We express our great appreciation to Jiayi Sun and Lu Yang at Innovative Institute of Chinese Medicine and Pharmacy, Chengdu University of Traditional Chinese Medicine, for the assistance with flow cytometry, Cuiping Chen at State Key Laboratory of Southwestern Chinese Medicine Resources, for the help with scanning electron microscopy. This work was supported by the National Natural Science Foundation of China [82104491], the Natural Science Foundation of Sichuan [2023NSFSC0674], and the Post-doctoral Science Foundation of China [2021M693789].

1. Cell line and cell culture
<ol>
	<li>Grow the human monocytic cell line THP-1 in RPMI-1640 complete culture medium with 10% fetal bovine serum, 1% penicillin-streptomycin and 0.05 mM &#946;-mercaptoethanol. Culture the cells at 37 &#176;C in 5% CO2 humidified air. Sub-culture cells every 2-3 days. 
	NOTE: THP-1 is a suspension cell, select to change half of the medium for sub-culturing. When observing many cell fragments under the light microscope, centrifuge at 300 x g for ...

Analyzing LPS/ATP-Triggered Cell Death Mechanisms in THP-1 Cells

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In this manuscript, two methods were used to detect LPS and ATP-induced death of PMA-differentiated THP-1 macrophages. Annexin V/7-AAD double staining was used, and the results were analyzed by flow cytometry from overall staining. As with other flow cytometric analysis, a group of unstained cells and two groups of single-stained cells were set up to exclude false positive and false negative results. The results show that after LPS/ATP stimulation, several cells lost membrane integrity, indicating that cell death may hav...

Cell death is a fundamental physiological process in all living organisms. In recent years, substantial studies have shown that cell death is involved in the immunity and balance within the organism. Studying cell death helps us better understand the onset and development of diseases. Several forms of programmed cell death have been described, and some key targets in these processes have been identified. Pyroptosis, apoptosis, and necroptosis are the three genetically defined programmed cell death pathways involved in internal balance and disease1.
Pyroptosis is characterized by the formation of membrane pores and the release of cell contents. Activated caspases or granzymes cleave gasdermins to separate their N-terminal domains, which then oligomerize, bind to the membrane, and form pores2,3,4. The gasdermin pore provides an atypical secretion channel across cellular membranes, resulting in downstream cell responses, including content release and ion influx2,3,4. Ultimately, the cells eventually experience plasma membrane rupture and pyroptotic lysis facilitated by ninjurin-15. In apoptosis, activated Bax and Bak form oligomers on the mitochondrial outer membrane and release cytochrome C, which is regulated by a balance between proapoptotic and antiapoptotic proteins of the BCL-2 family, initiator caspases (caspase-8, -9 and -10) and effector caspases (caspase-3, -6 and -7)1,6,7. The morphological changes of apoptosis include membrane blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and apoptotic body formation6,8. The receptor-interacting serine/threonine-protein kinase 1 (RIPK3) and mixed-lineage kinase domain-like (MLKL) are two downstream core components of the necroptotic mechanism1. RIPK3 recruits and phosphorylates MLKL, p-MLKL oligomerizes, associates with the cell membrane, initiates membrane perforations, causes ion influx, increases intracellular osmolarity, and eventually cell rupture6,9. Gasdermins and MLKL bind to the plasma membrane and mediate pyroptosis and necroptosis, respectively, while BAX/BAK mediates apoptosis by binding to the outer membrane of mitochondria6.
Although each pathway has specific mechanisms and outcomes, they lead to similar changes on the cell membrane. Under normal circumstances, phosphatidylserine (PS) is only localized in the inner leaflet of the plasma membrane. However, in the early stages of pyroptosis, apoptosis, and necroptosis, PS will be exposed, outside of the plasma membrane. Caspase-3/caspase-7 activates TMEM16 and XKR families, which leads to an asymmetrical cell membrane and externalizes&#160;PS during apoptosis10. Gasdermin D-mediated and MLKL-mediated Ca2+ influx leads to loss of the symmetry of the phospholipid bilayer on the cell membrane and the exposure of PS. The exposure occurs before the loss of cell membrane integrity11,12. Based on the similar changes in the membrane of these three types of programmed cell death, we use flow cytometry to analyze Annexin V/7-Aminoactinomycin D (7-AAD) double staining to detect cell death. Annexin V, a calcium-dependent phospholipid-binding protein, has a high affinity for PS, which can serve as a sensitive probe to detect exposed PS on the surface of the plasma membrane13. 7-AAD is a nucleic acid stain that cannot pass through the entire cell membrane. It is similar to propidium iodide (PI), a commonly used nucleic acid dye. They have similar fluorescence characteristics, but 7-AAD has a narrower emission spectrum and less interference with other detection channels. Owing to these similarities, it is not sufficient to distinguish between pyroptosis, apoptosis, and necroptosis. We used flow cytometry to detect the cell death from whole cells. A second method is used to capture the cell membrane using scanning electron microscopy (SEM) to observe the possible forms of cell death in individual cells.
We established a lipopolysaccharide (LPS) and adenosine triphosphate (ATP)-induced phorbol-12-myristate-13-acetate (PMA)-differentiated lipid deposition in human monocyte (THP-1) macrophage model to observe cell death. This protocol focuses on observing cell death rather than investigating mechanisms.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.25% pancreatic enzyme solution (excluding EDTA)</td>
			<td>BOSTER Biological Technology co.ltd</td>
			<td>PYG0068</td>
			<td></td>
		</tr>
		<tr>
			<td>5 mL Polystyrene Round-Bottom Tube</td>
			<td>CORNING</td>
			<td>352235</td>
			<td></td>
		</tr>
		<tr>
			<td>5 mL centrifuge tube</td>
			<td>Labgic Technology Co., Ltd.&#160;</td>
			<td>BS-50-M</td>
			<td></td>
		</tr>
		<tr>
			<td>6-well plate&#160;</td>
			<td>Sorfa Life Science Research Co.,Ltd</td>
			<td>220100</td>
			<td></td>
		</tr>
		<tr>
			<td>Annexin V-PE/7-AAD apoptosis analysis kit</td>
			<td>Absin (Shanghai) Biological Technology co.ltd</td>
			<td>abs50007</td>
			<td>Annexin V-PE, 7-AAD, 5&#215;Binding buffer, Apoptosis Positive Control Solution</td>
		</tr>
		<tr>
			<td>celculture CO2 incubator</td>
			<td>Esco (Shanghai) Enterprise Development Co., Ltd.</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>cell culture dish, 100 mm</td>
			<td>Sorfa Life Science Research Co.,Ltd</td>
			<td>230301</td>
			<td></td>
		</tr>
		<tr>
			<td>Cellometer K2 Fluorescent Cell Counter</td>
			<td>Nexcelom Bioscience LLC</td>
			<td>Cellometer K2</td>
			<td></td>
		</tr>
		<tr>
			<td>Cellometer SD100 Counting Chambers</td>
			<td>Nexcelom Bioscience LLC</td>
			<td>CHT4-SD100-002</td>
			<td></td>
		</tr>
		<tr>
			<td>centrifuge machine</td>
			<td>Hunan Xiangyi Laboratory Instrument Development Co., Ltd</td>
			<td>L530</td>
			<td></td>
		</tr>
		<tr>
			<td>chromium alum&#160;</td>
			<td>Guangdong Wengjiang Chemical Reagent Co., Ltd.</td>
			<td>PA04354</td>
			<td></td>
		</tr>
		<tr>
			<td>cover glasses, 9 mm</td>
			<td>Labgic Technology Co., Ltd.&#160;</td>
			<td>BS-09-RC</td>
			<td></td>
		</tr>
		<tr>
			<td>critical point dryer</td>
			<td>Quorum Technologies</td>
			<td>K850</td>
			<td></td>
		</tr>
		<tr>
			<td>dimethyl sulfoxide</td>
			<td>BOSTER Biological Technology co.ltd</td>
			<td>PYG0040</td>
			<td></td>
		</tr>
		<tr>
			<td>electron microscope fixative</td>
			<td>Servicebio Technology co.ltd&#160;</td>
			<td>G1102</td>
			<td>2.5% glutaric dialdehyde, 100 mM phosphorous salts</td>
		</tr>
		<tr>
			<td>electronic balance</td>
			<td>SHIMADZU</td>
			<td>ATX124</td>
			<td></td>
		</tr>
		<tr>
			<td>ethanol absolute</td>
			<td>Chengdu Kelong Chemical Co., Ltd</td>
			<td>2021033102</td>
			<td></td>
		</tr>
		<tr>
			<td>flow cytometer</td>
			<td>Becton,Dickinson and Company</td>
			<td>FACSCanto <img alt="Equation 1" src="/files/ftp_upload/66831/66831eq01.jpg" style="margin: auto;" /></td>
			<td></td>
		</tr>
		<tr>
			<td>flow cytometry analysis software</td>
			<td>Becton,Dickinson and Company</td>
			<td>BD FACSDivaTM Software</td>
			<td></td>
		</tr>
		<tr>
			<td>gelatin</td>
			<td>Guangdong Wengjiang Chemical Reagent Co., Ltd.</td>
			<td>PA00256&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>High resolution cold field emission scanning electron microscope</td>
			<td>TITACHI</td>
			<td>Regulus 8100</td>
			<td></td>
		</tr>
		<tr>
			<td>human monocytic cell line THP-1</td>
			<td>Procell Life Science&#38;Technology Co.,Ltd.</td>
			<td>CL0233</td>
			<td></td>
		</tr>
		<tr>
			<td>inverted microscope&#160;</td>
			<td>Leica Microsystems Co., Ltd</td>
			<td>DMi1</td>
			<td></td>
		</tr>
		<tr>
			<td>IR Vortex Mixer</td>
			<td>VELP Scientifica Srl</td>
			<td>ZX4</td>
			<td></td>
		</tr>
		<tr>
			<td>lipopolysaccharide&#160;</td>
			<td>Beijing Solarbio Science &#38; Technology Co.,Ltd.&#160;</td>
			<td>L8880</td>
			<td>LPS is derived from Escherichia coli 055:B5</td>
		</tr>
		<tr>
			<td>Na2ATP</td>
			<td>Beijing Solarbio Science &#38; Technology Co.,Ltd.&#160;</td>
			<td>A8270</td>
			<td></td>
		</tr>
		<tr>
			<td>phorbol-12-myristate-13-acetate&#160;</td>
			<td>Beijing Solarbio Science &#38; Technology Co.,Ltd.&#160;</td>
			<td>P6741</td>
			<td></td>
		</tr>
		<tr>
			<td>phosphate-buffered saline</td>
			<td>Servicebio Technology co.ltd&#160;</td>
			<td>G4202</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipette</td>
			<td>Eppendorf AG</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>pipette tips, 10 &#956;L</td>
			<td>Servicebio Technology co.ltd&#160;</td>
			<td>T-10PL</td>
			<td></td>
		</tr>
		<tr>
			<td>pipette tips, 1 mL&#160;</td>
			<td>Servicebio Technology co.ltd&#160;</td>
			<td>T-1250L</td>
			<td></td>
		</tr>
		<tr>
			<td>pipette tips, 200 &#956;L</td>
			<td>Servicebio Technology co.ltd&#160;</td>
			<td>T-200L</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI-1640 complete culture media</td>
			<td>Procell Life Science&#38;Technology Co.,Ltd.</td>
			<td>CM0233</td>
			<td>RPMI-1640 + 10% FBS + 0.05mM &#946;-mercaptoethanol + 1% P/S</td>
		</tr>
		<tr>
			<td>RPMI-1640 culture media&#160;</td>
			<td>Shanghai&#160;BasalMedia&#160;Technologies Co., LTD.</td>
			<td>K211104</td>
			<td></td>
		</tr>
		<tr>
			<td>sheath fluid</td>
			<td>BECKMAN COULTER</td>
			<td>8546733</td>
			<td></td>
		</tr>
		<tr>
			<td>sputter coater</td>
			<td>Cressington Scientific Instruments Ltd</td>
			<td>108</td>
			<td></td>
		</tr>
		<tr>
			<td>thermostatic water bath</td>
			<td>GUOHUA Electric Appliance CO.,Ltd&#160;</td>
			<td>HH-1</td>
			<td></td>
		</tr>
	</tbody>
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lps and atp-induced death of pma-differentiated thp-1 macrophages and its validation

Cell death is a fundamental process in all living organisms. The protocol establishes a lipopolysaccharide (LPS) and adenosine triphosphate (ATP)-induced phorbol-12-myristate-13-acetate (PMA)-differentiated lipid deposition in human monocyte (THP-1) macrophage model to observe cell death. LPS combined with ATP is a classic inflammatory induction method, often used to study pyroptosis, but apoptosis and necroptosis also respond to stimulation by LPS/ATP. Under normal circumstances, phosphatidylserine is only localized in the inner leaflet of the plasma membrane. However, in the early stages of pyroptosis, apoptosis, and necroptosis, the cell membrane remains intact and exposed to phosphatidylserine, and in the later stages, the cell membrane loses its integrity. Here, flow cytometry was used to analyze Annexin V and 7-Aminoactinomycin D (AAD) double staining to detect the cell death from the whole cells. The results show&#160;that substantial cells died after stimulation with LPS/ATP. Using scanning electron microscopy, we observe the possible forms of cell death in individual cells. The results indicate that cells may undergo pyroptosis, apoptosis, or necroptosis after stimulation with LPS/ATP. This protocol focuses on observing the death of macrophages after stimulation with LPS/ATP. The results showed that cell death after LPS and ATP stimulation is not limited to pyroptosis and that apoptosis and necrotic apoptosis can also occur, helping researchers better understand cell death after LPS and ATP stimulation and choose a better experimental method.

Author Spotlight: THP-1 Macrophage Response to LPS/ATP &#8212; Unveiling the Pyroptosis, Apoptosis, and Necroptosis Spectrum

LPS and ATP-induced Death of PMA-differentiated THP-1 Macrophages and its Validation

We are addressing LPS and ATP-introduced deaths of PMA-differentiated THP-1 macrophages. LPS and ATP-introduced deaths are not limited to pryoptosis but apoptosis and necroptosis can also occur. This will aid in a better understanding of cell death after LPS and ATP stimulation, and choosing more suitable experimental methods.Cryo-EM technology many studies the other structures in tissues, cells, and microorganisms. Cryo-EM provides neo native structure data for diverse molecular complexes. For example, using Cryo-Em techniques to perform 3D reconstruction can help us further understand the characteristic of apoptotic and necroptotic parts.Although pryoptosis is considered dominate in LPS and ATP-introduced cell death, one cannot determine the appropriation of these death forms or whether they all exist. Validating diverse cell death and measuring them will be our area of investigation in the future.

The cell samples were treated as described in the protocol and flow cytometry detection was done. Normal cells cannot be stained with Annexin V and 7-AAD (Annexin V-/7-AAD-). In the early stages of pyroptosis, apoptosis, and necroptosis, PS was exposed and bound to Annexin V, but the cell membrane was still intact and excluded 7-AAD from the extracellular space (Annexin V+/7-AAD-). In the later stages, the cell membrane loses its integrity, cells are simultaneously stained by Annexin V and 7-AAD, showing double positive ...

Read this Scientific Article Protocol about Author Spotlight: THP-1 Macrophage Response to LPS/ATP - Unveiling Pyroptosis, Apoptosis and Necroptosis Spectrum at JoVE.com

This protocol is based on LPS and ATP-induced death of PMA-differentiated THP-1 macrophages. We use flow cytometry to analyze Annexin V and 7-AAD double staining to detect cell death, using the whole cell and employing scanning electron microscopy to observe the cell membrane morphology.

Cell death is a fundamental process in all living organisms. The protocol establishes a lipopolysaccharide (LPS) and adenosine triphosphate (ATP)-induced ...