An oscillating magnetic field suppresses ice-crystal growth during rapid freezing of muscle tissue of mice

Regenerative medicine would benefit from a safe and efficient cryopreservation method to prevent the structural disruption caused by ice-crystal formation in cells and tissue. Various attempts have been made to overcome this problem, one of which is the use of an oscillating magnetic field (OMF). However, the underlying mechanism is unclear. In this study, to evaluate the effect of an OMF on ice-crystal formation in the leg muscles of mice, we used to use the frozen-section method with a slower freezing rate than is, usual which resulted in ice crystals forming in the tissue. We assessed the mean size and number per unit area of intracellular ice holes in sections of muscle tissue, with and without OMF. Ice-crystal growth was reduced in frozen tissue subjected to OMF. Furthermore, we evaluated the structure and function of proteins in frozen tissue subjected to OMF by immunostaining using an anti-dystrophin antibody and by enzymatic histochemistry for NADH-TR and myosin ATPase. The results imply that the ability of OMF to suppress ice-crystal growth might be related to their stabilization of bound water in biomolecules during freezing.

Elucidation of the control mechanism of dynamic tissues using freezing techniques

The preparation of histological specimens from animals and humans is a multi-step process comprising tissue collection, fixation, and dehydration, followed by paraffin embedding. Each process can be achieved using different methods and substances. For example, dehydration may not be required depending on the substance used for embedding. The freezing technique described in the present study can be used for tissue collection and fixation. Tissues obtained using "in vivo cryotechnique (IVCT)" reflect blood flow and protein localization in body fluids at the time of tissue collection, making it an indispensable method in histological analyses of the future. This study utilized the IVCT to capture histological images of dynamic objects from multiple viewpoints and elucidate the mechanism underlying their movement control at the molecular level.

Application of "in vivo cryotechnique" to morphological and immunohistochemical analyses of living mouse subepicardial microcirculation under various pathological conditions

"In vivo cryotechnique" (IVCT), which involves immediately cryofixing cells and tissues of living animals in situ, can display more native morphology in vivo and eliminate artificial changes in conventional preparations. However, the technical characteristics of IVCT are not known for the practical examination of subepicardial microcirculation of beating heart tissue. Histological sections of subepicardial area were prepared using IVCT and conventional fixation methods: quick freezing, immersion fixation, or perfusion fixation followed by alcohol dehydration, respectively from healthy mice. In addition, changes of erythrocyte shape, T-tubule, and microvasculature in mouse heart from a variety of models (acute increase of left ventricular afterload, myocardial ischemia, and cardiac arrest) were examined by IVCT. With IVCT, flowing erythrocytes, blood flow, microvasculature, and myocyte structure could be well preserved without artificial change of erythrocyte shape and translocation of serum proteins as displayed in conventional preparation samples. Furthermore, in various pathological models prepared by IVCT, T-tubules with albumin immuno-positive staining were arranged in a disorderly way and were decreased in volume in samples of acute increase of left ventricular afterload (IVCT-LAA). This was more evident in acute regional myocardial ischemia (IVCT-IC) and less evident in heart arrest (IVCT-HA). In addition, the leakage of serum proteins from microvasculature into myocyte was found only in IVCT-IC but not in IVCT-LAA and in IVCT-HA. In conclusion, IVCT is a new technique for examining morphology of subepicardial microcirculation without artifacts compared with conventional methods and is a more sensitive fixation technique in detecting pathological changes of the heart.

Immunohistochemical distribution of serum proteins in living mouse heart with In vivo cryotechnique

In vivo cryotechnique (IVCT), which immediately cryofixes target organs in situ, was used to clarify the morphological features of beating heart tissue of living mice. IVCT was performed for diastolic heart tissue under the condition of monitoring with electrocardiogram (ECG). Other mouse hearts were prepared with conventional perfusion-fixation (PF-DH) or immersion-fixation followed by dehydration (IM-DH), and quick-freezing of resected heart tissues (FQF). Immunolocalizations of albumin, immunoglobulin G1 (IgG1), intravenously injected bovine serum albumin (BSA), and connexin 43 were examined after different intervals of BSA injection. In the case of IVCT, the exact stop time of beating mouse hearts was recorded by ECG, and open blood vessels with flowing erythrocytes were observed with less artificial tissue shrinkage than with conventional preparation methods. Both albumin and BSA were well preserved in intercalated discs and t-tubules of cardiomyocytes in addition to blood vessels and interstitial matrices. IgG1 was immunolocalized in interstitial matrices of heart tissues in addition to their blood vessels. At 4 hr after BSA injection, it was immunolocalized in the intercalated discs of cardiomyocytes and lost later at 8 hr. IVCT should prove to be more useful for the morphofunctional examination of dynamically changing heart tissue than conventional preparation methods.

Histological study and LYVE-1 immunolocalization of mouse mesenteric lymph nodes with "In Vivo Cryotechnique"

The “in vivo cryotechnique” (IVCT) is a powerful tool to directly freeze living animal organs in order to maintain biological components in frozen tissues, reflecting their native states. In this study, mesenteric lymph nodes of living mice were directly frozen with IVCT, and we did morphological studies and immunohistochemical analyses on a hyaluronic acid receptor, LYVE-1. In lymph nodes, widely open lymphatic sinuses were observed, and many lymphocytes adhered to inner endothelial cells along subcapsular sinuses. The LYVE-1 was clearly immunolocalized at inner endothelial cells of subcapsular sinuses, as well as those of medullary sinuses. Conventional pre-embedding electron microscopy also showed LYVE-1 immunolocalization along both the apical and basal sides of cell membranes of inner endothelial cells. By triple-immunostaining for LYVE-1, smooth muscle actin, and type IV collagen, the LYVE-1 was immunolocalized only in the inner endothelial cells, but not in outer ones which were surrounded by collagen matrix and smooth muscle cells. Thus, the functional morphology of lymph nodes in vivo was demonstrated and LYVE-1 immunolocalization in inner endothelial cells of subcapsular sinuses suggests hyaluronic acid incorporation into lymph node parenchyma.

Immunohistochemical detection of soluble immunoglobulins in living mouse small intestines using an in vivo cryotechnique

Some morphological changes are inevitable during immersion- or perfusion-fixation and following alcohol-dehydration for tissue preparations. Common immunostaining techniques for these specimens have some limitations to capture accurate localizations of soluble proteins in cells and tissues. In this study, to examine in situ distributions of immunoglobulins (Igs), small intestinal tissues of living mice were prepared with our "in vivo cryotechnique" (IVCT). Thin sections were first stained with hematoxylin-eosin for morphology, and then some immunostainings were performed on serial sections for IgA, Ig kappa light chain, IgG1 heavy chain (IgG1), and IgM. Living morphological states of small intestinal tissues, including flowing erythrocytes and opening blood vessels, were observed on paraffin sections prepared with IVCT. IgA was immunolocalized in many plasma cells of the lamina mucosa propria, intestinal matrices, and also in epithelial cells of the intestinal villi and crypts. Both IgG1 and IgM immunoreactivities were mainly detected in blood vessels, whereas only IgG1 was also immunolocalized in interstitial matrices of mucous membranes. By perfusion-fixation and alcohol-dehydration, however, IgA immunoreactivity was observed in plasma cells, but not in epithelial cells or the lamina mucosa propria. Thus, IVCT was more useful to examine in vivo immunolocalizations of soluble Igs in small intestines.

Significance of 'in vivo cryotechnique' for morphofunctional analyses of living animal organs

Our final goal of morphological and immunohistochemical studies is that all findings examined in animal experiments should reflect the physiologically functional background. Therefore, the preservation of original components in cells and tissues of animals is necessary for describing the functional morphology of living animal organs. It is generally accepted that morphological findings of various organs were easily modified by stopping their blood supply. There had been a need to develop a new preparation technique for freezing the living animal organs in vivo and then obtaining acceptable morphology and also immunolocalization of original components in functioning cells and tissues. We already developed the 'in vivo cryotechnique' (IVCT) not only for their morphology, but also for immunohistochemistry of many soluble components in various living animal organs. All physiological processes of cells and tissues were immediately immobilized by IVCT, and every component in the cells and tissues was maintained in situ at the time of freezing. Thus, the ischaemic or anoxic effects on them could be minimized by IVCT. Our specially designed cryoknife with liquid cryogen has solved the morphological and immunohistochemical problems which are inevitable with the conventional preparation methods at a light or electron microscopic level. The IVCT will be extremely useful for arresting transient physiological processes and for maintaining any intracellular components in situ, such as rapidly changing signal molecules, membrane channels and receptors.

Immunohistochemical analyses of parathyroid hormone-dependent downregulation of renal type II Na-Pi cotransporters by cryobiopsy

The "in vivo cryotechnique" (IVCT) is a new method of morphological analysis which has the advantage of freezing tissues in living animals without stopping their blood circulation. The purpose of this study was to investigate the effect of parathyroid hormone (PTH) on renal type II Na-Pi transporters (NaPi-IIa and NaPi-IIc) and "cryobiopsy" (CB) using special cryoforceps as a simple method of the IVCT. The kidney tissues were biopsied at various time points after PTH administration by CB using liquid nitrogen as the cryogen. By hematoxylin-eosin (HE) staining the kidney tissues, well-frozen areas without visible ice crystals were obtained in the tissue surface areas, and the brush border membrane (BBM) of proximal tubules was well preserved at a light microscopic level. Immunohistochemical evaluation showed that PTH downregulated NaPi-IIa and NaPi-IIc at the BBM, being controlled by a different mechanism. In this method, the PTH-induced internalization of NaPi-IIc from microvilli to subapical compartments was not observed in the tissue preparations. NaPi-IIc protein appears to be degraded in microvilli of the proximal tubular cells after the injection of PTH. We suggest that CB using liquid nitrogen is useful to investigate renal type II Na-Pi transporters at the light microscopic level.

Permselectivity of blood follicle barriers in mouse ovaries of the mifepristone-induced polycystic ovary model revealed by in vivo cryotechnique

Despite the potential association of polycystic ovary (PCO) syndrome with hemodynamic changes, follicular microenvironment and the involvement of blood follicle barriers (BFB), a histopathological examination has been hampered by artifacts caused by conventional preparation methods. In this study, mouse ovaries of a mifepristone-induced PCO model were morphologically and immunohistochemically examined byin vivocryotechnique (IVCT), which prevents those technical artifacts. Ovarian specimens of PCO model mice were prepared by IVCT or the conventional perfusion fixation after s.c. injection of mifepristone. Their histology and immunolocalization of plasma proteins, including albumin (molecular mass, 69 kDa), immunoglobulin G (IgG, 150 kDa), inter-α-trypsin inhibitor (ITI, 220 kDa), fibrinogen (340 kDa), and IgM (900 kDa), were examined. In the PCO model, enlarged blood vessels with abundant blood flow were observed in addition to cystic follicles with degenerative membrana granulosa. The immunolocalization of albumin and IgM in the PCO model were similar to those in normal mice. Albumin immunolocalized in the blood vessels, interstitium or follicles, and IgM was mostly restricted within the blood vessels. In contrast, immunolocalization of IgG, ITI, and fibrinogen changed in the PCO model. Both IgG and ITI were clearly blocked by follicular basement membranes, and hardly observed in the membrana granulosa, though fibrinogen was mostly observed within blood vessels. These findings suggest that increased blood flow and enhanced selectivity of molecular permeation through the BFB are prominent features in the PCO ovaries, and changes in hemodynamic conditions and permselectivity of BFB are involved in the pathogenesis and pathophysiology of PCO syndrome.

Distribution of immunoglobulin-producing cells in immunized mouse spleens revealed with "in vivo cryotechnique"

To identify immunoglobulin (Ig)-producing cells with immunohistochemistry, conventional methods of preparation using chemical fixatives have problems such as the artificial diffusion of components and antigen masking. The "diffusion artifact" is caused by the translocation of soluble proteins like Ig from the serum to cytoplasm or vice versa. We have examined the immunolocalization of serum proteins, such as Ig kappa light chain (Igkappa), IgG1 heavy chain (IgG1), and albumin, in immunized mouse spleens after a peritoneal injection of human hemoglobin. Better preservation of morphology and immunoreactivity was obtained with the "in vivo cryotechnique" (IVCT) followed by freeze-substitution, than with conventional preparative methods. Although Ig-producing cells were not clearly detected in red pulp of 2-day-immunized spleens with the conventional methods, Igkappa-immunopositive cells with rich cytoplasm were detected in the red pulp with IVCT, especially in the subcapsular and peritrabecular areas, where IgG1-immunopositive cells were rarely observed. In 7-day-immunized spleens prepared with IVCT, Igkappa- or IgG1-immunopositive cells were mostly located in peritrabeculae. The development of Ig-producing cells was clarified in the specimens prepared with IVCT, which proved to be useful for analyzing the native morphology and distribution of Ig-producing cells.

Extracellular space in mouse cerebellar cortex revealed by in vivo cryotechnique

Conventional methods of preparing tissue specimens for morphological investigation of the central nervous system suffer from inevitable artifacts caused by anoxia during the processing. In the present study we performed ultrastructural analyses of mouse cerebellar cortex using the in vivo cryotechnique (IVCr), which minimizes ischemic artifacts of target organs through direct cryofixation in vivo. In molecular and Purkinje cell layers of the mouse cerebellum prepared with IVCr, considerably large extracellular spaces (ECS) were detected among cellular profiles and synaptic clefts. The ECS obtained with IVCr without ischemia were larger than those obtained with IVCr after 8-minute ischemia or a conventional quick-freezing method with fresh resected tissues (FQF), but did not decrease with IVCr after 30-second ischemia. By contrast, the parallel fibers observed with IVCr without ischemia were slightly smaller than those after 30-second ischemia, and significantly smaller than those prepared with IVCr after 8-minute ischemia or FQF. ECS were frequently preserved around synaptic clefts, although the rest were totally or partially enclosed with closely apposed glial processes. The estimated sizes of the ECS around synaptic clefts did not differ between the opened and enclosed synapses, suggesting that the opened synapses might be temporarily surrounded by glial sheaths dynamically extending or retracting throughout the perisynaptic ECS. These findings indicate IVCr to be useful for some morphological analyses of ECS in the central nervous system. The appreciable ECS around synapses would allow morphological and functional changes of neuronal and glial cells dynamically involved in synaptic remodeling or signal transduction.

Immunohistochemical detection of hypoxia in mouse liver tissues treated with pimonidazole using "in vivo cryotechnique"

To evaluate hypoxic cells in live mouse liver tissues, immunohistochemistry for protein adducts of reductively activated pimonidazole (PARaPi) was performed using the "in vivo cryotechnique (IVCT)" followed by freeze-substitution fixation. This method was used because cryotechniques have some merits for examining biological events in living animal organs with improved time-resolution compared to conventional perfusion and/or immersion chemical fixation. Pimonidazole was intraperitoneally injected into living mice, and then after various times of hypoxia, their livers were quickly frozen by IVCT. The frozen liver tissues were freeze-substituted in acetone containing 2% paraformaldehyde, and routinely embedded in paraffin wax. De-paraffinized sections were immunostained for PARaPi. In liver tissues of mice without hypoxia, almost no immunostained cells were detected. However, in liver tissues with 30 s of hypoxia, some hepatocytes in the pericentral zones were strongly immunostained. After 60 s of hypoxia, many hepatocytes were immunostained with various degrees of staining intensity in all lobular zones, indicating different reactivities of pimonidazole in the hepatocytes to hypoxia. At this time, the general immunoreactivity also appeared to be stronger around the central veins than other portal areas. Although many hepatocytes were immunostained for PARaPi in the liver tissues with perfusion fixation via heart, those with perfusion via portal vein were not immunostained. Thus, IVCT is useful to detect time-dependent hypoxic states with pimonidazole treatment in living animal organs.

Involvement of follicular basement membrane and vascular endothelium in blood–follicle barrier formation of mice revealed by ‘in vivo cryotechnique’

The molecular sieve with size- and charge selectivity in ovarian follicles, the so-called blood–follicle barrier (BFB), was examined during follicular development under physiological conditions to reveal ovarian structures responsible for the BFB by using our ‘in vivocryotechnique’ (IVCT). Mouse ovary specimens were prepared with different methods including IVCT, immersion, or perfusion chemical fixation and quick-freezing following resection or perfusion. Their paraffin sections or cryosections were stained with hematoxylin–eosin or immunostained for serum proteins with different molecular weights: albumin, immunoglobulin (Ig) G1 heavy chain, inter-α-trypsin inhibitor (IαI), fibrinogen, and IgM. Their immunoreactivity was better preserved with IVCT. The immunostaining for albumin was clearly observed in blood vessels, interstitium, and developing follicles, but that of IgG1, IαI, or fibrinogen was significantly decreased inside the follicles. IgM was immunohistochemically decreased throughout the interstitium outside blood vessels. The immunoreactivities of IgG1 and IgM, as compared with albumin, were clearly changed along follicular basement membranes and around vascular endothelial cells respectively. These findings indicate that BFB functions throughout follicular development, and the follicular basement membrane and the vascular endothelium could play some significant roles in the permselectivity for such soluble proteins with intermediate and high molecular weight respectively.

Conservation and alteration of chromosome territory arrangements in thyroid carcinoma cell nuclei

Chromosome territories (CTs) are intranuclear subregions occupied by individual chromosomes in an interphase cell. In this study, we investigated intranuclear CT positionings of chromosomes 10 (CS10), 18 (CS18), and 19 (CS19) in epithelial cells from four normal thyroid tissue (NT), four adenomatous goiters (AGs), six papillary carcinomas (PCs), and two undifferentiated carcinomas (UCs) using the multicolor fluorescence in situ hybridization method. In the NT and AGs, the radial positionings of CS10 and CS18 were detected at the periphery of nuclei in more than 60% and 80% of cells, respectively, whereas the radial positioning of CS19 was in the central region of the nuclei in more than 80% of cells. In the PCs, radial positioning pattern of CS10 and CS18 were similar to that in the NT. The nuclei with centrally located CS19 in PCs were less frequent than those in NT cells (p < 0.01). On the other hand, UCs with cells having DNA amplification demonstrated the locational abnormalities of the CS10, CS18, and CS19 radial positions. These findings indicate that alteration of CT positioning could be related to DNA amplification and, morphologically, may explain the nuclear atypia that accompanies the abnormal chromatin feature.

Application of periodic acid-Schiff fluorescence emission for immunohistochemistry of living mouse renal glomeruli by an "in vivo cryotechnique"

To identify the distribution of endogenous serum proteins in living mouse renal glomeruli under various hemodynamic conditions, we used the periodic acid-Schiff (PAS) and its fluorescence emission as a marker for the glomerular basement membrane (GBM). The immunostaining for collagen type IV was hardly observed without microwave treatment in specimens prepared by an "in vivo cryotechnique". However, PAS staining and its fluorescence emission could be clearly visualized at the GBM with the "in vivo cryotechnique". Under normotensive conditions, immunoreaction products of albumin and immunoglobulin G heavy and light chains (IgG(H+L)) were localized within glomerular capillary loops (GCL) but not colocalized with the PAS fluorescence emission of the GBM. Under heart-arrest conditions and with quick-freezing of resected tissues, albumin, IgG (H+L), immunoglobulin kappa light chain, and IgG1 heavy chain (IgG1) were immunolocalized within the GCL and mesangial areas, but only albumin and the kappa light chain were additionally immunolocalized in Bowman's space, indicating their passage through the GBM. Under acute hypertensive conditions, both albumin and the kappa light chain, but not IgG1, were clearly immunolocalized along the GBM and in the Bowman's space, indicating their increased passage through the GBM. The overlapping areas of PAS fluorescence emission and the albumin or kappa light chain appeared to be larger with quick-freezing and under the heart arrest or acute hypertensive conditions than under normal circulation, whereas those of PAS emission and IgG1 did not differ among these conditions. The serum proteins passing through the GBM were clearly visualized with the "in vivo cryotechnique", immunofluorescence staining, and PAS fluorescence emission.

Morphological analysis of lamellar structures in mouse type II pneumocytes by quick-freezing and freeze-drying with osmium tetroxide vapor-fixation

The lamellar body is a membranous structure periodically laminating in vesicles that is known as the most distinctive feature of type II pneumocytes by conventional preparation methods for transmission electron microscopy. The quick-freezing and freeze-drying method, followed by osmium tetroxide vapor-fixation (QF-FD-OsV), was performed to examine the in situ morphology of the lamellar body in type II pneumocytes of living mouse lungs. Typical lamellar structures were rarely seen in vesicles of the type II pneumocytes, but amorphous components and dispersed stripes were often detected in the vesicles, as revealed by the QF-FD-OsV method. To clarify how the lamellar body was formed during the conventional preparation steps, lung tissues of mice were treated with different fixation procedures, such as immersion-fixation with osmium tetroxide or perfusion-fixation with glutaraldehyde followed by osmium tetroxide, in combination with alcohol dehydration or QF-FD-OsV. In addition to lamellar bodies of type II pneumocytes in the specimens with alcohol dehydration, some lamellar structures were also formed even with the QF-FD-OsV method. These findings suggest that the labile lamellar body is easily modified and formed during both chemical fixation and alcohol dehydration steps.

Histochemical analyses of living mouse liver under different hemodynamic conditions by "in vivo cryotechnique"

Although the morphology and molecular distribution in animal liver tissues have been examined using conventional preparation methods, the findings are always affected by the technical artifacts caused by perfusion-fixation and tissue-resection. Using "in vivo cryotechnique" (IVCT), we have examined living mouse livers with histochemical, immunohistochemical and ultrastructural analyses. In samples prepared by IVCT, widely open sinusoids with many flowing erythrocytes were observed under normal blood circulation, and their collapse or blood congestion was seen in ischemic or heart-arrested mice. In contrast, the sinusoidal cavities were artificially dilated by perfusion-fixation, and collapsed by immersion-fixation and quick-freezing (QF) methods of resected tissues. The immunoreactivity of serum albumin and immunoglobulin G and intensity of periodic acid-Schiff-staining in hepatocytes were well preserved with the QF method and IVCT. Furthermore, following tissue resection, serum proteins were rapidly translocated into hepatocytes as demonstrated by immunoreactions on QF tissues frozen 1 or 5 min after resection. Translocation was not observed in IVCT samples, indicating that IVCT could be useful to examine cell membrane permeability of hepatocytes under different pathological conditions. Both dynamic morphology and immunodistribution of soluble components in living mouse livers, reflecting their physiological and pathological states, can be precisely examined by IVCT with higher time-resolution.

Immunolocalization of serum proteins in living mouse glomeruli under various hemodynamic conditions by "in vivo cryotechnique"

Distribution of serum proteins in renal glomeruli is important for histopathology in medical and biological fields, but mechanisms of their passage through glomerular capillary loops (GCL) are still difficult to clarify. We have tried to visualize topographical changes of the serum proteins passing through GCL by "in vivo cryotechnique" in combination with immunohistochemistry. Albumin and immunoglobulin G (IgG), Ig kappa light chain and IgG1 heavy chain were mainly immunolocalized in GCL, but not colocalized with zonula occludens-1 (ZO-1) under normotensive condition. Under heart-arrest condition and in quick-frozen fresh tissues, albumin and kappa light chain were immunolocalized in Bowman's space, indicating their passage caused by the stoppage of blood supply. However, under acute hypertensive condition, they were more clearly immunolocalized along basement membranes and in the Bowman's space, indicating their increased passage through GCL. IgG was also more clearly localized in mesangial areas under acute hypertension, compared with that under the normotensive or heart-arrest condition. This study is the first direct visualization for glomerular passage of serum proteins under abnormal hemodynamic conditions by the "in vivo cryotechnique", and the experimental protocol will be useful for morphofunctional examination of living mouse GCL and immunohistochemical analyses of dynamically changing proteins.