Class IIa HDAC Downregulation Contributes to Surgery-Induced Cognitive Impairment Through HMGB1-Mediated Inflammatory Response in the Hippocampi of Aged Mice.

OBJECTIVE: Perioperative neurocognitive disorders (PND) are a common complication in the elderly. Histone deacetylases (HDACs) are a class of enzymes that control the acetylation status of intracellular proteins. Thus, we explored whether HDACs trigger the release of high mobility group box 1 (HMGB1) through altering the acetylation status in the hippocampi of aged mice. MATERIALS AND METHODS: The effect of the Class IIa HDAC in PND was explored using an in vivo form of splenectomy. Sixteen-month-old healthy male C57BL/6J mice were randomly divided into five groups: control, anesthesia plus sham surgery, anesthesia plus splenectomy, LMK235 treatment, and PBS treatment. The hippocampi were harvested on either first, third, or seventh postoperative day. Cognitive function was assessed via a Morris water maze (MWM) test. Quantitative RT-PCR, Western blots and ELISAs were carried out to assess the targeted gene expression at transcriptional and translational levels. RESULTS: Splenectomy led to a significant deficiency in spatial memory acquisition, marked decreases in mRNA and protein levels of HDAC4 and HDAC5 in the hippocampus, and increases in the levels of total HMGB1 and acetylated HMGB1. In a similar fashion to splenectomy, treatment with the HDAC4/5 inhibitor LMK235 produced impaired spatial memory and an increase in the expression of HMGB1 and its acetylated counterpart in the hippocampus. CONCLUSION: These results suggest that surgery leads to PND through class IIa HDAC downregulation-triggered HMGB1 release in hippocampus of aged mice. HDACs may be a potential therapeutic target for postoperative cognitive dysfunction.

Surgery-induced downregulation of hippocampal sirtuin-1 contributes to cognitive dysfunction by inhibiting autophagy and activating apoptosis in aged mice.

OBJECTIVES: Elderly patients often suffer from cognitive dysfunction following surgery. However, the mechanisms underlying this phenomenon still remain unclear. This study investigated the critical part of Sirtuin-1 (SIRT1)-mediated autophagy and apoptosis in surgery-induced cognitive impairment. METHODS: The aged (16-month-old) male C57BL/6 mice underwent anesthesia and surgery. Some mice received intraperitoneal injections of resveratrol, which is an activator of SIRT1, prior to exposure to splenectomy. To examine learning and memory behavior in different sets, the study performed a Morris water maze. Tissues from the hippocampus were harvested 1, 3 and 7 days after surgery. Western blotting and immunofluorescence analysis determined the expression of autophagy- and apoptosis- associated protein. RESULTS: This article demonstrated surgery but not anesthesia considerably affected memory behavior and downregulated SIRT1 expression in the aged mice. Interestingly, rescue of hippocampal SIRT1 expression ameliorated the cognitive impairment in the elderly mice under splenectomy. In addition, surgical trauma decreased Beclin-1 protein levels and the LC3-II/LC3-I ratio, while expression of p62, Bax and cleaved caspase-3 in hippocampal neurons increased. However, rescue of hippocampal SIRT1 expression considerably attenuated the surgery-induced downregulation of Beclin-1, increased the ratio of LC3-II/LC3-I, and decreased expression of p62, Bax, and cleaved caspase-3. CONCLUSION: These findings suggest that surgery-induced downregulation of hippocampal SIRT1 participates in cognitive impairment after surgery by inhibiting the autophagy process and activating apoptosis.

HMGB1 gene silencing inhibits neuroinflammation via down-regulation of NF-κB signaling in primary hippocampal neurons induced by Aß25-35.

High mobility group box 1 protein (HMGB1) is potentially triggered by Aß oligomers and other sterile injuries, and is a non-histone DNA binding nuclear protein with roles in neural development and neurodegeneration, which contribute to memory impairment and chronic neuroinflammation in the brain. However, the exact molecular mechanisms of HMGB1 activation in Alzheimer's disease (AD) were previously unknown. The present study aimed to elucidate the effects of HMGB1 in Aß25-35-induced neuroinflammation in hippocampal neuron cultures. RNA interference (RNAi) HMGB1 treatment significantly reduced Aß25-35-induced HMGB1 expression by almost 70% in primary hippocampal neurons. Furthermore, quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and enzyme-linked immunosorbent assay (ELISA) demonstrated that short hairpin RNA (shRNA) for HMGB1 ameliorated Aß25-35-treated neuroinflammation, including activation of advanced glycosylation end product-specific receptor (RAGE), toll-like receptor 4 (TLR4), and nuclear factor-kappa B (NF-κB)-p65, as well as induced the release of inflammatory mediators such as tumor necrosis factor-α (TNF-α), interleukin 1ß (IL-1ß), IL-6, and HMGB1 in primary hippocampal neurons and the culture supernatant. In addition, pretreatment with HMGB1-shRNA dramatically reduced both the degree of nuclear-cytoplasmic HMGB1 translocation of HMGB1 and NF-κB DNA binding. Together, the data indicate that HMGB1 mediates the pathogenesis of AD by activating RAGE/TLR4 signaling and that shRNA targeting HMGB1 may be a promising therapeutic strategy for treating AD.