Protein kinase M ζ and the maintenance of long-term memory

Mechanisms of acupuncture-electroacupuncture on inflammatory pain

Acupuncture, as a traditional treatment, has been extensively used in China for thousands of years. According to the World Health Organization (WHO), acupuncture is recommended for the treatment of 77 diseases. And 16 of these diseases are related to inflammatory pain. As a combination of traditional acupuncture and modern electrotherapy, electroacupuncture (EA) has satisfactory analgesic effects on various acute and chronic pain. Because of its good analgesic effects and no side effects, acupuncture has been widely accepted all over the world. Despite the increase in the number of studies, the mechanisms via which acupuncture exerts its analgesic effects have not been conclusively established. A literature review of related research is of great significance to elaborate on its mechanisms and to inform on further research directions. We elucidated on its mechanisms of action on inflammatory pain from two levels: peripheral and central. It includes the mechanisms of acupuncture in the periphery (immune cells and neurons, purinergic pathway, nociceptive ion channel, cannabinoid receptor and endogenous opioid peptide system) and central nervous system (TPRV1, glutamate and its receptors, glial cells, GABAergic interneurons and signaling molecules). In this review, we collected relevant recent studies to systematically explain the mechanisms of acupuncture in treating inflammatory pain, with a view to providing direction for future applications of acupuncture in inflammatory pain and promoting clinical development.

The interplay among oxidative stress, brain insulin resistance and AMPK dysfunction contribute to neurodegeneration in type 2 diabetes and Alzheimer disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly followed by vascular dementia. In addition to clinically diagnosed dementia, cognitive dysfunction has been reported in diabetic patients. Recent studies are now beginning to recognize type 2 diabetes mellitus (T2DM), characterized by chronic hyperglycemia and insulin resistance, as a risk factor for AD and other cognitive disorders. While studies on insulin action have remained traditionally in the domain of peripheral tissues, the detrimental effects of insulin resistance in the central nervous system on cognitive dysfunction are increasingly being reported in recent clinical and preclinical studies. Brain functions require continuous supply of glucose and oxygen and a tight regulation of metabolic processes. Loss of this metabolic regulation has been proposed to be a contributor to memory dysfunction associated with neurodegeneration. Within the above scenario, this review will focus on the interplay among oxidative stress (OS), insulin resistance and AMPK dysfunctions in the brain by highlighting how these neurotoxic events contribute to neurodegeneration. We provide an overview on the detrimental effects of OS on proteins regulating insulin signaling and how these alterations impact cell metabolic dysfunctions through AMPK dysregulation. Such processes, we assert, are critically involved in the molecular pathways that underlie AD.

Cortical zeta-inhibitory peptide injection reduces local sleep need

Local sleep need within cortical circuits exhibits extensive interregional variability and appears to increase following learning during preceding waking. Although the biological mechanisms responsible for generating sleep need are unclear, this local variability could arise as a consequence of wake-dependent synaptic plasticity. To test whether cortical synaptic strength is a proximate driver of sleep homeostasis, we developed a novel experimental approach to alter local sleep need. One hour prior to light onset, we injected zeta-inhibitory peptide (ZIP), a pharmacological antagonist of protein kinase Mζ, which can produce pronounced synaptic depotentiation, into the right motor cortex of freely behaving rats. When compared with saline control, ZIP selectively reduced slow-wave activity (SWA; the best electrophysiological marker of sleep need) within the injected motor cortex without affecting SWA in a distal cortical site. This local reduction in SWA was associated with a significant reduction in the slope and amplitude of individual slow waves. Local ZIP injection did not significantly alter the amount of time spent in each behavioral state, locomotor activity, or EEG/LFP power during waking or REM sleep. Thus, local ZIP injection selectively produced a local reduction in sleep need; synaptic strength, therefore, may play a causal role in generating local homeostatic sleep need within the cortex.

Elevated Level of PKMζ Underlies the Excessive Anxiety in an Autism Model

Anxiety affects the life quality of a significant percentage of autism patients. To understand the possible biological basis of this high anxiety level, we used a valproic acid (VPA) model of autism. Anxiety level is significantly higher in VPA-injected mice, at both P35 and P70. In addition, protein kinase Mζ (PKMζ) level in the basolateral amygdala (BLA) is significantly higher in VPA mice at both ages. Consistent with this finding, infusion of a PKMζ-blocking peptide z-pseudosubstrate inhibitory peptide (ZIP) into BLA significantly reduced anxiety levels in VPA mice. Furthermore, viral overexpression of PKMζ in the BLA led to elevated anxiety level in Wild Type (WT) mice, with concomitant higher intrinsic excitability of BLA excitatory neurons. Altogether, our results indicate a key contribution of BLA PKMζ level to anxiety, especially in autism; and this finding may provide a further understanding of the pathogenesis as well as treatment of anxiety symptoms in autism patients.

Reversing Cocaine-Induced Plasticity with Zeta Inhibitory Peptide

Cocaine-induced plasticity persists during abstinence and is thought to underlie cue-evoked craving. Reversing this plasticity could provide an opportunity for therapeutic intervention. Converging evidence suggest that zeta inhibitory peptide (ZIP) eliminates memories for experience-dependent behaviors, including conditioned drug associations. However, the effect of ZIP on reward seeking and drug-induced plasticity is unknown. The current study examined the effect of ZIP administration in the nucleus accumbens on reinstatement (RI) of cocaine seeking, a rodent model of relapse. We demonstrate that intra-accumbal ZIP administration blocks cocaine-primed RI in rats when administered 24 h or 1 week before testing. These effects of ZIP on drug seeking are specific, as we did not see any effect of ZIP on RI of sucrose seeking. ZIP is a synthetic compound designed to inhibit the atypical PKC, PKMζ, a protein implicated in learning and memory. However, recent evidence from PKMζ-knock-out (KO) mice suggests that ZIP may function through alternative mechanisms. In support of this, we found that ZIP was able to block cue-induced RI in PKMζ-KO mice. One possible mechanism underlying addictive phenotypes is the ability of cocaine to block further plasticity. We hypothesized that ZIP may be working to reverse this anaplasticity. Although ZIP has no effect on accumbal LTD in slices from naive or yoked saline mice, it is able to restore both NMDA-dependent and mGluR5-dependent LTD in animals after cocaine self-administration and withdrawal. These findings demonstrate that intra-accumbal ZIP persistently reverses cocaine-induced behavioral and synaptic plasticity in male and female rodents.SIGNIFICANCE STATEMENT Zeta-inhibitory peptide (ZIP) has been shown to disrupt memory maintenance for experience-dependent behaviors. We examined the effect of ZIP infused into the nucleus accumbens on the reinstatement (RI) of cocaine seeking. We found that intra-accumbal ZIP blocked RI of cocaine seeking 24 h and 1 week later. This effect was specific to RI of cocaine seeking as ZIP did not disrupt RI of food seeking. In conjunction with these behavioral studies we examined the ability of ZIP to reverse cocaine-induced deficits in LTD. We found that ZIP was able to rescue two forms of LTD in cocaine-experienced mice. These studies demonstrate that ZIP is able to reverse cocaine-induced behavioral and synaptic plasticity in a persistent manner.

Post-translational modifications in MeHg-induced neurotoxicity

Mercury (Hg) exposure remains a major public health concern due to its widespread distribution in the environment. Organic mercurials, such as MeHg, have been extensively investigated especially because of their congenital effects. In this context, studies on the molecular mechanism of MeHg-induced neurotoxicity are pivotal to the understanding of its toxic effects and the development of preventive measures. Post-translational modifications (PTMs) of proteins, such as phosphorylation, ubiquitination, and acetylation are essential for the proper function of proteins and play important roles in the regulation of cellular homeostasis. The rapid and transient nature of many PTMs allows efficient signal transduction in response to stress. This review summarizes the current knowledge of PTMs in MeHg-induced neurotoxicity, including the most commonly PTMs, as well as PTMs induced by oxidative stress and PTMs of antioxidant proteins. Though PTMs represent an important molecular mechanism for maintaining cellular homeostasis and are involved in the neurotoxic effects of MeHg, we are far from understanding the complete picture on their role, and further research is warranted to increase our knowledge of PTMs in MeHg-induced neurotoxicity.

Biliverdin Reductase-A Mediates the Beneficial Effects of Intranasal Insulin in Alzheimer Disease

Impairment of biliverdin reductase-A (BVR-A) is an early event leading to brain insulin resistance in AD. Intranasal insulin (INI) administration is under evaluation as a strategy to alleviate brain insulin resistance; however, the molecular mechanisms underlying INI beneficial effects are still unclear. We show that INI improves insulin signaling activation in the hippocampus and cortex of adult and aged 3×Tg-AD mice by ameliorating BVR-A activation. These changes were associated with a reduction of nitrosative stress, Tau phosphorylation, and Aβ oligomers in brain, along with improved cognitive functions. The role of BVR-A was strengthened by showing that cells lacking BVR-A: (i) develop insulin resistance if treated with insulin and (ii) can be recovered from insulin resistance only if treated with a BVR-A-mimetic peptide. These novel findings shed light on the mechanisms underlying INI treatment effects and suggest BVR-A as potential therapeutic target to prevent brain insulin resistance in AD.

The Effect of Electroacupuncture on PKMzeta in the ACC in Regulating Anxiety-Like Behaviors in Rats Experiencing Chronic Inflammatory Pain

Chronic inflammatory pain can induce emotional diseases. Electroacupuncture (EA) has effects on chronic pain and pain-related anxiety. Protein kinase Mzeta (PKMzeta) has been proposed to be essential for the maintenance of pain and may interact with GluR1 to maintain CNS plasticity in the anterior cingulate cortex (ACC). We hypothesized that the PKMzeta-GluR1 pathway in the ACC may be involved in anxiety-like behaviors of chronic inflammatory pain and that the mechanism of EA regulation of pain emotion may involve the PKMzeta pathway in the ACC. Our results showed that chronic inflammatory pain model decreased the paw withdrawal threshold (PWT) and increased anxiety-like behaviors. The protein expression of PKCzeta, p-PKCzeta (T560), PKMzeta, p-PKMzeta (T560), and GluR1 in the ACC of the model group were remarkably enhanced. EA increased PWT and alleviated anxiety-like behaviors. EA significantly inhibited the protein expression of p-PKMzeta (T560) in the ACC, and only a downward trend effect for other substances. Further, the microinjection of ZIP remarkably reversed PWT and anxiety-like behaviors. The present study provides direct evidence that the PKCzeta/PKMzeta-GluR1 pathway is related to pain and pain-induced anxiety-like behaviors. EA treatment both increases pain-related somatosensory behavior and decreases pain-induced anxiety-like behaviors by suppressing PKMzeta activity in the ACC.