Recent developments in RNA sequencing increased the use of human brain tissue samples
in understanding transcriptional alterations in neurological and psychiatric diseases.
The human brain tissue samples typically cannot be processed immediately for RNA isolation.
Rather, the dissection of the brain is usually carried out hours after the death is
confirmed. Subsequently, the brains are stored frozen or in fixative before dissection
of RNA. Even the rare surgical samples cannot be processed on the site and need to
be transported to a laboratory for RNA isolation. RNA is not stable as it can be degraded
by RNases as well as its chemical decomposition can happen. These processes depend
on the microenvironment around the RNA, which may not be the same for the different
samples. Therefore, in the present study, we aimed to examine RNA quality in different
human brain samples stored in the Human Brain Tissue Bank of the Semmelweis University.
RNA quality was assessed by measuring the RNA integrity number (RIN) following an
RNA purification protocol combining the Trizol method and the columnar purification
steps. RNA quality varied depending on the brain, which the samples were dissected
from. The position of the brain tissue sample within the brain had less effect on
the RNA quality. Interestingly, once the RNA quality was good in a particular brain,
it remained stable for several hours and showed only limited degradation with postmortem
time (2 to 10 hours at room temperature). In contrast, neurosurgical samples (brain
tissue removed from the brain during neurosurgery), which have a small size, showed
fast degradation if stored at room temperature for 1 min to 3 hours. In addition to
these factors, the RNA quality also showed some dependency on the types of disease
the patient suffered from. In contrast, sex and age dependence was not found. These
data suggest that the brains have to be tested for RNA quality and dissections for
transcriptomics have to be performed only from selected brains with high RIN numbers.
In turn, a good quality RNA (better than RIN number 7) can be obtained from many brains
stored at -80 °C if properly processed.
Grant support was provided by HAS NAP2022-I-3/2022 and NAP2022-I-4/2022 NAP3 of the
Hungarian Academy of Sciences, EFOP-3.6.3-VEKOP-16-2017-00009 and Thematic Excellence
Program of the Semmelweis University.
