Tumor Budding, p53, and DNA Mismatch Repair Markers in Sinonasal Intestinal-Type Adenocarcinoma: A Retrospective Study Supports the Adverse Prognostic Impact of Tumor Budding

Sinonasal intestinal-type adenocarcinoma (ITAC) is a very rare, closely occupational-related tumor with strong histological similarities to colorectal cancer (CRC). In the latter, tumor budding (TB) is widely recognized as a negative prognostic parameter. The aim of this study was to evaluate the prognostic role of TB in ITAC and to correlate it with other established or emerging biomarkers of the disease, such as p53 and deficient DNA mismatch repair (MMR) system status/microsatellite instability (MSI). We retrospectively analyzed 32 consecutive specimens of patients with ITAC diagnosis treated in two institutions in Northern Italy. We reviewed surgical specimens for TB evaluation (low-intermediate/high); p53 expression and MMR proteins were evaluated via immunohistochemistry. Results were retrospectively stratified using clinical data and patients' outcomes. According to bud counts, patients were stratified into two groups: intermediate/high budding (>4 TB) and low budding (≤4 TB). Patients with high TB (>4) have an increased risk of recurrence and death compared to those with low TB, with a median survival of 13 and 54 months, respectively. On multivariate analysis, considering TB, therapy, and stage as covariates, TB emerged as an independent prognostic factor net of the stage of disease or type of therapy received. No impact of p53 status as a biomarker of prognosis was observed and no alterations regarding MMR proteins were identified. The results of the present work provide further significant evidence on the prognostic role of TB in ITAC and underline the need for larger multicenter studies to implement the use of TB in clinical practice.

Cardiac wasting in head and neck cancer and in cardiac autopsies from different cancer types: A study in a chemo-naïve setting

BACKGROUND

Cardiac wasting is a detrimental consequence of cancer that has been traditionally ignored and often misinterpreted as an iatrogenic effect.

METHODS

We conducted a retrospective study on 42 chemo-naive patients affected by locally advanced head and neck cancer (HNC). Based on unintentional weight loss, patients were divided into cachectic and non-cachectic. Left ventricular mass (LVM), LV wall thickness (LVWT), interventricular septal (IVS) thickness, left ventricular internal diameter diastolic (LVIDd), left ventricular internal diameter systolic (LVIDs), internal ventricular septum diastolic (IVSd), left ventricular posterior wall thickness diastolic (LVPWd) and LV ejection fraction (LVEF) were analysed by echocardiography. In parallel, we retrospectively analysed 28 cardiac autoptic specimens of patients who either died of cancer before chemotherapy or with a diagnosis of cancer at autopsy. Presence or absence of myocardial fibrosis at microscopic observation was used for sample stratification. Conventional histology was performed.

RESULTS

Cachectic and non-cachectic patients had a significantly different value of LVWT and IVS thickness and LVPWd. LVWT was 9.08 ± 1.57 versus 10.35 ± 1.41 mm (P = 0.011) in cachectic and non-cachectic patients, IVS was 10.00 mm (8.50-11.00) versus 11.00 mm (10.00-12.00) (P = 0.035), and LVPWd was 9.0 (8.5-10.0) and 10.00 mm (9.5-11.0) (P = 0.019) in cachectic and non-cachectic patients. LVM adjusted for body surface area or height squared did not differ between the two populations. Similarly, LVEF did not show any significant decline. At multivariate logistic regression analysis for some independent predictors of weight loss, only LVWT maintained significant difference between cachectic and non-cachectic patients (P = 0.035, OR = 0.240; P = 0.019). The secondary analysis on autoptic specimens showed no significant change in heart weight, whereas LVWT declined from 9.50 (7.25-11.00) to 7.50 mm (6.00-9.00) in cardiac specimens with myocardial fibrosis (P = 0.043). These data were confirmed in multivariate logistic regression analysis (P = 0.041, OR = 0.502). Histopathological analysis confirmed severe atrophy of cardiomyocytes, fibrosis and oedema as compared with controls.

CONCLUSIONS

Subtle changes in heart structure and function occur early in HNC patients. These can be detected with routine echocardiography and may help to select appropriate cancer treatment regimens for these patients. Histopathological analysis provided conclusive evidence that atrophy of cardiomyocytes, oedema and fibrosis occur during cancer progression and may precede the onset of overt cardiac pathology. To our knowledge, this is the first clinical study that establishes a direct relationship between tumour progression and cardiac remodelling in HNCs and the first pathological study conducted on human cardiac autopsies from selected chemo-naïve cancer patients.

Myocardial overexpression of ANKRD1 causes sinus venosus defects and progressive diastolic dysfunction

AIMS

Increased Ankyrin Repeat Domain 1 (ANKRD1) levels linked to gain of function mutations have been associated to total anomalous pulmonary venous return and adult cardiomyopathy occurrence in humans. The link between increased ANKRD1 level and cardiac structural and functional disease is not understood. To get insight into this problem, we have generated a gain of function ANKRD1 mouse model by overexpressing ANKRD1 in the myocardium.

METHODS AND RESULTS

Ankrd1 is expressed non-homogeneously in the embryonic myocardium, with a dynamic nucleo-sarcomeric localization in developing cardiomyocytes. ANKRD1 transgenic mice present sinus venosus defect, which originates during development by impaired remodelling of early embryonic heart. Adult transgenic hearts develop diastolic dysfunction with preserved ejection fraction, which progressively evolves into heart failure, as shown histologically and haemodynamically. Transgenic cardiomyocyte structure, sarcomeric assembly, and stability are progressively impaired from embryonic to adult life. Postnatal transgenic myofibrils also present characteristic functional alterations: impaired compliance at neonatal stage and impaired lusitropism in adult hearts. Altogether, our combined analyses suggest that impaired embryonic remodelling and adult heart dysfunction in ANKRD1 transgenic mice present a common ground of initial cardiomyocyte defects, which are exacerbated postnatally. Molecular analysis showed transient activation of GATA4-Nkx2.5 transcription in early transgenic embryos and subsequent dynamic transcriptional modulation within titin gene.

CONCLUSIONS

ANKRD1 is a fine mediator of cardiomyocyte response to haemodynamic load in the developing and adult heart. Increased ANKRD1 levels are sufficient to initiate an altered cellular phenotype, which is progressively exacerbated into a pathological organ response by the high ventricular workload during postnatal life. Our study defines for the first time a unifying picture for ANKRD1 role in heart development and disease and provides the first mechanistic link between ANKRD1 overexpression and cardiac disease onset.

How progressive cancer endangers the heart: an intriguing and underestimated problem

Since it came into being as a discipline, cardio-oncology has focused on the prevention and treatment of cardiotoxicity induced by antitumor chemotherapy and radiotherapy. Over time, it has been proved that even more detrimental is the direct effect generated by cancer cells that release pro-cachectic factors in the bloodstream. Secreted molecules target different organs at a distance, including the heart. Inflammatory and neuronal modulators released by the tumor bulk, either as free molecules or through exosomes, contribute to the pathogenesis of cardiac disease. Progressive cancer causes cachexia and severe cardiac muscle wasting accompanied by cardiomyocyte atrophy, tissue fibrosis, and several functional impairments up to heart failure. The molecular mechanisms responsible for such a cardiac muscle wasting have been partially elucidated in animal models, but minimally investigated in humans, although severe cardiac dysfunction exacerbates global cachexia and hampers efficient anti-cancer treatments. This review provides an overview of cancer-induced structural cardiac and functional damage, drawing on both clinical and scientific research. We start by looking at the pathophysiological mechanisms and evolving epidemiology and go on to discuss prevention, diagnosis, and a multimodal policy of intervention aimed at providing overall prognosis and global care for patients. Despite much interest in the cardiotoxicity of cancer therapies, the direct tumor effect on the heart remains poorly explored. There is still a lack of diagnostic criteria for the identification of the early stages of cardiac disease in cancer patients, while the possibilities that there are for effective prevention are largely underestimated. Research on innovative therapies has claimed considerable advances in preclinical studies, but none of the molecular targets suitable for clinical application has been approved for therapy. These issues are critically discussed here.

Development of Cancer in Patients With Heart Failure: How Systemic Inflammation Can Lay the Groundwork

In the last decade, cardiologists and oncologists have provided clinical and experimental evidence that cancer, and not only chemotherapeutic agents, can cause detrimental effects on heart structure and function, a consequence that has serious clinical implications for patient management. In parallel, the intriguing idea that heart failure (HF) may be an oncogenic condition has also received growing attention. A number of epidemiological and clinical studies have reported that patients with HF have a higher risk of developing cancer. Chronic low-grade systemic inflammation has been proposed as a major pathophysiological process linking the failing heart to the multi-step process of carcinogenesis. According to this view, pro-inflammatory mediators secreted by the damaged heart generate a favorable milieu that promotes tumor development and accelerates malignant transformation. HF-associated inflammation synergizes with tumor-associated inflammation, so that over time it is no longer possible to distinguish the effects of one or the other. Experimental studies have just begun to search for the molecular effectors of this process, with the ultimate goal that of identifying mechanisms suitable for anti-cancer target therapy to reduce the risk of incident cancer in patients already affected by HF. In this review we critically discuss strengths and limitations of clinical and experimental studies that support a causal relationship between HF and cancer, and focus on HF-associated inflammation, cardiokines and their endocrine functions linking one and the other disease.

Turning science into teaching: a challenge for scientists

This article was migrated. The article was marked as recommended. Teaching basic science in the medical school remains a challenge, and the lack of appropriate resources is one of important limitation. Building up such resources is difficult, time-costly and does not always result in effective, solid and student-centered instruction. This "personal view" aims to stimulate scientists and scientific journals to engage with new ideas and innovative resources for biomedical education. The time has now come to plan research and education as mutually beneficial activities, supporting each other rather than competing with each other. Scientific research should be converted into digital learning resources hosted by scientific journals on a regular basis, and subjected to peer-review to ensure quality and integration of contents, appropriate cognitive approach and rigorous criteria of selection. Turning science into teaching represents an investment with mutual benefits, for students and educators. Academic educators can produce resources to face the teaching burden, and gather the opportunity to increase personal productivity. Students can take advantage from being engaged in innovative learning environments where educators act as catalysts for learning, instead of just transmitters of knowledge.

A New Nested Primer Pair Improves the Specificity of Ck-19 Mrna Detection by Rt-Pcr in Occult Breast Cancer Cells

Reverse transcription polymerase chain reaction (RT-PCR) of cytokeratin-19 (CK-19) has been widely used to detect small numbers of circulating malignant epithelial cells in the bone marrow or the peripheral blood of patients with breast cancer. However, a high percentage of false positive results has been recorded and conflicting reports question the clinical relevance of this technical approach. We demonstrate that the use of a new nested primer pair for CK-19 RT-PCR avoids false positive results without affecting the sensitivity of the assay. Our experiments were carried out using MCF-7 cells alone or mixed with peripheral blood mononuclear cells (PBMNC) of healthy donors. The results were also validated in a large series of healthy donors and in a preliminary study on a limited number of patients with breast cancer, thus suggesting that our assay is feasible for application in the clinical evaluation of occult malignant epithelial cells.

Multicenter research into the quality of life of patients with advanced oropharyngeal carcinoma with long-term survival associated with human papilloma virus

The treatment of advanced-stage oropharyngeal squamous cell carcinoma may utilize various modes, including combining surgery with chemoradiotherapy (CTRT), or primary CTRT followed by rescue surgery. In previous literature it has been revealed how patients treated with combined modes report a low quality of life (QoL) and severe consequences following surgery, radiotherapy and chemotherapy, in the short and in the long-term. The decrease in the QoL of patients treated with high-intensity multi-modal strategies highlights the necessity of modifying treatments, particularly for young HPV-positive patients, where an increased survival rate has already been reported. The modified treatment for HPV-positive tumors in the tonsils and at the base of the tongue is based on the deintensification of therapies aiming to reduce toxicity and thereby improve QoL in the long term, whilst still maintaining therapeutic effectiveness. The aim of the present study was to evaluate the QoL in patients with a long-term survival, who were treated with combined therapy for squamous cell tumors in the tonsils and at the base of the tongue, and to compare the results observed in HPV-positive and HPV-negative patients. According to statistical analysis, differences in the general QoL and in the single scales of the European Organization for the Research and Treatment of Cancer questionnaires were not correlated with the type of therapy selected for the particular patient. QoL considered the presence of HPV, the type of treatment, the subregion of the tonsils vs. the base of the tongue and the disease stage at the time of diagnosis, and was determined to be non-influential with regard to these specific variables.

Targeting cellular and molecular drivers of head and neck squamous cell carcinoma: current options and emerging perspectives

Despite improvements in functional outcomes attributable to advances in radiotherapy, chemotherapy, surgical techniques, and imaging techniques, survival in head and neck squamous cell carcinoma (HNSCC) patients has improved only marginally during the last couple of decades, and optimal therapy has yet to be devised. Genomic complexity and intratumoral genetic heterogeneity may contribute to treatment resistance and the propensity for locoregional recurrence. Countering this, it demands a significant effort from both basic and clinical scientists in the search for more effective targeted therapies. Recent genomewide studies have provided valuable insights into the genetic basis of HNSCC, uncovering potential new therapeutic opportunities. In addition, several studies have elucidated how inflammatory, immune, and stromal cells contribute to the particular properties of these neoplasms. In the present review, we introduce recent findings on genomic aberrations resulting from whole-genome sequencing of HNSCC, we discuss how the particular microenvironment affects the pathogenesis of this disease, and we describe clinical trials exploring new perspectives on the use of combined genetic and cellular targeted therapies.

Optimized protocol for immunostaining of experimental GFP-expressing and human hearts

Morphological and histochemical analysis of the heart is fundamental for the understanding of cardiac physiology and pathology. The accurate detection of different myocardial cell populations, as well as the high-resolution imaging of protein expression and distribution, within the diverse intracellular compartments, is essential for basic research on disease mechanisms and for the translatability of the results to human pathophysiology. While enormous progress has been made on the imaging hardware and methods and on biotechnological tools [e.g., use of green fluorescent protein (GFP), viral-mediated gene transduction] to investigate heart cell structure and function, most of the protocols to prepare heart tissue samples for analysis have remained almost identical for decades. We here provide a detailed description of a novel protocol of heart processing, tailored to the simultaneous detection of tissue morphology, immunofluorescence markers and native emission of fluorescent proteins (i.e., GFP). We compared a variety of procedures of fixation, antigen unmasking and tissue permeabilization, to identify the best combination for preservation of myocardial morphology and native GFP fluorescence, while simultaneously allowing detection of antibody staining toward sarcomeric, membrane, cytosolic and nuclear markers. Furthermore, with minimal variations, we implemented such protocol for the study of human heart samples, including those already fixed and stored with conventional procedures, in tissue archives or bio-banks. In conclusion, a procedure is here presented for the laboratory investigation of the heart, in both rodents and humans, which accrues from the same tissue section information that would normally require the time-consuming and tissue-wasting observation of multiple serial sections.

From fish to amphibians to mammals: in search of novel strategies to optimize cardiac regeneration

Different vertebrate species have different cardiac regeneration rates: high in teleost fish, moderate in urodele amphibians, and almost negligible in mammals. Regeneration may occur through stem and progenitor cell differentiation or via dedifferentiation with residual cardiomyocytes reentering the cell cycle. In this review, we will examine the ability of zebrafish and newts to respond to cardiac damage with de novo cardiogenesis, whereas rodents and humans respond with a marked fibrogenic response and virtually no cardiomyocyte regeneration. Concerted strategies are needed to overcome this evolutionarily imposed barrier and optimize cardiac regeneration in mammals.

Cardiac interstitial cells express GATA4 and control dedifferentiation and cell cycle re-entry of adult cardiomyocytes

Interstitial cells of the adult rat heart were characterized with respect to i) expression of cardiac markers of commitment and differentiation, ii) myogenic potential in vitro and iii) ability to modulate cardiomyocyte differentiation state. We demonstrate for the first time that fibroblasts and a proportion of pericytes in the adult rat heart express the transcription factor GATA4. This appears to be a peculiar property of the heart. Fibroblasts that are also derived from the splanchnopleuric mesoderm, such as those of the gut, or fibroblasts of different embryological origin, such as those of skin and skeletal muscle, lack this property. Of note, a nestin+/GATA4+ putative stem cell population is also detected in the adult heart. GATA4+ cardiac interstitial cells do not display myogenic potential in vitro. However, cardiac fibroblasts, but not skin fibroblasts, stimulate dedifferentiation of adult cardiomyocytes and their re-entry into the cell cycle in vitro, as demonstrated by the high number of cardiomyocytes expressing Ki67, phosphorylated histone H3 (H3P) and incorporating 5-bromodeoxiuridine (BrdU) in the co-cultures. In conclusion, cardiac fibroblasts have peculiar expression of myogenic transcription factors, a property that may have an impact for reprogramming these cells to the myogenic differentiation. In addition, they are able to modulate the behavior of adult cardiomyocytes, a property that may be used to promote dedifferentiation and proliferation of cardiac cells in the damaged myocardium.

In vivo delivery of naked antisense oligos in aged mdx mice: analysis of dystrophin restoration in skeletal and cardiac muscle

Antisense-mediated exon skipping holds great potential for the treatment of DMD. In mdx mice, functional recovery of skeletal muscle has been obtained upon systemic delivery of "naked" oligonucleotides or viral vectors encoding for antisense snRNAs. However, amongst the studies reported so far, which used either neonatal or young adult animals--only one achieved dystrophin restoration in cardiac muscle, using an adeno-associated vector. Here we report the in vivo delivery of morpholino oligos in aged mdx mice, both in skeletal muscle, via intra-arterial injection, and in cardiac muscle, via intra-muscular injection. Localized intra-arterial delivery yielded high levels of dystrophin restoration and just two doses of 100 microg each resulted into detectable force recovery in the EDL muscles of treated limbs. On the other hand, upon intra-cardiac injections in the left ventricle wall the skipping effect was much lower than what obtained in tibialis anterior muscles injected with comparable amounts of oligos. This latter finding suggests that even upon direct delivery antisense-mediated dystrophin restoration in cardiac muscle might suffer from limitations that do not exist in skeletal muscle.

A lentiviral vector with a short troponin-I promoter for tracking cardiomyocyte differentiation of human embryonic stem cells

Human embryonic stem cells (hESCs) may become important for cardiac repair due to their potentially unlimited ability to generate cardiomyocytes (CMCs). Moreover, genetic manipulation of hESC-derived CMCs would be a very promising technique for curing myocardial disorders. At the present time, however, inducing the differentiation of hESCs into CMCs is extremely difficult and, therefore, an easy and standardizable technique is needed to evaluate differentiation strategies. Vectors driving cardiac-specific expression may represent an important tool not only for monitoring new cardiac-differentiation strategies, but also for the manipulation of cardiac differentiation of ESCs. To this aim, we generated cardiac-specific lentiviral vectors (LVVs) in which expression is driven by a short fragment of the cardiac troponin-I proximal promoter (TNNI3) with a human cardiac alpha-actin enhancer, and tested its suitability in inducing tissue-specific gene expression and ability to track the CMC lineage during differentiation of ESCs. We determined that (1) TNNI3-LVVs efficiently drive cardiac-specific gene expression and mark the cardiomyogenic lineage in human and mouse ESC differentiation systems (2) the cardiac alpha-actin enhancer confers a further increase in gene-expression specificity of TNNI3-LVVs in hESCs. Although this technique may not be useful in tracking small numbers of cells, data suggested that TNNI3-based LVVs are a powerful tool for manipulating human ESCs and modifying hESC-derived CMCs.

GATA elements control repression of cardiac troponin I promoter activity in skeletal muscle cells

Background

We reported previously that the cardiac troponin I (cTnI) promoter drives cardiac-specific expression of reporter genes in cardiac muscle cells and in transgenic mice, and that disruption of GATA elements inactivates the cTnI promoter in cultured cardiomyocytes. We have now examined the role of cTnI promoter GATA elements in skeletal muscle cells.

Results

Mutation or deletion of GATA elements induces a strong transcriptional activation of the cTnI promoter in regenerating skeletal muscle and in cultured skeletal muscle cells. Electrophoretic mobility shift assays show that proteins present in nuclear extracts of C2C12 muscle cells bind the GATA motifs present in the cTnI promoter. However, GATA protein complex formation is neither reduced nor supershifted by antibodies specific for GATA-2, -3 and -4, the only GATA transcripts present in muscle cells.

Conclusion

These findings indicate that the cTnI gene promoter is repressed in skeletal muscle cells by GATA-like factors and open the way to further studies aimed at identifying these factors.

Age is a risk factor for maladaptive changes in rats exposed to increased pressure loading of the right ventricular myocardium

OBJECTIVE

To study the adaptive potential of the right ventricular myocardium after 30 days of mechanical-induced overload in rats from two different age groups.

MATERIALS AND METHODS

We banded the pulmonary trunk, so as to increase the systolic work load of the right ventricle, in 19 adult Sprague-Dawley rats at the age of 10 weeks, and 16 weanlings when they were 3 weeks-old, using 10 adults and 10 weanlings as controls. We analysed the functional adaptation and structural changes of the right ventricular myocardium, blood vessels and interstitial tissue after 30 days of increased afterload.

RESULTS

The increased workload induced an increase of the right ventricular weight and free wall thickness in animals from both age groups when compared to controls. These changes were mostly related to cardiomyocytic hypertrophy, as confirmed by the expression of myocardial hypertrophic markers, without any apparent increase of their number, a "reactive" fibrosis especially evident in the adult rats, with p-value less than 0.0001, and a more extensive neocapillary network in the weanlings compared to the adults aubsequent to banding, the p-value being less than 0.0001.

CONCLUSION

In response to right ventricular afterload, weanlings showed a higher adaptive capillary growth, which hampered the development of fibrosis as seen in the adult rats. Age seems to be a risk factor for adverse structural-functional changes of right ventricle subjected to increased workload.

Differential availability/processing of decorin precursor in arterial and venous smooth muscle cells

The existence of specific differentiation markers for arterial smooth muscle (SM) cells is still a matter of debate. A clone named MM1 was isolated from a library of monoclonal antibodies to adult porcine aorta, which in vivo binds to arterial but not venous SM cells, except for the pulmonary vein. MM1 immunoreactivity in Western blotting involved bands in the range of M(r) 33-226 kDa, in both arterial and venous SM tissues. However, immunoprecipitation experiments revealed that MM1 bound to a 100-kDa polypeptide that was present only in the arterial SM extract. By mass spectrometry analysis of tryptic digests from MM1-positive 130- and 120-kDa polypeptides of aorta SM extract, the antigen recognized by the antibody was identified as a decorin precursor. Using a crude decorin preparation from this tissue MM1 reacted strongly with the 33-kDa polypeptide and this pattern did not change after chondroitinase ABC treatment. In vitro, decorin immunoreactivity was found in secreted grainy material produced by confluent arterial SM cells, although lesser amounts were also seen in venous SM cells. Western blotting of extracts from these cultures showed the presence of the 33-kDa band but not of the high-molecular-weight components, except for the 100-kDa monomer. The 100/33-kDa combination was more abundant in arterial SM cells than in the venous counterpart. In the early phase of neointima formation, induced by endothelial injury of the carotid artery or vein-to-artery transposition, the decorin precursor was not expressed, but it was up-regulated in the SM cells of the media underlying the neointima in both models. Collectively, these data suggest a different processing/utilization of the 100-kDa monomer of proteoglycan decorin in arterial and venous SM cells, which is abolished after vein injury.

Hybrid cardiomyocytes derived by cell fusion in heterotopic cardiac xenografts

Cardiomyocytes expressing host markers, such as the Y chromosome in sex-mismatched transplants, have been described in human allografts, suggesting that circulating cells can contribute to cardiac regeneration. It has not been established, however, whether host-derived cardiomyocytes result from transdifferentiation of stem cells or cell fusion. To address this issue, we used heterotopic heart xenografts and looked for markers of donor and recipient cells. Golden Syrian hamsters or transgenic mice expressing nuclear beta-galactosidase under the control of the cardiac troponin I promoter served as organ donors, while GFP+ transgenic rats were used as recipients. GFP+ cells, including abundant CD-45+ inflammatory cells and rare undifferentiated cells expressing early cardiac markers (GATA-4 or MEF2C), were found in xenografts harvested two weeks after surgery. In addition, rare GFP+ mature cardiomyocytes were found in 7 of 8 hamster xenografts and 6 of 6 mouse xenografts. The proportion of these cells was very low (0.0001% to 0.0344% in hamster xenografts) but similar to the one observed in control rat heart allografts. Without exception, all GFP+ cardiomyocytes also expressed donor markers, i.e., hamster membrane antigens or lacZ, so they must derive from cell fusion, not transdifferentiation.

Host-derived circulating cells do not significantly contribute to cardiac regeneration in heterotopic rat heart transplants

OBJECTIVES

The aim of this study was to investigate the contribution of host-derived circulating cells to cardiac repair after tissue damage using the model of heterotopic heart transplantation between transgenic recipient rats expressing green fluorescent protein (GFP) and wild-type donors.

METHODS

Unlabeled donor rat hearts, some of which underwent prolonged cold ischemia pretreatment, were transplanted into the abdominal cavity of GFP+ transgenic recipient rats and were analyzed 15 and 90 days after surgery. An additional experimental group underwent heart transplantation following administration of granulocyte-colony stimulatory factor (G-CSF) to mobilize bone marrow cells.

RESULTS

Most transplants contained GFP+ mature cardiomyocytes. However, systematic counting in the transplants showed that the proportion of GFP+ cardiomyocytes was only 0.0005% to 0.008% of all cardiomyocytes. These relative proportions did not change after G-CSF treatment, despite evidence for sustained marrow cell mobilization. Confocal image analysis showed that the majority of GFP+ cardiomyocytes contained a high number of nuclei, suggesting that these cells may derive from fusion events. Very rarely, small GFP+ undifferentiated cells, expressing GATA-4, were also identified. Occasionally, GFP+ endothelial cells, but not smooth muscle cells, were detected in blood vessels of some transplants.

CONCLUSIONS

Our results demonstrate that cardiomyocytes expressing a host transgenic marker are detectable in heterotopic heart transplants; however, they do not significantly contribute to repopulation of the damaged myocardium.

The impact of progenitor enrichment, serum, and cytokines on the ex vivo expansion of mobilized peripheral blood stem cells: a controlled trial

The aim of this study was to verify, and possibly improve, culture conditions to expand human mobilized peripheral blood stem cells (PBSCs). We investigated the role of three parameters: A) the culture medium (serum-free versus serum-dependent); B) the initial cell population (Ficoll-separated mononucleated cells versus CD34(+)-selected cells), and C) the low concentration of recombinant cytokines, flt3 ligand, and thrombopoietin in association with a basic cocktail of stem cell factor, interleukin (IL)-6, IL-3, GM-CSF, and erythropoietin. Eighteen leukapheresis samples were monitored in static culture for 15 days. The expansion potential was assessed at day 10 and 15 by total nuclear cells, colony-forming-units (CFUs) (burst-forming units-erythroid [BFU-E], colony-forming units-granulocyte-macrophage [CFU-GM], and colony-forming units-granulocyte-erythroid-macrophage-megakaryocyte [CFU-GEMM]), and flow cytometry immunophenotyping (CD34(+)/CD38(-), CD38(+), CD33(+), CD41(+), GlyA(+) progenitor cells). The results, evaluated by multivariate analysis of variance, emphasize that some variables affected the outcome of stem and progenitor cell expansion. CD34(+) enrichment increased expansion of total nuclear cells, number of CD38(+) and CD33(+) late precursors, and number of the CFU-GM compartment. Interestingly, however, quantitative expansion of GlyA(+) and the early progenitor cells (CD34(+)/CD38(-), CFU-GEMM, BFU-E) are favored by the use of unselected mononucleated cells. Regarding the role of serum, no significant difference was observed except for expansion of total nuclear cells, CFU-GM, and BFU-E. Cytokine combinations, in particular the use of flt3 ligand, stimulated expansion of almost all the cellular subsets, reaching a statistical significance for total nuclear cells and CFU-GM. Our study indicates that progenitor and late precursor multilineage cell compartments of mobilized PBSCs may be significantly expanded in short-term cultures by well-defined experimental conditions. Furthermore, these data might be useful when evaluating ex vivo expansion of hematopoietic cells for clinical purposes.

Contribution of adventitial fibroblasts to neointima formation and vascular remodeling: from innocent bystander to active participant

The adventitial layer surrounding the blood vessels has long been exclusively considered a supporting tissue the main function of which is to provide adequate nourishment to the muscle layers of tunica media. Although functionally interconnected, the adventitial and medial layers are structurally interfaced at the external elastic lamina level, clearly distinguishable at the maturational phase of vascular morphogenesis. Over the last few years the "passive" role that the adventitia seemed to play in experimental and spontaneous vascular pathologies involving proliferation, migration, differentiation, and apoptosis of vascular smooth muscle cells (VSMCs) has been questioned. It has been demonstrated that fibroblasts from the adventitia display an important partnership with the resident medial VSMCs in terms of phenotypic conversion, proliferation, apoptotic, and migratory properties the result of which is neointima formation and vascular remodeling. This article is an attempt at reviewing the major themes and more recent findings dealing with the phenotypic conversion process that leads adventitial "passive" (static) fibroblasts to become "activated" (mobile) myofibroblasts. This event shows some facets in common with vascular morphogenesis, ie, the process of recruitment, incorporation, and phenotypic conversion of cells surrounding the primitive endothelial tube in the definitive vessel wall. We hypothesize that during the response to vascular injuries in the adult, "activation" of adventitial fibroblasts is, at least in part, reminiscent of a developmental program that also invests, although with distinct spatiotemporal features, medial VSMCs.

Cell lineages and tissue boundaries in cardiac arterial and venous poles: developmental patterns, animal models, and implications for congenital vascular diseases

Multiple cell populations with different embryological histories are involved in the morphogenesis of the cardiac arterial and venous poles as well as in the correct alignment and connection of the developing vessels with the cardiac chambers. Formation of the aorta and the pulmonary trunk is a complicated process orchestrated via a specific sequence of highly integrated spatiotemporal events of cell proliferation, migration, differentiation, and apoptosis. The peculiar susceptibility of this intricate cell network to be altered explains the frequency of congenital cardiovascular diseases of the arterial and venous poles. We review this topic from the "vascular point of view," putting major emphasis on (1) the existence of different cell lineages from which smooth muscle cells of the aorticopulmonary trunk can be derived, (2) the establishment of cell/tissue boundaries in the cardiovascular connecting regions, and (3) the animal models that can mimic human congenital defects of the arterial and venous poles of the heart.

An atrioventricular canal domain defined by cardiac troponin I transgene expression in the embryonic myocardium

During early cardiac development the atrial myocardium is continuous with the ventricular myocardium throughout the atrioventricular canal. The atrioventricular canal undergoes complex remodelling involving septation, formation of atrioventricular valves and insulation between atria and ventricles except at the level of the atrioventricular node. Understanding of these processes has been hampered by the lack of markers specific for this heart region. We have generated transgenic mice expressing beta-galactosidase under the control of the cardiac troponin I gene that show transgene expression mainly confined to the atrioventricular canal myocardium during early embryonic development. With further development beta-galactosidase positive cells are observed in the atrioventricular node and in the lower rim of both right and left atria, supporting the view that atrioventricular canal myocardium contributes to the atrioventricular node and is in part incorporated into the lower rim of the atria. These results identify the atrioventricular canal myocardium as a distinct transcriptional domain.

Cardiac and smooth muscle cell contribution to the formation of the murine pulmonary veins

Previous studies have demonstrated that the primordial pulmonary veins originate as an outgrowth of the atrial cells and anastomosis with the pulmonary venous plexus. As a consequence of this embryologic origin the tunica media of these vessels is composed of cardiac cells that express atrial specific markers (Lyons et al. [1990] J Cell Biol 111:2427-2436; Jones et al. [1994] Dev Dyn 200:117-128). We used transgenic mice for the cardiac troponin I (cTNI) gene and smooth muscle (SM) myosin heavy chain as differentiation markers, to analyze how cardiac and SM cells contribute to the formation and structural remodeling of the pulmonary veins during development. We show here that the tunica media of the adult mouse pulmonary veins contains an outer layer of cardiac cells and an intermediate SM cell compartment lining down on the inner endothelium. This structural organization is well expressed in the intrapulmonary veins from the beginning of vasculogenesis, with cardiac cells accumulating over preexisting roots of endothelial and SM cells and extending to the third bifurcation of the pulmonary branches without reaching the more distal tips of the vessels. On the other hand, SM cells, which are widely distributed in the intrapulmonary veins from the embryonic stage E16, accumulate also in the extrapulmonary branches and reach the posterior wall of the left atrium, including the orifices of the pulmonary veins. This event takes place around birth when the pulmonary blood flow starts to function properly. A model for the development of the pulmonary veins is presented, based upon our analysis.

Combinatorial cis-acting elements control tissue-specific activation of the cardiac troponin I gene in vitro and in vivo

The cardiac troponin I gene is one of the few sarcomeric protein genes exclusively expressed in cardiac muscle. We show here that this specificity is controlled by a proximal promoter (-230/+16) in transfected cardiac cells in culture, in the adult hearts, and in transgenic animals. Functional analysis indicates that MEF2/Oct-1, Sp1, and GATA regulatory elements are required for optimal gene activation because selective mutations produce weak or inactive promoters. MEF2 and Oct-1 transcription factors bind to the same A/T-rich element. A mutation that blocks this binding markedly reduces gene activation in vivo and in vitro, and overexpression of MEF2A, MEF2C, and MEF2D in noncardiac cells transactivates the cardiac troponin I promoter. Disruption of these elements inactivates the cardiac troponin I promoter in cultured cardiac cells but has a less important role in transfected adult heart. Moreover, nuclear extracts from an almost pure population of adult cardiac cells contain much lower levels of GATA binding activity compared with fetal cardiac cells. These findings point to a differential role of GATA factors in the maintenance of gene expression in the adult heart as compared with the activation of cardiac genes in fetal cardiomyocytes. Overexpression of GATA family members transactivates the cardiac troponin I promoter, and GATA-5 and GATA-6 are stronger transactivators than GATA-4, a property apparently unique to the cardiac troponin I promoter. Transgenic mice carrying the -230/+126 base pair promoter express beta-galactosidase reporter gene in the heart both at early stages of cardiogenesis and in the adult animals. These results indicate that the ability of the cardiac troponin I proximal promoter to target expression of a downstream gene in the heart is also maintained when the transgene is integrated into the genome.

Myosin heavy chain gene expression changes in the diaphragm of patients with chronic lung hyperinflation

In striated muscle, chronic increases in workload result in changes in myosin phenotype. The aim of this study was to determine whether such changes occur in the diaphragm of patients with severe chronic obstructive pulmonary disease, a situation characterized by a chronic increase in respiratory load and lung volume. Diaphragm biopsies were obtained from 22 patients who underwent thoracic surgery. Myosin was characterized with electrophoresis in nondenaturing conditions, SDS-glycerol PAGE, and Western blotting with monoclonal antibodies specific for slow and fast myosin heavy chain (MHC) isoforms. Flow volume curves, total lung capacity, and functional residual capacity were measured before surgery in 20 patients. We found that the human diaphragm is composed of at least four myosin isoforms, one slow and three fast, resulting from the combination of three MHC species. Chronic overload was associated with an increase in the slow beta-MHC species at the expense of the fast species (beta-MHC, 78.2 +/- 4.6 and 50.0 +/- 6.5% in emphysematous and control patients, respectively; P < 0.005). Linear correlations were found between beta-MHC percentage and forced expiratory volume in 1 s (r = -0.52; P < 0.02), total lung capacity (r = 0.44; P < 0.05), and functional residual capacity (r = 0.65; P < 0.003). The human adult diaphragm is composed of a balanced proportion of slow and fast myosin isoforms. In patients with chronic obstructive pulmonary disease, the proportion of fast myosins decreases, whereas that of slow myosin increases. This increase appears to be closely related to lung hyperinflation and may reflect an adaptation of the diaphragm to the new functional requirements.

Structure and regulation of the mouse cardiac troponin I gene

The gene coding for mouse cardiac troponin I (TnI) has been cloned and sequenced. The cardiac TnI gene contains 8 exons and has an exon-intron organization similar to the quail fast skeletal TnI gene except for the region of exons 1-3, which is highly divergent. Comparative analysis suggests that cardiac TnI exon 1 corresponds to fast TnI exons 1 and 2 and that cardiac exon 3, which codes for most of the cardiac-specific amino-terminal extension and has no counterpart in the fast gene, evolved by exon insertion/deletion. The amino acid sequence of cardiac TnI exon 4 shows limited homology (36% identity) with fast TnI exon 4 but is remarkably similar (79% identity) to the corresponding sequence of slow TnI, possibly reflecting an isoform-specific TnC-binding site. The cardiac TnI gene is one of the very few contractile protein genes expressed exclusively in cardiac muscle. To identify the regulatory sequences responsible for the cardiac-specific expression of this gene we transfected cultured cardiac and skeletal muscle cells with fragments up to 4.0 kilobases of the 5'-flanking region linked to a reporter gene. Deletion analysis reveals four major regions in the 5'-flanking sequence, a minimal promoter region, which directs expression at low level in cardiac and skeletal muscle cells, and two upstream cardiac-specific positive regions separated by a negative region.

Type 2X-myosin heavy chain is coded by a muscle fiber type-specific and developmentally regulated gene

We have previously reported the identification of a distinct myosin heavy chain (MyHC) isoform in a major subpopulation of rat skeletal muscle fibers, referred to as 2X fibers (Schiaffino, S., L. Gorza, S. Sartore, L. Saggin, M. Vianello, K. Gundersen, and T. Lømo. 1989. J. Muscle Res. Cell Motil. 10:197-205). However, it was not known whether 2X-MyHC is the product of posttranslational modification of other MyHCs or is coded by a distinct mRNA. We report here the isolation and characterization of cDNAs coding a MyHC isoform that is expressed in type 2X skeletal muscle fibers. 2X-MyHC transcripts differ from other MyHC transcripts in their restriction map and 3' end sequence and are thus derived from a distinct gene. In situ hybridization analyses show that 2X-MyHC transcripts are expressed at high levels in the diaphragm and fast hindlimb muscles and can be coexpressed either with 2B- or 2A-MyHC transcripts in a number of fibers. At the single fiber level the distribution of each MyHC mRNA closely matches that of the corresponding protein, determined by specific antibodies on serial sections. In hindlimb muscles 2X-, 2A-, and 2B-MyHC transcripts are first detected by postnatal day 2-5 and display from the earliest stages a distinct pattern of distribution in different muscles and different fibers. The emergence of type 2 MyHC isoforms thus defines a distinct neonatal phase of fiber type differentiation during muscle development. The functional significance of MyHC isoforms is discussed with particular reference to the velocity of shortening of skeletal muscle fibers.

Expression of the calsequestrin gene in chicken cerebellum Purkinje neurons

Intracellular rapidly exchanging Ca2+ stores are identified and defined in terms of intralumenal low-affinity, high-capacity Ca(2+)-binding proteins, of which calsequestrin (CS) is the prototype in striated muscles. In chicken striated muscles, there is a single gene for CS [Choi and Clegg (1990) Dev. Biol. 142, 169-177]. In the chicken brain, the gene for CS was found to be selectively expressed in Purkinje neurons, as judged by Northern blotting, in situ hybridization and immunocytochemistry. The synthetic machinery for CS was found to be restricted to the cell body, i.e. excluded from dendrites and axon.

Myosin and troponin changes in rat soleus muscle after hindlimb suspension

We examined the myosin heavy-chain (MHC), troponin T (TnT), and troponin I (TnI) isoform composition in the rat soleus muscle after 21 days of hindlimb suspension using electrophoretic and immunoblotting analysis with specific monoclonal antibodies. The suspended soleus showed a shift in the MHC isoform distribution with a marked increase (from 1.0 to 33%) in the relative amount of type IIa and IIx MHC and a corresponding decrease in type I MHC. However, type IIb MHC, which represents a major component in fast-twitch muscles, was not detected in suspended soleus muscles. TnT and TnI isoform composition was also changed with the appearance of fast-type TnI and TnT bands. However, a high-mobility TnT band, which represents a major component in fast-twitch muscles, was not expressed in suspended soleus. These isoform transitions may be related to the increased maximal velocity of shortening and higher calcium sensitivity previously reported in the rat soleus after hindlimb suspension.

Regional differences in troponin I isoform switching during rat heart development

Expression of cardiac troponin I (TnIcardiac) and slow skeletal troponin I (TnIslow) genes was analyzed at the mRNA and protein level in the developing rat heart. TnIslow mRNA was detectable by in situ hybridization in the embryonic cardiac tube as early as the 13-somite stage (Embryonic Day 10). In contrast, TnIcardiac transcripts were first detected in the primordial atrium and ventricle of 11-day-old embryos, but were absent in the outflow tract region. TnIslow mRNA levels decreased after birth in atria and later in ventricles but persisted even in adult life in myocytes of the conduction system. TnIslow protein was detected by specific antibodies in atrial myocytes beginning from Embryonic Day 11; in contrast, ventricular myocytes were unreactive until Embryonic Day 18. Western blot analysis of 16-day-old fetal hearts confirmed the expression of TnIcardiac in atrial but not in ventricular myocardium. Slot blot analysis showed that at this stage equivalent amounts of TnIslow and TnIcardiac mRNAs are expressed in atria and ventricles. Similar differences in the expression of TnIslow and TnIcardiac mRNAs and proteins were observed in cultures of embryonic atrial and ventricular myocytes. The results suggest serial rather than simultaneous activation of TnIslow and TnIcardiac genes and they show that different regions of the developing heart differ in their patterns of TnIcardiac expression due to the operation of distinct mechanisms that separately affect the accumulation of TnIcardiac mRNA and protein.

Developmental expression of rat cardiac troponin I mRNA

We have isolated and sequenced a full-length cDNA clone of rat cardiac troponin I (TnI). The amino acid sequence of rat cardiac TnI is highly similar to that of other mammalian species in the portion of the molecule (residues 33–210) that is also homologous to skeletal muscle TnI isoforms. In contrast, a lower degree of similarity is present in the cardiac TnI-specific amino terminal extension (residues 1–32). This region contains a conserved serine residue that has been shown to be selectively phosphorylated by cAMP-dependent protein kinase. Cardiac TnI mRNA is weakly expressed in the 18-day fetal heart and accumulates in neonatal and postnatal stages. No difference can be demonstrated between TnI mRNAs present in fetal and postnatal heart by RNAase protection assays. The fetal and neonatal, but not the adult heart, contain significant amounts of slow skeletal TnI transcripts, detected by oligonucleotide probes specific for the 5′- and 3′-untranslated regions of slow skeletal TnI mRNA. In situ hybridization studies show that cardiac and slow skeletal TnI mRNAs are coexpressed in the rat heart from embryonic day 11 throughout fetal and perinatal stages. Changes in troponin isoform expression during development may be responsible for the difference in calcium sensitivity and in the response to beta-adrenergic stimulation between fetal and adult heart.

Cardiac troponin T in developing, regenerating and denervated rat skeletal muscle

Fetal rat skeletal muscles express a troponin T (TnT) isoform similar to the TnT isoform expressed in the embryonic heart with respect to electrophoretic mobility and immunoreactivity with cardiac TnT-specific monoclonal antibodies. Immunoblotting analyses reveal that both the embryonic and the adult isoforms of cardiac TnT are transiently expressed during the neonatal stages. In addition, other TnT species, different from both cardiac TnTs and from the TnT isoforms expressed in adult muscles, are present in skeletal muscles during the first two postnatal weeks. By immunocytochemistry, cardiac TnT is detectable at the somitic stage and throughout embryonic and fetal development, and disappears during the first weeks after birth, persisting exclusively in the bag fibers of the muscle spindles. Cardiac TnT is re-expressed in regenerating muscle fibers following a cold injury and in mature muscle fibers after denervation. Developmental regulation of this TnT variant is not coordinated with that of the embryonic myosin heavy chain with respect to timing of disappearance and cellular distribution. No obligatory correlation between the two proteins is likewise found in regenerating and denervated muscles.

Function, morphology and protein expression of ageing skeletal muscle: a cross-sectional study of elderly men with different training backgrounds

The function and morphology of knee extension/m. vastus lateralis and elbow flexion/m. biceps brachii were studied in young (28 +/- 0.1 years, n = 7) and elderly (68 +/- 0.5 years, n = 8) sedentary subjects and in elderly swimmers (69 +/- 1.9 years, n = 6), runners (70 +/- 0.7 years, n = 5) and strength-trained subjects (68 +/- 0.8 years, n = 7). On average, the training groups had, for the 12-17 years before the measurements were taken, performed their training regimen 3 +/- 0.1 times a week. Compared with the young subjects, the maximal isometric torque of the sedentary elderly subjects was 44% (P less than 0.05) lower in knee extension and 32% (P less than 0.05) lower in elbow flexion, and speed of movement was between 20 and 26% (P less than 0.05) lower in both knee extension and elbow flexion. The cross-sectional area of m. quadriceps femoris and the elbow flexors was also 24% (P less than 0.05) and 20% lower respectively, and the specific tension was 27% (P less than 0.05) lower in m. quadriceps femoris and 14% (P less than 0.05) lower in the elbow flexors. A 27% (P less than 0.05) higher content of myosin heavy chain type I and a 39% (P less than 0.05) higher content of the slow-type myosin light chain--2 was observed in m. vastus lateralis of the sedentary elderly subjects as compared with the young subjects. The same tendency was also seen with m. biceps brachii. Since the histochemical fibre-type distribution was identical and no major co-expression of type I and type II myosin heavy-chain isoforms was observed with immunocytochemistry, the increase in slow myosin isoforms with ageing seems mainly related to a larger relative area of type I fibres, induced by a selective atrophy of type II fibre area. An increased content of the beta-isoform of tropomyosin was also demonstrated with ageing. In contrast to the swimmers and runners, the elderly strength-trained subjects had maximal isometric torques, speed of movements, cross-sectional areas, specific tensions and a content of myosin and tropomyosin isoforms in both muscles studied identical to those of the young controls. These results seem to suggest that strength training can counteract the age-related changes in function and morphology of the ageing human skeletal muscle.

Expression of myosin heavy chain isoforms in stimulated fast and slow rat muscles

The expression of 4 myosin heavy chain (MHC) isoforms was analyzed in the rat soleus (SOL) and extensor digitorum longus (EDL) muscles after denervation and chronic electric stimulation. The stimulation frequencies used were 20 and 150 Hz and the amount of stimulation was either large (20 Hz), intermediate (150 Hz), or small (150 Hz). These patterns resemble some features of normal motor unit activity in SOL and EDL of freely moving rats (Hennig and Lømo, 1985). The relative expression of each MHC isoform depended strongly on the stimulation pattern. Furthermore, for any particular stimulation pattern, fibers in SOL and EDL expressed different MHCs. Coexistence of different MHC types in the same fiber was frequently observed in stimulated muscles. 20-Hz stimulation preserved normal expression of type 1-MHC in SOL but failed to induce type 1-MHC in type 2 fibers of the EDL, where type 2A- and 2X-MHC expression dominated and type 2B-MHC expression was completely suppressed. 150-Hz low-amount stimulation preserved nearly normal 2B-MHC expression in many type 2 fibers of the EDL but failed to induce type 2B-MHC expression in the SOL, where 2X-MHC became predominant. 150-Hz high-amount stimulation differed from 150-Hz small amount stimulation by suppressing almost all type 2B-MHC expression in EDL and by inducing considerable type 2A-MHC expression in the SOL. Scattered fibers in EDL that were probably the original type 1 fibers responded differently from both type 2 fibers in the EDL and from type 1 fibers in the SOL to stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Troponin I switching in the developing heart

Monoclonal antibodies identify two distinct isoforms of troponin I in rat cardiac muscle, one predominant in the embryonic and fetal heart and one predominant in the adult heart. The two isoforms can be resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with apparent molecular weights of 27,000 and 31,500, respectively. The adult isoform is specifically recognized by a monoclonal antibody that is unreactive with the embryonic variant, while two other monoclonal antibodies recognize both isoforms. A monoclonal antibody to cardiac troponin T was used to isolate by affinity chromatography the troponin complex from adult and neonatal rat heart. Affinity purified troponin from neonatal heart was found to contain both the embryonic and adult isoforms of troponin I. Comparative immunoblotting analysis with different muscle tissues shows that embryonic troponin I is identical with respect to electrophoretic mobility and pattern of immunoreactivity to the major troponin I isoform found in adult slow skeletal muscle. Troponin I switching may be implicated in developmental changes involving Ca2+ and pH sensitivity of the contractile system and response to beta-adrenergic stimulation.

Sarcoplasmic reticulum of human skeletal muscle: age-related changes and effect of training

The effect of ageing on human skeletal muscle was investigated using needle biopsies from young and aged subjects and from aged subjects trained with different activity patterns. Histochemical staining for myofibrillar ATPase of ageing m. vastus lateralis demonstrated an unchanged fibre type distribution but a selective atrophy of type IIa and type IIb fibres. Analysis of myosin heavy chain (MHC) composition showed that type I MHC increased with ageing (P less than 0.05). The relative content of the MHC isoforms correlated with the relative area of the respective fibre types. Sarcoplasmic reticulum (SR) proteins were investigated in muscle extracts by electrophoretic and immunoblotting techniques. When compared to a young control group (28 +/- 0.1 years old, n = 7) blots of post-myofibrillar supernatant proteins probed with polyclonal antibodies to the rabbit fast SR Ca-ATPase, a marker of extrajunctional SR, showed that the content of Ca-ATPase was significantly lower (P less than 0.05) in the old control group (68 +/- 0.5 years old, n = 8). On the other hand the content of calsequestrin (CS), the major intraluminal protein of SR terminal cisternae (TC), and of the 350-kDa ryanodine-binding protein, which is localized in the junctional regions of TC, did not show a concomitant decrease. These results suggest that ageing differentially affects extrajunctional and junctional SR of human skeletal muscle. These age-related changes were not observed within a group of old strength-trained subjects.

Three myosin heavy chain isoforms in type 2 skeletal muscle fibres

Mammalian skeletal muscles consist of three main fibre types, type 1,2A and 2B fibres, with different myosin heavy chain (MHC) composition. We have now identified another fibre type, called type 2X fibre, characterized by a specific MHC isoform. Type 2X fibres, which are widely distributed in rat skeletal muscles, can be distinguished from 2A and 2B fibres by histochemical ATPase activity and by their unique staining pattern with seven anti-MHC monoclonal antibodies. The existence of the 2X-MHC isoform was confirmed by immunoblotting analysis using muscles containing 2X fibres as a major component, such as the normal and hyperthyroid diaphragm, and the soleus muscle after high frequency chronic stimulation. 2X-MHC contains one determinant common to 2B-MHC and another common to all type 2-MHCs, but lacks epitopes specific for 2A- and 2B-MHCs, as well as an epitope present on all other MHCs. By SDS-polyacrylamide gel electrophoresis 2X-MHC shows a lower mobility compared to 2B-MHC and appears to comigrate with 2A-MHC. Muscles containing predominantly 2X-MHC display a velocity of shortening intermediate between that of slow muscles and that of fast muscles composed predominantly of 2B fibres.

An embryonic-like myosin heavy chain is transiently expressed in nodal conduction tissue of the rat heart

In the bovine nodal conduction tissue we have described the existence of a novel cardiac myosin isoform, immunologically related to the myosin types expressed during skeletal muscle development. Using different monoclonal antibodies specific for the embryonic and the neonatal skeletal myosin heavy chain types we investigated the myosin composition of the rat sino-atrial and atrio-ventricular nodes. We find that nodal conduction tissue fibers of the rat heart contain a distinct cardiac myosin isoform antigenically similar to the skeletal embryonic myosin heavy chain. The expression of this myosin isoform in nodal tissue appears to be developmentally regulated and partially controlled by thyroid hormone. Reactive cardiac fibers were detected in the nodal regions only during fetal development and a few days after birth, whereas very rare labelled fibers could be observed in the adult nodes. This myosin type does not represent a primordial cardiac myosin isoform since it was not detected in the embryonic heart before 13.5 days of gestation. When congenital hypothyroidism was induced in rats, the post-natal disappearance of reactive fibers in the nodal regions was delayed. On the other hand, hypothyroidism induced in the adult rats did not change the number of the reactive nodal fibers with respect to the euthyroid hearts.

Embryonic and neonatal myosin heavy chain in denervated and paralyzed rat skeletal muscle

Using immunofluorescence procedures with specific polyclonal and monoclonal antimyosin antibodies we have found that embryonic and neonatal myosin heavy chains (MHCs), which in rat skeletal muscle disappear during the first weeks after birth, are reexpressed in adult muscle after denervation. Reactivity for embryonic and neonatal MHCs was detected in some fibers as early as 3 days after denervation, became more evident by 7 days, and occurred exclusively in the type 2A fiber population. Paralysis of innervated muscles by tetrodotoxin block of the sciatic nerve also resulted in the reappearance of embryonic and neonatal MHCs in type 2A fibers. Significant variation in the degree of immunoreactivity was observed in different segments of the same muscle fiber, suggesting that coordination of muscle fiber nuclei in the control of myosin heavy chain gene expression is partially lost following denervation.

Fibre types in extraocular muscles: a new myosin isoform in the fast fibres

We report on the existence of a myosin heavy chain (MHC) isoform with unique structural properties in extraocular (EO) muscles. Differences in MHC composition are apparent using a polyclonal antibody prepared against myosin isolated from bovine EO muscle myosin. In enzyme immunoassays and western blotting experiments, this anti-EO myosin antibody reacted specifically with the heavy chains of EO muscle myosin and not with the heavy chains of other myosins. The distribution of this new MHC isoform in the globe rotating muscles from different mammalian species was analysed using a panel of specific anti-myosin antibodies and comparing the histochemical myosin ATPase profile of muscle fibres with their isomyosin content. Most fibres which display a type 2 ATPase reaction pattern were selectively labelled by anti-EO antibodies. A few type 2 fibres were found to react with both anti-EO and anti-2A myosin antibodies and others, located almost exclusively in the orbital layers, reacted with anti-foetals as well as anti-EO antibodies. The presence of a distinct form of myosin in EO muscle fibres is probably related to the particular functional characteristics of these muscles, which are known to be exceptionally fast-contracting but display a very low tension output.