Name: evaluation of caspase activation to assess innate immune cell death
Uploaded: 2023-01-20T13:00:00
Description: Watch this Scientific Journal Video about Evaluation of Caspase Activation to Assess Innate Immune Cell Death at JoVE.com

We thank members of the Kanneganti lab for their comments and suggestions, and we thank J. Gullett, PhD, for scientific editing support. Work in our lab is supported by National Institutes of Health (NIH) grants AI101935, AI124346, AI160179, AR056296, and CA253095 (to T.-D.K.) and by the American Lebanese Syrian Associated Charities (to T.-D.K.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

The animal use and procedures were approved by the St. Jude Children&#39;s Research Hospital Committee on the Use and Care of Animals.
1. Preparing the solutions
<ol>
	<li>Prepare L929-conditioned media.
	<ol>
		<li>Plate 1 &#215; 106 L929 cells (see Table of Materials) in a 182 cm2 tissue culture flask containing 50 mL of L929 culture media (see Table 1 for the preparation of the media).</li>
		<li>Grow the cells in a ...

Monitoring caspase cleavage and activation provides one of the most comprehensive pictures of innate immune PCD activation as part of the innate immune response. The protocol described here demonstrates a strategy to monitor caspase activation in response to IAV, HSV1, and F. novicida infections and the sterile trigger LPS + ATP, but numerous other stimuli can induce PCD and could be used in this method, as has been shown in several publications44,48<sup...

The innate immune system acts as the first line of defense during infection and in response to sterile stimuli, such as tissue injury and alterations in homeostasis. Innate immune sensors on the cell surface and in the cytoplasm respond to pathogen- or damage-associated molecular patterns (PAMPs or DAMPs, respectively) to trigger inflammatory signaling pathways and cellular responses. One of the key processes of the innate immune response is the induction of cell death to remove infected or damaged cells and drive further innate and adaptive immune responses. Programmed cell death (PCD) is a highly conserved process across species, highlighting its evolutionary importance as an innate immune mechanism.
There are several innate immune PCD pathways that can be activated in all cell types. Caspases are a key family of highly conserved, intracellular, cysteine-dependent proteases that are critical across many PCD pathways, including the traditionally non-inflammatory apoptosis pathway, as well as inflammatory PCD pathways such as pyroptosis, necroptosis, and PANoptosis1,2,3,4,5. There are 11 human and 10 murine caspases that are well defined, as well as pseudo-caspases that may be functional, and most are constitutively expressed as inactive monomeric or dimeric pro-caspases that require cleavage for activation6,7. Caspases also contain important domains for the recruitment and formation of multiprotein complexes. These include the caspase activation and recruitment domain (CARD), which can be found in caspase-1, caspase-2, caspase-4, caspase-5, caspase-9, and caspase-11, or the death effector domain (DED), which is found in caspase-8 and caspase-10. Through both their proteolytic activity and their ability to form multiprotein complexes, caspases are critical drivers of innate immune PCD.
The role of caspases in innate immune PCD was first identified in apoptosis, where the initiator caspases, caspase-2, caspase-8, caspase-9, and caspase-10, activate the executioner caspases, caspase-3, caspase-6, and caspase-7, to drive cell death8,9,10,11,12. Initiator caspases can be activated by diverse signaling cascades; the extrinsic pathway activates caspase-8 through extracellular ligand-induced death receptor signaling, and the intrinsic pathway activates caspase-9 through the disruption of mitochondrial integrity13. Activated initiator caspases cleave the linker separating the large and small catalytic subunits of executioner caspases to produce their active forms. The executioner caspases then cleave their substrates to disassemble the cell, resulting in DNA degradation, membrane blebbing, nuclear fragmentation, and the release of apoptotic bodies14,15. This process typically ends in a non-lytic and non-inflammatory form of cell death when coupled with the immediate clearance of the dying cells by efferocytosis16. However, defects in efferocytosis or a lack of phagocytic cells can lead to the accumulation of apoptotic cells, which then undergo lytic and inflammatory cell death17,18.
The inflammatory caspases, including caspase-1 (human and mouse), caspase-4 and caspase-5 (human), and caspase-11 (mouse), have been discovered to be activated during a form of inflammatory innate immune PCD (III-PCD) called pyroptosis. Caspase-1 activation is associated with the formation of inflammasomes, which are multiprotein complexes containing a cytosolic innate immune sensor, an adaptor molecule (apoptosis-associated speck-like protein containing a CARD [ASC]), and caspase-1. The formation of this complex allows caspase-1 to undergo proximity-mediated autoproteolysis to release its active form, which can cleave target substrates including the pro-inflammatory cytokines interleukin (IL)-1&#946; and IL-18 and the pore-forming molecule gasdermin D (GSDMD)19,20,21,22,23. Caspase-11, caspase-4, and caspase-5 can also activate GSDMD without the upstream formation of the inflammasome after sensing PAMPs such as lipopolysaccharide (LPS)19,20. These caspases undergo dimerization followed by oligomerization and self-cleavage for activation upon binding to cytosolic LPS, which leads to non-canonical inflammasome activation24,25,26&#160;and caspase-1 activation in a cell-intrinsic manner to induce IL-1&#946; and IL-18 maturation20. The maturation and release of these pro-inflammatory cytokines characterize these caspases as &#34;inflammatory.&#34;&#160;Additionally, the apoptotic caspase-8 has been found to localize to the inflammasome, providing a link between apoptotic and pyroptotic processes.&#160;Studies have found that the apoptotic caspase-8 is also critical for regulating another form of PCD&#160;called necroptosis. The loss of caspase-8 results in spontaneous receptor-interacting serine-threonine kinase 3 (RIPK3)-mediated mixed lineage kinase domain-like pseudokinase (MLKL) activation to drive the III-PCD pathway of&#160;necroptosis27,28,29,30,31,32,33,34,35.&#160;
While caspases have historically been classified as &#34;apoptotic&#34; or &#34;inflammatory&#34; based on the type of cell death they initiate, growing evidence suggests there is extensive crosstalk between the innate immune PCD pathways through caspases3,4. For instance, the inflammatory caspase-1 from inflammasomes cleaves the apoptotic caspase-7 at its canonical activation site34. Caspase-1 activation can also lead to the cleavage of apoptotic substrates such as poly(ADP-ribose) polymerase 1 (PARP1)36. In cells lacking GSDMD, caspase-1 can also cleave caspase-337,38. Additionally, the canonically apoptotic caspase-3 can cleave gasdermin E (GSDME) to induce PCD17,18&#160;and also processes GSDMD into an inactive form40. Furthermore, caspase-8 recruitment to the inflammasome complex has been observed39,40,41,42,43,44,45, and caspase-8 is a key regulator of canonical and noncanonical inflammasome activation39. There are also overlapping and redundant roles for caspase-8 and caspase-1 in many inflammatory conditions, and innate immune PCD characterized by the activation of pyroptotic, apoptotic, and necroptotic components occurs across the disease spectrum39,46,47,48,49,50.
Based on this crosstalk between inflammatory and apoptotic caspases, a key gap in the mechanistic understanding of innate immunity and PCD was identified, leading to the discovery of PANoptosis. PANoptosis is a unique form of III-PCD that is activated in response to pathogens, PAMPs, DAMPs, and alterations in homeostasis and is regulated by PANoptosomes - multifaceted macromolecular complexes that integrate components from other cell death pathways44,50,51,52,53,54,55. The totality of the biological effects in PANoptosis cannot be individually accounted for by pyroptosis, apoptosis, or necroptosis alone3,4,35,36,39,46,47,48, as PANoptosis is characterized by the activation of multiple caspases, including caspase-1, caspase-11, caspase-8, caspase-9, caspase-3, and/or caspase-7, depending on the context44,48,49,50,51,52,53,54,56,57,58,59,60,61,62. PANoptosis has been increasingly implicated in infectious and inflammatory diseases, as well as in cancers and cancer therapies3,4,35,36,39,44,46,47,48,49,50,51,52,53,54,56 
,57,58,59,60,61,62,63,64,65,66.
Given the essential role of caspases across cell death pathways, including in apoptosis, pyroptosis,&#160;necroptosis, and PANoptosis, it is important to develop techniques to characterize their activation and understand the full complexity of the PCD pathways. The protocol here details a method to stimulate cells and measure the subsequent activation of caspases (Figure 1). This method leverages the proteolytic cleavage of caspases, which is generally required for their activation, as a means to study them. Through western blotting, the protein sizes can be determined, allowing for the clear visualization and differentiation of inactive pro-caspases and their activated, cleaved forms.
The major advantages of this protocol are 1) its ability to assess the activation of multiple caspases in parallel from a single population of endogenous cells to more accurately determine PCD activation and 2) the use of relatively simple lab techniques that do not require extensive training or expensive equipment. Previous protocols have used western blotting, fluorescent reporters, or antibody staining to monitor caspase activation in culture supernatants, cell and tissue lysates, whole cells via microscopy, and in vivo67,68,69,70,71, but these techniques generally only monitor one or two caspases in a sample. Furthermore, while synthetic peptide substrates containing caspase cleavage sites that fluoresce upon cleavage have been used to monitor caspase activation in cell or tissue lysates69, these substrates can often be cleaved by more than one caspase, making it difficult to determine the specific activation of individual caspases in this system. Additionally, the use of western blotting rather than the use of fluorescent reporters or other tag-based methods allows researchers to use endogenous cells rather than creating specific cell lines with reporter genes. There are multiple advantages to using endogenous cells, including the fact that many immortalized cell lines are deficient in key cell death molecules72,73, which could affect the results. Additionally, using endogenous cells allows for the evaluation of diverse cell types, such as macrophages, epithelial cells, and endothelial cells, rather than a single lineage. Western blotting is also a relatively simple and cost-effective technique that can be carried out in labs around the world without the need for large, expensive equipment or complicated setups.
This protocol is widely applicable across biology to understand both the cell death-dependent and cell death-independent functions of caspases, including their scaffolding roles and functions in other inflammatory signaling pathways74. Applying this method allows for a unified approach in the study of innate immune PCD pathways and inflammatory signaling across diseases and conditions, and this protocol can be used to identify critical regulatory processes and mechanistic connections that will inform the development of future therapeutic strategies.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.45 &#956;m filter</td>
			<td>Millipore</td>
			<td>SCHVU05RE</td>
			<td></td>
		</tr>
		<tr>
			<td>10 mL syringe</td>
			<td>BD Biosciences</td>
			<td>309604</td>
			<td></td>
		</tr>
		<tr>
			<td>12% polyacrylamide gel with 10 wells&#160;</td>
			<td>Bio-Rad</td>
			<td>4561043</td>
			<td></td>
		</tr>
		<tr>
			<td>12-well plate&#160;</td>
			<td>Corning</td>
			<td>07-200-82</td>
			<td></td>
		</tr>
		<tr>
			<td>18 G needle&#160;</td>
			<td>BD Biosciences</td>
			<td>305195</td>
			<td></td>
		</tr>
		<tr>
			<td>25 G needle&#160;</td>
			<td>BD Biosciences</td>
			<td>305122</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL tube&#160;</td>
			<td>Fisher Scientific</td>
			<td>50-809-218</td>
			<td></td>
		</tr>
		<tr>
			<td>70 &#956;m cell strainer&#160;</td>
			<td>Corning</td>
			<td>431751</td>
			<td></td>
		</tr>
		<tr>
			<td>150 mm tissue culture dishes</td>
			<td>Corning</td>
			<td>430597</td>
			<td></td>
		</tr>
		<tr>
			<td>182-cm2 tissue culture flask</td>
			<td>Genesee Scientific</td>
			<td>25-211</td>
			<td></td>
		</tr>
		<tr>
			<td>Accessory white trans tray</td>
			<td>Cytiva</td>
			<td>29-0834-18</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;caspase-1 antibody</td>
			<td>AdipoGen</td>
			<td>AG-20B-0042-C100</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;caspase-11 antibody</td>
			<td>Novus Biologicals</td>
			<td>NB120-10454</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;caspase-3 antibody</td>
			<td>Cell Signaling Technology</td>
			<td>9662</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;caspase-7 antibody</td>
			<td>Cell Signaling Technology</td>
			<td>9492</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;caspase-8 antibody</td>
			<td>Cell Signaling Technology</td>
			<td>4927</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;caspase-9 antibody</td>
			<td>Cell Signaling Technology</td>
			<td>9504</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;cleaved caspase-3 antibody&#160;</td>
			<td>Cell Signaling Technology</td>
			<td>9661</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;cleaved caspase-7 antibody&#160;</td>
			<td>Cell Signaling Technology</td>
			<td>9491</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;cleaved caspase-8 antibody&#160;</td>
			<td>Cell Signaling Technology</td>
			<td>8592</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-mouse HRP-conjugated secondary antibody&#160;</td>
			<td>Jackson ImmunoResearch Laboratories</td>
			<td>315-035-047</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-rabbit HRP-conjugated secondary antibody&#160;</td>
			<td>Jackson ImmunoResearch Laboratories</td>
			<td>111-035-047</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-rat HRP-conjugated secondary antibody&#160;</td>
			<td>Jackson ImmunoResearch Laboratories</td>
			<td>112-035-003</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti&#8211;&#946;-Actin antibody (C4) HRP</td>
			<td>Santa Cruz</td>
			<td>sc-47778 HRP</td>
			<td></td>
		</tr>
		<tr>
			<td>ATP</td>
			<td>InvivoGen</td>
			<td>tlrl-atpl</td>
			<td></td>
		</tr>
		<tr>
			<td>BBL Trypticase Soy Broth</td>
			<td>BD Biosciences</td>
			<td>211768</td>
			<td></td>
		</tr>
		<tr>
			<td>Bead bath</td>
			<td>Chemglass Life Sciences</td>
			<td>CLS-4598-009</td>
			<td></td>
		</tr>
		<tr>
			<td>Biophotometer D30</td>
			<td>Eppendorf</td>
			<td>6133000010</td>
			<td></td>
		</tr>
		<tr>
			<td>BME</td>
			<td>Sigma</td>
			<td>M6250</td>
			<td></td>
		</tr>
		<tr>
			<td>Bromophenol blue&#160;</td>
			<td>Sigma</td>
			<td>BO126</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell scrapers</td>
			<td>CellTreat Scientific Products</td>
			<td>229315</td>
			<td></td>
		</tr>
		<tr>
			<td>Chemiluminescence imager (Amersham 600)&#160;</td>
			<td>Cytiva</td>
			<td>29083461</td>
			<td></td>
		</tr>
		<tr>
			<td>CO2&#160;chamber</td>
			<td>VetEquip</td>
			<td>901703</td>
			<td></td>
		</tr>
		<tr>
			<td>Cuvettes</td>
			<td>Fisher Scientific</td>
			<td>14-955-129</td>
			<td></td>
		</tr>
		<tr>
			<td>Dissecting scissors</td>
			<td>Thermo Fisher Scientific</td>
			<td>221S</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Thermo Fisher Scientific</td>
			<td>11995-073</td>
			<td></td>
		</tr>
		<tr>
			<td>DTT</td>
			<td>Sigma</td>
			<td>43815</td>
			<td></td>
		</tr>
		<tr>
			<td>Eelectrophoresis apparatus&#160;</td>
			<td>Bio-Rad</td>
			<td>1658004</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Pharmco</td>
			<td>111000200</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum&#160;</td>
			<td>Biowest</td>
			<td>S1620</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter paper</td>
			<td>Bio-Rad</td>
			<td>1703965</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Fisher Scientific</td>
			<td>22-327379</td>
			<td></td>
		</tr>
		<tr>
			<td>Francisella novicida (U112 strain)</td>
			<td>BEI Resources</td>
			<td>NR-13</td>
			<td></td>
		</tr>
		<tr>
			<td>Gel releaser&#160;</td>
			<td>Bio-Rad</td>
			<td>1653320</td>
			<td></td>
		</tr>
		<tr>
			<td>Gentamycin</td>
			<td>Gibco</td>
			<td>15750060</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Sigma</td>
			<td>G7893</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Sigma</td>
			<td>G8898</td>
			<td></td>
		</tr>
		<tr>
			<td>HCl</td>
			<td>Sigma</td>
			<td>H9892</td>
			<td></td>
		</tr>
		<tr>
			<td>Heat block</td>
			<td>Fisher Scientific</td>
			<td>23-043-160</td>
			<td></td>
		</tr>
		<tr>
			<td>Herpes simplex virus 1 (HF strain)</td>
			<td>ATCC</td>
			<td>VR-260</td>
			<td></td>
		</tr>
		<tr>
			<td>High glucose DMEM&#160;</td>
			<td>Sigma</td>
			<td>D6171</td>
			<td></td>
		</tr>
		<tr>
			<td>Human anti&#8211;caspase-1 antibody</td>
			<td>R&#38;D Systems</td>
			<td>MAB6215</td>
			<td></td>
		</tr>
		<tr>
			<td>Human anti&#8211;caspase-8 antibody</td>
			<td>Enzo</td>
			<td>ALX-804-242</td>
			<td></td>
		</tr>
		<tr>
			<td>Humidified incubator&#160;</td>
			<td>Thermo Fisher Scientific</td>
			<td>51026282</td>
			<td></td>
		</tr>
		<tr>
			<td>Image analysis software</td>
			<td>ImageJ</td>
			<td>v1.53a</td>
			<td></td>
		</tr>
		<tr>
			<td>IMDM</td>
			<td>Thermo Fisher Scientific</td>
			<td>12440-053</td>
			<td></td>
		</tr>
		<tr>
			<td>Influenza A virus (A/Puerto Rico/8/34, H1N1 [PR8])&#160;</td>
			<td>constructed per Hoffmann et al.</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>L929 cells</td>
			<td>ATCC</td>
			<td>CCL-1</td>
			<td>cell line for creating L929-conditioned media</td>
		</tr>
		<tr>
			<td>L-cysteine&#160;</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP376-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Luminata Forte Western HRP substrate</td>
			<td>Millipore</td>
			<td>WBLUF0500</td>
			<td>standard-sensitivity HRP substrate</td>
		</tr>
		<tr>
			<td>MDCK cells</td>
			<td>ATCC</td>
			<td>CCL-34</td>
			<td>cell line for determining IAV viral titer</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Sigma</td>
			<td>322415</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge</td>
			<td>Thermo Fisher Scientific</td>
			<td>75002401</td>
			<td></td>
		</tr>
		<tr>
			<td>Non-essential amino acids&#160;</td>
			<td>Gibco</td>
			<td>11140050</td>
			<td></td>
		</tr>
		<tr>
			<td>Nonfat dried milk powder</td>
			<td>Kroger</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NP-40 solution&#160;</td>
			<td>Sigma</td>
			<td>492016</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Thermo Fisher Scientific</td>
			<td>10010023</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin and streptomycin&#160;</td>
			<td>Sigma</td>
			<td>P4333</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri dish</td>
			<td>Fisher Scientific</td>
			<td>07-202-011</td>
			<td></td>
		</tr>
		<tr>
			<td>PhosSTOP</td>
			<td>Roche</td>
			<td>PHOSS-RO</td>
			<td></td>
		</tr>
		<tr>
			<td>Power source&#160;</td>
			<td>Bio-Rad</td>
			<td>164-5052</td>
			<td></td>
		</tr>
		<tr>
			<td>Protease inhibitor tablet</td>
			<td>Sigma</td>
			<td>S8820</td>
			<td></td>
		</tr>
		<tr>
			<td>PVDF membrane&#160;</td>
			<td>Millipore</td>
			<td>IPVH00010</td>
			<td></td>
		</tr>
		<tr>
			<td>Rocking shaker</td>
			<td>Labnet</td>
			<td>S2035-E</td>
			<td></td>
		</tr>
		<tr>
			<td>SDS</td>
			<td>Sigma</td>
			<td>L3771</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride&#160;</td>
			<td>Sigma</td>
			<td>S9888</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium deoxycholate</td>
			<td>Sigma</td>
			<td>30970</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Sigma</td>
			<td>72068</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyruvate&#160;</td>
			<td>Gibco</td>
			<td>11360-070</td>
			<td></td>
		</tr>
		<tr>
			<td>Square Petri dish</td>
			<td>Fisher Scientific</td>
			<td>FB0875711A</td>
			<td></td>
		</tr>
		<tr>
			<td>Stripping buffer</td>
			<td>Thermo Fisher Scientific</td>
			<td>21059</td>
			<td></td>
		</tr>
		<tr>
			<td>Super Signal Femto HRP substrate</td>
			<td>Thermo Fisher Scientific</td>
			<td>34580</td>
			<td>high-sensitivity HRP substrate</td>
		</tr>
		<tr>
			<td>Tabletop centrifuge</td>
			<td>Thermo Fisher Scientific</td>
			<td>75004524</td>
			<td></td>
		</tr>
		<tr>
			<td>Trans-Blot semi-dry system&#160;</td>
			<td>Bio-Rad</td>
			<td>170-3940</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris</td>
			<td>Sigma</td>
			<td>TRIS-RO</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20&#160;</td>
			<td>Sigma</td>
			<td>P1379</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrapure lipopolysaccharide (LPS) from E. coli 0111:B4</td>
			<td>InvivoGen</td>
			<td>tlrl-3pelps</td>
			<td></td>
		</tr>
		<tr>
			<td>Vero cells</td>
			<td>ATCC</td>
			<td>CCL-81</td>
			<td>cell line for determining HSV1 viral titer</td>
		</tr>
	</tbody>
</table>

evaluation of caspase activation to assess innate immune cell death

Innate immunity provides the critical first line of defense in response to pathogens and sterile insults. A key mechanistic component of this response is the initiation of innate immune programmed cell death (PCD) to eliminate infected or damaged cells and propagate immune responses. However, excess PCD is associated with inflammation and pathology. Therefore, understanding the activation and regulation of PCD is a central aspect of characterizing innate immune responses and identifying new therapeutic targets across the disease spectrum.
This protocol provides methods for characterizing innate immune PCD activation by monitoring caspases, a family of cysteine-dependent proteases that are often associated with diverse PCD pathways, including&#160;apoptosis,&#160;pyroptosis, necroptosis, and PANoptosis. Initial reports characterized caspase-2, caspase-8, caspase-9, and caspase-10 as initiator caspases and caspase-3, caspase-6, and caspase-7 as effector caspases in apoptosis, while later studies found the inflammatory caspases, caspase-1, caspase-4, caspase-5, and caspase-11, drive pyroptosis. It is now known that there is extensive crosstalk between the caspases and other innate immune and&#160;cell death molecules across the previously defined PCD pathways, identifying a key knowledge gap in the mechanistic understanding of innate immunity and PCD and&#160;leading to the characterization of PANoptosis. PANoptosis is a unique innate immune inflammatory PCD pathway regulated by PANoptosome complexes, which integrate components, including caspases,&#160;from other cell death pathways.
Here, methods for assessing the activation of caspases in response to various stimuli are provided. These methods allow for the characterization of PCD pathways both in vitro and in vivo, as activated caspases undergo proteolytic cleavage that can be visualized by western blotting using optimal antibodies and blotting conditions. A protocol and western blotting workflow have been established that allow for the assessment of the activation of multiple caspases from the same cellular population, providing a comprehensive characterization of the PCD processes. This method can be applied across research areas in development, homeostasis, infection, inflammation, and cancer to evaluate PCD pathways throughout cellular processes in health and disease.

PANoptosis has been observed in response to numerous bacterial, viral, and fungal infections and other inflammatory stimuli, as well as in cancer cells44,48,49,50,51,52,53,54,56,57,<...

Watch this Scientific Journal Video about Evaluation of Caspase Activation to Assess Innate Immune Cell Death at JoVE.com

Evaluation of Caspase Activation to Assess Innate Immune Cell Death

This protocol describes a comprehensive method for assessing caspase activation (caspase-1, caspase-3, caspase-7, caspase-8, caspase-9, and caspase-11) in response to both in vitro and in vivo (in mice) models of infection, sterile insults, and cancer to determine the initiation of cell death pathways, such as pyroptosis, apoptosis, necroptosis, and PANoptosis.

Innate immunity provides the critical first line of defense in response to pathogens and sterile insults. A key mechanistic component of this response is ...

This protocol provides a multifaceted understanding of the activation of cell death processes, which can provide critical insights into disease mechanisms and inform therapeutic strategies. This protocol relies on the use of a simpler technique and to access the activation of multiple caspases imperative from single population of endogenous cells to greatly determine activation. Innate immune cell death has been implicated across the disease spectrum, from infections to inflammatory diseases to cancers.Understanding the molecular mechanisms of cell death through caspase activation can provide critical insights into disease processes. Dr.Julieann, a post-doctoral research associate from a laboratory, will be demonstrating the procedure. After isolating the bone marrow and differentiating the BMDMs, infect the cells with the influenza A virus.Calculate the virus volume needed at a multiplicity of infection of 20 plaque-forming units. Remove the media from the BMDMs and wash the cells once with 500 microliters of PBS. Add 450 microliters of Influenza A virus in high glucose DMEM without heat inactivated FBS to each well, and incubate the plates at 37 degrees Celsius for one hour in a humidified incubator to allow absorption.At the end of the one-hour incubation, add 50 microliters of heat inactivated FBS and return the plates to the incubator at 37 degrees Celsius for a total of 12 hours. After 12 hours of incubation, remove the plate from the incubator. Aspirate 150 microliters of the supernatant and discard or save this for supernatant analysis.Do not remove the remaining supernatant. Now, create the protein collection solution by combining 50 microliters of caspase lysis buffer and 100 microliters of four XSDS buffer per well. Then, add 150 microliters of the mix to each well.For each well, pipette the mixture to collect the lysed cells and supernatant. While pipetting, scrape the bottom of the well with the pipette tip to disrupt the cells. After scraping and pipetting, collect the protein lysate into labeled 1.5 milliliter tubes.Using a heat block, heat all the tubes to 100 degrees Celsius for 12 minutes. Remove the tubes from the heat block and centrifuge at 14, 500 G for 30 seconds at room temperature to pellet any insoluble components. Prepare the electrophoresis apparatus with a 12%polyacrylamide gel with 10 wells.Fill the electrophoresis apparatus with running buffer and remove the gel comb. Then, heat the samples at 100 degrees Celsius for five minutes. Centrifuge the samples at 14, 500 G for 30 seconds at room temperature before loading.Then, slowly load 30 microliters of the sample into each well. Use combined supernatant and protein lysate and caspase lysis buffer or the tissue homogenate for caspase 1, 3, 7 and 8 blots, and use the protein lysate DN RIPA buffer described in the protocol or the tissue homogenate for caspase 11 and 9. To evaluate all six caspases at once, use the same procedure to load the same samples into each of the six gels.Connect the electrophoresis apparatus to the power source and set the power to 80 volts for 20 minutes to begin the gel run. After the initial 20 minutes, adjust the power to 100 volts for 45 to 60 minutes. Observe the dye front.Once the dye front reaches the bottom of the gel, turn the power off. While the gel runs, prepare the transfer buffer as described in the manuscript. Make the solution fresh each time.Remove the gel from the electrophoresis apparatus using the gel releaser. To set up the transfer stack for the gel, activate a PVDF membrane by soaking it in methanol for one minute. Pre-wet two pieces of filter paper, the gel, and the PVDF membrane and transfer buffer for five minutes.Keep the PVDF membrane and gel in separate containers during this five-minute incubation. Begin assembling the transfer stack on the semi-dry system. On the bottom platinum nano side, place one piece of filter paper, the PVDF membrane, the gel, and finally, one piece of filter paper.Gently roll out or press out air bubbles between the layers and close the top of the system. Now, connect to the power source. Set the power to 25 volts for 40 minutes.After the transfer, disassemble the transfer stack, collect the membrane, and place it in a square Petri dish. Next, perform membrane blocking by adding 15 milliliters of a 5%skim milk solution and incubate the membrane on a rocking shaker at 50 to 70 RPM at room temperature for one hour. After incubation, remove the blocking solution, add 10 milliliters of the diluted antibody solution, and incubate for two hours at room temperature or four degrees Celsius overnight on a rocking shaker, as demonstrated previously.Then, collect the antibody solution and wash the membrane by adding 15 milliliters of TBST to the membrane on a rocking shaker at room temperature for 10 minutes. Discard the TBST. Repeat the wash with 15 milliliters of TBST three times.Add 10 milliliters of the diluted secondary HRP conjugated antibody solution. Incubate on a rocking shaker at room temperature for one hour. At the end of the incubation, once the antibody solution is removed, wash the membrane by adding 15 milliliters of TBST on a rocking shaker at room temperature for 10 minutes.After completing the washing steps and removing the TBST, add 10 milliliters of the high sensitivity HRP substrate. Let it sit at room temperature for one minute. Remove the membrane from the substrate.Proceed directly to the imaging using a chemiluminescence imager with the accessory white trans tray inserted in the lower position. Expose the membrane using the auto exposure mode. The pro and activated caspase 1, 11, 3, 7, 8 and 9 in wild type and ZBP1 mutant after Influenza A virus infection, wild type and AIM2 mutant after HSV1 infection, and Francisella novicida infection, or wild type and NLRP3 mutant BDMs after lipopolysaccharide and ATP stimulation are analyzed.Cells lacking upstream PANoptosis sensors do not undergo robust cell death in response to the cognate PANoptosis-inducing stimuli. Influenza A virus infection induces the formation of the ZBP1-PANoptosome and the ZBP1 deficient cells are significantly protected from cell death during Influenza A virus infection. Similarly, HSV1 and Francisella novicida infections induce the formation of the AIM2 PANoptosome, and AIM2 deficient cells fail to undergo robust cell death in response to these infections.Cells lacking upstream inflammasome sensors are protected from cell death in response to their respective stimuli, and NLRP3 deficient cells do not undergo cell death in response to lipopolysaccharide and ATP. It is important to remember to prepare a mixture of both cell lysate to determine a specific caspase. After loading the jet, the luminous sample should be stored minus 20 degree to maintain integrity of the goals of caspase for following up In conjunction with this protocol, real-time cell death imaging or LDH assays can be used to monitor the execution of cell death, and ELIZAs can be used to check for the release of cytokines or DAMPs from cells undergoing different types of cell death.

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