This worked was supported by grants from National Health and Medical Research Council (GNT1125033 and GNT1140187) and Australian Research Council (DP170103790) to I.K.H.P.

1. Induction of Apoptosis
<ol>
	<li>Centrifuge cell sample at 300 x g for 5 min and discard supernatant to remove any pre-existing cell debris. 
	NOTE: When using adherent cells, seed cells in advance and wash with 1x phosphate-buffered solution (PBS) prior to apoptosis induction.</li>
	<li>Determine cell number and collect cells. 
	NOTE: Depending on the assay post-isolation, we recommend a starting cell number of at least 1 x 107 cells.</li>
	<li>Resuspend in complete media (respective medium containing 10% (vol/vol) fetal calf serum, 50 IU/mL penicillin, 50 &#181;g/mL streptomycin mixture) for a final concentration of 1 x 106 cells/mL.</li>
	<li>Aliquot ~2 x 106 cells per well of a 6 well plate.</li>
	<li>To induce apoptosis, remove the plate lid and irradiate cells at 150 mJ/cm2 using a UV irradiator. This should take approximately 30-60 s. 
	NOTE: Prior to irradiation, ensure that ~0.5 x 106 cells are retained for the &#39;Untreated&#39; cell control. 
	NOTE: Apoptosis can also be induced via other methods such as anti-Fas or serum starvation6.</li>
	<li>Incubate at 37&#176;C, 5% CO2 for 2-8 hours, depending on the cell line.</li>
	<li>Using a bench top light microscope, visualize cells to confirm the presence of apoptotic morphologies, such as blebbing, apoptopodia formation, and ApoBD formation. 
	NOTE: 40X magnification is sufficient</li>
	<li>Using a P1000 pipette, pipette and collect apoptotic samples.</li>
	<li>Wash the plate with 1x PBS and combine with remaining sample to ensure maximum yield.</li>
	<li>Collect ~1/10th for the &#39;Whole Apoptotic Sample&#39; (WAS) control.</li>
	<li>Collect the &#39;Untreated&#39; sample.</li>
	<li>Centrifuge both the WAS and Untreated samples at 3,000 x g for 6 min.</li>
	<li>Resuspend in 1 mL of 1x PBS and set aside on ice.</li>
	<li>For ApoBD isolation, continue to either step 2 or 3 with the remaining apoptotic sample.</li>
</ol>
2. ApoBD Isolation via FACS
<ol>
	<li>Centrifuge the entire sample at 3,000 x g for 6 min.</li>
	<li>Remove the majority of the supernatant without disrupting the pellet.</li>
	<li>Resuspend in a staining solution containing 1 mL of 1x A5 binding buffer, 75 &#181;L of A5-FITC, and 2 &#181;L of TO-PRO-3 per 1x107 cells.</li>
	<li>Incubate sample in the dark at room temperature for 10 min.</li>
	<li>Add 1-2 mL of 1x A5 binding buffer and centrifuge sample at 3,000 x g for 6 min to remove excess stain. 
	NOTE: For mixed cell populations or tissue samples, perform an antibody staining step using a combination of cell type-specific markers in 1x A5 binding buffer and incubate on ice for 20 min (or as per manufacturer&#39;s protocol) before centrifugation at 3,000 x g for 6 min.</li>
	<li>Resuspend sample pellet in 3 mL of FACS buffer (1x PBS, 1x A5 binding buffer, 10% FSC, 2 mM EDTA) per 1x107 cells.</li>
	<li>Filter through a 70 &#181;m cell strainer into a round-bottom, polypropylene (flow cytometry) tube and keep samples on ice and in the dark.</li>
	<li>Turn on the FACS machine and perform standard set up using a 100 &#181;m nozzle, perform the drop delay, and ensure a stable stream.</li>
	<li>Load the sample and set acquisition speed to ~1000 events/s.</li>
	<li>Adjust FSC, SSC, APC (TO-PRO-3) and FITC (A5) voltages and position events within the FACS plots to ensure populations can be clearly separated.</li>
	<li>Record 20,000 events.</li>
	<li>Set up a gating strategy as in part 4.</li>
	<li>In the sort layout, add the final ApoBD gate as the desired sorting population.</li>
	<li>Begin acquiring the sample and perform a test sort by collecting 5,000-10,000 ApoBDs into a new tube containing ~250 &#181;L FACS buffer.</li>
	<li>Perform a system back flush and load sorted ApoBDs.</li>
	<li>Acquire and record test-sort ApoBDs.</li>
	<li>Check that the ApoBD purity is ~99% by comparing FSC (y-axis) vs A5 (x-axis events). 
	NOTE: A5 staining may reduce slightly when re-analyzing samples due to laser bleaching.</li>
	<li>Once high purity is achieved, load original sample and continue sorting until the desired number of ApoBDs has been obtained. 
	NOTE: If necessary, dual sorting can be performed to simultaneously isolate ApoCells and ApoBDs. 
	NOTE: When sorting over a long period of time, we recommend incubating the collection tube at 4 &#176;C.</li>
	<li>Once sorting is complete, collect a small portion of post-sort ApoBDs, post-sort ApoCells, Untreated, and WAS to validate apoptosis and confirm post-sort purity. 
	NOTE: Although the test-sort and post-sort purity should not differ significantly, this is based on the stream settings and stability.</li>
</ol>
3. ApoBD Isolation via Differential Centrifugation
<ol>
	<li>Centrifuge the remaining apoptotic sample at 300 x g for 10 min.</li>
	<li>Collect the supernatant, leaving ~500 &#181;L to avoid disrupting the cell pellet, and add into a new 15 mL conical tube.</li>
	<li>Remove the remaining 500 &#181;L and resuspend the cell pellet in 2 mL of 1x PBS (this represents the &#39;ApoCell-enriched fraction&#39;.</li>
	<li>Centrifuge the collected supernatant for 20 min at 3,000 g.</li>
	<li>Check for a pellet and carefully remove the supernatant (the supernatant may contain small extracellular vesicles including microvesicles and exosomes).</li>
	<li>Resuspend the pellet in 1 mL of 1x PBS (this represents the &#39;ApoBD-enriched&#39; fraction)</li>
	<li>Collect 100 &#181;L of each Viable, WAS, ApoCell-enriched, and ApoBD-enriched samples in a new round-bottom, polystyrene (flow cytometry) tube.</li>
	<li>Add 100 &#181;L of stain containing 2x A5 binding buffer, 1:100 A5-FITC, and 1:1,000 TO-PRO-3</li>
	<li>Incubate at room temperature for 10 min in the dark.</li>
	<li>Analyze samples by flow cytometry, using the gating strategy as described above to validate the successful induction of apoptosis and purity of the ApoBD-enriched fraction.</li>
</ol>
4. Flow Cytometry Gating Strategy
<ol>
	<li>Plot TO-PRO-3 (y-axis) against FSC (x-axis) to separate necrotic cells (TO-PRO-3high) from all other non-permeabilized events (TO-PRO-3low/intermediate).</li>
	<li>Select all non-permeabilized events and plot SSC against A5. Gate two populations including population 1 (P1), SSCintermediate/high, A5low/intermediate cells and population 2 (P2), all other events.</li>
	<li>From P2, plot TO-PRO-3 against A5 and select A5intermediate/high events to exclude all cell debris.</li>
	<li>Select all A5 positive events and plot FSC against A5. Separate ApoBDs (FSClow) from ApoCells (FSCintermediate/high). 
	NOTE: When gating ApoBDs for ApoBD isolation via the FACS-based approach, we recommend a final step by selecting ApoBDs and comparing TO-PRO-3 to A5 and selecting all events. This ensures that the final sorting gate uses fluorescence rather than FSC/SSC parameters.</li>
	<li>For viable cell analysis, select P1 and perform one of two gating strategies. For general viable cell analysis, plot FSC against A5 and select all FSCintermediate/high cells, therefore removing remaining cell debris. Alternatively, for in-depth analysis, viable cells can be separated from A5- early ApoCells by plotting TO-PRO-3 against FSC. Select TO-PRO-3low, FSCintermediate/high viable cells and TO-PRO-3intermediate, FSCintermediate/high A5- early ApoCells.</li>
</ol>

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Flow cytometric detection of phosphatidylserine expression on early apoptotic cells using fluorescein labelled Annexin V.</a> Journal of Immunological Methods. 184, 39-51 (1995).</li><li>Jiang, L., 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+the+progression+of+cell+death+and+the+disassembly+of+dying+cells+by+flow+cytometry.">Monitoring the progression of cell death and the disassembly of dying cells by flow cytometry.</a> Nature Protocols. 11, 655-663 (2016).</li><li>Berda-Haddad, 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=Sterile+inflammation+of+endothelial+cell-derived+apoptotic+bodies+is+mediated+by+interleukin-1alpha.">Sterile inflammation of endothelial cell-derived apoptotic bodies is mediated by interleukin-1alpha.</a> Proceedings of the National Academy of Sciences of the United States of America. 108, 20684-20689 (2011).</li><li>Lleo, 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=Shotgun+proteomics:+identification+of+unique+protein+profiles+of+apoptotic+bodies+from+biliary+epithelial+cells.">Shotgun proteomics: identification of unique protein profiles of apoptotic bodies from biliary epithelial cells.</a> Hepatology. 60, 1314-1323 (2014).</li><li>Atkin-Smith, G. 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The authors have nothing to disclose.

Since its early description in the 1950s, the field of apoptosis has advanced markedly, becoming a prominent research area. Despite the broad interest and extensive efforts, certain aspects of apoptosis, in particular the formation of ApoBDs, have not been well studied due to the lack of appropriate methodologies. These notably include the limitation in tracking apoptosis progression and ApoBD formation simultaneously using the traditional flow cytometry A5/PI analysis and the impurities of ApoBD isolation. We have recen...

Apoptosis, a well-studied form of programmed cell death, is required to maintain physiological homeostasis and remove potentially harmful cells within the human body1. After the induction of apoptosis, apoptotic cells (ApoCells) can undergo a series of morphological changes and disassemble into small membrane-bound vesicles termed ApoBDs. Overall, this process is known as apoptotic cell disassembly and can be divided into 3 distinct steps based on morphology2,3. Step 1 (plasma membrane blebbing) is characterized by the formation of balloon-like structures on the cell surface known as blebs4,5. Step 2 (apoptotic protrusion formation) includes the formation of long membrane protrusions such as apoptopodia, beaded-apoptopodia and microtubule spikes6,7,8. Lastly, Step 3 (ApoBD formation) includes the fragmentation of the apoptotic protrusions and/or ApoCells to generate ApoBDs6,9. Previous findings have suggested a role of ApoBDs in aiding apoptotic cell clearance and mediating intercellular communication. For example, it is proposed that the fragmentation of an ApoCell into ApoBDs may generate small &#39;bite-sized&#39; pieces that could be easily removed by surrounding phagocytes2,10,11. Furthermore, ApoBDs may harbor a series of biomolecules such as DNA, RNA and proteins, which may be trafficked to surrounding cells to facilitate cell-cell communication12,13,14. To functionally investigate these processes, it is vital to confirm three key parameters including (i) validation of apoptosis induction and ApoBD formation, (ii) isolation of ApoBDs, and (iii) confirmation of ApoBD purity.
Previously, a number of methods including flow cytometry and electron microscopy have been used to study apoptosis and ApoBDs15,16,17,18. However, ApoBD detection and quantification are often difficult or overlooked. For instance, the most routinely-used flow cytometry-based apoptosis assay employs annexin V (A5, a protein that binds the externalized &#39;eat-me&#39; signal phosphatidylserine (PtdSer)) and nucleic acid stain propidium iodide (PI)19. However, by using this universal stain combination, analysis assumes that there are only three types of cell subsets (viable cells, ApoCells and necrotic cells) in the sample. Furthermore, though considered as &#34;a gold standard&#34; by many researchers for apoptosis, flow cytometry assays and subsequent data analysis often excludes ApoBDs through an initial gating step selecting FSC/SSCintermediate-high events. Therefore, we have recently developed a novel flow cytometry assay using A5 and TO-PRO-3, another nucleic stain that can be selectively taken up by caspase 3/7-activated pannexin 1 (PANX1) channels7,20. As caspase 3-induced PANX1 activation precedes PtdSer exposure at the early stage of apoptosis, TO-PRO-3 differentially stains apoptotic and necrotic cells. In addition, this approach combined with our novel gating strategy includes all acquired events during data analysis and as a result, six cell/particle subsets are identified, including: (i) viable cells (FSC/SSCintermediate/high, A5low, TO-PRO-3low), (ii) A5- early ApoCells (FSC/SSCintermediate/high, A5low, TO-PRO-3intermediate), (iii) A5+ ApoCells (FSC/SSCintermediate/high, A5high, TO-PRO-3intermediate), (iv) necrotic cells or late ApoCells (FSC/SSCintermediate/high, A5high, TO-PRO-3high), (v) ApoBDs (FSC/SSClow, A5intermediate, TO-PRO-3low/intermediate), and (vi) debris (FSC/SSClow, A5low, TO-PRO-3low)20. Our approach emphasizes the importance of analyzing all cells/particle subsets and, more importantly, the separation of ApoBDs from cells and debris20. Thus, this approach demonstrates an efficient technique to validate the induction of apoptosis and ApoBD formation simultaneously.
Traditionally, ApoBDs have been isolated through a variety of differential centrifugation approaches whereby ApoBDs can be separated from cells or other extracellular vesicles based on density. However, such centrifugation methods are often limited by low ApoBD purity, lack of a quantification step to confirm sample purity, and/or inability to separate cell type-specific ApoBDs17,21,22. Therefore, we recently developed two approaches, a FACS-based and a new differential centrifugation-based approach which can be coupled with our previously established flow cytometry method to validate the induction of apoptosis and sample purity23. ApoBD isolation via our FACS-based approach can enrich ApoBDs to up to 99% purity, and can be coupled with a variety of cell type-specific antibodies to isolate ApoBDs from mixed cell populations, tissue samples and bodily fluids23. Furthermore, our revised differential centrifugation approach demonstrates an efficient method to isolate ApoBDs to &#62;90% purity23.
In this paper, we describe in detail our experimental procedure to validate apoptosis induction, and to detect and quantify ApoBD formation. The ApoBD isolation workflows using FACS-based and differential centrifugation-based methods are also elaborated and compared. The representative data demonstrate that the described methodology provides an effective cutting-edge tool for future ApoBD studies.

<table><tbody><tr><td>Cells e.g. cultured human THP-1 monocytes (clone number: TIB-202)</td><td>ATCC</td><td>-</td><td></td></tr><tr><td>RPMI 1640 medium</td><td>Life Technologies</td><td>22400-089</td><td></td></tr><tr><td>Penicillin-streptomycin mixture</td><td>Life Technologies</td><td>15140122</td><td></td></tr><tr><td>FSC</td><td>Gibco</td><td>10099-141</td><td></td></tr><tr><td>1x PBS</td><td>-</td><td>-</td><td></td></tr><tr><td>Annexin V FITC</td><td>BD Bioscience</td><td>-</td><td></td></tr><tr><td>TO-PRO-3 iodide</td><td>Life Technologies</td><td>T3605</td><td>TO-PRO-3 may cause skin, eye and respiratory irration. Avoid direct contact.</td></tr><tr><td>10x Annexin V binding buffer</td><td>BD Bioscience</td><td>556454</td><td></td></tr><tr><td>EDTA</td><td>Sigma-Aldrich</td><td>1001710526</td><td></td></tr><tr><td>Centrifuge tube (15 mL)</td><td>Cellstar</td><td>188271</td><td></td></tr><tr><td>Microcentrifuge tube (1.5 mL)</td><td>Sarstedt</td><td>72.690.001</td><td></td></tr><tr><td>Tissue culture incubator (37 &amp;deg;C, 5% CO2)</td><td>-</td><td>-</td><td></td></tr><tr><td>Centrifuge</td><td>Beckman Coulter</td><td>392932</td><td></td></tr><tr><td>FACS ARIA III Flow cytometer, configured with two lasers for FITC and APC detection</td><td>BD Bioscience</td><td>-</td><td></td></tr><tr><td>FACS Canto II Flow cytometer, configured with two lasers for FITC and APC detection</td><td>BD Bioscience</td><td>-</td><td></td></tr><tr><td>FACS Diva 6.1.1 software</td><td>BD Bioscience</td><td>-</td><td></td></tr><tr><td>FlowJo 8.8.6 software</td><td>-</td><td>-</td><td></td></tr><tr><td>&amp;nbsp;UV Stratalinker 1800</td><td>Stratagene</td><td>-</td><td></td></tr></tbody></table>

detection and isolation of apoptotic bodies to high purity

Apoptotic bodies (ApoBDs), microvesicles and exosomes are the key members of the extracellular vesicle family, with ApoBDs being one of the largest type. It has been proposed that ApoBDs can aid cell clearance as well as intercellular communication through trafficking biomolecules. Conventional approaches used for the identification and isolation of ApoBDs are often limited by the lack of accurate quantification and low sample purity. Here, we describe a workflow to confirm the induction of apoptosis, validate ApoBD formation, and isolate ApoBDs to high purity. We will also outline and compare fluorescence-activated cell sorting (FACS) and differential centrifugation based approaches to isolate ApoBDs. Furthermore, the purity of isolated ApoBDs will be confirmed using a previously establish flow cytometry-based staining and analytical method. Taken together, using the described approach, THP-1 monocyte apoptosis and apoptotic cell disassembly was induced and validated, and ApoBD generated from THP-1 monocytes were isolated to a purity of 97-99%.

Using the procedure outlined here, THP-1 monocyte apoptosis was induced and ApoBDs were detected and isolated via either a FACS-based or a differential centrifugation approach (Figure 1). Firstly, apoptosis was induced by UV irradiation and samples were collected after 2-3 h of incubation when cells exhibited apoptotic morphologies, including blebbing, apoptotic membrane protrusion formation and the generation of ApoBDs6. A TO-PRO-3 an...

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Detection and Isolation of Apoptotic Bodies to High Purity

A workflow using flow cytometry or differential centrifugation is developed to detect, quantify and isolate apoptotic bodies from an apoptotic sample to high purity.

Apoptotic bodies (ApoBDs), microvesicles and exosomes are the key members of the extracellular vesicle family, with ApoBDs being one of the largest type. ...

detection-and-isolation-of-apoptotic-bodies-to-high-purity

Universidad San Sebastian

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Biochemistry

10.5K Views.  La Trobe University. A workflow using flow cytometry or differential centrifugation is developed to detect, quantify and isolate apoptotic bodies from an apoptotic sample to high purity. 

Video: Detection and Isolation of Apoptotic Bodies to High Purity

Flow Cytometric Detection of Newly-formed Breast Cancer Stem Cell-like Cells After Apoptosis Reversal

Cancer recurrence has long been studied by oncologists while the underlying mechanisms remain unclear. Recently, we and others found that a phenomenon named apoptosis reversal leads to increased tumorigenicity in various cell models under different stimuli. Previous studies have been focused on tracking this process in vitro and in vivo; however, the isolation of real reversed cells has yet to be achieved, which limits our understanding on the consequences of apoptosis reversal. Here, we take advantage of a Caspase-3/7 Green Detection dye to label cells with activated caspases after apoptotic induction. Cells with positive signals are further sorted out by fluorescence-activated cell sorting (FACS) for recovery. Morphological examination under confocal microscopy helps confirm the apoptotic status before FACS. An increase in tumorigenicity can often be attributed to the elevation in the percentage of cancer stem cell (CSC)-like cells. Also, given the heterogeneity of breast cancer, identifying the origin of these CSC-like cells would be critical to cancer treatment. Thus, we prepare breast non-stem cancer cells before triggering apoptosis, isolating caspase-activated cells and performing the apoptosis reversal procedure. Flow cytometry analysis reveals that breast CSC-like cells re-appear in the reversed group, indicating breast CSC-like cells are transited from breast non-stem cancer cells during apoptosis reversal. In summary, this protocol includes the isolation of apoptotic breast cancer cells and detection of changes in CSC percentage in reversed cells by flow cytometry.

Here, we present a protocol to isolate apoptotic breast cancer cells by fluorescence-activated cell sorting and further detect the transition of breast non-stem cancer cells to breast cancer stem cell-like cells after apoptosis reversal by flow cytometry.

Cancer recurrence has long been studied by oncologists while the underlying mechanisms remain unclear. Recently, we and others found that a phenomenon ...

Cancer Research

Monitoring Cleaved Caspase-3 Activity and Apoptosis of Immortalized Oligodendroglial Cells using Live-cell Imaging and Cleaveable Fluorogenic-dye Substrates Following Potassium-induced Membrane Depolarization

The central nervous system can experience a number of stresses and neurological insults, which can have numerous adverse effects that ultimately lead to a reduction in neuronal population and function. Damaged axons can release excitatory molecules including potassium or glutamate into the extracellular matrix, which in turn, can produce further insult and injury to the supporting glial cells including astrocytes and oligodendrocytes 8, 16. If the insult persists, cells will undergo programmed cell death (apoptosis), which is regulated and activated by a number of well-established signal transduction cascades 14. Apoptosis and tissue necrosis can occur after traumatic brain injury, cerebral ischemia, and seizures. A classical example of apoptotic regulation is the family of cysteine-dependent aspartate-directed proteases, or caspases. Activated proteases including caspases have also been implicated in cell death in response to chronic neurodegenerative diseases including Alzheimer's, Huntington's, and Multiple Sclerosis 4, 14, 3, 11, 7.
In this protocol we describe the use of the NucView 488 caspase-3 substrate to measure the rate of caspase-3 mediated apoptosis in immortalized N19-oligodendrocyte (OLG) cell cultures 15, 5, following exposure to different extracellular stresses such as high concentrations of potassium or glutamate. The conditionally-immortalized N19-OLG cell line (representing the O2A progenitor) was obtained from Dr. Anthony Campagnoni (UCLA Semel Institute for Neuroscience) 15, 5, and has been previously used to study molecular mechanisms of myelin gene expression and signal transduction leading to OLG differentiation (e.g.6, 10). We have found this cell line to be robust with respect to transfection with exogenous myelin basic protein (MBP) constructs fused to either RFP or GFP (red or green fluorescent protein) 13, 12. Here, the N19-OLG cell cultures were treated with either 80 mM potassium chloride or 100 mM sodium glutamate to mimic axonal leakage into the extracellular matrix to induce apoptosis 9. We used a bi-functional caspase-3 substrate containing a DEVD (Asp-Glu-Val-Asp) caspase-3 recognition subunit and a DNA-binding dye 2. The substrate quickly enters the cytoplasm where it is cleaved by intracellular caspase-3. The dye, NucView 488 is released and enters the cell nucleus where it binds DNA and fluoresces green at 488 nm, signaling apoptosis. Use of the NucView 488 caspase-3 substrate allows for live-cell imaging in real-time 1, 10. In this video, we also describe the culturing and transfection of immortalized N19-OLG cells, as well as live-cell imaging techniques.

Monitoring Cleaved Caspase-3 Activity and Apoptosis of Immortalized Oligodendroglial Cells using Live-cell Imaging and Cleaveable Fluorogenic-dye Substrates Following Potassium-induced Membrane Depola

Live-cell imaging of caspase-3 mediated apoptosis in immortalized N19-oligodendrocyte cell cultures using the NucView 488 caspase-3 substrate. This technique is applicable for programmed cell death assays in real-time in a variety of cell types and tissues.

The central nervous system can experience a number of stresses and neurological insults, which can have numerous adverse effects that ultimately lead to a ...

Neuroscience

Flow Cytometric Analysis of Apoptotic Biomarkers in Actinomycin D-Treated SiHa Cervical Cancer Cells

Apoptosis biomarkers were investigated in actinomycin D-treated SiHa cervical cancer cells using a benchtop flow cytometer. Early biomarkers (Annexin V and mitochondrial membrane potential) and late biomarkers (caspases 3 and 7, and DNA damage) of apoptosis were measured in experimental and control cultures. Cultures were incubated for 24 hours in a humidified incubator at 37 &#176;C with 5% CO2. The cells were then detached using trypsin and enumerated using a flow cytometric cell count assay. Cells were further analyzed for apoptosis using an Annexin V assay, a mitochondrial electrochemical transmembrane potential assay, a caspase 3/7 assay, and a DNA damage assay. This article provides an overview of apoptosis and traditional flow cytometry, and elaborates flow cytometric protocols for processing and analyzing SiHa cells. The results describe positive, negative, and sub-optimal experimental data. Also discussed are interpretation and caveats in performing flow cytometric analysis of apoptosis using this analytical platform. Flow cytometric analysis provides an accurate measurement of early and late biomarkers for apoptosis.

Apoptosis can be characterized by flow cytometric analysis of early and late apoptotic biomarkers. The cervical cancer cell line, SiHa, was analyzed for apoptosis biomarkers after treatment with Actinomycin D using a benchtop flow cytometer.

Apoptosis biomarkers were investigated in actinomycin D-treated SiHa cervical cancer cells using a benchtop flow cytometer. Early biomarkers (Annexin V ...

Use of a Caspase Multiplexing Assay to Determine Apoptosis in a Hypothalamic Cell Model

The ability to multiplex assays in studies of complex cellular mechanisms eliminates the need for repetitive experiments, provides internal controls, and decreases waste in costs and reagents. Here we describe optimization of a multiplex assay to assess apoptosis following a palmitic acid (PA) challenge in an in vitro hypothalamic model, using both fluorescent and luminescent based assays to measure viable cell counts and caspase-3/7 activity in a 96-well microtiter plate format. Following PA challenge, viable cells were determined by a resazurin-based fluorescent assay. Caspase-3/7 activity was then determined using a luminogenic substrate, DEVD, and normalized to cell number. This multiplexing assay is a useful technique for determining change in caspase activity following an apoptotic stimulus, such as saturated fatty acid challenge. The saturated fatty acid PA can increase hypothalamic oxidative stress and apoptosis, indicating the potential importance of assays such as that described here in studying the relationship between saturated fatty acids and neuronal function.

Multiplex assays can provide beneficial information for basic cellular mechanisms&#160;and eliminate waste of reagents and unnecessary repetitive experiments. We describe here a multiplex caspase-3/7 activity assay, using fluorescent- and luminescent-based methods, to determine cell viability in an in vitro hypothalamic model following oxidative challenge with palmitic acid.

The ability to multiplex assays in studies of complex cellular mechanisms eliminates the need for repetitive experiments, provides internal controls, and ...

Measuring Caspase Activity Using a Fluorometric Assay or Flow Cytometry

The activation of cysteine proteases, known as caspases, remains an important process in multiple forms of cell death. Caspases are critical initiators and executioners of apoptosis, the most studied form of programmed cell death. Apoptosis occurs during developmental processes and is a necessary event in tissue homeostasis. Pyroptosis is another form of cell death that utilizes caspases and is a critical process in activating the immune system through the activation of the inflammasome, which results in the release of members of the interleukin-1 (IL-1) family. To assess caspase activity, target substrates can be assessed. However, sensitivity can be an issue when examining single cells or low-level activity. We demonstrate how a fluorogenic substrate can be used with a population-based assay or single-cell assay by flow cytometry. With proper controls, different amino acid sequences can be used to identify which caspases are active. Using these assays, the simultaneous loss of the inhibitors of apoptosis proteins upon tumor necrosis factor (TNF) stimulation has been identified, which primarily induces apoptosis in macrophages rather than other forms of cell death.

The present protocol describes two methods to measure caspase activity through a fluorogenic substrate using flow cytometry or a spectrofluorometer.

The activation of cysteine proteases, known as caspases, remains an important process in multiple forms of cell death. Caspases are critical initiators ...

Modified Annexin V/Propidium Iodide Apoptosis Assay For Accurate Assessment of Cell Death

Studies of cellular apoptosis have been significantly impacted since the introduction of flow cytometry-based methods. Propidium iodide (PI) is widely used in conjunction with Annexin V to determine if cells are viable, apoptotic, or necrotic through differences in plasma membrane integrity and permeability1,2. The Annexin V/ PI protocol is a commonly used approach for studying apoptotic cells3. PI is used more often than other nuclear stains because it is economical, stable and a good indicator of cell viability, based on its capacity to exclude dye in living cells 4,5. The ability of PI to enter a cell is dependent upon the permeability of the membrane; PI does not stain live or early apoptotic cells due to the presence of an intact plasma membrane 1,2,6. In late apoptotic and necrotic cells, the integrity of the plasma and nuclear membranes decreases7,8, allowing PI to pass through the membranes, intercalate into nucleic acids, and display red fluorescence 1,2,9. Unfortunately, we find that conventional Annexin V/ PI protocols lead to a significant number of false positive events (up to 40%), which are associated with PI staining of RNA within the cytoplasmic compartment10. Primary cells and cell lines in a broad range of animal models are affected, with large cells (nuclear: cytoplasmic ratios &lt;0.5) showing the highest occurrence10. Herein, we demonstrate a modified Annexin V/ PI method that provides a significant improvement for assessment of cell death compared to conventional methods. This protocol takes advantage of changes in cellular permeability during cell fixing to promote entry of RNase A into cells following staining. Both the timing and concentration of RNase A have been optimized for removal of cytoplasmic RNA. The result is a significant improvement over conventional Annexin V/ PI protocols (&lt; 5% events with cytoplasmic PI staining).

An accurate method for the assessment of cell death is described. The protocol improves upon conventional Annexin V/ propidium iodide (PI) protocols, which display up to 40% false- positive events in cell lines and primary cells from a broad range of animal models.

Studies of cellular apoptosis have been significantly impacted since the introduction of flow cytometry-based methods. Propidium iodide (PI) is widely ...

Biology

Quantification of Efferocytosis by Single-cell Fluorescence Microscopy

Studying the regulation of efferocytosis requires methods that are able to accurately quantify the uptake of apoptotic cells and to probe the signaling and cellular processes that control efferocytosis. This quantification can be difficult to perform as apoptotic cells are often efferocytosed piecemeal, thus necessitating methods which can accurately delineate between the efferocytosed portion of an apoptotic target versus residual unengulfed cellular fragments. The approach outlined herein utilizes dual-labeling approaches to accurately quantify the dynamics of efferocytosis and efferocytic capacity of efferocytes such as macrophages. The cytosol of the apoptotic cell is labeled with a cell-tracking dye to enable monitoring of all apoptotic cell-derived materials, while surface biotinylation of the apoptotic cell allows for differentiation between internalized and non-internalized apoptotic cell fractions. The efferocytic capacity of efferocytes is determined by taking fluorescent images of live or fixed cells and quantifying the amount of bound versus internalized targets, as differentiated by streptavidin staining. This approach offers several advantages over methods such as flow cytometry, namely the accurate delineation of non-efferocytosed versus efferocytosed apoptotic cell fractions, the ability to measure efferocytic dynamics by live-cell microscopy, and the capacity to perform studies of cellular signaling in cells expressing fluorescently-labeled transgenes. Combined, the methods outlined in this protocol serve as the basis for a flexible experimental approach that can be used to accurately quantify efferocytic activity and interrogate cellular signaling pathways active during efferocytosis.

Efferocytosis, the phagocytic removal of apoptotic cells, is required to maintain homeostasis and is facilitated by receptors and signaling pathways that allow for the recognition, engulfment, and internalization of apoptotic cells. Herein, we present a fluorescence microscopy protocol for the quantification of efferocytosis and the activity of efferocytic signaling pathways.

Studying the regulation of efferocytosis requires methods that are able to accurately quantify the uptake of apoptotic cells and to probe the signaling ...

Immunology and Infection

Experimental Analysis of Apoptotic Thymocyte Engulfment by Macrophages

Cell apoptosis is a natural process and plays a critical role in embryonic development, homeostatic regulation, immune tolerance induction, and resolution of inflammation. Accumulation of apoptotic debris in the body may trigger chronic inflammatory responses that lead to systemic autoimmune diseases over time. Impaired apoptotic cell clearance has been implicated in a variety of autoimmune diseases. Apoptotic clearance is a complex process rarely detected under physiological conditions. It involves abundant surface receptors and signaling molecules. Studying the process of apoptotic cell clearance provides insightful molecular mechanisms and subsequent biological responses, which may lead to the development of new therapeutics. Here, we describe protocols for the induction of apoptotic thymocytes, the preparation of peritoneal macrophages, and the analysis of apoptotic cell clearance by flow cytometry and microscopy. All cells will undergo apoptosis at a certain stage, and many residential and circulating cells can uptake apoptotic debris. Therefore, the protocol described here can be used in many applications to characterize apoptotic cell binding and ingestion by many other cell types.

Here, we present a protocol to prepare apoptotic thymocytes and peritoneal macrophages and analyze the efficiency of efferocytosis and the specific inhibitor-mediated blocking of apoptotic thymocytes engulfment. This protocol has a broad application in cell-mediated clearance of other particles including artificial beads and bacteria.

Cell apoptosis is a natural process and plays a critical role in embryonic development, homeostatic regulation, immune tolerance induction, and resolution ...

Strategies for Tracking Anastasis, A Cell Survival Phenomenon that Reverses Apoptosis

Anastasis (Greek for &#8220;rising to life&#8221;) refers to the recovery of dying cells. Before these cells recover, they have passed through important checkpoints of apoptosis, including mitochondrial fragmentation, release of mitochondrial cytochrome c into the cytosol, activation of caspases, chromatin condensation, DNA damage, nuclear fragmentation, plasma membrane blebbing, cell shrinkage, cell surface exposure of phosphatidylserine, and formation of apoptotic bodies. Anastasis can occur when apoptotic stimuli are removed prior to death, thereby allowing dying cells to reverse apoptosis and potentially other death mechanisms. Therefore, anastasis appears to involve physiological healing processes that could also sustain damaged cells inappropriately. The functions and mechanisms of anastasis are still unclear, hampered in part by the limited tools for detecting past events after the recovery of apparently healthy cells. Strategies to detect anastasis will enable studies of the physiological mechanisms, the hazards of undead cells in disease pathology, and potential therapeutics to modulate anastasis. Here, we describe effective strategies using live cell microscopy and a mammalian caspase biosensor&#160;for identifying and tracking anastasis in mammalian cells.

The term anastasis refers to the phenomenon in which dying cells reverse a cell suicide process at a late stage, repair themselves, and ultimately survive. Here we demonstrate protocols for detecting and tracking cells that undergo anastasis.

Anastasis (Greek for &#8220;rising to life&#8221;) refers to the recovery of dying cells. Before these cells recover, they have passed through important ...

Identification of Intracellular Signaling Events Induced in Viable Cells by Interaction with Neighboring Cells Undergoing Apoptotic Cell Death

Cells dying by apoptosis, also referred to as regulated cell death, acquire multiple new activities that enable them to influence the function of adjacent live cells. Vital activities, such as survival, proliferation, growth, and differentiation, are among the many cellular functions modulated by apoptotic cells. The ability to recognize and respond to apoptotic cells appears to be a universal feature of all cells, regardless of lineage or organ of origination. However, the diversity and complexity of the response to apoptotic cells mandates that great care be taken in dissecting the signaling events and pathways responsible for any particular outcome. In particular, one must distinguish among the multiple mechanisms by which apoptotic cells can influence intracellular signaling pathways within viable responder cells, including: receptor-mediated recognition of the apoptotic cell, release of soluble mediators by the apoptotic cell, and/or engagement of the phagocytic machinery. Here, we provide a protocol for identifying intracellular signaling events that are induced in viable responder cells following their exposure to apoptotic cells. A major advantage of the protocol lies in the attention it pays to dissection of the mechanism by which apoptotic cells modulate signaling events within responding cells. While the protocol is specific for a conditionally immortalized mouse kidney proximal tubular cell line (BU.MPT cells), it is easily adapted to cell lines that are non-epithelial in origin and/or derived from organs other than the kidney. The use of dead cells as a stimulus introduces several unique factors that can hinder the detection of intracellular signaling events. These problems, as well as strategies to minimize or circumvent them, are discussed within the protocol. Application of this protocol should aid our expanding knowledge of the broad influence that dead or dying cells exert on their live neighbors, both in health and in disease.

Here, we present a protocol for the determination of intracellular signaling events induced in viable cells by physical interaction with adjacent dead or dying cells. The protocol focuses on signaling events induced by receptor-mediated recognition of the dead cells, as opposed to their phagocytic uptake or release of soluble mediators.

Cells dying by apoptosis, also referred to as regulated cell death, acquire multiple new activities that enable them to influence the function of adjacent ...