Synapses between engram cells are believed to be substrates for memory storage, and the weakening or loss of these synapses leads to the forgetting of related memories. We found engulfment of synaptic components by microglia in the hippocampi of healthy adult mice. Depletion of microglia or inhibition of microglial phagocytosis prevented forgetting and the dissociation of engram cells. By introducing CD55 to inhibit complement pathways, specifically in engram cells, we further demonstrated that microglia regulated forgetting in a complement- and activity-dependent manner. Additionally, microglia were involved in both neurogenesis-related and neurogenesis-unrelated memory degradation. Together, our findings revealed complement-dependent synapse elimination by microglia as a mechanism underlying the forgetting of remote memories.

Background. Heat shock protein 70 (Hsp70) has been shown to exert cardioprotection. Intracellular calcium ([Ca2+]i) overload induced by p38 mitogen-activated protein kinase (p38 MAPK) activation contributes to cardiac ischemia/reperfusion (I/R) injury. However, whether Hsp70 interacts with p38 MAPK signaling is unclear. Therefore, this study investigated the regulation of p38 MAPK by Hsp70 in I/R-induced cardiac injury. Methods. Neonatal rat cardiomyocytes were subjected to oxygen-glucose deprivation for 6 h followed by 2 h reoxygenation (OGD/R), and rats underwent left anterior artery ligation for 30 min followed by 30 min of reperfusion. The p38 MAPK inhibitor (SB203580), Hsp70 inhibitor (Quercetin), and Hsp70 short hairpin RNA (shRNA) were used prior to OGD/R or I/R. Cell viability, lactate dehydrogenase (LDH) release, serum cardiac troponin I (cTnI), [Ca2+]i levels, cell apoptosis, myocardial infarct size, mRNA level of IL-1β and IL-6, and protein expression of Hsp70, phosphorylated p38 MAPK (p-p38 MAPK), sarcoplasmic/endoplasmic reticulum Ca2+-ATPase2 (SERCA2), phosphorylated signal transducer and activator of transcription3 (p-STAT3), and cleaved caspase3 were assessed. Results. Pretreatment with a p38 MAPK inhibitor, SB203580, significantly attenuated OGD/R-induced cell injury or I/R-induced myocardial injury, as evidenced by improved cell viability and lower LDH release, resulted in lower serum cTnI and myocardial infarct size, alleviation of [Ca2+]i overload and cell apoptosis, inhibition of IL-1β and IL-6, and modulation of protein expressions of p-p38 MAPK, SERCA2, p-STAT3, and cleaved-caspase3. Knockdown of Hsp70 by shRNA exacerbated OGD/R-induced cell injury, which was effectively abolished by SB203580. Moreover, inhibition of Hsp70 by quercetin enhanced I/R-induced myocardial injury, while SB203580 pretreatment reversed the harmful effects caused by quercetin. Conclusions. Inhibition of Hsp70 aggravates [Ca2+]i overload, inflammation, and apoptosis through regulating p38 MAPK signaling during cardiac I/R injury, which may help provide novel insight into cardioprotective strategies.

Purpose Intracellular calcium ([Ca 2+ ]i) overload is a major cause of cell injury during myocardial ischemia/reperfusion (I/R). Dexmedetomidine (DEX) has been shown to exert anti-inflammatory and organ protective effects. This study aimed to investigate whether pretreatment with DEX could protect H9c2 cardiomyocytes against oxygen-glucose deprivation/reoxygenation (OGD/R) injury through regulating the Ca 2+ signaling. Methods H9c2 cardiomyocytes were subjected to OGD for 12 h, followed by 3 h of reoxygenation. DEX was administered 1 h prior to OGD/R. Cell viability, lactate dehydrogenase (LDH) release, level of [Ca 2+ ]i, cell apoptosis, and the expression of 12.6-kd FK506-binding protein/ryanodine receptor 2 (FKBP12.6/RyR2) and caspase-3 were assessed. Results Cells exposed to OGD/R had decreased cell viability, increased LDH release, elevated [Ca 2+ ]i level and apoptosis rate, down-regulated expression of FKBP12.6, and up-regulated expression of phosphorylated-Ser2814-RyR2 and cleaved caspase-3. Pretreatment with DEX significantly blocked the above-mentioned changes, alleviating the OGD/R-induced injury in H9c2 cells. Moreover, knockdown of FKBP12.6 by small interfering RNA abolished the protective effects of DEX. Conclusion This study indicates that DEX pretreatment protects the cardiomyocytes against OGD/R-induced injury by inhibiting [Ca 2+ ]i overload and cell apoptosis via regulating the FKBP12.6/RyR2 signaling. DEX may be used for preventing cardiac I/R injury in the clinical settings.

The most frequently mutated protein in human cancer is p53, a transcription factor (TF) that regulates myriad genes instrumental in diverse cellular outcomes including growth arrest and cell death. Cell context-dependent p53 modulation is critical for this life-or-death balance, yet remains incompletely understood. Here we identify sequence signatures enriched in genomic p53-binding sites modulated by the transcription cofactor iASPP. Moreover, our p53–iASPP crystal structure reveals that iASPP displaces the p53 L1 loop—which mediates sequence-specific interactions with the signature-corresponding base—without perturbing other DNA-recognizing modules of the p53 DNA-binding domain. A TF commonly uses multiple structural modules to recognize its cognate DNA, and thus this mechanism of a cofactor fine-tuning TF–DNA interactions through targeting a particular module is likely widespread. Previously, all tumor suppressors and oncoproteins that associate with the p53 DNA-binding domain—except the oncogenic E6 from human papillomaviruses (HPVs)—structurally cluster at the DNA-binding site of p53, complicating drug design. By contrast, iASPP inhibits p53 through a distinct surface overlapping the E6 footprint, opening prospects for p53-targeting precision medicine to improve cancer therapy.

Heat shock protein (HSP)60 is primarily a mitochondrial protein. Previous experiments have found that changes in the location of intracellular HSP60 have been associated with apoptosis. Extracellular HSP60 mediates apoptosis via its ligand, Toll‑like receptor (TLR)-4. TLR-4 is an important factor expressed on microglia, with a central role in generating neuroimmune responses in the pathogenesis of neurodegenerative disorders. Naloxone is a highly effective nonselective opioid receptor antagonist, and has been reported to be pharmacologically beneficial for the treatment of brain diseases through inhibiting microglia activation. However, the mechanisms underlying these beneficial effects of naloxone remain poorly understood. The present study aimed to investigate the role of HSP60 in the neuroprotective effects of naloxone on the production of proinflammatory mediators in lipopolysaccharide (LPS)-stimulated BV2 murine microglial cells and the possible signaling pathways involved. The results demonstrated that naloxone significantly inhibited the expression and release of HSP60 in BV2 cells. The expression levels of heat shock factor (HSF)-1 were upregulated in LPS‑activated BV2 cells, which indicated that the increased expression of HSP60 was driven by HSF-1 activation. However, increased HSF‑1 levels may be downregulated by naloxone. The levels of TLR‑4 were elevated in activated BV2 cells, and then inhibited by naloxone. Activation of TLR‑4 is characterized by activation of nuclear factor-κB (NF-κB) followed by the production of various proinflammatory and neurotoxic factors. Data from the present study demonstrated that naloxone reduced the expression levels of NF-κB and its upstream protein caspase‑3, and reduced the LPS-induced production of nitric oxide, inducible nitric oxide synthase, tumor necrosis factor α, interleukin-1β and interleukin-6 in BV2 microglia. In light of this data, it was concluded that naloxone may exert its neuroprotective and anti‑inflammatory effects by inhibiting microglia activation through a HSP60‑TLR‑4‑NF‑κB signaling pathway.

Oligodendrocytes are generated by the differentiation and maturation of oligodendrocyte precursor cells (OPCs). The failure of OPC differentiation is a major cause of demyelinating diseases; thus, identifying the molecular mechanisms that affect OPC differentiation is critical for understanding the myelination process and repairing after demyelination. Although prevailing evidence shows that OPC differentiation is a highly coordinated process controlled by multiple extrinsic and intrinsic factors, such as growth factors, axon signals, and transcription factors, the intracellular signaling in OPC differentiation is still unclear. Here, we showed that glycogen synthase kinase 3β (GSK3β) is an essential positive modulator of OPC differentiation. Both pharmacologic inhibition and knockdown of GSK3β remarkably suppressed OPC differentiation. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assays and Ki67 staining showed that the effect of GSK3β on OPC differentiation was not via cell death. Conversely, activated GSK3β was sufficient to promote OPC differentiation. Our results also demonstrated that the transcription of myelin genes was regulated by GSK3β inhibition, accompanying accumulated nuclear β-catenin, and reduced the expression of transcriptional factors that are relevant to the expression of myelin genes. Taken together, our study identified GSK3β as a profound positive regulator of OPC differentiation, suggesting that GSK3β may contribute to the inefficient regeneration of oligodendrocytes and myelin repair after demyelination.

Hypoxia-ischemia (HI) occurring in immature brains stimulates the expression of tissue-type plasminogen activator (tPA). Neuroserpin is a selected inhibitor of tPA in the central nerves system. However, the role that neuroserpin plays and the possible mechanisms involved during neonatal HI are poorly defi ned. In this study, an oxygen-glucose deprivation and reoxygenation (OGD/R) model was generated with cultured rat cortical neurons mimicking neonatal HI injury ex vivo, and an acute neuronal excitatory injury was induced by exposure to a high concentration of N-methyl-D-aspartic acid (NMDA). Cells received either neuroserpin or MK-801, an antagonist of the NMDA receptor, during OGD/R, and were incubated with or without neuroserpin after NMDA exposure. Cell viability and morphology were detected by a Cell Counting Kit-8 and immunohistochemical staining, respectively. TPA expression and activity were also assessed. We found that MK-801 alleviated injuries induced by OGD/R, suggesting an excitatory damage involvement. Neuroserpin provided a dosedependent neuroprotective eff ect in both OGD/R and acute excitatory injuries by inhibiting the activity of tPA, without aff ecting neuronal tPA expression. Neuroserpin protected neurons against OGD/R even after a delayed administration of 3h. Collectively, our data indicate that neuroserpin protects neurons against OGD/R. mainly by inhibiting tPA-mediated acute neuronal excitotoxicity.

Curcumin has anti-inflammatory and antioxidant properties and has been widely used to treat or prevent neurodegenerative diseases. However, the mechanisms underlying the neuroprotective effects of curcumin are not well known. In the present study, the effect of curcumin on lipopolysaccharide (LPS)-stimulated BV2 mouse microglia cells was investigated using enzyme-linked immunosorbent assays of the culture medium and western blotting of cell lysates. The results showed that curcumin significantly inhibited the LPS-induced expression and release of heat shock protein 60 (HSP60) in the BV2 cells. The level of heat shock factor (HSF)-1 was upregulated in LPS-activated BV2 microglia, indicating that the increased expression of HSP60 was driven by HSF-1 activation. However, the increased HSF-1 level was downregulated by curcumin. Extracellular HSP60 is a ligand of Toll-like receptor 4 (TLR-4), and the level of the latter was increased in the LPS-activated BV2 microglia and inhibited by curcumin. The activation of TLR-4 is known to be associated with the activation of myeloid differentiation primary response 88 (MyD88) and nuclear factor (NF)-κB, with the subsequent production of proinflammatory and neurotoxic factors. In the present study, curcumin demonstrated marked suppression of the LPS-induced expression of MyD88, NF-κB, caspase-3, inducible nitric oxide synthase, tumor necrosis factor-α, interleukin (IL)-1β and IL-6 in the microglia. These results indicate that curcumin may exert its neuroprotective and anti-inflammatory effects by inhibiting microglial activation through the HSP60/TLR-4/MyD88/NF-κB signaling wpathway. Therefore, curcumin may be useful for the treatment of neurodegenerative diseases that are associated with microglial activation.