Toxicity in vital fluorescence microscopy: effect of dimethylsulfoxide, rhodamine-123, and DiI-low density lipoprotein on fibroblast growth in vitro

"Second-generation" fluorogenic RNA-based sensors

A fluorogenic aptamer can specifically interact with a fluorophore to activate its fluorescence. These nucleic acid-based fluorogenic modules have been dramatically developed over the past decade, and have been used as versatile reporters in the sensor development and for intracellular imaging. In this review, we summarize the design principles, applications, and challenges of the first-generation fluorogenic RNA-based sensors. Moreover, we discuss some strategies to develop next-generation biosensors with improved sensitivity, selectivity, quantification property, and eukaryotic robustness. Using genetically encoded catalytic hairpin assembly strategy as an example, we further introduce a standard protocol to design, characterize, and apply these fluorogenic RNA-based sensors for in vitro detection and cellular imaging of target biomolecules. By incorporating natural RNA machineries, nucleic acid nanotechnology, and systematic evolution approaches, next-generation fluorogenic RNA-based devices can be potentially engineered to be widely applied in cell biology and biomedicine.

Intracellular Imaging with Genetically Encoded RNA-based Molecular Sensors

Genetically encodable sensors have been widely used in the detection of intracellular molecules ranging from metal ions and metabolites to nucleic acids and proteins. These biosensors are capable of monitoring in real-time the cellular levels, locations, and cell-to-cell variations of the target compounds in living systems. Traditionally, the majority of these sensors have been developed based on fluorescent proteins. As an exciting alternative, genetically encoded RNA-based molecular sensors (GERMS) have emerged over the past few years for the intracellular imaging and detection of various biological targets. In view of their ability for the general detection of a wide range of target analytes, and the modular and simple design principle, GERMS are becoming a popular choice for intracellular analysis. In this review, we summarize different design principles of GERMS based on various RNA recognition modules, transducer modules, and reporting systems. Some recent advances in the application of GERMS for intracellular imaging are also discussed. With further improvement in biostability, sensitivity, and robustness, GERMS can potentially be widely used in cell biology and biotechnology.

Mitochondrial morphology and function impaired by dimethyl sulfoxide and dimethyl Formamide

In this work, the effects of two non-ionic, non-hydroxyl organic solvents, dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) on the morphology and function of isolated rat hepatic mitochondria were investigated and compared. Mitochondrial ultrastructures impaired by DMSO and DMF were clearly observed by transmission electron microscopy. Spectroscopic and polarographic results demonstrated that organic solvents induced mitochondrial swelling, enhanced the permeation to H⁺/K⁺, collapsed the potential inner mitochondrial membrane (IMM), and increased the IMM fluidity. Moreover, with organic solvents addition, the outer mitochondrial membrane (OMM) was broken, accompanied with the release of Cytochrome c, which could activate cell apoptosis signaling pathway. The role of DMSO and DMF in enhancing permeation or transient water pore formation in the mitochondrial phospholipid bilayer might be the main reason for the mitochondrial morphology and function impaired. Mitochondrial dysfunctions induced by the two organic solvents were dose-dependent, but the extents varied. Ethanol (EtOH) showed the highest potential damage on the mitochondrial morphology and functions, followed by DMF and DMSO.

In vivo spectral imaging of different cell types in the small intestine by two-photon excited autofluorescence

Spectrally resolved two-photon excited autofluorescence imaging is used to distinguish different cell types and functional areas during dynamic processes in the living gut. Excitation and emission spectra of mucosal tissue and tissue components are correlated to spectra of endogenous chromophores. We show that selective excitation with only two different wavelengths within the tuning range of a Ti:sapphire femtosecond laser system yields excellent discrimination between enterocytes, antigen presenting cells and lysosomes based on the excitation and emission properties of their autofluorescence. The method is employed for time-lapse microscopy over up to 8 h. Changes of the spectral signature with the onset of photodamage are demonstrated, and their origin is discussed.

Intradiscal transplantation of synovial mesenchymal stem cells prevents intervertebral disc degeneration through suppression of matrix metalloproteinase-related genes in nucleus pulposus cells in rabbits

INTRODUCTION

Synovial mesenchymal stem cells (MSCs) have high proliferative and chondrogenic potentials, and MSCs transplanted into the articular cartilage defect produce abundant extracellular matrix. Because of similarities between the articular cartilage and the intervertebral disc cartilage, synovial MSCs are a potential cell source for disc regeneration. Here, we examined the effect of intradiscal transplantation of synovial MSCs after aspiration of nucleus pulposus in rabbits.

METHODS

The nucleus pulposus tissues of rabbit's intervertebral discs were aspirated to induce disc degeneration, and allogenic synovial MSCs were transplanted. At 2, 4, 6, 8, 16, 24 weeks postoperatively, we evaluated with imaging analyses such as X-ray and magnetic resonance imaging (MRI), and histological analysis. To investigate interaction between synovial MSCs and nucleus pulposus cells, human synovial MSCs and rat nucleus pulposus cells were co-cultured, and species specific microarray were performed.

RESULTS

The existence of transplanted cells labeled with DiI or derived from green fluorescent protein (GFP)-expressing transgenic rabbits was confirmed up until 24 weeks. X-ray analyses demonstrated that intervertebral disc height in the MSC group remained higher than that in the degeneration group. T2 weighted MR imaging showed higher signal intensity of nucleus pulposus in the MSC group. Immunohistological analyses revealed higher expression of type II collagen around nucleus pulposus cells in the MSC group compared with even that of the normal group. In co-culture of rat nucleus pulposus cells and human synovial MSCs, species specific microarray revealed that gene profiles of nucleus pulposus were altered markedly with suppression of genes relating matrix degradative enzymes and inflammatory cytokines.

CONCLUSIONS

Synovial MSCs injected into the nucleus pulposus space promoted synthesis of the remaining nucleus pulposus cells to type II collagen and inhibition of expressions of degradative enzymes and inflammatory cytokines, resulting in maintaining the structure of the intervertebral disc being maintained.

Comparison of mesenchymal tissues-derived stem cells for in vivo chondrogenesis: suitable conditions for cell therapy of cartilage defects in rabbit

We previously compared mesenchymal stem cells (MSCs) from a variety of mesenchymal tissues and demonstrated that synovium-MSCs had the best expansion and chondrogenic ability in vitro in humans and rats. In this study, we compared the in vivo chondrogenic potential of rabbit MSCs. We also examined other parameters to clarify suitable conditions for in vitro and in vivo cartilage formation. MSCs were isolated from bone marrow, synovium, adipose tissue, and muscle of adult rabbits. Proliferation potential and in vitro chondrogenic potential were compared. Toxicity of the tracer DiI for in vitro chondrogenesis was also examined. MSCs from each tissue were embedded in collagen gel and transplanted into full thickness cartilage defects of rabbits. Cartilage matrix production was compared histologically. The effects of cell density and periosteal patch on the in vivo chondrogenic potential of synovium-MSCs were also examined. Synovium- and muscle-MSCs had a higher proliferation potential than other cells. Pellets from synovium- and bone-marrow-MSCs showed abundant cartilage matrix. DiI had no significant influence on in vitro cartilage formation. After transplantation into cartilage defects, synovium- and bone-marrow-MSCs produced much more cartilage matrix than other cells. When synovium-MSCs were transplanted at a higher cell density and with a periosteal patch, more abundant cartilage matrix was observed. Thus, synovium- and bone-marrow-MSCs had greater in vivo chondrogenic potential than adipose- and muscle-MSCs, but synovium-MSCs had the advantage of a greater proliferation potential. Higher cell density and a periosteum patch were needed to obtain a high production of cartilage matrix by synovium-MSCs.

Synovial mesenchymal stem cells accelerate early remodeling of tendon-bone healing

Tendon-bone healing is important for the successful reconstruction of the anterior cruciate ligament by using the hamstring tendon. Mesenchymal stem cells (MSCs) have attracted much interest because of their self-renewing potential and multipotentiality for possible clinical use. We previously reported that MSCs derived from synovium had a higher proliferation and differentiation potential than the other MSCs that we examined. The purpose of this study was to investigate the effect and mechanism of the implantation of the synovial MSCs on tendon-bone healing in rats. Half of the Achilles' tendon grafts of rats were inserted into a bone tunnel from the tibial plateau to the tibial tuberosity with a suture-post fixation. The bone tunnel was filled with MSCs labeled with fluorescent marker DiI or without MSCs as the control. The tendon-bone interface was analyzed histologically, and collagen fibers were quantified. At 1 week, the tendon-bone interface was filled with abundant DiI-positive cells, and the proportion of collagen fiber area was significantly higher in the MSC group than in the control group. By 2 weeks, the proportion of oblique collagen fibers, which appeared to be Sharpey's fibers, was significantly higher in the MSC group than in the control group. At 4 weeks, the interface tissue disappeared, and the implanted tendon appeared to attach to the bone directly in both groups. DiI-labeled cells could no longer be observed. Implantation of synovial MSCs into bone tunnel thus accelerated early remodeling of tendon-bone healing, as shown histologically.

NMR Assessment of Me2SO in Decellularized Cryopreserved Aortic Valve Conduits

INTRODUCTION

Decellularized cryopreserved allograft vascular tissue may provide a nonimmunogenic scaffold that is suitable for repopulation by cells from a variety of sources, conferring the potential for growth and repair. Although dimethyl sulfoxide (Me(2)SO) is generally regarded as a safe cryoprotectant, even low levels may alter function of repopulating cells. We investigated the residual concentration of Me(2)SO in the aqueous compartment of cryopreserved ovine aortic valve conduits following decellularization.

MATERIALS AND METHODS

Aortic valve conduits from Suffolk sheep were cryopreserved in 1.1 M (7.5% vol/vol) Me(2)SO according to the protocol of our local tissue bank. Three aortic valve conduits were decellularized in a series of hypotonic and hypertonic Tris buffers. Tissue samples were taken at regular time intervals throughout the decellularization process and equilibrated in double distilled, deionized H(2)O for 28 days. Quantitative proton nuclear magnetic resonance spectroscopy was used to determine the residual Me(2)SO concentration in the equilibration solutions from which Me(2)SO tissue concentrations were calculated.

RESULTS

After thawing, the mean Me(2)SO concentration in the valve conduit was 0.302 +/- 0.081 M. The decellularization process resulted in a stepwise reduction in the Me(2)SO concentration to less than 8.56 x 10(-5) +/- 9 x 10(-5) M (P = 0.02). The diffusion coefficient was 2.5 x 10(-6) cm(2)/s.

CONCLUSIONS

Our study demonstrates that Me(2)SO is effectively washed out of the aortic valve conduit during decellularization, resulting in a final concentration that is several orders of magnitude less than Me(2)SO concentrations reported to alter cell function.

Synovial stem cells are regionally specified according to local microenvironments after implantation for cartilage regeneration

We previously demonstrated that synovium-derived MSCs had greater in vitro chondrogenic ability than other mesenchymal tissues, suggesting a superior cell source for cartilage regeneration. Here, we transplanted undifferentiated synovium-derived MSCs into a full-thickness articular cartilage defect of adult rabbits and defined the cellular events to elucidate the mechanisms that govern multilineage differentiation of MSCs. Full-thickness osteochondral defects were created in the knee; the defects were filled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate-labeled MSCs and covered with periosteum. After 4 weeks, although the cell density decreased, transplanted MSCs produced a great amount of cartilage matrix extensively. The periosteum became thinner, and chondroprogenitors in the periosteum produced a small amount of cartilage matrix. In the deeper zone, transplanted MSCs progressed to the hypertrophic chondrocyte-like cells. In the deep zone, some transplanted cells differentiated into bone cells and were replaced with host cells thereafter. In the next phase, the border between bone and cartilage moved upwards. In addition, integrations between native cartilage and regenerated tissue were improved. Chondrocyte-like cells derived from the transplanted MSCs still remained at least after 24 weeks. Histological scores of the MSC group improved continuously and were always better than those of two other control groups. Immunohistological analyses and transmission electron microscopy confirmed that the MSCs produced abundant cartilage matrix. We demonstrated that transplanted synovium-derived MSCs were altered over a time course according to the microenvironments. Our results will advance MSC-based therapeutic strategies for cartilage injury and provide the clues for the mechanisms that govern multilineage differentiation of MSCs.

Altered mitochondrial structure and motion dynamics in living cells with energy metabolism defects revealed by real time microscope imaging

Using the real time microscope (RTM), a system applying new developments in light microscopy, we documented the spatial and temporal dynamics of mitochondrial behavior in human cultured skin fibroblasts. Without the use of stains or probes, we resolved fibroblast mitochondria as dark slender filaments of approximately 0.2 m wide and up to 10 m long, as well as a few smaller ovoid forms. In the living cell, the three most common mitochondrial movements were: (1) small oscillatory movements; (2) larger movements including filament extension, retraction, and branching as well as combinations of these actions; and (3) whole transit movements of single mitochondrial filaments. Skin fibroblasts from patients with mitochondrial complex I deficiency and normal fibroblasts during incubation with rotenone, or antimycin A, contained higher proportions of mitochondria in the swollen filamentous forms, nodal filaments, and ovoid forms rather than the slender filamentous forms in normal cells. Interestingly, decreased motility was observed with the more ovoid mitochondrial forms compared to the filamentous forms. We conclude that mitochondrial morphology and dynamic motion are strongly associated with changes in mitochondrial energy metabolism. Images documenting our observations are presented both at single time points and as QuickTime videos.

Repair of patellar tendon injuries using a cell-collagen composite

Collagen gels were seeded with rabbit bone marrow-derived mesenchymal stem cells (MSCs) and contracted onto sutures at initial cell densities of 1, 4, and 8 million cells/ml. These MSC-collagen composites were then implanted into full thickness, full length, central defects created in the patellar tendons of the animals providing the cells. These autologous repairs were compared to natural repair of identical defects on the contralateral side. Biomechanical, histological, and morphometric analyses were performed on both repair tissue types at 6, 12, and 26 weeks after surgery. Repair tissues containing the MSC-collagen composites showed significantly higher maximum stresses and moduli than natural repair tissues at 12 and 26 weeks postsurgery. However, no significant differences were observed in any dimensional or mechanical properties of the repair tissues across seeding densities at each evaluation time. By 26 weeks, the repairs grafted with MSC-collagen composites were one-fourth of the maximum stress of the normal central portion of the patellar tendon with bone ends. The modulus and maximum stress of the repair tissues grafted with MSC-collagen composites increased at significantly faster rates than did natural repairs over time. Unexpectedly, 28% of the MSC-collagen grafted tendons formed bone in the regenerating repair site. Except for increased repair tissue volume, no significant differences in cellular organization or histological appearance were observed between the natural repairs and MSC-collagen grafted repairs. Overall, these results show that surgically implanting tissue engineered MSC-collagen composites significantly improves the biomechanical properties of tendon repair tissues, although greater MSC concentrations produced no additional significant histological or biomechanical improvement.

The effect of different solvents on the ATP/ADP content and growth properties of HeLa cells

Testing of the effects of xenobiotics in cultured cells often requires the use of organic solvents to effect suspension of the test agents in cell culture media. However, the toxic effects of the solvents themselves may introduce artifacts, which obscure interpretation of the experimental results. In this article, the toxicity of different solvents commonly used for solvation of a variety of xenobiotic agents was studied. We show that ethanol, acetone, isooctane, methanol, and hexane were considerably less toxic than the more commonly used solvent, DMSO, when ATP content and growth rates of HeLa cells exposed to these solvents was measured.

Combined effects of H-7 and cytochalasin B on outflow facility in monkeys

The serine-threonine protein kinase inhibitor H-7 and the fungal metabolite cytochalasin B (CB) disrupt the actin microfilament network by different mechanisms, and increase outflow facility similarly in live monkeys. Their combined effect has therefore determined on total outflow facility in cynomolgus monkeys by 2-level constant pressure perfusion. (1) After unilateral anterior chamber (AC) bolus injection of H-7 [10 micrometers, 100 micrometers (subthreshold for increasing facility when given alone) or 500 micrometers (just-threshold)] followed by bilateral AC bolus injection of CB [2 micrograms (strong but submaximal for increasing facility when given alone)], no significant difference between eyes was observed. (2) After bilateral AC exchange with a subthreshold dose of H-7 (10 micrometers) followed by unilateral AC bolus injection of a subthreshold dose of CB (0.02, 0.05, 0.1 or 0.5 microgram), 10 micrometers H-7 plus 0.1 or 0.5 microgram CB increased facility by approximately 40 or 80% compared to 10 micrometers H-7 alone. (3) After bilateral AC exchange with a maximal dose of H-7 (300 micrometers), followed by unilateral AC bolus injection of a subthreshold dose of CB (0.1 or 0.5 microgram), 300 micrometers H-7 plus 0.5 microgram CB increased outflow facility by 47% compared to 300 micrometers H-7 alone. (4) After unilateral AC exchange with a maximal dose of H-7 (300 micrometers) followed by bilateral AC bolus injection of a near-maximal dose of CB (2 micrograms), 300 micrometers H-7 plus 2 micrograms CB increased the facility by 67% compared to 2 micrograms CB alone. The significant effect of combined subthreshold doses of H-7 and CB on outflow facility, the potentiation of the facility-increasing effect of a maximal H-7 dose by both subthreshold and near-maximal CB doses, and the known cytoskeletal effects of both compounds, may suggest that both increase facility by disrupting actin filaments in the trabecular meshwork.

Dynamics of mitochondria in living cells: shape changes, dislocations, fusion, and fission of mitochondria

Mitochondria are semi-autonomous organelles which are endowed with the ability to change their shape (e.g., by elongation, shortening, branching, buckling, swelling) and their location inside a living cell. In addition they may fuse or divide. These dynamics are discussed. Dislocation of mitochondria may result from their interaction with elements of the cytoskeleton, with microtubules in particular, and from processes intrinsic to the mitochondria themselves. Morphological criteria and differences in the fate of some mitochondria argue for the presence of more than one mitochondrial population in some animal cells. Whether these reflect genetic differences remains obscure. Emphasis is laid on the methods for visualizing mitochondria in cells and following their behaviour. Fluorescence methods provide unique possibilities because of their high resolving power and because some of the mitochondria-specific fluorochromes can be used to reveal the membrane potential. Fusion and fission often occur in short time intervals within the same group of mitochondria. At sites of fusion of two mitochondria material of the inner membrane, the matrix compartment seems to accumulate. The original arrangement of the fusion partners is maintained for some minutes. Fission is a dynamic event which, like fusion, in most cases observed in vertebrate cell cultures is not a straight forward process but rather requires several "trials" until the division finally occurs. Regarding fusion and fission hitherto unpublished phase contrast micrographs, and electron micrographs have been included.

Evaluation of rhodamine 123 as a probe for monitoring mitochondrial function in Trypanosoma brucei spp

Rhodamine 123, a membrane potential-specific dye, has been evaluated as a probe to monitor the function of the mitochondrion in long slender bloodstream and procyclic trypomastigotes of several Trypanosoma brucei spp. By epifluorescence microscopy, mitochondrial development has been followed in long slender bloodstream and procyclic organisms stained with rhodamine 123. To photograph stained long slender bloodstream forms, it was necessary to develop a method to completely immobilize viable organisms. In both parasite forms, as the cell cycle progressed, the mitochondrion developed from a thread-like structure to a highly branched organelle. A dramatic reorganization occurred preceding cytokinesis to produce two progeny thread-like structures which were partitioned into newly formed daughter cells. The organelle within the long slender trypomastigote was found to stain optimally at 0.3 microgram/ml of rhodamine 123, while the procyclic form required 3.0 micrograms/ml. The results suggest that the plasma membrane potential is higher in the long slender parasite than in the procyclic form. The effects of inhibitors that disrupt mitochondrial function were examined in long slender and procyclic parasites, and some of these agents were shown to affect rhodamine 123 accumulation and retention. In long slender trypomastigotes the trypanosome alternative oxidase does not appear to be coupled to proton pumping, whereas in procyclic organisms the effects of inhibitors indicate that this oxidase may be coupled to a pathway that is branched preceding an antimycin A1-sensitive site.