Routinely frozen biopsies of human skeletal muscle are suitable for morphological and immunocytochemical analyses at transmission electron microscopy

Chemical and cryo-collection of muscle samples for transmission electron microscopy using Methacarn and dimethyl sulfoxide✰

Muscle samples are commonly chemically fixed or frozen immediately upon collection for biochemical and morphological analysis. Certain fixatives such as glutaraldehyde and osmium tetroxide are widely used for transmission electron microscopy (TEM) and lead to adequate preservation of muscle ultrastructure, but do not preserve the molecular features of samples. Methacarn is suggested to be a preferable chemical fixative for light microscopy because it maintains immunohistological features of samples. However, the efficacy of methacarn to preserve ultrastructural features as a primary chemical fixative for TEM is currently unclear. Additionally, cryo-preservation of samples for TEM analysis involves freezing processes such as plunge freezing, slam freezing, or high pressure freezing. High pressure freezing is the considered the gold standard but requires costly equipment and may not be a viable option for many labs collecting tissue samples from remote locations. Dimethyl sulfoxide (DMSO) is a commonly used cryoprotectant that may allow for better structural preservation of samples by impairing ice damage that occurs during plunge/snap freezing. We aimed to assess the effectiveness of methacarn as a primary chemical fixative and determine the effect of pre-coating samples with DMSO before plunge/snap freezing tissues to be prepared for TEM. The micrographs of the methcarn-fixed samples indicate a loss of Z-disk integrity, intermyofibrillar space, mitochondria structure, and lipids. Ultimately, methacarn is not a viable primary fixative for tissue sample preparation for TEM. Similarly, liquid nitrogen freezing of samples wrapped in aluminum foil produced non-uniform Z-disk alignments that appeared smeared with swollen mitochondria. DMSO coating before freezing appears to lessen the alterations to contractile and mitochondrial morphological structures. DMSO appears to be useful for preserving the ultrastructure of sarcomeres if samples are covered before freezing.

Ultrastructural histochemistry in biomedical research: Alive and kicking

The high-resolution images provided by the electron microscopy has constituted a limitless source of information in any research field of life and materials science since the early Thirties of the last century. Browsing the scientific literature, electron microscopy was especially popular from the 1970’s to 80’s, whereas during the 90’s, with the advent of innovative molecular techniques, electron microscopy seemed to be downgraded to a subordinate role, as a merely descriptive technique. Ultra -structural histochemistry was crucial to promote the Renaissance of electron microscopy, when it became evident that a precise localization of molecules in the biological environment was necessary to fully understand their functional role. Nowadays, electron microscopy is still irreplaceable for ultrastructural morphology in basic and applied biomedical research, while the application of correlative light and electron microscopy and of refined ultrastructural histochemical techniques gives electron microscopy a central role in functional cell and tissue biology, as a really unique tool for high-resolution molecular biology in situ.

HAM/TSP-derived HTLV-1-infected T cell lines promote morphological and functional changes in human astrocytes cell lines: possible role in the enhanced T cells recruitment into Central Nervous System

BACKGROUND

The mechanisms through which HTLV-1 leads to and maintains damage in the central nervous system of patients undergoing HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) are still poorly understood. In recent years, increasing evidence indicates that, not only lymphocytes but also glial cells, in particular astrocytes, play a role in the pathophysiology of HAM/TSP. In this study we used a model of co-culture between human HTLV-1-infected (CIB and C91PL) and non-infected (CEM) T lymphocyte cell lines and astrocyte (U251 and U87) cell lines to mimic the in vivo T cell-astrocyte interactions.

RESULTS

We first observed that CIB and C91PL adhere strongly to cultured astrocytes cell lines, and that co-cultures of HTLV-1 infected and astrocyte cell lines cells resulted in rapid syncytium formation, accompanied by severe morphological alterations and increased apoptotic cell death of astrocyte cells. Additionally, cultures of astrocyte cell lines in presence of supernatants harvested from HTLV-1-infected T cell cultures resulted in significant increase in the mRNA of CCL2, CXCL1, CXCL2, CXCL3, CXCL10, IL-13, IL-8, NFKB1, TLR4, TNF, MMP8 and VCAM1, as compared with the values obtained when we applied supernatants of non-infected T- cell lines. Lastly, soluble factors secreted by cultured astrocytic cell lines primed through 1-h interaction with infected T cell lines, further enhanced migratory responses, as compared to the effect seen when supernatants from astrocytic cell lines were primed with non-infected T cell lines.

CONCLUSION

Collectively, our results show that HTLV-1 infected T lymphocyte cell lines interact strongly with astrocyte cell lines, leading to astrocyte damage and increased secretion of attracting cytokines, which in turn may participate in the further attraction of HTLV-1-infected T cells into central nervous system (CNS), thus amplifying and prolonging the immune damage of CNS.

Muscle biopsy evaluation in neuromuscular disorders

This article reviews the indications for a muscle biopsy, and then gives a step-by-step description of the processes of muscle selection through to interpreting the biopsy report. The article aims to aid the clinician in preparing for a muscle biopsy procedure to avoid common pitfalls and obtain optimal results from this minimally invasive procedure. The basic anatomic structure of normal muscle is reviewed to provide a foundation for understanding common patterns of pathologic change observed in muscle disease and common and disease-specific histopathologic findings are presented, focusing on a select group of neuromuscular diseases.

On the future contents of a small journal of histochemistry

In the last three years, more than 70,000 scientific articles have been published in peer reviewed journals on the application of histochemistry in the biomedical field: most of them did not appear in strictly histochemical journals, but in others dealing with cell and molecular biology, medicine or biotechnology. This proves that histochemistry is still an active and innovative discipline with relevance in basic and applied biological research, but also demonstrates that especially the small histochemical journals should likely reconsider their scopes and strategies to preserve their authorship. A review of the last three years volumes of the European Journal of Histochemistry, taken as an example of a long-time established small journal, confirmed that the published articles were widely heterogeneous in their topics and experimental models, as in this journal's tradition. This strongly suggests that a journal of histochemistry should keep its role as a forum open to an audience as broad as possible, publishing papers on cell and tissue biology in a wide variety of models. This will improve knowledge of the basic mechanisms of development and differentiation, while helping to increase the number of potential authors since scientists who generally do not use histochemistry in their research will find hints for the applications of histochemical techniques to novel still unexplored subjects.

Skeletal muscle features in myotonic dystrophy and sarcopenia: do similar nuclear mechanisms lead to skeletal muscle wasting?

In the cell nucleus, the gene primary transcripts undergo molecular processing to generate mature RNAs, which are finally exported to the cytoplasm. These mRNA maturation events are chronologically and spatially ordered, and mostly occur on distinct ribonucleoprotein (RNP)-containing structures. Defects in the mRNA maturation pathways have been demonstrated in myotonic dystrophy type 1 (DM1) and type 2 (DM2) whose characteristic multisystemic features are caused by the expansion of two distinct nucleotide sequences: (CTG)n in the DMPK gene on chromosome 19q13 in DM1, and (CCTG)n in the ZNF9 gene on chromosome 3q21 in DM2. By combining biomolecular and cytochemical techniques, it has been shown that the basic mechanisms of DMs reside in the accumulation of CUG- or CCUG-containing transcripts in intranuclear foci where several RNA-binding proteins necessary for the physiological processing of pre-mRNA are sequestered. Moreover, a nucleoplasmic accumulation of splicing and cleavage factors has been found in DMs. This suggests that the dystrophic phenotype could depend on a general alteration of the pre-mRNA post-transcriptional pathway. Interestingly, the accumulation of pre-mRNA processing factors in the myonuclei of DM1 and DM2 patients is reminiscent of the nuclear alterations typical of sarcopenia, i.e., the loss of muscle mass and function which physiologically occurs during ageing. Consistently, in an in vitro study, we observed that satellite-cell-derived DM2 myoblasts show cell senescence alterations and impairment of the pre-mRNA maturation pathways earlier than the myoblasts from healthy patient. These results suggest possible common cellular mechanisms responsible for skeletal muscle wasting in sarcopenia and in myotonic dystrophy.

Identifying pathological biomarkers: histochemistry still ranks high in the omics era

In recent years, omic analyses have been proposed as possible approaches to diagnosis, in particular for tumours, as they should be able to provide quantitative tools to detect and measure abnormalities in gene and protein expression, through the evaluation of transcription and translation products in the abnormal vs normal tissues. Unfortunately, this approach proved to be much less powerful than expected, due to both intrinsic technical limits and the nature itself of the pathological tissues to be investigated, the heterogeneity deriving from polyclonality and tissue phenotype variability between patients being a major limiting factor in the search for unique omic biomarkers. Especially in the last few years, the application of refined techniques for investigating gene expression in situ has greatly increased the diagnostic/prognostic potential of histochemistry, while the progress in light microscopy technology and in the methods for imaging molecules in vivo have provided valuable tools for elucidating the molecular events and the basic mechanisms leading to a pathological condition. Histochemical techniques thus remain irreplaceable in pathologist's armamentarium, and it may be expected that even in the future histochemistry will keep a leading position among the methodological approaches for clinical pathology.

Cultured myoblasts from patients affected by myotonic dystrophy type 2 exhibit senescence-related features: ultrastructural evidence

Myotonic dystrophy type 2 (DM2) is an autosomal dominant disorder caused by the expansion of the tetranucleotidic repeat (CCTG)n in the first intron of the Zinc Finger Protein-9 gene. In DM2 tissues, the expanded mutant transcripts accumulate in nuclear focal aggregates where splicing factors are sequestered, thus affecting mRNA processing. Interestingly, the ultrastructural alterations in the splicing machinery observed in the myonuclei of DM2 skeletal muscles are reminiscent of the nuclear changes occurring in age-related muscle atrophy. Here, we investigated in vitro structural and functional features of satellite cell-derived myoblasts from biceps brachii, in the attempt to investigate cell senescence indices in DM2 patients by ultrastructural cytochemistry. We observed that in satellite cell-derived DM2 myoblasts, cell-senescence alterations such as cytoplasmic vacuolization, reduction of the proteosynthetic apparatus, accumulation of heterochromatin and impairment of the pre-mRNA maturation pathways occur earlier than in myoblasts from healthy patients. These results, together with preliminary in vitro observations on the early onset of defective structural features in DM2 myoblast derived-myotubes, suggest that the regeneration capability of DM2 satellite cells may be impaired, thus contributing to the muscular dystrophy in DM2 patients.

RNA processing is altered in skeletal muscle nuclei of patients affected by myotonic dystrophy

Myotonic dystrophies (DMs) are characterised by highly variable clinical manifestations consisting of muscle weakness and atrophy, and a wide spectrum of extramuscular manifestations. In both DM1 and DM2 forms, expanded nucleotide sequences cause the accumulation of mutant transcripts in the nucleus, thus deregulating the function of some RNA-binding proteins and providing a plausible explanation for the multifactorial phenotype of DM patients. However, at the skeletal muscle level, no mechanistic explanation for the muscle wasting has so far been proposed. We therefore performed a study in situ by immunoelectron microscopy on biceps brachii biopsies from DM1, DM2 and healthy subjects, providing the first ultrastructural evidence on the distribution of some nuclear ribonucleoprotein (RNP)-containing structures and molecular factors involved in pre-mRNA transcription and maturation in dystrophic myonuclei. Our results demonstrated an accumulation of splicing and cleavage factors in myonuclei of both DM1 and DM2 patients, suggesting an impairment of post-transcriptional pre-mRNA pathways. The transcription of the expanded sequences in DM myonuclei would therefore hamper functionality of the whole splicing machinery, slowing down the intranuclear molecular trafficking; this would reduce the capability of myonuclei to respond to anabolic stimuli thus contributing to muscle wasting.

Histochemistry through the years, browsing a long-established journal: novelties in traditional subjects

Histochemical journals represent a traditional forum where methodological and technological improvements can be presented and validated in view of their applications to investigate not only cytology and histology in normal and diseased conditions but to test as well hypotheses on more basic issues for life sciences, such as comparative and evolutionary biology. The earliest scientific journals on histochemistry began their publication in the first half of the ‘50s of the last century, and their readership did not probably change over the years; rather, the authors’ interests may have progressively been changing as well as the main topics of their articles. This hypothesis is discussed, based on the subjects of the article published in the first and last ten years in the European Journal of Histochemistry, as an example of old journal which started publication in 1954, being since then the official organ of the Italian Society of Histochemistry. This survey confirmed that histochemistry has provided and still offers unique opportunities for studying the structure, chemical composition and function of cells and tissues in a wide variety of living organisms, especially when the topological distribution of specific molecular components has diagnostic or predictive significance, as it occurs in human and veterinary biology and pathology. Some subjects (e.g. histochemistry applied to muscle cells or to mineralized tissues) have recently become rather popular, whereas a wider application of the histochemical approach may be envisaged for plant cells and tissues.

Structural and functional alterations of the cell nucleus in skeletal muscle wasting: the evidence in situ

The histochemical and ultrastructural analysis of the nuclear components involved in RNA transcription and splicing can reveal the occurrence of cellular dysfunctions eventually related to the onset of a pathological phenotype. In recent years, nuclear histochemistry at light and electron microscopy has increasingly been used to investigate the basic mechanisms of skeletal muscle diseases; the in situ study of nuclei of myofibres and satellite cells proved to be crucial for understanding the pathogenesis of skeletal muscle wasting in sarcopenia, myotonic dystrophy and laminopathies.