with the specific collagenase antibody is followed by reaction with a tagged anti-IgG reagent. This allows the visualization of the enzyme-substrate complex. The procedure is illustrated in sections of the heart and the aorta, as well as in the isolated cardiomyocytes and the collagen distribution is verified using collagens type I and IV specific antibodies. In all instances the collagenase staining pattern includes all structural features seen individually with the type specific anticollagen antibodies.