Understanding trauma-induced hippocampal subfield volume changes in the context of age and health. Response to Malhi et al

Accelerated hippocampal biological aging in bipolar disorder

OBJECTIVES

Evidence suggests accelerated aging mechanisms in bipolar disorder (BD), including DNA methylation (DNAm) aging in blood. However, it is unknown whether such mechanisms are also evident in the brain, in particular in association with other biological clocks. To investigate this, we interrogated genome-wide DNAm in postmortem hippocampus from 32 BD-I patients and 32 non-psychiatric controls group-matched for age and sex from the NIMH Human Brain Collection Core.

METHODS

DNAm age and epigenetic aging acceleration were estimated using the Horvath method. Telomere length (TL) and mitochondrial DNA (mtDNA) copy number were quantified by real-time PCR. Between-group differences were assessed by linear regression and univariate general linear models with age, sex, race, postmortem interval, tissue pH, smoking, and body mass index included as co-variates.

RESULTS

Groups did not differ for epigenetic aging acceleration when considering the entire sample. However, after splitting the sample by the median age, an epigenetic aging acceleration was detected in patients compared to controls among older subjects (P = .042). While TL did not differ between groups, a reduction in mtDNA copy number was observed in patients compared to controls (P = .047). In addition, significant correlations were observed between epigenetic aging acceleration and TL (r = -.337, P = .006), as well as between TL and mtDNA copy number (r = .274, P = .028).

CONCLUSIONS

Hippocampal aging may underlie neurocognitive dysfunctions observed in BD patients. Moreover, our results suggest a complex cross-talk between biological clocks in hippocampus that may underlie clinical manifestations of premature aging in BD.

The Ring of Fire: Childhood Trauma, Emotional Reactivity, and Mixed States in Mood Disorders

Childhood trauma (CT) is strongly associated with bipolar disorder, possibly through emotional hyperreactivity (EH). Mixed symptoms/states (MSs) are associated with increased illness severity. The authors tested through a systematic review the association between CT and MSs. The authors systematically looked for studies exploring associations between MSs and CT, CT and EH, and EH and MSs. Most literature agrees that MSs are associated with CT; the latter was found to be associated to EH, which is in turn associated with MSs. The literature supports an association between CT and later development of MSs, possibly mediated through EH.