Name: measuring relative insulin secretion using a co-secreted luciferase surrogate
Uploaded: 2019-06-25T15:00:00
Description: Watch this Scientific Journal Video about Measuring Relative Insulin Secretion using a Co-Secreted Luciferase Surrogate at JoVE.com

The authors thank all current and former members of the Cobb laboratory for valuable work and discussions, and Dionne Ware for administrative assistance. Michael Kalwat is supported by a Juvenile Diabetes Research Foundation SRA-2019-702-Q-R. This work was made possible through NIH R37 DK34128 and Welch Foundation Grant I1243 to Melanie Cobb. Early parts of this work were also supported by an NIH F32 DK100113 to Michael Kalwat.

1. Preparation of reagents, media and buffers (Table 1)
<ol>
	<li>Prepare MIN6 complete media in 500 mL of high-glucose (4.5 g/L) Dulbecco&#39;s modified Eagle medium (DMEM) with the following additives: 15% fetal bovine serum (FBS), 100 units/mL penicillin, 100 &#956;g/mL streptomycin, 292 &#956;g/mL L-glutamine, and 50 &#956;M &#946;-mercaptoethanol. 
	NOTE: The stable cell line in this case is maintained in 250 &#181;g/mL of G418 antibiotic.</li>
	<li>Prepare Krebs-Ringer bicarbonate buffer (KRBH) by making a s...

<ol>
	<li>Kalwat, M. A., 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=Insulin+promoter-driven+Gaussia+luciferase-based+insulin+secretion+biosensor+assay+for+discovery+of+beta-cell+glucose-sensing+pathways.">Insulin promoter-driven Gaussia luciferase-based insulin secretion biosensor assay for discovery of beta-cell glucose-sensing pathways.</a> ACS Sensors. 1 (10), 1208-1212 (2016).</li><li>Burns, S. 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=High-throughput+luminescent+reporter+of+insulin+secretion+for+discovering+regulators+of+pancreatic+Beta-cell+function.">High-throughput luminescent reporter of insulin secretion for discovering regulators of pancreatic Beta-cell function.</a> Cell Metabolism. 21 (1), 126-137 (2015).</li><li>Rajan, S., 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=In+vitro+processing+and+secretion+of+mutant+insulin+proteins+that+cause+permanent+neonatal+diabetes.">In vitro processing and secretion of mutant insulin proteins that cause permanent neonatal diabetes.</a> American Journal of Physiology - Endocrinology and Metabolism. 298 (3), E403-E410 (2010).</li><li>Watkins, S., 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=Imaging+Secretory+Vesicles+by+Fluorescent+Protein+Insertion+in+Propeptide+Rather+Than+Mature+Secreted+Peptide.">Imaging Secretory Vesicles by Fluorescent Protein Insertion in Propeptide Rather Than Mature Secreted Peptide.</a> Traffic. 3 (7), 461-471 (2002).</li><li>Welsh, J. 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S., 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=Connexin-36+Gap+Junctions+Regulate+In+Vivo+First-+and+Second-Phase+Insulin+Secretion+Dynamics+and+Glucose+Tolerance+in+the+Conscious.">Connexin-36 Gap Junctions Regulate In Vivo First- and Second-Phase Insulin Secretion Dynamics and Glucose Tolerance in the Conscious.</a> Diabetes. 61 (7), 1700-1707 (2012).</li><li>Benninger, R. K. P., Head, W. S., Zhang, M., Satin, L. S., Piston, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gap+junctions+and+other+mechanisms+of+cell-cell+communication+regulate+basal+insulin+secretion+in+the+pancreatic+islet.">Gap junctions and other mechanisms of cell-cell communication regulate basal insulin secretion in the pancreatic islet.</a> The Journal of Physiology. 589 (22), 5453-5466 (2011).</li><li>Konstantinova, I., 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=EphA-Ephrin-A-mediated+beta+cell+communication+regulates+insulin+secretion+from+pancreatic+islets.">EphA-Ephrin-A-mediated beta cell communication regulates insulin secretion from pancreatic islets.</a> Cell. 129 (2), 359-370 (2007).</li><li>Jaques, F., 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=Dual+effect+of+cell-cell+contact+disruption+on+cytosolic+calcium+and+insulin+secretion.">Dual effect of cell-cell contact disruption on cytosolic calcium and insulin secretion.</a> Endocrinology. 149 (5), 2494-2505 (2008).</li><li>Calabrese, A., 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=Connexin+36+Controls+Synchronization+of+Ca2++Oscillations+and+Insulin+Secretion+in+MIN6+Cells.">Connexin 36 Controls Synchronization of Ca2+ Oscillations and Insulin Secretion in MIN6 Cells.</a> Diabetes. 52 (2), 417-424 (2003).</li><li>Bielefeld-Sevigny, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AlphaLISA+immunoassay+platform-+the+&amp;#34;no-wash&amp;#34;+high-throughput+alternative+to+ELISA.">AlphaLISA immunoassay platform- the &amp;#34;no-wash&amp;#34; high-throughput alternative to ELISA.</a> Assay and Drug Development Technologies. 7 (1), 90-92 (2009).</li><li>Aslanoglou, D., George, E. 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A., 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=Optical+tools+for+understanding+the+complexity+of+beta-cell+signalling+and+insulin+release.">Optical tools for understanding the complexity of beta-cell signalling and insulin release.</a> Nature Reviews Endocrinology. 14 (12), 721-737 (2018).</li><li>Zhu, S., 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=Monitoring+C-Peptide+Storage+and+Secretion+in+Islet+beta-Cells+In+Vitro+and+In+Vivo.">Monitoring C-Peptide Storage and Secretion in Islet beta-Cells In Vitro and In Vivo.</a> Diabetes. 65 (3), 699-709 (2016).</li></ol>

Herein we present a method to rapidly assess glucose-stimulated insulin secretion responses from MIN6 &#946; cells. For the best responses in the assay it is important to seed the MIN6 cells at the proper density and allow them to become 85-95% confluent. This improves &#946; cell responses to glucose because of improved cell-cell contacts and synchronization, which&#160; occurs both in primary islets17,18,19,<sup cla...

The method presented here allows insulin secretion from a genetically-modified beta cell line to be assayed rapidly and affordably in 96-well-plate format. The key to this protocol is a modified version of insulin with the naturally-secreted Gaussia luciferase (GLuc, ~18 kDa) inserted (see Figure 1) into the C-peptide to generate insulin-Gaussia (InsGLuc)1,2. Other larger proteins, such as GFP (~25 kDa), have been successfully inserted into the C-peptide of insulin and exhibited the expected post-translational processing from proinsulin-GFP to insulin and GFP-C-peptide3,4. For the assay in this protocol, GLuc has been codon-optimized for mammalian expression and two mutations have been introduced to enhance glow-like kinetics5,6. Multiple combinations and replicates of treatment conditions can be easily tested in 96-well-plate format and the secretion results can be obtained immediately following the experiment.
A major advantage, as previously noted2, is the low cost of this luciferase-based secretion measurement (&#60; $0.01/well) which differentiates it from the relatively higher costs and technical aspects of enzyme-linked immunosorbent assays (ELISAs) (&#62; $2/well) and homogenous time-resolved fluorescence (HTRF) or other F&#246;rster resonance energy transfer (FRET)-based antibody (&#62; $1/well) assays. In comparison to these antibody-based assays, which measure the concentration of insulin by referencing a standard curve, the InsGLuc assay measures secretory activity as a relative comparison to control wells on the plate. For that reason, every experiment requires the inclusion of proper controls. This distinction is a trade-off to allow rapid and inexpensive measurements. However, InsGLuc secretion has been demonstrated to be highly correlated with insulin secretion as measured by ELISA1,2. This technology has been scaled up for high-throughput screening1,2,7 and has led to the identification of novel modulators of insulin secretion including a voltage-gated potassium channel inhibitor7 as well as a natural product inhibitor of &#946; cell function, chromomycin A28. The use of InsGLuc is most appropriate for researchers who plan to continually test many different treatment conditions for their impact on insulin secretion. In follow-up experiments it is necessary to repeat key findings in a parental &#946; cell line, and optimally in murine or human islets, and measure insulin secretion using an antibody-based assay.

<table>
	<tbody>
		<tr>
			<td>Cell culture materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>rIns-GLuc stable MIN6 cells</td>
			<td></td>
			<td></td>
			<td>Parental MIN6 cell line stably expressing pcDNA3.1+rInsp-Ins-eGLuc and maintained in 250 ug/ml G418</td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Sigma</td>
			<td>D6429</td>
			<td>4.5 g/L glucose media</td>
		</tr>
		<tr>
			<td>fetal bovine serum, heat-inactivated</td>
			<td>Sigma</td>
			<td>F4135</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin</td>
			<td>Thermo-Fisher Scientific</td>
			<td>SV30010</td>
			<td></td>
		</tr>
		<tr>
			<td>beta-mercaptoethanol</td>
			<td>Thermo-Fisher Scientific</td>
			<td>BP 176-100</td>
			<td></td>
		</tr>
		<tr>
			<td>glutamine</td>
			<td>Thermo-Fisher Scientific</td>
			<td>BP379-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA</td>
			<td>Sigma</td>
			<td>T3924-500</td>
			<td></td>
		</tr>
		<tr>
			<td>G418</td>
			<td>Gold Biotechnology</td>
			<td>G418-10</td>
			<td>Stock solution 250 mg/mL in water. Freeze aliquots at -20C.</td>
		</tr>
		<tr>
			<td>T75 tissue culture flasks</td>
			<td>Fisher Scientific</td>
			<td>07-202-000</td>
			<td></td>
		</tr>
		<tr>
			<td>96 well tissue culture plates</td>
			<td>Celltreat</td>
			<td>229196</td>
			<td></td>
		</tr>
		<tr>
			<td>Reagent reservoirs (50 mL)</td>
			<td>Corning</td>
			<td>4870</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Secretion assay reagents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>BSA (RIA grade)</td>
			<td>Thermo-Fisher Scientific</td>
			<td>50-146-952</td>
			<td></td>
		</tr>
		<tr>
			<td>D-(+)-Glucose</td>
			<td>Sigma</td>
			<td>G8270-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Thermo-Fisher Scientific</td>
			<td>P217-500</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Thermo-Fisher Scientific</td>
			<td>S271-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Hepes, pH 7.4</td>
			<td>Thermo-Fisher Scientific</td>
			<td>50-213-365</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Thermo-Fisher Scientific</td>
			<td>15568414</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Thermo-Fisher Scientific</td>
			<td>M9272-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma</td>
			<td>C-7902</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Optional drugs for stimulation experiments</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Diazoxide</td>
			<td>Sigma</td>
			<td>D9035</td>
			<td>Stock solution: 50 mM in 0.1N NaOH. Add equal amount of 0.1N HCl to any buffer where diazoxide is added.</td>
		</tr>
		<tr>
			<td>epinephrine (bitartrate salt)</td>
			<td>Sigma</td>
			<td>E4375</td>
			<td>Stock solution: 5 mM in water</td>
		</tr>
		<tr>
			<td>PMA (phorbol 12-myristate)</td>
			<td>Sigma</td>
			<td>P1585</td>
			<td>Stock solution: 100 &#181;M in DMSO</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Guassia assay materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Disodium phosphate (Na2HPO4)</td>
			<td>Thermo-Fisher Scientific</td>
			<td>S374-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Thermo-Fisher Scientific</td>
			<td>G334</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Bromide</td>
			<td>Thermo-Fisher Scientific</td>
			<td>AC44680-1000</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Thermo-Fisher Scientific</td>
			<td>AC44608-5000</td>
			<td>Stock solution: 0.5 M pH 8</td>
		</tr>
		<tr>
			<td>Tris base</td>
			<td>RPI</td>
			<td>T60040-1000.0</td>
			<td>Stock solution: 1 M pH 8</td>
		</tr>
		<tr>
			<td>Ascorbic Acid</td>
			<td>Fisher Scientific</td>
			<td>AAA1775922</td>
			<td>US Patent US7718389 suggested ascorbate can increase coelenterazine stability.</td>
		</tr>
		<tr>
			<td>Na2SO3</td>
			<td>Sigma</td>
			<td>S0505-250G</td>
			<td>US Patent US8367357 suggested sulfite may decrease background due to BSA</td>
		</tr>
		<tr>
			<td>Coelenterazine (native)</td>
			<td>Nanolight / Prolume</td>
			<td>3035MG</td>
			<td>Stock solution: 1 mg/ml in acidified MeOH (2.36 mM)</td>
		</tr>
		<tr>
			<td>OptiPlate-96, White Opaque 96-well Microplate</td>
			<td>Perkin Elmer</td>
			<td>6005290</td>
			<td>Any opaque white 96 well plate should be sufficient. Clear bottom plates will also work, however some signal will be lost.</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Synergy H1 Hybrid plate reader or equivalent</td>
			<td>BioTek</td>
			<td>8041000</td>
			<td>A plate reader with luminescence detection and 96-well plate capabilities is required.</td>
		</tr>
		<tr>
			<td>8-channel VOYAGER Pipette (50-1250 &#181;L)</td>
			<td>Integra</td>
			<td>4724</td>
			<td>An automated multichannel pipette is extremely useful for rapid addition of luciferase reagents and plating cells in 96 well format</td>
		</tr>
		<tr>
			<td>8-channel 200 &#181;L pipette</td>
			<td>Transferpette S 20-200 &#181;L</td>
			<td>2703710</td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring relative insulin secretion using a co-secreted luciferase surrogate

Performing antibody-based assays for secreted insulin post-sample collection usually requires a few hours to a day of assay time and can be expensive, depending on the specific assay. Secreted luciferase assays expedite results and lower the assay cost per sample substantially. Here we present a relatively underused approach to gauge insulin secretory activity from pancreatic &#946; cells by using Gaussia luciferase genetically inserted within the C-peptide. During proteolytic processing of proinsulin, the C-peptide is excised releasing the luciferase within the insulin secretory vesicle where it is co-secreted with insulin. Results can be obtained within minutes after sample collection because of the speed of luciferase assays. A limitation of the assay is that it is a relative measurement of insulin secretion and not an absolute quantitation. However, this protocol is economical, scalable, and can be performed using most standard luminescence plate readers. Analog and digital multichannel pipettes facilitate multiple steps of the assay. Many different experimental variations can be tested simultaneously. Once a focused set of conditions are decided upon, insulin concentrations should be measured directly using antibody-based assays with standard curves to confirm the luciferase assay results.

To gauge the performance of the assay under control conditions, a simple glucose dose-response curve or a stimulation using the diazoxide paradigm can be completed. In the case of the former, pre-incubating the cells for 1 h in glucose-free conditions followed by treating for 1 h with increasing glucose concentrations should result in very little secretory activity at and below 5 mM, while increased secretion is observed above 8 mM glucose (Figure 2). Stimula...

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Measuring Relative Insulin Secretion using a Co-Secreted Luciferase Surrogate

This protocol describes how to perform rapid low-cost luciferase assays at medium-throughput using an insulin-linked Gaussia luciferase as a proxy for insulin secretion from beta cells. The assay can be performed with most luminescence plate readers and multichannel pipettes.

Performing antibody-based assays for secreted insulin post-sample collection usually requires a few hours to a day of assay time and can be expensive, ...

This protocol describes an alternate rapid approach for assaying insulin secretion from beta cell lines to expedite drug discovery and characterization. This approach is useful because multiple treatments can be tested simultaneously, the results are available immediately following the experiment, and this assay is more affordable than others. The application of this method towards screening for new small molecule modulators of insulin secretion may identify lead compounds for future diabetes therapies.Increased knowledge of beta cell function can contribute to greater understanding of protein or neurotransmitter secretion in general. This insulin secretion reporter has been established to work in a lentiviral system in other beta cells lines and in human islets. This assay should be very straightforward to individuals familiar with cell culture and operating multichannel pipettes.Before planning any experiments, verify that your parental or stable beta cell lines are responding properly to glucose using an insulin ELISA. Begin by preparing Krebs-Ringer Bicarbonate Buffer or KRBH and gaussia luciferase working solution according to the manuscript directions. Grow MIN6 cells in T75 flasks using standard cell culture techniques.Prepare the InsGLuc MIN6 cells for plating by washing a confluent flask of cells twice with PBS and adding two milliliters of trypsin. Incubate the cells at 37 degrees celsius for about five minutes, or until the cells dissociate from the flask. Determine the cell concentration and dilute the cells in complete media to one million cells per milliliter, which equates to 100, 000 cells per 100 microliters in each well of a 96 well plate.The cells should be sufficiently confluent for the assay after three to four days. On the day of the assay, prepare enough glucose free KRBH for the experiment and set up a reservoir. Decant the medium from the 96 well plate by quickly inverting it over a laboratory sink and then blotting firmly on a stack of paper towels to remove excess medium.Wash the plate twice with 100 microliters of glucose free KRBH per well, and if performing drug treatments, add drugs to the KRBH according to the manuscript directions. Then, add 100 microliters of glucose free KRBH to each well and incubate at 37 degrees celsius for one hour. After the incubation, decant the buffer and blot the plate on a paper towel.Add 100 microliters of glucose free KRBH per well to wash away any accumulated background and then decant the plate. Add control and stimulatory conditions with or without drug treatments at 100 microliters per well and incubate the plate at 37 degrees celsius for one hour. It's important to include basal and stimulated controls on each plate in order to determine the responsiveness of the cells in a given experiment.If the cells have lost their response over time, reculture them from a fresh liquid nitrogen stock. Carefully collect 50 microliters of supernatant using a multichannel pipette, transfer it to an opaque white 96 well assay plate, and keep the sample at room temperature on the bench until ready for the luciferase assay. Prepare the gaussia luciferase assay working solution by pipetting the required amount of CTZ solution into the GLuc assay buffer, taking care to prevent the CTZ from warming.Use a multichannel pipette to quickly add the GLuc assay working solution to the plate with the KRBH supernatants. If there are any droplets on the sides of the wells, briefly spin the plate in a tabletop, swing bucket centrifuge. Then put the plate in the plate reader and read the luminescence with a 0.1 second integration time.This assay has been tested under control conditions by measuring insulin secretion as a response to increasing glucose concentrations. Very little secretory activity is observed below five millimolar glucose, and increased secretion is observed above eight millimolar. The cells exhibit the expected secretory response when challenged with the diazoxide paradigm.Diazoxide treatment blocks insulin secretion if there is no extracellular potassium chloride. When potassium chloride is present, secretion can be amplified with further addition of glucose. It has also been demonstrated that the InsGLuc MIN6 cells respond as expected to secretion modulating compounds such as potassium chloride, diazoxide, PMA, and epinephrin.Following this procedure, critical results should be confirmed by analyzing KRBH supernatants in antibody based ELISA or HTRF assays which allow for the determination of insulin concentrations. A lot of pioneering work has been done by a group at the Broad Institute, which paved the way for me to increasingly use this assay in my research. Multiple research groups including us and the group at the Broad, are using this approach in drug discovery efforts in the field of diabetes.

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Biology

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