Comprehensive Analysis of Proteasomal Complexes in Mouse Brain Regions Detects ENO2 as a Potential Partner of the proteasome in the Striatum

Defects in the activity of the proteasome or its regulators are linked to several pathologies including neurodegenerative diseases. We hypothesize that proteasome heterogeneity and its selective partners vary across brain regions and have a large impact on proteasomal catalytic activities. Using neuronal cell cultures and brain tissues obtained from mice, we compared proteasomal activities from two distinct brain regions affected in neurodegenerative diseases, the striatum and the hippocampus. The results indicated that proteasome activities and their responses to proteasome inhibitors are determined by their subcellular localizations and their brain regions. Using a iodixanol gradient fractionation method, proteasome complexes were isolated, followed by proteomic analysis for proteasomal interaction partners. Proteomic results revealed gamma enolase (ENO2), a known proteasome partner, has more affinity to proteasome complexes purified from the striatum than to those from the hippocampus. These results highlight a potential key role for non-proteasomal partners of proteasome regarding the diverse activities of the proteasome complex recorded in several brain regions.

Abstract 323: Gamma-Enolase in Adult Cardiac Myocytes: A Study of Subcellular Localization and Post-Myocardial Infarction Modulation

Background: Gamma-enolase, or neuron-specific enolase, is a multifunctional protein which is primarily found in neurons and neuroendocrine cells. Although the main role of gamma-enolase is associated with enzymatic activity during aerobic glycolysis, recently, it has been implicated in a variety of pathophysiological processes including inflammation, extracellular matrix degradation and cell survival after ischemic insult. Over the last decades, there have been a number of reports demonstrating the expression of gamma-enolase in the heart. Surprisingly, the latter finding has not received much attention in the past. Considering that this protein can play an important role in cellular adaptation to the ischemic environment we decided to examine the expression of gamma-enolase in the heart at different time points following a myocardial infarction (MI). Methods: A transmural MI was induced in male, middle-aged Sprague-Dawley rats by permanent left coronary artery ligation. The rats were euthanized 3 days, 1, 2, 4 and 8 weeks after MI and their hearts were processed into paraffin for immunostaining and quantitative morphometry. Results: We found that in post-MI heart gamma-enolase protein was expressed in cardiac myocytes of the remote myocardium as well as in the muscle cells surviving inside the transmural scar. On a subcellular level, the gamma-enolase expression overlapped with the I-bands of the sarcomeres. Despite the heterogeneity of the gamma-enolase fluorescence intensity among individual cardiac myocytes, there was no evident correlation between the size of the cells and the intensity of the gamma-enolase immunofluorescence in any region of the post-MI heart, although the immunofluorescence intensity of gamma-enolase in myocytes of the remote myocardium was always greater than that in myocytes surviving within the transmural scar. Most importantly, we determined that the intensity of gamma-enolase immunofluorescence recorded in cardiac myocytes has experienced an evident stepwise reduction at 1 and 8 weeks following MI. Conclusions: Taken together, our findings reveal that the cardiac myocytes of the adult rat heart express gamma-enolase and that the expression of this protein has been altered during post-MI cardiac remodeling.

Proteomic Analysis of Hippocampus and Cortex in Streptozotocin-Induced Diabetic Model Mice Showing Dementia

Aim. Diabetes with its associated hyperglycemia induces various type of peripheral damage and also impairs the central nervous system (CNS). This study is aimed at clarifying the precise mechanism of diabetes-induced dementia as an impairment of CNS. Methods. The proteomic analysis of the hippocampus and cortex in streptozotocin- (STZ-) treated mouse diabetic model showing dementia was performed using two-dimensional gel electrophoresis (2-DE) followed by mass spectrometry (n=3/group). Results. Significant changes in the expression of 32 proteins and 7 phosphoproteins were observed in the hippocampus and cortex. These identified proteins and phosphoproteins could be functionally classified as cytoskeletal protein, oxidoreductase, protein deubiquitination, energy metabolism, GTPase activation, heme binding, hydrolase, iron storage, neurotransmitter release, protease inhibitor, transcription, glycolysis, antiapoptosis, calcium ion binding, heme metabolic process, protein degradation, vesicular transport, and unknown in the hippocampus or cortex. Additionally, Western blotting validated the changes in translationally controlled tumor protein, ATP-specific succinyl-CoA synthetase beta subunit, and gamma-enolase isoform 1. Conclusions. These findings showed that STZ-induced diabetes changed the expression of proteins and phosphoproteins in the hippocampus and cortex. We propose that alterations in expression levels of these proteins play an important role in diabetes-induced dementia.

Gamma-enolase: a well-known tumour marker, with a less-known role in cancer

Background. Gamma-enolase, known also as neuron-specific enolase (NSE), is an enzyme of the glycolytic pathway, which is expressed predominantly in neurons and cells of the neuroendocrine system. As a tumour marker it is used in diagnosis and prognosis of cancer; however, the mechanisms enrolling it in malignant progression remain elusive. As a cytoplasmic enzyme gamma-enolase is involved in increased aerobic glycolysis, the main source of energy in cancer cells, supporting cell proliferation. However, different cellular localisation at pathophysiological conditions, proposes other cellular engagements. Conclusions. The C-terminal part of the molecule, which is not related to glycolytic pathway, was shown to promote survival of neuronal cells by regulating neuronal growth factor receptor dependent signalling pathways, resulting also in extensive actin cytoskeleton remodelling. This additional function could be important also in cancer cells either to protect cells from stressful conditions and therapeutic agents or to promote tumour cell migration and invasion. Gamma-enolase might therefore have a multifunctional role in cancer progression: it supports increased tumour cell metabolic demands, protects tumour cells from stressful conditions and promotes their invasion and migration.