Time-Course Changes and New Expressions of MIP-3α and Its Receptor, CCR6, in the Gerbil Hippocampal CA1 Area Following Transient Global Cerebral Ischemia

The role of lymphocytes in neonatal encephalopathy

Neonatal encephalopathy is a syndrome characterised by abnormal neurological function often caused by a hypoxic insult during childbirth. Triggers such as hypoxia-ischaemia result in the release of cytokines and chemokines inducing the infiltration of neutrophils, natural killer cells, B cells, T cells and innate T cells into the brain. However, the role of these cells in the development of the brain injury is poorly understood. We review the mechanisms by which lymphocytes contribute to brain damage in NE. NK, T and innate T cells release proinflammatory cytokines contributing to the neurodegeneration in the secondary and tertiary phase of injury, whereas B cells and regulatory T cells produce IL-10 protecting the brain in NE. Targeting lymphocytes may have therapeutic potential in the treatment of NE in terms of management of inflammation and brain damage, particularly in the tertiary or persistent phases.

Estrogenic hormones receptors in Alzheimer's disease

Estrogens are hormones that play a critical role during development and growth for the adequate functioning of the reproductive system of women, as well as for maintaining bones, metabolism, and cognition. During menopause, the levels of estrogens are decreased, altering their signaling mediated by their intracellular receptors such as estrogen receptor alpha and beta (ERα and ERβ), and G protein-coupled estrogen receptor (GPER). In the brain, the reduction of molecular pathways mediated by estrogenic receptors seems to favor the progression of Alzheimer's disease (AD) in postmenopausal women. In this review, we investigate the participation of estrogen receptors in AD in women during aging.

Age‑dependent alterations in the immunoreactivity of macrophage inflammatory protein‑3α and its receptor CCR6 in the gerbil hippocampus

Neuroinflammation is a primary characteristic of the aging brain. During normal aging, macrophage inflammatory protein-3α (MIP-3α) and its receptor C-C chemokine receptor type 6 (CCR6) serve pivotal roles in the neuroinflammatory process in the brain. The aim of the present study was to investigate age-dependent alterations in the immunoreactivity of MIP-3α and CCR6 in the gerbil hippocampus at postnatal month (PM) 1, 6, 12 and 24 via immunohistochemistry. In the PM 1 group, both MIP-3α and CCR6 immunoreactivity were observed primarily in the stratum pyramidale in the hippocampus proper and in the granule cell layer in the dentate gyrus. In the PM 6 and PM 12 groups, MIP-3α in the stratum pyramidale and granule cell layer was decreased compared with the PM 1 group, and CCR6 immunoreactivity in both layers was faint. In the PM 24 group, MIP-3α expression in the stratum pyramidale and granule cell layer was higher than that in the PM 1 group, and CCR6 immunoreactivity in both layers was increased compared with the PM 12 group; however, it was decreased compared with the PM 1 group. In conclusion, MIP-3α and CCR6 immunoreactivity were altered in the hippocampus during normal aging. The results of the current study suggested that age-dependent alterations of MIP-3α and CCR6 may be associated with age-related neuroinflammation in the hippocampus.

Change of Nurr1 expression in mouse hippocampal CA3 region following excitotoxic neuronal damage

Objective(s):

Nuclear receptor-related protein 1 (Nurr1), one of immediate-early genes, is a member of orphan nuclear receptor family. The aim of this study was to investigate the time-dependent change of Nurr1 protein expression in the mouse hippocampal CA3 region following kainic acid (KA)-induced excitotoxic neuronal damage.

Materials and Methods:

Male ICR mice were used as experimental animals, and 30 mg/kg KA was administered intraperitoneally. To confirm the KA-induced neuronal damage in the hippocampal CA3 region, Fluoro-Jade B histofluorescence staining was performed. In addition, the time-dependent change of Nurr1 protein expression was also examined using immunohistochemistry and western blot analysis.

Results:

Marked neuronal damage was observed in the hippocampal CA3 region at 24 hr after KA injection. In addition, both Nurr1 immunoreactivity and protein level were significantly increased at 6 hr and 12 hr after KA injection, and then decreased at 24 hr after KA injection.

Conclusion:

This result indicates that KA-induced alteration of Nurr1 protein expression may be associated with the neuronal degeneration in the hippocampal CA3 region after KA injection.

High-Mobility Group Box 1 Contributes to Cerebral Cortex Injury in a Neonatal Hypoxic-Ischemic Rat Model by Regulating the Phenotypic Polarization of Microglia

Neonatal hypoxic-ischemic (HI) encephalopathy is a severe disease for which there is currently no curative treatment. Recent evidence suggests that high-mobility group box 1 (HMGB1) protein can promote neuroinflammation after stroke in adult rodents, but its role in perinatal hypoxic-ischemic brain damage (HIBD) remains largely uninvestigated. In the present work, the potential role of HMGB1 in the pathogenesis of HIBD was explored. A HIBD model was established in postpartum day 7 rat pups. HMGB1 expression, the cellular distribution of HMGB1, and microglial activation were all evaluated. Glycyrrhizin (GL), an inhibitor of HMGB1, was used to investigate whether the inhibition of HMGB1 modulated microglial M1/M2 polarization or attenuated brain damage after HI. HAPI microglial cells and primary neurons were cultured in vitro and an oxygen-glucose deprivation model was established to evaluate the effects of different microglial-conditioned media on neurons using GL and recombinant HMGB1. Results showed that the expression of HMGB1 was increased in both the ipsilateral cortex and peripheral blood 72 h after HI. Immunofluorescence analyses showed that HMGB1 in the cortex was primarily expressed in neurons. This increase in cortical HMGB1 expression 72 h after HI was characterized by increased co-expression with microglia, rather than neurons or astrocytes. The expression of both M1 and M2 microglia was upregulated 72 h after HI. The administration of GL significantly suppressed M1 microglial polarization and promoted M2 microglial polarization. Meanwhile, GL pretreatment significantly alleviated brain edema and cerebral infarction. In vitro experimentation showed that HMGB1-induced M1-conditioned media aggravated neuronal damage, but this effect was neutralized by GL. These findings suggest that HMGB1 may result in an imbalance of M1/M2 microglial polarization in the cortex and thus cause neuronal injury. Pharmacological blockade of HMGB1 signaling may attenuate this imbalanced polarization of microglia and thus could be used as a therapeutic strategy against brain injury in HIBD.

Altered Nurr1 protein expression in the hippocampal CA1 region following transient global cerebral ischemia

Nuclear receptor related 1 protein (Nurr1), a member of the nuclear receptor 4 family of orphan nuclear receptors, has been reported to display anti‑inflammatory properties. The present study investigated the alteration of Nurr1 immunoreactivity in the gerbil hippocampus proper following 5 min of transient global cerebral ischemia. In sham operated gerbils, Nurr1 immunoreactivity was observed in pyramidal neurons in all cornu ammonis 1‑3 (CA1‑3) subfields of the hippocampus proper. In ischemia‑operated gerbils, Nurr1 immunoreactivity was altered in the CA1 subfield. Nurr1 immunoreactivity in CA1 pyramidal neurons gradually decreased until 2 days post‑ischemia, and, at 4 days post‑ischemia, Nurr1 immunoreactivity was concentrated in CA1 pyramidal neurons. Additionally, Nurr1 immunoreactivity was newly expressed in microglia in the CA1 subfield at 4 days post‑ischemia. Conversely, in the CA2/3 subfield, time‑dependent alteration of Nurr1 immunoreactivity was not identified at any time following ischemia. These results indicated that the alteration of Nurr1 expression in the CA1 subfield in the hippocampus may be associated with the death of CA1 pyramidal neurons.