Effect of Sirt3 on hippocampal MnSOD activity, mitochondrial function, physiology, and cognition in an aged murine model.

The NAD(+)-dependent deacetylase SIRT3 is a proven mitochondrial metabolic stress sensor. It has been linked to the regulation of the mitochondrial acetylome and activation of several metabolic enzymes (e.g., manganese superoxide dismutase [MnSOD]) to protect mitochondrial function and redox homeostasis, which are vital for survival, excitability, and synaptic signaling of neurons mediating short- and long-term memory formation as well as retention. Eighteen-month-old male and female wild-type (WT) and Sirt3 mice were behaviorally tested for hippocampus-dependent cognitive performance in a Morris water maze paradigm. Cognitive impairment was displayed during the probe trial by female and male Sirt3 mice but not WT mice. Upon sacrifice, brains were fixed, and morphological assessments were conducted on hippocampal tissues. Both female and male Sirt3 mice demonstrated impaired spatial memory retention implying that SIRT3 plays a role in long-term memory function. Golgi-staining studies revealed decreased dendritic arborization and dendritic length in the hippocampi of male Sirt3 compared to WT animals. Sirt3 deletion significantly increased NR1, NR2A, and NR2B expression in the hippocampus of female mice only. Enzymatic activity of MnSOD, a major mitochondrial deacetylation target of SIRT3, was significantly decreased in both female and male Sirt3 mice. Similarly, both female and male Sirt3 mice demonstrated a significant decrease in their respiratory control ratio during Complex I-driven respiration, which was apparent only in female Sirt3 mice during Complex II-driven respiration.