Ben-Shachar 2017 MiP2017
Mitochondrial complex I (CoI) deficit, associated with mitochondrial dysfunction, has been observed in schizophrenia (SZ), a devastating psychotic disorder characterized by cognitive, emotional and behavioral abnormalities with a world-wide prevalence of 1%. Altered expression of CoI nuclear DNA encoded subunits NDUFV1, NDUFV2 and NDUFS1, has been consistently reported in SZ patients. These three interchangeable (labile) subunits comprise the N module of CoI, involved in binding and oxidation of NADH. The aim of the present study was to unravel the defects in holo-CoI homeostasis that are involved in mitochondrial dysfunction in SZ. Epstein-Barr virus transformed lymphocyte cell lines from SZ patients and healthy subjects were used. Deficits, specifically in CoI-driven respiration in SZ-permeabilized cells were associated with reduced in-gel activity of isolated holo-CoI, indicating an impairment of CoI per-se. CoI and CoI-bound labile subunits level were similar in both cohorts, yet CoI synthesis rate was decreased in patients. This may be due to a decrease in subunits degradation rates as observed for NDUFV1 and NDUFV2 in patient cells. The latter is in line with a higher level of mitochondrial cAMP, which inhibits the degradation of these subunits, and the reduced variability in CoI-bound labile subunits between patients' cell lines compared to controls. To study the mechanism involved in the hitherto described deficits, we focused on NDUFV2, the most affected subunit in SZ. Although CoI-bound NDUFV2 level did not alter in patients, its mitochondrial level was lower. We therefore studied NDUFV2 import into the mitochondria following in-vitro translation of its RT-PCR product. We observed an impaired import in the patients, which was due to both protein and mitochondria source (patients or controls). As translation was performed in-vitro, we assumed that NDUFV2 transcript is impaired in patients. While Sanger sequencing showed no difference in transcript sequence between SZ and controls, it showed a mix of products in SZ cells. Different factors can interfere with the reverse transcriptase (RT) and hamper cDNA synthesis. In patients' samples, RT reaction at high and low dNTPs concentration followed by PCR resulted in a significantly greater difficulty in synthesizing cDNA than in controls. Notably, in the control but not in SZ samples, the extent of difficulty showed a strong and significant correlation with NDUFV2 cytosolic pre-protein level, suggesting that the interference with mRNA transcription has a functional effect on translation. NDUFV2 has a pseudogene (NDUFV2P1), which is an attractive candidate for the regulation of RNA transcription as are other non-coding RNAs. We therefore analyzed NDUFV2P1 expression in lymphoblast and frontal cortex postmortem specimens from patients and controls. We observed a significantly higher NDUFV2P1 transcript levels in patients' samples. Increased NDUFV2P1 transcripts can interfere with NDUFV2 reverse transcription, translation and import, lead to changes in synthesis and degradation rates of CoI, its abnormal activity and mitochondrial dysfunction in SZ.
• Bioblast editor: Kandolf G
Labels: MiParea: mtDNA;mt-genetics, mt-Medicine, Patients
Tissue;cell: Lymphocyte Preparation: Permeabilized cells
- Lab Psychobiology, Dept Psychiatry, Rambam Health Care Campus, B. Rappaport Fac Medicine Rappaport Family Inst Research Medical Sciences, Technion IIT, Haifa, Israel. - [email protected]