HT22 cells are an immortalized mouse hippocampal neuronal cell line, a widely used tool in neuroscience research. These cells provide a consistent and reproducible model for investigating cellular processes relevant to brain function and dysfunction. Their stable characteristics allow controlled experiments over extended periods. Their consistency makes them a reliable system for exploring complex biological mechanisms.
Origin and Cellular Characteristics
HT22 cells originate from the hippocampus of the mouse brain, subcloned from the parental HT4 cell line. The HT4 cell line was immortalized by introducing a temperature-sensitive Simian Virus 40 (SV40) T-antigen. Immortalization enables these cells to divide indefinitely in laboratory conditions, unlike primary cells which have a limited lifespan.
These cells exhibit a neuronal-like appearance and adhere to culture surfaces. A distinguishing feature is their lack of ionotropic glutamate receptors and cholinergic receptors, found on mature hippocampal neurons. This absence makes them unsuitable for studies involving receptor-mediated excitotoxicity or memory functions. However, this characteristic makes HT22 cells useful for studying non-receptor-mediated cellular pathways, especially those related to oxidative stress.
Modeling Oxidative Stress and Glutamate Toxicity
HT22 cells are a frequently used model for oxytosis, a specific form of cell death triggered by elevated glutamate. Unlike excitotoxicity, which involves overactivation of glutamate receptors, cell death in HT22 cells occurs through a different pathway. In this model, high extracellular glutamate inhibits the cystine/glutamate antiporter, which transports cystine into the cell. Cystine is a precursor for glutathione, a major intracellular antioxidant.
Inhibition of cystine uptake depletes intracellular glutathione levels. This reduction in antioxidant defense results in an accumulation of reactive oxygen species (ROS) within the cell, particularly mitochondrial superoxide. The buildup of ROS causes oxidative stress, lipid peroxidation, and mitochondrial dysfunction, initiating cell damage and death. This mechanism makes HT22 cells an effective system for studying the cellular responses to oxidative insults and testing potential protective compounds.
Role in Neurodegenerative Disease Studies
The oxidative stress pathway observed in HT22 cells is relevant to the pathology of various human neurodegenerative diseases. Oxidative damage is a recognized component in conditions such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis (ALS). In Alzheimer’s disease, for instance, increased oxidative stress is linked to neuronal death. Similarly, Parkinson’s disease involves oxidative degeneration of dopaminergic neurons.
Studying HT22 cells helps scientists understand the mechanisms of oxidative damage that contribute to these diseases. Researchers can use this model to investigate how different compounds or genetic manipulations might protect neurons from oxidative injury. This allows for the screening and evaluation of potential neuroprotective therapies, offering insights into new treatment strategies.
Common Laboratory Procedures
Culturing HT22 cells in a laboratory setting involves standard cell culture techniques to maintain their viability and growth. These cells are typically grown in a complete growth medium, such as Dulbecco’s Modified Eagle Medium (DMEM), supplemented with 10% fetal bovine serum (FBS) and 1% penicillin-streptomycin. The FBS provides essential growth factors and nutrients, while penicillin-streptomycin helps prevent bacterial contamination. Cells are incubated at 37°C in a humidified atmosphere containing 5% carbon dioxide.
To maintain a healthy cell population, HT22 cells undergo passaging or splitting every few days, typically at a 1:3 to 1:6 ratio. This involves detaching cells from the culture flask using trypsin-EDTA, diluting them, and transferring them to new flasks. Common assays include cell viability assays, such as the MTT assay, which measures metabolic activity as an indicator of live cells. These procedures ensure consistent experimental conditions.