Regular Article

Regulation of Atypical ζ-Protein Kinase C in Cellular Signaling

Social stress, including bullying during adolescence, is a risk factor for common psychopathologies such as depression. To investigate the neural mechanisms associated with juvenile social stress-induced mood-related endophenotypes, we examined the behavioral, morphological, and biochemical effects of the social defeat stress model of depression on hippocampal dendritic spines within the CA1 stratum radiatum. Adolescent (postnatal day 35) male C57BL/6 mice were subjected to defeat episodes for 10 consecutive days. Twenty-four h later, separate groups of mice were tested on the social interaction and tail suspension tests.

Hippocampi were then dissected and Western blots were conducted to quantify protein levels for various markers important for synaptic plasticity including protein kinase M zeta (PKMζ), protein kinase C zeta (PKCζ), the dopamine-1 (D1) receptor, tyrosine hydroxylase (TH), and the dopamine transporter (DAT). Furthermore, we examined the presence of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptor subunit GluA2 as well as colocalization with the post-synaptic density 95 (PSD95) protein, within different spine subtypes (filopodia, stubby, long-thin, mushroom) using an immunohistochemistry and Golgi-Cox staining technique. The results revealed that social defeat induced a depression-like behavioral profile, as inferred from decreased social interaction levels, increased immobility on the tail suspension test, and decreases in body weight. Whole hippocampal immunoblots revealed decreases in GluA2, with a concomitant increase in DAT and TH levels in the stressed group. Spine morphology analyses further showed that defeated mice displayed a significant decrease in stubby spines, and an increase in long-thin spines within the CA1 stratum radiatum. Further evaluation of GluA2/PSD95 containing-spines demonstrated a decrease of these markers within long-thin and mushroom spine types. Together, these results indicate that juvenile social stress induces GluA2- and dopamine-associated dysregulation in the hippocampus – a neurobiological mechanism potentially underlying the development of mood-related syndromes as a consequence of adolescent bullying.

The aim of the present research was to analyze the pathways for phosphatidic acid metabolism in purified nuclei from liver. Lipid phosphate phosphatase, diacylglycerol lipase, monoacylglycerol lipase and PA-phospholipase type A activities were detected. The presence of lysophosphatidic acid significantly reduced DAG production while sphingosine 1-phoshate and ceramide 1-phosphate reduced MAG formation from PA. Using different enzymatic modulators (detergents and ions) an increase in the PA metabolism by phospholipase type A was observed. Our findings evidence an active PA metabolism in purified liver nuclei which generates important lipid second messengers, and which could thus be involved in nuclear processes such as gene transcription.

Diabetic macular edema is a major cause of visual impairment. The pathogenesis of macular edema appears to be multifactorial. Laser photocoagulation is the standard of care for macular edema. However, there are cases that are not responsive to laser therapy. Several therapeutic options have been proposed for the treatment of this condition. In this review we discuss several factors and mechanisms implicated in the etiology of macular edema (vasoactive factors, biochemical pathways, anatomical abnormalities). It seems that combined pharmacologic and surgical therapy may be the best approach for the management of macular edema in diabetic patients.

Although the signaling pathways regulating learning and the initial consolidation of memory have been extensively studied, the molecular mechanism maintaining memory storage has been unknown. Work on the maintenance of long-term potentiation (LTP), however, has identified a simple molecular mechanism involving gene expression of a constitutively active form of protein kinase C (PKC), protein kinase Mzeta (PKMζ), which sustains synaptic potentiation over time. Recent studies have shown that PKMζ also maintains the storage of memory for days to weeks. This chapter reviews the current state of knowledge on PKMζ, focusing on its discovery and the elucidation of its unique structure as an autonomously active form of PKC, its function in LTP maintenance, and its role in normal memory storage and disorders of memory.

Protein kinase Mζ (PKMζ) is a newly described form of PKC that is necessary and sufficient for the maintenance of hippocampal long term potentiation (LTP) and the persistence of memory in Drosophila. PKMζ is the independent catalytic domain of the atypical PKCζ isoform and produces long term effects at synapses because it is persistently active, lacking autoinhibition from the regulatory domain of PKCζ. PKM has been thought of as a proteolytic fragment of PKC. Here we report that brain PKMζ is a new PKC isoform, synthesized from a PKMζ mRNA encoding a PKCζ catalytic domain without a regulatory domain. Multiple ζ-specific antisera show that PKMζ is expressed in rat forebrain as the major form of ζ in the near absence of full-length PKCζ. A PKCζ knockout mouse, in which the regulatory domain was disrupted and catalytic domain spared, still expresses brain PKMζ, indicating that this form of PKM is not a PKCζ proteolytic fragment. Furthermore, the distribution of brain PKMζ does not correlate with PKCζ mRNA but instead with an alternate ζ RNA transcript thought incapable of producing protein. In vitro translation of this RNA, however, generates PKMζ of the same molecular weight as that in brain. Metabolic labeling of hippocampal slices shows increased de novo synthesis of PKMζ in LTP. Because PKMζ is a kinase synthesized in an autonomously active form and is necessary and sufficient for maintaining LTP, it serves as an example of a link coupling gene expression directly to synaptic plasticity.

In this study we report that protein kinase C ζ (PKC ζ), one of the atypical isoforms of the PKC family located predominantly in cytosol, is redistributed by C2-ceramide treatment in isolated hepatocytes. PKC ζ increased in membrane and nuclear fractions after 30 min of treatment with C2-ceramide in a dose- and time-dependent manner. The action of C2-ceramide was inhibited by wortmannin and LY 294002, indicating that C2-ceramide-induced PKC ζ increase in both nucleus and membrane fractions is mediated by phosphatidylinositol 3-kinase (PI3-kinase) activation. In addition, a significant translocation of PI3-kinase to the nucleus was observed after C2-ceramide treatment.