Sequential changes in the distribution of type I and III collagens in the infarct zone: immunohistochemical study of experimental myocardial infarction in the rat

The theatrics of collagens in the myocardium: the supreme architect of the fibrotic heart

Heart failure (HF) mediated by cardiac fibrosis (CF) is characterized by an excessive accumulation of collagen-based extracellular matrix (ECM) in the myocardium. CF is a common pathophysiological condition in many heart diseases and can be distinctly categorized into two types: replacement and interstitial. In ischemic heart diseases, sudden loss of cardiomyocytes leads to the replacement of CF to prevent ventricular rupture. In contrast, excessive collagen deposition in the interstitial space between cardiomyocytes (often in response to pressure overload, chronic cardiac stress, hypertension, etc.) is termed interstitial CF. The progression of HF due to cardiac fibrosis is mainly driven by compromised diastolic function, resulting from increased stiffness of the heart wall muscle due to collagen-based scar formation. Increased myocardial stiffness is primarily catalyzed by the differential cross linking of deposited collagens forming the scar in the fibrotic heart. Although collagen deposition remained a hallmark of fibrosis, the pathophysiological progression due to biochemical alterations and mechanistic discrepancy of collagens across cardiac fibrosis subtypes remains elusive. With the advent of next-generation RNA sequencing and high-resolution mass spectrometry, mechanistic insights into collagen-mediated scar maturation have gained impetus. A deeper understanding of the spatiocellular transcriptional heterogeneity and site-specific collagen posttranslational modifications (PTMs) in maneuvering ECM remodeling is gaining attention. The unexplored mechanisms of posttranslational modifications and subsequent collagen cross linking in various cardiac fibrosis may provide the prime target for therapeutic interventions. This review comprehensively summarizes the detailed pattern, role, signaling, and mechanical contributions of different collagens and their PTMs, including cross-linking patterns as newer therapeutic regimens during cardiac fibrosis.

Targeted delivery of TAPI-1 via biomimetic nanoparticles ameliorates post-infarct left ventricle function and remodelling

AIMS

The potential of nanoparticles as effective drug delivery tools for treating failing hearts in heart failure remains a challenge. Leveraging the rapid infiltration of neutrophils into infarcted hearts after myocardial infarction (MI), we developed a nanoparticle platform engineered with neutrophil membrane proteins for the targeted delivery of TAPI-1, a TACE/ADAM17 inhibitor, to the inflamed myocardium, aiming to treat cardiac dysfunction and remodelling in rats with MI.

METHODS AND RESULTS

Neutrophil-mimic liposomal nanoparticles (Neu-LNPs) were constructed by integrating synthesized liposomal nanoparticles with LPS-stimulated neutrophil membrane fragments and then loaded with TAPI-1. MI rats were treated with TAPI-1 delivered via Neu-LNPs for 4 weeks. Left ventricular function was assessed by echocardiography and cardiac fibrosis was evaluated post-treatment. The novel Neu-LNPs maintained typical nanoparticle features, but with increased biocompatibility. Neu-LNPs demonstrated improved targeting ability and cellular internalization, facilitated by LFA1/Mac1/ICAM-1 interaction. Neu-LNPs displayed higher accumulation and cellular uptake by macrophages and cardiomyocytes in infarcted hearts post-MI, with a sustained duration. Treatments with TAPI-1-Neu-LNPs demonstrated greater protection against myocardial injury and cardiac dysfunction in MI rats compared to untargeted TAPI-1, along with reduced cardiac collagen deposition and expression of fibrosis biomarkers as well as altered immune cell compositions within the hearts.

CONCLUSIONS

Targeted treatment with TACE/ADAM17 inhibitor delivered via biomimetic nanoparticles exhibited pronounced advantages in improving left ventricle function, mitigating cardiac remodelling, and reducing inflammatory responses within the infarcted hearts. This study underscores the effectiveness of Neu-LNPs as a drug delivery strategy to enhance therapeutic efficacy in clinical settings.

Generation of Self-Induced Myocardial Ischemia in Large-Sized Cardiac Spheroids without Alteration of Environmental Conditions Recreates Fibrotic Remodeling and Tissue Stiffening Revealed by Constriction Assays

A combination of human-induced pluripotent stem cells (hiPSCs) and 3D microtissue culture techniques allows the generation of models that recapitulate the cardiac microenvironment for preclinical research of new treatments. In particular, spheroids represent the simplest approach to culture cells in 3D and generate gradients of cellular access to the media, mimicking the effects of an ischemic event. However, previous models required incubation under low oxygen conditions or deprived nutrient media to recreate ischemia. Here, we describe the generation of large spheroids (i.e., larger than 500 μm diameter) that self-induce an ischemic core. Spheroids were generated by coculture of cardiomyocytes derived from hiPSCs (hiPSC-CMs) and primary human cardiac fibroblast (hCF). In the proper medium, cells formed aggregates that generated an ischemic core 2 days after seeding. Spheroids also showed spontaneous cellular reorganization after 10 days, with hiPSC-CMs located at the center and surrounded by hCFs. This led to an increase in microtissue stiffness, characterized by the implementation of a constriction assay. All in all, these phenomena are hints of the fibrotic tissue remodeling secondary to a cardiac ischemic event, thus demonstrating the suitability of these spheroids for the modeling of human cardiac ischemia and its potential application for new treatments and drug research.

Extracellular Matrix in Ischemic Heart Disease, Part 4/4: JACC Focus Seminar

Myocardial ischemia and infarction, both in the acute and chronic phases, are associated with cardiomyocyte loss and dramatic changes in the cardiac extracellular matrix (ECM). It has long been appreciated that these changes in the cardiac ECM result in altered mechanical properties of ischemic or infarcted myocardial segments. However, a growing body of evidence now clearly demonstrates that these alterations of the ECM not only affect the structural properties of the ischemic and post-infarct heart, but they also play a crucial and sometimes direct role in mediating a range of biological pathways, including the orchestration of inflammatory and reparative processes, as well as the pathogenesis of adverse remodeling. This final part of a 4-part JACC Focus Seminar reviews the evidence on the role of the ECM in relation to the ischemic and infarcted heart, as well as its contribution to cardiac dysfunction and adverse clinical outcomes.

The Extracellular Matrix in Ischemic and Nonischemic Heart Failure

The ECM (extracellular matrix) network plays a crucial role in cardiac homeostasis, not only by providing structural support, but also by facilitating force transmission, and by transducing key signals to cardiomyocytes, vascular cells, and interstitial cells. Changes in the profile and biochemistry of the ECM may be critically implicated in the pathogenesis of both heart failure with reduced ejection fraction and heart failure with preserved ejection fraction. The patterns of molecular and biochemical ECM alterations in failing hearts are dependent on the type of underlying injury. Pressure overload triggers early activation of a matrix-synthetic program in cardiac fibroblasts, inducing myofibroblast conversion, and stimulating synthesis of both structural and matricellular ECM proteins. Expansion of the cardiac ECM may increase myocardial stiffness promoting diastolic dysfunction. Cardiomyocytes, vascular cells and immune cells, activated through mechanosensitive pathways or neurohumoral mediators may play a critical role in fibroblast activation through secretion of cytokines and growth factors. Sustained pressure overload leads to dilative remodeling and systolic dysfunction that may be mediated by changes in the interstitial protease/antiprotease balance. On the other hand, ischemic injury causes dynamic changes in the cardiac ECM that contribute to regulation of inflammation and repair and may mediate adverse cardiac remodeling. In other pathophysiologic conditions, such as volume overload, diabetes mellitus, and obesity, the cell biological effectors mediating ECM remodeling are poorly understood and the molecular links between the primary insult and the changes in the matrix environment are unknown. This review article discusses the role of ECM macromolecules in heart failure, focusing on both structural ECM proteins (such as fibrillar and nonfibrillar collagens), and specialized injury-associated matrix macromolecules (such as fibronectin and matricellular proteins). Understanding the role of the ECM in heart failure may identify therapeutic targets to reduce geometric remodeling, to attenuate cardiomyocyte dysfunction, and even to promote myocardial regeneration.

Cathepsin K-deficiency impairs mouse cardiac function after myocardial infarction

BACKGROUND

Extracellular matrix metabolism and cardiac cell death participate centrally in myocardial infarction (MI). This study tested the roles of collagenolytic cathepsin K (CatK) in post-MI left ventricular remodeling.

METHODS AND RESULTS

Patients with acute MI had higher plasma CatK levels (20.49 ± 7.07 pmol/L, n = 26) than those in subjects with stable angina pectoris (8.34 ± 1.66 pmol/L, n = 28, P = .01) or those without coronary heart disease (6.63 ± 0.84 pmol/L, n = 93, P = .01). CatK protein expression increases in mouse hearts at 7 and 28 days post-MI. Immunofluorescent staining localized CatK expression in cardiomyocytes, endothelial cells, fibroblasts, macrophages, and CD4⁺ T cells in infarcted mouse hearts at 7 days post-MI. To probe the direct participation of CatK in MI, we produced experimental MI in CatK-deficient mice (Ctsk^-/-) and their wild-type (Ctsk^+/+) littermates. CatK-deficiency yielded worsened cardiac function at 7 and 28 days post-MI, compared to Ctsk^+/+ littermates (fractional shortening percentage: 5.01 ± 0.68 vs. 8.62 ± 1.04, P < .01, 7 days post-MI; 4.32 ± 0.52 vs. 7.60 ± 0.82, P < .01, 28 days post-MI). At 7 days post-MI, hearts from Ctsk^-/- mice contained less CatK-specific type-I collagen fragments (10.37 ± 1.91 vs. 4.60 ± 0.49 ng/mg tissue extract, P = .003) and more fibrosis (1.67 ± 0.93 vs. 0.69 ± 0.20 type-III collagen positive area percentage, P = .01; 14.25 ± 4.12 vs. 6.59 ± 0.79 α-smooth muscle actin-positive area percentage, P = .016; and 0.82 ± 0.06 vs. 0.31 ± 0.08 CD90-positive area percentage, P = .008) than those of Ctsk^+/+ mice. Immunostaining demonstrated that CatK-deficiency yielded elevated cardiac cell death but reduced cardiac cell proliferation. In vitro studies supported a role of CatK in cardiomyocyte survival.

CONCLUSION

Plasma CatK levels are increased in MI patients. Heart CatK expression is also elevated post-MI, but CatK-deficiency impairs post-MI cardiac function in mice by increasing myocardial fibrosis and cardiomyocyte death.

Autoantibodies against basement membrane collagen type IV are associated with myocardial infarction

Background

Collagen type IV is the major constituent of basement membranes underlying endothelial cells and is important for endothelial cell attachment and function. Autoantibodies against native collagen type IV have been found in various autoimmune diseases. Oxidation of LDL in the vascular wall results in the formation of reactive aldehydes, which could modify surrounding matrix proteins. Like oxidized LDL, these modified matrix proteins are likely to induce immune responses. We examined whether autoantibodies against native or aldehyde-modified collagen type IV are associated with myocardial infarction.

Methods

IgM and IgG against native and aldehyde-modified collagen type IV were measured by ELISA in serum from 387 survivors of a first myocardial infarction and 387 age- and sex-matched controls.

Results

Post-infarction patients had significantly increased levels of IgM against native collagen type IV, and IgG against native collagen type IV was present at detectable level in 17% of patients as opposed to 7% of controls (p < 0.001). Controlling for major cardiovascular risk factors demonstrated that the presence of IgG against native collagen type IV was associated with myocardial infarction (OR 2.9 (1.6–5.4), p = 0.001). Similarly, subjects in the highest quartile of IgM against native collagen type IV had increased risk of having suffered myocardial infarction (OR 3.11 (1.8–5.4), p < 0.001) after adjusting for cardiovascular risk factors. In contrast, IgG against aldehyde-modified collagen type IV was decreased in myocardial infarction patients, but this association was not independent of established cardiovascular risk factors.

Conclusion

Autoantibodies against collagen type IV are associated with myocardial infarction independently of traditional cardiovascular risk factors.

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We measured native and MDA-collagen type IV IgM and IgG in MI patients and controls.

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Post-infarction patients had increased levels of IgM against native collagen type IV.

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Presence of IgG against native collagen type IV was associated with MI.

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In contrast, IgG against MDA-collagen type IV was decreased in MI patients.

Fibroblasts facilitate the engraftment of embryonic stem cell-derived cardiomyocytes on three-dimensional collagen matrices and aggregation in hanging drops

There is growing interest in the use of cardiomyocytes purified from embryonic stem (ES) cells for tissue engineering and cardiomyoplasty. However, most transplanted cells are lost shortly after transplantation due to the lack of integration into the host tissue and subsequent apoptosis. Here we examine whether murine embryonic fibroblasts (MEFs) can support the integration of purified murine ES cell-derived cardiomyocytes in a 3-dimensional tissue culture model based on a freezed-dryed collagen matrix with tubular structure. Collagen matrix was seeded either with cardiomyocytes alone or in combination with MEFs. The collagen sponges that were transplanted with cardiomyocytes alone showed neither morphological nor functional integration of viable cells. Cardiomyocytes also did not appear to be capable of attaching quantitatively to any of 16 different 2-dimensional biomaterials. However, cardiomyocytes co-cultured with MEFs formed fiber-like structures of rod-shaped cells with organized sarcomeric structure that contracted spontaneously. Electrical coupling between cardiomyocytes was suggested by strong expression of connexin 43. In addition, MEFs as well as cardiac fibroblasts supported re-aggregation of dissociated cardiomyocytes in hanging drops in the absence of collagen matrix. We conclude that fibroblasts promote cardiomyocyte engraftment and formation of functional 3-dimensional tissue in vitro. Elucidation of the mechanism of this phenomenon may help improve the integration of cardiomyocytes in vivo.

Melatonin augments expression of the procollagen α1 (I) and α1 (III) genes in the infarcted heart scar of pinealectomized rats

The pineal gland is involved in the regulation of collagen accumulation in peripheral wounds and scars of the infarcted heart. This study is aimed to provide an explanation of whether the pineal gland and melatonin (MLT) is involved in the regulation of α1 (I) and α1 (III) procollagen gene expression. A secondary aim is the investigation of whether the mechanism of changes could be explained by the direct influence of MLT on myofibroblasts isolated from the scar. Myocardial infarction was induced by left coronary artery ligation in all rats. Animals were divided into groups: control, vehicle-treated rats, those injected with MLT, sham-operated animals, pinealectomized (Px) rats, and Px rats injected with vehicle or treated with MLT. In the second part of the study, cells from the scar of the infarcted heart were isolated and cultured with MLT at concentrations of 10⁻⁷ and 10⁻⁹ M. Both α1 (I) and α1 (III) procollagen gene expressions were evaluated by reverse transcription-polymerase chain reaction. Neither MLT given to intact animals nor pinealectomy alone have an influence on procollagen gene expression. However, administration of MLT to the Px animals increased the expression of α1 (I) and α1 (III) procollagen genes. Cells isolated from the heart scar were identified as myofibroblasts. MLT did not influence collagen gene expression in cultured myofibroblasts. The results indicate that MLT has an influence on procollagen gene expression in Px animals. Because the pineal product does not have an influence on the myofibroblast of the scar, the indirect mechanism of MLT action is suggested. This study may have practical implications in patients with a low level of MLT (elderly subjects, patients treated with β-adrenergic blockers).

Regulatory influence of melatonin on collagen accumulation in the infarcted heart scar

The regulatory influence of the pineal gland on superficial wound healing and collagen content is documented. The aim of the present study was to determine whether the pineal gland and its secretory product melatonin regulate collagen accumulation in the scar of the infarcted heart and to explain the mechanisms of its action. To induce myocardial infarction in rats the left coronary artery was ligated. Metoprolol at the dose of 0.2 mg/100 g body weight (b.w.) was injected intraperitoneally to inhibit melatonin secretion. Pinealectomy was performed on some animals. For the in vitro study, cells were isolated from the heart scar and cultured in Dulbecco's modified Eagle medium with 3% fetal calf serum and antibiotics. Collagen content was evaluated as hydroxyproline content according to the Woessner method. Melatonin subcutaneously injected into the rats at the doses of 30 microg/100 g or 60 microg/100 g b.w. increased collagen accumulation in the heart scar. The doses of 3 microg/100 g b.w. and 300 microg/100 g b.w. were not effective. Surgical and pharmacological pinealectomies had opposite effects and reduced collagen content in the scar. However, melatonin administration (60 microg/100 g b.w.) to pinealectomized rats reversed the effect of pinealectomy and normalized collagen levels in heart after infarction. Cells isolated from the heart scar were identified as myofibroblasts. Melatonin (10(-7)-10(-8) m) increased collagen accumulation in the cultures. Collagen accumulation in the scar of the infarcted heart is regulated by melatonin and it exerts effects directly on the myofibroblasts of the infarcted area. Therefore, melatonin-induced collagen accumulation in the infarcted heart could be considered as the event improving the tensile strength of the scar and retarding the development of complications.

Versican is induced in infiltrating monocytes in myocardial infarction

Versican, a large chondroitin sulfate proteoglycan, plays a role in conditions such as wound healing and tissue remodelling. To test the hypothesis that versican expression is transiently upregulated and plays a role in the infarcted heart, we examined its expression in a rat model of myocardial infarction. Northern blot analysis demonstrated increased expression of versican mRNA. Quantitative real-time RT-PCR analysis revealed that versican mRNA began to increase as early as 6 h and reached its maximal level 2 days after coronary artery ligation. Versican mRNA then gradually decreased, while the mRNA of decorin, another small proteoglycan, increased thereafter. Versican mRNA was localized in monocytes, as indicated by CD68-positive staining, around the infarct tissue. The induction of versican mRNA was accelerated by ischemia/reperfusion (I/R), which was characterized by massive cell infiltration and enhanced inflammatory response. To examine the alteration of versican expression in monocytes/macrophages, we isolated human peripheral blood mononuclear cells and stimulated them with granulocyte/macrophage colony-stimulating factor (GM-CSF). Stimulation of mononuclear cells with GM-CSF increased the expression of versican mRNA as well as cytokine induction. The production of versican by monocytes in the infarct area represents a novel finding of the expression of an extracellular matrix gene by monocytes in the infarcted heart. We suggest that upregulation of versican in the infarcted myocardium may have a role in the inflammatory reaction, which mediates subsequent chemotaxis in the infarcted heart.

Exaggerated left ventricular dilation and reduced collagen deposition after myocardial infarction in mice lacking osteopontin

Osteopontin (OPN), an extracellular matrix protein, is expressed in the myocardium with hypertrophy and failure. We tested the hypothesis that OPN plays a role in left ventricular (LV) remodeling after myocardial infarction (MI). Accordingly, OPN expression and LV structural and functional remodeling were determined in wild-type (WT) and OPN knockout (KO) mice 4 weeks after MI. Northern analysis showed increased OPN expression in the infarcted region, peaking 3 days after MI and gradually decreasing over the next 28 days. In the remote LV, OPN expression was biphasic, with peaks at 3 and 28 days. In situ hybridization and immunohistochemical analyses showed increased OPN mRNA and protein primarily in the interstitium. Infarct size, heart weight, and survival were similar in KO and WT mice after MI (P=NS), whereas the lung wet weight/dry weight ratio was increased in the KO mice (P<0.005 versus sham-operated mice). Peak LV developed pressure was reduced to a similar degree after MI in the KO and WT mice. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive myocytes was similar in KO and WT mice after MI. In contrast, post-MI LV chamber dilation was approximately twice as great in KO versus WT mice (P<0.001). Myocyte length increased after MI in WT mice (P<0.001) but not in KO mice. Electron microscopy showed increased collagen content in WT mice after MI but not in KO mice after MI. Type I collagen content was increased approximately 3-fold and approximately 7-fold in remote and infarcted regions, respectively, of WT hearts after MI but not in KO hearts (P<0.01 versus WT hearts). Likewise, Northern analyses showed increased collagen I(alpha(1)) mRNA after MI in remote regions of WT hearts but not in KO hearts. Thus, increased OPN expression plays an important role in regulating post-MI LV remodeling, at least in part, by promoting collagen synthesis and accumulation.

Changes in extracellular matrix and in transforming growth factor beta isoforms after coronary artery ligation in rats

Extensive myocardial remodeling occurs after transmural myocardial infarction (MI). The infarcted myocardium is being replaced by scar tissue after gradual resorption of the necrotic tissue. The remodeling process involves both synthesis and degradation of collagens as major components of the extracellular matrix (ECM). In the present study we have analyzed the time-dependent changes of the processes related to this fibrosis in the infarct area and in the non-infarcted left ventricle (LV) six hours to 82 days after occlusion of the left anterior descending coronary artery (LAD) in rats. We also examined whether changes occurred in the expression pattern of the transforming growth factor (TGF) beta isoforms, since this cytokine is known as powerful inductor of fibrosis. Elevation in colligin expression preceded the pronounced increase in mRNA expression of both type I and type III collagen after MI from day three onwards. The maximal increase in colligin protein in the infarct area coincided with the most pronounced expression of collagen I and collagen III mRNA expression. Also, the expression and activity of matrix metalloproteinases (MMPs) and of tissue inhibitor of matrix metalloproteinase (TIMP)-2 mRNA were increased predominantly in the infarct area. TGF beta(1)and TGF-beta(2)expression increased within the first days after MI, whereas TGF-beta(3)expression was elevated predominantly in the infarct area. This pronounced increase in TGF-beta(3)persisted up to 82 days and correlated positively with the parameters of ECM metabolism. Thus, the scar formation is an ongoing dynamic process in which TGF-beta(3)seems to play an active role in the complex ventricular remodeling.

Time-dependent changes of decorin in the infarct zone after experimentally induced myocardial infarction in rats: comparison with biglycan

Decorin, a small dermatan sulphate proteoglycan, has been postulated to interact with other components of the extracellular matrix. We examined time-dependent changes of decorin in the infarct zone after experimentally induced myocardial infarction in rats by Northern blotting, in situ hybridization, and immunohistochemistry. The expression of decorin mRNA was compared to that of biglycan mRNA. Northern blotting demonstrated that the decorin mRNA expression was not increased in the infarct zone on day 2, while increased biglycan mRNA was observed at that time (average 3.1-fold increase). Decorin mRNA expression was increased on day 7, and reached a peak (average 2.2-fold increase) around day 14. Biglycan mRNA expression also reached a peak level around day 14 (average 13.3-fold increase). In situ hybridization revealed that mRNA signals for decorin did not appear in the infarct zone on day 2, while biglycan mRNA signals were observed. Decorin mRNA signals were observed in spindle-shaped mesenchymal cells in the infarct peripheral zone on day 7. The decorin mRNA signals appeared later than those of biglycan. Immunopositive staining for decorin was observed in the infarct zone on day 7. The present results demonstrated a time-dependent increase in decorin mRNA expression in mesenchymal cells in the infarct zone in rats. Decorin mRNA appeared later and was increased to a lower extent in the infarct zone than biglycan mRNA.

Greater than normal expression of the collagen-binding stress protein heat-shock protein-47 in the infarct zone in rats after experimentally-induced myocardial infarction

BACKGROUND

The heat-shock protein with relative molecular mass 47,000 (HSP47) can bind to procollagen molecules in the endoplasmic reticulum, and acts as a molecular chaperone during the processing and secretion of procollagen.

OBJECTIVE

To test our hypothesis that HSP47 is expressed in the myocardial infarct zone.

METHODS

We induced myocardial infarction in male Sprague-Dawley rats by ligation of left coronary artery. The expression of HSP47 was examined by Northern blotting, in-situ hybridization, Western blotting and immunohistochemistry. The time-dependent change in the distribution of HSP47 messenger RNA (mRNA) signal was compared with the changes in expression of alpha 1(I) and alpha 1(III) collagen mRNA by in-situ hybridization. The hypoxic induction of HSP47 in cultured cardiac fibroblasts was examined by Northern-blot analysis.

RESULTS

Northern blotting demonstrated that the expression of HSP47 mRNA had increased on day 2, reaching a maximum level around day 14 (induced 3.5-fold compared with the preligation hearts) and was maintained at a high level up to day 28. In-situ hybridization analysis revealed HSP47 mRNA signals in spindle-shaped mesenchymal cells located between surviving myocytes in the infarct's peripheral zone 24 h after the ligation, and in the entire infarct zone on day 14. The sequential changes in distribution of HSP47 mRNA signal were identical to those of the alpha 1(I) and alpha 1(III) collagen mRNA. Western blotting demonstrated that expression of HSP47 protein in the infarct zone had increased. Immunofluorescent staining revealed positivity for HSP47 in the infarct's peripheral zone on day 2 and in the entire infarct zone on day 14. Northern blotting revealed that the expression of HSP47 mRNA in cultured cardiac fibroblasts in hypoxic cultures was greater than that in normoxic cultures.

CONCLUSION

The present data demonstrated that an increase in expression of HSP47 is produced by spindle-shaped mesenchymal cells in the infarct zone. Expression of HSP47 mRNA was concurrent with the expression of collagen mRNA of types I and III. Hypoxia is one of the factors which induces expression of HSP47.

Sequential changes in the localization of the type IV collagen alpha chain in the infarct zone: immunohistochemical study of experimental myocardial infarction in the rat

Collagen, as a component of the extracellular matrix, have a role in the healing process after myocardial infarction (MI). For type IV collagen, a major structural protein present in the basal membrane of myocytes, six alpha chains [alpha 1 (IV)-alpha 6(IV)] have been identified. We examined the sequential changes in the appearance and localization of the alpha 1 (IV)-alpha 5(IV) after experimental MI in rats. Hearts were excised from 1 day to 8 weeks after permanent left coronary artery ligation. Immunohistochemical staining with monoclonal antibodies was performed. On day 3, staining for both alpha 1(IV) and alpha 2(IV) first appeared, forming a wavy pattern in the infarct peripheral zone, and the staining was not restricted to the cell membrane. The staining intensity and distribution for both alpha 1(IV) and alpha 2(IV) in the peripheral zone then gradually increased, reaching a maximum around day 7. The distribution progressed from the peripheral to the central zone of the infarct for 1-2 days, reaching the center point after 2 weeks. The staining distribution gradually decreased after reaching the maximum, but the staining had not completely disappeared at 8 weeks. In contrast, no positive staining for alpha 3(IV), alpha 4(IV) or alpha 5(IV) was observed at any time during the 8-week observation period. Thus, the present results demonstrated that in rats, type IV collagen consisting of alpha 1 and alpha 2 chains appears in the infarct zone at a relatively early phase after MI, indicating that type IV collagen composed of alpha 1 and alpha 2 chains contributes to infarct healing.