We thank Professor Wolf Frommer (Carnegie Institution for Science, Stanford University) for kindly providing us with the glucose FRET plasmid and Dr. Uwe Ludewig (Hohenheim University) for kindly supplying the glutamine FRET construct in the pUTKan plant expression vector. AB is funded by the BBSRC Targeted Priority Studentships program.&#160;Both CK and KP are supported by RCUK Fellowships in Biopharmaceuticals Processing.&#160;CK also wishes to thank Lonza Biologics for their financial support.&#160;The Centre for Synthetic Biology and Innovation is generously supported by the EPSRC.

1. Cell Line Revival and Maintenance
<ol>
	<li>Revive CHO cells in 9 ml&#160;CD-CHO medium supplemented with 8 mM L-Glutamine and 10 ml/L&#160;100x&#160;hypoxanthine/thymidine supplement (complete growth medium).</li>
	<li>Centrifuge at 100 x g for 5 min.</li>
	<li>Resuspend the cells in 10 ml&#160;of fresh complete growth medium.</li>
	<li>Remove a 1 ml&#160;sample and determine the viable cell concentration by light microscopy using the trypan blue dye exclusion method in a hemocytometer.</li>
	<li>Initiate a culture at a seeding density of 3 x 105 cells/ml&#160;in 125 ml&#160;shake flasks.</li>
	<li>Maintain the culture in an incubator at 37 &#176;C, a humidified atmosphere of 5% CO2, on an orbital shaking platform rotating at 120 rpm.</li>
	<li>Subculture every 3-4 days in the complete growth medium at a seeding density of 2 x 105 cells/ml.</li>
</ol>
2. Transfection of the Cell Line with the Plasmid Containing the Biosensor Gene
<ol>
	<li>Prepare plasmid DNA using a large-scale plasmid purification kit.</li>
	<li>Maintain cells at the appropriate conditions (37 &#176;C, 5% CO2) 12-24 hr&#160;prior to transfection to ensure the cells are actively dividing at the time of transfection.</li>
	<li>Count the cells using the trypan blue dye exclusion method, then prepare a working volume of 20 ml&#160;of cell culture in a 125 ml&#160;shake flask at a concentration of 1 x 106 cells/ml.</li>
	<li>Use a suitable transfection kit for the cell line in use. The plasmid DNA to transfection reagents ratio will be dependent on the cell line and vector.&#160;It is recommended that this is optimized by testing a range of ratios within the range specified by the manufacturer prior to conducting the final transfections. Also maintain at least one negative control culture containing the cells but no DNA.</li>
	<li>Incubate for 4 days in static mode and then transfer to a shaking platform rotating at 125 rpm.</li>
	<li>Add the appropriate antibiotic for plasmid selection to a suitable concentration as determined by a kill curve. In this study, zeocin was added to a final concentration of 400 &#956;g/ml&#160;for selection of transfected cells.</li>
	<li>Change media at an appropriate time interval for the cell line, adding antibiotic each time, until cells in control well have died.</li>
	<li>Use the most confluent wells to progress to shaking cultures.</li>
	<li>Establish a cell bank by freezing the cells in cryogenic vials containing 107&#160;viable cells in 1 ml&#160;of freeze mix. In this work, this consists of 92.5% growth medium and 7.5% dimethyl sulfoxide.</li>
</ol>
3. Batch and Fed-batch Cell Growth Curve
<ol>
	<li>Follow instructions for cell maintenance above to establish triplicate cell cultures of the transfected CHO cells in 250 ml&#160;shake flasks with a working volume of 50 ml.</li>
	<li>Maintain the cultures in a humidified cell incubator at 37 &#176;C, with 5% CO2, on an orbital shaking platform rotating at 125 rpm, and remove 4.1 ml&#160;samples from each growing culture at 24 hr intervals.</li>
	<li>Use 100 &#956;l&#160;of the sample to determine the viable cell concentration and cell viability with the trypan blue dye exclusion method.</li>
	<li>Repeat until the viable cell concentration is reduced to zero.</li>
	<li>Repeat for the fed-batch cell cultures supplementing with the appropriate amount of glucose or glutamine on day 6 to restore their concentrations to their initial values of 36 mM and 4 mM, respectively. It is recommended that additional control cultures are also maintained, which are to be fed with the same volume (12 ml&#160;in this case) of pure water.</li>
</ol>
4. FRET Ratio Measurements
<ol>
	<li>Take 2 ml&#160;of the daily samples removed in step 3.2 above and centrifuge at 100 x g for 5 min&#160;at 4 &#176;C.</li>
	<li>Resuspended the cell pellet in 2 ml&#160;of ice cold phosphate buffered saline (PBS). Transfer this into a 6-well plate and add a blank sample containing no cells to one well.</li>
	<li>Measure the levels of blue and yellow fluorescence immediately at an excitation wavelength of 430/435 nm and emission wavelengths of 465/435 nm (blue) and 520/510 nm (yellow).</li>
	<li>Calculate the FRET ratios (ratio of yellow fluorescence detected over blue fluorescence detected).</li>
</ol>
5. Metabolite Assays
<ol>
	<li>Take 2 ml&#160;of the daily samples removed in step 3.2 above and centrifuge at 100 x g for 5 min&#160;at 4 &#176;C. Remove the supernatant.</li>
	<li>Resuspend the cell pellet in 3 ml&#160;ice cold PBS and centrifuge again at 100 x g for 5 min.</li>
	<li>Remove the supernatant and resuspend the cell pellet in 3 ml&#160;ice cold PBS as above. Sonicate the sample 5x for 3 min&#160;each at a pulse of 15 sec&#160;on and 15 sec&#160;off. At this point, the cell extracts may be frozen if desired.</li>
	<li>Use an appropriate glucose assay kit as per the manufacturer&#8217;s instructions on samples of cell extracts to determine the intracellular glucose concentration (see table of materials). 
	Note: Use appropriate standards to construct a standard curve. In this work, the concentration of standards ranged between 0-100 mM.</li>
	<li>Using the readings for the standards, construct the standard curve and find the linear equation of best fit (in this case: y = 1310.51x - 723.43 where y is the absorbance reading and x is the glucose concentration).</li>
	<li>Calculate the glucose concentrations using the standard curve and taking the dilution into account. The intracellular glucose concentration can then be calculated using this equation: 
	<img alt="" fo:content-width="4.5in" src="/files/ftp_upload/51200/book_bg.png" width="500" /> 
	For CHO cells, the single cell volume was calculated using a cell diameter of 12 &#956;M&#160;12.</li>
	<li>Use an appropriate glutamine assay kit as per the manufacturer&#8217;s instructions on samples of cell extracts to determine the intracellular glutamine concentration (see table of materials). 
	Note: Use appropriate standards to construct a standard curve. In this work, the concentration of standards ranged between 0-2 mM.</li>
	<li>As in 5.5 above, construct the calibration curve (in this case y = 203.1x + 17.1 where y is the absorbance reading and x is the glucose concentration)</li>
	<li>Using the standard curve, calculate the glutamine concentration of the samples, taking the dilution into account. The intracellular glutamine concentration can be calculated using Equation 1 above.</li>
</ol>

<ol>
	<li>Moser, I., Jobst, G., Urban, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biosensor+arrays+for+simultaneous+measurement+of+glucose,+lactate,+glutamate,+and+glutamine.">Biosensor arrays for simultaneous measurement of glucose, lactate, glutamate, and glutamine.</a> Biosens. Bioelectron. 17 (4), 297-302 (2002).</li><li>Billingsley, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+nano-optodes+for+glucose+detection.">Fluorescent nano-optodes for glucose detection.</a> Anal. Chem. 82 (9), 3707-3713 (2010).</li><li>Dattelbaum, J. D., Lakowicz, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+Determination+of+Glutamine+Using+a+Genetically+Engineered+Protein.">Optical Determination of Glutamine Using a Genetically Engineered Protein.</a> Anal. Biochem. 291 (1), 88-95 (2001).</li><li>Kfouri, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+a+miniaturized+wireless+fluorescence-based+diagnostic+imaging+system.">Toward a miniaturized wireless fluorescence-based diagnostic imaging system.</a> IEEE J. Sel. Top. Quantum Electron. 14 (1), 226-234 (2008).</li><li>Dittrich, P. S., Manz, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-molecule+fluorescence+detection+in+microfluidic+channels&#8212;the+Holy+Grail+in+muTAS.">Single-molecule fluorescence detection in microfluidic channels&#8212;the Holy Grail in muTAS.</a> Analytical and Bioanalytical Chemistry. 382 (8), 1771-1782 (2005).</li><li>Hou, B. H., Codamo, J., Pilbrough, W., Hughes, B., Gray, P. P., Munro, T. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+sensors+for+monitoring+dynamic+changes+of+intracellular+metabolite+levels+in+mammalian+cells.">Optical sensors for monitoring dynamic changes of intracellular metabolite levels in mammalian cells.</a> Nat. Protoc. 6 (7), 1818-1833 (2011).</li><li>Bermejo, C., Haerizadeh, F., Takanaga, H., Chermak, D., Frommer, W. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+analysis+of+cytosolic+glucose+and+ATP+levels+in+yeast+using+optical+sensors.">Dynamic analysis of cytosolic glucose and ATP levels in yeast using optical sensors.</a> Biochem. J. 432, 399-406 (2010).</li><li>Yang, H. Y., Bogner, M., Stierhof, Y. D., Ludewig, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=H(+)-independent+glutamine+transport+in+plant+root+tips.">H(+)-independent glutamine transport in plant root tips.</a> Plos One. 5, (2010).</li><li>Fehr, M., Takanaga, H., Ehrhardt, D. W., Frommer, W. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+for+high-cavacity+bidirectional+glucose+transport+across+the+endoplasmic+reticulum+membrane+by+genetically+encoded+fluorescence+resonance+energy+transfer+nanosensors.">Evidence for high-cavacity bidirectional glucose transport across the endoplasmic reticulum membrane by genetically encoded fluorescence resonance energy transfer nanosensors.</a> Mol. Cell. Biol. 25 (24), 11102-11112 (2005).</li><li>Ai, H. W., Hazelwood, K. L., Davidson, M. W., Campbell, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+protein+FRET+pairs+for+ratiometric+imaging+of+dual+biosensors.">Fluorescent protein FRET pairs for ratiometric imaging of dual biosensors.</a> Nat. Methods. 5 (5), 401-403 (2008).</li><li>Ouyang, M. X., Sun, J., Chien, S., Wang, Y. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+hierarchical+relationship+of+Src+and+Rac+at+subcellular+locations+with+FRET+biosensors.">Determination of hierarchical relationship of Src and Rac at subcellular locations with FRET biosensors.</a> Proc. Natl. Acad. Sci. U.S.A. 105 (38), 14353-14358 (2008).</li><li>Han, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cultivation+of+recombinant+Chinese+hamster+ovary+cells+grown+as+suspended+aggregates+in+stirred+vessels.">Cultivation of recombinant Chinese hamster ovary cells grown as suspended aggregates in stirred vessels.</a> J. Biosci. Bioeng. 102 (5), 430-435 (2006).</li><li>Deuschle, K., Okumoto, S., Fehr, M., Looger, L. L., Kozhukh, L., Frommer, W. 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The authors have nothing to disclose.

The FIBS enable in vivo and in situ quantitation of key molecules, in this case growth-limiting nutrients, removing uncertainties arising from quenching and extraction methods. The findings suggest that there is a good correlation between the FIBS signal and the intracellular concentrations in the range of 1-5 mM for glucose and 0.3-2 mM for glutamine. In batch CHO cell culture, these concentrations are encountered in the exponential, stationary, and early decline phases. The exponential and stationary ...

Metabolite monitoring has various applications in bioprocessing, including process development, media and feed design, and metabolic engineering. Various methods are available for concentration measurements through the use of enzymatic1, chemical2, or binding assays3. An interesting option is the use of fluorescent, protein-based in vivo biological sensors as reporters of the intracellular concentration of key metabolites. In ultra-low volume assays, fluorescence is a convenient tool as miniaturization actually improves the signal-to-noise ratio4,5 and protein-based sensors can be genetically encoded meaning that no exogenous reagents are necessary for metabolite analysis. F&#246;rster Resonance Energy Transfer (FRET) biosensors consist of two fluorescent proteins connected by a ligand binding domain. FRET is a nonradiative transfer of energy from a photo-excited donor to an acceptor fluorescent molecule located in close proximity (&#60;100). Ligand cleavage or binding causes a conformational change in the sensor, which, in turn, induces a change in the proximity of the fluorophores, leading to a change in FRET efficiency measured by the change in the emission spectrum. FRET integrated biological sensors (FIBS) are constitutively produced within the cell line and their spectral characteristics change based on the concentration of metabolite within the cell. FIBS have fast response times making them ideal for taking measurements for dynamic models6. Previous applications include monitoring single7-9 and multiple10 metabolites&#160;and providing data on spatiotemporal distribution11. FIBS can be created in two configurations: Apo-Max, where ligand binding disrupts the proximity of the fluorophores lowering energy transfer and Apo-Min, where ligand binding brings the two fluorophores into closer contact (Figure 1).
In this work, a protocol is presented for constructing Chinese hamster ovary (CHO) cell lines that constitutively express a FIBS for a metabolite, glucose or glutamine. A methodology is established for the calibration of the sensor in vivo to enable future quantitative measurements of intracellular metabolite concentration, as presented in Figure 2. Based on this, the intracellular concentration of glucose or glutamine can be determined in fed-batch CHO cell cultures, to which the two nutrients were added in high concentrations in-process. The results demonstrate that using the fluorescent signal from the FIBS and the previously constructed calibration curve, accurately prediction of the intracellular concentration is possible, as confirmed by an independent enzymatic assay. This method offers substantial advantages over current analytical technologies because it is noninvasive, low-cost and fast, giving a real-time signal of the FIBS that can be monitored throughout the culture.

<table border="0" cellpadding="0" cellspacing="0" width="936">
	<colgroup>
		<col />
		<col span="2" />
		<col />
	</colgroup>
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">CHO-S Cells</td>
			<td style="width:120px;">Life Tecnologies</td>
			<td style="width:120px;">11619-012</td>
			<td style="width:459px;">Cell line will vary depending on the goals of the study</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">pCDNA4/TO vector&#160;</td>
			<td style="width:120px;">Life Tecnologies</td>
			<td style="width:120px;"></td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">TransIT-PRO Transfection Reagent</td>
			<td style="width:120px;">Mirus Bio</td>
			<td style="width:120px;">MIR 5700</td>
			<td style="width:459px;">Transfections can be accomplished using any method suitable for the cell line under study</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">Zeocin</td>
			<td style="width:120px;">Invivogen</td>
			<td style="width:120px;"></td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">CD-CHO medium</td>
			<td style="width:120px;">Life Technologies</td>
			<td style="width:120px;">10743-011</td>
			<td style="width:459px;">Cell growth medium is dependent upon the cells under study</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">100X HT Supplement</td>
			<td style="width:120px;">Life Technologies</td>
			<td style="width:120px;">11067-030</td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">L-Glutamine 200 mM (100X), Liquid</td>
			<td style="width:120px;">Life Technologies</td>
			<td style="width:120px;">25030032</td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">InfinitePRO 200 plate reader</td>
			<td style="width:120px;">Tecan</td>
			<td style="width:120px;">FLx800TBI</td>
			<td style="width:459px;">Any 96-well fluorescence plate reader that can access the required wavelengths can be substituted</td>
		</tr>
		<tr height="21">
			<td height="190" rowspan="6" style="height:190px;width:239px;">Filters for plate reader</td>
			<td rowspan="6" style="width:120px;">Tecan</td>
			<td align="right" style="width:120px;">30000463</td>
			<td rowspan="6" style="width:459px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:120px;">(520NM BW 10NM)</td>
		</tr>
		<tr height="21">
			<td align="right" height="21" style="height:21px;width:120px;">30022786</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:120px;">(430NM BW 35NM)</td>
		</tr>
		<tr height="21">
			<td align="right" height="21" style="height:21px;width:120px;">30022787</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:120px;">(465NM BW 35NM)</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">Maxiprep Plasmid Purification Kit</td>
			<td style="width:120px;">Qiagen</td>
			<td style="width:120px;">12163</td>
			<td style="width:459px;">Any suitable kit can be substituted</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">Amplex Red glucose/glucose oxidase assay kit</td>
			<td style="width:120px;">Invitrogen</td>
			<td style="width:120px;">A22189</td>
			<td style="width:459px;">Any suitable kit can be substituted</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">EnzyChrom&#160; Glutamine Assay Kit</td>
			<td style="width:120px;">BioAssay systems</td>
			<td style="width:120px;">EOAC-100</td>
			<td style="width:459px;">Any suitable kit can be substituted</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">Improved Neubauer haemocytometer</td>
			<td style="width:120px;">Fisher Scientific</td>
			<td style="width:120px;">MNK-420-010N</td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">Incubator&#160;</td>
			<td style="width:120px;">Nuaire</td>
			<td style="width:120px;">NU-5510E</td>
			<td style="width:459px;"></td>
		</tr>
	</tbody>
</table>

fibs-enabled noninvasive metabolic profiling

In the era of computational biology, new high throughput experimental systems are necessary in order to populate and refine models so that they can be validated for predictive purposes. Ideally such systems would be low volume, which precludes sampling and destructive analyses when time course data are to be obtained. What is needed is an in situ monitoring tool which can report the necessary information in real-time and noninvasively. An interesting option is the use of fluorescent, protein-based in vivo biological sensors as reporters of intracellular concentrations. One particular class of in vivo biosensors that has found applications in metabolite quantification is based on F&#246;rster Resonance Energy Transfer (FRET) between two fluorescent proteins connected by a ligand binding domain. FRET integrated biological sensors (FIBS) are constitutively produced within the cell line, they have fast response times and their spectral characteristics change based on the concentration of metabolite within the cell. In this paper, the method for constructing Chinese hamster ovary (CHO) cell lines that constitutively express a FIBS for glucose and glutamine and calibrating the FIBS in vivo in batch cell culture in order to enable future quantification of intracellular metabolite concentration is described. Data from fed-batch CHO cell cultures demonstrates that the FIBS was able in each case to detect the resulting change in the intracellular concentration. Using the fluorescent signal from the FIBS and the previously constructed calibration curve, the intracellular concentration was accurately determined as confirmed by an independent enzymatic assay.

An overview of the methodology is presented in Figure 2. In the work presented herein, CHO cells were transfected with the FIBS vector and stable cell lines were selected at an antibiotic pressure of 400 &#956;g/ml&#160;zeocin. Two separate stable cell lines constitutively expressing the glucose and glutamine sensors were therefore created. Figure 1 depicts the configurations of the two biosensors used in this study. The glucose sensor is based on the Apo-Max principle and the correspond...

Watch this Scientific Journal Video about FIBS-enabled Noninvasive Metabolic Profiling at JoVE.com

FIBS-enabled Noninvasive Metabolic Profiling

A description of how to calibrate F&#246;rster Resonance Energy Transfer integrated biological sensors (FIBS) for in situ metabolic profiling is presented.&#160;The FIBS can be used to measure intracellular levels of metabolites noninvasively aiding in the development of metabolic models and high throughput screening of bioprocess conditions.

In the era of computational biology, new high throughput experimental systems are necessary in order to populate and refine models so that they can be ...

fibs-enabled-noninvasive-metabolic-profiling

Research

JoVE Journal

Bioengineering

9.6K Aufrufe.  Imperial College London.  Eine Beschreibung, wie Förster Resonance Energy Transfer integriert biologischen Sensoren (FIBS) zur in-situ-Kalibrierung Metabolic Profiling vorgestellt. Die FIBS kann verwendet werden, um die intrazellulären Spiegel von Metaboliten nicht-invasiv Unterstützung bei der Entwicklung von Stoffwechselmodelle und Hochdurchsatz-Screening von Bioprozess-Bedingungen zu messen. 

Serie: FIBS-enabled Noninvasive Metabolic Profiling

High Throughput MicroRNA Profiling: Optimized Multiplex qRT-PCR at Nanoliter Scale on the Fluidigm Dynamic ArrayTM IFCs

The broad involvement of miRNAs in critical processes underlying development, tissue homoeostasis and disease has led to a surging interest among the research and pharmaceutical communities. To study miRNAs, it is essential that the quantification of microRNA levels is accurate and robust. By comparing wild-type to small RNA deficient mouse embryonic stem cells (mESC), we revealed a lack of accuracy and robustness in previous published multiplex qRT-PCR techniques. Here, we describe an optimized method, including purifying away excessive primers from previous multiplex steps before singleplex real time detection, which dramatically increases the accuracy and robustness of the technique. Furthermore, we explain how performing the technique on a microfluidic chip at nanoliter volumes significantly reduces reagent costs and permits time effective high throughput miRNA expression profiling.

Here we describe an optimized multiplex reverse transcriptase quantitative PCR (qRT-PCR) protocol in combination with a microfluidic platform as a cost and time effective high-throughput screening tool for microRNA (miRNA) expression levels, especially when working with limited amounts of sample.

The broad involvement of miRNAs in critical processes underlying development, tissue homoeostasis and disease has led to a surging interest among the ...

In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

This study demonstrates a novel biomechanics testing protocol. The advantage of this protocol includes the use of an in situ loading device coupled to a high resolution X-ray microscope, thus enabling visualization of internal structural elements under simulated physiological loads and wet conditions. Experimental specimens will include intact bone-periodontal ligament (PDL)-tooth fibrous joints. Results will illustrate three important features of the protocol as they can be applied to organ level biomechanics: 1) reactionary force vs. displacement: tooth displacement within the alveolar socket and its reactionary response to loading, 2) three-dimensional (3D) spatial configuration and morphometrics: geometric relationship of the tooth with the alveolar socket, and 3) changes in readouts 1 and 2 due to a change in loading axis, i.e. from concentric to eccentric loads. Efficacy of the proposed protocol will be evaluated by coupling mechanical testing readouts to 3D morphometrics and overall biomechanics of the joint. In addition, this technique will emphasize on the need to equilibrate experimental conditions, specifically reactionary loads prior to acquiring tomograms of fibrous joints. It should be noted that the proposed protocol is limited to testing specimens under ex vivo conditions, and that use of contrast agents to visualize soft tissue mechanical response could lead to erroneous conclusions about tissue and organ-level biomechanics.

In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

In this study, the use of an in situ loading device coupled with micro-X-ray computed tomography for fibrous joint biomechanics will be discussed. Experimental readouts identifiable with an overall change in joint biomechanics will include: 1) reactionary force vs. displacement, i.e. tooth displacement within the alveolar socket and its reactionary response to loading, 2) three-dimensional (3D) spatial configuration and morphometrics, i.e.&#160;geometric relationship of the tooth with the alveolar socket, and 3) changes in readouts 1 and 2 due to a change in loading axis, i.e. concentric or eccentric loads.

This study demonstrates a novel biomechanics testing protocol. The advantage of this protocol includes the use of an in situ loading device coupled to a ...

Quantification and Size-profiling of Extracellular Vesicles Using Tunable Resistive Pulse Sensing

Extracellular vesicles (EVs), including &#8216;microvesicles&#8217; and &#8216;exosomes&#8217;, are highly abundant in bodily fluids. Recent years have witnessed a tremendous increase in interest in EVs. EVs have been shown to play important roles in various physiological and pathological processes, including coagulation, immune responses, and cancer. In addition, EVs have potential as therapeutic agents, for instance as drug delivery vehicles or as regenerative medicine. Because of their small size (50 to 1,000 nm) accurate quantification and size profiling of EVs is technically challenging.
This protocol describes how tunable resistive pulse sensing (tRPS) technology, using the qNano system, can be used to determine the concentration and size of EVs. The method, which relies on the detection of EVs upon their transfer through a nano sized pore, is relatively fast, suffices the use of small sample volumes and does not require the purification and concentration of EVs. Next to the regular operation protocol an alternative approach is described using samples spiked with polystyrene beads of known size and concentration. This real-time calibration technique can be used to overcome technical hurdles encountered when measuring EVs directly in biological fluids.

Extracellular vesicles play important roles in physiological and pathological processes, including coagulation, immune responses, and cancer or as potential therapeutic agents in drug delivery or regenerative medicine. This protocol presents methods for the quantification and size characterization of isolated and non-isolated extracellular vesicles in various fluids using tunable resistive pulse sensing.

Extracellular vesicles (EVs), including &#8216;microvesicles&#8217; and &#8216;exosomes&#8217;, are highly abundant in bodily fluids. Recent years have ...

Easy and Accurate Mechano-profiling on Micropost Arrays

Cell culture substrates with integrated flexible microposts enable a user to study the mechanical interactions between cells and their immediate surroundings. Particularly, cell-substrate interactions are the main interest. Today micropost arrays are a well-characterized and established method with a broad range of applications that have been published over the last decade. However, there seems to be a reservation among biologists to adapt the technique due to the lengthy and challenging process of micropost manufacture along with the lack of easily approachable software for analyzing images of cells interacting with microposts. 
The force read-out from microposts is surprisingly easy. A micropost acts like a spring with the cell ideally attached at its tip. Depending on size a cell applies force from its cytoskeleton through one or multiple focal adhesion points to the micropost, thus deflecting the micropost. The amount of deflection correlates directly to the applied force in direction and in magnitude. The number of microposts covered by a cell and the post deflection patterns are characteristic and allow determination of values like force per post and many biologically relevant parameters that allow &#8220;mechano-profiling&#8221; of cell phenotypes.
A convenient method for mechano-profiling is described here combining the first generation of ready-to-use commercially available microposts with an in-house developed software package that is now accessible to all researchers. As a demonstration of typical application, single images of bone cancer cells were taken in bright-field microscopy for mechano-profiling of cell line models of metastasis. This combination of commercial traction force sensors and open source software for analysis allows for the first time a rapid implementation of the micropost array technique into routine lab work done by non-expert users. Furthermore, a robust and streamlined analysis process enables a user to analyze a large number of micropost images in a highly time-efficient manner.

Described are protocols for quantifying mechanical interactions between adherent cells and microstructured substrates. These interactions are closely linked to essential cell behaviors including migration, proliferation, differentiation, and apoptosis. The protocols present an open-source image analysis software called MechProfiler, which enables determination of involved forces for each micropost.

Cell culture substrates with integrated flexible microposts enable a user to study the mechanical interactions between cells and their immediate ...

Metabolic Glycoengineering of Sialic Acid Using N-acyl-modified Mannosamines

Sialic acid (Sia) is a highly important constituent of glycoconjugates, such as N- and O-glycans or glycolipids. Due to its position at the non-reducing termini of oligo- and polysaccharides, as well as its unique chemical characteristics, sialic acid is involved in a multitude of different receptor-ligand interactions. By modifying the expression of sialic acid on the cell surface, sialic acid-dependent interactions will consequently be influenced. This can be helpful to investigate sialic acid-dependent interactions and has the potential to influence certain diseases in a beneficial way. Via metabolic glycoengineering (MGE), the expression of sialic acid on the cell surface can be modulated. Herein, cells, tissues, or even entire animals are treated with C2-modified derivatives of N-acetylmannosamine (ManNAc). These amino sugars act as sialic acid precursor molecules and therefore are metabolized to the corresponding sialic acid species and expressed on glycoconjugates. Applying this method produces intriguing effects on various biological processes. For example, it can drastically reduce&#160;the expression of polysialic acid (polySia) in treated neuronal cells and thus affects neuronal growth and differentiation. Here, we show the chemical synthesis of two of the most common C2-modified N-acylmannosamine derivatives, N-propionylmannosamine (ManNProp) as well as N-butanoylmannosamine (ManNBut), and further show how these non-natural amino sugars can be applied in cell culture experiments. The expression of modified sialic acid species is quantified by high performance liquid chromatography (HPLC) and further analyzed via mass spectrometry. The effects on polysialic acid expression are elucidated via Western blot using a commercially available polysialic acid antibody.

Metabolic Glycoengineering of Sialic Acid Using N-acyl-modified Mannosamines

Sialic acid is a typical monosaccharide-unit found in glycoconjugates. It is involved in a plethora of molecular and cellular interactions. Here we present a method to modify cell surface sialic acid expression using metabolic glycoengineering with N-acetylmannosamine derivatives.

Sialic acid (Sia) is a highly important constituent of glycoconjugates, such as N- and O-glycans or glycolipids. Due to its position at the non-reducing ...

Metabolic Support of Excised, Living Brain Tissues During Magnetic Resonance Microscopy Acquisition

This protocol describes the procedures necessary to support normal metabolic functions of acute brain slice preparations during the collection of magnetic resonance (MR) microscopy data. While it is possible to perform MR collections on living, excised mammalian tissue, such experiments have traditionally been constrained by resolution limits and are thus incapable of visualizing tissue microstructure. Conversely, MR protocols that did achieve microscopic image resolution required the use of fixed samples to accommodate the need for static, unchanging conditions over lengthy scan times. The current protocol describes the first available MR technique that enables imaging of living, mammalian tissue samples at microscopic resolutions. Such data is of great importance to the understanding of how pathology-based contrast changes occurring at the microscopic level influence the content of macroscopic MR scans such as those used in the clinic. Once such an understanding is realized, diagnostic methods with greater sensitivity and accuracy can be developed, which will translate directly to earlier disease treatment, more accurate therapy monitoring and improved patient outcomes.
While the described methodology focuses on brain slice preparations, the protocol is adaptable to any excised tissue slice given that changes are made to the gas and perfusate preparations to accommodate the tissue&#39;s specific metabolic needs. Successful execution of the protocol should result in living, acute slice preparations that exhibit MR diffusion signal stability for periods up to 15.5 h. The primary advantages of the current system over other MR compatible perfusion apparatuses are its compatibility with the MR microscopy hardware required to attain higher resolution images and ability to provide constant, uninterrupted flow with carefully regulated perfusate conditions. Reduced sample throughput is a consideration with this design as only one tissue slice may be imaged at a time.

The current protocol describes a method by which users can maintain viability of acute hippocampal and cortical slice preparations during the collection of magnetic resonance microscopy data.

This protocol describes the procedures necessary to support normal metabolic functions of acute brain slice preparations during the collection of magnetic ...

Calorespirometry: A Powerful, Noninvasive Approach to Investigate Cellular Energy Metabolism

Many cell lines used in basic biological and biomedical research maintain energy homeostasis through a combination of both aerobic and anaerobic respiration. However, the extent to which both pathways contribute to the landscape of cellular energy production is consistently overlooked. Transformed cells cultured in saturating levels of glucose often show a decreased dependency on oxidative phosphorylation for ATP production, which is compensated by an increase in substrate-level phosphorylation. This shift in metabolic poise allows cells to proliferate despite the presence of mitochondrial toxins. In neglecting the altered metabolic poise of transformed cells, results from a pharmaceutical screening may be misinterpreted since the potentially mitotoxic effects may not be detected using model cell lines cultured in the presence of high glucose concentrations. This protocol describes the pairing of two powerful techniques, respirometry and calorimetry, which allows for the quantitative and noninvasive assessment of both aerobic and anaerobic contributions to cellular ATP production. Both aerobic and anaerobic respirations generate heat, which can be monitored via calorimetry. Meanwhile, measuring the rate of oxygen consumption can assess the extent of aerobic respiration. When both heat dissipation and oxygen consumption are measured simultaneously, the calorespirometric ratio can be determined. The experimentally obtained value can then be compared to the theoretical oxycaloric equivalent and the extent of the anaerobic respiration can be judged. Thus, calorespirometry provides a unique method to analyze a wide range of biological questions, including drug development, microbial growth, and fundamental bioenergetics under both normoxic and hypoxic conditions.

This protocol describes calorespirometry, the direct and simultaneous measurement of both heat dissipation and respiration, which provides a noninvasive approach to assess energy metabolism. This technique is used to assess the contribution of both aerobic and anaerobic pathways to energy utilization by monitoring the total cellular energy flow.

Many cell lines used in basic biological and biomedical research maintain energy homeostasis through a combination of both aerobic and anaerobic ...

Nanosensors to Detect Protease Activity In Vivo for Noninvasive Diagnostics

Proteases are multi-functional enzymes that specialize in the hydrolysis of peptide-bonds and control broad biological processes including homeostasis and allostasis. Moreover, dysregulated protease activity drives pathogenesis and is a functional biomarker of diseases such as cancer; therefore, the ability to detect protease activity in vivo may provide clinically relevant information for biomedical diagnostics. The goal of this protocol is to create nanosensors that probe for protease activity in vivo by producing a quantifiable signal in urine. These protease nanosensors consist of two components: a nanoparticle and substrate. The nanoparticle functions to increase circulation half-life and substrate delivery to target disease sites. The substrate is a short peptide sequence (6-8 AA), which is designed to be specific to a target protease or group of proteases. The substrate is conjugated to the surface of the nanoparticle and is terminated by a reporter, such as a fluorescent marker, for detection. As dysregulated proteases cleave the peptide substrate, the reporter is filtered into urine for quantification as a biomarker of protease activity. Herein we describe construction of a nanosensor for matrix metalloproteinase 9 (MMP9), which is associated with tumor progression and metastasis, for detection of colorectal cancer in a mouse model.

Nanosensors to Detect Protease Activity In Vivo for Noninvasive Diagnostics

Proteases are tightly regulated enzymes involved in fundamental biological processes, and dysregulated protease activity drives progression of complex diseases such as cancer. This method&#39;s goal is to create nanosensors that measure protease activity in vivo by producing a cleavage signal that is detectable from host urine and discriminates disease.

Proteases are multi-functional enzymes that specialize in the hydrolysis of peptide-bonds and control broad biological processes including homeostasis and ...

Measuring Global Cellular Matrix Metalloproteinase and Metabolic Activity in 3D Hydrogels

Three-dimensional (3D) cell culture systems often more closely recapitulate in vivo cellular responses and functions than traditional two-dimensional (2D) culture systems. However, measurement of cell function in 3D culture is often more challenging. Many biological assays require retrieval of cellular material which can be difficult in 3D cultures. One way to address this challenge is to develop new materials that enable measurement of cell function within the material. Here, a method is presented for measurement of cellular matrix metalloproteinase (MMP) activity in 3D hydrogels in a 96-well format. In this system, a poly(ethylene glycol) (PEG) hydrogel is functionalized with a fluorogenic MMP cleavable sensor. Cellular MMP activity is proportional to fluorescence intensity and can be measured with a standard microplate reader. Miniaturization of this assay to a 96-well format reduced the time required for experimental set up by 50% and reagent usage by 80% per condition as compared to the previous 24-well version of the assay. This assay is also compatible with other measurements of cellular function. For example, a metabolic activity assay is demonstrated here, which can be conducted simultaneously with MMP activity measurements within the same hydrogel. The assay is demonstrated with human melanoma cells encapsulated across a range of cell seeding densities to determine the appropriate encapsulation density for the working range of the assay. After 24 h of cell encapsulation, MMP and metabolic activity readouts were proportional to cell seeding density. While the assay is demonstrated here with one fluorogenic degradable substrate, the assay and methodology could be adapted for a wide variety of hydrogel systems and other fluorescent sensors. Such an assay provides a practical, efficient and easily accessible 3D culturing platform for a wide variety of applications.

Here, a protocol is presented for encapsulating and culturing cells in poly(ethylene glycol) (PEG) hydrogels functionalized with a fluorogenic matrix metalloproteinase (MMP)-degradable peptide. Cellular MMP and metabolic activity are measured directly from the hydrogel cultures using a standard microplate reader.

Three-dimensional (3D) cell culture systems often more closely recapitulate in vivo cellular responses and functions than traditional two-dimensional (2D) ...

A Human 3D Extracellular Matrix-Adipocyte Culture Model for Studying Matrix-Cell Metabolic Crosstalk

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of cellular function. The ECM plays a particularly important role in adipose tissue function in obesity, and alterations in adipose tissue ECM deposition and composition are associated with metabolic disease in mice and humans. Tractable in vitro models that permit dissection of the roles of the ECM and cells in contributing to global tissue phenotype are sparse. We describe a novel 3D in vitro model of human ECM-adipocyte culture that permits study of the specific roles of the ECM and adipocytes in regulating adipose tissue metabolic phenotype. Human adipose tissue is decellularized to isolate ECM, which is subsequently repopulated with preadipocytes that are then differentiated within the ECM into mature adipocytes. This method creates ECM-adipocyte constructs that are metabolically active and retain characteristics of the tissues and patients from which they are derived. We have used this system to demonstrate disease-specific ECM-adipocyte crosstalk in human adipose tissue. This culture model provides a tool for dissecting the roles of the ECM and adipocytes in contributing to global adipose tissue metabolic phenotype and permits study of the role of the ECM in regulating adipose tissue homeostasis.

We describe a 3D human extracellular matrix-adipocyte in vitro culture system that permits dissection of the roles of the matrix and adipocytes in contributing to adipose tissue metabolic phenotype.

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of ...