Tissue slices represent the organs or intact tissue for in vitro studies such as biochemical analyses, live-cell imaging, electro-physiological, and pharmacological studies.
Theoretically, tissue slices are short-lived and should be used immediately. In practice, tissue slices can be temporarily maintained in cold storage or cryopreserved to reduce or stop their metabolic activities, thus extending their viability.
An alternative approach is to use tissue slices as explants and culture them in a sterile condition. Unlike tissue slice preservation, slice culture fosters the biochemical activities of the tissue slices, so that the cells retain their viability and behave similarly to their condition in situ.[1]
Tissue slices are cultured at an optimal temperature and given oxygen, essential nutrients, and factors, which allow the cells to regain the biochemical and cytological characteristics that represent their sources in vivo.
Slice culture can be broadly categorized into acute and organotypic slice cultures based on the culture duration—the time interval between culture initiation and analysis.
Considered more of a preparation method, freshly prepared tissue slices can be cultured temporarily in acute slice culture. Tissue slices are maintained at a steady temperature, given the necessary nutrients, and oxygen so that the cells can recapitulate their essential features before the tissue slices are used in the intended studies.[2-3]
As the name implies, acute slice cultures are prepared shortly before analysis because the slices can be cultured only for a few days before they start to decline and no longer represent their originating tissue or organs. However, this type of slice culture is relatively simple, non-laborious, and can be swiftly used for experimental studies.[1,3]
In most cases, acute slices are used in analyses involving instant cellular responses.
For example, cytological, electrophysiological, and metabolic profiles of the tissue slices before and after treatments with drug candidates, or changes in the microenvironment. [2-3]
Another relevant use is in analyses that call for tissue slices from mature or aging tissues, or tissues that are highly sensitive to disturbance. To illustrate, hippocampus slices are often prepared from the fully developed brains found in adult animals where the plasticity is remarkedly lower than that of the developing brains in neonatal animals.
The isolation of the hippocampus is also highly susceptible to glial cell activation, which can damage the surrounding healthy cells if the tissue slices are cultured for weeks or months.[3]
In organotypic slice culture, tissue slices are typically taken from tissues or organs of animals in neonatal or early postnatal stages.
The slices are cultured and maintained at a stable temperature, given oxygen, appropriate nutrients, and a substrate where they can adhere. Slice adherence enables the tissue explants to be cultured for weeks or months in organotypic slice culture.[1]
Tissue explants can be maintained as organotypic slice culture using the following substrate and culture methods:
The choice between the three substrates and culture methods depends on the tissue slices, especially slice thickness, type of cells in the tissue slices, culture duration, and the intended applications. Roller-tube and interface cultures are more fitting to slice cultures that extend over several weeks and months due to higher oxygen supply.[1]
The main advantage of organotypic slice culture is the length of time tissue slices remain viable. The prolonged cultivation period in a sterile condition can remove injured and dead cells that arise from slicing trauma, allowing the cells in the slices to recover and exhibit features and characteristics that most resemble their originating tissues and organs.
For this reason, organotypic slice culture is often used for studies that require users to observe the tissue slice over time. For instance, modeling neurodegenerative diseases and proteinopathies typically involve tracking changes in cellular morphology, organelle rearrangement, or protein abundance in the tissue.
Similarly, studies detailing cell or tissue differentiation, development, or regeneration would necessitate organotypic slice cultures which can be cultured and maintained over weeks or months.[1,3]
Organotypic slice culture is also applicable to cellular response analyses that cannot be conducted using acute slice culture. Namely, the long-term consequence of exposure or chronic application of substances such as chemicals, drugs, or toxins. These types of studies typically call for repeated observations of one sample over a while.[1]
The choice between acute slice and organotypic slice cultures depends primarily on the objectives of the study and the originating tissues or organs.
Briefly, tissue slices for acute and organotypic cultures can be prepared in the following steps:
First and foremost, tissue or organ is extracted from euthanized or anesthetized animals as quickly as possible. The extracted tissue or organ, including clinical samples, should be immediately chilled in a culture or preservation medium.[3]
Tissue and organ are dissected and sliced. Depending on tissue types, tissue slices can be prepared using a rotary microtome or tissue slicers such as a Krumdieck Tissue Slicer or tissue chopper.
The tools, equipment, and slicing buffers should be chilled before and during slicing. Each slice preparation technique has its advantages and limitations, to learn more about them, check out our article on the type of tissue slice techniques.
For organotypic slice culture, the surgical blade and slicing buffers that come into contact with the tissue slices must be pre-sterilized before use. Also, the culture medium and vessels should be warmed and prepared before slicing is commenced.[3]
After slicing, tissue slices are incubated according to tissue type and specific protocols. Typically, tissue slices for organotypic culture are first planted onto a substrate of choice before it is cultured.
For acute slice culture, tissue slices are usually incubated in an incubation chamber until they are used. Nowadays, equipment combines steps in tissue slicing and analysis for acute slice culture and integrates them into one workstation, enabling users to save time in preparing acute slice culture and conducting their analysis in one place.
Check out our article on semi-automated slice labs to learn how they work.
Tissue slice culture is an alternative approach that extends the vitality of tissue slices. Rather than halting the cellular biochemical reactions, nutrients and oxygen are supplied to the slices and maintained at a steady temperature. The ultimate goal is to let the tissue slices recoup their features and characteristics most like their sources in situ.
Tissue slices are embedded in a substrate to establish organotypic slice cultures, which are used for analysis that requires observations over weeks or months. Acute slice cultures are often used for studies that can be performed hours or days after slicing.
If you are looking for an efficient and affordable semi-automatic slice lab, check out our semi-automated workstation!
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