Kainic acid (KA)-induced Ca2+/Calmodulin-dependent protein kinase II (CaMK II) expression in the neurons, astrocytes and microglia of the mouse hippocampal CA3 region, and the phosphorylated CaMK II only in the hippocampal neurons

Proposed mechanisms of tau: relationships to traumatic brain injury, Alzheimer's disease, and epilepsy

Traumatic brain injury (TBI), Alzheimer's disease (AD), and epilepsy share proposed mechanisms of injury, including neuronal excitotoxicity, cascade signaling, and activation of protein biomarkers such as tau. Although tau is typically present intracellularly, in tauopathies, phosphorylated (p-) and hyper-phosphorylated (hp-) tau are released extracellularly, the latter leading to decreased neuronal stability and neurofibrillary tangles (NFTs). Tau cleavage at particular sites increases susceptibility to hyper-phosphorylation, NFT formation, and eventual cell death. The relationship between tau and inflammation, however, is unknown. In this review, we present evidence for an imbalanced endoplasmic reticulum (ER) stress response and inflammatory signaling pathways resulting in atypical p-tau, hp-tau and NFT formation. Further, we propose tau as a biomarker for neuronal injury severity in TBI, AD, and epilepsy. We present a hypothesis of tau phosphorylation as an initial acute neuroprotective response to seizures/TBI. However, if the underlying seizure pathology or TBI recurrence is not effectively treated, and the pathway becomes chronically activated, we propose a "tipping point" hypothesis that identifies a transition of tau phosphorylation from neuroprotective to injurious. We outline the role of amyloid beta (Aβ) as a "last ditch effort" to revert the cell to programmed death signaling, that, when fails, transitions the mechanism from injurious to neurodegenerative. Lastly, we discuss targets along these pathways for therapeutic intervention in AD, TBI, and epilepsy.

A circuit from dorsal hippocampal CA3 to parvafox nucleus mediates chronic social defeat stress-induced deficits in preference for social novelty

The preference for social novelty is crucial to the social life of humans and rodents. However, the neural mechanisms underlying social novelty preference are poorly understood. Here, we found that chronic social defeat stress (CSDS) reduced the preference for social novelty in mice by impairing the response of CaMKIIα⁺ neurons in the CA3 region of dorsal hippocampus (dCA3) during approach to an unfamiliar mouse. The deficits of social novelty preference in CSDS-treated mice were reversed by activating the output from dCA3 to the GABAergic neurons in the lateral septum (LS). The activation of GABAergic projection from LS recruited a circuit that inhibited the Foxb1⁺ neurons in the parvafox nucleus (PFN), which drove social avoidance by projecting to the lateral periaqueductal gray (lPAG). These results suggest that a previously unidentified circuit of dCA3^CaMKIIα+→LS^GABA+→PFN^Foxb1+→lPAG mediates the deficits of social novelty preference induced by CSDS.

Regulation of microglia population dynamics throughout development, health, and disease

The dynamic expansions and contractions of the microglia population in the central nervous system (CNS) to achieve homeostasis are likely vital for their function. Microglia respond to injury or disease but also help guide neurodevelopment, modulate neural circuitry throughout life, and direct regeneration. Throughout these processes, microglia density changes, as does the volume of area that each microglia surveys. Given that microglia are responsible for sensing subtle alterations to their environment, a change in their density could affect their capacity to mobilize rapidly. In this review, we attempt to synthesize the current literature on the ligands and conditions that promote microglial proliferation across development, adulthood, and neurodegenerative conditions. Microglia display an impressive proliferative capacity during development and in neurodegenerative diseases that is almost completely absent at homeostasis. However, the appropriate function of microglia in each state is critically dependent on density fluctuations that are primarily induced by proliferation. Proliferation is a natural microglial response to insult and often serves neuroprotective functions. In contrast, inappropriate microglial proliferation, whether too much or too little, often precipitates undesirable consequences for nervous system health. Thus, fluctuations in the microglia population are tightly regulated to ensure these immune cells can execute their diverse functions.

Proteomic Profile of Carbonylated Proteins Screen the Regulation of Calmodulin-Dependent Protein Kinases-AMPK-Beclin1 in Aerobic Exercise-Induced Autophagy in Middle-Aged Rat Hippocampus

BACKGROUND

Carbonylation is an oxidative modification of the proteins and a marker of oxidative stress. The accumulation of toxic carbonylated proteins might be one of the onsets of pathogenesis in hippocampal aging or neurodegeneration. Enormous evidence indicates that regular aerobic exercise might alleviate the dysfunction of carbonylated proteins, but the adaptational mechanisms in response to exercise are unclear.

OBJECTIVE

This study explored the carbonyl stress mechanism in the hippocampus using proteomics and the role of calmodulin-dependent protein kinases (CAMK)-AMP-activated protein kinase (AMPK)-Beclin1 signaling pathways in alleviating aging or improving function with regular aerobic exercise.

METHODS

Twenty-four healthy 13-month-old male Sprague-Dawley rats (average 693.21 ± 68.85 g) were randomly divided into middle-aged sedentary control group (M-SED, n = 12) and middle-aged aerobic exercise runner group (M-EX, n = 12). The M-EX group participated in regular aerobic exercise - treadmill running - with exercise intensity increasing gradually from 50-55% to 65-70% of maximum oxygen consumption (V˙O2max) over 10 weeks. The targeted proteins of oxidative modification were profiled by avidin magnetic beads and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q-TOF-MS). Western blots were used to test for molecular targets.

RESULTS

Regular aerobic exercise restores the intersessional habituation and rescues the hippocampus morphological structure in middle-aged rats. -ESI-Q-TOF-MS screened 56 carbonylated proteins only found in M-SED and 16 carbonylated proteins only found in M-EX, indicating aerobic exercise decreased carbonyl stress. Intriguingly, Ca2+/CAMK II alpha (CAMKIIα) was carbonylated only in the M-SED group at the oxidative modification site of 4-hydroxynonenal adducts, while regular aerobic exercise alleviated CAMKIIα carbonylation. Regular aerobic exercise significantly increased the expression and phosphorylated, active levels of CAMKIIα and AMPKα1. It also upregulated the expression of Beclin1 and microtubule-associated protein1-light chain 3 in the hippocampus.

CONCLUSION

Quantification of CAMKIIα carbonylation may be a potential biomarker of the hippocampal senescence. Additionally, regular aerobic exercise-induced autophagy via the activation of CAMK-AMPK-Beclin1 signaling pathway may mitigate the hippocampal neurodegeneration or pathological changes by alleviating protein carbonylation (carbonyl stress).

Expression of mutant human DISC1 in mice supports abnormalities in differentiation of oligodendrocytes

Abnormalities in oligodendrocyte (OLG) differentiation and OLG gene expression deficit have been described in schizophrenia (SZ). Recent studies revealed a critical requirement for Disrupted-in-Schizophrenia 1 (DISC1) in neural development. Transgenic mice with forebrain restricted expression of mutant human DISC1 (ΔhDISC1) are characterized by neuroanatomical and behavioral abnormalities reminiscent of some features of SZ. We sought to determine whether the expression of ΔhDISC1 may influence the development of OLGs in this mouse model. OLG- and cell cycle-associated gene and protein expression were characterized in the forebrain of ΔhDISC1 mice during different stages of neurodevelopment (E15 and P1 days) and in adulthood. The results suggest that the expression of ΔhDISC1 exerts a significant influence on oligodendrocyte differentiation and function, evidenced by premature OLG differentiation and increased proliferation of their progenitors. Additional findings showed that neuregulin 1 and its receptors may be contributing factors to the observed upregulation of OLG genes. Thus, OLG function may be perturbed by mutant hDISC1 in a model system that provides new avenues for studying aspects of the pathogenesis of SZ.

A decrease in phosphorylation of cAMP-response element-binding protein (CREBP) promotes retinal degeneration

Excitotoxicity, induced either by N-Methyl-d-aspartate (NMDA) or kainic acid (KA), promotes irreversible loss of retinal ganglion cells (RGCs). Although the intracellular signaling mechanisms underlying excitotoxic cell death are still unclear, recent studies on the retina indicate that NMDA promotes RGC death by increasing phosphorylation of cyclic AMP (cAMP) response element (CRE)-binding protein (CREBP), while studies on the central nervous system indicate that KA promotes neuronal cell death by decreasing phosphorylation of CREBP, suggesting that CREBP can elicit dual responses depending on the excitotoxic-agent. Interestingly, the role of CREBP in KA-mediated death of RGCs has not been investigated. Therefore, by using an animal model of excitotoxicity, the aim of this study was to investigate whether excitotoxicity induces RGC death by decreasing Ser(133)-CREBP in the retina. Death of RGCs was induced in CD-1 mice by an intravitreal injection of 20 nmoles of kainic acid (KA). Decrease in CREBP levels was determined by immunohistochemistry, western blot analysis, and electrophoretic mobility gel shift assays (EMSAs). Immunohistochemical analysis indicated that CREBP was constitutively expressed in the nuclei of cells both in the ganglion cell layer (GCL) and in the inner nuclear layer (INL) of CD-1 mice. At 6 h after KA injection, nuclear localization of Ser(133)-CREBP was decreased in the GCL. At 24 h after KA injection, Ser(133)-CREBP was decreased further in GCL and the INL, and a decrease in Ser(133)-CREBP correlated with apoptotic death of RGCs and amacrine cells. Western blot analysis indicated that KA decreased Ser(133)-CREBP levels in retinal protein extracts. EMSA assays indicated that KA also reduced the binding of Ser(133)-CREBP to CRE consensus oligonucleotides. In contrast, intravitreal injection of CNQX, a non-NMDA glutamate receptor antagonist, restored the KA-induced decrease in Ser(133)-CREBP both in the GCL and INL, and inhibited loss of RGCs and amacrine cells. These results, for the first time, suggest that KA promotes retinal degeneration by reducing phosphorylation of Ser(133)-CREBP in the retina.

Calcium/calmodulin-dependent protein kinase II regulates the phosphorylation of CREB in NMDA-induced retinal neurotoxicity

We examined the role of the phosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) and cyclic AMP-response element binding protein (CREB) in N-methyl-d-aspartate (NMDA)-induced neurotoxicity in the rat retina. Western blot analysis showed early elevation of phosphorylated CaMKII (p-CaMKII) protein levels and subsequential elevation of phosphorylated CREB (p-CREB) protein after NMDA injection. Immunohistochemistry showed that p-CaMKII was colocalized with Thy-1-positive retinal ganglion cells (RGCs) after NMDA injection. The increase in the p-CaMKII protein level was significantly inhibited by the preinjection of CaMKII small interfering RNA (siRNA), whereas negative control siRNA did not affect. Moreover, the increase in the p-CREB protein level after NMDA injection was also prevented by preinjection of CaMKII siRNA. In addition, our morphometric study of neurotracer retrograde labeling and Thy-1-positive cells showed that CaMKII siRNA significantly accelerated NMDA-induced RGC loss. Furthermore, the prevention of CREB binding by CRE decoy oligonucleotide also exacerbated RGC loss. These results suggest that the activation of CaMKII may regulate CREB phosphorylation and that the transient phosphorylation of CaMKII and CREB may be a neuroprotective response against NMDA-induced neurotoxicity.