Usnic acid

Infectious-disease experiments test how pathogens interact with host barriers, innate immune receptors, inflammatory signaling, pathogen replication, and tissue injury; pattern-recognition receptors such as TLRs, RIG-I-like receptors, NOD-like receptors, and inflammasomes detect microbial molecules and activate NF-κB, interferon, and cytokine responses. The central hypothesis is that infection severity reflects the balance between pathogen burden and host response: protective inflammation restricts pathogen growth, whereas excessive or mislocalized inflammation contributes to tissue damage and disease phenotype. Unresolved questions include which host pathways are protective versus pathogenic, why some infection models fail to translate to human disease, and which combined readouts best predict clinically relevant infection outcomes.

By lysing cells, releasing RNA, and removing impurities such as proteins and DNA, high-purity RNA products are finally obtained. The commonly used traditional method is the guanidine isothiocyanate/phenol/chloroform method (Trizol), which is suitable for a variety of animal materials including animal tissues, microorganisms, cultured cells, etc., and most plant materials.

Apoptosis, also called programmed cell death, is generally characterized by distinct morphological characteristics.

TUNEL staining detects DNA strand breaks by using terminal deoxynucleotidyl transferase to add labeled nucleotides to exposed 3′-OH DNA termini, generating either microscopic staining in fixed cells or tissue sections, or fluorescence/cytometric signal in cell suspensions. TUNEL positivity reflects DNA fragmentation but should not be interpreted alone as definitive apoptosis, because TUNEL can also label necrotic, autolytic, mechanically damaged, or DNA-repair-associated DNA breaks.

Flow cytometric DNA-content cell-cycle staining measures the fluorescence intensity of DNA-bound fluorochromes in single cells or nuclei to estimate DNA content distributions, allowing assignment of populations to G0/G1, S, and G2/M phases by DNA histogram deconvolution. Propidium iodide (PI) intercalates into DNA, and PI fluorescence is proportional to cellular DNA content when staining is performed under conditions that make DNA accessible and minimize non-DNA signal. Cells with G2/M DNA content are expected to show approximately twice the fluorescence intensity of G0/G1 cells, while S-phase cells occupy intermediate fluorescence values. PI-based DNA-content analysis can also detect cells with fractional DNA content, often reported as sub-G1, when DNA fragmentation and extraction during staining reduce retained DNA signal in apoptotic cells. DAPI is an alternative DNA fluorochrome for univariate DNA-content analysis, while bivariate approaches combining DNA content with proliferation

Annexin V-based apoptosis assays rely on the detection of phosphatidylserine (PS) externalization from the inner leaflet of the plasma membrane to the outer leaflet, an early biochemical hallmark of apoptosis. Fluorescently labeled Annexin V binds PS in a calcium-dependent manner, enabling identification of early apoptotic cells by flow cytometry or fluorescence microscopy. When combined with a membrane-impermeant DNA-binding dye (e. g. , propidium iodide), this approach allows discrimination between viable (Annexin V−/dye−), early apoptotic (Annexin V+/dye−), and late apoptotic or necrotic (Annexin V+/dye+) cell populations by assessing membrane integrity and PS exposure.

Bromodeoxyuridine (BrdU) incorporation assay is based on the principle that BrdU, a thymidine analog, is incorporated into newly synthesized DNA during the S phase of the cell cycle, thereby serving as a marker of DNA replication and cellular proliferation. Incorporated BrdU can be detected using anti-BrdU antibodies following DNA denaturation, enabling visualization or quantification of proliferating cells through immunochemical detection methods such as immunofluorescence or immunohistochemistry.

Apoptosis is a regulated, generally non-lytic cell-death pathway that removes unwanted, damaged, infected, or abnormal cells through coordinated morphological changes, caspase activation, DNA fragmentation, and membrane remodeling. The intrinsic apoptosis pathway is controlled mainly by mitochondrial outer membrane permeabilization, BCL-2 family proteins, cytochrome c release, apoptosome formation, caspase-9 activation, and downstream executioner caspase-3/7 activation. The extrinsic apoptosis pathway is initiated by death receptors such as Fas, TNFR, and TRAIL receptors, which recruit adaptor proteins and activate caspase-8 before engaging executioner caspases or mitochondrial amplification through BID cleavage. Apoptosis is linked to many phenotypes, including cancer cell killing, tissue homeostasis, immune regulation, neurodegeneration, infection response, and treatment-induced cytotoxicity; unresolved questions include how apoptosis interacts with necroptosis, pyroptosis, ferroptos

Cell-cycle analysis by flow cytometry measures DNA content in single cells to estimate the fraction of cells in G0/G1, S, and G2/M phases. Propidium iodide intercalates into DNA, and after RNA removal with RNase, fluorescence intensity reflects cellular DNA content: 2N cells are assigned to G0/G1, cells between 2N and 4N to S phase, and 4N cells to G2/M. DNA-content analysis alone cannot reliably separate G0 from G1 or G2 from M. Ki-67 can distinguish quiescent G0 cells from cycling cells, EdU or BrdU incorporation marks active DNA synthesis in S phase, and phospho-histone H3 staining identifies mitotic cells within the 4N population.

The NLRP3 inflammasome is a cytosolic innate immune signaling platform that integrates priming signals and danger-signal activation to promote caspase-1 activation, maturation of IL-1β and IL-18, and gasdermin D-mediated pyroptotic cell death. The core experimental logic is to determine whether inflammatory disease phenotypes are driven by increased NLRP3 expression, ASC-containing inflammasome assembly, caspase-1 cleavage, GSDMD cleavage, and extracellular release of IL-1β/IL-18 rather than by nonspecific cell injury alone. The pathway is strongly linked to inflammation-related disease phenotypes because monosodium urate crystals activate NALP3/NLRP3 inflammasome signaling in gout-like crystal inflammation, cholesterol crystals activate NLRP3 inflammasomes in atherogenesis models, and DSS-induced intestinal inflammation has been reported to involve NLRP3 inflammasome activity. However, experimental colitis studies also show context-dependent protective effects of NLRP3 inflammasome co

Ferroptosis is an iron-dependent, non-apoptotic form of regulated cell death characterized by lethal lipid peroxidation and sensitivity to suppression by iron chelators or lipophilic radical-trapping antioxidants. The core pathway links cystine uptake through system Xc−, glutathione availability, GPX4-dependent detoxification of phospholipid hydroperoxides, iron-dependent oxidative reactions, and polyunsaturated-phospholipid metabolism into a cell-death program that is biochemically and morphologically distinct from apoptosis, necrosis, and autophagy. The ferroptosis pathway is experimentally linked to phenotype through chemical and genetic perturbation. Erastin induces ferroptosis by inhibiting cystine uptake through system Xc− and weakening antioxidant defenses, while GPX4 inhibition or depletion causes lipid peroxide accumulation and ferroptotic cancer-cell death. ACSL4 and oxidizable arachidonoyl- or adrenoyl-containing phosphatidylethanolamines shape ferroptosis sensitivity by con

Osteoclast differentiation is an in vitro induction assay in which monocyte/macrophage-lineage precursors are exposed to macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL), generating multinucleated osteoclasts that are commonly identified by tartrate-resistant acid phosphatase (TRAP) staining and functionally confirmed by resorption pits on dentin, bone, or mineralized substrates. M-CSF supports survival and expansion of osteoclast precursors, while RANKL binding to RANK drives osteoclast commitment, fusion, maturation, and resorptive function; osteoprotegerin inhibits this pathway by binding RANKL and preventing RANK activation. The main readouts are the number of TRAP-positive multinucleated cells, formation of F-actin rings, and resorbed surface area; TRAP-positive multinucleated cells indicate osteoclast differentiation, whereas pit formation on dentin, bone, or mineralized coating indicates functional bone-resorbing activity.