The relative importance of premortem acidosis and postmortem interval for human brain gene expression studies:
P J Harrison1, P R Heath, S L Eastwood
1Department of Psychiatry, University of Oxford, UK.
Abstract:
To help account for the variable quality and quantity of RNA in human brain, we have studied the effect of premortem (agonal state) and postmortem factors on the detection of poly(A)+mRNA and eight mRNAs. For comparison, the influence of the same factors upon gene products encoded by the mRNAs was studied immunocytochemically or by receptor autoradiography. Brain pH declined with increasing age at death and was related to agonal state severity, but was independent of postmortem interval and the histological presence of hypoxic changes. By linear regression, pH was significantly associated with the abundance of several of the RNAs, but not with poly(A)+mRNA, immunoreactivities, or binding site densities. Postmortem interval had a limited influence upon mRNA and protein products. Freezer storage time showed no effect. Parallel rat brain studies showed no relationship between postmortem interval (0-48 h) and amounts of total RNA, poly(A)+RNA, or two individual mRNAs; however, RNA content was reduced by 40% at 96 h after death. pH is superior to clinical assessments of agonal state or mode of death in predicting mRNA preservation. It provides a simple means to improve human brain gene expression studies. pH is stable after death and during freezer storage and can be measured either in cerebrospinal fluid or in homogenised tissue.
Insights
Brain pH is a superior predictor of mRNA preservation than clinical assessments. Maintaining optimal pH levels can significantly improve human brain gene expression studies.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- RNA quality and quantity in human brain samples are highly variable.
- Premortem and postmortem factors can significantly impact RNA integrity.
- Accurate assessment of gene expression requires reliable RNA preservation.
Purpose of the Study:
- To investigate the effects of premortem and postmortem factors on poly(A)+mRNA and mRNA detection in human brain.
- To compare the influence of these factors on both RNA and protein products.
- To identify reliable indicators for predicting mRNA preservation in postmortem brain tissue.
Main Methods:
- Studied human brain samples, assessing poly(A)+mRNA and eight mRNAs.
- Utilized immunocytochemistry and receptor autoradiography for protein product analysis.
- Analyzed the correlation between brain pH, agonal state, postmortem interval, and RNA/protein levels.
- Conducted parallel studies in rat brains to validate findings.
Main Results:
- Brain pH declined with age and agonal state severity but was independent of postmortem interval.
- pH was significantly associated with the abundance of several RNAs, but not poly(A)+mRNA or protein products.
- Postmortem interval and freezer storage time had limited effects on mRNA and protein preservation.
- Rat brain studies showed RNA content reduction only after 96 hours postmortem.
Conclusions:
- Brain pH is a more accurate predictor of mRNA preservation than clinical agonal state assessments.
- Measuring brain pH offers a simple and effective method to enhance human brain gene expression studies.
- pH is stable postmortem and during freezer storage, allowing for reliable measurement.
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