Monitoring Therapy Response of Experimental Arthritis with Radiolabeled Tracers Targeting Fibroblasts, Macrophages, or Integrin αvß3.

UNLABELLED: Rheumatoid arthritis is an autoimmune disease resulting in chronic synovial inflammation. Molecular imaging could be used to monitor therapy response, thus enabling tailored therapy regimens and enhancing therapeutic outcome. Here, we hypothesized that response to etanercept could be monitored by radionuclide imaging in arthritic mice. We tested 3 different targets, namely fibroblast activation protein (FAP), macrophages, and integrin αvß3. METHODS: Male DBA/1J mice with collagen-induced arthritis were treated with etanercept. SPECT/CT scans were acquired at 1, 24, and 48 h after injection of (111)In-RGD2 (integrin αvß3), (111)In-anti-F4/80-A3-1 (antimurine macrophage antibody), or (111)In-28H1 (anti-FAP antibody), respectively, with nonspecific controls included. Mice were dissected after the last scan, and scans were analyzed quantitatively and were correlated with macroscopic scoring. RESULTS: Experimental arthritis was imaged with (111)In-28H1 (anti-FAP), (111)In-anti-F4/80-A3-1, and (111)In-RGD2. Tracer uptake in joints correlated with arthritis score. Treatment decreased joint uptake of tracers from 23 ± 15, 8 ± 4, and 2 ± 1 percentage injected dose per gram (%ID/g) to 11 ± 11 (P < 0.001), 4 ± 4 (P < 0.001), and 1 ± 0.2 %ID/g (P < 0.01) for (111)In-28H1, (111)In-anti-F4/80-A3-1, and (111)In-RGD2, respectively. Arthritis-to-blood ratios (in mice with arthritis score 2 per joint) were higher for (111)In-28H1 (5.5 ± 1; excluding values > 25), (111)In-anti-F4/80-A3-1 (10.4 ± 4), and (111)In-RGD2 (7.2 ± 1) than for control (111)In-DP47GS (0.7 ± 0.5; P = 0.002), (111)In-rat IgG2b (0.5 ± 0.2; P = 0.002), or coinjection of excess RGD2 (3.5), indicating specific uptake of all tracers in arthritic joints. CONCLUSION: (111)In-28H1, (111)In-anti-F4/80-A3-1, and (111)In-RGD2 can be used to specifically monitor the response to therapy in experimental arthritis at the molecular level. Further studies, however, still need to be performed.

Evaluation of Glucose Uptake in Normal and Cancer Cell Lines by Positron Emission Tomography.

To date, there is no definitive demonstration of the utility of positron emission tomography (PET) in studying glucose metabolism in cultured cell lines. Thus, this study was designed to compare PET to more standardized methods for the quantitative assessment of glucose uptake in nontransformed and transformed living cells and to validate PET for metabolic studies in vitro. Human colon and breast carcinoma cell lines and mouse embryo fibroblasts were evaluated for [(18)F]fluorodeoxyglucose ([(18)F]FDG) uptake by PET and autoradiography and 2-deoxyglucose (2-DG) incorporation by colorimetric assay and analyzed for the radiotoxic effects of [(18)F]FDG and the expression levels of glucose transporters. Indeed, [(18)F]FDG incorporation on PET was comparable to [(18)F]FDG uptake by autoradiography and 2-DG incorporation by colorimetric assay, although radiotracer-based methods exhibited more pronounced differences between individual cell lines. As expected, these data correlated with glucose transporters 1 to 4 and hexokinase II expression in tumor cell lines and mouse fibroblasts. Notably, [(18)F]FDG incorporation resulted in low apoptotic rates, with fibroblasts being slightly more sensitive to radiotracer-induced cell death. The quantitative analysis of [(18)F]FDG uptake in living cells by PET represents a valuable and reproducible method to study tumor cell metabolism in vitro, being representative of the differences in the molecular profile of normal and tumor cell lines.

Acute toxic effects of sonodynamic therapy on hypertrophic scar fibroblasts of rabbit ears.

The objective of this study was to observe the acute cytotoxic effects of hematoporphyrin monomethyl ether sonodynamic therapy (HMME-SDT) on hypertrophic scar fibroblasts of rabbit ears. We first assessed the effects of different irradiation times and HMME concentrations on the survival of hypertrophic scar fibroblasts using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay to determine the optimum irradiation time and HMME concentration. The hypertrophic scar fibroblast cell suspensions of the rabbit ears were divided into four groups, the survival rates were detected using the MTT assay, and the type of cell death was detected by Annexin V/propidium iodide (PI) double staining flow cytometry. Our results showed that HMME-SDT significantly reduced the viability of hypertrophic scar fibroblasts of rabbit ears at ultrasonic irradiation times of 30, 60, and 90 s, but not 10 s (P < 0.05). HMME alone had no significant effect on the cell survival rate at any irradiation time (P > 0.05). In contrast, the cell survival rate was significantly decreased at an irradiation time of 10 s and HMME concentrations of 20 and 50 µg/mL (P < 0.05). Furthermore, Annexin V/PI double staining showed necrosis and apoptosis of the hypertrophic scar fibroblasts. Given our results, HMME might be an effective sound-sensitive agent for SDT as it has a significant lethal effect on hypertrophic scar fibroblasts of rabbit ear cultured in vitro. HMME-SDT may therefore provide a new method for the treatment of hypertrophic scar formation.

Immuno-PET and Immuno-SPECT of Rheumatoid Arthritis with Radiolabeled Anti-Fibroblast Activation Protein Antibody Correlates with Severity of Arthritis.

UNLABELLED: One of the most prominent cell populations playing a role in rheumatoid arthritis (RA) is activated fibroblast-like synoviocytes. Among many other proteins, fibroblast-like synoviocytes dominantly express fibroblast activation protein (FAP). Because of the high expression of FAP in arthritic joints, radioimmunoimaging of activated fibroblasts with anti-FAP antibodies might be an attractive noninvasive imaging tool in RA. METHODS: SPECT and PET with (111)In- and (89)Zr-labeled anti-FAP antibody 28H1 was performed in mice with CIA. The radioactivity uptake in joints was quantified and correlated with arthritis score. RESULTS: Both (111)In-28H1 and (89)Zr-28H1 showed high uptake in inflamed joints, being 3-fold higher than that of the irrelevant isotype-matched control antibody DP47GS, clearly indicating specific accumulation of 28H1. Uptake of (111)In-28H1 ranged from 2.2 percentage injected dose per gram (%ID/g) in noninflamed joints to 32.1 %ID/g in severely inflamed joints. DP47GS accumulation ranged from 1.6 %ID/g in noninflamed tissue to 12.0 %ID/g in severely inflamed joints. Uptake of 28H1 in inflamed joints correlated with arthritis score (Spearman ρ, 0.69; P < 0.0001) and increased with severity of arthritis. CONCLUSION: SPECT/CT imaging with the anti-FAP antibody (111)In-28H1 specifically visualized arthritic joints with high resolution, and tracer accumulation correlated with the severity of the inflammation in murine experimental arthritis. Background uptake of the radiolabeled antibody was low, resulting in excellent image quality. (89)Zr-28H1 was less favorable for RA imaging because of an elevated bone uptake of (89)Zr. Future studies will focus on the potential role of 28H1 as a tool to monitor therapy response early on.

Effects of 35 kHz, low-frequency ultrasound application in vitro on human fibroblast morphology and migration patterns.

Low-frequency ultrasound (LFU) in the frequency range 30-40 kHz administered using different delivery methods (waterbath and noncontact spray) has shown positive effects on chronic wound healing rates in humans, but the underlying mechanisms are only beginning to be explored. To examine the effects of LFU delivered at 35 kHz on the morphology and migration of human fibroblasts, real-time videography was used to record the rate and character of cultured human fibroblast migration at 8-hour increments for 48 hours in a wound assay model. Cells were treated with 35 kHz LFU or saline only (control). Cellular morphology (cell shape, packing, and apparent length) and migration patterns including orientation were analyzed using time-lapse videography. LFU delivered at a frequency of 35 kHz produced a different pattern of fibroblast migration in vitro (varied orientation versus vertical orientation for untreated cells) and altered cell morphology compared to controls. The observed pattern of migration was more varied and widely distributed across multiple angles versus the predominant parallel orientation of the migrating untreated cells. The potential implications of these findings on collagen placement in the extracellular matrix, which may affect degree of soft tissue scarring, should be further investigated.

PCH-2 regulates Caenorhabditis elegans lifespan.

Components or downstream targets of many signaling pathways such as Insulin/IGF-1 and TOR, as well as genes involved in cellular metabolism and bioenergetics can extend worm lifespan 20% or more. The C. elegans gene pch-2 and its homologs, including TRIP13 in humans, have been studied for their functions in cell mitosis and meiosis, but have never been implicated in lifespan regulation. Here we show that over-expression of TRIP13 in human fibroblasts confers resistance to environmental stressors such as UV radiation and oxidative stress. Furthermore, pch-2 overexpression in C. elegans extends worm lifespan, and enhances worm survival in response to various stressors. Conversely, reducing pch-2 expression with RNAi shortens worm lifespan. Additional genetic epistasis analysis indicates that the molecular mechanism of pch-2 in worm longevity is tied to functions of the sirtuin family, implying that pch-2 is another chromatin regulator for worm longevity. These findings suggest a novel function of the pch-2 gene involved in lifespan determination.

PET imaging of cardiac wound healing using a novel [68Ga]-labeled NGR probe in rat myocardial infarction.

PURPOSE: Peptides containing the asparagine-glycine-arginine (NGR) motif bind to aminopeptidase N (CD13), which is expressed on inflammatory cells, endothelial cells, and fibroblasts. It is unclear whether radiolabeled NGR-containing tracers could be used for in vivo imaging of the early wound-healing phase after myocardial infarction (MI) using positron emission tomography (PET). PROCEDURES: Uptake of novel tracer [(68)Ga]NGR was assessed together with [(68)Ga]arginine-glycine-aspartic acid ([(68)Ga]RGD) and 2-deoxy-2-[(18) F]fluoro-D-glucose after myocardial ischemia/reperfusion (MI/R) injury using µ-PET and autoradiography, and relative expressions of CD13 and integrin ß3 were assessed in fibroblasts, inflammatory cells, and endothelial cells by immunohistochemistry. RESULTS: In the infarcted myocardium, uptake of [(68)Ga]NGR was maximal from days 3 to 7 after MI/R, and correlated with fibroblast and inflammatory cell infiltration as well as [(68)Ga]RGD uptake. CONCLUSIONS: [(68)Ga]NGR allows noninvasive and sequential determination of CD13 expression in fibroblasts and inflammatory cells by PET. This will facilitate monitoring of CD13 in the individual wound healing processes, allowing patient-specific therapies to improve outcome after MI.

In-vivo comparison of the acute retention of stem cell derivatives and fibroblasts after intramyocardial transplantation in the mouse model.

PURPOSE: Various strategies have been applied to increase the engraftment of an intramyocardial cell transplant (Tx) to treat ischemic myocardium. Thereby, co-transplanted fibroblasts (FB) improve the long-term survival of stem cell derivatives (SCD) in a murine model of myocardial infarction. For therapeutic use, the time frame in which FB exert putative supportive effects needs to be identified. Therefore, we tracked the biodistribution and retention of SCD and FB in vivo using highly sensitive positron emission tomography (PET) imaging. METHODS: Murine [(18)F]-fluorodeoxyglucose (FDG) labeled SCD and FB were transplanted after left anterior descending artery (LAD) ligation into the border zone of the ischemic area in female C57BL/6 mice. Cardiac retention and biodistribution during the initial 2 h after injection were measured via PET imaging. RESULTS: Massive initial cell loss occurred independently of the cell type. Thereby, FB were retained slightly, yet significantly better than SCD until 60 min post-injection (7.5 ± 1.7 vs. 5.2 ± 0.7% ID at 25 min and 7.0 ± 1.5 vs. 4.8 ± 0.8% ID at 60 min). Thereafter, a fraction of ∼ 5% that withstood the massive initial washout remained at the site of injection independently of the applied cell type (120 min, SCD vs. FB P = 0.64). Most of the lost cells were detected in the lungs (∼ 30 % ID). CONCLUSIONS: We were able to quantitatively define the retention and biodistribution of different cell types via PET imaging in a mouse model after intramyocardial Tx. The utmost accuracy was achieved through this cell- and organ-specific approach by correcting PET data for cellular FDG efflux. Thereby, we observed a massive initial cell loss of ∼ 95%, causing low rates of long-term engraftment for both SCD and FB. We conclude that FB are not privileged compared to SCD regarding their acute retention kinetics, and therefore exert their beneficial effects at a later time point.

Bystander effect induced by UVC radiation in Chinese hamster V79 cells.

In past decades, researches on radiation-induced bystander effect mainly focused on ionizing radiation such as α-particle, ß-particle, X-ray and γ-ray. But few researches have been conducted on the ability of ultraviolet (UV) radiation-induced bystander effect, and knowledge of UVC-induced bystander effect is far limited. Here, we adopted medium transfer experiment to detect whether UVC could cause bystander effect in Chinese hamster V79 cells. We determined the cell viability, apoptosis rate, chromosome aberration and ultrastructure changes, respectively. Our results showed that: (1) the viability of UVC-irradiated V79 cells declined significantly with the dosage of UVC; (2) similar to the irradiated cells, the main death type of bystander cells cultured in irradiation conditioned medium (ICMs) was also apoptosis; (3) soluble factors secreted by UVC-irradiated cells could induce bystander effect in V79 cells; (4) cells treated with 4 h ICM collected from 90 mJ cm(-2) UVC-irradiated cells displayed the strongest response. Our data revealed that UVC could cause bystander effect through the medium soluble factors excreted from irradiated cells and this bystander effect was a novel quantitative and kinetic response. These findings might provide a foundation to further explore the exact soluble bystander factors and detailed mechanism underlying UVC-induced bystander effect.

Non-invasive assessment of elastic modulus of arterial constructs during cell culture using ultrasound elasticity imaging.

Mechanical strength is a key design factor in tissue engineering of arteries. Most existing techniques assess the mechanical property of arterial constructs destructively, leading to sacrifice of a large number of animals. We propose an ultrasound-based non-invasive technique for the assessment of the mechanical strength of engineered arterial constructs. Tubular scaffolds made from a biodegradable elastomer and seeded with vascular fibroblasts and smooth muscle cells were cultured in a pulsatile-flow bioreactor. Scaffold distension was computed from ultrasound radiofrequency signals of the pulsating scaffold via 2-D phase-sensitive speckle tracking. Young's modulus was then calculated by solving the inverse problem from the distension and the recorded pulse pressure. The stiffness thus computed from ultrasound correlated well with direct mechanical testing results. As the scaffolds matured in culture, ultrasound measurements indicated an increase in Young's modulus, and histology confirmed the growth of cells and collagen fibrils in the constructs. The results indicate that ultrasound elastography can be used to assess and monitor non-invasively the mechanical properties of arterial constructs.

Induction of adhesion-dependent signals using low-intensity ultrasound.

In multicellular organisms, cell behavior is dictated by interactions with the extracellular matrix. Consequences of matrix-engagement range from regulation of cell migration and proliferation, to secretion and even differentiation. The signals underlying each of these complex processes arise from the molecular interactions of extracellular matrix receptors on the surface of the cell. Integrins are the prototypic receptors and provide a mechanical link between extracellular matrix and the cytoskeleton, as well as initiating some of the adhesion-dependent signaling cascades. However, it is becoming increasingly apparent that additional transmembrane receptors function alongside the integrins to regulate both the integrin itself and signals downstream. The most elegant of these examples is the transmembrane proteoglycan, syndecan-4, which cooperates with α(5)ß(1)-integrin during adhesion to fibronectin. In vivo models demonstrate the importance of syndecan-4 signaling, as syndecan-4-knockout mice exhibit healing retardation due to inefficient fibroblast migration. In wild-type animals, migration of fibroblasts toward a wound is triggered by the appearance of fibronectin that leaks from damaged capillaries and is deposited by macrophages in injured tissue. Therefore there is great interest in discovering strategies that enhance fibronectin-dependent signaling and could accelerate repair processes. The integrin-mediated and syndecan-4-mediated components of fibronectin-dependent signaling can be separated by stimulating cells with recombinant fibronectin fragments. Although integrin engagement is essential for cell adhesion, certain fibronectin-dependent signals are regulated by syndecan-4. Syndecan-4 activates the Rac1 protrusive signal, causes integrin redistribution, triggers recruitment of cytoskeletal molecules, such as vinculin, to focal adhesions, and thereby induces directional migration. We have looked for alternative strategies for activating such signals and found that low-intensity pulsed ultrasound (LIPUS) can mimic the effects of syndecan-4 engagement. In this protocol we describe the method by which 30 mW/cm(2), 1.5 MHz ultrasound, pulsed at 1 kHz (Fig. 1) can be applied to fibroblasts in culture (Fig. 2) to induce Rac1 activation and focal adhesion formation. Ultrasound stimulation is applied for a maximum of 20 minutes, as this combination of parameters has been found to be most efficacious for acceleration of clinical fracture repair. The method uses recombinant fibronectin fragments to engage α(5)ß(1)-integrin, without engagement of syndecan-4, and requires inhibition of protein synthesis by cycloheximide to block deposition of additional matrix by the fibroblasts. The positive effect of ultrasound on repair mechanisms is well documented, and by understanding the molecular effect of ultrasound in culture we should be able to refine the therapeutic technique to improve clinical outcomes.

Stable cavitation induces increased cytoplasmic calcium in L929 fibroblasts exposed to 1-MHz pulsed ultrasound.

An increase in cytoplasmic calcium (Ca(2+) increase) is a second messenger that is often observed under ultrasound irradiation. We hypothesize that cavitation is a physical mechanism that underlies the increase in Ca(2+) in these experiments. To control the presence of cavitation, the wave type was controlled in a sonication chamber. One wave type largely contained a traveling wave (wave type A) while the other wave type largely contained a standing wave (wave type B). Fast Fourier transform (FFT) analysis of a sound field produced by the wave types ascertained that stable cavitation was present only under wave type A ultrasound irradiation. Under the two controlled wave types, the increase in Ca(2+) in L929 fibroblasts was observed with fluorescence imaging. Under wave type A ultrasound irradiation, an increase in Ca(2+) was observed; however, no increase in Ca(2+) was observed under wave type B ultrasound irradiation. We conclude that stable cavitation is involved in the increase of Ca(2+) in cells subjected to pulsed ultrasound.

Fibroblastic rheumatism: an addition to fibromatosis.

Fibroblastic rheumatism (FR) is a rare rheumatologic entity of unknown etiology. It is characterized by symmetrical polyarthritis associated with multiple cutaneous nodules. Bone erosion can occur as the disease progresses and destructive arthropathy is not rare. We report on an 18-year-old man with FR who presented a 6-year history of cutaneous nodules localized at para-articular sites with only minimal oligoarthralgia on exertion. There was no visceral involvement, and all the routine and immunological tests were normal. The diagnosis of FR was confirmed by histological examination of a nodule, which composed of myofibroblastic proliferation and thickened collagen fibers. Most skin lesions resolved after treated with IFN-α, however there was sequelae of permanent disability due to the progressive bone erosion despite weekly methotrexate treatment.

A study of the biological effects of modulated 6 MV radiation fields.

The delivery of spatially modulated radiation fields has been shown to impact on in vitro cell survival responses. To study the effect of modulated fields on cell survival, dose response curves were determined for human DU-145 prostate, T98G glioma tumour cells and normal primary AGO-1552 fibroblast cells exposed to modulated and non-modulated field configurations delivered using a 6 MV Linac with multi-leaf collimator. When exposed to uniform fields delivered as a non-modulated or modulated configuration, no significant differences in survival were observed with the exception of DU-145 cells at a dose of 8 Gy (p = 0.024). Survival responses were determined for exposure to non-uniform-modulated beams in DU-145 and T98G and showed no deviation from the survival response observed following uniform non-modulated exposures. The results of these experiments indicate no major deviation in response to modulated fields compared to uniform exposures.

Hyaluronic acid modulates gene expression of connective tissue growth factor (CTGF), transforming growth factor-beta1 (TGF-beta1), and vascular endothelial growth factor (VEGF) in human fibroblast-like synovial cells from advanced-stage osteoarthritis in vitro.

Intraarticular injection of hyaluronan (hyaluronic acid; HA) is the common way to treat osteoarthritis (OA) of knees. This treatment cannot only maintain the viscoelastic properties of knee but also release the OA pain. However, the exact molecular mechanism is unknown. In this study, after human synovial cells were stimulated with HA and Hylan (Synvisc) for 24 h, real-time polymerase chain reaction (real-time PCR) was used to detect the alteration of connective tissue growth factor (CTGF), transforming growth factor-beta1 (TGF-beta1), and vascular endothelial growth factor (VEGF) gene expression, which were specific genes related to pathogenesis of OA knees. Our results illustrated that both HA and Hylan might not cause cytotoxicity or apoptosis of synovial cells in serum deprivation environment. The gene expressions of TGF-beta1 and VEGF were significantly increased at the concentration of 0.1 mg/mL HA and 0.1 mg/mL Hylan, respectively (alpha < 0.05). The synovial cells with treatment of 0.1 mg/mL Hylan decreased the CTGF gene expression (0.66-fold) and VEGF (0.78-fold) compared to 0.1 mg/mL HA (alpha < 0.05). We suggested that the profile of CTGF, TGF-beta1, and VEGF gene expressions in our study might provide the rational mechanism for the therapeutic effect of hyaluronan on OA knees.

Molecular imaging for efficacy of pharmacologic intervention in myocardial remodeling.

OBJECTIVES: Using molecular imaging techniques, we examined interstitial alterations during postmyocardial infarction (MI) remodeling and assessed the efficacy of antiangiotensin and antimineralocorticoid intervention, alone and in combination. BACKGROUND: The antagonists of the renin-angiotensin-aldosterone axis restrict myocardial fibrosis and cardiac remodeling after MI and contribute to improved survival. Radionuclide imaging with technetium-99m-labeled Cy5.5 RGD imaging peptide (CRIP) targets myofibroblasts and indirectly allows monitoring of the extent of collagen deposition post-MI. METHODS: CRIP was intravenously administered for gamma imaging after 4 weeks of MI in 63 Swiss-Webster mice and in 6 unmanipulated mice. Of 63 animals, 50 were treated with captopril (C), losartan (L), spironolactone (S) alone, or in combination (CL, SC, SL, and SCL), 8 mice received no treatment. Echocardiography was performed for assessment of cardiac remodeling. Hearts were characterized histopathologically for the presence of myofibroblasts and thick and thin collagen fiber deposition. RESULTS: Acute MI size was similar in all groups. The quantitative CRIP percent injected dose per gram uptake was greatest in the infarct area of untreated control mice (2.30 +/- 0.14%) and decreased significantly in animals treated with 1 agent (C, L, or S; 1.71 +/- 0.35%; p = 0.0002). The addition of 2 (CL, SC, or SL 1.31 +/- 0.40%; p < 0.0001) or 3 agents (SCL; 1.16 +/- 0.26%; p < 0.0001) demonstrated further reduction in tracer uptake. The decrease in echocardiographic left ventricular function, strain and rotation parameters, as well as histologically verified deposition of thin collagen fibers, was significantly reduced in treatment groups and correlated with CRIP uptake. CONCLUSIONS: Radiolabeled CRIP allows for the evaluation of the efficacy of neurohumoral antagonists after MI and reconfirms superiority of combination therapy. If proven clinically, molecular imaging of the myocardial healing process may help plan an optimal treatment for patients susceptible to heart failure.

Assessment of fibroblast cells submitted to ultrasonic irradiation.

Physiotherapists consider ultrasound an indispensable tool, which is commonly employed in clinical practice as a treatment aid for musculoskeletal dysfunctions. The aim of our study has been to analyze fibroblast cell structures following low-intensity pulsed ultrasonic irradiation. Fibroblast cell cultures irradiated with ultrasound were analyzed through electron microscopy to determine an ideal irradiation beam that preserved cell morphology and integrity. Analysis by fluorescence microscopy and transmission electron microscopy was used to follow morphological changes of the nucleus and cytoskeleton following different ultrasound irradiation intensities. According to the parameters used in the pulsed irradiation of fibroblast cultures, control over the intensity employed is fundamental to the optimal use of therapeutic ultrasound. Cell cultures submitted to low-intensity pulsed ultrasonic irradiation (0.2-0.6 W/cm2) at 10% (1:9 duty cycle) and 20% (2:8 duty cycle) maintained shape and cellular integrity, with little damage. In the group irradiated with an intensity of 0.8 W/cm2, a loss of adhesion was observed along with an alteration in the morphology of some cells at an intensity of 1.0 W/cm2, which resulted in the presence of cellular fragments and a decrease of adhering cells. In cells irradiated at 2.0 W/cm2, there was a complete loss of adhesion and aggregation of cellular fragments. The present study confirms that biophysical properties of pulsed ultrasound may accelerate proliferation processes in different biological tissues.

Light optical precision measurements of the active and inactive Prader-Willi syndrome imprinted regions in human cell nuclei.

Despite the major advancements during the last decade with respect to both knowledge of higher order chromatin organization in the cell nucleus and the elucidation of epigenetic mechanisms of gene control, the true three-dimensional (3D) chromatin structure of endogenous active and inactive gene loci is not known. The present study was initiated as an attempt to close this gap. As a model case, we compared the chromatin architecture between the genetically active and inactive domains of the imprinted Prader-Willi syndrome (PWS) locus in human fibroblast and lymphoblastoid cell nuclei by 3D fluorescence in situ hybridization and quantitative confocal laser scanning microscopy. The volumes and 3D compactions of identified maternal and paternal PWS domains were determined in stacks of light optical serial sections using a novel threshold-independent approach. Our failure to detect volume and compaction differences indicates that possible differences are below the limits of light optical resolution. To overcome this limitation, spectral precision distance microscopy, a method of localization microscopy at the nanometer scale, was used to measure 3D distances between differentially labeled probes located both within the PWS region and in its neighborhood. This approach allows the detection of intranuclear differences between 3D distances down to about 70-90 nm, but again did not reveal clearly detectable differences between active and inactive PWS domains. Despite this failure, a comparison of the experimental 3D distance measurements with computer simulations of chromatin folding strongly supports a non-random higher order chromatin configuration of the PWS locus and argues against 3D configurations based on giant chromatin loops. Our results indicate that the search for differences between endogenous active and inactive PWS domains must be continued at still smaller scales than hitherto possible with conventional light microscopic procedures. The possibilities to achieve this goal are discussed.