Using Postmortem hippocampi tissue can interfere with differential gene expression analysis of the epileptogenic process

Author(s)

Lopes Born, Joao Paulo ; Matos, Heloisa de Carvalho ; de Araujo, Mykaella Andrade ; Castro, Olagide Wagner ; Duzzioni, Marcelo ; Peixoto-Santos, Jose Eduardo ; Leite, Joao Pereira ; Garcia-Cairasco, Norberto ; Paco-Larson, Maria Luisa ; Goes Gitai, Daniel Leite

• Document type: Journal article
• Source: PLoS One; v. 12, n. 8 AUG 4 2017.
• Web of Science Citations: 5

Abstract

Neuropathological studies often use autopsy brain tissue as controls to evaluate changes in protein or RNA levels in several diseases. In mesial temporal lobe epilepsy (MTLE), several genes are up or down regulated throughout the epileptogenic and chronic stages of the disease. Given that postmortem changes in several gene transcripts could impact the detection of changes in case-control studies, we evaluated the effect of using autopsy specimens with different postmortem intervals (PMI) on differential gene expression of the Pilocarpine (PILO) induced Status Epilepticus (SE) of MTLE. For this, we selected six genes (Gfap, Ppia, Gad65, Gad67, Npy, and Tnf-alpha) whose expression patterns in the hippocampus of PILO-injected rats are well known. Initially, we compared hippocampal expression of naive rats whose hippocampi were harvested immediately after death (0h-PMI) with those harvested at 6h postmortem interval (6h-PMI): Npy and Ppia transcripts increased and Tnf-alpha transcripts decreased in the 6h-PMI group (p<0.05). We then investigated if these PMI-related changes in gene expression have the potential to adulterate or mask RT-qPCR results obtained with PILO-injected rats euthanized at acute or chronic phases. In the acute group, Npy transcript was significantly higher when compared with 0h-PMI rats, whereas Ppia transcript was lower than 6h-PMI group. When we used epileptic rats (chronic group), the RT-qPCR results showed higher Tnf-alpha only when compared to 6h-PMI group. In conclusion, our study demonstrates that PMI influences gene transcription and can mask changes in gene transcription seen during epileptogenesis in the PILO-SE model. Thus, to avoid erroneous conclusions, we strongly recommend that researchers account for changes in postmortem gene expression in their experimental design. (AU)

• FAPESP's process: 15/20840-9 - Histopathological correlates of magnetic resonance imaging in patients with drug-resistant epilepsies
• Grantee: José Eduardo Peixoto Santos
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 16/17882-4 - Drug-resistant epilepsies: diagnostic challenges, associated comorbidities and new experimental approaches
• Grantee: João Pereira Leite
• Support Opportunities: Research Projects - Thematic Grants